Occupational Exposure to Respirable Crystalline Silica

AGENCY:

Occupational Safety and Health Administration (OSHA), Department of Labor.

ACTION:

Final rule.

SUMMARY:

The Occupational Safety and Health Administration (OSHA) is amending its existing standards for occupational exposure to respirable crystalline silica. OSHA has determined that employees exposed to respirable crystalline silica at the previous permissible exposure limits face a significant risk of material impairment to their health. The evidence in the record for this rulemaking indicates that workers exposed to respirable crystalline silica are at increased risk of developing silicosis and other non-malignant respiratory diseases, lung cancer, and kidney disease. This final rule establishes a new permissible exposure limit of 50 micrograms of respirable crystalline silica per cubic meter of air (50 μg/m³) as an 8-hour time-weighted average in all industries covered by the rule. It also includes other provisions to protect employees, such as requirements for exposure assessment, methods for controlling exposure, respiratory protection, medical surveillance, hazard communication, and recordkeeping.

OSHA is issuing two separate standards—one for general industry and maritime, and the other for construction—in order to tailor requirements to the circumstances found in these sectors.

DATES:

The final rule is effective on June 23, 2016. Start-up dates for specific provisions are set in § 1910.1053(l) for general industry and maritime and in § 1926.1153(k) for construction.

Collections of Information

There are a number of collections of information contained in this final rule (see Section VIII, Paperwork Reduction Act). Notwithstanding the general date of applicability that applies to all other requirements contained in the final rule, affected parties do not have to comply with the collections of information until the Department of Labor publishes a separate notice in the Federal Register announcing the Office of Management and Budget has approved them under the Paperwork Reduction Act.

ADDRESSES:

In accordance with 28 U.S.C. 2112(a), the Agency designates Ann Rosenthal, Associate Solicitor of Labor for Occupational Safety and Health, Office of the Solicitor of Labor, Room S-4004, U.S. Department of Labor, 200 Constitution Avenue NW., Washington, DC 20210, to receive petitions for review of the final rule.

FOR FURTHER INFORMATION CONTACT:

For general information and press inquiries, contact Frank Meilinger, Director, Office of Communications, Room N-3647, OSHA, U.S. Department of Labor, 200 Constitution Avenue NW., Washington, DC 20210; telephone (202) 693-1999; email meilinger.francis2@dol.gov.

For technical inquiries, contact William Perry or David O'Connor, Directorate of Standards and Guidance, Room N-3718, OSHA, U.S. Department of Labor, 200 Constitution Avenue NW., Washington, DC 20210; telephone (202) 693-1950.

SUPPLEMENTARY INFORMATION:

The preamble to the rule on occupational exposure to respirable crystalline silica follows this outline:

I. Executive Summary

II. Pertinent Legal Authority

III. Events Leading to the Final Standards

IV. Chemical Properties and Industrial Uses

V. Health Effects

VI. Final Quantitative Risk Assessment and Significance of Risk

VII. Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis

VIII. Paperwork Reduction Act

IX. Federalism

X. State-Plan States

XI. Unfunded Mandates

XII. Protecting Children From Environmental Health and Safety Risks

XIII. Consultation and Coordination With Indian Tribal Governments

XIV. Environmental Impacts

XV. Summary and Explanation of the Standards

Scope

Definitions

Specified Exposure Control Methods

Alternative Exposure Control Methods

Permissible Exposure Limit

Exposure Assessment

Regulated Areas

Methods of Compliance

Respiratory Protection

Housekeeping

Written Exposure Control Plan

Medical Surveillance

Communication of Respirable Crystalline Silica Hazards to Employees

Recordkeeping

Dates

Authority and Signature

Citation Method

In the docket for the respirable crystalline silica rulemaking, found at http://www.regulations.gov , every submission was assigned a document identification (ID) number that consists of the docket number (OSHA-2010-0034) followed by an additional four-digit number. For example, the document ID number for OSHA's Preliminary Economic Analysis and Initial Regulatory Flexibility Analysis is OSHA-2010-0034-1720. Some document ID numbers include one or more attachments, such as the National Institute for Occupational Safety and Health (NIOSH) prehearing submission (see Document ID OSHA 2010-0034-2177).

When citing exhibits in the docket, OSHA includes the term “Document ID” followed by the last four digits of the document ID number, the attachment number or other attachment identifier, if applicable, page numbers (designated “p.” or “Tr.” for pages from a hearing transcript), and in a limited number of cases a footnote number (designated “Fn”). In a citation that contains two or more document ID numbers, the document ID numbers are separated by semi-colons. For example, a citation referring to the NIOSH prehearing comments and NIOSH testimony obtained from the hearing transcript would be indicated as follows: (Document ID 2177, Attachment B, pp. 2-3; 3579, Tr. 132). In some sections, such as Section V, Health Effects, author names and year of study publication are included before the document ID number in a citation, for example: (Hughes et al., 2001, Document ID 1060; McDonald et al., 2001, 1091; McDonald et al., 2005, 1092; Rando et al., 2001, 0415).

I. Executive Summary

This final rule establishes a permissible exposure limit (PEL) for respirable crystalline silica of 50 μg/m³ as an 8-hour time-weighted average (TWA) in all industries covered by the rule. In addition to the PEL, the rule includes provisions to protect employees such as requirements for exposure assessment, methods for controlling exposure, respiratory protection, medical surveillance, hazard communication, and recordkeeping. OSHA is issuing two separate standards—one for general industry and maritime, and the other for construction—in order to tailor requirements to the circumstances found in these sectors. There are, however, numerous common elements in the two standards.

The final rule is based on the requirements of the Occupational Safety and Health Act (OSH Act) and court interpretations of the Act. For health standards issued under section 6(b)(5) of the OSH Act, OSHA is required to promulgate a standard that reduces significant risk to the extent that it is technologically and economically feasible to do so. See Section II, Pertinent Legal Authority, for a full discussion of OSH Act legal requirements.

OSHA has conducted an extensive review of the literature on adverse health effects associated with exposure to respirable crystalline silica. OSHA has also developed estimates of the risk of silica-related diseases, assuming exposure over a working lifetime, at the preceding PELs as well as at the revised PEL and action level. Comments received on OSHA's preliminary analysis, and the Agency's final findings, are discussed in Section V, Health Effects, and Section VI, Final Quantitative Risk Assessment and Significance of Risk. OSHA finds that employees exposed to respirable crystalline silica at the preceding PELs are at an increased risk of lung cancer mortality and silicosis mortality and morbidity. Occupational exposures to respirable crystalline silica also result in increased risk of death from other nonmalignant respiratory diseases including chronic obstructive pulmonary disease (COPD), and from kidney disease. OSHA further concludes that exposure to respirable crystalline silica constitutes a significant risk of material impairment to health and that the final rule will substantially lower that risk. The Agency considers the level of risk remaining at the new PEL to be significant. However, based on the evidence evaluated during the rulemaking process, OSHA has determined a PEL of 50 μg/m³ is appropriate because it is the lowest level feasible for all affected industries.

OSHA's examination of the technological and economic feasibility of the rule is presented in the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA), and is summarized in Section VII of this preamble. OSHA concludes that the PEL of 50 μg/m³ is technologically feasible for most operations in all affected industries, although it will be a technological challenge for several affected sectors and will require the use of respirators for a limited number of job categories and tasks.

OSHA developed quantitative estimates of the compliance costs of the rule for each of the affected industry sectors. The estimated compliance costs were compared with industry revenues and profits to provide a screening analysis of the economic feasibility of complying with the rule and an evaluation of the economic impacts. Industries with unusually high costs as a percentage of revenues or profits were further analyzed for possible economic feasibility issues. After performing these analyses, OSHA finds that compliance with the requirements of the rule is economically feasible in every affected industry sector.

The final rule includes several major changes from the proposed rule as a result of OSHA's analysis of comments and evidence received during the comment periods and public hearings. The major changes are summarized below and are fully discussed in Section XV, Summary and Explanation of the Standards.

Scope. As proposed, the standards covered all occupational exposures to respirable crystalline silica with the exception of agricultural operations covered under 29 CFR part 1928. OSHA has made a final determination to exclude exposures in general industry and maritime where the employer has objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 μg/m³ as an 8-hour TWA under any foreseeable conditions. OSHA is also excluding exposures in construction where employee exposure to respirable crystalline silica will remain below 25 μg/m³ as an 8-hour TWA under any foreseeable conditions. In addition, OSHA is excluding exposures that result from the processing of sorptive clays from the scope of the rule. The standard for general industry and maritime also allows employers to comply with the standard for construction in certain circumstances.

Specified Exposure Control Methods. OSHA has revised the structure of the standard for construction to emphasize the specified exposure control methods for construction tasks that are presented in Table 1 of the standard. Unlike in the proposed rule, employers who fully and properly implement the controls listed on Table 1 are not separately required to comply with the PEL, and are not subject to provisions for exposure assessment and methods of compliance. The entries on Table 1 have also been revised extensively.

Protective Clothing. The proposed rule would have required use of protective clothing in certain limited situations. The final rule does not include requirements for use of protective clothing to address exposure to respirable crystalline silica.

Housekeeping. The proposed rule would have prohibited use of compressed air, dry sweeping, and dry brushing to clean clothing or surfaces contaminated with crystalline silica where such activities could contribute to employee exposure to respirable crystalline silica that exceeds the PEL. The final rule allows for use of compressed air, dry sweeping, and dry brushing in certain limited situations.

Written Exposure Control Plan. OSHA did not propose a requirement for employers to develop a written exposure control plan. The final rule includes a requirement for employers covered by the rule to develop a written exposure control plan, and the standard for construction includes a provision for a competent person (i.e., a designated individual who is capable of identifying crystalline silica hazards in the workplace and who possesses the authority to take corrective measures to address them) to implement the written exposure control plan.

Regulated Areas. OSHA proposed to provide employers covered by the rule with the alternative of either establishing a regulated area or an access control plan to limit access to areas where exposure to respirable crystalline silica exceeds the PEL. The final standard for general industry and maritime requires employers to establish a regulated area in such circumstances. The final standard for construction does not include a provision for regulated areas, but includes a requirement that the written exposure control plan include procedures used to restrict access to work areas, when necessary, to minimize the numbers of employees exposed to respirable crystalline silica and their level of exposure. The access control plan alternative is not included in the final rule.

Medical Surveillance. The proposed rule would have required employers to make medical surveillance available to employees exposed to respirable crystalline silica above the PEL for 30 or more days per year. The final standard for general industry and maritime requires that medical surveillance be made available to employees exposed to respirable crystalline silica at or above the action level of 25 μg/m³ as an 8-hour TWA for 30 or more days per year. The final standard for construction requires that medical surveillance be made available to employees who are required by the standard to use respirators for 30 or more days per year.

The rule requires the employer to obtain a written medical opinion from physicians or other licensed health care professionals (PLHCPs) for medical examinations provided under the rule but limits the information provided to the employer to the date of the examination, a statement that the examination has met the requirements of the standard, and any recommended limitations on the employee's use of respirators. The proposed rule would have required that such opinions contain additional information, without requiring employee authorization, such as any recommended limitations upon the employee's exposure to respirable crystalline silica, and any referral to a specialist. In the final rule, the written opinion provided to the employer will only include recommended limitations on the employee's exposure to respirable crystalline silica and referral to a specialist if the employee provides written authorization. The final rule requires a separate written medical report provided to the employee to include this additional information, as well as detailed information related to the employee's health.

Dates. OSHA proposed identical requirements for both standards: an effective date 60 days after publication of the rule; a date for compliance with all provisions except engineering controls and laboratory requirements of 180 days after the effective date; a date for compliance with engineering controls requirements, which was one year after the effective date; and a date for compliance with laboratory requirements of two years after the effective date.

OSHA has revised the proposed compliance dates in both standards. The final rule is effective 90 days after publication. For general industry and maritime, all obligations for compliance commence two years after the effective date, with two exceptions: The obligation for engineering controls commences five years after the effective date for hydraulic fracturing operations in the oil and gas industry; and the obligation for employers in general industry and maritime to offer medical surveillance commences two years after the effective date for employees exposed above the PEL, and four years after the effective date for employees exposed at or above the action level. For construction, all obligations for compliance commence one year after the effective date, with the exception that certain requirements for laboratory analysis commence two years after the effective date.

Under the OSH Act's legal standard directing OSHA to set health standards based on findings of significant risk of material impairment and technological and economic feasibility, OSHA does not use cost-benefit analysis to determine the PEL or other aspects of the rule. It does, however, determine and analyze costs and benefits for its own informational purposes and to meet certain Executive Order requirements, as discussed in Section VII. Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis and in the FEA. Table I-1—which is derived from material presented in Section VII of this preamble—provides a summary of OSHA's best estimate of the costs and benefits of the rule using a discount rate of 3 percent. As shown, the rule is estimated to prevent 642 fatalities and 918 moderate-to-severe silicosis cases annually once it is fully effective, and the estimated cost of the rule is $1,030 million annually. Also as shown in Table I-1, the discounted monetized benefits of the rule are estimated to be $8.7 billion annually, and the rule is estimated to generate net benefits of approximately $7.7 billion annually.

II. Pertinent Legal Authority

The purpose of the Occupational Safety and Health Act (29 U.S.C. 651 et seq.) (“the Act” or “the OSH Act”), is “to assure so far as possible every working man and woman in the Nation safe and healthful working conditions and to preserve our human resources” (29 U.S.C. 651(b)). To achieve this goal Congress authorized the Secretary of Labor (“the Secretary”) “to set mandatory occupational safety and health standards applicable to businesses affecting interstate commerce” (29 U.S.C. 651(b)(3); see 29 U.S.C. 654(a) (requiring employers to comply with OSHA standards), 655(a) (authorizing summary adoption of existing consensus and federal standards within two years of the Act's enactment), and 655(b) (authorizing promulgation, modification or revocation of standards pursuant to notice and comment)). The primary statutory provision relied upon by the Agency in promulgating health standards is section 6(b)(5) of the Act; other sections of the OSH Act, however, authorize the Occupational Safety and Health Administration (OSHA) to require labeling and other appropriate forms of warning, exposure assessment, medical examinations, and recordkeeping in its standards (29 U.S.C. 655(b)(5), 655(b)(7), 657(c)).

The Act provides that in promulgating standards dealing with toxic materials or harmful physical agents, such as respirable crystalline silica, the Secretary shall set the standard which “most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health . . . even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life” (29 U.S.C. 655(b)(5)). Thus, “[w]hen Congress passed the Occupational Safety and Health Act in 1970, it chose to place pre-eminent value on assuring employees a safe and healthful working environment, limited only by the feasibility of achieving such an environment” (American Textile Mfrs. Institute, Inc. v. Donovan, 452 US 490, 541 (1981) (“Cotton Dust”)).

OSHA proposed this new standard for respirable crystalline silica and conducted its rulemaking pursuant to section 6(b)(5) of the Act ((29 U.S.C. 655(b)(5)). The preceding silica standard, however, was adopted under the Secretary's authority in section 6(a) of the OSH Act (29 U.S.C. 655(a)), to adopt national consensus and established Federal standards within two years of the Act's enactment (see 29 CFR 1910.1000 Table Z-1). Any rule that “differs substantially from an existing national consensus standard” must “better effectuate the purposes of this Act than the national consensus standard” (29 U.S.C. 655(b)(8)). Several additional legal requirements arise from the statutory language in sections 3(8) and 6(b)(5) of the Act (29 U.S.C. 652(8), 655(b)(5)). The remainder of this section discusses these requirements, which OSHA must consider and meet before it may promulgate this occupational health standard regulating exposure to respirable crystalline silica.

Material Impairment of Health

Subject to the limitations discussed below, when setting standards regulating exposure to toxic materials or harmful physical agents, the Secretary is required to set health standards that ensure that “no employee will suffer material impairment of health or functional capacity . . .” (29 U.S.C. 655(b)(5)). OSHA has, under this section, considered medical conditions such as irritation of the skin, eyes, and respiratory system, asthma, and cancer to be material impairments of health. What constitutes material impairment in any given case is a policy determination on which OSHA is given substantial leeway. “OSHA is not required to state with scientific certainty or precision the exact point at which each type of [harm] becomes a material impairment” (AFL-CIO v. OSHA, 965 F.2d 962, 975 (11th Cir. 1992)). Courts have also noted that OSHA should consider all forms and degrees of material impairment—not just death or serious physical harm (AFL-CIO, 965 F.2d at 975). Thus the Agency has taken the position that “subclinical” health effects, which may be precursors to more serious disease, can be material impairments of health that OSHA should address when feasible (43 FR 52952, 52954 (11/14/78) (Preamble to the Lead Standard)).

Significant Risk

Section 3(8) of the Act requires that workplace safety and health standards be “reasonably necessary or appropriate to provide safe or healthful employment” (29 U.S.C. 652(8)). The Supreme Court, in its decision on OSHA's benzene standard, interpreted section 3(8) to mean that “before promulgating any standard, the Secretary must make a finding that the workplaces in question are not safe” (Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607, 642 (1980) (plurality opinion) (“Benzene”)). The Court further described OSHA's obligation as requiring it to evaluate “whether significant risks are present and can be eliminated or lessened by a change in practices” (Benzene, 448 U.S. at 642). The Court's holding is consistent with evidence in the legislative record, with regard to section 6(b)(5) of the Act (29 U.S.C. 655(b)(5)), that Congress intended the Agency to regulate unacceptably severe occupational hazards, and not “to establish a utopia free from any hazards” or to address risks comparable to those that exist in virtually any occupation or workplace (116 Cong. Rec. 37614 (1970), Leg. Hist. 480-82). It is also consistent with Section 6(g) of the OSH Act, which states that, in determining regulatory priorities, “the Secretary shall give due regard to the urgency of the need for mandatory safety and health standards for particular industries, trades, crafts, occupations, businesses, workplaces or work environments” (29 U.S.C. 655(g)).

The Supreme Court in Benzene clarified that OSHA has considerable latitude in defining significant risk and in determining the significance of any particular risk. The Court did not specify a means to distinguish significant from insignificant risks, but rather instructed OSHA to develop a reasonable approach to making its significant risk determination. The Court stated that “[i]t is the Agency's responsibility to determine, in the first instance, what it considers to be a `significant' risk” (Benzene, 448 U.S. at 655), and it did not “express any opinion on the . . . difficult question of what factual determinations would warrant a conclusion that significant risks are present which make promulgation of a new standard reasonably necessary or appropriate” (Benzene, 448 U.S. at 659). The Court stated, however, that the section 6(f) (29 U.S.C. 655(b)(f)) substantial evidence standard applicable to OSHA's significant risk determination does not require the Agency “to support its finding that a significant risk exists with anything approaching scientific certainty” (Benzene, 448 U.S. at 656). Rather, OSHA may rely on “a body of reputable scientific thought” to which “conservative assumptions in interpreting the data . . . ” may be applied, “risking error on the side of overprotection” (Benzene, 448 U.S. at 656; see also United Steelworkers of Am., AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1248 (D.C. Cir. 1980) (“Lead I”) (noting the Benzene Court's application of this principle to carcinogens and applying it to the lead standard, which was not based on carcinogenic effects)). OSHA may thus act with a “pronounced bias towards worker safety” in making its risk determinations (Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1266 (D.C. Cir. 1988) (“Asbestos II”).

The Supreme Court further recognized that what constitutes “significant risk” is “not a mathematical straitjacket” (Benzene, 448 U.S. at 655) and will be “based largely on policy considerations” (Benzene, 448 U.S. at 655 n.62). The Court gave the following example:

If . . . the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. On the other hand, if the odds are one in a thousand that regular inhalation of gasoline vapors that are 2% benzene will be fatal, a reasonable person might well consider the risk significant . . . (Benzene, 448 U.S. at 655).

Following Benzene, OSHA has, in many of its health standards, considered the one-in-a-thousand metric when determining whether a significant risk exists. Moreover, as “a prerequisite to more stringent regulation” in all subsequent health standards, OSHA has, consistent with the Benzene plurality decision, based each standard on a finding of significant risk at the “then prevailing standard” of exposure to the relevant hazardous substance (Asbestos II, 838 F.2d at 1263). Once a significant risk of material impairment of health is demonstrated, it is of no import that the incidence of the illness may be declining (see Nat'l Min. Assoc. v. Sec'y, U.S. Dep't of Labor, Nos. 14-11942, 14-12163, slip op. at 80 (11th Cir. Jan. 25, 2016) (interpreting the Mine Act, 30 U.S.C. 811(a)(6)(A), which contains the same language as section 6(b)(5) of the OSH Act requiring the Secretary to set standards that assure no employee will suffer material impairment of health)).

The Agency's final risk assessment is derived from existing scientific and enforcement data and its final conclusions are made only after considering all evidence in the rulemaking record. Courts reviewing the validity of these standards have uniformly held the Secretary to the significant risk standard first articulated by the Benzene plurality and have generally upheld the Secretary's significant risk determinations as supported by substantial evidence and “a reasoned explanation for his policy assumptions and conclusions” (Asbestos II, 838 F.2d at 1266).

Once OSHA makes its significant risk finding, the “more stringent regulation” (Asbestos II, 838 F.2d at 1263) it promulgates must be “reasonably necessary or appropriate” to reduce or eliminate that risk, within the meaning of section 3(8) of the Act (29 U.S.C. 652(8)) and Benzene (448 U.S. at 642) (see Asbestos II, 838 F.2d at 1269). The courts have interpreted section 6(b)(5) of the OSH Act as requiring OSHA to set the standard that eliminates or reduces risk to the lowest feasible level; as discussed below, the limits of technological and economic feasibility usually determine where the new standard is set (see UAW v. Pendergrass, 878 F.2d 389, 390 (D.C. Cir. 1989)). In choosing among regulatory alternatives, however, “[t]he determination that [one standard] is appropriate, as opposed to a marginally [more or less protective] standard, is a technical decision entrusted to the expertise of the agency. . . ” (Nat'l Mining Ass'n v. Mine Safety and Health Admin., 116 F.3d 520, 528 (D.C. Cir. 1997)) (analyzing a Mine Safety and Health Administration (“MSHA”) standard under the Benzene significant risk standard). In making its choice, OSHA may incorporate a margin of safety even if it theoretically regulates below the lower limit of significant risk (Nat'l Mining Ass'n, 116 F.3d at 528 (citing American Petroleum Inst. v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1982))).

Working Life Assumption

The OSH Act requires OSHA to set the standard that most adequately protects employees against harmful workplace exposures for the period of their “working life” (29 U.S.C. 655(b)(5)). OSHA's longstanding policy is to define “working life” as constituting 45 years; thus, it assumes 45 years of exposure when evaluating the risk of material impairment to health caused by a toxic or hazardous substance. This policy is not based on empirical data that most employees are exposed to a particular hazard for 45 years. Instead, OSHA has adopted the practice to be consistent with the statutory directive that “no employee” suffer material impairment of health “even if” such employee is exposed to the hazard for the period of his or her working life (see 74 FR 44796 (8/31/09)). OSHA's policy was given judicial approval in a challenge to an OSHA standard that lowered the permissible exposure limit (PEL) for asbestos (Asbestos II, 838 F.2d at 1264-1265). In that case, the petitioners claimed that the median duration of employment in the affected industry sectors was only five years. Therefore, according to petitioners, OSHA erred in assuming a 45-year working life in calculating the risk of health effects caused by asbestos exposure. The D.C. Circuit disagreed, stating,

Even if it is only the rare worker who stays with asbestos-related tasks for 45 years, that worker would face a 64/1000 excess risk of contracting cancer; Congress clearly authorized OSHA to protect such a worker (Asbestos II, 838 F.2d at 1264-1265).

OSHA might calculate the health risks of exposure, and the related benefits of lowering the exposure limit, based on an assumption of a shorter working life, such as 25 years, but such estimates are for informational purposes only.

Best Available Evidence

Section 6(b)(5) of the Act requires OSHA to set standards “on the basis of the best available evidence” and to consider the “latest available scientific data in the field” (29 U.S.C. 655(b)(5)). As noted above, the Supreme Court, in its Benzene decision, explained that OSHA must look to “a body of reputable scientific thought” in making its material harm and significant risk determinations, while noting that a reviewing court must “give OSHA some leeway where its findings must be made on the frontiers of scientific knowledge” (Benzene, 448 U.S. at 656). The courts of appeals have afforded OSHA similar latitude to issue health standards in the face of scientific uncertainty. The Second Circuit, in upholding the vinyl chloride standard, stated:

. . . the ultimate facts here in dispute are `on the frontiers of scientific knowledge', and, though the factual finger points, it does not conclude. Under the command of OSHA, it remains the duty of the Secretary to act to protect the workingman, and to act even in circumstances where existing methodology or research is deficient (Society of the Plastics Industry, Inc. v. OSHA, 509 F.2d 1301, 1308 (2d Cir. 1975) (quoting Indus. Union Dep't, AFL-CIO v. Hodgson, 499 F.2d 467, 474 (D.C. Cir. 1974) (“Asbestos I”))).

The D.C. Circuit, in upholding the cotton dust standard, stated: “OSHA's mandate necessarily requires it to act even if information is incomplete when the best available evidence indicates a serious threat to the health of workers” (Am. Fed'n of Labor & Cong. of Indus. Orgs. v. Marshall, 617 F.2d 636, 651 (D.C. Cir. 1979), aff'd in part and vacated in part on other grounds, American Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490 (1981)).

When there is disputed scientific evidence, OSHA must review the evidence on both sides and “reasonably resolve” the dispute (Pub. Citizen Health Research Grp. v. Tyson, 796 F.2d 1479, 1500 (D.C. Cir. 1986)). In Public Citizen, there was disputed scientific evidence regarding whether there was a threshold exposure level for the health effects of ethylene oxide. The Court noted that, where “OSHA has the expertise we lack and it has exercised that expertise by carefully reviewing the scientific data,” a dispute within the scientific community is not occasion for it to take sides about which view is correct (Pub. Citizen Health Research Grp., 796 F.2d at 1500). “Indeed, Congress did `not [intend] that the Secretary be paralyzed by debate surrounding diverse medical opinions' ” (Pub. Citizen Health Research Grp., 796 F.2d at 1497 (quoting H.R.Rep. No. 91-1291, 91st Cong., 2d Sess. 18 (1970), reprinted in Legislative History of the Occupational Safety and Health Act of 1970 at 848 (1971))).

A recent decision by the Eleventh Circuit Court of Appeals upholding a coal dust standard promulgated by MSHA emphasized that courts should give “an extreme degree of deference to the agency when it is evaluating scientific data within its technical expertise” (Nat'l Min. Assoc. v. Sec'y, U.S. Dep't of Labor, Nos. 14-11942, 14-12163, slip op. at 43 (11th Cir. Jan. 25, 2016) (quoting Kennecott Greens Creek Min. Co. v. MSHA, 476 F.3d 946, 954-955 (D.C. Cir. 2007) (internal quotation marks omitted)). The Court emphasized that because the Mine Act, like the OSH Act, “evinces a clear bias in favor of [ ] health and safety,” the agency's responsibility to use the best evidence and consider feasibility should not be used as a counterweight to the agency's duty to protect the lives and health of workers (Nat'l Min. Assoc., Nos. 14-11942, 14-12163, slip op. at 43 (11th Cir. Jan. 25, 2016)).

Feasibility

The OSH Act requires that, in setting a standard, OSHA must eliminate the risk of material health impairment “to the extent feasible” (29 U.S.C. 655(b)(5)). The statutory mandate to consider the feasibility of the standard encompasses both technological and economic feasibility; these analyses have been done primarily on an industry-by-industry basis (Lead I, 647 F.2d at 1264, 1301) in general industry. The Agency has also used application groups, defined by common tasks, as the structure for its feasibility analyses in construction (Pub. Citizen Health Research Grp. v. OSHA, 557 F.3d 165, 177-179 (3d Cir. 2009) (“Chromium (VI)”). The Supreme Court has broadly defined feasible as “capable of being done” (Cotton Dust, 452 U.S. at 509-510).

Although OSHA must set the most protective PEL that the Agency finds to be technologically and economically feasible, it retains discretion to set a uniform PEL even when the evidence demonstrates that certain industries or operations could reasonably be expected to meet a lower PEL. OSHA health standards generally set a single PEL for all affected employers; OSHA exercised this discretion most recently in its final rule on occupational exposure to chromium (VI) (71 FR 10100, 10337-10338 (2/28/2006); see also 62 FR 1494, 1575 (1/10/97) (methylene chloride)). In its decision upholding the chromium (VI) standard, including the uniform PEL, the Court of Appeals for the Third Circuit addressed this issue as one of deference, stating “OSHA's decision to select a uniform exposure limit is a legislative policy decision that we will uphold as long as it was reasonably drawn from the record” (Chromium (VI), 557 F.3d at 183 (3d Cir. 2009)); see also Am. Iron & Steel Inst. v. OSHA, 577 F.2d 825, 833 (3d Cir. 1978)). OSHA's reasons for choosing one chromium (VI) PEL, rather than imposing different PELs on different application groups or industries, included: Multiple PELs would create enforcement and compliance problems because many workplaces, and even workers, were affected by multiple categories of chromium (VI) exposure; discerning individual PELs for different groups of establishments would impose a huge evidentiary burden on the Agency and unnecessarily delay implementation of the standard; and a uniform PEL would, by eliminating confusion and simplifying compliance, enhance worker protection (Chromium (VI), 557 F.3d at 173, 183-184). The Court held that OSHA's rationale for choosing a uniform PEL, despite evidence that some application groups or industries could meet a lower PEL, was reasonably drawn from the record and that the Agency's decision was within its discretion and supported by past practice (Chromium (VI), 557 F.3d at 183-184).

Technological Feasibility

A standard is technologically feasible if the protective measures it requires already exist, can be brought into existence with available technology, or can be created with technology that can reasonably be expected to be developed (Lead I, 647 F.2d at 1272; Amer. Iron & Steel Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991) (“Lead II”)). While the test for technological feasibility is normally articulated in terms of the ability of employers to decrease exposures to the PEL, provisions such as exposure measurement requirements must also be technologically feasible (Forging Indus. Ass'n v. Sec'y of Labor, 773 F.2d 1436, 1453 (4th Cir. 1985)).

OSHA's standards may be “technology forcing,” i.e., where the Agency gives an industry a reasonable amount of time to develop new technologies, OSHA is not bound by the “technological status quo” (Lead I, 647 F.2d at 1264); see also Kennecott Greens Creek Min. Co. v. MSHA, 476 F.3d 946, 957 (D.C. Cir. 2007) (MSHA standards, like OSHA standards, may be technology-forcing); Nat'l Petrochemical & Refiners Ass'n v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002) (agency is “not obliged to provide detailed solutions to every engineering problem,” but only to “identify the major steps for improvement and give plausible reasons for its belief that the industry will be able to solve those problems in the time remaining.”).

In its Lead decisions, the D.C. Circuit described OSHA's obligation to demonstrate the technological feasibility of reducing occupational exposure to a hazardous substance.

[W]ithin the limits of the best available evidence . . . OSHA must prove a reasonable possibility that the typical firm will be able to develop and install engineering and work practice controls that can meet the PEL in most of its operations . . . The effect of such proof is to establish a presumption that industry can meet the PEL without relying on respirators . . . Insufficient proof of technological feasibility for a few isolated operations within an industry, or even OSHA's concession that respirators will be necessary in a few such operations, will not undermine this general presumption in favor of feasibility. Rather, in such operations firms will remain responsible for installing engineering and work practice controls to the extent feasible, and for using them to reduce . . . exposure as far as these controls can do so (Lead I, 647 F.2d at 1272).

Additionally, the D.C. Circuit explained that “[f]easibility of compliance turns on whether exposure levels at or below [the PEL] can be met in most operations most of the time . . .” (Lead II, 939 F.2d at 990).

Courts have given OSHA significant deference in reviewing its technological feasibility findings.

So long as we require OSHA to show that any required means of compliance, even if it carries no guarantee of meeting the PEL, will substantially lower . . . exposure, we can uphold OSHA's determination that every firm must exploit all possible means to meet the standard (Lead I, 647 F.2d at 1273).

Even in the face of significant uncertainty about technological feasibility in a given industry, OSHA has been granted broad discretion in making its findings (Lead I, 647 F.2d at 1285).

OSHA cannot let workers suffer while it awaits . . . scientific certainty. It can and must make reasonable [technological feasibility] predictions on the basis of `credible sources of information,' whether data from existing plants or expert testimony (Lead I, 647 F.2d at 1266 (quoting Am. Fed'n of Labor & Cong. of Indus. Orgs., 617 F.2d at 658)).

For example, in Lead I, the D.C. Circuit allowed OSHA to use, as best available evidence, information about new and expensive industrial smelting processes that had not yet been adopted in the U.S. and would require the rebuilding of plants (Lead I, 647 F.2d at 1283-1284). Even under circumstances where OSHA's feasibility findings were less certain and the Agency was relying on its “legitimate policy of technology forcing,” the D.C. Circuit approved of OSHA's feasibility findings when the Agency granted lengthy phase-in periods to allow particular industries time to comply (Lead I, 647 F.2d at 1279-1281, 1285).

OSHA is permitted to adopt a standard that some employers will not be able to meet some of the time, with employers limited to challenging feasibility at the enforcement stage (Lead I, 647 F.2d at 1273 & n. 125; Asbestos II, 838 F.2d at 1268). Even when the Agency recognized that it might have to balance its general feasibility findings with flexible enforcement of the standard in individual cases, the courts of appeals have generally upheld OSHA's technological feasibility findings (Lead II, 939 F.2d at 980; see Lead I, 647 F.2d at 1266-1273; Asbestos II, 838 F.2d at 1268). Flexible enforcement policies have been approved where there is variability in measurement of the regulated hazardous substance or where exposures can fluctuate uncontrollably (Asbestos II, 838 F.2d at 1267-1268; Lead II, 939 F.2d at 991). A common means of dealing with the measurement variability inherent in sampling and analysis is for the Agency to add the standard sampling error to its exposure measurements before determining whether to issue a citation (e.g., 51 FR 22612, 22654 (06/20/86) (Preamble to the Asbestos Standard)).

Economic Feasibility

In addition to technological feasibility, OSHA is required to demonstrate that its standards are economically feasible. A reviewing court will examine the cost of compliance with an OSHA standard “in relation to the financial health and profitability of the industry and the likely effect of such costs on unit consumer prices . . .” (Lead I, 647 F.2d at 1265 (omitting citation)). As articulated by the D.C. Circuit in Lead I,

OSHA must construct a reasonable estimate of compliance costs and demonstrate a reasonable likelihood that these costs will not threaten the existence or competitive structure of an industry, even if it does portend disaster for some marginal firms (Lead I, 647 F.2d at 1272).

A reasonable estimate entails assessing “the likely range of costs and the likely effects of those costs on the industry” (Lead I, 647 F.2d at 1266). As with OSHA's consideration of scientific data and control technology, however, the estimates need not be precise (Cotton Dust, 452 U.S. at 528-29 & n.54) as long as they are adequately explained. Thus, as the D.C. Circuit further explained:

Standards may be economically feasible even though, from the standpoint of employers, they are financially burdensome and affect profit margins adversely. Nor does the concept of economic feasibility necessarily guarantee the continued existence of individual employers. It would appear to be consistent with the purposes of the Act to envisage the economic demise of an employer who has lagged behind the rest of the industry in protecting the health and safety of employees and is consequently financially unable to comply with new standards as quickly as other employers. As the effect becomes more widespread within an industry, the problem of economic feasibility becomes more pressing (Asbestos I, 499 F.2d. at 478).

OSHA standards therefore satisfy the economic feasibility criterion even if they impose significant costs on regulated industries so long as they do not cause massive economic dislocations within a particular industry or imperil the very existence of the industry (Lead II, 939 F.2d at 980; Lead I, 647 F.2d at 1272; Asbestos I, 499 F.2d. at 478). As with its other legal findings, OSHA “is not required to prove economic feasibility with certainty, but is required to use the best available evidence and to support its conclusions with substantial evidence” (Lead II, 939 F.2d at 980-981) (citing Lead I, 647 F.2d at 1267)). Granting industries additional time to comply with new PELs may enhance the economic, as well as technological, feasibility of a standard (Lead I, 647 F.2d at 1265).

Because section 6(b)(5) of the Act explicitly imposes the “to the extent feasible” limitation on the setting of health standards, OSHA is not permitted to use cost-benefit analysis to make its standards-setting decisions (29 U.S.C. 655(b)(5)).

Congress itself defined the basic relationship between costs and benefits, by placing the “benefit” of worker health above all other considerations save those making attainment of this “benefit” unachievable. Any standard based on a balancing of costs and benefits by the Secretary that strikes a different balance than that struck by Congress would be inconsistent with the command set forth in § 6(b)(5) (Cotton Dust, 452 U.S. at 509).

Thus, while OSHA estimates the costs and benefits of its proposed and final rules, these calculations do not form the basis for the Agency's regulatory decisions; rather, they are performed in acknowledgement of requirements such as those in Executive Orders 12866 and 13563.

Structure of OSHA Health Standards

OSHA's health standards traditionally incorporate a comprehensive approach to reducing occupational disease. OSHA substance-specific health standards generally include the “hierarchy of controls,” which, as a matter of OSHA's preferred policy, mandates that employers install and implement all feasible engineering and work practice controls before respirators may be used. The Agency's adherence to the hierarchy of controls has been upheld by the courts (ASARCO, Inc. v. OSHA, 746 F.2d 483, 496-498 (9th Cir. 1984); Am. Iron & Steel Inst. v. OSHA, 182 F.3d 1261, 1271 (11th Cir. 1999)). In fact, courts view the legal standard for proving technological feasibility as incorporating the hierarchy:

OSHA must prove a reasonable possibility that the typical firm will be able to develop and install engineering and work practice controls that can meet the PEL in most of its operations. . . . The effect of such proof is to establish a presumption that industry can meet the PEL without relying on respirators (Lead I, 647 F.2d at 1272).

The hierarchy of controls focuses on removing harmful materials at their source. OSHA allows employers to rely on respiratory protection to protect their employees only when engineering and work practice controls are insufficient or infeasible. In fact, in the control of “those occupational diseases caused by breathing air contaminated with harmful dusts, fogs, fumes, mists, gases, smokes, sprays, or vapors,” the employers' primary objective “shall be to prevent atmospheric contamination. This shall be accomplished as far as feasible by accepted engineering control measures (for example, enclosure or confinement of the operation, general and local ventilation, and substitution of less toxic materials). When effective engineering controls are not feasible, or while they are being instituted, appropriate respirators shall be used pursuant to this section” (29 CFR 1910.134).

The reasons supporting OSHA's continued reliance on the hierarchy of controls, as well as its reasons for limiting the use of respirators, are numerous and grounded in good industrial hygiene principles (see Section XV, Summary and Explanation of the Standards, Methods of Compliance). Courts have upheld OSHA's emphasis on engineering and work practice controls over personal protective equipment in challenges to previous health standards, such as chromium (VI): “Nothing in . . . any case reviewing an airborne toxin standard, can be read to support a technological feasibility rule that would effectively encourage the routine and widespread use of respirators to comply with a PEL” (Chromium (VI), 557 F.3d at 179; see Am. Fed'n of Labor & Cong. of Indus. Orgs. v. Marshall, 617 F.2d 636, 653 (D.C. Cir. 1979) cert. granted, judgment vacated sub nom. Cotton Warehouse Ass'n v. Marshall, 449 U.S. 809 (1980) and aff'd in part, vacated in part sub nom. Am. Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490 (1981) (finding “uncontradicted testimony in the record that respirators can cause severe physical discomfort and create safety problems of their own”)).

In health standards such as this one, the hierarchy of controls is augmented by ancillary provisions. These provisions work with the hierarchy of controls and personal protective equipment requirements to provide comprehensive protection to employees in affected workplaces. Such provisions typically include exposure assessment, medical surveillance, hazard communication, and recordkeeping. This approach is recognized as effective in dealing with air contaminants such as respirable crystalline silica; for example, the industry standards for respirable crystalline silica, ASTM E 1132-06, Standard Practice for Health Requirements Relating to Occupational Exposure to Respirable Crystalline Silica, and ASTM E 2626-09, Standard Practice for Controlling Occupational Exposure to Respirable Crystalline Silica for Construction and Demolition Activities, take a similar comprehensive approach (Document ID 1466; 1504).

The OSH Act compels OSHA to require all feasible measures for reducing significant health risks (29 U.S.C. 655(b)(5); Pub. Citizen Health Research Grp., 796 F.2d at 1505 (“if in fact a STEL [short-term exposure limit] would further reduce a significant health risk and is feasible to implement, then the OSH Act compels the agency to adopt it (barring alternative avenues to the same result)”). When there is significant risk below the PEL, as is the case with respirable crystalline silica, the DC Circuit indicated that OSHA should use its regulatory authority to impose additional requirements on employers when those requirements will result in a greater than de minimis incremental benefit to workers' health (Asbestos II, 838 F.2d at 1274). The Supreme Court alluded to a similar issue in Benzene, pointing out that “in setting a permissible exposure level in reliance on less-than-perfect methods, OSHA would have the benefit of a backstop in the form of monitoring and medical testing” (Benzene, 448 U.S. at 657). OSHA believes that the ancillary provisions in this final standard provide significant benefits to worker health by providing additional layers and types of protection to employees exposed to respirable crystalline silica.

Finally, while OSHA is bound by evidence in the rulemaking record, and generally looks to its prior standards for guidance on how to structure and specify requirements in a new standard, it is not limited to past approaches to regulation. In promulgating health standards, “[w]henever practicable, the standard promulgated shall be expressed in terms of objective criteria and of the performance desired” (29 U.S.C. 655(b)(5)). In cases of industries or tasks presenting unique challenges in terms of assessing and controlling exposures, it may be more practicable and provide greater certainty to require specific controls with a demonstrated track record of efficacy in reducing exposures and, therefore, risk (especially when supplemented by appropriate respirator usage). Such an approach could more effectively protect workers than the traditional exposure assessment-and-control approach when exposures may vary because of factors such as changing environmental conditions or materials, and an assessment may not reflect typical exposures associated with a task or operation. As discussed at length in Section XV, Summary and Explanation of the Standards, the specified exposure control measures option in the construction standard (i.e., Table 1, in paragraph (c)(1)) for respirable crystalline silica represents the type of innovative, objective approach available to the Secretary when fashioning a rule under these circumstances.

III. Events Leading to the Final Standards

The Occupational Safety and Health Administration's (OSHA's) previous standards for workplace exposure to respirable crystalline silica were adopted in 1971, pursuant to section 6(a) of the Occupational Safety and Health Act (29 U.S.C. 651 et seq.) (“the Act” or “the OSH Act”) (36 FR 10466 (5/29/71)). Section 6(a) (29 U.S.C. 655(a)) authorized OSHA, in the first two years after the effective date of the Act, to promulgate “start-up” standards, on an expedited basis and without public hearing or comment, based on national consensus or established Federal standards that improved employee safety or health. Pursuant to that authority, OSHA in 1971 promulgated approximately 425 permissible exposure limits (PELs) for air contaminants, including crystalline silica, which were derived principally from Federal standards applicable to government contractors under the Walsh-Healey Public Contracts Act, 41 U.S.C. 35, and the Contract Work Hours and Safety Standards Act (commonly known as the Construction Safety Act), 40 U.S.C. 333. The Walsh-Healey Act and Construction Safety Act standards had been adopted primarily from recommendations of the American Conference of Governmental Industrial Hygienists (ACGIH).

For general industry (see 29 CFR 1910.1000, Table Z-3), the PEL for crystalline silica in the form of respirable quartz was based on two alternative formulas: (1) A particle-count formula, PEL_mppcf=250/(% quartz + 5) as respirable dust; and (2) a mass formula proposed by ACGIH in 1968, PEL=(10 mg/m³)/(% quartz + 2) as respirable dust. The general industry PELs for crystalline silica in the form of cristobalite and tridymite were one-half of the value calculated from either of the above two formulas for quartz. For construction (see 29 CFR 1926.55, Appendix A) and shipyards (see 29 CFR 1915.1000, Table Z), the formula for the PEL for crystalline silica in the form of quartz (PEL_mppcf=250/(% quartz + 5) as respirable dust), which requires particle counting, was derived from the 1970 ACGIH threshold limit value (TLV). Based on the formulas, the PELs for quartz, expressed as time-weighted averages (TWAs), were approximately equivalent to 100 μg/m³ for general industry and 250 μg/m³ for construction and shipyards. The PELs were not supplemented by additional protective provisions—such as medical surveillance requirements—as are included in other OSHA standards. OSHA believes that the formula based on particle-counting technology used in the general industry, construction, and shipyard PELs has been rendered obsolete by respirable mass (gravimetric) sampling.

In 1974, the National Institute for Occupational Safety and Health (NIOSH), an agency within the Department of Health and Human Services created by the OSH Act and designed to carry out research and recommend standards for occupational safety and health hazards, evaluated crystalline silica as a workplace hazard and issued criteria for a recommended standard (29 U.S.C. 669, 671; Document ID 0388). NIOSH recommended that occupational exposure to crystalline silica be controlled so that no worker is exposed to a TWA of free (respirable crystalline) silica greater than 50 μg/m³ as determined by a full-shift sample for up to a 10-hour workday over a 40-hour workweek. The document also recommended a number of ancillary provisions for a standard, such as exposure monitoring and medical surveillance.

In December 1974, OSHA published an Advance Notice of Proposed Rulemaking (ANPRM) based on the recommendations in the NIOSH criteria document (39 FR 44771 (12/27/74)). In the ANPRM, OSHA solicited “public participation on the issues of whether a new standard for crystalline silica should be issued on the basis of the [NIOSH] criteria or any other information, and, if so, what should be the contents of a proposed standard for crystalline silica” (39 FR at 44771). OSHA also set forth the particular issues of concern on which comments were requested. The Agency did not issue a proposed rule or pursue a final rule for crystalline silica at that time.

As information on the health effects of silica exposure developed during the 1980s and 1990s, national and international classification organizations came to recognize crystalline silica as a human carcinogen. In June 1986, the International Agency for Research on Cancer (IARC), which is the specialized cancer agency within the World Health Organization, evaluated the available evidence regarding crystalline silica carcinogenicity and concluded, in 1987, that crystalline silica is probably carcinogenic to humans ( http://monographs.iarc.fr/ENG/Monographs/suppl7/Suppl7.pdf ). An IARC working group met again in October 1996 to evaluate the complete body of research, including research that had been conducted since the initial 1986 evaluation. IARC concluded, more decisively this time, that “crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans” (Document ID 2258, Attachment 8, p. 211). In 2012, IARC reaffirmed that “Crystalline silica in the form of quartz or cristobalite dust is carcinogenic to humans” (Document ID 1473, p. 396).

In 1991, in the Sixth Annual Report on Carcinogens, the U.S. National Toxicology Program (NTP), within the U.S. Department of Health and Human Services, concluded that respirable crystalline silica was “reasonably anticipated to be a human carcinogen” (as referenced in Document ID 1417, p. 1). NTP reevaluated the available evidence and concluded, in the Ninth Report on Carcinogens, that “respirable crystalline silica (RCS), primarily quartz dust occurring in industrial and occupational settings, is known to be a human carcinogen, based on sufficient evidence of carcinogenicity from studies in humans indicating a causal relationship between exposure to RCS and increased lung cancer rates in workers exposed to crystalline silica dust” (Document ID 1417, p. 1). ACGIH listed respirable crystalline silica (in the form of quartz) as a suspected human carcinogen in 2000, while lowering the TLV to 0.05 mg/m₃ (50 μg/m₃) (Document ID 1503, p. 15). ACGIH subsequently lowered the TLV for crystalline silica to 0.025 mg/m₃ (25 μg/m₃) in 2006, which is ACGIH's current recommended exposure limit (Document ID 1503, pp. 1, 15).

In 1989, OSHA established 8-hour TWA PELs of 0.1 mg/m₃ (100 μg/m₃) for quartz and 0.05 mg/m₃ (50 μg/m₃) for cristobalite and tridymite, as part of the Air Contaminants final rule for general industry (54 FR 2332 (1/19/89)). OSHA stated that these limits presented no substantial change from the Agency's former formula limits, but would simplify sampling procedures. In providing comments on the proposed rule, NIOSH recommended that crystalline silica be considered a potential carcinogen.

In 1992, OSHA, as part of the Air Contaminants proposed rule for maritime, construction, and agriculture, proposed the same PELs as for general industry, to make the PELs consistent across all the OSHA-regulated sectors (57 FR 26002 (6/12/92)). However, the U.S. Court of Appeals for the Eleventh Circuit vacated the 1989 Air Contaminants final rule for general industry (Am. Fed'n of Labor and Cong. of Indus. Orgs. v. OSHA, 965 F.2d 962 (1992)), and also mooted the proposed rule for maritime, construction, and agriculture. The Court's decision to vacate the rule forced the Agency to return to the original 1971 PELs for all compounds, including silica, adopted as section 6(a) standards.

In 1994, OSHA initiated a process to determine which safety and health hazards in the U.S. needed the most attention. A priority planning committee included safety and health experts from OSHA, NIOSH, and the Mine Safety and Health Administration (MSHA). The committee reviewed available information on occupational deaths, injuries, and illnesses and communicated extensively with representatives of labor, industry, professional and academic organizations, the States, voluntary standards organizations, and the public. The OSHA National Advisory Committee on Occupational Safety and Health and the Advisory Committee on Construction Safety and Health (ACCSH) also made recommendations. Rulemaking for crystalline silica exposure was one of the priorities designated by this process. OSHA indicated that crystalline silica would be added to the Agency's regulatory agenda as other standards were completed and resources became available.

In 1996, OSHA instituted a Special Emphasis Program (SEP) to step up enforcement of the crystalline silica standards. The SEP was intended to reduce worker silica dust exposures that can cause silicosis and lung cancer. It included extensive outreach designed to educate and train employers and employees about the hazards of silica and how to control them, as well as inspections to enforce the standards. Among the outreach materials available were slides presenting information on hazard recognition and crystalline silica control technology, a video on crystalline silica and silicosis, and informational cards for workers explaining crystalline silica, health effects related to exposure, and methods of control. The SEP provided guidance for targeting inspections of worksites that had employees at risk of developing silicosis. The inspections resulted in the collection of exposure data from the various worksites visited by OSHA's compliance officers.

As a follow-up to the SEP, OSHA undertook numerous non-regulatory actions to address silica exposures. For example, in October of 1996, OSHA launched a joint silicosis prevention effort with MSHA, NIOSH, and the American Lung Association (see https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=NEWS_RELEASES&p_id=14110 ). This public education campaign involved distribution of materials on how to prevent silicosis, including a guide for working safely with silica and stickers for hard hats to remind workers of crystalline silica hazards. Spanish language versions of these materials were also made available. OSHA and MSHA inspectors distributed materials at mines, construction sites, and other affected workplaces. The joint silicosis prevention effort included a National Conference to Eliminate Silicosis in Washington, DC, in March of 1997, which brought together approximately 650 participants from labor, business, government, and the health and safety professions to exchange ideas and share solutions regarding the goal of eliminating silicosis (see https://industrydocuments.library.ucsf.edu/documentstore/s/h/d/p//shdp0052/shdp0052.pdf ).

In 1997, OSHA announced in its Unified Agenda under Long-Term Actions that it planned to publish a proposed rule on crystalline silica

. . . because the agency has concluded that there will be no significant progress in the prevention of silica-related diseases without the adoption of a full and comprehensive silica standard, including provisions for product substitution, engineering controls, training and education, respiratory protection and medical screening and surveillance. A full standard will improve worker protection, ensure adequate prevention programs, and further reduce silica-related diseases (62 FR 57755, 57758 (10/29/97)).

In November 1998, OSHA moved “Occupational Exposure to Crystalline Silica” to the pre-rule stage in the Regulatory Plan (63 FR 61284, 61303-61304 (11/9/98)). OSHA held a series of stakeholder meetings in 1999 and 2000 to get input on the rulemaking. Stakeholder meetings for all industry sectors were held in Washington, Chicago, and San Francisco. A separate stakeholder meeting for the construction sector was held in Atlanta.

OSHA initiated Small Business Regulatory Enforcement Fairness Act (SBREFA) proceedings in 2003, seeking the advice of small business representatives on the proposed rule (68 FR 30583, 30584 (5/27/03)). The SBREFA panel, including representatives from OSHA, the Small Business Administration's Office of Advocacy, and the Office of Management and Budget (OMB), was convened on October 20, 2003. The panel conferred with small entity representatives (SERs) from general industry, maritime, and construction on November 10 and 12, 2003, and delivered its final report, which included comments from the SERs and recommendations to OSHA for the proposed rule, to OSHA's Assistant Secretary on December 19, 2003 (Document ID 0937).

In 2003, OSHA examined enforcement data for the years 1997 to 2002 and identified high rates of noncompliance with the OSHA respirable crystalline silica PELs, particularly in construction. This period covers the first five years of the SEP. These enforcement data, presented in Table III-1, indicate that 24 percent of silica samples from the construction industry and 13 percent from general industry were at least three times the then-existing OSHA PELs. The data indicate that 66 percent of the silica samples obtained during inspections in general industry were in compliance with the PEL, while only 58 percent of the samples collected in construction were in compliance.

In an effort to expand the 1996 SEP, on January 24, 2008, OSHA implemented a National Emphasis Program (NEP) to identify and reduce or eliminate the health hazards associated with occupational exposure to crystalline silica (CPL-03-007 (1/24/08)). The NEP targeted worksites with elevated exposures to crystalline silica and included new program evaluation procedures designed to ensure that the goals of the NEP were measured as accurately as possible, detailed procedures for conducting inspections, updated information for selecting sites for inspection, development of outreach programs by each Regional and Area Office emphasizing the formation of voluntary partnerships to share information, and guidance on calculating PELs in construction and shipyards. In each OSHA Region, at least two percent of inspections every year are silica-related inspections. Additionally, the silica-related inspections are conducted at a range of facilities reasonably representing the distribution of general industry and construction work sites in that region.

A more recent analysis of OSHA enforcement data from January 2003 to December 2009 (covering the period of continued implementation of the SEP and the first two years of the NEP) shows that considerable noncompliance with the then-existing PELs continued to occur. These enforcement data, presented in Table III-2, indicate that 14 percent of silica samples from the construction industry and 19 percent for general industry were at least three times the OSHA PEL during this period. The data indicate that 70 percent of the silica samples obtained during inspections in general industry were in compliance with the PEL, and 75 percent of the samples collected in construction were in compliance.

Both industry and worker groups have recognized that a comprehensive standard is needed to protect workers exposed to respirable crystalline silica. For example, ASTM International (originally known as the American Society for Testing and Materials) has published voluntary consensus standards for addressing the hazards of crystalline silica, and the Building and Construction Trades Department, AFL-CIO also has recommended a comprehensive program standard. These recommended standards include provisions for methods of compliance, exposure monitoring, training, and medical surveillance. The National Industrial Sand Association has also developed an occupational exposure program for crystalline silica that addresses exposure assessment and medical surveillance.

Throughout the crystalline silica rulemaking process, OSHA has presented information to, and consulted with, ACCSH and the Maritime Advisory Committee on Occupational Safety and Health. In December of 2009, OSHA representatives met with ACCSH to discuss the rulemaking and receive their comments and recommendations. On December 11, 2009, ACCSH passed motions supporting the concept of Table 1 in the draft proposed construction rule, recognizing that the controls listed in Table 1 are effective. As discussed with regard to paragraph (f) of the proposed standard for construction (paragraph (c) of the final standard for construction), Table 1 presents specified control measures for selected construction tasks. ACCSH also recommended that OSHA maintain the protective clothing provision found in the SBREFA panel draft regulatory text and restore the “competent person” requirement and responsibilities to the proposed rule. Additionally, the group recommended that OSHA move forward expeditiously with the rulemaking process.

In January 2010, OSHA completed a peer review of the draft Health Effects Analysis and Preliminary Quantitative Risk Assessment following procedures set forth by OMB in the Final Information Quality Bulletin for Peer Review, published on the OMB Web site on December 16, 2004 (see 70 FR 2664 (1/14/05)). Each peer reviewer submitted a written report to OSHA. The Agency revised its draft documents as appropriate and made the revised documents available to the public as part of its Notice of Proposed Rulemaking (NPRM). OSHA also made the written charge to the peer reviewers, the peer reviewers' names, the peer reviewers' reports, and the Agency's response to the peer reviewers' reports publicly available with publication of the proposed rule (Document ID 1711; 1716). Five of the seven original peer reviewers submitted post-hearing reports, commenting on OSHA's disposition of their original peer review comments in the proposed rule, as well as commenting on written and oral testimony presented at the silica hearing (Document ID 3574).

On August 23, 2013, OSHA posted its NPRM for respirable crystalline silica on its Web site and requested comments on the proposed rule. On September 12, 2013, OSHA published the NPRM in the Federal Register (78 FR 56273 (9/12/13)). In the NPRM, the Agency made a preliminary determination that employees exposed to respirable crystalline silica at the current PELs face a significant risk to their health and that promulgating the proposed standards would substantially reduce that risk. The NPRM required commenters to submit their comments by December 11, 2013. In response to stakeholder requests, OSHA extended the comment period until January 27, 2014 (78 FR 65242 (10/31/13)). On January 14, 2014, OSHA held a web chat to provide small businesses and other stakeholders an additional opportunity to obtain information from the Agency about the proposed rule. Subsequently, OSHA further extended the comment period to February 11, 2014 (79 FR 4641 (1/29/14)).

As part of the instructions for submitting comments, OSHA requested (but did not require) that parties submitting technical or scientific studies or research results and those submitting comments or testimony on the Agency's analyses disclose the nature of financial relationships with (e.g., consulting agreement), and extent of review by, parties interested in or affected by the rulemaking (78 FR 56274). Parties submitting studies or research results were also asked to disclose sources of funding and sponsorship for their research. OSHA intended for the disclosure of such information to promote the transparency and scientific integrity of evidence submitted to the record and stated that the request was consistent with Executive Order 13563.

The Agency received several comments related to this request. For example, an industrial hygiene engineer supported the disclosure of potential conflict of interest information (Document ID 2278, p. 5). Other commenters, such as congressional representatives and industry associations, opposed the request, asserting that it could lead to prejudgment or questioning of integrity, in addition to dissuading participation in the rulemaking; some also questioned the legality of such a request or OSHA's interpretation of Executive Order 13563 (e.g., Document ID 1811, p. 2; 2101, pp. 2-3). A number of stakeholders from academia and industry submitted information related to the request for funding, sponsorships, and review by interested parties (e.g., Document ID 1766, p. 1; 2004, p. 2; 2211, p. 2; 2195, p. 17). OSHA emphasizes that it reviewed and considered all evidence submitted to the record.

An informal public hearing on the proposed standards was held in Washington, DC from March 18 through April 4, 2014. Administrative Law Judges Daniel F. Solomon and Stephen L. Purcell presided over the hearing. The Agency heard testimony from over 200 stakeholders representing more than 70 organizations, such as public health groups, trade associations, and labor unions. Chief Administrative Law Judge Stephen L. Purcell closed the public hearing on April 4, 2014, allowing 45 days—until May 19, 2014—for participants who filed a notice of intention to appear at the hearings to submit additional evidence and data, and an additional 45 days—until July 3, 2014—to submit final briefs, arguments, and summations (Document ID 3589, Tr. 4415-4416). After the hearing concluded, OSHA extended the deadline to give those participants who filed a notice of intention to appear at the hearings until June 3, 2014 to submit additional information and data to the record, and until July 18, 2014 to submit final briefs and arguments (Document ID 3569). Based upon requests from stakeholders, the second deadline was extended, and parties who filed a notice of intention to appear at the hearing were given until August 18, 2014, to submit their final briefs and arguments (Document ID 4192).

OSHA provided the public with multiple opportunities to participate in the rulemaking process, including stakeholder meetings, the SBREFA panel, two comment periods (pre- and post-hearing), and a 14-day public hearing. Commenters were provided more than five months to comment on the rule before the hearing, and nearly as long to submit additional information, final briefs, and arguments after the hearing. OSHA received more than 2,000 comments on the silica NPRM during the entire pre-and post-hearing public participation period. In OSHA's view, therefore, the public was given sufficient opportunities and ample time to fully participate in this rulemaking.

The final rule on occupational exposure to respirable crystalline silica is based on consideration of the entire record of this rulemaking proceeding, including materials discussed or relied upon in the proposal, the record of the hearing, and all written comments and exhibits timely received. Thus, in promulgating this final rule, OSHA considered all comments in the record, including those that suggested that OSHA withdraw its proposal and merely enforce the existing silica standards, as well as those that argued the proposed rule was not protective enough. Based on this comprehensive record, OSHA concludes that employees exposed to respirable crystalline silica are at significant risk of developing silicosis and other non-malignant respiratory disease, lung cancer, kidney effects, and immune system effects. The Agency concludes that the PEL of 50 μg/m³ reduces the significant risks of material impairments of health posed to workers by occupational exposure to respirable crystalline silica to the maximum extent that is technologically and economically feasible. OSHA's substantive determinations with regard to the comments, testimony, and other information in the record, the legal standards governing the decision-making process, and the Agency's analysis of the data resulting in its assessments of risks, benefits, technological and economic feasibility, and compliance costs are discussed elsewhere in this preamble.

IV. Chemical Properties and Industrial Uses

Silica is a compound composed of the elements silicon and oxygen (chemical formula SiO₂). Silica has a molecular weight of 60.08, and exists in crystalline and amorphous states, both in the natural environment and as produced during manufacturing or other processes. These substances are odorless solids, have no vapor pressure, and create non-explosive dusts when particles are suspended in air (Document ID 3637, pp. 1-3).

Silica is classified as part of the “silicate” class of minerals, which includes compounds that are composed of silicon and oxygen and which may also be bonded to metal ions or their oxides. The basic structural units of silicates are silicon tetrahedrons (SiO₄), pyramidal structures with four triangular sides where a silicon atom is located in the center of the structure and an oxygen atom is located at each of the four corners. When silica tetrahedrons bond exclusively with other silica tetrahedrons, each oxygen atom is bonded to the silicon atom of its original ion, as well as to the silicon atom from another silica ion. This results in a ratio of one atom of silicon to two atoms of oxygen, expressed as SiO₂. The silicon-oxygen bonds within the tetrahedrons use only one-half of each oxygen's total bonding energy. This leaves negatively charged oxygen ions available to bond with available positively charged ions. When they bond with metal and metal oxides, commonly of iron, magnesium, aluminum, sodium, potassium, and calcium, they form the silicate minerals commonly found in nature (Document ID 1334, p. 7).

In crystalline silica, the silicon and oxygen atoms are arranged in a three-dimensional repeating pattern. Silica is said to be polymorphic, as different forms are created when the silica tetrahedrons combine in different crystalline structures. The primary forms of crystalline silica are quartz, cristobalite, and tridymite. In an amorphous state, silicon and oxygen atoms are present in the same proportions but are not organized in a repeating pattern. Amorphous silica includes natural and manufactured glasses (vitreous and fused silica, quartz glass), biogenic silica, and opals, which are amorphous silica hydrates (Document ID 2258, Attachment 8, pp. 45-50).

Quartz is the most common form of crystalline silica and accounts for almost 12% by volume of the earth's crust. Alpha quartz, the quartz form that is stable below 573 °C, is the most prevalent form of crystalline silica found in the workplace. It accounts for the overwhelming majority of naturally found silica and is present in varying amounts in almost every type of mineral. Alpha quartz is found in igneous, sedimentary, and metamorphic rock, and all soils contain at least a trace amount of quartz (Document ID 1334, p. 9). Alpha quartz is used in many products throughout various industries and is a common component of building materials (Document ID 1334, pp. 11-15). Common trade names for commercially available quartz include: CSQZ, DQ 12, Min-U-Sil, Sil-Co-Sil, Snowit, Sykron F300, and Sykron F600 (Document ID 2258, Attachment 8, p. 43).

Cristobalite is a form of crystalline silica that is formed at high temperatures (>1470 °C). Although naturally occurring cristobalite is relatively rare, volcanic eruptions, such as Mount St. Helens, can release cristobalite dust into the air. Cristobalite can also be created during some processes conducted in the workplace. For example, flux-calcined diatomaceous earth is a material used as a filtering aid and as a filler in other products (Document ID 2258, Attachment 8, p. 44). It is produced when diatomaceous earth (diatomite), a geological product of decayed unicellular organisms called diatoms, is heated with flux. The finished product can contain between 40 and 60 percent cristobalite. Also, high temperature furnaces are often lined with bricks that contain quartz. When subjected to prolonged high temperatures, this quartz can convert to cristobalite.

Tridymite is another material formed at high temperatures (>870 °C) that is associated with volcanic activity. The creation of tridymite requires the presence of a flux such as sodium oxide. Tridymite is rarely found in nature and rarely reported in the workplace (Document ID 1424 pp. 5, 14).

When heated or cooled sufficiently, crystalline silica can transition between the polymorphic forms, with specific transitions occurring at different temperatures. At higher temperatures the linkages between the silica tetrahedrons break and reform, resulting in new crystalline structures. Quartz converts to cristobalite at 1470 °C, and at 1723 °C cristobalite loses its crystalline structure and becomes amorphous fused silica. These high temperature transitions reverse themselves at extremely slow rates, with different forms co-existing for a long time after the crystal cools (Document ID 2258, Attachment 8, p. 47).

Other types of transitions occur at lower temperatures when the silica-oxygen bonds in the silica tetrahedron rotate or stretch, resulting in a new crystalline structure. These low-temperature, or alpha to beta, transitions are readily and rapidly reversed as the crystal cools. At temperatures encountered by workers, only the alpha form of crystalline silica exists (Document ID 2258, Attachment 8, pp. 46-48).

Crystalline silica minerals produce distinct X-ray diffraction patterns, specific to their crystalline structure. The patterns can be used to distinguish the crystalline polymorphs from each other and from amorphous silica (Document ID 2258, Attachment 8, p. 45).

The specific gravity and melting point of silica vary between polymorphs. Silica is insoluble in water at 20 °C and in most acids, but its solubility increases with higher temperatures and pH, and it dissolves readily in hydrofluoric acid. Solubility is also affected by the presence of trace metals and by particle size. Under humid conditions water vapor in the air reacts with the surface of silica particles to form an external layer of silinols (SiOH). When these silinols are present the crystalline silica becomes more hydrophilic. Heating or acid washing reduces the amount of silinols on the surface area of crystalline silica particles. There is an external amorphous layer found in aged quartz, called the Beilby layer, which is not found on freshly cut quartz. This amorphous layer is more water soluble than the underlying crystalline core. Etching with hydrofluoric acid removes the Beilby layer as well as the principal metal impurities on quartz (Document ID 2258, Attachment 8, pp. 44-49).

Crystalline silica has limited chemical reactivity. It reacts with alkaline aqueous solutions, but does not readily react with most acids, with the exception of hydrofluoric acid. In contrast, amorphous silica and most silicates react with most mineral acids and alkaline solutions. Analytical chemists relied on this difference in acid reactivity to develop the silica point count analytical method that was widely used prior to the current X-ray diffraction and infrared methods (Document ID 2258, Attachment 8, pp. 48-51; 1355, p. 994).

Crystalline silica is used in industry in a wide variety of applications. Sand and gravel are used in road building and concrete construction. Sand with greater than 98% silica is used in the manufacture of glass and ceramics. Silica sand is used to form molds for metal castings in foundries, and in abrasive blasting operations. Silica is also used as a filler in plastics, rubber, and paint, and as an abrasive in soaps and scouring cleansers. Silica sand is used to filter impurities from municipal water and sewage treatment plants, and in hydraulic fracturing for oil and gas recovery (Document ID 1334, p. 11). Silica is also used to manufacture artificial stone products used as bathroom and kitchen countertops, and the silica content in those products can exceed 85 percent (Document ID 1477, pp. 3 and 11; 2178, Attachment 5, p. 420).

There are over 30 major industries and operations where exposures to crystalline silica can occur. They include such diverse workplaces as foundries, dental laboratories, concrete products and paint and coating manufacture, as well as construction activities including masonry cutting, drilling, grinding and tuckpointing, and use of heavy equipment during demolition activities involving silica-containing materials. A more detailed discussion of the industries affected by the proposed standard is presented in Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis. Crystalline silica exposures can also occur in mining (which is under the jurisdiction of the Mine Safety and Health Administration), and in agriculture during plowing and harvesting.

V. Health Effects

A. Introduction

As discussed more thoroughly in Section II of this preamble, Pertinent Legal Authority, section 6(b)(5) of the Occupational Safety and Health Act (OSH Act or Act) requires the Secretary of Labor, in promulgating standards dealing with toxic materials or harmful physical agents, to “set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life” (29 U.S.C. 655). Thus, in order to set a new health standard, the Secretary must determine that there is a significant risk of material impairment of health at the existing PEL and that issuance of a new standard will significantly reduce or eliminate that risk.

The Secretary's significant risk and material impairment determinations must be made “on the basis of the best available evidence” (29 U.S.C. 655(b)(5)). Although the Supreme Court, in its decision on OSHA's Benzene standard, explained that OSHA must look to “a body of reputable scientific thought” in making its material harm and significant risk determinations, the Court added that a reviewing court must “give OSHA some leeway where its findings must be made on the frontiers of scientific knowledge” (Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607, 656 (1980) (plurality opinion) (“Benzene”)). Thus, while OSHA's significant risk determination must be supported by substantial evidence, the Agency “is not required to support the finding that a significant risk exists with anything approaching scientific certainty” (Benzene, 448 U.S. at 656).

This section provides an overview of OSHA's material harm and significant risk determinations: (1) Summarizing OSHA's preliminary methods and findings from the proposal; (2) addressing public comments dealing with OSHA's evaluation of the scientific literature and methods used to estimate quantitative risk; and (3) presenting OSHA's final conclusions, with consideration of the rulemaking record, on the health effects and quantitative risk estimates associated with worker exposure to respirable crystalline silica. The quantitative risk estimates and significance of those risks are then discussed in detail in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

B. Summary of Health and Risk Findings

As discussed in detail throughout this section and in Section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA finds, based upon the best available evidence in the published, peer-reviewed scientific literature, that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, other non-malignant respiratory disease (NMRD), and renal and autoimmune effects. In its Preliminary Quantitative Risk Assessment (QRA), OSHA used the best available exposure-response data from epidemiological studies to estimate quantitative risks. After carefully reviewing stakeholder comments on the Preliminary QRA and new information provided to the rulemaking record, OSHA finds there to be a clearly significant risk at the previous PELs for respirable crystalline silica (equivalent to approximately 100 μg/m³ for general industry and between 250 and 500 μg/m³ for construction/shipyards), with excess lifetime risk estimates for lung cancer mortality, silicosis mortality, and NMRD mortality each being much greater than 1 death per 1,000 workers exposed for a working life of 45 years. Cumulative risk estimates for silicosis morbidity are also well above 1 case per 1,000 workers exposed at the previous PELs. At the revised PEL of 50 μg/m³ respirable crystalline silica, these estimated risks are substantially reduced. Thus, OSHA concludes that the new PEL of 50 μg/m³ provides a large reduction in the lifetime and cumulative risk posed to workers exposed to respirable crystalline silica.

These findings and conclusions are consistent with those of the World Health Organization's International Agency for Research on Cancer (IARC), the U.S. Department of Health and Human Services' (HHS) National Toxicology Program (NTP), the National Institute for Occupational Safety and Health (NIOSH), and many other organizations and individuals, as evidenced in the rulemaking record and further discussed below. Many other scientific organizations and governments have recognized the strong body of scientific evidence pointing to the health risks of respirable crystalline silica and have deemed it necessary to take action to reduce those risks. As far back as 1974, NIOSH recommended that the exposure limit for crystalline silica be reduced to 50 μg/m³ (Document ID 2177b, p. 2). In 2000, the American Conference of Governmental Industrial Hygienists (ACGIH), a professional society that has recommended workplace exposure limits for six decades, revised their Threshold Limit Value (TLV) for respirable crystalline silica to 50 μg/m³ and has since further lowered its TLV for respirable crystalline silica to 25 μg/m³. OSHA is setting its revised PEL at 50 μg/m³ based on consideration of the body of evidence describing the health risks of crystalline silica as well as on technological feasibility considerations, as discussed in Section VII of this preamble and Chapter IV of the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA).

To reach these conclusions, OSHA performed an extensive search and review of the peer-reviewed scientific literature on the health effects of inhalation exposure to crystalline silica, particularly silicosis, lung cancer, other NMRD, and renal and autoimmune effects (Document ID 1711, pp. 7-265). Based upon this review, OSHA preliminarily determined that there was substantial evidence that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, NMRD, and renal and autoimmune effects (Document ID 1711, pp. 164, 181-208, 229). OSHA also found there to be suitable exposure-response data from many well-conducted epidemiological studies that permitted the Agency to estimate quantitative risks for lung cancer mortality, silicosis and NMRD mortality, renal disease mortality, and silicosis morbidity (Document ID 1711, p. 266).

As part of the preliminary quantitative risk assessment, OSHA calculated estimates of the risk of silica-related diseases assuming exposure over a working life (45 years) to 25, 50, 100, 250, and 500 μg/m³ respirable crystalline silica (corresponding to cumulative exposures over 45 years to 1.125, 2.25, 4.5, 11.25, and 22.5 mg/m³-yrs) (see Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1264-65 (D.C. Cir. 1988) approving OSHA's policy of using 45 years for the working life of an employee in setting a toxic substance standard). To estimate lifetime excess mortality risks at these exposure levels, OSHA used, for each key study, the exposure-response risk model(s) and regression coefficient from the model(s) in a life table analysis that accounted for competing causes of death due to background causes and cumulated risk through age 85 (Document ID 1711, pp. 360-378). For these analyses, OSHA used lung cancer, NMRD, or renal disease mortality and all-cause mortality rates to account for background risks and competing risks (U.S. 2006 data for lung cancer and NMRD mortality in all males, 1998 data for renal disease mortality, obtained from cause-specific death rate tables published by the National Center for Health Statistics (2009, Document ID 1104)). The mortality risk estimates were presented in terms of lifetime excess risk per 1,000 workers for exposure over an 8-hour working day, 250 days per year, and a 45-year working lifetime. For silicosis morbidity, OSHA based its risk estimates on the cumulative risk model(s) used in each study to develop quantitative exposure-response relationships. These models characterized the risk of developing silicosis, as detected by chest radiography, up to the time that cohort members, including both active and retired workers, were last examined (78 FR 56273, 56312 (9/12/13)).

OSHA then combined its review of the health effects literature and preliminary quantitative risk assessment into a draft document, entitled “Occupational Exposure to Respirable Crystalline Silica—Review of Health Effects Literature and Preliminary Quantitative Risk Assessment,” and submitted it to a panel of scientific experts for independent peer review, in accordance with the Office of Management and Budget's (OMB) “Final Information Quality Bulletin for Peer Review” (Document ID 1336). The peer reviewers reviewed OSHA's draft Review of Health Effects Literature and Preliminary QRA. The peer-review panel responded to nearly 20 charge questions from OSHA and commented on various aspects of OSHA's analysis (Document ID 1716).

Overall, the peer reviewers found that OSHA was very thorough in its review of the literature and was reasonable in its interpretation of the studies with regards to the various endpoints examined, such that the Agency's conclusions on health effects were generally well founded (Document ID 1711, p. 381). The reviewers had various comments on OSHA's draft Preliminary QRA (Document ID 1716, pp. 107-218). OSHA provided a response to each comment in the Review of Health Effects Literature and Preliminary QRA and, where appropriate, made revisions (Document ID 1711, pp. 381-399). The Agency then placed the Review of Health Effects Literature and Preliminary QRA into the rulemaking docket as a background document (Document ID 1711). With the publication of the Notice of Proposed Rulemaking (78 FR 56723 on 9/12/13), all aspects of the Review of Health Effects Literature and Preliminary QRA were open for public comment.

Following the publication of the proposed rule (78 FR 56273 (9/12/13)) and accompanying revised Review of Health Effects Literature and Preliminary QRA (Document ID 1711), the peer reviewers were invited to review the revised analysis, examine the written comments in the docket, and attend the public hearing to listen to oral testimony as it applied to the health effects and quantitative risk assessment. Five peer reviewers were available and attended. In their final comments, provided to OSHA following the hearings, all five peer reviewers indicated that OSHA had adequately addressed their original comments (Document ID 3574). The peer reviewers also offered additional comments on concerns raised during the hearing. Many of the reviewers commented on the difficulty of evaluating exposure-response thresholds, and responded to public comments regarding causation and other specific issues (Document ID 3574). OSHA has incorporated many of the peer reviewers' additional comments into its risk assessment discussion in the preamble. Thus, OSHA believes that the external, independent peer-review process supports and lends legitimacy to its risk assessment methods and findings.

OSHA also received substantial public comment and testimony from a wide variety of stakeholders supporting its Review of Health Effects Literature and Preliminary QRA. In general, supportive comments and testimony were received from NIOSH (Document ID 2177; 3998; 4233), the public health and medical community, labor unions, affected workers, private citizens, and others.

Regarding health effects, NIOSH commented that the adverse health effects of exposure to respirable crystalline silica are “well-known, long lasting, and preventable” (Document ID 2177b, p. 2). Darius Sivin, Ph.D., of the UAW, commented, “[o]ccupational exposure to silica has been recognized for centuries as a serious workplace hazard” (Document ID 2282, Attachment 3, p. 4). Similarly, David Goldsmith, Ph.D., testified:

There have been literally thousands of research studies on exposure to crystalline silica in the past 30 years. Almost every study tells the occupational research community that workers need better protection to prevent severe chronic respiratory diseases, including lung cancer and other diseases in the future. What OSHA is proposing to do in revising the workplace standard for silica seems to be a rational response to the accumulation of published evidence (Document ID 3577, Tr. 865-866).

Franklin Mirer, Ph.D., CIH, Professor of Environmental and Occupational Health at CUNY School of Public Health, on behalf of the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), reiterated that silica “is a clear and present danger to workers health at exposure levels prevailing now in a large number of industries. Workers are at significant risk for mortality and illnesses including lung cancer and non-malignant respiratory disease including COPD, and silicosis” (Document ID 2256, Attachment 3, p. 3). The AFL-CIO also noted that there is “overwhelming evidence in the record that exposure to respirable crystalline silica poses a significant health risk to workers” (Document ID 4204, p. 11). The Building and Construction Trades Department, AFL-CIO, further commented that the rulemaking record “clearly supports OSHA's risk determination” (Document ID 4223, p. 2). Likewise, the Sorptive Minerals Institute, a national trade association, commented, “It is beyond dispute that OSHA has correctly determined that industrial exposure to certain types of silica can cause extremely serious, sometimes even fatal disease. In the massive rulemaking docket being compiled by the Agency, credible claims to the contrary are sparse to non-existent” (Document ID 4230, p. 8). OSHA also received numerous comments supportive of the revised standard from affected workers and citizens (e.g., Document ID 1724, 1726, 1731, 1752, 1756, 1759, 1762, 1764, 1787, 1798, 1800, 1802).

Regarding OSHA's literature review for its quantitative risk assessment, the American Public Health Association (APHA) and the National Consumers League (NCL) commented, “OSHA has thoroughly reviewed and evaluated the peer-reviewed literature on the health effects associated with exposure to respirable crystalline silica. OSHA's quantitative risk assessment is sound. The agency has relied on the best available evidence and acted appropriately in giving greater weight to those studies with the most robust designs and statistical analyses” (Document ID 2178, Attachment 1, p. 1; 2373, p. 1).

Dr. Mirer, who has served on several National Academy of Sciences committees setting risk assessment guidelines, further commented that OSHA's risk analysis is “scientifically correct, and consistent with the latest thinking on risk assessment,” (Document ID 2256, Attachment 3, p. 3), citing the National Academies' National Research Council's Science and Decisions: Advancing Risk Assessment (Document ID 4052), which makes technical recommendations on risk assessment and risk-based decision making (Document ID 3578, Tr. 935-936). In post-hearing comments expanding on this testimony, the AFL-CIO also noted that OSHA's risk assessment methodologies are transparent and consistent with practices recommended by the National Research Council in its publication, Risk Assessment in the Federal Government: Managing the Process, and with the Environmental Protection Agency's Guidelines for Carcinogenic Risk Assessment (Document ID 4204, p. 20). Similarly, Kyle Steenland, Ph.D., Professor in the Department of Environmental Health at Rollins School of Public Health, Emory University, one of the researchers on whose studies OSHA relied, testified that “OSHA has done a very capable job in conducting the summary of the literature and doing its own risk assessment” (Document ID 3580, Tr. 1235). Collectively, these comments and testimony support OSHA's use of the best available evidence and methods to estimate quantitative risks of lung cancer mortality, silicosis and NMRD mortality, renal disease mortality, and silicosis morbidity from exposure to respirable crystalline silica.

Based on OSHA's Preliminary QRA, many commenters recognized that reducing the permissible exposure limit is necessary to reduce significant risks presented by exposure to respirable crystalline silica (Document ID 4204, pp. 11-12; 2080, p. 1; 2339, p. 2). For example, the AFL-CIO stated that “OSHA based its proposal on more than adequate evidence, but more recent publications have described further the risk posed by silica exposure, and further justify the need for new silica standards” (Document ID 4204, pp. 11-12). Similarly, the American Society of Safety Engineers (ASSE) remarked that “[w]hile some may debate the science underlying the findings set forth in the proposed rule, overexposure to crystalline silica has been linked to occupational illness since the time of the ancient Greeks, and reduction of the current permissible exposure limit (PEL) to that recommended for years by the National Institute for Occupational Safety and Health (NIOSH) is long overdue” (Document ID 2339, p. 2).

Not every commenter agreed, however, as OSHA also received critical comments and testimony from various employers and their representatives, as well as some organizations representing affected industries. In general, these comments were critical of the underlying studies on which OSHA relied for its quantitative risk assessment, or with the methods used by OSHA to estimate quantitative risks. Some commenters also presented additional studies for OSHA to consider. OSHA thoroughly reviewed these and did not find them adequate to alter OSHA's overall conclusions of health risk, as discussed in great detail in the sections that follow.

After considering the evidence and testimony in the record, as discussed below, OSHA affirms its approach to quantify health risks related to exposure to respirable crystalline silica and the Agency's preliminary conclusions. In the final risk assessment that is now presented as part of this final rule in Section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA concludes that there is a clearly significant risk at the previous PELs for respirable crystalline silica, with excess lifetime risk estimates for lung cancer mortality, silicosis mortality, and NMRD mortality each being much greater than 1 death per 1,000 workers as a result of exposure for 45 working years (see Section VI, Final Quantitative Risk Assessment and Significance of Risk). At the revised PEL of 50 µg/m³ respirable crystalline silica, OSHA finds the estimated risks to be substantially reduced. Cumulative risk estimates for silicosis morbidity are also well above 1 case per 1,000 workers at the previous PELs, with a substantial reduction at the revised PEL (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1).

The health effects associated with silica exposure are well-established and supported by the record. Based on the record evidence, OSHA concludes that exposure to respirable crystalline silica causes silicosis and is the only known cause of silicosis. This causal relationship has long been accepted in the scientific and medical communities. In fact, the Department of Labor produced a video in 1938 featuring then Secretary of Labor Frances Perkins discussing the occurrence of silicosis among workers exposed to silica (see https://www.osha.gov/silica/index.html ). Silicosis is a progressive disease induced by the inflammatory effects of respirable crystalline silica in the lung, which leads to lung damage and scarring and, in some cases, progresses to complications resulting in disability and death (see Section VI, Final Quantitative Risk Assessment and Significance of Risk). OSHA used a weight-of-evidence approach to evaluate the scientific studies in the literature to determine their overall quality and whether there is substantial evidence that exposure to respirable crystalline silica increases the risk of a particular health effect.

For lung cancer, OSHA reviewed the published, peer-reviewed scientific literature, including 60 epidemiological studies covering more than 30 occupational groups in over a dozen industrial sectors (see Document ID 1711, pp. 77-170). Based on this comprehensive review, and after considering the rulemaking record as a whole, OSHA concludes that the data provide ample evidence that exposure to respirable crystalline silica increases the risk of lung cancer among workers (see Document ID 1711, p. 164). OSHA's conclusion is consistent with that of IARC, which is the specialized cancer agency that is part of the World Health Organization and utilizes interdisciplinary (e.g., biostatistics, epidemiology, and laboratory sciences) experts to comprehensively identify the causes of cancer. In 1997, IARC classified respirable crystalline silica dust, in the form of quartz or cristobalite, as Group 1, i.e., “carcinogenic to humans,” following a thorough expert committee review of the peer-reviewed scientific literature (Document ID 2258, Attachment 8, p. 211). OSHA notes that IARC classifications and accompanying monographs are well recognized in the scientific community, having been described as “the most comprehensive and respected collection of systematically evaluated agents in the field of cancer epidemiology” (Demetriou et al., 2012, Document ID 4131, p. 1273). For silica, IARC's overall finding was based on studies of nine occupational cohorts that it considered to be the least influenced by confounding factors (see Document ID 1711, p. 76). OSHA included these studies in its review, in addition to several other studies (Document ID 1711, pp. 77-170).

Since IARC's 1997 determination that respirable crystalline silica is a Group 1 carcinogen, the scientific community has reaffirmed the soundness of this finding. In March of 2009, 27 scientists from eight countries participated in an additional IARC review of the scientific literature and reaffirmed that respirable crystalline silica dust is a Group 1 human carcinogen (Document ID 1473, p. 396). Additionally, in 2000, the NTP, which is a widely-respected interagency program under HHS that evaluates chemicals for possible toxic effects on public health, also concluded that respirable crystalline silica is a known human carcinogen (Document ID 1164, p. 1).

For NMRD other than silicosis, based on its review of several studies and all subsequent record evidence, OSHA concludes that exposure to respirable crystalline silica increases the risk of emphysema, chronic bronchitis, and pulmonary function impairment (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 181-208). For renal disease, OSHA reviewed the epidemiological literature and finds that a number of epidemiological studies reported statistically significant associations between occupational exposure to silica dust and chronic renal disease, subclinical renal changes, end-stage renal disease morbidity, chronic renal disease mortality, and granulomatosis with polyangitis (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 228). For autoimmune effects, OSHA reviewed epidemiological information in the record suggesting an association between respirable crystalline silica exposure and increased risk of systemic autoimmune diseases, including scleroderma, rheumatoid arthritis, and systemic lupus erythematosus (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229). Therefore, OSHA concludes that there is substantial evidence that silica exposure increases the risks of renal and of autoimmune disease (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229).

OSHA also finds there to be suitable exposure-response data from many well-conducted studies that permit the Agency to estimate quantitative risks for lung cancer mortality, silicosis and NMRD mortality, renal disease mortality, and silicosis morbidity (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 266). OSHA believes the exposure-response data in these studies collectively represent the best available evidence for use in estimating the quantitative risks related to silica exposure. For lung cancer mortality, OSHA relies upon a number of published studies that analyzed exposure-response relationships between respirable crystalline silica and lung cancer. These included studies of cohorts from several industry sectors: Diatomaceous earth workers (Rice et al., 2001, Document ID 1118), Vermont granite workers (Attfield and Costello, 2004, Document ID 0285), North American industrial sand workers (Hughes et al., 2001, Document ID 1060), and British coal miners (Miller and MacCalman, 2009, Document ID 1306). These studies are scientifically sound due to their sufficient size and adequate years of follow-up, sufficient quantitative exposure data, lack of serious confounding by exposure to other occupational carcinogens, consideration (for the most part) of potential confounding by smoking, and absence of any apparent selection bias (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 165). They all demonstrated positive, statistically significant exposure-response relationships between exposure to crystalline silica and lung cancer mortality. Also compelling was a pooled analysis (Steenland et al., 2001a, Document ID 0452) of 10 occupational cohorts (with a total of 65,980 workers and 1,072 lung cancer deaths), which was also used as a basis for IARC's 2009 reaffirmation of respirable crystalline silica as a human carcinogen. This analysis by Steenland et al. found an overall positive exposure-response relationship between cumulative exposure to crystalline silica and lung cancer mortality (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 269-292). Based on these studies, OSHA estimates that the lifetime lung cancer mortality excess risk associated with 45 years of exposure to respirable crystalline silica ranges from 11 to 54 deaths per 1,000 workers at the previous general industry PEL of 100 µg/m³ respirable crystalline silica, and 5 to 23 deaths per 1,000 workers at the revised PEL of 50 µg/m³ respirable crystalline silica (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). These estimates exceed by a substantial margin the one in a thousand benchmark that OSHA has generally applied to its health standards following the Supreme Court's Benzene decision (448 U.S. 607, 655 (1980)).

For silicosis and NMRD mortality, OSHA relies upon two published, peer-reviewed studies: A pooled analysis of silicosis mortality data from six epidemiological studies (Mannetje et al., 2002b, Document ID 1089), and an exposure-response analysis of NMRD mortality among diatomaceous earth workers (Park et al, 2002, Document ID 0405) (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 292). The pooled analysis had a total of 18,634 subjects, 150 silicosis deaths, and 20 deaths from unspecified pneumoconiosis, and demonstrated an increasing mortality rate with silica exposure (Mannetje et al., 2002b, Document ID 1089; see also 1711, pp. 292-295). To estimate the risks of silicosis mortality, OSHA used the model described by Mannetje et al. but used rate ratios that were estimated from a sensitivity analysis conducted by ToxaChemica, Inc. that was expected to better control for age and exposure measurement uncertainty (2004, Document ID 0469; 1711, p. 295). OSHA's estimate of lifetime silicosis mortality risk is 11 deaths per 1,000 workers at the previous general industry PEL, and 7 deaths per 1,000 workers at the revised PEL (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1).

The NMRD analysis by Park et al. (2002, Document 0405) included pneumoconiosis (including silicosis), chronic bronchitis, and emphysema, since silicosis is a cause of death that is often misclassified as emphysema or chronic bronchitis (see Document ID 1711, p. 295). Positive exposure-response relationships were found between exposure to crystalline silica and excess risk for NMRD mortality (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 204-206, 295-297). OSHA's estimate of excess lifetime NMRD mortality risk, calculated using the results from Park et al., is 85 deaths per 1,000 workers at the previous general industry PEL of 100 µg/m respirable crystalline silica, and 44 deaths per 1,000 workers at the revised PEL (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1).

For renal disease mortality, Steenland et al. (2002a, Document ID 0448) conducted a pooled analysis of three cohorts (with a total of 13,382 workers) that found a positive exposure-response relationship for both multiple-cause mortality (i.e., any mention of renal disease on the death certificate) and underlying cause mortality. OSHA used the Steenland et al. (2002a, Document ID 0448) pooled analysis to estimate risks, given its large number of workers from cohorts with sufficient exposure data (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 314-315). OSHA's analysis for renal disease mortality shows estimated lifetime excess risk of 39 deaths per 1,000 workers at the previous general industry PEL of 100 µg/m³ respirable crystalline silica, and 32 deaths per 1,000 workers exposed at the revised PEL of 50 µg/m³ (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). OSHA acknowledges, however, that there are considerably less data for renal disease mortality, and thus the findings based on them are less robust than those for silicosis, lung cancer, and NMRD mortality (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229). For autoimmune disease, there were no quantitative exposure-response data available for a quantitative risk assessment (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229).

For silicosis morbidity, OSHA reviewed the principal studies available in the scientific literature that have characterized the risk to exposed workers of acquiring silicosis, as detected by the appearance of opacities on chest radiographs (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 357). The most reliable estimates of silicosis morbidity came from five studies that evaluated radiographs over time, including after workers left employment: The U.S. gold miner cohort studied by Steenland and Brown (1995b, Document ID 0451); the Scottish coal miner cohort studied by Buchanan et al. (2003, Document ID 0306); the Chinese tin mining cohort studied by Chen et al. (2001, Document ID 0332); the Chinese tin, tungsten, and pottery worker cohorts studied by Chen et al. (2005, Document ID 0985); and the South African gold miner cohort studied by Hnizdo and Sluis-Cremer (1993, Document ID 1052) (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 316-343). These studies demonstrated positive exposure-response relationships between exposure to crystalline silica and silicosis risk. Based on the results of these studies, OSHA estimates a cumulative risk for silicosis morbidity of between 60 and 773 cases per 1,000 workers for a 45-year exposure to the previous general industry PEL of 100 µg/m³ respirable crystalline silica depending upon the study used, and between 20 and 170 cases per 1,000 workers exposed at the new PEL of 50 µg/m³ depending upon the study used (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). Thus, like OSHA's risk estimates for other health endpoints, the risk is substantially lower, though still significant, at the revised PEL.

In conclusion, OSHA finds, based on the best available evidence and methods to estimate quantitative risks of disease resulting from exposure to respirable crystalline silica, that there are significant risks of material health impairment at the former PELs for respirable crystalline silica, which would be substantially reduced (but not entirely eliminated) at the new PEL of 50 μg/m³. In meeting its legal burden to estimate the health risks posed by respirable crystalline silica, OSHA has used the best available evidence and methods to estimate quantitative risks of disease resulting from exposure to respirable crystalline silica. As a result, the Agency finds that the lifetime excess mortality risks (for lung cancer, NMRD and silicosis, and renal disease) and cumulative risk (silicosis morbidity) posed to workers exposed to respirable crystalline silica over a working life represent significant risks that warrant mitigation, and that these risks will be substantially reduced at the revised PEL of 50 μg/m³ respirable crystalline silica.

C. Summary of the Review of Health Effects Literature and Preliminary QRA

As noted above, a wide variety of stakeholders offered comments and testimony in this rulemaking on issues related to health and risk. Many of these comments were submitted in response to OSHA's preliminary risk and material impairment determinations, which were presented in two background documents, entitled “Occupational Exposure to Respirable Crystalline Silica—Review of Health Effects Literature and Preliminary Quantitative Risk Assessment” (Document ID 1711) and “Supplemental Literature Review of Epidemiological Studies on Lung Cancer Associated with Exposure to Respirable Crystalline Silica” (Document ID 1711, Attachment 1), and summarized in the proposal in Section V, Health Effects Summary, and Section VI, Summary of OSHA's Preliminary Quantitative Risk Assessment.

In this subsection, OSHA summarizes the major findings of the two background documents. The Agency intends for this subsection to provide the detailed background necessary to fully understand stakeholders' comments and OSHA's responses.

1. Background

As noted above, OSHA's Review and Supplemental Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711; 1711, Attachment 1) were the result of the Agency's extensive search and review of the peer-reviewed scientific literature on the health effects of inhalation exposure to crystalline silica, particularly silicosis, lung cancer and cancer at other sites, non-malignant respiratory diseases (NMRD) other than silicosis, and renal and autoimmune effects. The purposes of this detailed search and scientific review were to determine the nature of the hazards presented by exposure to respirable crystalline silica, and to evaluate whether there was an adequate basis, with suitable data availability, for quantitative risk assessment.

Much of the scientific evidence that describes the health effects and risks associated with exposure to crystalline silica consisted of epidemiological studies of worker populations; OSHA also reviewed animal and in vitro studies. OSHA used a weight-of-evidence approach in evaluating this evidence. Under this approach, OSHA evaluated the relevant studies to determine their overall quality. Factors considered in assessing the quality of studies included: (1) The size of the cohort studied and the power of the study to detect a sufficiently low level of disease risk; (2) the duration of follow-up of the study population; (3) the potential for study bias (e.g., selection bias in case-control studies or survivor effects in cross-sectional studies); and (4) the adequacy of underlying exposure information for examining exposure-response relationships. Studies were deemed suitable for inclusion in OSHA's Preliminary Quantitative Risk Assessment (QRA) where there was adequate quantitative information on exposure and disease risks and the study was judged to be sufficiently high quality according to these criteria.

Based upon this weight-of-evidence approach, OSHA preliminarily determined that there is substantial evidence in the peer-reviewed scientific literature that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, other NMRD, and renal and autoimmune effects. The Preliminary QRA indicated that, for silicosis and NMRD mortality, lung cancer mortality, and renal disease mortality, there is a significant risk at the previous PELs for respirable crystalline silica, with excess lifetime risk estimates substantially greater than 1 death per 1,000 workers as a result of exposure over a working life (45 years, from age 20 to age 65). At the revised PEL of 50 μg/m³ respirable crystalline silica, OSHA estimated that these risks would be substantially reduced. Cumulative risk estimates for silicosis morbidity were also well above 1 case per 1,000 workers at the previous PELs, with a substantial reduction at the revised PEL.

2. Summary of the Review of Health Effects Literature

In its Review of Health Effects Literature, OSHA identified the adverse health effects associated with the inhalation of respirable crystalline silica (Document ID 1711). OSHA covered the following topics: Silicosis (including relevant data from U.S. disease surveillance efforts), lung cancer and cancer at other sites, non-malignant respiratory diseases (NMRD) other than silicosis, renal and autoimmune effects, and physical factors affecting the toxicity of crystalline silica. Most of the evidence that described the health risks associated with exposure to silica consisted of epidemiological studies of worker populations; animal and in vitro studies on mode of action and molecular toxicology were also described. OSHA focused solely on those studies associated with airborne exposure to respirable crystalline silica due to the lack of evidence of health hazards from dermal or oral exposure. The review was further confined to issues related to the inhalation of respirable dust, which is generally defined as particles that are capable of reaching the pulmonary region of the lung (i.e., particles less than 10 microns (μm) in aerodynamic diameter), in the form of either quartz or cristobalite, the two forms of crystalline silica most often encountered in the workplace.

a. Silicosis

i. Types

Silicosis is an irreversible, progressive disease induced by the inflammatory effects of respirable crystalline silica in the lung, leading to lung damage and scarring and, in some cases, progressing to complications resulting in disability and death. Exposure to respirable crystalline silica is the only known cause of silicosis. Three types of silicosis have been described: An acute form following intense exposure to respirable dust of high crystalline silica content for a relatively short period (i.e., a few months or years); an accelerated form, resulting from about 5 to 15 years of heavy exposure to respirable dusts of high crystalline silica content; and, most commonly, a chronic form that typically follows less intense exposure of more than 20 years (Becklake, 1994, Document ID 0294; Balaan and Banks, 1992, 0289). In both the accelerated and chronic forms of the disease, lung inflammation leads to the formation of excess connective tissue, or fibrosis, in the lung. The hallmark of the chronic form of silicosis is the silicotic islet or nodule, one of the few agent-specific lesions in pathology (Balaan and Banks, 1992, Document ID 0289). As the disease progresses, these nodules, or fibrotic lesions, increase in density and can develop into large fibrotic masses, resulting in progressive massive fibrosis (PMF). Once established, the fibrotic process of chronic silicosis is thought to be irreversible (Becklake, 1994, Document ID 0294). There is no specific treatment for silicosis (Davis, 1996, Document ID 0998; Banks, 2005, 0291).

Chronic silicosis is the most frequently observed type of silicosis in the U.S. today. Affected workers may have a dry chronic cough, sputum production, shortness of breath, and reduced pulmonary function. These symptoms result from airway restriction and/or obstruction caused by the development of fibrotic scarring in the alveolar sacs and lower region of the lung. Prospective studies that follow the exposed cohort over a long period of time with periodic examinations can provide the best information on factors affecting the development and progression of silicosis, which has a latency period (the interval between beginning of exposure to silica and the onset of disease) from 10 to 30 years after first exposure (Weissman and Wagner, 2005; Document ID 0481).

ii. Diagnosis

The scarring caused by silicosis can be detected by chest x-ray or computerized tomography (CT) when the lesions become large enough to appear as visible opacities. The clinical diagnosis of silicosis has three requirements: Recognition by the physician that exposure to crystalline silica has occurred; the presence of chest radiographic abnormalities consistent with silicosis; the absence of other illnesses that could resemble silicosis on a chest radiograph (e.g., pulmonary fungal infection or tuberculosis) (Balaan and Banks, 1992, Document ID 0289; Banks, 2005, 0291). A standardized system to classify opacities seen in chest radiographs was developed by the International Labour Organization (ILO) to describe the presence and severity of silicosis on the basis of size, shape, and density of opacities, which together indicate the severity and extent of lung involvement (ILO, 1980, Document ID 1063; ILO, 2002, 1064; ILO, 2011, 1475; Merchant and Schwartz, 1998, 1096; NIOSH, 2011, 1513). The density of opacities seen on chest radiographs is classified on a 4-point category scale (0, 1, 2, or 3), with each category divided into three, giving a 12-subcategory scale between 0/0 and 3/+. For each subcategory, the top number indicates the major category that the profusion most closely resembles, and the bottom number indicates the major category that was given secondary consideration. Category 0 indicates the absence of visible opacities and categories 1 to 3 reflect increasing profusion of opacities and a concomitant increase in severity of disease. The bottom number can deviate from the top number by 1. At the extremes of the scale, a designation of 0/− or 3/+ may be used. Subcategory 0/− represents a radiograph that is obviously absent of small opacities. Subcategory 3/+ represents a radiograph that shows much greater profusion than depicted on a standard 3/3 radiograph.

To address the low sensitivity of chest x-rays for detecting silicosis, Hnizdo et al. (1993, Document ID 1050) recommended that radiographs consistent with an ILO category of 0/1 or greater be considered indicative of silicosis among workers exposed to a high concentration of silica-containing dust. In like manner, to maintain high specificity, chest x-rays classified as category 1/0 or 1/1 should be considered as a positive diagnosis of silicosis. A biopsy is not necessary to make a diagnosis and a diagnosis does not require that chest x-ray films or digital radiographic images be rated using the ILO system (NIOSH, 2002, Document ID 1110).

iii. Review of Occupation-Based Epidemiological Studies

The causal relationship between exposure to crystalline silica and silicosis has long been accepted in the scientific and medical communities. OSHA reviewed a large number of cross-sectional and retrospective studies conducted to estimate the quantitative relationship between exposure to crystalline silica and the development of silicosis (e.g., Kreiss and Zhen, 1996, Document ID 1080; Love et al., 1999, 0369; Ng and Chan, 1994, 0382; Rosenman et al., 1996, 0423; Churchyard et al., 2003, 1295; Churchyard et al., 2004, 0986; Hughes et al., 1998, 1059; Muir et al., 1989a, 1102; Muir et al., 1989b, 1101; Park et al., 2002, 0405; Chen et al., 2001, 0332; Chen et al., 2005, 0985; Hnizdo and Sluis-Cremer, 1993, 1052; Miller et al., 1998, 0374; Buchanan et al., 2003, 0306; Steenland and Brown, 1995b, 0451). In general, these studies, particularly those that included retirees, found a risk of radiological silicosis (usually defined as x-ray films classified as ILO major category 1 or greater) among workers exposed near the range of cumulative exposures permitted by current exposure limits. The studies' methods and findings are presented in detail in the Preliminary QRA (Document ID 1711, pp. 316-340); those studies on which OSHA relied for its risk estimates are also discussed in the Summary of the Preliminary QRA, below.

OSHA's review of the silicosis literature also focused on specific issues associated with the factors that affect the progression of the disease and the relationship between the appearance of radiological abnormalities indicative of silicosis and pulmonary function decline. From its review of the health literature, OSHA made a number of preliminary findings. First, the size of opacities apparent on initial x-ray films is a determinant of future disease progression, with subjects exhibiting large opacities more likely to experience progression than those having smaller opacities (Hughes et al., 1982, Document ID 0362; Lee et al., 2001, 1086; Ogawa et al., 2003, 0398). Second, continued exposure to respirable crystalline silica following diagnosis of radiological silicosis increases the probability of disease progression compared to those who are not further exposed (Hessel et al., 1988, Document ID 1042), although there remains a likelihood of progression even absent continued exposure (Hessel et al., 1988, Document ID 1042; Miller et al., 1998, 0374; Ogawa et al., 2003, 0398; Yang et al., 2006, 1134).

With respect to the relationship between radiological silicosis and pulmonary function declines, literature findings are mixed. A number of studies have reported pulmonary function declines among workers exhibiting a degree of small-opacity profusion consistent with ILO categories 2 and 3 (e.g., Ng and Chan, 1992, Document ID 1107). However, although some studies have not found pulmonary function declines associated with silicosis scored as ILO category 1, a number of other studies have documented declines in pulmonary function in persons exposed to silica and whose radiograph readings are in the major ILO category 1 (i.e., 1/0, 1/1, 1/2), or even before changes were seen on chest x-ray (Cowie, 1998, 0993; Cowie and Mabena, 1991, 0342; Ng et al., 1987(a), 1108; Wang et al., 1997, 0478). Thus, OSHA preliminarily concluded that at least some individuals will develop pulmonary function declines absent radiological changes indicative of silicosis. The Agency posited that this may reflect the relatively poor sensitivity of x-ray films in detecting silicosis or may be due to pulmonary function declines related to silica-induced chronic obstructive pulmonary disease (see Document ID 1711, pp. 49-75).

iv. Surveillance

Unlike most occupational diseases, surveillance statistics are available on silicosis mortality and morbidity in the U.S. The most comprehensive and current source of surveillance data in the U.S. related to occupational lung diseases, including silicosis, is the National Institute for Occupational Safety and Health (NIOSH) Work-Related Lung Disease (WoRLD) Surveillance System (NIOSH, 2008c, Document ID 1308). Other sources are detailed in the Review of Health Effects Literature (Document ID 1711). Mortality data are compiled from death certificates reported to state vital statistics offices, which are collected by the National Center for Health Statistics (NCHS), an agency within the Centers for Disease Control and Prevention (e.g., CDC, 2005, Document ID 0319).

Silicosis-related mortality has declined in the U.S. over the time period for which these data have been collected. From 1968 to 2005, the annual number of silicosis deaths decreased from 1,157 to 161 (NIOSH, 2008c, Document ID 1308; http://wwwn.cdc.gov/eworld ). The CDC cited two main factors that were likely responsible for the declining trend in silicosis mortality since 1968 (CDC, 2005, Document ID 0319). First, many deaths during the early part of the study period were among workers whose main exposure to respirable crystalline silica probably occurred before introduction of national silica standards established by OSHA and the Mine Safety and Health Administration (MSHA) (i.e., permissible exposure limits (PELs)); these standards likely led to reduced silica dust exposure beginning in the 1970s. Second, employment has declined in heavy industries (e.g., foundries) where silica exposure was prevalent (CDC, 2005, Document ID 0319).

Despite this decline, silicosis deaths among workers of all ages result in significant premature mortality; between 1996 and 2005, a total of 1,746 deaths resulted in a total of 20,234 years of life lost from life expectancy, with an average of 11.6 years of life lost. For the same period, among 307 decedents who died before age 65 (the end of a working life), there were 3,045 years of life lost up to age 65, with an average of 9.9 years of life lost from a working life (NIOSH, 2008c, Document ID 1308).

Surveillance data on silicosis morbidity, primarily from hospital discharge records, are available only from the few states that have administered disease surveillance programs for silicosis. For the reporting period 1993-2002, these states recorded 879 cases of silicosis (NIOSH 2008c, Document ID 1308). Nationwide hospital discharge data compiled by NIOSH (2008c, Document ID 1308) and the Council of State and Territorial Epidemiologists (CSTE, 2005, Document ID 0996) indicate that, for the years 1970 to 2004, there were at least 1,000 hospitalizations that were coded for silicosis each year, except one.

Relying exclusively on such passive case-based disease surveillance systems that depend on the health care community to generate records is likely to understate the prevalence of diseases associated with respirable crystalline silica (Froines et al., 1989, Document ID 0385). In order to diagnose occupational diseases, health care professionals must have information about occupational histories and must be able to recognize occupational diseases (Goldman and Peters, 1981, Document ID 1027; Rutstein et al., 1983, 0425). The first criterion to be met in diagnosing silicosis is knowing a patient's history of exposure to crystalline silica. In addition to the lack of information about exposure histories, difficulty in recognizing occupational illnesses like silicosis, that manifest themselves long after initial exposure, contributes to under-recognition and underreporting by health care providers. Based on an analysis of data from Michigan's silicosis surveillance activities, Rosenman et al. (2003, Document ID 0420) estimated that silicosis mortality and morbidity were understated by a factor of between 2.5 and 5, and estimated that between 3,600 and 7,300 new cases of silicosis likely occurred in the U.S. annually between 1987 and 1996.

b. Lung Cancer

i. International Agency for Research on Cancer (IARC) Classification

In 1997, the IARC determined that there was sufficient evidence to regard crystalline silica as a human carcinogen (IARC, 1997, Document ID 1062). This finding was based largely on nine studies of cohorts in four industry sectors that IARC considered to be the least influenced by confounding factors (sectors included quarries and granite works, gold mining, ceramic/pottery/refractory brick industries, and the diatomaceous earth industry). NIOSH also determined that crystalline silica is a human carcinogen after evaluating updated literature (2002, Document ID 1110).

ii. Review of Occupation-Based Epidemiological Studies

OSHA conducted an independent review of the epidemiological literature on exposure to respirable crystalline silica and lung cancer, covering more than 30 occupational groups in over a dozen industrial sectors. OSHA's review included approximately 60 primary epidemiological studies. Based on this review, OSHA preliminarily concluded that the human data provides ample evidence that exposure to respirable crystalline silica increases the risk of lung cancer among workers.

The strongest evidence for carcinogenicity came from studies in five industry sectors:

• Diatomaceous Earth Workers (Checkoway et al., 1993, Document ID 0324; Checkoway et al., 1996, 0325; Checkoway et al., 1997, 0326; Checkoway et al., 1999, 0327; Seixas et al., 1997, 0431);
• British Pottery Workers (Cherry et al., 1998, Document ID 0335; McDonald et al., 1995, 0371);
• Vermont Granite Workers (Attfield and Costello, 2004, Document ID 0285; Graham et al., 2004, 1031; Costello and Graham, 1988, 0991; Davis et al., 1983, 0999);
• North American Industrial Sand Workers (Hughes et al., 2001, Document ID 1060; McDonald et al., 2001, 1091; McDonald et al., 2005, 1092; Rando et al., 2001, 0415; Sanderson et al., 2000, 0429; Steenland and Sanderson, 2001, 0455); and
• British Coal Miners (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306).

OSHA considered these studies as providing the strongest evidence for several reasons. They were all retrospective cohort or case-control studies that demonstrated positive, statistically significant exposure-response relationships between exposure to crystalline silica and lung cancer mortality. Except for the British pottery studies, where exposure-response trends were noted for average exposure only, lung cancer risk was found to be related to cumulative exposure. In general, these studies were of sufficient size and had adequate years of follow up, and had sufficient quantitative exposure data to reliably estimate exposures of cohort members. As part of their analyses, the authors of these studies also found positive exposure-response relationships for silicosis, indicating that underlying estimates of worker exposures were not likely to be substantially misclassified. Furthermore, the authors of these studies addressed potential confounding due to other carcinogenic exposures through study design or data analysis.

In the diatomaceous earth industry, Checkoway et al. developed a “semi-quantitative” cumulative exposure estimate that demonstrated a statistically significant positive exposure-response trend between duration of employment or cumulative exposure and lung cancer mortality (1993, Document ID 0324). The quartile analysis with a 15-year lag showed an increasing trend in relative risks (RR) of lung cancer mortality, with the highest exposure quartile having a RR of 2.74 for lung cancer mortality. Checkoway et al. conducted a re-analysis to address criticisms of potential confounding due to asbestos and again demonstrated a positive exposure-response risk gradient when controlling for asbestos exposure and other variables (1996, Document ID 0325). Rice et al. (2001, Document ID 1118) conducted a re-analysis and quantitative risk assessment of the Checkoway et al. (1997, Document ID 0326) study, finding that exposure to crystalline silica was a significant predictor of lung cancer mortality. OSHA included this re-analysis in its Preliminary QRA (Document ID 1711).

In the British pottery industry, excess lung cancer risk was found to be associated with crystalline silica exposure among workers in a proportionate mortality ratio (PMR) study (McDonald et al., 1995, Document ID 0371) and in a cohort and nested case-control study (Cherry et al., 1998, Document ID 0335). In the former, elevated PMRs for lung cancer were found after adjusting for potential confounding by asbestos exposure. In the study by Cherry et al., odds ratios for lung cancer mortality were statistically significantly elevated after adjusting for smoking. Odds ratios were related to average, but not cumulative, exposure to crystalline silica.

In the Vermont granite cohort, Costello and Graham (1988, Document ID 0991) and Graham et al. (2004, Document ID 1031) in a follow-up study found that workers employed prior to 1930 had an excess risk of lung cancer. Lung cancer mortality among granite workers hired after 1940 (post-implementation of controls), however, was not elevated in the Costello and Graham study and was only somewhat elevated (not statistically significant) in the Graham et al. study. Graham et al. (2004, Document ID 1031) concluded that their results did not support a causal relationship between granite dust exposure and lung cancer mortality.

Looking at the same population, Attfield and Costello (2004, Document ID 0285) developed a quantitative estimate of cumulative exposure (8 exposure categories) adapted from a job exposure matrix developed by Davis et al. (1983, Document ID 0999). They found a statistically significant trend between lung cancer mortality and log-transformed cumulative exposure to crystalline silica. Lung cancer mortality rose reasonably consistently through the first seven increasing exposure groups, but fell in the highest cumulative exposure group. With the highest exposure group omitted, a strong positive dose-response trend was found for both untransformed and log-transformed cumulative exposures. The authors explained that the highest exposure group would have included the most unreliable exposure estimates being reconstructed from exposures 20 years prior to study initiation when exposure estimation was less precise. OSHA expressed its belief that the study by Attfield and Costello (2004, Document ID 0285) was of superior design in that it used quantitative estimates of exposure and evaluated lung cancer mortality rates by exposure group. In contrast, the findings by Graham et al. (2004, Document ID 1031) were based on a dichotomous comparison of risk among high- versus low-exposure groups, where date-of-hire before and after implementation of ventilation controls was used as a surrogate for exposure. Consequently, OSHA used the Attfield and Costello study in its Preliminary QRA (Document ID 1711). In its Supplemental Literature Review of Epidemiological Studies on Lung Cancer Associated with Exposure to Respirable Crystalline Silica, OSHA also discussed a more recent study of Vermont granite workers by Vacek et al. (2011, Document ID 1486) that did not find an association between silica exposure and lung cancer mortality (Document ID 1711, Attachment 1, pp. 2-5). (OSHA examines this study in great length in Section V.F, Comments and Responses Concerning Lung Cancer Mortality.)

In the North American industrial sand industry, studies of two overlapping cohorts found a statistically significant increased risk of lung cancer mortality with increased cumulative exposure in both categorical and continuous analyses (Hughes et al., 2001, Document ID 1060; McDonald et al., 2001, 1091; McDonald et al., 2005, 1092; Rando et al., 2001, 0415; Sanderson et al., 2000, 0429; Steenland and Sanderson, 2001, 0455). McDonald et al. (2001, Document ID 1091) examined a cohort that entered the workforce, on average, a decade earlier than the cohorts that Steenland and Sanderson (2001, Document ID 0455) examined. The McDonald cohort, drawn from eight plants, had more years of exposure in the industry (19 versus 8.8 years). The Steenland and Sanderson (2001, Document ID 0455) cohort worked in 16 plants, 7 of which overlapped with the McDonald, et al. (2001, Document ID 1091) cohort. McDonald et al. (2001, Document ID 1091), Hughes et al. (2001, Document ID 1060), and Rando et al. (2001, Document ID 0415) had access to smoking histories, plant records, and exposure measurements that allowed for historical reconstruction and the development of a job exposure matrix. The McDonald et al. (2005, Document ID 1092) study was a later update, with follow-up through 2000, of both the cohort and nested case-control studies. Steenland and Sanderson (2001, Document ID 0455) had limited access to plant facilities, less detailed historic exposure data, and used MSHA enforcement records for estimates of recent exposure. These studies (Hughes et al., 2001, Document ID 1060; McDonald et al., 2005, 1092; Steenland and Sanderson, 2001, 0455) showed very similar exposure-response patterns of increased lung cancer mortality with increased exposure. OSHA included the quantitative exposure-response analysis from the Hughes et al. (2001, Document ID 1060) study in its Preliminary QRA, as it allowed for individual job, exposure, and smoking histories to be taken into account.

OSHA noted that Brown and Rushton (2005a, Document ID 0303; 2005b, 0304) found no association between risk of lung cancer mortality and exposure to respirable crystalline silica among British industrial sand workers. However, a large portion of the cohort had relatively short service times in the industry, with over one-half the cohort deaths and almost three-fourths of the lung cancer mortalities having had less than 10 years of service. Considering the apparent high turnover in this industry and the absence of prior occupational histories, exposures from work experience other than in the industrial sand industry could be a significant confounder (Document ID 1711, p. 131). Additionally, as Steenland noted in a letter review (2005a, Document ID 1313), the cumulative exposures of workers in the Brown and Ruston (2005b, Document ID 0304) study were over 10 times lower than the cumulative exposures experienced by the cohorts in the pooled analysis that Steenland et al. (2001a, Document ID 0452) performed. The low exposures experienced by this cohort would have made detecting a positive association with lung cancer mortality even more difficult.

In British coal miners, excess lung cancer mortality was reported in a large cohort study, which examined the mortality experience of 17,800 miners through the end of 2005 (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306). By that time, the cohort had accumulated 516,431 person years of observation (an average of 29 years per miner), with 10,698 deaths from all causes. Overall lung cancer mortality was elevated (SMR = 115.7, 95% C.I. 104.8-127.7), and a positive exposure-response relationship with crystalline silica exposure was determined from Cox regression after adjusting for smoking history. Three of the strengths of this study were the detailed time-exposure measurements of both quartz and total mine dust, detailed individual work histories, and individual smoking histories. For lung cancer, analyses based on Cox regression provided strong evidence that, for these coal miners, although quartz exposures were associated with increased lung cancer risk, simultaneous exposures to coal dust did not cause increased lung cancer risk. Because of these strengths, OSHA included this study in its Preliminary QRA (Document ID 1711).

In addition to the studies in these cohorts, OSHA also reviewed studies of lung cancer mortality in metal ore mining populations. Many of these mining studies, which showed mixed results, were subject to confounding due to exposure to other potential carcinogens such as radon and arsenic. IARC noted that only a few ore mining studies accounted for confounding from other occupational carcinogens and that, when confounding was absent or accounted for, an association between silica exposure and lung cancer was absent (1997, Document ID 1062). Many of the studies conducted since IARC's review, however, more strongly implicate crystalline silica as a human carcinogen (1997, Document ID 1062). Pelucchi et al. (2006, Document ID 0408), in a meta-analysis of studies conducted since IARC's (1997, Document ID 1062) review, reported statistically significantly elevated relative risks of lung cancer mortality in underground and surface miners in three cohort and four case-control studies. Cassidy et al., in a pooled case-control analysis, showed a statistically significant increased risk of lung cancer mortality among miners (OR = 1.48), and demonstrated a linear trend of increasing odds ratios with increasing exposures (2007, Document ID 0313).

OSHA also preliminarily determined that the results of the studies conducted in three industry sectors (foundry, silicon carbide, and construction sectors) were confounded by the presence of exposures to other carcinogens. Exposure data from these studies were not sufficient to distinguish between exposure to silica dust and exposure to other occupational carcinogens. IARC previously made a similar determination in reference to the foundry industry. However, with respect to the construction industry, Cassidy et al. (2007, Document ID 0313), in a large European community-based case-control study, reported finding a clear linear trend of increasing odds ratios with increasing cumulative exposure to crystalline silica (estimated semi-quantitatively) after adjusting for smoking and exposure to insulation and wood dusts.

In addition, an analysis of 4.8 million death certificates from 27 states within the U.S. for the years 1982 to 1995 showed statistically significant excesses in lung cancer mortality, silicosis mortality, tuberculosis, and NMRD among persons with occupations involving medium and high exposure to respirable crystalline silica (Calvert et al., 2003, Document ID 0309). A national records and death certificate study was also conducted in Finland by Pukkala et al., who found a statistically significant excess of lung cancer incidence among men and women with estimated medium and heavy exposures (2005, Document ID 0412).

One of the more compelling studies OSHA evaluated and used in the Preliminary QRA (Document ID 1711) was Steenland et al.'s (2001a, Document ID 0452) pooled analysis of 10 occupational cohorts (5 mines and 5 industrial facilities), which demonstrated an overall positive exposure-response relationship between cumulative exposure to crystalline silica and lung cancer mortality. These 10 cohorts included 65,980 workers and 1,072 lung cancer deaths, and were selected because of the availability of raw data on exposure to crystalline silica and health outcomes. The investigators found lung cancer risk increased with increasing cumulative exposure, log cumulative exposure, and average exposure. Exposure-response trends were similar between mining and non-mining cohorts.

iii. Confounding

Smoking is known to be a major risk factor for lung cancer. However, OSHA maintained in the Preliminary QRA that it is unlikely that smoking explained the observed exposure-response trends in the studies described above (Document ID 1711). Studies by Hnizdo et al. (1997, Document ID 1049), McLaughlin et al. (1992, Document ID 0372), Hughes et al. (2001, Document ID 1060), McDonald et al. (2001, Document ID 1091; 2005, 1092), Miller and MacCalman (2009, Document ID 1306), and Cassidy et al. (2007, Document ID 0313) had detailed smoking histories with sufficiently large populations and a sufficient number of years of follow-up time to quantify the interaction between crystalline silica exposure and cigarette smoking. In a cohort of white South African gold miners (Hnizdo and Sluis-Cremer, 1991, Document ID 1051) and in the follow-up nested case-control study (Hnizdo et al., 1997, Document ID 1049), the combined effect of exposure to respirable crystalline silica and smoking was greater than additive, suggesting a multiplicative effect. This effect appeared to be greatest for miners with greater than 35 pack-years of smoking and higher cumulative exposure to silica. In the Chinese nested case-control studies (McLaughlin et al., 1992, Document ID 0372), cigarette smoking was associated with lung cancer, but control for smoking did not influence the association between silica and lung cancer in the mining and pottery cohorts studied. The studies of industrial sand workers (Hughes et al., 2001, Document ID 1060) and British coal workers (Miller and MacCalman, 2009, Document ID 1306) found positive exposure-response trends after adjusting for smoking histories, as did Cassidy et al. (2007, Document ID 0313) in their community-based case-control study of exposed European workers.

Given these findings of investigators who have accounted for the impact of smoking, OSHA preliminarily determined that the weight of the evidence reviewed identified respirable crystalline silica as an independent risk factor for lung cancer mortality. OSHA also determined that its finding was further supported by animal studies demonstrating that exposure to silica alone can cause lung cancer (e.g., Muhle et al., 1995, Document ID 0378).

iv. Lung Cancer and Silicosis

Animal and in vitro studies have demonstrated that the early steps in the proposed mechanistic pathways that lead to silicosis and lung cancer seem to share some common features (see Document ID 1711, pp. 171-172). This has led some researchers to suggest that silicosis is a prerequisite to lung cancer. Some have suggested that any increased lung cancer risk associated with silica may be a consequence of inflammation (and concomitant oxidative stress) and increased epithelial cell proliferation associated with the development of silicosis. However, other researchers have noted additional genotoxic and non-genotoxic mechanisms that may also be involved in carcinogenesis induced by silica (see Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, and Document ID 1711, pp. 230-239). IARC also noted that a direct genotoxic mechanism from silica to induce a carcinogenic effect cannot be ruled out (2012, Document ID 1473). Thus, OSHA preliminarily concluded that available animal and in vitro studies do not support the hypothesis that development of silicosis is necessary for silica exposure to cause lung cancer.

In general, studies of workers with silicosis, as well as meta-analyses that include these studies, have shown that workers with radiologic evidence of silicosis have higher lung cancer risk than those without radiologic abnormalities or mixed cohorts. Three meta-analyses attempted to look at the association of increasing ILO radiographic categories of silicosis with increasing lung cancer mortality. Two of these analyses (Kurihara and Wada, 2004, Document ID 1084; Tsuda et al., 1997, 1127) showed no association with increasing lung cancer mortality, while Lacasse et al. (2005, Document ID 0365) demonstrated a positive dose-response for lung cancer with increasing ILO radiographic category. A number of other studies found increased lung cancer risk among exposed workers absent radiological evidence of silicosis (Cassidy et al., 2007, Document ID 0313; Checkoway et al., 1999, 0327; Cherry et al., 1998, 0335; Hnizdo et al., 1997, 1049; McLaughlin et al., 1992, 0372). For example, the diatomaceous earth study by Checkoway et al. showed a statistically significant exposure-response relationship for lung cancer among persons without silicosis (1999, Document ID 0327). Checkoway and Franzblau, reviewing the international literature, found that all epidemiological studies conducted to that date were insufficient to conclusively determine the role of silicosis in the etiology of lung cancer (2000, Document ID 0323). OSHA preliminarily concluded that the more recent pooled and meta-analyses do not provide compelling evidence that silicosis is a necessary precursor to lung cancer.

c. Non-Malignant Respiratory Diseases (Other Than Silicosis)

In addition to causing silicosis, exposure to crystalline silica has been associated with increased risks of other non-malignant respiratory diseases (NMRD), primarily chronic obstructive pulmonary disease (COPD), chronic bronchitis, and emphysema. COPD is a disease state characterized by airflow limitation that is usually progressive and not fully reversible. In patients with COPD, either chronic bronchitis or emphysema may be present or both conditions may be present together.

As detailed in the Review of Health Effects Literature, OSHA reviewed several studies of NMRD morbidity and preliminarily concluded that exposure to respirable crystalline silica may increase the risk of emphysema, chronic bronchitis, and pulmonary function impairment, regardless of whether signs of silicosis are present (Document ID 1711). Smokers may be at an increased risk relative to nonsmokers.

OSHA also reviewed studies of NMRD mortality that focused on causes of death other than silicosis. Wyndham et al. found a significant excess mortality for chronic respiratory diseases in a cohort of white South African gold miners (1986, Document ID 0490). A case-referent analysis found that, although the major risk factor for chronic respiratory disease was smoking, there was a statistically significant additional effect of cumulative exposure to silica-containing dust. A multiplicative effect of smoking and cumulative dust exposure on mortality from COPD was found in another study of white South African gold miners (Hnizdo, 1990, Document ID 1045). Analysis of various combinations of dust exposure and smoking found a trend in odds ratios that indicated this synergism. There was a statistically significant increasing trend for dust particle-years and for cigarette-years of smoking.

Park et al. (2002, Document ID 0405) analyzed the California diatomaceous earth cohort data originally studied by Checkoway et al. (1997, Document ID 0326), consisting of 2,570 diatomaceous earth workers employed for 12 months or more from 1942 to 1994, to quantify the relationship between exposure to cristobalite and mortality from chronic lung disease other than cancer (LDOC). Diseases in this category included pneumoconiosis (which included silicosis), chronic bronchitis, and emphysema, but excluded pneumonia and other infectious diseases. Smoking information was available for about 50 percent of the cohort and for 22 of the 67 LDOC deaths available for analysis, permitting at least partial adjustment for smoking. Using the exposure estimates developed for the cohort by Rice et al. (2001, Document ID 1118) in their exposure-response study of lung cancer risks, Park et al. (2002, Document 0405) evaluated the quantitative exposure-response relationship for LDOC mortality and found a strong positive relationship with exposure to respirable crystalline silica. OSHA found this study particularly compelling because of the strengths of the study design and availability of smoking history data on part of the cohort, as well as the high-quality exposure and job history data. The study authors noted:

Data on smoking, collected since the 1960s in the company's radiographic screening programme, were available for 1171 of the subjects (50%). However, smoking habits were unknown for 45 of the 67 workers that died from LDOC (67%). Our Poisson regression analyses for LDOC, stratified on smoking, have partially rectified the confounding by smoking issue. Furthermore, analyses performed without control for smoking produced slightly smaller and less precise estimates of the effects of silica, suggesting that smoking is a negative confounder. In their analysis of this cohort, Checkoway et al. applied the method of Axelson concluding that it was very unlikely that cigarette smoking could account for the association found between mortality from LDOC and cumulative exposure to silica (Document ID 0405, p. 41).

Consequently, OSHA used this study in its Preliminary QRA (Document ID 1711, pp. 295-298).

Based on this evidence, and the other studies discussed in the Review of Health Effects Literature, OSHA preliminarily concluded that respirable crystalline silica increases the risk for mortality from non-malignant respiratory disease (not including silicosis) in an exposure-related manner. The Agency also preliminarily concluded that the risk is strongly influenced by smoking, and opined that the effects of smoking and silica exposure may be synergistic.

d. Renal Disease and Autoimmune Diseases

In its Review of Health Effects Literature, OSHA described the available experimental and epidemiological data evaluating respirable crystalline silica exposure and renal and/or autoimmune effects (Document ID 1711). In addition to a number of case reports, epidemiological studies have found statistically significant associations between occupational exposure to silica dust and chronic renal disease (Calvert et al., 1997, Document ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID 0386), end-stage renal disease morbidity (Steenland et al., 1990, Document ID 1125), chronic renal disease mortality (Steenland et al., 2001b, Document ID 0456; 2002a, 0448), and granulomatosis with polyangitis, a condition that can affect the kidneys (Nuyts et al., 1995, Document ID 0397). In other findings, silica-exposed individuals, both with and without silicosis, had an increased prevalence of abnormal renal function (Hotz et al., 1995, Document ID 0361), and renal effects have been reported to persist after cessation of silica exposure (Ng et al., 1992c, Document ID 0386). Possible mechanisms suggested for silica-induced renal disease include a direct toxic effect on the kidney, deposition of immune complexes (IgA) in the kidney following silica related pulmonary inflammation, and an autoimmune mechanism (Calvert et al., 1997, Document ID 0976; Gregorini et al., 1993, 1032).

In a pooled cohort analysis, Steenland et al. (2002a, Document ID 0448) combined the industrial sand cohort from Steenland et al. (2001b, Document ID 0456), the gold mining cohort from Steenland and Brown (1995a, Document ID 0450), and the Vermont granite cohort studies by Costello and Graham (1988, Document ID 0991). In all, the combined cohort consisted of 13,382 workers with exposure information available for 12,783. The analysis demonstrated statistically significant exposure-response trends for acute and chronic renal disease mortality with quartiles of cumulative exposure to respirable crystalline silica. In a nested case-control study design, a positive exposure-response relationship was found across the three cohorts for both multiple-cause mortality (i.e., any mention of renal disease on the death certificate) and underlying cause mortality. Renal disease risk was most prevalent among workers with cumulative exposures of 500 µg/m³ or more (Steenland et al., 2002a, Document ID 0448).

OSHA noted that other studies failed to find an excess renal disease risk among silica-exposed workers. Davis et al. (1983, Document ID 0999) found elevated, but not statistically significant, mortality from diseases of the genitourinary system among Vermont granite shed workers. There was no observed relationship between mortality from this cause and cumulative exposure. A similar finding was reported by Koskela et al. (1987, Document ID 0363) among Finnish granite workers, where there were 4 deaths due to urinary tract disease compared to 1.8 expected. Both Carta et al. (1994, Document ID 0312) and Cocco et al. (1994, Document ID 0988) reported finding no increased mortality from urinary tract disease among workers in an Italian lead mine and zinc mine. However, Cocco et al. (1994, Document ID 0988) commented that exposures to respirable crystalline silica were low, averaging 7 and 90 µg/m³ in the two mines, respectively, and that their study in particular had low statistical power to detect excess mortality.

OSHA expressed its belief that there is substantial evidence, particularly the 3-cohort pooled analysis conducted by Steenland et al. (2002a, Document ID 0448), on which to base a finding that exposure to respirable crystalline silica increases the risk of renal disease mortality and morbidity. The pooled analysis by Steenland et al. involved a large number of workers from three cohorts with well-documented, validated job-exposure matrices; it found a positive, monotonic increase in renal disease risk with increasing exposure for both underlying and multiple cause data (2002a, Document ID 0448). However, there are considerably less data available for renal disease than there are for silicosis mortality and lung cancer mortality. The findings based on these data are, therefore, less robust. Nevertheless, OSHA preliminarily concluded that the underlying data are sufficient to provide useful estimates of risk and included the Steenland et al. (2002a, Document ID 0448) analysis in its Preliminary QRA.

For autoimmune effects, OSHA reviewed epidemiological information suggesting an association between respirable silica exposure and autoimmune diseases, including scleroderma (Sluis-Cremer et al., 1985, Document ID 0439), rheumatoid arthritis (Klockars et al., 1987, Document ID 1075; Rosenman and Zhu, 1995, 0424), and systemic lupus erythematosus (Brown et al., 1997, Document ID 0974). However, there were no quantitative exposure-response data available on which to base a quantitative risk assessment for autoimmune diseases.

e. Physical Factors Affecting Toxicity of Crystalline Silica

OSHA also examined evidence on the comparative toxicity of the silica polymorphs (quartz, cristobalite, and tridymite). A number of animal studies appear to suggest that cristobalite and tridymite are more toxic to the lung than quartz and more tumorigenic (e.g., King et al., 1953, Document ID 1072; Wagner et al., 1980, 0476). However, in contrast to these findings, several authors have reviewed the studies done in this area and concluded that cristobalite and tridymite are not more toxic than quartz (e.g., Bolsaitis and Wallace, 1996, Document ID 0298; Guthrie and Heaney, 1995, 1035). Furthermore, a difference in toxicity between cristobalite and quartz has not been observed in epidemiological studies (tridymite has not been studied) (NIOSH, 2002, Document ID 1110). In an analysis of exposure-response for lung cancer, Steenland et al. found similar exposure-response trends between cristobalite-exposed workers and other cohorts exposed to quartz (2001a, Document ID 0452).

OSHA also discussed other physical factors that may influence the toxicologic potency of crystalline silica. A number of animal studies compared the toxicity of freshly fractured silica to that of aged silica (Porter et al., 2002, Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al., 1995, 1128). These studies have demonstrated that although freshly fractured silica is more toxic than aged silica, aged silica still retains significant toxicity. There have been no studies comparing workers exposed to freshly fractured silica to those exposed to aged silica. However, similarities between the results of animal and human studies involving freshly fractured silica suggest that the animal studies involving aged silica may also apply to humans. For example, studies of workers exposed to freshly fractured silica have demonstrated that these workers exhibit the same cellular effects as seen in animals exposed to freshly fractured silica (Castranova et al., 1998, Document ID 1294; Goodman et al., 1992, 1029). Animal studies also suggest that pulmonary reactions of rats to short-duration exposure to freshly fractured silica mimic those seen in acute silicosis in humans (Vallyathan et al., 1995, Document ID 1128).

Surface impurities, particularly metals, have been shown to alter silica toxicity. Iron, depending on its state and quantity, has been shown to either increase or decrease toxicity (see Document ID 1711, pp. 247-258). Aluminum has been shown to decrease toxicity (Castranova et al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini, 1998, 1016). Silica coated with aluminosilicate clay exhibits lower toxicity, possibly as a result of reduced bioavailability of the silica particle surface (Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998, 1016). Aluminum as well as other metal ions are thought to modify silanol groups on the silica surface, thus decreasing the membranolytic and cytotoxic potency and resulting in enhanced particle clearance from the lung before damage can take place (Fubini, 1998, Document ID 1016). An epidemiological study found that the risk of silicosis was less in pottery workers than in tin and tungsten miners (Chen et al., 2005, Document ID 0985; Harrison et al., 2005, 1036), possibly reflecting that pottery workers were exposed to silica particles having less biologically-available, non-clay-occluded surface area than was the case for miners.

Although it is evident that a number of factors can act to mediate the toxicological potency of crystalline silica, it is not clear how such considerations should be taken into account to evaluate lung cancer and silicosis risks to exposed workers. After evaluating many in vitro studies that investigated the surface characteristics of crystalline silica particles and their influence on fibrogenic activity, NIOSH concluded that further research is needed to associate specific surface characteristics that can affect toxicity with specific occupational exposure situations and consequent health risks to workers (2002, Document ID 1110). Thus, OSHA preliminarily concluded that while there was considerable evidence that several environmental influences can modify surface activity to either enhance or diminish the toxicity of silica, the available information was insufficient to determine in any quantitative way how these influences may affect disease risk to workers in any particular workplace setting.

3. Summary of the Preliminary QRA

OSHA presented in the Preliminary QRA estimates of the risk of silica-related diseases assuming exposure over a working life (45 years, from age 20 to age 65) to the revised 8-hour time-weighted average (TWA) PEL of 50 µg/m³ respirable crystalline silica, the new action level of 25 µg/m³, and the previous PELs. OSHA's previous general industry PEL for respirable quartz was expressed both in terms of a particle count formula and a gravimetric concentration formula; the previous construction and shipyard employment PELs for respirable quartz were only expressed in terms of a particle count formula. For general industry, as the quartz content increases, the gravimetric PEL approached a limit of 100 µg/m³ respirable quartz. For construction and shipyard employment, OSHA's previous PELs used a formula that limits exposure to respirable dust, depending upon the quartz content, expressed as a respirable particle count concentration. There was no single mass concentration equivalent for the construction and shipyard employment PELs; OSHA reviewed several studies that suggest that the previous construction/shipyard PEL likely was between 250 and 500 µg/m³ respirable quartz. In general industry, for both the gravimetric and particle count PELs, OSHA's previous PELs for cristobalite and tridymite were half the value for quartz. Based upon these previous PELs and the new action level, OSHA presented risk estimates associated with exposure over a working life to 25, 50, 100, 250, and 500 µg/m³ respirable silica (corresponding to cumulative exposures over 45 years to 1.125, 2.25, 4.5, 11.25, and 22.5 mg/m³-yrs).

To estimate lifetime excess mortality risks at these exposure levels, OSHA implemented each of the risk models in a life table analysis that accounted for competing causes of death due to background causes and cumulated risk through age 85. For these analyses, OSHA used lung cancer, NMRD, or renal disease mortality and all-cause mortality rates to account for background risks and competing risks (U.S. 2006 data for lung cancer and NMRD mortality in all males, 1998 data for renal disease mortality, obtained from cause-specific death rate tables published by the National Center for Health Statistics (2009, Document ID 1104)). OSHA calculated these risk estimates assuming occupational exposure from age 20 to age 65. The mortality risk estimates were presented in terms of lifetime excess risk per 1,000 workers for exposure over an 8-hour working day, 250 days per year, and a 45-year working life.

For silicosis morbidity, OSHA based its risk estimates on cumulative risk models used by various investigators to develop quantitative exposure-response relationships. These models characterized the risk of developing silicosis (as detected by chest radiography) up to the time that cohort members (including both active and retired workers) were last examined. Thus, risk estimates derived from these studies represented less-than-lifetime risks of developing radiographic silicosis. OSHA did not attempt to estimate lifetime risk (i.e., up to age 85) for silicosis morbidity because the relationships between age, time, and disease onset post-exposure have not been well characterized.

a. Silicosis and NMRD Mortality

i. Exposure-Response Studies

In the Preliminary QRA, OSHA relied upon two published quantitative risk studies of silicosis and NMRD mortality (Document ID 1711). The first, Mannetje et al. (2002b, Document ID 1089) conducted a pooled analysis of silicosis mortality in which there were 18,634 subjects, 150 silicosis deaths, and 20 deaths from unspecified pneumoconiosis. Rates for silicosis adjusted for age, calendar time, and study were estimated by Poisson regression and increased nearly monotonically with deciles of cumulative exposure, from a mortality rate of 5/100,000 person-years in the lowest exposure category (0-0.99 mg/m³-yrs) to 299/100,000 person-years in the highest category (>28.10 mg/m³-yrs).

As previously discussed, the second, Park et al. (2002, Document ID 0405) analyzed the California diatomaceous earth cohort data from Checkoway et al. (1997, Document ID 0326), and examined mortality from chronic lung disease other than cancer (LDOC; also known as non-malignant respiratory disease (NMRD)). Smoking information was available for about 50 percent of the cohort and for 22 of the 67 LDOC deaths available for analysis, permitting Park et al. (2002, Document ID 0405) to partially adjust for smoking. Estimates of LDOC mortality risks were derived via Poisson and Cox proportional hazards models; a variety of relative rate model forms were fit to the data, with a linear relative rate model selected for estimating risks.

ii. Risk Estimates

As silicosis is only caused by exposure to respirable crystalline silica (i.e., there is no background rate of silicosis in the unexposed population), absolute risks of silicosis mortality rather than excess risks were calculated for the Mannetje et al. pooled analysis (2002b, Document ID 1089). These risk estimates were derived from the rate ratios incorporating simulated measurement error reported by ToxaChemica (Document ID 0469). OSHA's estimate of lifetime risk of silicosis mortality, for 45 years of exposure to the previous general industry PEL, was 11 deaths per 1,000 workers for the pooled analysis (Document ID 1711). At the revised PEL, the risk estimate was 7 deaths per 1,000.

OSHA also calculated preliminary risk estimates for NMRD mortality. These estimates were derived from Park et al. (2002, Document ID 0405). For 45 years of exposure to the previous general industry PEL, OSHA preliminarily estimated lifetime excess risk at 83 deaths per 1,000 workers. At the revised PEL, OSHA estimated 43 deaths per 1,000 workers.

OSHA noted that, for exposures up to 250 µg/m³, the mortality risk estimates based on Park et al. (2002, Document ID 0405) are about 5 to 11 times as great as those calculated for the pooled analysis of silicosis mortality (Mannetje et al., 2002b, Document ID 1089). These two sets of risk estimates, however, are not directly comparable, as the endpoint for the Park et al. (2002, Document ID 0405) analysis was death from all non-cancer lung diseases, including pneumoconiosis, emphysema, and chronic bronchitis, whereas the pooled analysis by Mannetje et al. (2002b, Document ID 1089) included only deaths coded as silicosis or other pneumoconiosis. Less than 25 percent of the LDOC deaths in the Park et al. analysis were coded as silicosis or other pneumoconiosis (15 of 67), suggesting that silicosis as a cause of death may be misclassified as emphysema or chronic bronchitis. Thus, Mannetje et al.'s (2002b, Document ID 1089) selection of deaths may tend to underestimate the true risk of silicosis mortality, and Park et al.'s (2002, Document ID 0405) analysis may more completely capture the total respiratory mortality risk from all non-malignant causes.

Since the time of OSHA's analysis, NCHS has released updated all-cause mortality and NMRD mortality background rates from 2011 ( http://wonder.cdc.gov/ucd-icd10.html ); OSHA's final risk estimates for NMRD mortality, which incorporate these updated rates (ICD10 codes J40-J47, chronic lower respiratory diseases; J60-J66, J68, pneumoconiosis and chemical effects), are available in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

b. Lung Cancer Mortality

i. Exposure-Response Studies

In 1997, when IARC determined that there was sufficient evidence to regard crystalline silica as a human carcinogen, it also noted that some epidemiological studies did not demonstrate an excess risk of lung cancer and that exposure-response trends were not always consistent among studies that were able to describe such trends (Document ID 1062). These findings led Steenland et al. (2001a, Document ID 0452) to conduct a comprehensive exposure-response analysis—the IARC multi-center study—of the risk of lung cancer associated with exposure to crystalline silica. This study relied on all available cohort data from previously-published epidemiological studies for which there were adequate quantitative data on worker silica exposures to derive pooled estimates of disease risk. In addition, as discussed previously, OSHA identified four more recent studies suitable for quantitative risk assessment: (1) An exposure-response analysis by Rice et al. (2001, Document ID 1118) of a cohort of diatomaceous earth workers primarily exposed to cristobalite; (2) an analysis by Attfield and Costello (2004, Document ID 0285) of U.S. granite workers; (3) an exposure-response analysis by Hughes et al. (2001, Document ID 1060) of U.S. industrial sand workers; and (4) a risk analysis by Miller et al. (2007, Document ID 1305) and Miller and MacCalman (2009, Document ID 1306) of British coal miners. OSHA thoroughly described each of these studies in its Preliminary QRA (Document ID 1711); a brief summary of the exposure-response models used in each study is provided here.

The Steenland et al. pooled exposure-response analysis was based on data obtained from ten cohorts of silica-exposed workers (65,980 workers, 1,072 lung cancer deaths) (2001a, Document ID 0452). The pooled analysis cohorts included U.S. gold miners (Steenland and Brown, 1995a, Document ID 0450), U.S. diatomaceous earth workers (Checkoway et al., 1997, Document ID 0326), Australian gold miners (de Klerk and Musk, 1998, Document ID 0345), Finnish granite workers (Koskela et al., 1994, Document ID 1078), U.S. industrial sand employees (Steenland and Sanderson, 2001, Document ID 0455), Vermont granite workers (Costello and Graham, 1988, Document ID 0991), South African gold miners (Hnizdo and Sluis-Cremer, 1991, Document ID 1051; Hnizdo et al., 1997, 1049), and Chinese pottery workers, tin miners, and tungsten miners (Chen et al., 1992, Document ID 0329).

Steenland et al. (2001a, Document ID 0452) performed a nested case-control analysis via Cox regression. There were 100 controls chosen for each case randomly from among cohort members who survived past the age at which the case died; controls were matched on age (the time variable in Cox regression), study, race/ethnicity, sex, and date of birth within 5 years. Steenland et al. found that the use of any of the following continuous exposure variables in a log linear relative risk model resulted in positive statistically significant (p ≤ 0.05) exposure-response coefficients: (1) Cumulative exposure with a 15-year lag; (2) the log of cumulative exposure with a 15-year lag; and (3) average exposure (2001a, Document ID 0452). The models that provided the best fit to the data used cumulative exposure and log-transformed cumulative exposure. Models that used log-transformed cumulative exposure also showed no statistically significant heterogeneity among cohorts (p = 0.36), possibly because they are less influenced by very high exposures. At OSHA's request, Steenland (2010, Document ID 1312) also conducted a categorical analysis of the pooled data set and additional analyses using linear relative risk models (with and without the log transformation of cumulative exposure) as well as a two-piece spline model (see Document ID 1711, pp. 276-278).

Rice et al. (2001, Document ID 1118) applied a variety of exposure-response models to the California diatomaceous earth cohort data originally studied by Checkoway et al. (1993, Document ID 0324; 1996, 0325; 1997, 0326) and included in the Steenland et al. (2001a, Document ID 0452) pooled analysis. The cohort consisted of 2,342 white males employed for at least one year between 1942 and 1987 in a California diatomaceous earth mining and processing plant. The cohort was followed until 1994, and included 77 lung cancer deaths. Rice et al. reported that exposure to crystalline silica was a significant predictor of lung cancer mortality for nearly all of the models employed, with the linear relative risk model providing the best fit to the data in the Poisson regression analysis (2001, Document ID 1118).

Attfield and Costello (2004, Document ID 0285) analyzed the U.S. granite cohort originally studied by Costello and Graham (1988, Document ID 0991) and Davis et al. (1983, Document ID 0999) and included in the Steenland et al. (2001a, Document ID 0452) pooled analysis. The cohort consisted of 5,414 male granite workers who were employed in the Vermont granite industry between 1950 and 1982 and who had received at least one chest x-ray from the surveillance program of the Vermont Department of Industrial Hygiene. The 2004 report by Attfield and Costello extended follow-up from 1982 to 1994, and found 201 deaths (Document ID 0285). Using Poisson regression models, the results of a categorical analysis showed a generally increasing trend of lung cancer rate ratios with increasing cumulative exposure.

As mentioned previously, however, the rate ratio for the highest exposure group in the Attfield and Costello analysis (cumulative exposures of 6.0 mg/m³-yrs or higher) was substantially lower than that for other exposure groups (2004, Document ID 0285). The authors reported that the best-fitting model had a 15-year lag, untransformed cumulative exposure, and the omission of this highest exposure group. The authors argued that it was appropriate to omit the highest exposure group for several reasons, including that the exposure estimates for the highest exposure group were less reliable, and there was a greater likelihood of cohort selection effects, competing causes of death, and misdiagnosis (Document ID 0285, p. 136).

McDonald et al. (2001, Document ID 1091), Hughes et al. (2001, Document ID 1060) and McDonald et al. (2005, Document ID 1092) followed up on a cohort study of North American industrial sand workers included in the Steenland et al. (2001a, Document ID 0452) pooled analysis. The McDonald et al. cohort included 2,670 men employed before 1980 for three years or more in one of nine North American (8 U.S. and 1 Canadian) sand-producing plants, including 1 large associated office complex (2001, Document ID 1091). A nested case-control study based on 90 lung cancer deaths (through 1994) from this cohort was conducted by Hughes et al. (2001, Document ID 1060). A subsequent update (through 2000, 105 lung cancer deaths) eliminated the Canadian plant, following 2,452 men from the eight U.S. plants (McDonald et al., 2005, Document ID 1092). These nested case-control studies, Hughes et al. (2001, Document ID 1060) and McDonald et al. (2005, Document ID 1092), allowed for individual job, exposure, and smoking histories to be taken into account in the exposure-response analysis. Hughes et al. (2001, Document ID 1060) found statistically significant positive exposure-response trends for lung cancer for both cumulative exposure (lagged 15 years) and average exposure concentration, but not for duration of employment. With exposure lagged 15 years and after adjusting for smoking, increasing quartiles of cumulative silica exposure were also associated with lung cancer mortality (p-value for trend = 0.04). McDonald et al. (2005, Document ID 1092) found very similar results, with increasing quartiles of cumulative silica exposure (lagged 15 years) associated with lung cancer mortality (p-value for trend = 0.006). Because McDonald et al. (2005, Document ID 1092) did not report the medians of the exposure categories, and given the similar results of both case-control studies, OSHA chose to base its risk estimates on the Hughes et al. (2001, Document ID 1060) study.

Miller et al. (2007, Document ID 1305) and Miller and MacCalman (2009, Document ID 1306) continued a follow-up mortality study, begun in 1970, of coal miners from 10 British coal mines initially followed through the end of 1992 (Miller et al., 1997, Document ID 1304) and extended it to 2005. In the analysis using internal controls and Cox regression methods, the relative risk of lung cancer mortality, adjusted for concurrent dust exposure and smoking status, at a cumulative quartz exposure (lagged 15 years) equivalent of approximately 55 μg/m³ for 45 years was 1.14 (95% C.I., 1.04 to 1.25).

ii. Risk Estimates

In the Preliminary QRA, OSHA presented estimates of excess lung cancer mortality risk from occupational exposure to crystalline silica, based on data from the five epidemiology studies discussed above (Document ID 1711). In its preliminary analysis, OSHA used background all-cause mortality and lung cancer mortality rates from 2006, as reported by the National Center for Health Statistics (NCHS) (Document ID 1104). These rates were used in life table analyses to estimate lifetime risks at the exposure levels of interest, ranging from 25 to 500 μg/m³ respirable crystalline silica.

OSHA's preliminary estimates of lifetime excess lung cancer risk associated with 45 years of exposure to crystalline silica at 100 μg/m³ (approximately the previous general industry PEL) ranged between 13 and 60 deaths per 1,000 workers, depending upon the study used. For exposure to the revised PEL of 50 μg/m³, the lifetime risk estimates were in the range of between 6 and 26 deaths per 1,000 workers, depending upon the study used. For a 45 year exposure at the new action level of 25 μg/m³, OSHA estimated the risk to range between 3 and 23 deaths per 1,000 workers. The Agency found that the results from these preliminary assessments were reasonably consistent despite the use of data from different cohorts and the reliance on different analytical techniques for evaluating dose-response relationships.

OSHA also estimated the lung cancer risk associated with 45 years of exposure to the previous construction/shipyard PEL (in the range of 250 μg/m³ to 500 μg/m³) to range between 37 and 653 deaths per 1,000 workers, depending upon the study used. OSHA acknowledges that the 653 deaths is the upper limit for 45 years of exposure to 500 μg/m³, and recognizes that actual risk, to the extent that workers are exposed for less than 45 years or intermittently, is likely to be lower. In addition, exposure to 250 or 500 μg/m³ over 45 years represents cumulative exposures of 11.25 and 22.5 mg/m³-yrs, respectively. This range of cumulative exposure is well above the median cumulative exposure for most of the cohorts used in the preliminary risk assessment. Thus, OSHA explained that estimating lung cancer excess risks over this higher range of cumulative exposures of interest to OSHA required some degree of upward extrapolation of the exposure-response function to model these high exposures, thus adding uncertainty to the estimates.

Since the time of that original analysis, NCHS has released updated all-cause mortality and lung cancer mortality background rates from 2011. OSHA's final risk estimates, which incorporate these updated rates, are available in this preamble at Section VI, Final Quantitative Risk Assessment and Significance of Risk.

c. Uncertainty Analysis of Pooled Studies of Lung Cancer Mortality and Silicosis Mortality

In the Preliminary QRA, OSHA recognized that risk estimates can be inherently uncertain and can be affected by confounding, selection bias, and measurement error (Document ID 1711). OSHA presented several reasons as to why it does not believe that confounding or selection bias had a substantial impact on the risk estimates for lung cancer or silicosis mortality (Document ID 1711, pp. 299-302). However, because it was more difficult to assess the importance of exposure measurement error, OSHA's contractor, ToxaChemica, Inc., commissioned Drs. Kyle Steenland and Scott Bartell to perform an uncertainty analysis to examine the effect of uncertainty due to measurement error in the pooled studies (Steenland et al., 2001a, Document ID 0452; Mannetje 2002b, 1089) on the lung cancer and silicosis mortality risk estimates (ToxaChemica, Inc., 2004, Document ID 0469).

There are two main sources of error in the silica exposure measurements. The first arises from the assignment of individual workers' exposures based on either exposure measurements for a sample of workers in the same job or estimated exposure levels for specific jobs in the past when no measurements were available, via a job-exposure matrix (JEM) (Mannetje et al., 2002a, Document ID 1090). The second arises from the conversion of historically-available dust measurements, typically particle count concentrations, to gravimetric respirable silica concentrations. ToxaChemica, Inc. conducted an uncertainty analysis using the raw data from the IARC multi-centric study to address these sources of error (2004, Document ID 0469).

i. Lung Cancer Mortality

To examine the effect of error in the assignment of individual exposure values in the cohorts studied by Steenland et al. (2001a, Document ID 0452), ToxaChemica, Inc. used a Monte Carlo analysis (a type of simulation analysis that varies the values of an uncertain input to an analysis—in this case, exposure estimates—to explore the effects of different values on the outcome of the analysis) to randomly sample new values for each worker's job-specific exposure levels from a distribution that they believed characterized the variability in exposures of individual workers in each job (see Document ID 1711, pp. 303-305). That is, ToxaChemica created a distribution of values for each member of each cohort where the mean exposure for each member was equal to the original exposure value and the distribution of exposure values was based on a log-normal distribution having a standard deviation that was based on the exposure variation observed in industrial sand plants observed by Steenland and Sanderson (2001, Document ID 0455). From this distribution, new sets of exposure values from each cohort member were randomly drawn for 50 trials. This simulation was designed to test whether sets of exposure values that were plausibly different from the original estimates would lead to substantially different results of the exposure-response analysis. Except for the simulated exposure values and the correction of a few minor errors in the original data sets, the simulation analysis used the same data as the original analyses conducted by Steenland et al. (2001a, Document ID 0452).

When an entire set of cumulative exposure values was assembled for all workers based on these randomly sampled values, the set was used in a conditional logistic regression to fit a new exposure-response model. The extent to which altering the exposure values led to changes in the results indicated how sensitive the previously presented risk estimates may have been to error in the exposure estimates. Among the individual cohorts, most of the mean regression coefficients resulting from the simulation analysis were consistent with the coefficients from the exposure-response analyses reported in Steenland et al. (2001, Document ID 0455) and ToxaChemica, Inc. (2004, Document ID 0469) (following correction for minor data entry and rounding errors). An exception was the mean of the simulation coefficients based on the South Africa gold cohort (0.26), which was lower than the previously calculated exposure coefficient (0.582). ToxaChemica, Inc. (2004, Document ID 0469) concluded that this error source probably did not appreciably change the estimated exposure-response coefficient for the pooled data set.

To examine the effect of error in estimating gravimetric respirable crystalline silica exposures from historical dust concentration data (i.e., particle count data), ToxaChemica, Inc. (2004, Document ID 0469) used a procedure similar to that used to assess uncertainties in individual exposure value assignments. ToxaChemica, Inc. assumed that, for each job in the dataset, a specific conversion factor existed that related workers' exposures measured as particle concentrations to gravimetric respirable silica exposures, and that this conversion factor came from a normal distribution with a standard deviation σ = 1/2 its mean μ. The use of a normal distribution was a reasonable choice in that it allowed the sampled conversion factors to fall above or below the original values with equal probability, as the authors had no information to suggest that error in either direction was more likely. The normal distribution also assigned higher probability to conversion values closer to the original values. The choice of the normal distribution therefore reflected the study authors' judgment that their original conversion factors were more likely to be approximately correct than not, while allowing for the possibility of significant error in the original values.

A new conversion factor was then sampled for each job from the appropriate distribution, and the complete set of sampled conversion factors was then used to re-run the risk analysis used by Steenland et al. (2001a, Document ID 0452). The results were similar to the coefficients originally derived from each cohort; the only coefficient substantially affected by the procedure was that for the South African cohort, with an average value of 0.350 across ten runs compared to the original value of 0.582 (see Table II-5, Document ID 1711, p. 307). This suggests that the results of exposure-response analyses conducted using the South African cohort are sensitive to error in exposure estimates; therefore, there is greater uncertainty due to potential exposure estimation error in an exposure-response model based on this cohort than is the case for the other nine cohorts in Steenland et al's analysis.

To explore the potential effects of both kinds of random uncertainty described above, ToxaChemica, Inc. (2004, Document ID 0469) used the distributions representing the error in job-specific exposure assignment and the error in converting exposure metrics to generate 50 new exposure simulations for each cohort. A study-specific coefficient and a pooled coefficient were fit for each new simulation, with the assumption that the two sources of uncertainty were independent. The results indicated that the only cohort for which the mean of the exposure coefficients derived from the 50 simulations differed substantially from the previously calculated exposure coefficient was the South African gold cohort (simulation mean of 0.181 vs. original coefficient of 0.582). For the pooled analysis, the mean coefficient estimate from the simulations was 0.057, just slightly lower than the previous estimate of 0.060. Based on these results, OSHA concludes that random error in the underlying exposure estimates in the Steenland et al. (2001a, Document ID 0452) pooled cohort study of lung cancer is not likely to have substantially influenced the original risk estimates derived from the pooled data set, although the model coefficient for one of the ten cohorts (the South African gold miner cohort) appeared to be sensitive to measurement errors (see Table II-5, Document ID 1711, p. 307).

Drs. Steenland and Bartell also examined the effects of systematic bias in conversion factors, considering the possibility that these may have been consistently under-estimated or over-estimated for any given cohort. They addressed possible biases in either direction, conducting simulations where the true silica content was assumed to be either half or double the estimated silica content of measured exposures. For the conditional logistic regression model using log cumulative exposure with a 15-year lag, doubling or halving the exposure for a specific study resulted in virtually no change in the exposure-response coefficient for that study or for the pooled analysis overall. This is due to the use of log-transformed exposure metrics, which ensured that any multiplicative bias in exposure would have virtually no effect on conditional logistic regression coefficients (Document ID 0469, p. 17). That is, for this model, a systematic error in exposure estimation for any study had little effect on the lung cancer response rate for either the specific study or the pooled analysis overall.

ii. Silicosis Mortality

Following the procedures described above for the lung cancer analysis, Toxachemica, Inc. (2004, Document ID 0469) combined both sources of random measurement error in a Monte Carlo analysis of the silicosis mortality data from Mannetje et al. (2002b, Document ID 1089). Categorical analyses were performed with a nested case control model, in contrast to the Poisson model used previously by Mannetje et al. (2002b, Document ID 1089). The nested case control model was expected to control more effectively for age. This model yielded categorical rate ratio results using the original data (prior to simulation of measurement error) which were approximately 20-25 percent lower than those reported by Mannetje et al. (2002b, Document ID 1089). The silicosis mortality dataset thus appeared to be more sensitive to possible error in exposure measurement than the lung cancer dataset, for which the mean of the simulation coefficients was virtually identical to the original. OSHA notes that its risk estimates derived from the pooled analysis (Mannetje et al., 2002b, Document ID 1089), incorporated ToxaChemica, Inc.'s simulated measurement error (2004, Document ID 0469). More information is provided in the Preliminary QRA (Document ID 1711, pp. 310-314).

d. Renal Disease Mortality

i. Exposure-Response Studies

Steenland et al. (2002a, Document ID 0448) examined renal disease mortality in a pooled analysis of three cohorts, as discussed previously. These cohorts were chosen because data were available for both underlying cause mortality and multiple cause mortality. The combined cohort for the pooled analysis (Steenland et al., 2002a, Document ID 0448) consisted of 13,382 workers with exposure information available for 12,783 (95 percent). SMRs (compared to the U.S. population) for renal disease (acute and chronic glomerulonephritis, nephrotic syndrome, acute and chronic renal failure, renal sclerosis, and nephritis/nephropathy) were statistically significantly elevated using multiple cause data (SMR 1.29, 95% CI 1.10-1.47, 193 deaths) and underlying cause data (SMR 1.41, 95% CI 1.05-1.85, 51 observed deaths).

ii. Risk Estimates

As detailed in the Preliminary QRA, OSHA estimated that exposure to the previous (100 μg/m³) and revised (50 μg/m³) general industry PELs, over a 45-year working life, would result in a lifetime excess renal disease mortality risk of 39 and 32 deaths per 1,000 workers, respectively. For exposure to the previous construction/shipyard PELs, OSHA estimated the lifetime excess risk to range from 52 to 63 deaths per 1,000 workers at exposures of 250 and 500 μg/m³, respectively. These risks reflect the 1998 background all-cause mortality and renal mortality rates for U.S. males. Background rates were not adjusted for the renal disease risk estimates because the CDC significantly changed the classification of renal diseases after 1998; they are now inconsistent with those used by Steenland et al. (2002a, Document ID 0448) to ascertain the cause of death of workers in their study.

e. Silicosis Morbidity

i. Exposure-Response Studies

OSHA summarized, in its Preliminary QRA, the principal cross-sectional and cohort studies that quantitatively characterized relationships between exposure to crystalline silica and the development of radiographic evidence of silicosis (Document ID 1711). Each of these studies relied on estimates of cumulative exposure to evaluate the relationship between exposure and silicosis prevalence. The health endpoint of interest in these studies was the appearance of opacities on chest radiographs indicative of pulmonary fibrosis. Most of the studies reviewed by OSHA considered a finding consistent with an ILO classification of 1/1 to be a positive diagnosis of silicosis, although some also considered an x-ray classification of 1/0 or 0/1 to be positive. OSHA noted its belief, in the Preliminary QRA, that the most reliable estimates of silicosis morbidity, as detected by chest radiographs, come from the studies that evaluated radiographs over time, included radiographic evaluation of workers after they left employment, and derived cumulative or lifetime estimates of silicosis disease risk. OSHA also pointed out that the low sensitivity of chest radiography in detecting silicosis suggests that risk estimates derived from radiographic evidence likely underestimate the true risk.

Hnizdo and Sluis-Cremer (1993, Document ID 1052) described the results of a retrospective cohort study of 2,235 white gold miners in South Africa. A total of 313 miners had developed silicosis (x-ray with ILO 1/1 or greater) and had been exposed for an average of 27 years at the time of diagnosis. The average latency for the cohort was 35 years (range of 18-50 years) from the start of exposure to diagnosis. The average respirable dust exposure for the cohort overall was 290 μg/m³ (range 110-470), corresponding to an estimated average respirable silica concentration of 90 μg/m³ (range 33-140). The average cumulative dust exposure for the overall cohort was 6.6 mg/m³-yrs (range 1.2-18.7). Silicosis risk increased exponentially with cumulative exposure to respirable dust in models using log-logistic regression. Using the exposure-response relationship developed by Hnizdo and Sluis-Cremer (1993, Document ID 1052), and assuming a quartz content of 30 percent in respirable dust, Rice and Stayner (1995, Document ID 0418) estimated the risk of silicosis to be 13 percent for a 45-year exposure to 50 μg/m³ respirable crystalline silica.

Steenland and Brown (1995b, Document ID 0451) studied 3,330 South Dakota gold miners who had worked at least a year underground between 1940 and 1965. Chest x-rays were obtained in cross-sectional surveys in 1960 and 1976 and used along with death certificates to ascertain cases of silicosis; 128 cases were found via death certificate, 29 were found by x-ray (defined as ILO 1/1 or greater), and 13 were found by both. OSHA notes that the inclusion of death certificate diagnoses complicates interpretation of the risk estimate from this study since, as noted by Finkelstein (2000, Document ID 1015), it is not known how well such diagnoses correlate with ILO radiographic interpretations; as such, the risk estimates derived from this study may not be directly comparable to others that rely exclusively on radiographic findings to evaluate silicosis morbidity risk. The mean exposure concentration was 50 μg/m³ for the overall cohort, with those hired before 1930 exposed to an average of 150 μg/m³. The average duration of exposure for workers with silicosis was 20 years (s.d. = 8.7) compared to 8.2 years (s.d. = 7.9) for the rest of the cohort. This study found that cumulative exposure was the best disease predictor, followed by duration of exposure and average exposure. Lifetime risks were estimated from Poisson regression models using standard life table techniques; the results indicated an estimated risk of 47 percent associated with 45 years of exposure to 90 μg/m³ respirable crystalline silica, which reduced to 35 percent after adjustment for age and calendar time.

OSHA used the same life table approach as described for estimating lung cancer and NMRD mortality risks to estimate lifetime silicosis risk based on the silicosis rates, adjusted for age and calendar time, calculated by Steenland and Brown (1995b, Table 2, Document ID 0451). Silicosis risk was estimated through age 85, assuming exposure from age 20 through 65, and assuming that the silicosis rate remains constant after age 65. All-cause mortality rates to all males for calendar year 2006 were used to account for background competing risk. From this analysis, OSHA estimated the risk from exposure to the previous general industry PEL of 100 μg/m³ to be 43 percent; this is somewhat higher than estimated by Steenland and Brown (1995b) because of the use by OSHA of more recent mortality data and calculation of risk through age 85 rather than 75. For exposure to the revised PEL of 50 μg/m³, OSHA estimated the lifetime risk to be 7 percent. Since the time of the original analysis, NCHS has released updated all-cause mortality background rates from 2011; OSHA's final risk estimates, which incorporate these updated rates, are available in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

Miller et al. (1995, Document ID 1097; 1998, 0374) and Buchanan et al. (2003, Document ID 0306) reported on a follow-up study conducted in 1990 and 1991 of 547 survivors of a 1,416 member cohort of Scottish coal workers from a single mine. These men all worked in the mine during a period between early 1971 and mid-1976, during which they had experienced “unusually high concentrations of freshly cut quartz in mixed coalmine dust” (Document ID 0374, p.52). Thus, this cohort allowed for the study of exposure-rate effects on the development of silicosis. The men all had radiographs dating from before, during, or just after this high concentration period, and the 547 participating survivors received follow-up chest x-rays between November 1990 and April 1991.

Buchanan et al. (2003, Document ID 0306) presented logistic regression models in stages. In the first stage they compared the effect of pre- vs. post-1964 cumulative quartz exposures on odds ratios; this yielded a statistically significant odds ratio estimate for post-1964 exposures. In the second stage they added total dust levels both pre- and post-1964, age, smoking status, and the number of hours worked pre-1954; only post-1964 cumulative exposures remained significant. Finally, in the third stage, they started with only the statistically significant post-1964 cumulative exposures, and separated these exposures into two quartz bands, one for exposure to concentrations less than 2,000 μg/m³ respirable quartz and the other for concentrations greater than or equal to 2,000 μg/m³. Both concentration bands were highly statistically significant in the presence of the other, with the coefficient for exposure concentrations greater than or equal to 2000 μg/m³ being three times that of the coefficient for concentrations less than 2000 μg/m³. From this, the authors concluded that their analysis showed that “the risks of silicosis over a working lifetime can rise dramatically with exposure to such high concentrations over a timescale of merely a few months” (Buchanan et al. 2003, Document ID 0306, p. 163). The authors then used the model to estimate the risk of acquiring a chest x-ray classified as ILO category 2/1+, 15 years after exposure, as a function of both low (<2000 μg/m³) and high (>2000 μg/m³) quartz concentrations. OSHA chose to use this model to estimate the risk of radiological silicosis consistent with an ILO category 2/1+ chest x-ray for several exposure scenarios; in each, it assumed 45 years of exposure, 2000 hours/year of exposure, and no exposure above a concentration of 2000 μg/m³. The results showed that occupational exposures to the revised PEL of 50 μg/m³ led to an estimated risk of 55 cases per 1,000 workers. Exposure at the previous general industry PEL of 100 μg/m³ increased the estimate to 301 cases per 1,000 workers. At higher exposure levels the risk estimates rose quickly to near certainty.

Chen et al. (2001, Document ID 0332) reported the results of a retrospective study of a Chinese cohort of 3,010 underground miners who had worked in tin mines at least one year between 1960 and 1965. They were followed through 1994, by which time 2,426 (80.6 percent) workers had either retired or died, and only 400 (13.3 percent) remained employed at the mines. Annual radiographs were taken beginning in 1963 and cohort members continued to have chest x-rays taken every 2 or 3 years after leaving work. Silicosis was diagnosed when at least 2 of 3 radiologists classified a radiograph as being a suspected case or at Stage I, II, or III under the 1986 Chinese pneumoconiosis roentgen diagnostic criteria, which the authors reported agreed closely with ILO categories 0/1, Category 1, Category 2, and Category 3, respectively. Silicosis was observed in 33.7 percent of the group; 67.4 percent of the cases developed after exposure ended.

Chen et al. (2001, Document ID 0332) found that a Weibull model provided the best fit to relate cumulative silicosis risk to eight categories of cumulative total dust exposure. The risk of silicosis was strongly related to cumulative silica exposure. The investigators predicted a 55-percent risk of silicosis associated with 45 years of exposure to 100 μg/m³. The paper did not report the risk associated with a 45-year exposure to 50 μg/m³, but OSHA estimated the risk to be about 17 percent (based on the parameters of the Weibull model).

In a later study, Chen et al. (2005, Document ID 0985) investigated silicosis morbidity risks among three cohorts to determine if the risk varied among workers exposed to silica dust having different characteristics. The cohorts consisted of 4,547 pottery workers, 4,028 tin miners, and 14,427 tungsten miners, all employed after January 1, 1950 and selected from a total of 20 workplaces. The approximate mean cumulative exposures to respirable silica for pottery, tin, and tungsten workers were 6.4 mg/m³-yrs, 2.4 mg/m³-yrs, and 3.2 mg/m³-yrs, respectively. Measurement of particle surface occlusion (presence of a mineral coating that may affect the biological availability of the quartz component) indicated that, on average, 45 percent of the surface area of respirable particles collected from pottery factory samples was occluded, compared to 18 percent of the particle surface area for tin mine samples and 13 percent of particle surface area for tungsten mines. When cumulative silica exposure was adjusted to reflect exposure to surface-active quartz particles (i.e., not occluded), the estimated cumulative risk among pottery workers more closely approximated those of the tin and tungsten miners, suggesting to the authors that alumino silicate occlusion of the crystalline particles in pottery factories at least partially explained the lower risk seen among pottery workers, despite their having been more heavily exposed. Based on Chen et al. (2005, Document ID 0985), OSHA estimated the cumulative silicosis risk associated with 45 years of exposure to 100 μg/m³ respirable crystalline silica to be 6 percent for pottery workers, 12 percent for tungsten miners, and 40 percent for tin miners. For 45 years of exposure to 50 μg/m³, cumulative silicosis morbidity risks were estimated to be 2 percent for pottery workers, 2 percent for tungsten miners, and 10 percent for tin miners.

ii. Risk Estimates

OSHA's risk estimates for silicosis morbidity ranged between 60 and 773 per 1,000 workers for a 45-year exposure to the previous general industry PEL of 100 μg/m³, and between 20 and 170 per 1,000 workers for a 45-year exposure to the revised PEL of 50 μg/m³, depending upon the study used. OSHA recognizes that actual risk, to the extent that workers are exposed for less than 45 years or intermittently, is likely to be lower, but also recognizes that silicosis can progress for years after exposure ends. Also, given the consistent finding of a monotonic exposure-response relationship for silicosis morbidity with cumulative exposure in the studies reviewed, OSHA continues to find that cumulative exposure is a reasonable exposure metric upon which to base risk estimates in the exposure range of interest.

D. Comments and Responses Concerning Silicosis and Non-Malignant Respiratory Disease Mortality and Morbidity

In this section, OSHA focuses on comments pertaining to the literature used by the Agency to assess risk for silicosis and non-malignant respiratory disease (NMRD) mortality and morbidity. As discussed in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711) and in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, of this preamble, OSHA used two studies (ToxaChemica, 2004, Document ID 0469; Park et al., 2002, 0405) to determine lifetime risk for silicosis and NMRD mortality and five studies (Buchanan et al., 2003, Document ID 0306; Chen et al., 2001, 0332; Chen et al., 2005, 0985; Hnizdo and Sluis-Cremer, 1993, 1052; and Steenland and Brown, 1995b, 0451) to determine cumulative risk for silicosis morbidity. OSHA discussed the reasons for selecting these scientific studies for quantitative risk assessment in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 340-342). Briefly, OSHA concluded that the aforementioned studies used scientifically accepted techniques to measure silica exposures and health effects in order to determine exposure-response relationships. The Agency believed, and continues to believe, that these studies, as a group, provide the best available evidence of the exposure-response relationships between silica exposure and silicosis morbidity, silicosis mortality, and NMRD mortality and that they constitute a solid and reliable foundation for OSHA's final risk assessment.

OSHA received both supportive and critical comments and testimony regarding these studies. Comments largely focused on how the authors of these studies analyzed their data, and concerns expressed by commenters generally focused on exposure levels and measurement, potential biases, confounding, statistical significance of study results, and model forms. This section does not include extensive discussion on exposure measurement error, potential biases, thresholds, confounding factors, and the use of the cumulative exposure metric, which are discussed in depth in other sections of this preamble, including V.J Comments and Responses Concerning Biases in Key Studies and V.K Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis. OSHA addresses comments on general model form and various other issues here and concludes that these comments do not meaningfully affect OSHA's reliance on the studies discussed herein or the results of the Agency's final risk assessment.

1. Silicosis and NMRD Mortality

There are two published studies that report quantitative risk assessments of silicosis and NMRD mortality (see Document ID 1711, pp. 292-298). The first is an exposure-response analysis of diatomaceous earth (DE) workers (Park et al., 2002, Document ID 0405). Park et al. quantified the relationship between cristobalite exposure and mortality caused by NMRD, which includes silicosis, pneumoconiosis, emphysema, and chronic bronchitis (Park et al. refers to these conditions as “lung disease other than cancer (LDOC),” while OSHA uses the term “NMRD”). Because NMRD captures much of the silicosis misclassification that results in underestimation of the disease and includes risks from other lung diseases associated with crystalline silica exposures, OSHA believes the risk estimates derived from the Park et al. study reasonably reflect the risk of death from silica-related respiratory diseases, including silicosis (Document ID 1711, pp. 297-298). The second study (Mannetje et al. 2002b, Document ID 1089) is a pooled analysis of six epidemiological studies that were part of an IARC effort. OSHA's contractor ToxaChemica later conducted a reanalysis and uncertainty analysis using these data (ToxaChemica, 2004, Document ID 0469). OSHA believes that the estimates from the pooled study represent credible estimates of mortality risk from silicosis across a range of industrial workplaces, but are likely to understate the actual risk because silicosis is under-reported as a cause of death.

a. Park et al. (2002)

The American Chemistry Council (ACC) submitted several comments pertaining to the Park et al. (2002, Document ID 0405) study, including comments on the cohort's exposure concentrations. In its post-hearing brief, the ACC noted that the mean crystalline silica exposure in Park's DE cohort was estimated to be more than three times the former general industry PEL of 100 μg/m³ and the mean estimated exposure of the workers with silicosis could have been close to 10 times that level. According to the ACC, extrapolating risks from the high exposure levels in this cohort to the much lower levels relevant to OSHA's risk assessment (the previous general industry PEL of 100 μg/m³ and the revised PEL of 50 μg/m³) is “fraught with uncertainty” (Document ID 4209, pp. 84-85).

OSHA acknowledges that there is some uncertainty in using models heavily influenced by exposures above the previous PEL due to potential deviance at areas of the relationship with fewer data points. However, OSHA believes that the ACC's characterization of exposures in the Park et al. (2002) study as vastly higher than the final and former PELs is incorrect. The ACC focused on mean exposure concentrations, reported by Park et al. as 290 μg/m³, to make this argument (Document ID 0405, p. 37). However, in the Park et al. study, the mean cumulative exposure of the cohort was 2.16 mg/m³-yrs, lower than what the final rule would permit over 45 years of exposure (2.25 mg/m³-yrs) (Document ID 0405, p. 37). Thus, whereas some participants in the Park et al. study had higher average-8-hour exposures than were typical under the previous PEL, they were quite comparable to the exposures workers might accumulate over their working lives under the final PEL of 50 μg/m³. In addition, as discussed in Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric, OSHA believes that the evidence in the rulemaking record, including comments and testimony from NIOSH (Document ID 3579, Tr. 127), Kyle Steenland, Ph.D. (Document ID 3580, Tr. 1227), and OSHA peer reviewer Kenneth Crump, Ph.D. (Document ID 1716, p. 166), points to cumulative exposure as a reasonable and appropriate dose metric for deriving exposure-response relationships. In sum, OSHA does not agree that the Park study should be discounted based on the ACC's concerns about the estimated exposure concentrations in the diatomaceous earth cohort.

The ACC also criticized the Park study for its treatment of possible confounding by smoking and exposure to asbestos. The ACC commented in its pre-hearing brief that data on smoking was available for only half of the cohort (Document ID 2307, Attachment A, p. 108). The Panel also wrote that, “while Park et al. dismissed asbestos as a potential confounder and omitted asbestos exposure in their final models, the situation is not as clear-cut as they would have one believe” (Document ID 2307, Attachment A, p. 109). The Panel highlighted that Checkoway et al. (1997), the study upon which Park relied to dismiss asbestos as a potential confounder, noted that “misclassification of asbestos exposure may have hindered our ability to control for asbestos as a potential confounder” (Document ID 0326, p. 685; 2307, Attachment A, p. 109).

OSHA has reviewed the ACC's concerns, and maintains that Park et al. adequately addressed the issues of possible confounding by smoking and exposure to asbestos in this data set. Smoking habits of a third of the individuals who died from NMRD were known in the Park et al. (2002) study. Based on that partial knowledge of smoking habits, Park et al. presented analyses indicating that confounding by smoking was unlikely to significantly impact the observed relationship between cumulative exposure to crystalline silica and NMRD mortality (Document ID 0405, p. 41). Specifically, Park et al. (2002) performed internally standardized analyses, which tend to be less susceptible to confounding by smoking since they compare the mortality experience of groups of workers within the cohort rather than comparing the mortality experience of the cohort with an external population (such as by using national mortality rates); the authors found that the internally standardized models yielded only slightly lower exposure-response coefficients than externally adjusted models (Document ID 0405; 1711, p. 302). These results suggested that estimates of NMRD mortality risks based on this cohort are not likely to be exaggerated due to cohort members' smoking habits. Park et al. also stated that the authors' findings regarding possible confounding by smoking were consistent with those of Checkoway et al., who also concluded there it was “very unlikely” that smoking could explain the association between mortality from NMRD and silica exposure in this cohort (Document ID 0405, p. 41; 0326, p. 687). NIOSH noted that “[r]esidual confounding from poorly characterized smoking could have an effect,” but that effect could be either positive or negative (Document ID 4233, pp. 32-33). While OSHA agrees that comprehensive smoking data would be ideal, the Agency believes that the approach taken by Park et al. to address this issue was reasonable.

Asbestos exposure was estimated for all workers in Park et al., which enabled the researchers to directly test confounding. They “found no confounding by asbestos” and, accordingly, omitted asbestos exposure in their final modeling (Document ID 0405, p. 41). As discussed in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 301-302), exposure to asbestos was particularly prevalent among workers employed prior to 1930; after 1930, asbestos was presumably no longer used in the process (Gibbs, 1998, Document ID 1024, p. 307; Checkoway et al., 1998, 0984, p. 309). Checkoway et al. (1998), who evaluated the issue of asbestos confounding for the same cohort used by Park et al., found that the risk ratio for the highest silica exposure group after excluding the workers employed before 1930 from the cohort (Relative Risk (RR) = 1.73) was almost identical to the risk ratio of the high-exposure group before excluding those same workers (RR = 1.74) (Document ID 0984, p. 309). In addition, Checkoway's reanalysis of the original cohort study (Checkoway et al., 1993) examined those members of the cohort for whom there was quantitative information on asbestos exposure, based on a mixture of historical exposure monitoring data, production records, and recorded quantities of asbestos included in mixed products of the plant (Checkoway et al., 1996, Document ID 0325). The authors found an increasing trend in lung cancer mortality with exposure to crystalline silica after controlling for asbestos exposure and found only minor changes in relative risk estimates after adjusting for asbestos exposure (1996, Document ID 0325). Finally, Checkoway et al. (1998) reported that the prevalence of pleural abnormalities (indicators of asbestos exposure) among workers hired before 1930 (4.2 percent) was similar to that of workers hired after 1930 who presumably had no asbestos exposure (4.9 percent), suggesting that asbestos exposure was not a confounder for lung abnormalities in this group of workers (Document ID 0984, p. 309). Therefore, Checkoway et al. (1998) concluded that asbestos was not likely to significantly confound the exposure-response relationship observed between lung cancer mortality and exposure to crystalline silica in diatomaceous earth workers.

Rice et al. also utilized Checkoway's (1997, Document ID 0326) data to test for confounding by asbestos in their Poisson and Cox proportional hazards models. Finding no evidence of confounding, Rice et al. did not include asbestos exposure as a variable in the final models presented in their 2001 paper (Document ID 1118, p. 41). Based on these numerous assessments of the effects of exposure to asbestos in the diatomaceous earth workers cohort used by Park et al. (2002), OSHA concludes that concerns about asbestos confounding in this cohort have been adequately addressed and that the additional analyses performed by Park et al. on this issue confirmed the findings of prior researchers that confounding by asbestos exposure was not likely to have a large effect on exposure-response relationships.

The ACC also expressed concern about model selection. Louis Anthony Cox, Jr., Ph.D., of Cox Associates, on behalf of the ACC, was concerned that the linear relative rate model was not appropriate because it is not designed to test for exposure-response thresholds and, similarly, the ACC has argued that threshold models are appropriate for crystalline silica-related diseases (Document ID 2307, Attachment 4, pp. 91). The ACC claimed that the Park et al. (2002) study is “fully consistent” with a threshold above the 100 μg/m³ concentration for NMRD, including silicosis, mortality (Document ID 2307, Attachment A, p. 107).

In its post-hearing comments, NIOSH explained that categorical analysis for NMRD indicated no threshold existed with cumulative exposure corresponding to 25 μg/m³ over 40 years of exposure, which is below the cumulative exposure equivalent to the new PEL over 45 years (Document ID 4233, p. 27). Park et al. did not estimate a threshold below that level because the data lacked the power needed to discern a threshold (Document ID 4233, p. 27). OSHA agrees with NIOSH's assessment. In addition, as discussed extensively in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases, OSHA has carefully reviewed the issue of thresholds and has concluded, based on the best available evidence, that workers with cumulative and average exposure levels permitted under the previous PEL of 100 μg/m³ are at risk of silica-related disease (that is, there is unlikely to be an exposure-response threshold at or near 100 μg/m³). For these reasons, OSHA disagrees with Dr. Cox's criticism of Park et al.'s reliance on the linear relative rate model.

The ACC then questioned the use of unlagged cumulative exposures as the metric in Park et al. (2002). Dr. Cox noted that “[u]nlagged models are not very biologically plausible for dust-related NMRD deaths (if any) caused by exposure concentrations in the range of interest. Unresolved chronic inflammation and degradation of lung defenses takes years to decades to manifest” (Document ID 2307, Attachment 4, p. 92). OSHA considers this criticism overstated. Park et al. considered a range of lag periods, from two years to 15. They found that “[u]nlagged models seemed to provide the best fit to the data in Poisson analyses although lagged models performed almost as well” (Document ID 0405, p. 37). Based on those findings, as well as acknowledgments that NMRD effects other than silicosis (e.g., chronic bronchitis) may be observable without a relatively long lag time (unlike cancer) and that the majority of deaths observed in the cohort were indeed NMRD other than silicosis, the researchers decided to use an unlagged model. Because Park found the differences between the lagged and unlagged models for this cohort and the NMRD endpoint to be insignificant, OSHA finds that Park's final choice to use an unlagged model does not detract from OSHA's decision to utilize lagged models in its risk assessment.

The ACC was also concerned about the truncation of cumulative exposures in the Park et al. (2002) paper. Peter Morfeld, Dr. rer. medic, stated that Park et al.:

suffers from a methodological drawback. . . . The authors truncated the cumulative RCS dust exposures before doing the final analyses based on their observation of where the cases were found. The maximum in the study was 62.5 mg/m³-years but exposures were only used up to 32 mg/m³-years because no LDOC deaths occurred at exposures higher than that level. Such a selection distorts the estimated exposure-response relationship because it is based on the outcome of the study and on the exposure variable. Because high exposures with no effects were deliberately ignored, the exposure-response effect estimates are biased upward (Document ID 2307, Attachment 2, p. 27).

OSHA acknowledges this concern about the truncation of data in the study, and asked Mr. Park about it at the public hearing. Mr. Park testified that there were good reasons to truncate the part of the exposed workforce at the high end of cumulative exposure. He noted several plausible reasons for the drop-off in the number of cases at high exposures (attenuation), including random variance in susceptibility to disease among different people and the healthy worker survivor effect (Document ID 3579, Tr. 242-243). He also stated that this attenuation is a common occurrence in studies of workers (Document ID 3579, Tr. 242). Mr. Park then emphasized that how one describes the higher end of the exposure-response relationship is inconsequential for the risk assessment process because the relationship at the lower end of the spectrum, where the PEL was determined, is more important for rulemaking (Document ID 3579, Tr. 242-243). He also stated, in a post-hearing comment, that “[f]or the purpose of low exposure extrapolation, adding a quadratic term [to better describe the entirety of the exposure-response relationship] would result in loss of precision with no advantage [gained] over truncation of high cumulative exposure observation time” (Document ID 4233, p. 26). To summarize, Mr. Park stated that there are good scientific reasons to expect attenuation of exposure-response at the high end of the cumulative exposure range and that use of higher-exposure data affected by healthy worker survivor effect or other issues could reduce precision of the exposure-response model at the lower exposures that are more relevant to the final silica standard. OSHA finds that Mr. Park's approach in his study, along with his explanations in the rulemaking record, are reasonable and that he has fully responded to the concerns of the ACC.

Dr. Morfeld also noted that alternative techniques that do not require truncation are available to account for a healthy worker survivor effect (Document ID 2307, Attachment 2, pp. 27-28). OSHA believes such techniques, such as g-estimation, to be relatively new or not yet in standard use in occupational epidemiology. As discussed above, OSHA finds Mr. Park's approach in his study to be reasonable.

Finally, Dr. Cox stated in his comments that:

key studies relied on by OSHA, such as Park et al. (2002), do not correct for biases in reported ER [exposure-response] relations due to residual confounding by age (within age categories), i.e., the fact that older workers may tend to have both higher lung cancer risks and higher values of occupational exposure metrics, even if one does not cause the other. This can induce a non-causal association between the occupational exposure metrics and the risk of cancer (Document ID 2307, Attachment 4, p. 29).

Confounding occurs in an epidemiological study when the contribution of a causal factor cannot be separated from the effect of another variable (e.g., age) not accounted for in the analysis. Residual confounding occurs when attempts to control for confounding are not precise enough (e.g., controlling for age by using groups with age spans that are too wide), or subjects are misclassified with respect to confounders (Document ID 3607, p. 1). However, the Park et al. (2002) study of non-malignant respiratory disease mortality, which Dr. Cox cited as not considering residual confounding by age, actually addressed this issue by using 13 five-year age groups (<25, 25-29, 30-34, etc.) in the models (Document ID 0405, p. 37). Further discussion on residual confounding bias is found in Section V.J, Comments and Responses Concerning Biases in Key Studies.

The inclusion of Park et al. (2002) (Document ID 0405) in OSHA's risk assessment has additional support in the record. OSHA's expert peer-review panel supported including the Park et al. study in the risk assessment, with Gary Ginsberg, Ph.D., stating that it “represents a reasonable estimate of silica-induced total respiratory mortality” (Document ID 3574, p. 29). In addition, as OSHA noted in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 355-356), the Park et al. study is complemented by the Mannetje et al. multi-cohort silicosis mortality pooled study, which included several cohorts that had exposure concentrations in the range of interest for this rulemaking and also showed clear evidence of significant risk of silicosis and other NMRD at the previous general industry and construction PELs (2002b, Document ID 1089).

b. Mannetje et al. (2002b) and ToxaChemica (2004)

The ACC also submitted several comments on the Mannetje et al. (2002b) study of silicosis mortality; the data from Mannetje et al. were used in the ToxaChemica (2004) re-analysis. As noted above, the Mannetje et al. (2002b) study was a pooled analysis of silicosis mortality data from six epidemiological cohorts. This study showed a statistically significant association between silicosis mortality and workers' cumulative exposure, as well as with average exposure and exposure duration. The ACC's pre-hearing brief stated that the study “provided no justification for the relative rate model forms [Mannetje et al.] used to evaluate exposure-response” (Document ID 2307, Attachment A, p. 113). The concern expressed was that the study may not have considered all potential exposure-response relationships and was unable to discern differences between monotonic and non-monotonic characteristics (Document ID 2307, Attachment A, p. 113-114).

Mannetje et al. (2002b, Document ID 1089) did not discuss whether models other than relative rate models were tested. However, Mannetje's data was reexamined by ToxaChemica, Inc. on request from OSHA and the reexamined data was used by OSHA to help estimate lifetime risk for silicosis mortality (2004, Document ID 0469; 1711, pp. 310-314). The ToxaChemica reanalysis of the data included a categorical analysis and a five-knot restricted spline analysis, in addition to a logistic model, using the log of cumulative exposure (Document ID 0469, p. 50). ToxaChemica also corrected some errors found in the original data set and used a nested case-control approach, which they stated would control more precisely for age than the Poisson regression approach used by Mannetje et al. (Document ID 0469, p. 18). As shown in Figure 5 of ToxaChemica's report, the restricted spline model (which has considerable flexibility to represent non-monotonic features of exposure-response data) appeared to be monotonic, while the categorical analysis appeared largely monotonic but for one exposure group (Document ID 0469, p. 40, 50). When not adjusted for measurement error, the second highest exposure group deviated from the monotonic relationship existing between the other groups. However, the deviation was resolved when two sources of measurement error were accounted for (Document ID 0469, p. 40). The categorical analysis, restricted spline model, and logistic model yielded roughly similar exposure-response curves (Document ID 0469, p. 50). OSHA concludes that the ToxaChemica reanalysis addresses the concerns raised by the ACC by finding similar exposure-response relationships regardless of the model as well as providing greater validation of a monotonic curve.

The ACC next questioned the odds ratios generated in the Mannetje et al. (2002b) study (Document ID 2307, p. 114; 4209, p. 88). The Panel noted that “the exposure-response relationship is not even fully monotonic” and that the silica odds ratios in the pooled analysis have overlapping confidence intervals, suggesting no statistically significant difference (Document ID 2307, p. 114). The Panel concluded that “the data indicate that there is no clear effect of exposure on odds ratios over the entire range considered by the authors; hence, the study provides no basis for concluding that reducing exposures will reduce the odds ratio for silicosis mortality” (Document ID 4209, p. 88). Essentially, the ACC argued that the data do not appear to fit a monotonic relationship and that the confidence intervals for each exposure level overlap too much to discern any differences in risk ratios between those exposures.

OSHA believes that the ACC overstated its contention about confidence interval overlap between groups in the Mannetje et al. (2002b) paper. Although the original data set reported in the study lacks a monotonic relationship on the upper end of the exposure spectrum (>9.58 mg/m³-yrs) (possibly due to a healthy worker survivor effect, as explained above), OSHA notes that the 95 percent confidence intervals reported do not contradict the presence of a monotonic relationship (Document ID 1089). First, the confidence intervals of the lower exposed groups did not overlap with those of the higher exposed groups in that study (Document ID 1089). Second, even if they did, overlap in confidence intervals does not mean that there is not a significant difference between those groups. While it is true that, if 95 percent confidence intervals do not overlap, the represented populations are statistically significantly different, the converse—that, if confidence intervals do overlap, there is no statistically significant difference—is not always true (Nathaniel Schenker and Jane F. Gentleman. “On Judging the Significance of Differences by Examining the Overlap Between Confidence Intervals.” The American Statistician. 55(3): 2001. 182-186. ( http://www.tandfonline.com/doi/abs/10.1198/000313001317097960 ).

Finally, as discussed above and in detail in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, the ToxaChemica et al. (2004) re-analysis of the corrected Mannetje et al. (2002b) data adjusting for two sources of measurement error resulted in a monotonic relationship for the risk ratios (Document ID 0469).

2. Silicosis Morbidity

OSHA relied on five studies for determining risk for silicosis morbidity: Buchanan et al., 2003 (Document ID 0306), Chen et al., 2001 (Document ID 0332), Chen et al., 2005 (Document ID 0985), Hnizdo and Sluis-Cremer, 1993 (Document ID 1052), and Steenland and Brown, 1995b (Document ID 0451). OSHA finds that the most reliable estimates of silicosis morbidity, as detected by chest radiographs, come from these five studies because they evaluated radiographs over time, included post-employment radiographic evaluations, and derived cumulative or lifetime estimates of silicosis disease risk. OSHA received several comments about these studies.

a. Buchanan et al. (2003)

Buchanan et al. (2003) reported on a cohort of Scottish coal workers (Document ID 0306). The authors found a statistically significant relationship between silicosis and cumulative exposure acquired after 1964 (Document ID 0306). They also found that the risks of silicosis over a working lifetime can rise dramatically with exposure to high concentrations over a timescale of merely a few months (Document ID 0306). In the Preliminary QRA, OSHA considered this study to be of the highest overall quality of the studies relied upon to assess silicosis morbidity risks, in large measure because the underlying exposure data was based on modern exposure measurement methods and avoided the need to estimate historical exposures. The risk estimates derived from this study were lower than those derived from any of the other studies criticized by the ACC. One reason for this is because Buchanan et al. only included cases with chest x-ray findings having an ILO score of 2/1 or higher, whereas the other studies included cases with less damage, having a lower degree of perfusion on x-ray (ILO 1/0 or 1/1) (Document ID 0306). Thus, OSHA considered the risk estimates derived from the Buchanan et al. study to be more likely to understate risks.

Dr. Cox commented that age needed to be included for modeling in Dr. Miller's 1998 paper, the data from which were used in the Buchanan et al. (2003) paper (Document ID 2307, Attachment 4, p. 97). However, the Miller et al. (1998) study explicitly states that age was one of several variables that were tried in the model but did not improve the model's fit, as was time spent working in the poorly characterized conditions before 1954 (Document ID 0374, p. 57). OSHA concludes that the original paper did assess these variables and how they related to the exposure-response relationship. Buchanan et al. (2003) also noted their own finding that differences in age and exposure both failed to improve fit, in agreement with Miller et al.'s conclusion (Document ID 0306, p. 161). OSHA therefore finds no credible reason that age should have been included as a variable in Miller et al. (1998).

Dr. Cox also questioned the modeling methods in the Buchanan paper, which presented logistic regression in progressive stages to search for significance (Document ID 2307, Attachment 4, pp. 97-98; 0306, pp. 161-163). Dr. Cox claimed that this is an example of uncorrected multiple testing bias where the post hoc selection of data, variables, and models can make independent variables appear to be statistically significant in the prediction model. He suggested that corrections for bias are needed to determine if the reported significance is causal or statistical (Document ID 2307, Attachment 4, pp. 97-98). OSHA peer reviewer Brian Miller, Ph.D., stated that Dr. Cox's claim that the model was affected by multiple testing bias is unfounded (Document ID 3574, pp. 31-32). He noted that the model was based on a detailed knowledge of the history of exposures at that colliery, and represented the researchers' attempt to build “a reality-driven and `best-fitting' model,” (Document ID 3574, p. 31, quoting 2307, Attachment 4, p. 4). Furthermore, none of OSHA's peer reviewers raised any concerns about the approach taken by Buchanan et al. to develop their exposure-response model and none suggested that corrections needed to be made for multiple testing bias; all of them supported the study's inclusion in OSHA's risk assessment (Document ID 3574). Finally, the cumulative risk for silicosis morbidity derived from this study is similar to values from other papers reported in the QRA (see OSHA's Final Quantitative Risk Assessment in Section VI). Therefore, for the reasons discussed above, OSHA is not convinced by Dr. Cox's arguments and finds no credible reason to remove Buchanan et al. (2003) from consideration.

b. Chen et al. (2001, 2005), Steenland and Brown (1995), and Hnizdo and Sluis-Cremer (1993)

The ACC also commented on several other studies used by OSHA to estimate silicosis morbidity risks; these were the studies by Chen et al. (2001, Document ID 0332; 2005, 0985), Steenland and Brown (1995b, Document ID 0451), and Hnizdo and Sluis-Cremer (1993, Document ID 1052). The ACC's comments focus on uncertainties in estimating the historical exposures of cohort members (Document ID 2307, Attachment A, pp. 117-122, 124-130, 132-136). Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, discusses the record in detail with respect to the general issue of uncertainties in estimating historical exposures to respirable crystalline silica in epidemiological studies. The issues specific to the studies relied upon by OSHA in its risk estimates for silicosis morbidity will be discussed below.

In the Chen et al. studies, which focused on mining (i.e., tin, tungsten) and pottery cohorts, high volume area samplers collected dust and the respirable crystalline silica concentration was determined from those samples (2001, Document ID 0332; 2005, 0985). However, according to the ACC, the rest of the collected dust was not assessed for chemicals that potentially could also cause radiographic opacities (Document ID 2307, Attachment A, pp. 132-135). Neither study expressed reason to be concerned about the non-silica portion of the dust samples. OSHA recognizes that uncertainty about potential unknown exposures exists in retrospective studies, which describes most epidemiological research. However, OSHA emphasizes that the risk values derived from the Chen et al. studies do not differ remarkably from other silicosis morbidity studies used in the risk assessment (Document ID 0306, 1052, 0451). Therefore, OSHA concludes that it is unlikely that an unknown compound significantly impacted the exposure-response relationships reported in both Chen studies.

The study on gold miners (Steenland and Brown, 1995b, Document ID 0451), which found that cumulative exposure was the best disease predictor, followed by duration of exposure and average exposure, was also criticized by the ACC, which alleged that the exposure assessment suffered from “enormous uncertainty” (Document ID 2307, Attachment A, pp. 146-147). The ACC noted that exposure measurements were not available for the years prior to 1937 or after 1975 and that this limitation of the exposure information may have resulted in an underestimation of exposures (Document ID 2307, Attachment A, pp. 124-126). OSHA agrees that these are potential sources of uncertainty in the exposure estimates, but recognizes exposure uncertainty to be a common occurrence in occupational epidemiology studies. OSHA believes that the authors used the best measurement data available to them in their study.

The ACC also took issue with Steenland and Brown's conversion factor for converting particle count to respirable silica mass (10 mppcf = 100 μg/m³), which was somewhat higher than that used in the Vermont granite worker studies (10 mppcf = 75 μg/m³) (Document ID 2307, Attachment A, p. 126). OSHA notes that the study's reasoning for adopting that specific particle count conversion factor was to address the higher percentage of silica found in the gold mine samples applicable to their cohort in comparison to the Vermont granite study (Document ID 0451, p. 1373). OSHA finds this decision, which was based on the specific known exposure conditions of this cohort, to be reasonable.

With respect to the Hnizdo and Sluis-Cremer (1993, Document ID 1052) study, which found that silicosis risk increased exponentially with cumulative exposure to respirable dust (Document ID 1052, p. 447), the ACC questioned three assumptions the study made about exposures. First, exposures were assumed to be static from the 1930s to the 1960s, based on measurements from the late 1950s to mid-1960s, an assumption that, according to the ACC, might underestimate exposure for workers employed before the late 1950s (Document ID 2307, Attachment A, pp. 117-119). Second, although respirable dust, by definition, includes particles up to 10 μm, the study only considered particles sized between 0.5 and 5 μm in diameter (Document ID 1052, p. 449). The ACC contends this exclusion may have resulted in underestimated exposure and overestimated risk (Document ID 2307, Attachment A, p. 119). OSHA agrees that uncertainty in exposure estimates is an important issue in the silica risk assessment, and generally discusses the issue of exposure measurement uncertainty in depth in a quantitative uncertainty analysis described in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis. As discussed there, after accounting for the likely effects of exposure measurement uncertainty in the risk assessment, OSHA affirms the conclusion of the risk assessment that there is significant risk of silicosis to workers exposed at the previous PELs.

Thirdly, the ACC challenged the authors' estimate of the quartz content of the dust as 30 percent when it should have been 54 percent (Document ID 1052, p. 450; 2307, Attachment A, p. 120). According to the ACC, the 30 percent estimate was based on an incorrect assumption that the samples had been acid-washed (resulting in a reduction in silica content) before the quartz content was measured (Document ID 2307, Attachment A, pp. 120-122). This assumption would greatly underestimate the exposures of the cohort and the exposures needed to cause adverse effects, thus overestimating actual risk (Document ID 2307, Attachment A, pp. 121-122). The ACC recommended that the quartz content in the Hnizdo and Sluis-Cremer study be increased from 30 to 54 percent, based on the Gibbs and Du Toit study (2002, Document ID 1025, p. 602).

OSHA considered this issue in the Preliminary QRA (Document ID 1711, p. 332). OSHA noted that the California Environmental Protection Agency's Office of Environmental Health Hazard Assessment reviewed the source data for Hnizdo and Sluis-Cremer, located in the Page-Shipp and Harris (1972, Document ID 0583) study, and compared them to the quartz exposures calculated by Hnizdo and Sluis-Cremer (OEHHA, 2005, Document ID 1322, p. 29). OEHHA concluded after analyzing the data that the samples likely were not acid-washed and that the Hnizdo and Sluis-Cremer paper erred in describing that aspect of the samples. Additionally, OEHHA reported data that suggests that the 30 percent quartz concentration may actually overestimate the exposure. It noted that recent investigations found the quartz content of respirable dust in South African gold mines to be less than 30 percent (Document ID 1322). In summary, OSHA concludes that no meaningful evidence was submitted to the rulemaking record that changes OSHA's original decision to include the Hnizdo and Sluis-Cremer study in its risk assessment.

Despite the uncertainties inherent in estimating the exposures of occupational cohorts in silicosis morbidity studies, the resulting estimates of risk for the previous general industry PEL of 100 μg/m³ are in reasonable agreement and indicate that lifetime risks of silicosis morbidity at this level, and, by extension, risks at the higher previous PELs for maritime and construction (see section VI, Final Quantitative Risk Assessment and Significance of Risk) are in the range of hundreds of cases per 1,000 workers. Even in the unlikely event that exposure estimates underlying all of these studies were systematically understated by several fold, the magnitude of resulting risks would likely still be such that OSHA would determine them to be significant.

3. Conclusion

After carefully considering all of the comments on the studies relied on by OSHA to estimate silicosis and NMRD mortality and silicosis morbidity risks, OSHA concludes that the scientific evidence used in its quantitative risk assessment substantially supports the Agency's finding of significant risk for silicosis and non-malignant respiratory disease. In its risk estimates in the Preliminary QRA, OSHA acknowledged the uncertainties raised by the ACC and other commenters, but the Agency nevertheless concluded that the assessment was sufficient for evaluating the significance of the risk. After evaluating the evidence in the record on this topic, OSHA continues to conclude that its risk assessment (see Final Quantitative Risk Assessment in Section VI.C of this preamble) provides a reasonable and well-supported estimate of the risk faced by workers who are exposed to respirable crystalline silica.

E. Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality

As discussed above in this preamble, OSHA has relied on epidemiological studies to assess the risk of silicosis, a debilitating and potentially fatal occupationally-related lung disease caused by exposure to respirable crystalline silica. In the proposed rule (78 FR 56273, 56298; also Document ID 1711, pp. 31-49), OSHA also discussed data from silicosis surveillance programs that provide some information about the number of silicosis-associated deaths or the extent of silicosis morbidity in the U.S. (78 FR at 56298). However, as OSHA explained, the surveillance data are not sufficient for estimating the risks of health effects associated with exposure to silica, nor are they sufficient for estimating the benefits of any potential regulatory action. This is because silicosis-related surveillance data are only available from a few states and do not provide exposure data that can be matched to surveillance data. Consequently, there is no way of knowing how much silica a person was exposed to before developing fatal silicosis (78 FR at 56298).

In addition, the available data likely understate the resulting death and disease rates in U.S. workers exposed to crystalline silica (78 FR 56298). This understatement is due in large part to: (1) The passive nature of these surveillance systems, which rely on healthcare providers' awareness of a reporting requirement and submission of the appropriate information on standardized forms to health departments; (2) the long latency period of silicosis; (3) incomplete occupational exposure histories, and (4) other factors that result in a lack of recognition of silicosis by healthcare providers, including the low sensitivity, or ability of chest x-rays to identify cases of silicosis (78 FR 56298). Specific to death certificate data, information on usual industry and occupation are available from only 26 states for the period 1985 to 1999, and those codes are not verifiable (Document ID 1711). Added to these limitations is the “lagging” nature of surveillance data; it often takes years for cases to be reported, confirmed, and recorded. Furthermore, in many cases, the available surveillance systems lack information about actual exposures or even information about the usual occupation or industry of the deceased individual, which could provide some information about occupational exposure (see 78 FR at 56298). Therefore, the Agency did not use these surveillance data to estimate the risk of silicosis for the purpose of meeting its legal requirements to prove a significant risk of material impairment of health (see 29 U.S.C. 655(b)(5); Benzene, 448 U.S. 607, 642 (1980)).

Comments and testimony focusing on the silicosis surveillance data alleged that OSHA should have used the surveillance data in its risk estimates. Stakeholders argued that the declining numbers of reported silicosis deaths prove the lack of necessity for a new silica standard. Commenters also claimed that the surveillance data prove that OSHA overestimated both the risks at the former permissible exposure limits (PELs) and the benefits of the new rule.

After reviewing the rulemaking record, OSHA maintains its view that these silicosis surveillance data, although useful for providing context and an illustration of a significant general trend in the reduction of deaths associated with silicosis over the past 4-5 decades, are not sufficient for estimating the magnitude of the risk or the expected benefits. In the case of silicosis, surveillance data are useful for describing general trends nationally and a few states have the ability to use the data at the local or state level to identify “sentinel events” that would justify initiating an inspection of a workplace, for example. The overall data, however, are inadequate and inappropriate for estimating risks or benefits associated with various exposure levels, as is required of OSHA's regulatory process, in part because they significantly understate the extent of silicosis in workers in the United States and because they lack information about exposure levels, exposure sources (e.g., type of job), controls, and health effects that is necessary to examine the effects of lowering the PEL. Thus, for these reasons and the ones discussed below, OSHA has continued to rely on epidemiological data to meet its burden of demonstrating that workers exposed to respirable crystalline silica at the previous PELs face a significant risk of developing silicosis and that risk will be reduced when the new limit is fully implemented. Another related concern identified by stakeholders is the apparent inconsistency between surveillance data and risk and benefits estimates derived from modeling epidemiological data (Document ID 4194, pp. 7-10; 4209, pp. 3-4). However, this difference is not an inconsistency, but the result of comparing two distinctly different items. Surveillance data, primarily death certificate data, are known to be under-reported and lack associated exposure data necessary to model relationships between various exposure levels and observance of health effects. For these reasons, OSHA relied on epidemiologic studies with detailed exposure-response relationships to evaluate the significance of risk at the preceding and new PELs. Thus, the silicosis mortality data derived from death certificates and estimates of silica-related mortality risks derived from well-conducted epidemiologic studies cannot be directly compared in any meaningful way. With respect to silicosis morbidity, OSHA notes that the estimates by Rosenman et al. (2003, Document ID 0420) of the number of cases of silicosis estimated to occur in the U.S. (between 2,700 and 5,475 estimated to be in OSHA's jurisdiction (i.e., excluding miners)) each year is in reasonable agreement with the estimates derived from epidemiologic studies, assuming either a 13-year or 45-year working life (see Chapter VII, Table VII-2 of the FEA).

1. Surveillance Data on Silicosis Mortality

The principal source of data on annual silicosis mortality in the U.S. is the National Institute for Occupational Safety and Health (NIOSH) Work-Related Lung Disease (WoRLD) Surveillance System (e.g., NIOSH, 2008c, Document ID 1308), which compiles cause-of-death data from death certificates reported to state vital statistics offices and collected by the National Center for Health Statistics (NCHS). Paper copies were published in 2003 and 2008 (Document ID 1307; 1308) and data are updated periodically in the electronic version on the CDC Web site ( http://www.cdc.gov/eworld ). NIOSH also developed and manages the National Occupational Respiratory Mortality System (NORMS), a data-storage and interactive data retrieval system that reflects death certificate data compiled by NCHS ( http://webappa.cdc.gov/ords/norms.html ).

From 1968 to 2002, silicosis was recorded as an underlying or contributing cause of death on 16,305 death certificates; of these, a total of 15,944 (98 percent) deaths occurred in males (CDC, 2005, Document ID 0319). Over time, silicosis-related mortality has declined in the U.S., but has not been eliminated. Based on the death certificate data, the number of recognized and coded deaths for which silicosis was an underlying or contributing cause decreased from 1,157 in 1968 to 161 in 2005, corresponding to an 86-percent decline (Document ID 1711, p. 33; 1308, p. 55) ( http://wwwn.cdc.gov/eworld ). The crude mortality rate, expressed as the number of silicosis deaths per 1,000,000 general population (age 15 and higher) fell from about 8.9 per million to about 0.5 per million over that same time frame, a decline of 94 percent (Document ID 1711, p. 33; 1308, p. 55) ( http://wwwn.cdc.gov/eworld ).

OSHA's Review of Health Effects Literature and Preliminary QRA included death certificate statistics for silicosis up to and including 2005 (Document ID 1711, p. 33). OSHA has since reviewed the more recent NORMS and NCHS data, up to and including 2013, which appear to show a general downward trend in mortality, as presented in Table V-1.

However, more detailed examination of the most recent data collected through NCHS (Table V-2) indicates that the decline in the number of deaths with silicosis as an underlying or contributing cause has leveled off in more recent years, suggesting that the number of silicosis deaths being recorded and captured by death certificates may be stabilizing after 30 or more years of decline.

Robert Cohen, M.D., representing the American Thoracic Society, noted this apparent plateau effect, testifying that “[t]he data from the NIOSH work-related lung disease surveillance report and others show a plateau in silicosis mortality since the 1990s, and we are concerned that that has been the same without any further reduction for more than 20 years. So we think that we still have work to do” (Document ID 3577, p. 775).

Some commenters raised the question about whether decedents who died more recently were exposed to high levels of silica (pre-1970s) and therefore wouldn't necessarily reflect mortalities relevant to the current OSHA standard (Document ID 4194, p. 9; 4209, pp. 7-8). OSHA has no information on the age of these decedents, or the timing of their exposure to silica. If we assume that workers born in 1940-1950 would have started working around 1960, at the earliest, and into the 1970's, and life expectancy in general of 70 years, or 60-70 years to account for years of life lost due to silicosis, most of these workers' working life would have been spent after the 1971 PEL went into effect. It is likely that some of the more recent decedents were exposed to silica prior to 1971; however, it is less likely that all were exposed prior to 1971. At the end of the day, there is no actual exposure information on these decedents, and this generalization does not account for overexposures, which have persisted over time.

2. Surveillance Data on Silicosis Morbidity

There is no nation-wide system for collecting silicosis morbidity case data. The data available are from three sources: (1) The National Hospital Discharge Survey (Document ID 1711, p. 40-43); (2) the Agency for Healthcare Research and Quality's (AHRQ) Nationwide Inpatient Survey (Document ID 3425, p. 2; https://www.hcup-us.ahrq.gov/nisoverview.jsp ); and (3) states that administer silicosis and/or pneumoconiosis disease surveillance (see Document ID 1711, p. 40-43; http://www.cdc.gov/niosh/topics/surveillance/ords/StateBasedSurveillance/stateprograms.html ).

Both of the first two sources of data on silicosis morbidity cases are surveys that provide estimates of hospital discharges. The first is the National Hospital Discharge Survey (NHDS), which was conducted annually from 1965-2010. The NHDS was a national probability survey designed to meet the need for information on characteristics of inpatients discharged from non-Federal short-stay hospitals in the United States (see http://www.cdc.gov/nchs/nhds.htm ). Estimates of silicosis listed as a diagnosis on hospital discharge records are available from the NHDS for the years 1985 to 2010 (see http://www.cdc.gov/nchs/nhds.htm ). National estimates were rounded to the nearest 1,000, and the NHDS has consistently reported approximately 1,000 discharges/hospitalizations annually since 1980 (e.g., Document ID 1307; 1308). The second survey, the National (Nationwide) Inpatient Sample (NIS), is conducted annually by the AHRQ. Dr. Kenneth Rosenman, Division Chief and Professor of Medicine at Michigan State University and who oversees one of the few occupational disease surveillance systems in the U.S., testified that data from the NIS indicated that the nationwide number of hospitalizations where silicosis was one of the discharge diagnoses has remained constant, with 2,028 hospitalizations reported in 1993 and 2,082 in 2011 (Document ID 3425, p. 2).

Morbidity data are also available from the states that administer silicosis and/or pneumoconiosis disease surveillance. These programs rely primarily on hospital discharge records and also may get some reports of cases from the medical community and workers' compensation programs. Currently, NIOSH funds the State-Based Occupational Safety and Health Surveillance cooperative agreements (Document ID 1711, p. 40-41; http://www.cdc.gov/niosh/topics/surveillance/ords/StateBasedSurveillance.html ). All states funded under a cooperative agreement conduct population-based surveillance for pneumoconiosis (hospitalizations and mortality), and a few states (currently Michigan and New Jersey) have expanded surveillance specifically for silicosis (Document ID 1711, p. 40-42; http://www.cdc.gov/niosh/topics/surveillance/ords/StateBasedSurveillance/stateprograms.html ).

State-based hospital discharge data are a useful population-based surveillance data source for quantifying pneumoconiosis (including silicosis), even though only a small number of individuals with pneumoconiosis are hospitalized for that condition (Document ID 0996), and the data refer to hospitalizations with a diagnosis of silicosis, and not specific people. In addition to mortality data, NIOSH has updated its WoRLD Surveillance System with some state-based morbidity case data ( http://wwwn.cdc.gov/eworld/Grouping/Silicosis/94 ). State-based surveillance systems can provide more detailed information on a few cases of silicosis.

NIOSH has published aggregated state case data in its WoRLD Reports (Document ID 1308; 1307) for two ten-year periods that overlap, 1989 to 1998 and 1993 to 2002. State morbidity case data are compiled and evaluated by variables such as ascertainment source, primary industry, and occupations. For the time period 1989 to 1998, Michigan reported 589 cases of silicosis, New Jersey 191 cases, and Ohio 400 cases (Document ID 1307, p. 69). In its last published report, for the later and partially overlapping time period 1993 to 2002, Michigan reported 465 cases, New Jersey 135, and Ohio 279 (Document ID 1308, p. 72). Data for the years 2003 to 2011, from the CDC/NIOSH electronic report, eWoRld, show a modest decline in the number of cases of silicosis in these three states; however, decreases are not nearly as substantial as are those seen in the mortality rates (see Table V-3). Annual averages for the two ten-year periods and the nine-year time period were calculated by OSHA solely for the purpose of comparing cases of silicosis reported over time.

3. Critical Comments Received on Surveillance Data

Industry representatives, including ACC's Crystalline Silica Panel and Dr. Jonathan Borak, representing the Chamber of Commerce (Chamber), contended that the steep decline seen in the number and rate of silicosis deaths since 1968 proves that OSHA cannot meet its burden of demonstrating that a more protective standard is necessary (e.g., Document ID 4209, p. 10; 2376, p. 8; 4016, p. 9). Similarly, other commenters, such as the American Petroleum Institute, the Independent Petroleum Association of America, the National Mining Association, the American Foundry Society (AFS), the National Utility & Excavating Contractors Association, Acme Brick, the National Ready Mixed Concrete Association, and the Small Business Administration's Office of Advocacy stated that surveillance data demonstrate that the previous OSHA PEL was sufficiently effective in reducing the number of deaths from silicosis (Document ID 3589, Tr. 4041; 4122; 2301, pp. 3, 7-9; 2211, p. 2; 2379, pp. 23-25; 2171, p. 1; 3730, p. 5; 3586, Tr. 3358-3360; 3589, Tr. 4311; 2349, pp. 3-4). Industry commenters also argued that the number of recorded silicosis-related deaths in recent years, as reflected in the surveillance data, is far lower than the number of lives that OSHA projected would be saved by a more stringent rule, indicating that OSHA's risk assessment is flawed (e.g., Document ID 3578, Tr. 1074-1075; 4209, p. 3-4).

The Chamber, along with others, declared that OSHA ignored steep declines in silicosis mortality, which in its view indicates that there is no further need to reduce the PEL (Document ID 4194, pp. 7-8). OSHA has not ignored the fact that the available surveillance data indicate a decline in silicosis mortality. As discussed above and in the proposal, the Agency has acknowledged that the available surveillance data do show a decline in the silicosis mortality since 1968. Furthermore, OSHA has no information on whether underreporting has increased or decreased over time, and does not believe that differing rates of reporting and underreporting of silicosis on death certificates explains the observed decline in silicosis mortality. OSHA believes that the reductions in deaths attributable to silicosis are real, and not a statistical artifact. However, OSHA disagrees with commenters' argument that this trend shows the lack of a need for this new rule. First, as explained above, there is strong evidence that the death certificate data do not capture the entirety of silicosis mortality that actually exists, due to underreporting of silicosis as a cause of death. Second, the stakeholders' argument assumes that mortality will continue to decline, even in the absence of a stronger silica standard, and that OSHA and workers should wait for this decline to hit bottom (e.g., Document ID 4209, p. 7). However, testimony in the record suggests that the decline in the number of deaths has leveled off since 2000, probably because of the deaths of those historically exposed to higher levels of silica occurred before then (e.g., Document ID 3577, p. 775).

Third, the decline in silicosis deaths recorded over the past several decades cannot be solely explained by improved working conditions, but also reflects the decline in employment in industries that historically were associated with high workplace exposures to crystalline silica. One of OSHA's peer reviewers for the Review of Health Effects Literature and Preliminary QRA, Bruce Allen, commented that the observed decline in mortality “. . . in no way adjusts for the declining employment in jobs with silica exposure,” making “its interpretation problematic. To emphasize the contribution of historic declines in exposure as the underlying cause is spurious; no information is given to allow one to account for declining employment” (Document ID 3574, p. 7). The CDC/NIOSH also identified declining employment in heavy industries where silica exposure was prevalent as a “major factor” in the reduction over time in silicosis mortality (Document ID 0319, p. 2). As discussed below, however, some silica-generating operations or industries are new or becoming more prevalent.

In his written testimony, Dr. Rosenman pointed out that there are “two aspects to the frequency of occurrence of disease (1) . . . the risk of disease based on the level of exposure and (2) the number of individuals at risk” (Document ID 3425, pp. 3-4). Dr. Rosenman estimated the decline in the number of workers in Michigan foundries (75 percent) and the number of abrasive blasting companies in Michigan (71 percent), and then compared these percentages to the percentage decline in the number of recorded silicosis deaths (80 percent) over a similar time period. The similarities in these values led him to attribute “almost all” of the decrease in silicosis deaths to a decrease in the population at risk (Document ID 3425, pp. 3-4).

Finally, OSHA's reliance on epidemiological data for its risk assessment purposes does not suggest that the Agency ignored the available surveillance data. As discussed above, the data are inadequate and inappropriate for estimating risks or benefits associated with various exposure levels, as is required of OSHA's regulatory process. Even in the limited cases where surveillance data are available, OSHA generally relies on epidemiological data, to the extent they include sufficiently detailed information on exposures, exposure sources (e.g., type of job), and health effects, to satisfy its statutory requirement to use the best available evidence to evaluate the significance of risk associated with exposure to hazardous substances.

Some stakeholders provided comments to the rulemaking record consistent with OSHA's assessment. For example, Dr. Borak stated that the surveillance data “provide little or no basis” (Document ID 2376, p. 8) for OSHA to evaluate the protectiveness of the previous PELs. Similarly, NIOSH asserted that relying on the surveillance data to show that there is no need for a lower PEL or that there is no significant risk at 100 μg/m³ would be “a misuse of surveillance data” (Document ID 3579, Tr. 167). NIOSH also added that, because the surveillance data do not include information about exposures, it is not the kind of data that could be used for a quantitative risk assessment. NIOSH concluded that surveillance data are, in fact, “really not germane to the risk assessment” (Document ID 3579, Tr. 248). OSHA agrees with both Dr. Borak and NIOSH that the surveillance data cannot and do not inform the Agency on the need for a lower PEL, nor is there a role for surveillance data in making its significant risk findings. Therefore, for its findings of significant risk at the current PEL, the Agency relied on evidence derived from detailed exposure-response relationships from well-conducted epidemiologic studies, and not surveillance data, which have no associated exposure information. In this case, epidemiologic data provided the best available evidence.

In its testimony, the AFL-CIO pointed out that a recent U.S. Government Accountability Office (GAO) report on the Mine Safety and Health Administration's (MSHA) proposed coal dust standard references the National Academy of Sciences (NAS) conclusion that risk assessments based on epidemiological data, not surveillance data, were an appropriate means to assess risk for coal-dust exposures (Document ID 4204, p. 21; 4072, Attachment 48, pp. 7-8). The NAS emphasized that the surveillance data available to MSHA did not include individual miners' levels of exposure to coal mine dust and, therefore, could not be used for the purpose of estimating disease risk for miners. “Based on principles of epidemiology and statistical modeling, measures of past exposures to coal mine dust are critical to assessing the relationship between miners' cumulative coal mine dust exposure and their risk of developing [pneumoconiosis]” (Document ID 4072, Attachment 48, p. 8). The same rationale applies here. Thus, OSHA's decision to rely on epidemiological data is well supported by the record.

Commenters from companies and industry groups also argued that they had no knowledge of workers acquiring silicosis in their companies or industry (e.g., Document ID 2384, p. 2; 2338, p. 3; 2365, p. 2; 2185, p. 3; 2426, p. 1). OSHA received similar comments as part of a letter campaign in which over 100 letters from brick industry representatives claimed there to be little or no silicosis observed in the industry despite historical exposures above the PEL (e.g., Document ID 2009). OSHA considered these comments and believes that many companies, including companies in the brick industry, may not have active medical surveillance programs for silicosis. Silicosis may not develop until after retirement as a result of its long latency period. In addition, silica exposures in some workplaces may be well below the final PEL as a result of the environment in which workers operate, including existing controls. Thus, OSHA believes that it is difficult to draw conclusions about the rate of silicosis morbidity in specific workplaces without having detailed information on medical surveillance, silica exposures, and follow-up. This is why OSHA relies heavily on epidemiological studies with detailed exposure data and extended follow-up, and uses these data to evaluate exposure-response relationships to assess health risks at the preceding and new PELs.

Commenters also argued that, due to the long latency of the disease, silicosis cases diagnosed today are the result of exposures that occurred before the former PELs were adopted, and thus reflect exposures considerably higher than the previous PELs (e.g., Document ID 2376, p. 3; 2307, p. 12; 4194, p. 9; 3582, Tr. 1935). OSHA notes that the evidence shows that the declining trend in silicosis mortality does not provide a complete picture with regard to silicosis trends in the United States. Although many silicosis deaths reported today are likely the result of higher exposures (both magnitude and duration), some of which may have occurred before OSHA adopted the previous PELs, silicosis cases continue to occur today—some in occupations and industries where exposures are new and/or increasing. For example, five states reported cases of silicosis in dental technicians for the years 1994 to 2000 (CDC, MMWR Weekly, 2004, 53(09), pp. 195-197), for the first time. For the patients described in this report, the only identified source of crystalline silica exposure was their work as dental technicians. Exposure to respirable crystalline silica in dental laboratories can occur during procedures that generate airborne dust (e.g., mixing powders, removing castings from molds, grinding and polishing castings and porcelain, and using silica sand for abrasive blasting). In 2015, the CDC reported the first case of silicosis (progressive massive fibrosis) associated with exposure to quartz surfacing materials (countertop fabrication and installation) in the U.S. The patient was exposed to dust for 10 years from working with conglomerate or quartz surfacing materials containing 70%-90% crystalline silica. Cases had previously been reported in Israel, Italy and Spain (MMWR, 2015, 64(05); 129-130). Recently, hazardous silica exposures have been newly documented during hydraulic fracturing of gas and oil wells (Bang et al., MMWR, 2015, 64(05); 117-120).

Dr. Rosenman's testimony provides support for this point. He testified that newer industries with high silica exposures may also be under-recognized because workers in those industries have not yet begun to be diagnosed with silicosis due to the latency period (Document ID 3577, p. 858). Dr. Rosenman submitted to the record a study by Valiante et al. (2004, Document ID 3926) that identified newly exposed construction workers in the growing industry of roadway repair, which began using current methods for repair in the 1980s. These methods use quick-setting concrete that generates dust containing silica above the OSHA PEL when workers perform jackhammering, and sawing and milling concrete operations. State surveillance systems identified 576 confirmed silicosis cases in New Jersey, Michigan, and Ohio that were reported to NIOSH for the years 1993 through 1997. Of these, 45 (8 percent) cases were in construction workers, three of which had been engaged in highway repair.

Sample results for this study indicated a significant risk of overexposure to crystalline silica for workers who performed the five highway repair tasks involving concrete. Sample results in excess of the OSHA PEL were found for operating a jackhammer (88 percent of samples), sawing concrete and milling concrete tasks (100 percent of samples); cleaning up concrete tasks (67 percent of samples); and drilling dowels (100 percent of samples). No measured exposures in excess of the PEL were found for milling asphalt and cleaning up asphalt; however, of the eight samples collected for milling asphalt, six (55 percent) results approached the OSHA PEL, and one was at 92 percent of the PEL. No dust-control measures were in place during the sampling of these highway repair operations.

The authors pointed out that surveillance systems such as those implemented by these states are limited in their ability to detect diseases with long latencies in highway repair working populations because of the relatively short period of time that modern repair methods had been in use when the study was conducted. Nevertheless, a few cases were identified, although the authors explain that the work histories of these cases were incomplete, and the authors recommended ongoing research to evaluate the silicosis disease potential among this growing worker population (Document ID 3926, pp. 876-880). In construction, use of equipment such as blades used on handheld saws to dry-cut masonry materials have increased both efficiency and silica exposures for workers over the past few decades (Document ID 4223, p. 11-13). Exposure data collected by OSHA as part of its technological feasibility analysis demonstrates that exposures frequently exceed previous exposure limits for these operations when no dust controls are used (see Chapter IV of the FEA). Another operation seeing new and increasing exposures to respirable crystalline silica is hydraulic fracturing in the oil and gas industry (Document ID 3588, p. 3773). Information in the record from medical professionals noted that lung diseases caused by silica exposures are “not relics of the past,” and that they continue to see cases of silicosis and other related diseases, even among younger workers who entered the workforce after the former PEL was enacted (see Document ID 3577, Tr. 773).

Furthermore, the general declining trend seen in the death certificate data is considerably more modest in silicosis morbidity data. In his written testimony, Dr. Rosenman stated that the nationwide number of hospitalizations where silicosis was one of the discharge diagnoses has remained constant, with 2,028 hospitalizations reported in 1993 and 2,082 in 2011 (Document ID 3425, p. 2). It is the opinion of medical professionals including the American Thoracic Society and the American College of Chest Physicians that these hospitalizations likely represent “the tip of the iceberg” (of silicosis cases) since milder cases are not likely to be admitted to the hospital (Document ID 2175, p. 3). Again, this evidence shows that the declining trend observed in silicosis mortality statistics does not provide a complete picture with regard to silicosis trends in the United States. While silicosis mortality has decreased substantially since records were first available in 1968, the number of silicosis related deaths appears to have leveled off (see Table V-2; Document ID 3577, Tr. 775). Workers are still dying from silicosis today, and new cases are being identified by surveillance systems, where they exist.

Based on the testimony and evidence described above, OSHA finds that the surveillance data describing trends in silicosis mortality and morbidity provide useful evidence of a continuing problem, but are not suitable for evaluating either the adequacy of the previous PELs or whether a more protective standard is needed. In fact, it would not be possible to derive estimates of risk at various exposure levels from the available surveillance data for silica. OSHA therefore appropriately continues to rely on epidemiological data and its quantitative risk assessment to support the need to reduce the previous PELs in its final rule.

Commenters also argued that OSHA has failed to prove that a new standard is necessary because silica-associated deaths are due to existing exposures in excess of the previous PELs; therefore, the Agency should focus on better enforcing the previous PELs, rather than enacting a new standard (e.g., Document ID 2376, p. 8; 2307, p. 12; 4016, pp. 9-10; 3582, Tr. 1936). OSHA does not find this argument persuasive. First, many of the commenters used OSHA's targeted enforcement data to make this point. These data were obtained during inspections where OSHA suspected that exposures would be above the previous PELs. Consequently, the data by their very nature are skewed in the direction of exceeding the previous PELs, and such enforcement serves a deterrence function, encouraging future compliance with the PEL.

Second, not all commenters agreed that overexposures were “widespread.” A few other commenters (e.g., AFS) thought that OSHA substantially overstated the number of workers occupationally exposed above 100 μg/m³ in its PEA (Document ID 2379, p. 25). However OSHA's risk analyses evaluated various exposure levels in determining risks to workers, and did not rely on surveillance data, which rarely have associated exposure data. Although OSHA relied on exposure data from inspections to assess technological feasibility, it did not rely on inspection data for its risk assessment because these exposure data are not tied to specific health outcomes. Instead, the exposure data used for risk assessment purposes is found in the scientific studies discussed throughout this preamble section.

The surveillance data are also not comparable to OSHA's estimate of deaths avoided by the final rule because, as is broadly acknowledged, silicosis is underreported as a cause of death on death certificates. Thus, the surveillance data capture only a portion of the actual silicosis mortality. This point was raised by several rulemaking participants, including Dr. Rosenman; Dr. James Cone, MD, MPH, Occupational Medicine Physician at the New York City Department of Health, the AFL-CIO; and the American Thoracic Society (ATS) (Document ID 3425, p. 2; 3577, Tr. 855, 867; 4204, p. 17; 2175, p. 3; 3577, Tr. 772).

The rulemaking record includes one study that evaluated underreporting of silicosis mortality. Goodwin et al. (2003, Document ID 1030) estimated, through radiological confirmation, the prevalence of unrecognized silicosis in a group of decedents presumed to be occupationally exposed to silica, but whose causes of death were identified as respiratory diseases other than silicosis. In order to assess whether silicosis had been overlooked and under-diagnosed by physicians, the authors looked at x-rays of decedents whose underlying cause of death was listed as tuberculosis, cor pulmonale, chronic bronchitis, emphysema, or chronic airway obstruction, and whose usual industry was listed as mining, construction, plastics, soaps, glass, cement, concrete, structural clay, pottery, miscellaneous mineral/stone, blast furnaces, foundries, primary metals, or shipbuilding and repair.

Any decedent found to have evidence of silicosis on chest x-ray with a profusion score of 1/0 was considered to be a missed diagnosis. Of the 177 individuals who met study criteria, radiographic evidence of silicosis was found in 15 (8.5 percent). The authors concluded that silicosis goes undetected even when the state administers a case-based surveillance system. Goodwin et al. (2003, Document ID 1030) also cites mortality studies of Davis et al. (1983, Document ID 0999) and Hughes (1982, Document ID 0362) who reported finding decedents with past chest x-ray records showing evidence of silicosis but no mention of silicosis on the death certificate.

The Goodwin et al. (2003) study illustrates the importance of information about the decedent's usual occupation and usual industry on death certificates. Yet for the years 1985 to 1999, only 26 states coded this information for inclusion on death certificates. If no occupational information is available, recognizing exposure to silica, which is necessary to diagnose silicosis, becomes even more difficult, further contributing to possible underreporting.

Dr. Rosenman, a physician, epidemiologist and B-reader, testified that in his research he found silicosis recorded on only 14 percent of the death certificates of individuals with confirmed silicosis (Document ID 3425, p. 2; 3577, Tr. 854; see also 3756, Attachment 11). This means that as much as 86 percent of deaths related to silicosis are missing from the NIOSH WoRLD database, substantially compromising the accuracy of the surveillance information. Dr. Rosenman also found that silicosis is listed as the cause of death in a small percentage of individuals who have an advanced stage of silicosis; 18 percent in those with progressive massive fibrosis (PMF) and 10 percent in those with category 3 profusion.

As noted above, factors that contribute to underreporting by health care providers include lack of information about exposure histories and difficulty recognizing occupational illnesses that have long latency periods, like silicosis (e.g., Document ID 4214, p. 13; 3584, Tr. 2557). Dr. Rosenman's testimony indicated that many physicians are unfamiliar with silicosis and this lack of recognition is one factor that contributes to the low recording rate for silicosis on death certificates (Document ID 3577, Tr. 855). In order to identify cases of silicosis, a health care provider must be informed of the patient's history of occupational exposure to dust containing respirable silica, a critical piece of information in identifying and reporting cases of silicosis. However, information on a decedent's usual occupation and/or industry is often not available at the time of death or is too general to be useful. If the physician completing the death certificate is unaware of the decedent's occupational exposure history to crystalline silica, and does not have that information available to her/him on a medical record, a diagnosis of silicosis on the death certificate is unlikely. According to a study submitted by the Laborers' Health and Safety Fund of North America, (Wexelman et al., 2010), a sample of physician residents surveyed in New York City did not believe that cause of death reporting is accurate; this was a general finding, and not specific to silicosis (Document ID 3756, Attachment 7).

The ATS and the American College of Chest Physicians commented that physicians often fail to recognize or misdiagnose silicosis as another lung disease on the death certificate, leading to under-reporting on death certificates (3577, Tr. 821, 826-827) and under-recognize and underreport cases of silicosis (Document ID 2175, p. 3). As Dr. Weissman from NIOSH responded:

. . . it's well known that death certificates don't capture all of the people that have a condition when they pass away, and so there would be many that probably would not be captured if the silicosis didn't directly contribute to the death and depending on who filled out the death certificate, and the conditions of the death and all those kinds of things. So it's an under-representation of people who die with the condition . . . . (Document ID 3579, pp. 166-167).

Although there is little empirical evidence describing the extent to which silicosis is underreported as a cause of death, OSHA finds, based on this evidence as well as on testimony in the record, that the available silicosis surveillance data are likely to significantly understate the number of deaths that occur in the U.S. where silicosis is an underlying or contributing cause. This is in large part due to physicians and medical residents who record causes of death not being familiar or having access to the patient's work or medical history (see Wexelman et al., 2010, Document ID 3756, Attachment 7; Al-Samarri et al., Prev. Chronic Dis. 10:120210,2013). According to Goodwin et al. (2003, Document ID 1030, p. 310), most primary care physicians do not take occupational histories, nor do they receive formal training in occupational disease. They further stated that, since it is likely that a person would not retain the same health care provider over many years, even if the presence of silicosis in a patient might have been known by a physician who cared for them, it would not necessarily be known by another physician or resident who recorded cause of death years or decades later and who did not have access to the patient's medical or work history. OSHA finds the testimony of Dr. Rosenman compelling, who found that silicosis was not recorded as an underlying or contributing cause of death even where there was chest x-ray evidence of progressive massive fibrosis related to exposure to crystalline silica.

Some commenters stated that the decline in silicosis mortality demonstrates that there is a threshold for silicosis above the prior PEL of 100 μg/m³ (Document ID 4224, p. 2-5; 3582, Tr. 1951-1963). OSHA finds this argument irrelevant as the threshold concept does not apply to historical surveillance data. As noted above and discussed in Section V.I, Comments and Responses Concerning Threshold for Silica-Related Diseases, OSHA believes that surveillance data should not be used for quantitative risk analysis (including determination of threshold effects) because it lacks an exposure characterization based on sampling. Thus, the surveillance data cannot demonstrate the existence of a population threshold.

There is also evidence in the record that silicosis morbidity statistics reviewed earlier in this section are underreported. This can be due, in part, to the relative insensitivity of chest roentgenograms for detecting lung fibrosis. Hnizdo et al. (1993) evaluated the sensitivity, specificity and predictive value of radiography by correlating radiological and pathological (autopsy) findings of silicosis. “Sensitivity” and “specificity” refer to the ability of a test to correctly identify those with the disease (true positive rate), and those without the disease (true negative). Because pathological findings are the most definitive for silicosis, findings on biopsy and autopsy provide the best comparison for determining sensitivity and specificity of chest imaging.

The study used three readers and defined a profusion score of 1/1 as positive for silicosis. Sensitivity was defined as the probability of a positive radiological reading (ILO category >1/1) given that silicotic nodules were found in the lungs at autopsy. Specificity was defined as the probability of a negative radiological reading (ILO category <1/1) given that no, or only an insignificant number of silicotic nodules were found at autopsy. The average sensitivity values were low for each of the three readers (0.39, 0.37, and 0.24), whereas the average specificity values were high (0.99, 0.97, and 0.98). For all readers, the proportion of true positive readings (i.e., the sensitivity) increased with the extent of silicosis found at autopsy (Document ID 1050).

In the only published study that quantified the extent of underreporting of silicosis mortality and morbidity, Rosenman et al. estimated the number of new cases of silicosis occurring annually in the U.S. at between 3,600 and 7,300 based on the ratio of living to deceased persons identified and confirmed as silicotics in the Michigan surveillance data and extrapolating that ratio using the number of deaths due to silicosis for the U.S. as a whole (2003, Document ID 0420). OSHA reviewed the study in its Review of the Health Effects Literature (Document ID 1711, p. 48). Patrick Hessel, Ph.D., criticized the methods used by Dr. Rosenman, and deemed the resulting estimates unreliable, stating that the actual number of new silicosis cases arising each year is likely to be lower than the authors estimated (Document ID 2332, p. 2; 3576, Tr. 323-331).

OSHA disagrees with the criticisms that Dr. Hessel, commenting on behalf of the Chamber, offered on the study by Rosenman et al. (2003, Document ID 0420). Specifically, Dr. Hessel argued: (1) That the silicosis-related deaths used by Rosenman et al. occurred during the period 1987 through 1996, and do not reflect the declining numbers after that time period; (2) that the Michigan surveillance system relied on a single B-reader who was biased toward finding silicosis in patients who were brought to his attention for suspected silicosis; and (3) that the Michigan population was not representative of the rest of the country, since about 80 percent of the workers diagnosed with silicosis worked in foundries, which are not prevalent in most other states. Finally, in his hearing testimony, Dr. Hessel criticized the capture-recapture analysis used by Rosenman et al. to estimate the extent of underreporting of cases, stating that a number of underlying assumptions used in the analysis were not met (Document ID 3576, Tr. 323-332).

Dr. Rosenman addressed many of these criticisms in the study and at the rulemaking hearing. Regarding the fact that the number of silicosis-related deaths does not reflect the decline in deaths after 1996, Dr. Rosenman testified that, although the number of recorded silicosis deaths have declined since then, the ratio of cases to deaths has increased because the number of cases has not declined. “The living to dead ratio that we reported in our published study in 2003 was 6.44. This ratio has actually increased in recent years to 15.2. A similar ratio . . . [was] found in the New Jersey surveillance data, which went from 5.97 to 11.5 times” (Document ID 3577, Tr. 854). If one were to apply the more recent ratio from Michigan (more than double the ratio used by Rosenman et al.) to the more recent number of deaths in the country (about half that recorded in the mid-1990s; see Table V-1) to extrapolate the number of silicosis cases for the U.S. overall, the result would be even greater than the estimate in Rosenman et al. (2003).

At the hearing, Dr. Rosenman testified that he was the sole B-reader of lung x-rays for the study, and that he received the x-ray films from other radiologists who suspected but did not confirm the presence of silicosis (Document ID 3577, Tr. 877-878). Dr. Rosenman, while acknowledging that there could be differences between readers in scoring x-ray films, argued that such differences in scoring—for example, whether a film is scored a 3/3, 3/2, or 2/3—did not affect this study since the study design only required that a case be identified and confirmed (diagnosis requires a chest radiograph interpretation showing rounded opacities of 1/0 or greater profusion) (Document ID 3577, Tr. 877-878; 0420, p. 142).

Dr. Rosenman also addressed the criticism that Michigan's worker population with silica exposure is significantly different from the rest of the country. In the study, Rosenman et al. reported that the ratio of cases to deaths was about the same for Ohio as for Michigan and, during the public hearing, Dr. Rosenman testified that the ratio of cases to deaths for New Jersey was also similar to Michigan's (11.5 vs. 15.2) (Document ID 0420, p. 146; 3577, Tr. 854). This similarity was despite the fact that New Jersey had a different industrial mix, with fewer foundries (Document ID 3577, Tr. 878). Furthermore, the estimates made by Rosenman et al. depended on the ratio of cases to deaths in Michigan, rather than just the number of cases in that state. The authors believed that the ratio would be unaffected by the level of industrialization in Michigan (Document ID 0420, p. 146).

Finally, regarding the capture-recapture analysis, OSHA notes that Dr. Hessel acknowledged that this technique has been used in epidemiology to estimate sizes of populations identified from multiple overlapping sources (Document ID 2332, p. 2), which is the purpose for which Rosenman et al. used the approach. In addition, the Rosenman et al. study noted that the assumptions used in capture-recapture analysis could not be fully met in most epidemiological study designs, but that the effect of violating these assumptions was either negligible or was evaluated using interaction terms in the regression models employed. The investigators also reported that the capture-recapture analysis used on Ohio state surveillance data found that the total number of cases estimated for the state was between 3.03 and 3.18 times the number of cases identified, a result that is comparable to that for Michigan (Document ID 0420, pp. 146-147). After considering Dr. Hessel's written testimony, Dr. Rosenman testified that “. . . overall I don't think his comments make a difference in my data” (Document ID 3577, Tr. 877).

OSHA finds all of Dr. Rosenman's responses to Dr. Hessel's criticisms to be reasonable. And based on Dr. Rosenman's comments and testimony, OSHA continues to believe that the Rosenman et al. (2003) analysis and resulting estimates of the number of new silicosis cases that arise each year are reasonable. Additionally, Dr. Rosenman, in updating his data for his testimony for this rulemaking, found that the ratio had increased from 6.44 in the published study to 15.2 times in more recent years (Document ID 3577, Tr. 854). The study supports OSHA's hypothesis that silicosis is a much more widespread problem than the surveillance data suggest and that OSHA's estimates of the non-fatal illnesses that will be avoided as a result of this new silica standard are not unreasonable. Regardless, even assuming commenters' criticisms have merit, they do not significantly affect OSHA's own estimates from the epidemiological evidence of the risks of silicosis.

Accordingly, after careful consideration of the available surveillance data, stakeholders' comments and testimony, and the remainder of the record as a whole, OSHA has determined that the available silicosis surveillance data are useful for providing context and an illustration of a significant general trend in the reduction of deaths associated with silicosis over the past four to five decades. As discussed above, and in large part because the data themselves are limited and incomplete, OSHA believes reliance upon them for the purpose of estimating the magnitude of the risk would be inappropriate. The Agency has chosen instead to follow its well-established practice of relying on epidemiological data to meet its burden of demonstrating that workers exposed to respirable crystalline silica at the previous PELs face a significant risk of developing silicosis and that such risk will be reduced when the new limit is fully implemented.

F. Comments and Responses Concerning Lung Cancer Mortality

OSHA received numerous comments regarding the carcinogenic potential of crystalline silica as well as the studies of lung cancer mortality that the Agency relied upon in the Preliminary Quantitative Risk Assessment (QRA). Many of these comments, particularly from the ACC, asserted that (1) OSHA should have relied upon additional epidemiological studies, and (2) the studies that the Agency did rely upon (Steenland et al., 2001a, as re-analyzed in ToxaChemica, 2004; Rice et al., 2001; Attfield and Costello, 2004; Hughes et al., 2001; and Miller and MacCalman, 2009) were flawed or biased. In this section, OSHA presents these comments and its responses to them.

1. Carcinogenicity of Crystalline Silica

As discussed in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 76-77), in 1997, the World Health Organization's International Agency for Research on Cancer (IARC) conducted a thorough expert committee review of the peer-reviewed scientific literature and classified crystalline silica dust, in the form of quartz or cristobalite, as Group 1, “carcinogenic to humans” (Document ID 2258, Attachment 8, p. 211). IARC's overall finding for silica was based on studies of nine occupational cohorts that it considered to be the least influenced by confounding factors (Document ID 1711, p. 76). In March of 2009, 27 scientists from eight countries participated in an additional IARC review of the scientific literature and subsequently, in 2012, IARC reaffirmed that respirable crystalline silica dust is a Group 1 human carcinogen that causes lung cancer (Document ID 1473, p. 396). Additionally, in 2000, the National Toxicology Program (NTP) of HHS concluded that respirable crystalline silica is a known human carcinogen (Document ID 1164, p. 1).

The ACC, in its pre-hearing comments, questioned the carcinogenic potential of crystalline silica, asserting that IARC's 1996 recommendation that crystalline silica be classified as a Group 1 carcinogen was controversial (Document ID 2307, Attachment A, p. 29). The ACC cited Dr. Patrick Hessel's 2005 review of epidemiological studies, published after the initial IARC determination, in which he concluded that “the silica-lung cancer hypothesis remained questionable” (Document ID 2307, Attachment A, p. 31). The ACC reasserted this position in its post-hearing brief, contending that “epidemiological studies have been negative as often as they have been positive” (Document ID 4209, pp. 33-34).

After the publication of Dr. Hessel's 2005 review article, IARC reaffirmed in 2012 its earlier Group 1 classification for crystalline silica dust (Document ID 1473). As pointed out by Steenland and Ward, IARC is one of “2 agencies that are usually considered to be authoritative regarding whether a substance causes cancer in humans,” the other being the NTP, which has also determined crystalline silica to be carcinogenic on two separate occasions (2013, article included in Document ID 2340, p. 5). David Goldsmith, Ph.D., who coauthored one of the first published articles linking silica exposure to lung cancer, echoed Steenland and Ward:

It is important to recognize that evidence for silica's carcinogenicity has been reviewed three times by the International Agency for Research on Cancer, once in 1987, 1997, and 2012. It has been evaluated by California's Proposition 65 in 1988, by the National Toxicology Program in 2000 and reaffirmed in 2011, and by the National Institute for Occupational Safety and Health in 2002 (Document ID 3577, Tr. 861-862).

Multiple organizations with great expertise in this area, including the American Cancer Society, submitted comments supporting the thorough and authoritative nature of IARC's findings regarding silica's carcinogenicity (e.g., Document ID 1171; 1878). OSHA likewise places great weight on the IARC and NTP classifications and, based on their findings, concludes that the carcinogenic nature of crystalline silica dust has been well established. Further support for this finding is discussed in Section V.L, Comments and Responses Concerning Causation.

2. Silicosis and Lung Cancer

In addition to debating the conclusions of IARC, Peter Morfeld, Dr. rer. medic, testifying on behalf of the ACC Crystalline Silica Panel, concluded that OSHA's risk estimates for lung cancer are “unreliable” because they “ignore threshold effects and the apparent mediating role of silicosis” (Document ID 2307, Attachment 2, p. 16). Dr. Morfeld argued that silicosis is a necessary prerequisite for silica-related lung cancer. Commenters' arguments about silicosis being a prerequisite for lung cancer and silicosis having a threshold are linked; if it were shown both that silicosis requires a certain threshold of exposure and that only persons with silicosis get lung cancer, then silica-related lung cancer would also have an exposure threshold. As discussed in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases, commenters claimed that there is a threshold for silicosis above the previous PEL for general industry, which would make any threshold for lung cancer above that level as well. OSHA discusses these comments in detail in that section, and has determined that even if lung cancer does not occur in the absence of silicosis, the record strongly supports the conclusion that workers exposed to respirable crystalline silica would still be at risk of developing lung cancer as a result of their exposure because silicosis can develop among workers whose average and cumulative exposures are below the levels permitted by the previous PELs.

OSHA received comments from other stakeholders, including Robert Glenn, representing the Brick Industry Association, and the AFS on the possible mediating role of silicosis in the development of lung cancer (Document ID 2307, pp. 29-35; 2343, Attachment 1, pp. 42-45; 2379, Attachment 2, pp. 24-25). The ACC cited several review articles in support of its claim that “silica exposures have not been shown to increase the risk of lung cancer in the absence of silicosis” (Document ID 2307, Attachment A, pp. 29, 32, 35). These articles included: A 2004 review of studies by Kurihara and Wada that found that while silicosis is a risk factor for lung cancer, exposure to silica itself may not be a risk factor (Document ID 1084); a 2006 review by Pelucchi et al. that determined that the issue of whether silica itself increases lung cancer risk in the absence of silicosis has not been resolved (Document ID 0408); and a 2011 review by Erren et al. that concluded it is unclear whether silica causes lung cancer in persons who do not already have silicosis (Document ID 3873). Similarly, the AFS cited a review by the Health and Safety Executive (2003) that concluded that increased risks of lung cancer are restricted to those groups with the highest cumulative exposures, with evidence tending to show that excess lung cancer mortality is restricted to those with silicosis (Document ID 2379, Attachment 2, pp. 24-25). Having reviewed the studies cited by commenters, OSHA has come to the conclusion that none of the cited studies demonstrates that silicosis is a necessary precursor to lung cancer, but acknowledges that uncertainty remains about what percentage of lung cancers in silica-exposed workers are independent of silicosis.

Similarly, the ACC stated that none of the studies of lung cancer mortality that OSHA relied upon in the Preliminary QRA demonstrates that silica exposure causes lung cancer in the absence of silicosis (Document ID 2307, Attachment A, p. 66). During the rulemaking hearing, NIOSH scientists addressed the issue of whether silicosis is a necessary precursor to the development of lung cancer. They stated that it is a difficult issue to resolve because the two diseases may have a similar pathway, such that they can develop independently but still appear correlated. Mr. Robert Park also added that:

[S]ilicosis isn't detectable until there's splotches on the lung that are visible in x-rays. So prior to that point, somebody could have [been] developing lung disease and you just can't see it. So, of course, people that have silicosis are going to have higher lung cancer, and it's going to look like a threshold because you didn't see the silicosis in other people that have lower lung cancer risk. To really separate those two, you'd have to do a really big study. You'd have to have some measures, independent measures of lung physiological pathology, and see what's going on with silicosis as a necessary condition for development of lung cancer (Document ID 3579, Tr. 245-247).

Similarly, David Weissman, MD, concurred that “there's quite a bit of reason as Bob [Park] said to think that the two processes [development of silicosis and development of lung cancer] don't require each other, and it would be extraordinarily difficult to sort things out in human data” (Document ID 3579, Tr. 247). Indeed, Checkoway and Franzblau (2000) reviewed the epidemiological literature addressing this topic, and found that the “limitations of existing epidemiologic literature that bears on the question at hand suggest that prospects for a conclusive answer are bleak” (Document ID 0323, p. 257). The authors concluded that silicosis and lung cancer should be treated in risk assessments as “separate entities whose cause/effect relations are not necessarily linked” (Document ID 0323, p. 257). Brian Miller, Ph.D., a peer reviewer of OSHA's Review of Health Effects Literature and Preliminary QRA, likewise wrote in his post-hearing comments, “I consider this issue unanswerable, given that we cannot investigate for early fibrotic lesions in the living, but must rely on radiographs” (Document ID 3574, p. 31).

During the public rulemaking hearing, several stakeholders pointed to a recent study of Chinese pottery workers and miners by Liu et al. (2013, article included in Document ID 2340) as evidence that exposure to crystalline silica is associated with lung cancer even in the absence of silicosis (Document ID 3580, Tr. 1232-1235; 3577, Tr. 803-804, 862-863). In this study, the authors excluded 15 percent of the cohort (including 119 lung cancer deaths) with radiographic evidence of silicosis and found that the risk of lung cancer mortality still increased with cumulative exposure to crystalline silica, suggesting that clinically-apparent silicosis is not a prerequisite for silica-related lung cancer (article included in Document ID 2340, pp. 3, 7).

The ACC argued that it is “premature to draw that conclusion,” stating that the Liu study's conclusions are not supported by the data and raising questions about uncertainty in the exposure estimates, modeling and statistics, confounding, and the silicosis status of cohort members (Document ID 2307, Attachment A, p. 48; 4027, pp. 35-36; 4209, pp. 40-51). With regard to exposure estimates, the ACC had a number of concerns, including that conversion factors determined by side-by-side sampling in 1988-1989 were used to convert Chinese total dust concentrations to respirable crystalline silica exposures (Document ID 4209, pp. 40-41). Dr. Cox expressed concern that these conversion factors from 1988-1989 might not have been applicable to other time periods, as particle size distributions could change over time (Document ID 4027, p. 32). OSHA acknowledges this concern, but given the “insufficient historical particle size data . . . to analyze whether there were changes in particle size distributions from the 1950s to the 1990s,” believes that the authors were justified in making their exposure assumptions (Document ID 4027, p. 32). Dr. Cox's concerns involving modeling and statistics (see Document ID 4027, pp. 33-36) in the study, including the absence of model diagnostics, the use of inappropriate or misspecified models, the lack of a discussion of residual confounding and model uncertainty, and the use of inappropriate data adjustments and transformations, are discussed in detail in Section V.J, Comments and Responses Concerning Biases in Key Studies.

On the issue of confounding, the ACC noted that Liu et al. (2013) used a subcohort of 34,018 participants from 6 tungsten mines, 1 iron mine, and 4 potteries derived from a total cohort of 74,040 participants from 29 mines and pottery factories studied previously by Chen et al. (2007, Document ID 1469; 2307, Attachment A, pp. 48-50). Liu et al. (2013) excluded participants in the original cohort if detailed information on work history or smoking was not available, or if they worked in copper mines or tin mines where the analysis could be confounded by other exposures, namely radon and carcinogenic polycyclic aromatic hydrocarbons (PAHs) in the former and arsenic in the latter (article included in Document ID 2340, p. 2). The ACC's main concern was that Liu et al. (2013) did not adjust for these confounders in their analyses, but rather claimed that there were no confounding exposures in their smaller cohort on the basis of the exclusion criteria (Document ID 2307, Attachment A, p. 49).

The ACC also noted that Chen et al. (2007) stated that the Chinese pottery workers were exposed to PAHs, and some of the iron-copper miners were exposed to PAHs and radon progeny (Document ID 2307, Attachment A, p. 49). Chen et al. (2007) initially found an association between respirable silica and lung cancer mortality in the pottery workers and iron-copper miners, but it disappeared after adjusting for PAH exposures (Document ID 1469). In the tungsten miners, Chen et al. (2007) found no significant association for lung cancer mortality, while Liu et al. (2013) did. Similarly, the ACC pointed out that a subsequent study by Chen et al. (2012, article included in Document ID 2340) also failed to find a statistically significant increase in the hazard ratio for lung cancer, meaning that there was no significant positive exposure-response relationship between cumulative silica exposure and lung cancer mortality (Document ID 4209, p. 45). Dr. Morfeld concluded, “Unless and until these issues are resolved, Liu et al. (2013) should not be used to draw conclusions regarding exposure-response relationships between RCS [respirable crystalline silica], silicosis and lung cancer risk” (Document ID 2307, Attachment 2, pp. 15-16).

During the public hearing, counsel to the ACC asked Dr. Steenland, a co-author on the Liu et al. (2013) study, if he would provide measurement data on the PAH exposures in the potteries, as well as present the data from the Liu et al. (2013) study separately for pottery factories and tungsten mines, as they were in Chen et al. (2007, Document ID 1469) (Document ID 3580, Tr. 1237-1240). Dr. Steenland subsequently provided the requested data for inclusion in the rulemaking record (Document ID 3954).

With respect to the PAH data for the potteries, Dr. Weihong Chen, the study's first author, reported that, in measurements in 1987-1988 in the four potteries that were excluded from the Liu et al. (2013) analysis, the mean total PAHs was 38.9 µg/m³ and the mean carcinogenic PAHs was 4.7 µg/m³. In the four potteries that were included in the Liu et al. (2013) analysis, the mean total and carcinogenic PAHs, as measured in 1987-1988, were substantially lower at 11.6 and 2.5 µg/m³, respectively. When the measurements were repeated in 2006, the mean total and carcinogenic PAHs in the four potteries included in the analysis were still lower, at 2.2 and 0.08 µg/m³, levels that were “not much higher than environmental PAH in many [Chinese] cities” (Document ID 3954, p. 2). Dr. Chen also reported that, when comparing levels within six job titles, there was no significant correlation between total or carcinogenic PAHs (based on the 2006 measurements) and respirable silica dust. When the results were presented separately for the mines and potteries, in analyses using continuous cumulative exposure, the relationship between silica exposure and lung cancer mortality remained significant for the pottery factories, but not the metal mines. In the categorical analyses using quartiles of cumulative exposure, the results were mixed: The association between silica exposure and lung cancer mortality was statistically significant in some exposure quartiles for both metal mines and pottery factories (Document ID 3954, p. 2).

Based upon these subsequent data, the ACC concluded that PAHs were likely present in the potteries but not in the mines (Document ID 4209, p. 45). OSHA believes this conclusion, although plausible, to be speculative. What is known is that the potteries that were excluded had a higher average level of PAHs, and that a significant association between cumulative silica exposure and lung cancer mortality remained in the included potteries even after the analysis was separated by potteries and mines. However, the association was less clear in the metal mines.

The ACC also raised concerns about the silicosis status of lung cancer cases in the Liu cohort, asserting that some workers may not have had post-employment radiography given that social health insurance only recently began to pay for it. As such, the ACC asserted that some workers who developed lung cancer post-employment may have also had undiagnosed silicosis (Document ID 4209, pp. 49-50). OSHA acknowledges the limitations of the study, as with any retrospective study, but also notes that no evidence was put forth to indicate that workers with silicosis were misclassified in the study as workers without silicosis. Further, Dr. Goldsmith testified that the method used by Liu et al. for excluding workers with silicosis (x-ray findings) was “very eminently reasonable,” given that the only foolproof means of proving the absence of silicosis—autopsy—was not available for this particular cohort (Document ID 3577, Tr. 874-875).

Thus, OSHA concludes that the Liu et al. (2013) study preliminarily suggests that silicosis is not required for the development of lung cancer; however, no one study will settle the question of the role of silicosis in the carcinogenicity of crystalline silica. As acknowledged by Dr. Cox, the Agency did not rely upon the Liu et al. (2013) study in its preliminary or final QRA (Document ID 2307, Attachment 4, p. 37).

Overall, after giving lengthy consideration to all evidence in the record regarding whether silicosis is a necessary precursor to the development of lung cancer, including the Liu study, the NIOSH testimony, and the mechanistic evidence for the carcinogenicity of crystalline silica discussed in Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, OSHA concludes that the mediating role of silicosis in the development of lung cancer is not “apparent,” as suggested by Dr. Morfeld and the ACC (Document ID 2307, Attachment 2, p. 16). As such, OSHA continues to believe that substantial evidence supports the Agency's decision to consider lung cancer as a separate, independent health endpoint in its risk analysis. The Agency also notes that even if lung cancer does not occur in the absence of silicosis, the record strongly supports the conclusion that workers exposed to respirable crystalline silica would still be at risk of developing lung cancer as a result of their exposure because silicosis can develop from average and cumulative exposures below the levels allowed at the previous PEL (see Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.)

3. Additional Studies

Stakeholders also suggested several additional studies that they believe OSHA should include in its QRA on lung cancer. The AFS commented that OSHA's Preliminary QRA overlooked a 2003 report by the Health and Safety Executive (HSE, Document ID 1057), asserting that over 40 percent of the references cited by HSE were omitted in OSHA's review (Document ID 4035, p. 2). OSHA disagrees with this assessment of overlooking the report, noting that the Agency reviewed and referenced the HSE report in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, p. 77). As discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, OSHA used a weight-of-evidence approach to evaluate the scientific studies in the literature to determine their overall quality. In so doing, OSHA thoroughly reviewed approximately 60 published, peer-reviewed primary epidemiological studies covering more than 30 occupational cohorts in over a dozen industrial sectors, as well as the IARC pooled study and several meta-analyses (Document ID 1711, pp. 75-172).

The AFS also submitted a 2011 review of 30 foundry epidemiology studies by the Industrial Industries Advisory Council (IIAC) and noted that only 7 of those 30 studies were included in OSHA's Review of Health Effects Literature and Preliminary QRA (Document ID 2379, p. 24). AFS wrote:

The PQRA largely dismisses the foundry epidemiology studies, based on assertions of positive confounding. However, a study showing that there is no adverse effect despite a positive confounder is not only still relevant to the question, but should be more persuasive than a study without positive confounders because the data then show that even with an additive risk, there is no increase in effect at the reported exposure levels (Document ID 2379, p. 24).

In response to this comment, OSHA gathered the remaining 23 foundry studies cited in the submitted report and placed them in the rulemaking docket during the post-hearing comment period. OSHA notes, in the first instance, that most of these studies were not designed to study the effects of silica exposure on foundry workers, and did not even attempt to do so; rather, their purpose was to examine lung cancer mortality and/or morbidity in foundry work, which involves many toxic and otherwise harmful substances besides silica. Therefore, OSHA would likely be unable to suitably use these studies as a basis for a quantitative risk assessment regarding respirable crystalline silica by itself.

With respect to AFS's assertions of studies showing “no adverse effect,” OSHA notes that the summary section of the IIAC review report, submitted as evidence by AFS, stated that, “The cohort mortality studies and two morbidity studies suggest an increased risk of lung cancer in foundry workers when considered overall, but do not support a doubling of risk. . . . Findings in the case-control studies, the majority of which adjust for the effects of smoking . . . tend to support those of the cohort studies” (Document ID 3991, p. 5). As such, this review of 30 foundry epidemiology studies showed an increased excess risk of lung cancer from foundry work; the fact that the excess risk was not increased by a factor of two is irrelevant to the current proceedings. The factor of two appears to be used by the IIAC in determining whether monetary benefits should be paid to foundry workers in Great Britain and is completely unrelated to OSHA's statutory requirements for determining whether workers exposed to silica are at a significant risk of material impairment of health. Given that excess lung cancer was observed in many of these studies, OSHA rejects the AFS's assertion that, even with positive confounding, there was no increase in adverse effect (i.e., lung cancer).

OSHA also notes that the IIAC's finding of an elevated risk of lung cancer in foundries is not surprising. As Dr. Mirer stated during his testimony, IARC categorized foundry work as Group 1, carcinogenic to humans, in 1987 based on observed lung cancer (Document ID 2257, Attachment 3, p. 5). IARC reaffirmed its Group 1 classification for foundry work in 2012 (Document ID 4130). However, as noted by OSHA in its Review of Health Effects Literature, the foundry epidemiology studies were profoundly confounded by the presence of exposures to other carcinogens, including PAHs, aromatic amines, and metals (Document ID 1711, p. 264). Because of this confounding, as well as the fact that most of these studies did not specifically study the effects of silica exposure on foundry workers, OSHA has decided not to include them in its QRA.

The ACC likewise cited several individual studies that it believed found no relationship between silica exposure and lung cancer risk (Document ID 2307, Attachment A, pp. 33-35). These included studies by: (1) Yu et al. (2007), which found no consistent exposure-response relationship between silica exposure and lung cancer death in workers with silicosis in Hong Kong (Document ID 3872); (2) Chen et al. (2007), which found, as mentioned in relation to the Liu et al. (2013) study, no relationship between silica exposure and lung cancer after adjusting for confounders in a study of Chinese tungsten miners, tin miners, iron-copper miners, and pottery workers (Document ID 1469); (3) Birk et al. (2009), which found the standardized mortality ratio (SMR) for lung cancer was not elevated in a subgroup of men who worked in areas of German porcelain plants with the highest likely silica exposures (Document ID 1468); (4) Mundt et al. (2011), which found, in a subsequent analysis of the German porcelain industry, that cumulative silica exposure was not associated with lung cancer mortality, mortality from kidney cancer, or any other cause of death other than silicosis (Document ID 1478); and (5) Westberg et al. (2013), which found that cumulative silica exposure was not associated with lung cancer morbidity (Document ID 4054).

Briefly, Chen et al. (2007) examined a cohort of male workers in 29 Chinese mines and factories, and initially found a significant trend between cumulative silica exposure and lung cancer mortality in pottery workers and tin miners; this trend was no longer significant after adjustment for occupational confounders (carcinogenic PAHs in potteries, arsenic in tin mines) (Document ID 1469, pp. 320, 323-324). On the contrary, Liu et al. (2013) demonstrated a statistically significant association between cumulative silica exposure and lung cancer mortality after excluding mines and factories with confounding exposures (article included in Document ID 2340). As noted previously, there are questions of how confounding exposures to radon, PAHs, and arsenic were handled in both the Chen et al. (2007) and Liu et al. (2013) studies. One important difference between the two studies, however, was the follow-up time. While Chen et al. (2007) had follow-up to 1994 and identified 511 lung cancer deaths in a cohort of 47,108 workers (Document ID 1469, pp. 321-322), Liu et al. (2013) had follow-up to 2003 and identified 546 lung cancer deaths in a cohort of 34,018 workers (article included in Document ID 2340, pp. 2-4).

OSHA discussed the Birk et al. (2009, Document ID 1468) and Mundt et al. (2011, Document ID 1478) studies of the German porcelain industry in its Supplemental Literature Review, noting several limitations that are applicable to both studies and might preclude the conclusion that there was no association between silica exposure and lung cancer (Document ID 1711, Attachment 1, pp. 6-12). One such limitation was the mean age of subjects—35 years—at the start of follow-up, making this a relatively young cohort in which to observe lung cancer. The mean follow-up period of 19 years per subject was also a limitation, given the long latency for lung cancer and the young age of the cohort at the start of follow-up; only 9.2 percent of the cohort was deceased by the end of the follow-up period. OSHA noted that Mundt et al. (2011) acknowledged that additional follow-up of the cohort may be valuable (Document ID 1711, Attachment 1, pp. 10-11; 1478, p. 288). In addition, Mundt et al. (2011) had only 74 male lung cancer deaths, some of whom had possible or probable prior silica exposure that could have resulted in cumulative exposure misclassification (Document ID 1478, pp. 285, 288). The authors also reported statistically significantly elevated lung cancer hazard ratios for some categories of average silica exposure, but did not present any trend analysis data (Document ID 1478, p. 285). It also does not appear that Mundt et al. performed any lagged analyses for lung cancer to account for the latency period of lung cancer.

Following the ACC's citation of the Yu et al. (2007) and Westberg et al. (2013) studies in its pre-hearing comments, OSHA obtained and reviewed these studies, and added them to the rulemaking docket (Document ID 3872; 4054). Yu et al. (2007) followed a cohort of 2,789 workers in Hong Kong diagnosed with silicosis between 1981 and 1998. The average follow-up time was 9 years, with 30.6 percent of the cohort deceased when the study ended in 1999. The SMR for lung cancer was not statistically significantly elevated following indirect adjustment for cigarette smoking; similarly, the authors did not find a significant exposure-response relationship between cumulative silica exposure and lung cancer mortality (Document ID 3872). Westberg et al. (2013) studied a group of 3,045 male Swedish foundry workers to determine lung cancer incidence and morbidity. Although the lung cancer incidence was statistically significantly elevated, the authors did not find a significant exposure-response relationship with cumulative quartz exposure (Document ID 4054, p. 499).

Regarding these studies, OSHA notes that the Westberg et al. (2013) study, like other foundry studies, is confounded by other carcinogenic substances present in foundries, including, as the authors pointed out, phenol, formaldehyde, furfuryl alcohols, PAHs, carbon black, isocyanates, and asbestos (Document ID 4054, p. 499). The Yu et al. (2007) study had an average follow-up period of only 9 years (Document ID 3872, p. 1058, Table 1), which is a short follow-up period when considering the latency period for the development of cancer. In addition, the Yu et al. study (2007), as described in the earlier Tse et al. (2007) study, used a job exposure matrix developed from expert opinion to assign estimated past levels of silica exposure to individuals based on self-reported work history; changes in exposure intensity with calendar year were not considered because of limited data (Document ID 3841, p. 88; 3872, p. 1057). OSHA notes that this exposure estimation may have included considerable misclassification due to inaccuracies in self-reported work history, the use of expert opinion to estimate past exposure levels rather than actual measurements for the subjects under study, and the failure to incorporate any changes in exposure levels over calendar time into the exposure estimates. Although these exposure estimates were used in an analysis that found a significant exposure-response for NMRD mortality among workers with silicosis (Tse et al., 2007, Document ID 3841), an exposure-response for lung cancer mortality may not be as strong and may be harder to detect, requiring more accurate exposure information. OSHA also notes that NMRD mortality is likely to be a competing cause of death with lung cancer, such that some workers may have died from NMRD before developing lung cancer. The workers with silicosis in this study also had high exposures (mean cumulative exposure of 10.89 mg/m³-yrs) (Document ID 3872, p. 1058), possibly making it difficult to detect an exposure-response for lung cancer when exposures are relatively homogenous and high. Selection effects would have been extreme in these highly-exposed workers, whose all-cause mortality was double what would be expected (853 deaths observed, 406 expected) in the general population of males in Hong Kong and whose respiratory disease mortality was an astounding six times the expected level (445 deaths observed, 75 expected) (Document ID 3872, p. 1059).

OSHA acknowledges that not every study reaches the same results and conclusions. This is typically true in epidemiology, as there are different cohorts, measurements, study designs, and analytical methods, among other factors. As a result, scientists critically examine the studies, both individually and overall, in the body of literature to draw weight-of-evidence conclusions. IARC noted, with respect to its 1997 carcinogenicity determination:

[N]ot all studies reviewed demonstrated an excess of cancer of the lung and, given the wide range of populations and exposure circumstances studied, some non-uniformity of results had been expected. However, overall, the epidemiological findings at the time supported an association between cancer of the lung and inhaled crystalline silica (α-quartz and cristobalite) resulting from occupational exposure (Document ID 1473, p. 370).

Given IARC's re-affirmation of this finding in 2012, OSHA does not believe that the individual studies mentioned above fundamentally change the weight of evidence in the body of literature supporting the carcinogenicity of crystalline silica. The best available evidence in the rulemaking record continues to indicate that exposure to respirable crystalline silica causes lung cancer. OSHA acknowledges, however, that there is some uncertainty with respect to the exact magnitude of the lung cancer risk, as each of the key studies relied upon provides slightly different risk estimates, as indicated in Table VI-1.

Further, the ACC focused extensively on and advocated for a study by Vacek et al. (2011) that found no significant association between respirable silica exposure and lung cancer mortality in a cohort of Vermont granite workers (Document ID 1486, pp. 75-81). Included in the rulemaking docket are the peer-reviewed published version of the study (Document ID 1486) and the earlier Final Report to the ACC, whose Crystalline Silica Panel funded the study (Document ID 2307, Attachment 6), as well as comments from two of the authors of Vacek et al. (2011) responding to OSHA's treatment of the study in its Supplemental Literature Review (Document ID 1804). The ACC stated:

Perhaps of most interest and relevance for present purposes—because the cohort has been studied so extensively in the past and because the present PEL is based indirectly on experience in the Vermont granite industry—is the mortality study of Vermont granite workers published in 2011. While the Vermont granite workers cohort has been studied on a number of previous occasions, this is the most comprehensive mortality study of Vermont granite workers to date (Document ID 2307, Attachment A, p. 36).

The ACC criticized OSHA for rejecting the Vacek et al. (2011) study in its Supplemental Literature Review and instead relying upon the Attfield and Costello (2004, Document ID 0284) study of Vermont granite workers (Document ID 2307, Attachment A, pp. 36-47; 4209, pp. 34-36). The ACC asserted several differences between the studies. First, while Attfield and Costello had 5,414 workers (201 lung cancer deaths) in the cohort, Vacek et al. had 7,052 workers (356 lung cancer deaths) as they extended the follow-up period by 10 years to 2004. Vacek et al. also claimed to have more complete mortality data, finding that “162 workers, whom Attfield assumed were alive in 1994, had died before that time and some decades earlier” (Document ID 2307, Attachment A, p. 38). In addition, Vacek et al. used exposure measurements and raw data not used by Attfield and Costello; for example, Vacek et al. used pension records and interviews from other studies to account for gaps in employment and changes in jobs, while Attfield and Costello assumed that a person remained in the same job between chest x-rays at the Vermont Department of Industrial Health surveillance program. Different conversion factors to estimate gravimetric concentrations from particle count data were also used: Attfield and Costello used a factor of 10 mppcf = 75 µg/m³ while Vacek et al. used a factor of 10 mppcf = 100 µg/m³ (Document ID 2307, Attachment A, pp. 36-39; 1804, p. 3). OSHA notes that this discrepancy in gravimetric conversion factors should not affect the detection of an exposure-response relationship, as all exposures would differ by a constant factor.

The ACC also pointed out that Attfield and Costello's exposure estimate for sandblasters was 60 µg/m³ prior to 1940, 50 µg/m³ from 1940-1950, and 40 µg/m³ after 1950, maintaining these numbers were too low compared to Vacek et al.'s estimates of 240, 160, and 70 µg/m³, respectively (Document ID 2307, Attachment A, p. 39; 1486, p. 313). Attfield and Costello took these estimates for sand blasters from the Davis et al. (1983, Document ID 0999) study, discussed in detail below; the estimates were based on six published industrial hygiene measurement studies.

Lastly, the ACC posited that Attfield and Costello inappropriately excluded the highest exposure group, stating:

Vacek et al. used all their data in evaluating potential E-R [exposure-response] trends with increasing exposure. Attfield and Costello did not. Instead, on a post hoc basis, they excluded the highest exposure category from their analysis when they discovered that the E-R trend for lung cancer was not significant if that group was included (even though the trends for non-malignant respiratory diseases were significant when all the data were used). This is an example of both data selection bias and confirmation bias (Document ID 2307, Attachment A, p. 40).

Based upon these assertions, the ACC concluded, “In sum, when judged without a result-oriented confirmation bias, the larger, more recent, more comprehensive, and more detailed study by Vacek et al. (2011) must be deemed to supersede Attfield and Costello (2004) as the basis for evaluating potential silica-related lung cancer risks in the Vermont granite industry” (Document ID 2307, Attachment A, p. 41).

OSHA initially discussed some issues surrounding the Vacek et al. (2011) study in its Supplemental Literature Review (Document ID 1711, Attachment 1, pp. 2-5). Specifically, OSHA noted that (1) the cumulative exposure quintiles used in the Vacek et al. (2011) analysis were higher than the values used in the Attfield and Costello (2004) analysis; (2) the regression models used in the Vacek et al. (2011) study exhibited signs of uncontrolled confounding, as workers in the second lowest cumulative exposure stratum in the models (except for silicosis) exhibited a lower risk than those in the lowest stratum, while all outcomes (except NMRD) in the highest exposure stratum showed a decline in the odds ratio (a measure of the association between silica exposure and health outcome) compared to the next lower stratum; and (3) Vacek et al. (2011) found a statistically significant excess of lung cancer (SMR = 1.37, with almost 100 excess lung cancer deaths) in the cohort when compared to U.S. white males (Document ID 1486, p. 315). Regarding the excess lung cancer deaths, although they were unable to obtain information on smoking for many of the cohort members, Vacek et al. suggested that the elevated SMR for lung cancer was due, at least in part, to the differences between the smoking habits of the cohort and reference populations (Document ID 1486, p. 317). OSHA noted that although the SMR for other NMRD was elevated, there was no significant SMR elevation for other smoking-associated diseases, including cancers of the digestive organs, larynx, and bladder, as well as bronchitis, emphysema, and asthma (Document ID 1711, Attachment 1, p. 5). Elevated SMRs for these diseases would be expected if workers in the study population smoked more than those in the reference population; in fact, for all heart disease, the mortality in the study population (SMR = 0.89) was statistically significantly lower than the reference population (Document ID 1486, p. 315). These data do not support Vacek et al.'s assertion that smoking was responsible for the increased lung cancer SMR in the cohort. In addition, Davis et al. (1983) noted that granite shed workers employed during the 1970's smoked only slightly more than U.S. white males (Document ID 0999, p. 717). OSHA also pointed out that the SMR may have been understated, as Vacek et al. did not account for a healthy worker effect (HWE).

The ACC did not agree with OSHA's review of the Vacek et al. study, noting that OSHA “rejects Vacek et al. (2011) on grounds that are confusing and unfounded” (Document ID 2307, Attachment A, p. 41). The ACC argued that the quintiles of cumulative exposure used by Vacek et al. were not higher than typical values for lung cancer, and that OSHA, in its Supplemental Literature Review, compared the Vacek et al. quintiles of cumulative exposure for silicosis with the Attfield and Costello groups used for both silicosis and lung cancer (Document ID 2307, Attachment A, pp. 41-42). OSHA acknowledges this discrepancy and, given that Vacek et al. used quintiles of cumulative exposure that differed for each health endpoint, agrees that the quintiles for lung cancer used by Vacek et al. were not appreciably higher than the exposure groups used by Attfield and Costello, though the Agency recognizes that there may be alternative explanations for the patterns observed in the Vacek et al. data. Regarding uncontrolled confounding, the ACC stated that “The Vermont granite worker cohort, after all, supposedly is free of confounding exposures,” (Document ID 2307, Attachment A, p. 43 (citing Attfield and Costello, 2004, 0284)). Vacek et al. also pointed out that although the odds ratios for the second lowest exposure stratums were lower than those for the lowest categories for each of the diseases, they were not statistically significantly lower (Document ID 1804, pp. 1-2).

Although OSHA notes that this latter phenomenon, in which the odds ratio for the second lowest exposure stratum is lower than that for the lowest stratum, is commonly observed and often attributable to some form of selection confounding, the Agency recognizes that there may be alternative explanations for the patterns observed in the Vacek et al. data. One such explanation for the decreased odds ratios in the highest exposure group is potential attenuation resulting from a HWE.

The HWE, as defined by Stayner et al. (2003), has two components: (1) A healthy initial hire effect, in which bias is “introduced by the initial selection of workers healthy enough to work . . . and the use of general population rates for the comparison group, which includes people who are not healthy enough to work,” and (2) a healthy worker survivor effect, referring “to the tendency of workers with ill health to drop from the workforce and the effect this dropout may have on exposure-response relationships in which cumulative exposure is the measure of interest” (Document ID 1484, p. 318). Thus, the healthy initial hire effect occurs in the scenario in which the death rate in a worker group is compared to that in the general population; because the general population has many people who are sick, the death rate for workers may be lower, such that a direct comparison of the two death rates results in a bias. The healthy worker survivor effect occurs in the scenario in which less healthy workers transfer out of certain jobs into less labor-intensive jobs due to decreased physical fitness or illness, or leave the workforce early due to exposure-related illness prior to the start of follow-up in the study. As a result, the healthier workers accumulate the highest exposures such that the risk of disease at higher exposures may appear to be constant or decrease.

OSHA disagrees with the ACC's statement that “the possibility of a potential HWE in this cohort could not have affected the E-R analyses” in Vacek et al. (2011) (Document ID 2307, Attachment A, p. 46), and with the similar statement by study authors Pamela Vacek, Ph.D. and Peter Callas, Ph.D., both of the University of Vermont, who asserted that the HWE could not have impacted their exposure-response analyses “because they were not based on an external reference population” (Document ID 1804, p. 2). This explanation only considers one component of the HWE, the healthy initial hire effect. An internal control analysis, such as that performed by Vacek et al., will generally minimize the healthy initial hire effect but does not address the healthy worker survivor effect (see Document ID 1484, p. 318 (Stayner et al. (2003)). Thus, the statement by the ACC that there could be no HWE in the internal case control analysis of Vacek et al. (2011) is incorrect, as it considered only the healthy initial hire effect and not the healthy worker survivor bias.

In contrast, Attfield and Costello's stated rationale for excluding the highest exposure group is related to the healthy worker survivor effect:

We do know that this group is distinctive in entering the cohort with substantial exposures—83% had worked for 20 years or more in the high dust levels prevalent prior to controls. They were, therefore, a highly selected healthy worker group. A further reason may be that in the days when tuberculosis and silicosis were the main health concerns in these workers, lung cancer may have been obscured in this group as a cause of death in some cases” (Document ID 0284, p. 136).

Support for Attfield and Costello's reasoning is provided by a study by Applebaum et al. (2007), which re-analyzed the data from the Attfield and Costello (2004) paper and concluded that there was a healthy worker survivor effect present (study cited by Vacek et al., 2009, Document ID 2307, Attachment 6, p. 3). Applebaum et al. (2007) split the cohort of Vermont granite workers into two groups: (1) Those that began working before the start of the study follow-up, i.e., prevalent hires; and (2) those that began working after the start of the study follow-up, i.e., incident hires. The rationale for splitting the cohort into these two groups was to examine if a healthy worker survivor effect was more likely in the prevalent hire group, as this group would be affected by workers that were more susceptible to health effects and left the industry workforce prior to the start of the study follow-up (Applebaum et al., 2007, pp. 681-682). Using spline models to examine exposure-response relationships without forcing a particular form (e.g., linear, linear-quadratic) on the observed data, the authors found that the inclusion of prevalent hires in the analysis weakened the association between cumulative silica exposure and lung cancer because of bias from the healthy worker survivor effect. The bias can be reduced by including only incident hires, or keeping the date of hire close to the start of follow-up (Applebaum et al., 2007, pp. 685-686). An alternative explanation for this trend offered by Applebaum et al. may be that, assuming that there was more measurement error in the older data, the prevalent hires had more exposure misclassification (2007, p. 686); in such a case, however, the inclusion of prevalent hires would still bias the results towards the null. Given the findings of the Applebaum et al. (2007) study, OSHA believes that Attfield and Costello (2004) had good reasons for removing the highest exposure group, which was composed mostly of prevalent workers (83 percent of workers in the highest exposure group had worked at least 20 years prior to the start of the follow-up period) (Document ID 0284, p. 136).

Vacek et al. (2011), on the other hand, excluded 609 workers in the design of their study cohort due to insufficient information. However, the majority of the workers excluded from the cohort were incident hires who began work after 1950 (Document ID 2307, Attachment 6, p. 12; 1486, p. 314). The final Vacek et al. (2011) cohort included 2,851 prevalent hires (began employment before 1950) compared to 4,201 incident hires (began employment in or after 1950) (Document ID 2307, Attachment 6, p. 12; 1486, p. 314). By composing about 40 percent of their cohort with prevalent hires and excluding many incident hires, Vacek et al. (2011) may have introduced additional healthy worker survivor effect bias into their study. Interestingly, Vacek et al. described the Applebaum et al. (2007) results in their 2009 report, stating, “They [Applebaum et al.] found that decreasing the relative proportion of prevalent to incident hires [in the data used by Attfield and Costello] resulted in a stronger association between cumulative silica exposure and lung cancer mortality” (Document ID 2307, Attachment 6, p. 3). Despite their acknowledgement of the Applebaum et al. (2007) findings, Vacek et al. (2011) did not conduct any analysis of only the incident hires, or use statistical methods to better determine the presence and effect of a healthy worker survivor effect in their study.

The ACC also commented on Vacek et al.'s suggestion that the elevated SMR observed for lung cancer in the cohort (when compared to a reference population of U.S. white males) was due to differences in the smoking habits of the cohort and reference population, which OSHA criticized in its Supplemental Literature Review (Document ID 1486, p. 317; 1711, Attachment 1, p. 5). The ACC stated, “OSHA suggests that the lack of complete smoking data for the cohort is a problem and contends that smoking could not explain the elevated SMR for lung cancer. This criticism, as Dr. Vacek explains, is overstated, and, in any event, does not detract from the study's findings regarding the absence of an association between silica exposure and lung cancer” (Document ID 2307, Attachment A, pp. 46-47; 1804, p. 2).

Vacek et al. (2011) estimated the relative smoking prevalence in the cohort to be 1.35 times that in the reference population; using this estimated relative smoking prevalence, the authors estimated that “the expected number of lung cancer deaths in the cohort after adjusting the reference rates for smoking would be 353, yielding a [non-significant] SMR of 1.02” (Document ID 1486, p. 317). OSHA notes that this method used by Vacek et al. to adjust the SMR for smoking neglects the healthy worker survivor effect (i.e., smokers may leave the workforce sooner than nonsmokers because smoking is a risk factor for poor health). Absent control for the healthy worker survivor effect, smoking would (and perhaps did) become a negative confounder because long duration—high cumulative exposure—workers would tend toward lower smoking attributes. The method used by Vacek et al. is also inconsistent with the frequently cited Axelson (1978) method, which is used to adjust the SMR when the exposed population has a higher percentage of smokers than the reference population (Checkoway et al. 1997, Document ID 0326; Chan et al. 2000, 0983). As a result, Vacek et al. (2011) likely overestimated the confounding effect of smoking in this cohort.

In addition, as previously noted by OSHA, the SMRs for cancers largely attributable to smoking, such as those of the buccal cavity and pharynx (SMR = 1.01), larynx (SMR = 0.99), and esophagus (SMR = 1.15) were not significant in the Vacek et al. study (Document ID 1486, p. 315; 2307, Attachment 6, p. 14). The SMR of 0.94 for bronchitis, emphysema, and asthma also was not significant. If smoking were truly responsible for the highly statistically significant SMR (1.37) observed for lung cancer, the SMRs for these other diseases should be significant as well. OSHA likewise notes that other studies have found that smoking does not have a substantial impact on the association between crystalline silica exposure and lung cancer mortality (e.g., Checkoway et al., 1997, Document ID 0326; Steenland et al., 2001a, 0452, p. 781) and that crystalline silica is a risk factor for lung cancer independent of smoking (Kachuri et al., 2014, Document ID 3907, p. 138; Preller et al., 2010, 4055, p. 657).

OSHA is also concerned about some features of the study design and exposure assessment in Vacek et al. (2011). Regarding the study design, in their nested case-control analyses, Vacek et al. sorted cases into risk sets based on year of birth and year of death, and then matched three controls to each risk set; from the data presented in Table 5 of the study, the actual number of controls per lung cancer case can be calculated as 2.64 (Document ID 1486, p. 316). Vacek et al.'s decision to use such a small number of controls per case was unnecessarily restrictive, as there were additional cohort members who could have been used as controls for the lung cancer deaths. Typically, if the relevant information is available, four or more (or all eligible) controls are used per case to increase study power to detect an association. OSHA notes that Steenland et al. (2001a), in their nested case-control pooled analysis, used 100 controls per case (Document ID 0452, p. 777).

In addition, Vacek et al. stated that for the categorical analysis, cut points on cumulative exposure were based on quintiles of the combined distribution for cases and controls (Document ID 1486, p. 314). Therefore, there should be an approximately equal total number of subjects (cases plus controls) in each group (or quintile). OSHA's examination of Table 5 in the Vacek et al. (2011) study shows that there is an approximately equal distribution of subjects for all endpoints except lung cancer; for example, the silicosis groups each had 43-44 subjects, the NMRD groups each had 125-130 subjects, the kidney cancer groups each had 22-23 subjects, and the kidney disease groups each had 25 subjects. However, the lung cancer groups, ranging from the lowest to the highest exposure, had 325, 232, 297, 241, and 202 subjects (Document ID 1486, p. 316). OSHA could find no explanation for this discrepancy in the text of the Vacek et al. (2011) study, and questions how the lung cancer groups were composed.

With respect to the different job exposure matrices, OSHA has reason to believe that the exposure data reported in the Attfield and Costello study are more accurate than the data Vacek et al. used. OSHA is particularly concerned that Vacek et al.'s pre-1940 exposure estimate of 150 µg/m³ for one job (channel bar operator) was much lower than Attfield and Costello's estimate, from the Davis et al. (1983) matrix, of 1070 µg/m³ (Document ID 1486, p. 313; 0284, p. 131). As NIOSH observed in its post-hearing comments, changing the exposure estimate for channel bar operators could have “major consequences” on the exposure-response analysis, as the job occurred frequently (Document ID 4233, p. 22). NIOSH then pointed out that the Attfield and Costello (2004) exposure estimate for channel bar operators was based on multiple exposure measurements conducted by Davis et al. (1983), whereas Vacek et al. based their exposure estimate “on only three dust measurements” in which “only wet drilling was used. Thus, their study used not only very limited sampling data but also values that were biased towards low levels, since the samples were taken when water was being used to control dust,” a practice that was not typically used for this occupation at the time (Document ID 4233, p. 22). In fact, photographs from Hosey et al. (1957) showed channel bar drilling in 1936 and 1937 with and without dust control; the caption for the photo without dust control states that the “operator in background is barely visible through dust cloud” (Document ID 4233, p. 24, citing 3998, Attachment 14b). As NIOSH explained,

If there is a true [linear] relationship between exposure to silica dust and lung cancer mortality, classifying highly exposed workers incorrectly as low-exposed shifts the elevated risks to the low exposure range. The impact is to spuriously elevate risks at low exposures and lower them at high exposures, resulting in the exposure-response trend being flattened or even obscured. Ultimately, the true relationship may not be evident, or if it is, may be attenuated (Document ID 4233, p. 22, n. 1).

Vacek et al. reported in their study that they conducted a sensitivity analysis that did not change the exposure-response relationship between silica exposure and lung cancer risk, even when Attfield and Costello's pre-1940 exposure estimates were used for channel bar operators (Document ID 2340, pp. 317-318; 2307, Attachment 6, p. 31). Part of the problem may be the way that channel bar operators were defined by Vacek et al. As noted by NIOSH, “Leyner driller and channel bar operator or driller are synonyms” (Document ID 4233, p. 22, n. 3). Attfield and Costello defined channel bar operators in that way, with a pre-1940 exposure estimate of 1070 µg/m³ (Document ID 0284, p. 131). Vacek et al., on the contrary, assigned channel bar operators to a category called “channel bar (wet)” and assigned a pre-1940 exposure estimate of 150 µg/m³ (Document ID 2307, Attachment 6, Appendix B, pp. 7, 15). They included Leyner drillers under a general category called “driller” with a pre-1940 exposure estimate of 1070 µg/m³ (Document ID 2307, Attachment 6, Appendix B, pp. 7, 15). Included in the Vacek et al. (2009) category of “drillers” were plug drillers (Document ID 2307, Attachment 6, Appendix B, p. 15); OSHA notes that Attfield and Costello used a lower pre-1940 exposure estimate of 650 µg/m³ for plug drillers, as defined by Davis et al. (1983). OSHA believes that Vacek et al. underestimated the exposures of some channel bar operators, and overestimated the exposures of plug drillers, which may have contributed to the lack of association, and that the categorization used by Attfield and Costello, with the synonymous channel bar operators and Leyner drillers in one category, and plug drillers in a separate category, was more appropriate. Thus, even in Vacek et al' s sensitivity analysis, in which they used Attfield and Costello's exposure estimate of 1070 µg/m³ for channel bar operators and drillers, the plug drillers would still have had a higher exposure estimate (1070 µg/m³ versus Attfield and Costello's 650 µg/m³), making the analysis different from that of Attfield and Costello.

For the reasons discussed herein, OSHA has decided not to reject the Attfield and Costello (2004) study in favor of the Vacek et al. (2011) study as a basis for risk assessment. OSHA maintains that it has performed an objective analysis of the Attfield and Costello (2004) and Vacek et al. (2011) studies. OSHA agrees with some of the ACC's criticisms regarding the Agency's initial evaluation of the exposure groupings and confounding in the Vacek et al. (2011) study. OSHA is concerned, however, as discussed above, about several aspects of Vacek et al. (2011), including a potential bias from the healthy worker survivor effect, which was shown to exist in this cohort (see Applebaum et al., 2007, cited in Document ID 2307, Attachment 6, p. 3), as well as about job categorization that may have resulted in exposure misclassification for certain job categories (e.g., the synonymous channel bar operators and Leyner drillers). Despite its concerns with the Vacek et al. study, OSHA acknowledges that comprehensive studies, such as Attfield and Costello (2004) and Vacek et al. (2011), in the Vermont granite industry have shown conflicting results with respect to lung cancer mortality (Document ID 0284; 1486). As discussed earlier, conflicting results are often observed in epidemiological studies due to differences in study designs, analytical methods, exposure assessments, populations, and other factors. In addition, the exposure-response relationship between silica and lung cancer may be easily obscured by bias, as crystalline silica is a comparably weaker carcinogen (i.e., the increase in risk per unit exposure is smaller) than other well-studied, more potent carcinogens such as hexavalent chromium (Steenland et al., 2001, Document ID 0452, p. 781). Although OSHA believes that the Attfield and Costello (2004) study is the most appropriate Vermont granite study to use in its QRA, the Agency notes that, even in the absence of the Attfield and Costello (2004) study, the risk estimates for lung cancer mortality based on other studies still provide substantial evidence that respirable crystalline silica poses a significant risk of serious health conditions to exposed workers.

4. Comments on Specific Studies Relied Upon by OSHA in Its QRA

a. Attfield and Costello (2004)

As stated above, OSHA disagrees with the ACC's contention that Vacek et al. provides a more reliable scientific basis for estimating risk than Attfield and Costello. While it is true that the final risk estimate (54 deaths per 1,000 workers) derived from the Attfield and Costello study for an exposure level of 100 µg/m³ is the highest when compared to the other studies, it is not true that the final risk estimate (22 deaths per 1,000 workers) derived from the Attfield and Costello study is the highest for the final rule's PEL of 50 µg/m³. In fact, it is within the range of risk estimates derived from the ToxaChemica (2004) pooled analysis of 16 to 23 deaths per 1,000 workers at the final PEL. Thus OSHA has decided to retain its reliance on the Attfield and Costello (2004) study and, again, notes that, even without the Attfield and Costello (2004) study, all of the other studies in the Final QRA demonstrate a clearly significant risk of lung cancer mortality (11 to 54 deaths per 1,000 workers) at an exposure level of 100 µg/m³, with a reduced, albeit still significant, risk (5 to 23 deaths per 1,000 workers) at an exposure level of 50 µg/m³ (see Table VI-1 in Section VI, Final Quantitative Risk Assessment and Significance of Risk). Excluding Attfield and Costello (2004), in other words, would not change OSHA's final conclusion regarding the risk of death from lung cancer.

b. Miller and MacCalman (2009)

According to the ACC, OSHA's risk estimates based on the Miller and MacCalman (2009, Document ID 1306) study are “more credible than the others—because [the study] involved a very large cohort and was of higher quality in terms of design, conduct, and detail of exposure measurements,” and also adjusted for smoking histories (Document ID 2307, Attachment A, p. 73). Although the risk estimates generated from the Miller and MacCalman data were the lowest of the lung cancer mortality estimates, the ACC next asserted that they were biased upwards for several reasons. First, the ACC stated that exposure information was lacking for cohort members after the mines closed in the mid-1980's, and quoted OSHA as stating, “Not accounting for this exposure, if there were any, would bias the risk estimates upwards” (Document ID 2307, Attachment A, p. 74 (quoting 1711, p. 289)). OSHA, however, does not believe there to have been additional substantial quartz exposures. As the study authors wrote, “Because of the steep decline of the British coal industry, the opportunities for further extensive coal mine exposure were vanishingly small” (Document ID 1306, p. 11). Thus OSHA believes it to be unlikely that the risk estimates are biased upwards to any meaningful degree based on lack of exposure information at the end of the study period.

The ACC also stated that the unrestricted smoking of cohort members after the closure of the mines would have resulted in risk estimates that were biased upwards (Document ID 2307, Attachment A, p. 74). OSHA has no reason to believe, nor did the ACC submit any evidence in support of its contention, that unrestricted smoking occurred, however, and notes that the authors stated that the period after the mines closed was one of “greater anti-smoking health promotion campaigns” (Document ID 1306, p. 11).

Finally, the ACC noted that Miller and MacCalman did not adjust significance levels for the multiple comparisons bias with respect to lag selection that Dr. Cox alleged affected their study (Document ID 2307, Attachment A, p. 74). Dr. Cox claimed that trying multiple comparisons of alternative approaches, such as different lag periods, and then selecting a final choice based on the results of these multiple comparisons, leads to a multiple comparisons bias that could result in false-positive associations (Document ID 2307, Attachment 4, p. 28; see Section V.J, Comments and Responses Concerning Biases in Key Studies). He argued that the authors should have reduced the significance level (typically p = 0.05) at which a result is considered to be significant. “Lag” refers to the exclusion of the more recent years of exposure (e.g., 10-year lag, 15-year lag) to account for the fact that diseases like cancer often have a long latency period (i.e., that the cancer may not be detected until years after the initiating exposure, and exposures experienced shortly before detection probably did not contribute to the development of disease). “Lag selection,” therefore, refers to the choice of an appropriate lag period. As addressed later in the Section V.J, Comments and Responses Concerning Biases in Key Studies, OSHA does not necessarily believe such an adjustment of significance levels to be appropriate, based upon the testimony of Mr. Park of NIOSH, nor is it typically performed in the occupational epidemiology literature (Document ID 3579, Tr. 151-152). Similarly, the ACC stated that the confidence intervals are overly narrow because they ignore model uncertainty, and that multiple imputation of uncertain exposure values should have been performed (Document ID 2307, Attachment A, p. 75). OSHA rejects this assertion on the grounds that the authors used detailed exposure estimates that the ACC recognized raised the credibility of the study; the ACC wrote, regarding the study, “it involved a very large cohort and was of higher quality in terms of design, conduct, and detail of exposure measurements” (Document ID 2307, Attachment A, p. 73). Lastly, the ACC argued that an exposure threshold should have been examined (Document ID 2307, Attachment A, p. 75). OSHA discusses at length this issue of thresholds, and the difficulty in ruling them in or out at low exposures, in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.

In summary, OSHA notes that the ACC has not provided any non-speculative evidence to support its claims that the risk estimates derived from the Miller and MacCalman (2009) study are biased upwards. As stated in the Review of Health Effects Literature and Preliminary QRA, and acknowledged by the ACC (Document ID 2307, p. 73), OSHA believes these risk estimates to be very credible, as the study was based on well-defined union membership rolls with good reporting, had over 17,000 participants with nearly 30 years of follow-up, and had detailed exposure measurements of both dust and quartz, as well as smoking histories (Document ID 1711, pp. 288-289).

c. Steenland (2001a) and ToxaChemica (2004)

OSHA also received several comments on the ToxaChemica (2004, Document ID 0469) analysis, which was based on the Steenland et al. (2001a, Document ID 0452) pooled analysis. First, the ACC claimed that there is significant heterogeneity in the exposure-response coefficients, derived from the individual studies. Because the risk estimates based on these coefficients differ by almost two orders of magnitude, the ACC suggested that these models are misspecified for the data (Document ID 2307, Attachment A, pp. 75-76). Essentially, the ACC claimed that the exposure-response coefficients differ too much among the individual studies, and asserted that it is therefore inappropriate to use the pooled models. Dr. Cox wrote: “Steenland et al. did not address the heterogeneity, but artificially suppressed it by unjustifiably applying a log transformation. This is not a valid statistical approach for exposure estimates with substantial estimation errors” (Document ID 2307, Attachment 4, p. 75). During the public hearing, however, Dr. Steenland explained to OSHA's satisfaction how the data in his study was transformed, using accepted statistical methods. Specifically, referring to his use of a log transformation to address the heterogeneity, Dr. Steenland testified:

[I]t reduces the effect of the very highest exposures being able to drive an exposure-response curve because those exposures are often [skewed] way out—skewed to the right, because occupational exposure data is often log normal. With some very high exposures, they are sort of extreme, and that can drive your exposure-response curve. And you take the log, it pulls them in, and so therefore gives less influence to those high data points. And I think those high data points are often measured with more error (Document ID 3580, Tr. 1265-1266).

OSHA finds this testimony to be persuasive and, therefore, believes that Dr. Steenland's use of a log transformation to address the heterogeneity was appropriate. The log transformation also permits a better model fit when attenuation of the response is observed at high cumulative exposures.

Dr. Morfeld commented that Steenland et al. did not take into account smoking, which could explain the observed excess lung cancer of 20 percent (SMR = 1.2). Dr. Morfeld stated, “Thus, lung cancer excess risks were demonstrated only under rather high occupational exposures to RCS dust, and, even then, an upward bias due to smoking and a necessary intermediate role for silicosis could not be ruled out” (Document ID 2307, Attachment 2, p. 10). Dr. Steenland addressed the concern about a potential smoking bias during his testimony:

We concluded that this positive exposure response was not likely due to different smoking habits between high exposed and low exposed workers. And the reason we did that was twofold. First, workers tend to smoke similar amounts regardless of their exposure level in general. We often worry about comparing workers to the general population because workers tend to smoke more than the general population. But, in internal analyses, we don't have this problem very often. When we have smoking data, we see that it is not related to exposure, so a priori we don't think it is likely to be a strong confounder in internal analyses. Secondly, a number of the studies we used in our pool[ed] cohort had smoking data, either for the whole cohort or partially. And when they took that into account, their results did not change. In fact, they also found that smoking was not related to exposure in their studies, which means that it won't affect the exposure-disease relationship because if it is going to do that, it has to differ between the high exposed and the low exposed, and it generally did not (Document ID 3580, Tr. 1227-1228).

In addition, Brown and Rushton (2009), in their review article submitted to the rulemaking record by Dr. Morfeld, appeared to agree with Dr. Steenland, stating, “This [Steenland et al.] internal analysis removed the possibility of confounding by smoking” (Document ID 3573, Attachment 5, p. 150). Thus, OSHA rejects Dr. Morfeld's assessment that the risk estimates may be biased upwards due to smoking.

The ACC also commented that exposure misclassification due to uncertain exposure estimates in Steenland's pooled cohort could have created the appearance of a monotonic relationship, in which the response increases with the exposure, even if the true response was not monotonic (Document ID 2307, Attachment A, p. 76). The ACC, along with Dr. Borak (representing the U.S. Chamber of Commerce) and others, likewise cited OSHA's statement from the Review of Health Effects Literature and Preliminary QRA, in which the Agency acknowledged that uncertainty in the exposure estimates that underlie each of the 10 studies in the pooled analysis was likely to represent one of the most important sources of uncertainty in the risk estimates (Document ID 1711, p. 292; 2376, p. 16). Dr. Borak also quoted Mannetje et al. (2002), who developed quantitative exposure data for the pooled analysis, as stating, “While some measurement error certainly occurred in our estimates, a categorical analysis based on broad exposure groups should not be much affected by the resulting level of misclassification” (Document ID 2376, p. 17, quoting 1090, p. 84). From this statement, Dr. Borak concluded that the researchers themselves believed the data were only adequate for “categorical analyses which might lead to qualitative conclusions” (Document ID 2376, p. 17).

OSHA disagrees with Dr. Borak's interpretation of the Mannetje et al. statement, as categorical analyses are typically quantitative in nature, with the data being used to draw quantitative conclusions. However, OSHA recognized the possibility for uncertainty in the exposure estimates, and it is for this reason that OSHA commissioned a quantitative analysis of uncertainty in Steenland's pooled study (ToxaChemica, 2004, Document ID 0469). This analysis suggested that exposure misclassification had little effect on the pooled exposure coefficient (and the variance around that estimate) for the lung cancer risk model (Document ID 1711, pp. 313-314). Given this analysis, OSHA also disagrees with the ACC's statement that “it is virtually certain that substantial exposure estimation error infused the pooled analysis, resulting in exposure misclassification that would create a false appearance of a monotonically increasing exposure-response even where none exists” (Document ID 2307, Attachment A, p. 78). OSHA notes that this statement is not supported with any evidence from the Steenland et al. (2001) study. In addition, as discussed at length in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, exposure estimation error can also bias results towards the null (weaken or obscure the exposure-response relationship) (Document ID 3580, Tr. 1266-67; 3576, Tr. 358-359; 3574, p. 21). Other criticisms from the ACC concerning alleged modeling errors and biases in the Steenland study and the alleged threshold for the health effects of silica exposure are discussed generally in Section V.J, Comments and Responses Concerning Biases in Key Studies, and Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases. Dr. Cox's and Dr. Morfeld's criticisms of the uncertainty analysis performed by Toxachemica are addressed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis. For the reasons stated in those sections, OSHA is unpersuaded by these criticisms.

The ACC concluded:

For all these reasons, the pooled analysis by Steenland et al. (2001) does not yield credible or reliable estimates of silica-related lung cancer risk. But, even if risk estimates based on Steenland et al. (2001) were not so problematic, that study would not demonstrate that reducing the PEL from 0.1 mg/m³ [100 µg/m³] to 0.05 mg/m³ [50 µg/m³] will result in a substantial reduction in the risk of lung cancer (Document ID 2307, Attachment A, p. 81).

The ACC then discussed the ToxaChemica report (2004), which the ACC claimed shows that “under the spline model (which the authors prefer over the log cumulative model because of biological plausibility)” reducing the PEL from 100 µg/m³ to 50 µg/m³ would negligibly reduce the excess risk of lung cancer mortality from 0.017 (17/1,000) to 0.016 (16/1,000), “risk values that are indistinguishable given the overlapping confidence limits of the two estimates” (Document ID 2307, Attachment A, p. 81). In addition, the ACC noted that the excess risk at 150 µg/m³ and 250 µg/m³ in the spline model is the same as the excess risk at 50 µg/m³, while that at 200 µg/m³ is lower. “Estimates of lung cancer risk in the neighborhood of the current general industry PEL are hugely uncertain—with the data suggesting that a greater reduction in lung cancer risk could be achieved by doubling the PEL to 200 µg/m³ than by cutting it in half to a level of 50 µg/m³” (Document ID 2307, Attachment A, pp. 81-82).

OSHA notes that these risk estimates cited by the ACC were the original estimates for the spline model provided to OSHA by ToxaChemica in its 2004 report (Document ID 0469). These are not the risk estimates used by OSHA. Instead, to estimate the risks published in this final rule, the Agency used the exposure-response coefficients from the study in an updated life table analysis using background all-cause mortality and lung cancer mortality rates from 2006 and 2011, respectively. The risk estimates using the 2011 background data are the most updated numbers with which to make the comparisons ACC has suggested. With the 2011 background data, the estimated excess risk is 20 deaths per 1,000 workers at 100 µg/m³, and 16 deaths per 1,000 workers at 50 µg/m³, a reduction of 4 deaths. OSHA's estimated excess risk at 250 µg/m³ is 24 deaths per 1,000 workers, an increase in 8 deaths when compared to 50 µg/m³. Thus it is not the case, as ACC suggested, that increasing the PEL would cause a reduction in lung cancer mortality risk.

In addition, the linear spline model employed by Steenland et al. (2001) was only one of three models used by OSHA to estimate quantitative risks from the pooled analysis. OSHA also used the log-linear model with log cumulative exposure as well as the linear model with log cumulative exposure (see Section VI, Final Quantitative Risk Assessment and Significance of Risk). OSHA notes that all three models indicated a reduction in risk when comparing an exposure level of 100 µg/m³ to 50 µg/m³.

In summary, OSHA disagrees with the ACC's assertion that the Steenland et al. pooled analysis does not yield credible risk estimates for lung cancer mortality. Dr. Morfeld's assertion that the risk estimates were biased upwards due to smoking is quite unlikely to be true, given that the study was an internal (worker to worker) analysis. The ACC's claim that exposure estimation error resulted in false exposure-response relationships was not supported by any actual data; as discussed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, exposure estimation error can also bias results towards the null (weaken or obscure the exposure-response relationship) (Document ID 3580, Tr. 1266-67; 3576, Tr. 358-359; 3574, p. 21). For these reasons, OSHA rejects the ACC's claims that the Steenland study of lung cancer mortality does not yield credible risk estimates. Rather, based upon its review, OSHA believes this pooled analysis to be of high quality. As Dr. Steenland testified during the informal public hearings, this pooled analysis, with its more than 60,000 workers and 1,000 lung cancer deaths, involved “a rich dataset with high statistical power to see anything, if there was anything to see” (Document ID 3580, Tr. 1227). In fact, OSHA believes the Steenland et al. (2001a) study to be among the best available studies in the peer-reviewed literature on the topic of silica exposure and its relationship to lung cancer mortality.

d. Rice et al. (2001)

The ACC also commented on the Rice et al. (2001, Document ID 1118) study of diatomaceous earth workers, which found a significant risk of lung cancer mortality that increased with cumulative silica exposure in a cohort of diatomaceous earth workers. The ACC claimed that it had a high likelihood of exposure misclassification. Dr. Cox contended that the practice of “[a]ssigning each worker a single estimated cumulative exposure based on estimated mean values produces biased results and artificially narrow confidence intervals (and hence excess false-positive associations)” (Document ID 2307, Attachment 4, p. 76). OSHA notes that Rice et al. (2001) described the exposure estimation procedure in their paper. There were more than 6,000 measurements of dust exposure taken from 1948-1988; particle count data were converted to gravimetric data using linear regression modeling. Cumulative exposures to respirable crystalline silica were then estimated for each worker using detailed employment records (Document ID 1118, p. 39). OSHA concludes it is highly unlikely that the exposure estimates are biased to such an extent, as Dr. Cox suggests, that they would produce false-positive associations.

The ACC also noted that the mean crystalline silica exposure in the diatomaceous earth worker cohort was 290 μg/m³, approximately three times the former PEL for general industry (Document ID 2307, Attachment A, p. 83). OSHA, however, believes that the cumulative respirable crystalline silica dust concentration is the metric of concern here, as that is what was used in the regression models. The mean cumulative respirable crystalline silica dust concentration in the study was 2.16 mg/m³-yrs, which is a very realistic cumulative exposure for many workers (Document ID 1118, p. 39).

The ACC also stated that the results of the Rice study were confounded by smoking and possibly asbestos exposure (Document ID 2307, Attachment A, p. 83). OSHA previously addressed the possible confounding in this cohort in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 139-143). Rice et al. (2001) used the same cohort originally reported on by Checkoway et al. (1993, Document ID 0324; 1996, 0325; 1997, 0326). The Rice study discussed the smoking confounding analysis performed by Checkoway et al. (1997), in which the Axelson method (1978) was used to make a worst case estimate (assuming 20 times greater lung cancer risk in smokers compared to non-smokers) and indirectly adjust the relative risk (RR) estimates for lung cancer for differences in smoking rates (Document ID 1118, pp. 40-41). With exposures in the Checkoway study lagged 15 years to account for the latency period, the worst case effect was to reduce the RR for lung cancer in the highest exposure group from 2.15 to 1.67. Checkoway et al. concluded that the association between respirable silica exposure and lung cancer was unlikely to be confounded by cigarette exposure (Document ID 0326, pp. 684, 687). Regarding confounding by asbestos exposure, Rice et al. (2001) stated:

Checkoway et al. found no evidence that exposure to asbestos accounted for the observed association between mortality from lung cancer and cumulative exposure to silica. Our analyses of their data also found no evidence of confounding by asbestos in the Poisson regression or Cox's proportional hazards models regardless of lag period; therefore, exposure to asbestos was not included in the models presented in this paper (Document ID 1118, p. 41).

Based upon these analyses, OSHA rejects the ACC's unsupported assertion that the results of Rice et al. (2001) were confounded by smoking and asbestos exposure.

Lastly, Dr. Cox asserted that there were several biases in Rice et al. (2001), including multiple-testing bias from testing multiple lag periods, exposure groupings, and model forms; model specification bias; and a lack of model diagnostics (Document ID 2307, Attachment 4, pp. 63-64, 77). OSHA addressed these issues generally in Section V.J, Comments and Responses Concerning Biases in Key Studies, and rejects these assertions for the same reasons. OSHA also discussed regression diagnostics at length in the same section. In summary, despite the criticisms directed at the Rice et al. study by the ACC, OSHA continues to believe that the quantitative exposure-response analysis by Rice et al. (2001) is of high quality and appropriate for inclusion in the QRA (Document ID 1711, p. 143).

e. Hughes et al. (2001)

The ACC, through the comments of Dr. Cox, presented a similar critique of the study of North American industrial sand workers by Hughes et al. (2001, Document ID 1060). This study found a statistically significant association (increased odds ratios) between lung cancer mortality and cumulative silica exposure as well as average silica concentration (Document ID 1060). In this study, according to Dr. Cox, “The selected model form guarantees a monotonic exposure-response relation, independent of the data. Model uncertainty and errors in exposure estimates have both been ignored, so the slope estimate from Hughes et al. (2001), as well as the resulting excess risk estimates, are likely to be biased and erroneous” (Document ID 2307, Attachment 4, p. 85). The ACC also noted that this cohort had incomplete smoking information, with the proportion of “ever smokers” significantly higher in cases than in controls. In addition, the ACC asserted that asbestos exposure may have also occurred, as three death certificates listed mesothelioma as the cause of death (Document ID 2307, Attachment A, pp. 85-86).

OSHA discussed the Hughes et al. (2001, Document ID 1060) study in its Review of Health Effects Literature and Preliminary QRA, highlighting as strengths the individual job, exposure, and smoking histories that were available (Document ID 1711, p. 285). Exposure levels over time were estimated via a job exposure matrix constructed by Rando et al. (2001, Document ID 0415) utilizing substantial exposure data, including 14,249 respirable dust and silica samples taken from 1974 to 1998 in nine plants (Document ID 1711, pp. 88, 124-128; 1060, 202). Smoking data were collected from medical records supplemented by information from next of kin or living subjects for 91 percent of cases and controls (Document ID 1060, p. 202). OSHA believes these smoking histories allowed the authors to adequately control for confounding by smoking in their analyses. Regarding the three death certificates listing mesothelioma, McDonald et al. (2001) explained that two were for workers not included in the case/control study because they were hired at or after age 40 with less than 10 years of work time; the third was for a worker hired at age 19 who then accumulated 32 years of experience in maintenance jobs (Document ID 1091, p. 195). As such, OSHA does not believe it likely that asbestos exposure was a large source of confounding in typical industrial sand operations in this study. OSHA also notes that the positive findings of this study were consistent with those of other studies of workers in this cohort, including Steenland and Sanderson (2001, Document ID 0455) and McDonald et al. (2005, Document ID 1092).

The ACC also noted that there was no consistent correlation in Hughes et al. (2001) between employment duration and lung cancer risk (Document ID 2307, Attachment A, p. 86), with Dr. Cox suggesting that model specification error was to blame (Document ID 2307, Attachment 4, p. 86). OSHA believes that cumulative exposure is a more appropriate metric for determining risk than is duration of exposure because the cumulative exposure metric considers both the duration and intensity of exposure. For example, some workers may have been employed for a very long duration with low exposures, whereas others may have been employed for a short duration but with high exposures; both groups could have similar cumulative exposures.

In summary, OSHA considers the Hughes et al. (2001) study to be of high enough quality to provide risk estimates for excess lung cancer from silica exposure, as the study is unlikely to be substantially confounded. For these reasons, the Agency finds the assertion that the risk estimates based on this study are erroneous to be unconvincing.

Overall, regarding all of the studies upon which OSHA relied in its Preliminary QRA, the ACC concluded, “In sum, none of the studies on which OSHA relies is inconsistent with a concentration threshold above 100 μg/m³ for any risk of silica-related lung cancer; none demonstrates an increased lung cancer risk in the absence of silicosis; and none provides a sound basis for estimating lung cancer risks at RCS [respirable crystalline silica] exposure levels of 100 μg/m³ and below” (Document ID 2307, Attachment A, p. 87).

OSHA is not persuaded that the evidence presented by the ACC supports these conclusions. On the contrary, as OSHA discussed in the Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases, demonstrating the absence of a threshold is not a feasible scientific pursuit, and some models produce threshold estimates well below the PELs. Similarly, the ACC has not put forward any study that has proven that silicosis must be a precursor for lung cancer and, as discussed in Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, some studies have shown genotoxic mechanisms by which exposure to crystalline silica may lead to lung cancer. The strong epidemiological evidence for carcinogenicity, supported by evidence from experimental animal and mechanistic studies, allowed IARC to conclude on multiple occasions that respirable crystalline silica is a Group I carcinogen. OSHA places great weight on this conclusion given IARC's authority and standing in the international scientific community. In addition, all of the lung cancer studies relied upon by OSHA used models that allow for the estimation of lung cancer risks at crystalline silica exposure levels of 100 μg/m³ and below. OSHA believes these studies (Steenland et al., 2001a, Document ID 0452, as re-analyzed in ToxaChemica, 2004, 0469; Rice et al., 2001, 1118; Attfield and Costello, 2004, 0284; Hughes et al., 2001, 1060; and Miller and MacCalman, 2009, 1306) are of high quality and contain well-supported findings. Thus, OSHA continues to rely upon these studies for deriving quantitative risk estimates in its QRA and continues to believe that workers exposed to respirable crystalline silica at levels at or near the previous and new PELs are faced with a significant risk of dying from lung cancer. As such, the Agency believes it would be irresponsible as a scientific matter, and inconsistent with its statutory obligations to issue standards based on the best available evidence after conducting an extensive rulemaking, to retain the regulatory status quo.

G. Comments and Responses Concerning Renal Disease Mortality

OSHA estimated quantitative risks for renal disease mortality (Document ID 1711, pp. 314-316) using data from a pooled analysis of renal disease, conducted by Steenland et al. (2002a, Document ID 0448). As illustrated in Table VI-1, the lifetime renal disease mortality risk estimate for 45 years of exposure to the previous general industry PEL (100 μg/m³ respirable crystalline silica) is 39 deaths per 1,000 workers. However, for the final PEL (50 μg/m³), it is 32 deaths per 1,000 workers. Although OSHA acknowledges that there are considerably less data for renal disease mortality, and thus the risk findings based on them are less robust than those for silicosis, lung cancer, and non-malignant respiratory disease (NMRD) mortality, the Agency believes the renal disease risk findings are based on credible data. Indeed, the Steenland et al. pooled analysis had a large number of workers from three cohorts with sufficient exposure data, and exposure matrices for the three cohorts had been used in previous studies that showed positive exposure-response trends for silicosis morbidity or mortality, thus tending to validate the underlying exposure and work history data (see Document ID 1711, pp. 215-216). Nevertheless, OSHA received comments that were critical of its risk estimates for renal disease mortality. Based upon its review of the best available evidence, OSHA finds that these comments do not alter its overall conclusions on renal disease mortality. In addition, OSHA notes that even if the risk of renal disease mortality is discounted, there would remain clearly significant risks of lung cancer mortality, silicosis and NMRD mortality, and silicosis morbidity, with more robust risk estimates based upon a larger amount of data from numerous studies (see Table VI-1).

OSHA received several comments from the ACC regarding the Agency's quantitative risk estimates for renal disease mortality. Specifically, the ACC argued that: (1) The pooled study (Steenland et al., 2002a, Document ID 0448) that OSHA relied upon did not provide sufficient data to estimate quantitative risks; (2) the individual studies included in the pooled study had several limitations; and (3) most epidemiological studies have not demonstrated a statistically significant association between silica exposure and renal disease mortality (Document ID 2307, Attachment A, pp. 139-157; 4209, pp. 92-96). As explained below, and as stated above, although the Agency acknowledges there is greater uncertainty in the risk estimates related to renal disease than other silica-related diseases, the best available evidence is of sufficient quality to quantify the risk of renal disease in the final risk assessment.

1. Pooled Study

Some commenters expressed concern about the Steenland et al. (2002a, Document ID 0448) pooled study of renal disease mortality, which OSHA and its contractor, ToxaChemica, used to calculate quantitative risk estimates. Specifically, the ACC questioned why the analysis only used three studies (Homestake, North Dakota gold miners, Steenland and Brown, 1995a, Document ID 0450; U.S. industrial sand workers, Steenland et al., 2001b, Document ID 0456; Vermont granite workers, Costello and Graham, 1988, Document ID 0991) out of the ten originally used in the pooled study of lung cancer mortality (Steenland et al., 2001a, Document ID 0452). Peter Morfeld, Dr. rer. medic., representing the ACC, wrote in his written testimony that although Steenland et al. (2002a, Document ID 0448) indicated that the three studies were selected because they were the only ones to have information on multiple cause mortality, all 10 studies had information on renal disease as an underlying cause of death (Document ID 2308, Attachment 4, pp. 24-25). Since ToxaChemica focused on underlying cause results in their discussion, Dr. Morfeld argued that not having used all 10 studies in the pooled analysis “raises a suspicion of study selection bias” (Document ID 2308, Attachment 4, pp. 24-25).

OSHA finds this assertion of study selection bias by the ACC and Dr. Morfeld to be unpersuasive because Steenland et al.'s explanation (2002a) for including only three studies in the pooled analysis was sound. The authors reported in their pooled study that both underlying cause and multiple cause mortality were available for only three cohorts of silica-exposed workers, and “multiple cause (any mention on the death certificate) was of particular interest because renal disease is often listed on death certificates without being the underlying cause” (Document ID 0448, p. 5). The authors likewise cited a study (Steenland et al., 1992), indicating that the ratio of chronic renal disease mortality shown anywhere on a U.S. death certificate versus being shown as an underlying cause is 4.75 (Document ID 0453, Table 2, pp. 860-861). Indeed, in their pooled analysis of renal disease mortality, Steenland et al. noted that there were 51 renal disease deaths when using underlying cause, but 204 when using multiple cause mortality (Document ID 0448, p. 5). As renal disease is a serious disabling disease, the use of multiple cause mortality gives a much better sense of the burden of excess disease than does the use of underlying cause of death as an endpoint. As such, Steenland et al. calculated odds ratios by quartile of cumulative silica exposure for renal disease in a nested case-control analysis that considered any mention of renal disease on the death certificate as well as underlying cause. For multiple-cause mortality, the exposure-response trend was statistically significant for both cumulative exposure (p = 0.004) and log cumulative exposure (p = 0.0002); whereas for underlying cause mortality, the trend was statistically significant only for log cumulative exposure (p = 0.03) (Document ID 1711, p. 315). Thus, OSHA believes that Steenland et al. (2002a, Document ID 0448) were justified in including only the three cohorts with all-cause mortality in their pooled analysis.

Concern was also expressed about the model selection in the pooled analysis. Dr. Morfeld noted that a statistically significant association between exposure to crystalline silica and renal disease mortality was only found in the underlying cause analysis in which the model was logged (p = 0.03) (Document ID 2308, Attachment 4, p. 25). Dr. Morfeld commented, “The authors stated that the log-model fit better, but evidence was not given (e.g., information criteria), and it is unclear whether the results are robust to other transformations” (Document ID 2308, Attachment 4, p. 25).

OSHA disagrees with this criticism because a log transformation of the cumulative exposure metric is reasonable, given that exposure variables are often lognormally distributed in epidemiological studies, as discussed in Section V.J, Comments and Responses Concerning Biases in Key Studies. Also, while it is true that Steenland et al. (2002a) only found a statistically significant association in the continuous underlying cause analysis when the cumulative exposure metric was logged (p = 0.03), OSHA notes that the authors also found a statistically significant association in the highest quartile of unlogged cumulative silica exposure (1.67 + mg/m³-yr) in the categorical underlying cause analysis (95% confidence interval: 1.31-11.76) (Document ID 0448, Table 2, p. 7). Thus, for the highest cumulative exposures, there was a significant association with renal disease mortality even without a log transformation of the exposure metric. Dr. Morfeld also failed to mention that Steenland et al. (2002a) found statistically significant associations in the continuous analyses (for both untransformed and log-transformed cumulative exposure) using any mention of renal disease on the death certificate, which adds weight to the study's findings that exposure to respirable crystalline silica is associated with renal disease mortality (Document ID 0448, Table 2, p. 7). In light of this, OSHA concludes that Dr. Morfeld's criticism of the pooled analysis is without merit.

The ACC also noted that the authors of this study, Drs. Kyle Steenland and Scott Bartell, acknowledged the limitations of the data in their 2004 ToxaChemica report to OSHA. Specifically, in reference to the 51 renal deaths (underlying cause) and 23 renal cases in the pooled study, Drs. Steenland and Bartell wrote, “This amount of data is insufficient to provide robust estimates of risk” (Document ID 2307, Attachment A, p. 139, citing 0469, p. 27). Given this acknowledgement, the ACC concluded that OSHA's inclusion of the renal disease mortality risk estimates in the significant risk determination and calculation of expected benefits was speculative (Document ID 2307, Attachment A, pp. 139-140). During the hearing, Dr. Steenland further explained, “I think there is pretty good evidence that silica causes renal disease. I just think that there is not as big a database as there is for lung cancer and silicosis. And so there is more uncertainty” (Document ID 3580, Tr. 1245). OSHA agrees with Dr. Steenland and acknowledges, as it did in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, p. 357), that its quantitative risk estimates for renal disease mortality have more uncertainty and are less robust than those for the other health effects examined (i.e., lung cancer mortality, silicosis and NMRD mortality, and silicosis morbidity). However, OSHA disagrees with the ACC's suggestion that the Agency's renal disease risk estimates are “rank speculation” (Document ID 4209, pp. 95-96), as these estimates are based on the best available evidence in the form of a published, peer-reviewed pooled analysis (Steenland et al. 2002a, Document ID 0448) that uses sound epidemiological and statistical methods. Thus, OSHA believes that it is appropriate to present the risk estimates along with the associated uncertainty estimate (e.g., 95% confidence intervals) (see Document ID 1711, p. 316).

2. Individual Studies in the Pooled Study

The ACC also identified limitations in each of the three epidemiological studies included in the Steenland et al. (2002a, Document ID 0448) pooled study. First, with respect to the Steenland and Brown (1995a, Document ID 0450) study of North Dakota gold miners, the ACC noted there was a significantly elevated standardized mortality ratio (SMR) for chronic renal disease only in the men hired prior to 1930. It noted that there were no silica exposure measurement data available for this early time period, such that Steenland and Brown (1995a, Document ID 0450) instead estimated a median exposure (150 μg/m³) that was seven times higher for men hired prior to 1930, versus men hired after 1950 (20 μg/m³) (Document ID 2307, Attachment A, p. 147). The ACC maintained that these exposure estimates were likely to be understated and not credible, while also suggesting “the existence of an average exposure threshold ≥150 μg/m³ for any risk of silica-related renal disease mortality” (Document ID 2307, Attachment A, p. 147).

OSHA finds the ACC's suggestion of a threshold to be unpersuasive, as the ACC provided no analysis to indicate a threshold in this study. OSHA addresses the Steenland and Brown (1995a, Document ID 0450) exposure assessment in Section V.D, Comments and Responses Concerning Silicosis and Non-Malignant Respiratory Disease Mortality and Morbidity. The ACC also ignored the alternative explanation, that elevated chronic renal disease mortality may have only been seen in the workers hired prior to 1930 because they had a higher cumulative exposure than workers hired later, not because there was necessarily a threshold.

The ACC had a similar criticism of the Steenland et al. (2001b, Document ID 0456) study of North American industrial sand workers. The ACC posited that the exposure estimates were highly uncertain and likely to be understated (Document ID 2307, Attachment A, p. 149). The ACC noted that these exposure estimates, developed by Sanderson et al. (2000, Document ID 0429), were considerably lower than those developed by Rando et al. (2001, Document ID 0415) for another study of North American industrial sand workers (Document ID 2307, Attachment A, p. 149). After discussing several differences between these two exposure assessments, the ACC pointed to OSHA's discussion in the lung cancer section of the preamble to the Proposed Rule (78 FR at 56302) in which the Agency acknowledged that McDonald et al. (2001, Document ID 1091), Hughes et al. (2001, Document ID 1060) and Rando et al. (2001, Document ID 0415) had access to smoking histories, plant records, and exposure measurements that allowed for the development of a job exposure matrix, while Steenland and Sanderson (2001, Document ID 0455) had limited access to plant facilities, less detailed historic exposure data, and used MSHA enforcement records for estimates of recent exposure (Document ID 2307, Attachment A, pp. 149-151). The ACC then noted that the McDonald et al. study (2005, Document ID 1092), using the Rando et al. (2001, Document ID 0415) exposure assessment, found no association between end-stage renal disease or renal cancer and cumulative silica exposure (Document ID 2307, Attachment A, pp. 149, 152).

The ACC also noted that, based on underlying cause of death, the SMR for acute renal death in the Steenland et al. (2001b, Document ID 0456) study was not significant (95% confidence interval: 0.70-9.86), and the SMR for chronic renal disease was barely significant (95% confidence interval: 1.06-4.08) (Document ID 2307, Attachment A, p. 151). In light of this, the ACC maintained that Steenland et al. based their exposure-response analyses on multiple-cause mortality data, using all deaths with any mention of renal disease on the death certificate even if it was not listed as the underlying cause. The ACC asserted that “only the underlying cause data involve actual deaths from renal disease” (Document ID 2307, Attachment A, p. 152).

OSHA does not find this criticism persuasive. For regulatory purposes, multiple-cause mortality data is, if anything, more relevant because renal disease constitutes the type of material impairment of health that the Agency is authorized to protect against through regulation regardless of whether it is determined to be the underlying cause of a worker's death. Moreover, the discrepancy in the renal disease mortality findings is a moot point, as only the model in the pooled study with renal disease as an underlying cause was used to estimate risks in the Preliminary QRA (Document ID 1711, p. 316). In any event, OSHA notes an important difference between the Steenland et al. study (2001b, Document ID 0456) and the McDonald study (2005, Document ID 1092): They did not look at the same cohort of North American industrial sand workers. Steenland et al. (2001b) examined a cohort of 4,626 workers from 18 plants; the average year of first employment was 1967, with follow-up through 1996 (Document ID 0456, pp. 406-408). McDonald et al. (2005) examined a cohort of 2,452 workers employed between 1940 and 1979 at eight plants, with follow-up through 2000 (Document ID 1092, p. 368). Although there was overlap of about six plants in the studies (Document ID 1711, p. 127), these were clearly two fairly different cohorts of industrial sand workers. These differences in the cohorts might explain the discrepancy in the studies' results. In addition, OSHA notes that McDonald et al. (2005, Document ID 1092) observed statistically significant excess mortality from nephritis/nephrosis in their study that was not explained by the findings of their silica exposure-response analyses (Document ID 1092, p. 369).

The ACC further argued that the Steenland et al. (2002a, Document ID 0448) pooled study is inferior to the Vacek et al. (2011, Document ID 2340) study of Vermont granite workers, which found no association between cumulative silica exposure and mortality from either kidney cancer or non-malignant kidney disease and which it contended has better mortality and exposure data (Document ID 2307, Attachment A, p. 154) (citing Vacek et al. (2011, Document ID 2340). In particular, it argued that the Vacek et al. study is more reliable for this purpose than the unpublished Attfield and Costello data (2004, Document ID 0285) on Vermont granite workers, which Steenland et al. relied on in finding an association between silica exposure and renal disease.

OSHA notes that Steenland et al. acknowledged in their pooled study that that unpublished data had not undergone peer review (Document ID 0448, p. 5). Despite this limitation, OSHA is also unpersuaded that the Vacek et al. study, although it observed no increased kidney disease mortality (Document ID 2340, Table 3, p. 315), negates Steenland et al.'s overall conclusions. OSHA discussed several substantial differences between these two studies in Section V.F, Comments and Responses Concerning Lung Cancer Mortality.

3. Additional Studies

The ACC also submitted to the record several additional studies that did not show a statistically significant association between exposure to crystalline silica and renal disease mortality. These included the aforementioned studies by McDonald et al. (2005, Document ID 1092) and Vacek et al. (2011, Document ID 2340), as well as studies by Davis et al. (1983, Document ID 0999), Koskela et al. (1987, Document ID 0363), Cherry et al. (2012, article included in Document ID 2340), Birk et al. (2009, Document ID 1468), Mundt et al. (2011, Document ID 1478), Steenland et al. (2002b, Document ID 0454), Rosenman et al. (2000, Document ID 1120), and Calvert et al. (2003, Document ID 0309) (Document ID 2307, Attachment A, pp. 140-145). In light of its assertions on the limitations of the three studies in the pooled analysis, and because the three studies “run counter to a larger number of studies in which a causal association between silica exposure and renal disease was not found,” the ACC concluded that “the three studies relied on by OSHA do not provide a reliable or supportable basis for projecting any risk of renal disease mortality from silica exposure” (Document ID 4209, p. 94). Similarly, the AFS argued that renal disease was only “found in a couple of selected studies and not observed in most others,” including no foundry studies (Document ID 2379, Attachment 1, pp. 1-3).

In light of the analysis contained in the Review of Health Effects Literature and Preliminary QRA, and OSHA's confirmation of its preliminary findings through examination of the record, OSHA finds these claims to be lacking in merit (Document ID 1711, pp. 211-229). In the Review of Health Effects Literature and Preliminary QRA, OSHA presented a comprehensive analysis of several studies that showed an association between crystalline silica and renal disease, as well as discussing other studies that did not (Document ID 1711, pp. 211-229). Based upon its overall analysis of the literature, including the negative studies, OSHA concluded that there was substantial evidence suggesting an association between exposure to crystalline silica and increased risks of renal disease. This conclusion was supported by a number of case reports and epidemiological studies that found statistically significant associations between occupational exposure to silica dust and chronic renal disease (Calvert et al., 1997, Document ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID 0386), end-stage renal disease morbidity (Steenland et al., 1990, Document ID 1125), end-stage renal disease incidence (Steenland et al. 2001b, Document ID 0456), chronic renal disease mortality (Steenland et al., 2002a, 0448), and granulomatosis with polyangitis (Nuyts et al., 1995, Document ID 0397). In other findings, silica-exposed individuals, both with and without silicosis, had an increased prevalence of abnormal renal function (Hotz et al., 1995, Document ID 0361), and renal effects were reported to persist after cessation of silica exposure (Ng et al., 1992c, Document ID 0386). While the mechanism of causation is presently unknown, possible mechanisms suggested for silica-induced renal disease included a direct toxic effect on the kidney, deposition in the kidney of immune complexes (IgA) following silica-related pulmonary inflammation, or an autoimmune mechanism (Calvert et al., 1997, Document ID 0976; Gregorini et al., 1993, 1032).

From this review of the studies on renal disease, OSHA concluded that there were considerably less data, and thus the findings based on them were less robust, than the data available for silicosis and NMRD mortality, lung cancer mortality, or silicosis morbidity. Nevertheless, OSHA concluded that the Steenland et al. (2002a, Document ID 0448) pooled study had a large number of workers and validated exposure information, such that it was sufficient to provide useful estimates of risk of renal disease mortality. With regard to the additional negative studies presented by the ACC, OSHA notes that it discussed the Birk et al. (2009, Document ID 1468) and Mundt et al. (2011, Document ID 1478) studies in the Supplemental Literature Review of the Review of Health Effects Literature and Preliminary QRA, noting the short follow-up period as a limitation, which makes it unlikely to observe the presence of renal disease (Document ID 1711, Supplement, pp. 6-12). OSHA likewise discussed the Vacek et al. (2011, Document ID 2340) study earlier in this section, and notes that Cherry et al. reported a statistically significant excess of non-malignant renal disease mortality in the cohort for the period 1985-2008, with an unexplained cause (2012, p. 151, article included in Document ID 2340). Although these latter two studies did not find a significant association between silica exposure and renal disease mortality, OSHA does not believe that they substantially change its conclusions on renal disease mortality from the Preliminary QRA, given the number of positive studies presented and the limitations of those two studies.

Thus, OSHA recognizes that the renal risk estimates are less robust and have more uncertainty than those for the other health endpoints for which there is a stronger case for causality (i.e., lung cancer mortality, silicosis and NMRD mortality, and silicosis morbidity). But, for the reasons stated above, OSHA believes that the evidence supporting causality regarding renal risk outweighs the evidence casting doubt on that conclusion. Scientific certainty is not the legal standard under which OSHA acts. OSHA is setting the standard based upon the clearly significant risks of lung cancer mortality, silicosis and NMRD mortality, silicosis morbidity, and renal disease mortality at the previous PELs; even if the risk of renal disease mortality is discounted, the conclusion would not change that regulation is needed to reduce the significant risk of material impairment of health (see Society of the Plastics Industry, Inc. v. OSHA, 509 F.2d 1301, 1308 (2d Cir. 1975)).

H. Mechanisms of Silica-Induced Adverse Health Effects

In this section, OSHA describes the mechanisms by which silica exposure may cause silica-related health effects, and responds to comments criticizing the Agency's analysis on this topic. In the proposal as well as this final rule, OSHA relied principally on epidemiological studies to establish the adverse health effects of silica exposure. The Agency also, however, reviewed animal studies (in vivo and in vitro) as well as in vitro human studies that provide information about the mechanisms by which respirable crystalline silica causes such effects, particularly silicosis and lung cancer. OSHA's review of this material can be found in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (QRA), which provided background and support for the proposed rule (Document ID 1711, pp. 229-261).

As described in the Review of Health Effects Literature, OSHA performed an extensive evaluation of the scientific literature pertaining to inhalation of respirable crystalline silica (Document ID 1711, pp. 7-265). Due to the lack of evidence of health hazards from dermal or oral exposure, the Agency focused solely on the studies addressing the inhalation hazards of respirable crystalline silica. OSHA determined, based on the best available scientific information, that several cellular events, such as cytotoxicity (i.e., cellular damage), oxidative stress, genotoxicity (i.e., damage to cellular DNA), cellular proliferation, and inflammation can contribute to a range of neoplastic (i.e., tumor-forming) and non-neoplastic health effects in the lung. While the exact mechanisms have yet to be fully elucidated, they are likely initiated by damage to lung cells from interaction directly with the silica particle itself or through silica particle activation of alveolar macrophages following phagocytosis (i.e., engulfing particulate matter in the lung for the purpose of removing or destroying foreign particles). The crystalline structure and unusually reactive surface properties of the silica particle appear to cause the early cellular effects. Silicosis and lung cancer share common features that arise from these early cellular interactions but OSHA, in its Review of Health Effects Literature and Preliminary QRA, “preliminarily conclude[d] that available animal and in vitro studies have not conclusively demonstrated that silicosis is a prerequisite for lung cancer in silica-exposed individuals” (Document ID 1711, p. 259). Although the health effects associated with inhalation of respirable crystalline silica are seen primarily in the lung, other observed health effects include kidney and immune dysfunctions.

Below, OSHA reviews the record evidence and responds to comments it received on the mechanisms underlying respirable crystalline silica-induced lung cancer and silicosis. The Agency also addresses comments regarding the use of animal studies to characterize adverse health effects in humans caused by exposure to respirable crystalline silica.

1. Mechanisms for Silica-Related Health Effects

In 2012, IARC reevaluated the available scientific information regarding respirable crystalline silica and lung cancer and reaffirmed that crystalline silica is carcinogenic to humans, i.e., a Group 1 carcinogen (Document ID 1473, p. 396). OSHA's review of all the evidence now in the rulemaking record, including the results of IARC's reevaluation, indicates that silica may lead to increased risk of lung cancer in humans by a multistage process that involves a combination of genotoxic (i.e., causing damage to cellular DNA) and non-genotoxic (i.e., not involving damage to DNA) mechanisms. Respirable crystalline silica may cause genotoxicity as a result of reactive oxygen species (ROS) produced by activated alveolar macrophages and other lung cells exposed to crystalline silica particles during phagocytosis. ROS have been shown to damage DNA in human lung cells in vitro (see Document ID 1711, pp. 236-239). This genotoxic mechanism is believed to contribute to neoplastic transformation and silica-induced carcinogenesis. ROS is not only produced during the early cellular interaction with crystalline silica but also produced by PMNs (polymorphonuclear leukocytes) and lymphocytes recruited during the inflammatory response to crystalline silica. In addition to genotoxicity contributed by ROS, it is also plausible that reactive molecules on the surface of crystalline silica itself may bind directly to DNA and result in genotoxicity (Document ID 1711, p. 236). It should be noted that the mechanistic evidence summarized above suggests that crystalline silica may cause early genotoxic events that are independent of the advanced chronic inflammatory response and silicosis (Document ID 1473, pp. 391-392).

Non-genotoxic mechanisms are also believed to contribute to the lung cancer caused by respirable crystalline silica. Phagocytic activation as well as silica-induced cytotoxicity trigger release of the aforementioned ROS, cytokines (e.g., TNFα), and growth factors (see Document ID 1711, pp. 233-235). These agents are able to cause cellular proliferation, loss of cell cycle regulation, activation of oncogenes (genes that have the potential to cause cancer), and inhibition of tumor suppressor genes, all of which are non-genotoxic mechanisms known to promote the carcinogenic process. It is plausible that these mechanisms may be involved in silica-induced tumorigenesis. The biopersistence and cytotoxic nature of crystalline silica leads to a cycle of cell death (i.e., cytotoxicity), activation of alveolar macrophages, recruitment of inflammatory cells (e.g., PMNs, leukocytes), and continual release of the non-genotoxic mediators (i.e., ROS, cytokines) able to promote carcinogenesis. The non-genotoxic mechanisms caused by early cellular responses (e.g., phagocytic activation, cytotoxicity) are regarded, along with genotoxicity, as important potential pathways that lead to the development of tumors (Document ID 1711, pp. 232-239; 1473, pp. 394-396).

The same non-genotoxic processes that may cause lung cancer from respirable crystalline silica exposure are also believed to lead to chronic inflammation, lung scarring, fibrotic lesions, and eventually silicosis. This would occur when inflammatory cells move from the alveolar space through the interstitium of the lung as part of the clearance process. In the interstitium, respirable crystalline silica-laden cells—macrophages and neutrophils—release ROS and TNF-α, as well as other cytokines, stimulating the proliferation of fibroblasts (i.e., the major lung cell type in silicosis). Proliferating fibroblasts deposit collagen and connective tissue, inducing the typical scarring that is observed with silicosis. Alternatively, alveolar epithelial cells containing respirable crystalline silica die and may be replaced by fibroblasts due to necrosis of the epithelium. This allows for uninhibited growth of fibroblasts and formation of connective tissue where scarring proliferates (i.e., silicosis). As scarring increases, there is a reduction in lung elasticity concomitant with a reduction of the lung surface area capable of gas exchange, thus reducing pulmonary function and making breathing more difficult (Document ID 0314; 0315). It should be noted that silicosis involves many of the same mechanisms that occur during the early cellular interaction with crystalline silica. Therefore, it is plausible that development of silicosis may also potentially contribute to silica-induced lung cancer. However, the relative contributions of silicosis-dependent and silicosis-independent pathways are not known.

Although it is clear that exposure to respirable crystalline silica increases the risk of lung cancer in exposed workers (see Section VI, Final Quantitative Risk Assessment and Significance of Risk), some commenters claimed that such exposure cannot cause lung cancer independently of silicosis (i.e., only those workers who already have silicosis can get lung cancer) (Document ID 2307, Attachment A, p. 53). This claim is inconsistent with the credible scientific evidence presented above that genotoxic and non-genotoxic mechanisms triggered by early cellular responses to crystalline silica prior to development of silicosis may contribute to crystalline silica-induced carcinogenesis. OSHA finds, based on its review of all the evidence in the rulemaking record, that workers without silicosis, as well as those with silicosis, are at risk of lung cancer if regularly exposed to respirable crystalline silica at levels permitted under the previous and new PELs. The Agency also emphasizes that, regardless of the mechanism by which respirable crystalline silica exposure increases lung cancer risk, the fact remains that workers exposed to respirable crystalline silica continue to be diagnosed with lung cancer at a higher rate than the general population. Therefore, as discussed in section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA has met its burden of proving that workers exposed to previously allowed levels of respirable crystalline silica are at significant risk, by one or more of these mechanisms, of serious and life-threatening health effects, including both silicosis and lung cancer.

2. Relevance of Animal Models to Humans

Animal data has been used for decades to evaluate hazards and make inferences regarding causal relationships between human health effects and exposure to toxic substances. The National Academies of Science has endorsed the use of well-conducted animal studies to support hazard evaluation in the risk assessment process (Document ID 4052, p. 81) and OSHA's policy has been to rely on such studies when regulating carcinogens. In the case of respirable crystalline silica, OSHA has used evidence from animal studies, along with human epidemiology and other relevant information, to establish that occupational exposure is associated with silicosis, lung cancer, and other non-malignant respiratory diseases, as well as renal and autoimmune effects (Document ID 1711, pp. 261-266). Exposure to various forms of respirable crystalline silica by inhalation and intratracheal instillation has consistently caused lung cancer in rats (IARC, 1997, Document ID 1062, pp. 150-163). These results led IARC and NTP to conclude that there is sufficient evidence in experimental animals to demonstrate the carcinogenicity of crystalline silica in the form of quartz dust. IARC also concluded that there is sufficient evidence in human studies for the carcinogenicity of crystalline silica in the form of quartz or cristobalite.

In its pre-hearing comments and post-hearing brief, the ACC noted that increased lung cancer risks from exposure to respirable crystalline silica have not been found in animal species other than rats, and questioned the relevance of the rat model for evaluating potential lung carcinogenicity in humans (Document ID 2307, Attachment A, p. 30; 4209, p. 32). Specifically, the ACC highlighted studies by Holland (1995) and Saffiotti et al. (1996) indicating that bioassays in respirable crystalline silica-exposed mice, guinea pigs, and Syrian hamsters have not found increased lung cancer (Document ID 2307, Attachment A, p. 30, f. 51).

The ACC proposed that the increased lung cancer risk in respirable crystalline silica-exposed rats is due to a particle overload phenomenon, in which lung clearance of nonfibrous durable particles initiates a non-specific response that results in intrapulmonary lung tumors (Document ID 2307, Attachment A, p. 30, n. 51). Dr. Cox, on behalf of the ACC, citing Mauderly (1997, included in Document ID 3600), Oberdorster (1996, Document ID 3969), and Nikula et al. (1997, included in Document ID 3600), likewise commented that rats are “uniquely sensitive to particulate pollution, for species-specific reasons that do not generalize to other rodents or mammals, including humans” (Document ID 2307, Attachment 4, p. 83). OSHA reviewed the three studies referenced by Dr. Cox and notes that two actually appear to support the use of the rat model and the third does not reject it. Mauderly (1997) noted that the rat model was the only one to correctly predict carcinogenicity after inhalation exposure to several types of asbestos, and highlighted the shortcomings of other models, such as those using hamsters, which are highly insensitive to particle-induced lung cancers (article included in Document ID 3600, pp. 1339-1343). While Mauderly (1997) advised caution when using the rat because it is the most sensitive rodent species for lung cancer, he concluded that “there is evidence supporting continued use of rats in exploration of carcinogenic hazards of inhaled particles,” and that the other test species are problematic because they provide too many false negatives to be predictive (article included in Document ID 3600, p. 1343). Similarly, Oberdorster (1996), in discussing particle parameters used in the evaluation of exposure-dose-relationships of inhaled particles, stated that “the rat model should not be dismissed prematurely” (Document ID 3969, p. 73). Oberdorster (1996) postulated that humans and rats have very similar responses to particle-induced effects when analyzing the exposure-response relationship using particle surface area, rather than particle mass, as the exposure metric. Oberdorster concluded that there simply was not enough known regarding exact mechanisms to reject the model outright (Document ID 3969, pp. 85-87). The remaining paper cited by Dr. Cox, Nikula et al. (1997), evaluated the anatomical differences between primate and rodent responses to inhaled particulate matter and the role of clearance patterns and physiological responses to inhaled toxicants. The study noted that the differences between primate clearance patterns and rat clearance patterns may play a role in the pathogenesis from inhaled poorly soluble particles but did not dismiss the rat model as irrelevant to humans (Nikula, 1997, included in Document ID 3600, pp. 83, 93, 97).

Thus, OSHA finds that the Mauderly (1997) and Oberdorster (1996) articles generally support the rat as an appropriate model for qualitatively assessing the hazards associated with particle inhalation. OSHA likewise notes that the rat model is a common and well-accepted toxicological model used to assess human health effects from toxicant inhalation (ILSI, 2000, Document ID 3906, pp. 2-9). OSHA evaluated the available studies in the record, both positive and non-positive, and believes that it is appropriate to regard positive findings in experimental studies using rats as supportive evidence for the carcinogenicity of crystalline silica. This determination is consistent with that of IARC (Document ID 1473, p. 388) and NTP (Document ID 1164, p. 1), which also regarded the significant increases in incidence of malignant lung tumors in rats from multiple studies by both inhalation and intratracheal instillation of crystalline silica to be sufficient evidence of carcinogenicity in experimental animals and, therefore, to contribute to the evidence for carcinogenicity in humans.

3. Hypothesis That Lung Cancer Is Dependent on Silicosis

The ACC asserted in its comments that “if it exists at all, silica-related carcinogenicity most likely arises through a silicosis pathway or some other inflammation-mediated mechanism, rather than by means of a direct genotoxic effect” (Document ID 2307, Attachment A, p. 52; 4209, p. 51; 2343, Attachment 1, pp. 40-44). It explained that the “silicosis pathway” means that lung cancer stems from chronic inflammatory lung damage, which in turn, “implies that there is a threshold for any causal association between silica exposure and risk of lung cancer” (Document ID 2307, Attachment A, pp. 52-53). The ACC went on to state that a mechanism that involves ROS, growth factors, and inflammatory cytokines from alveolar macrophages is “most consistent” with development of advanced chronic inflammation (e.g., epithelial hyperplasia, lung tissue damage, fibrosis, and silicosis). According to this hypothesis, silica-related lung cancer is restricted to people who have silicosis (Document ID 2307, Attachment 2, p. 7). Regarding this hypothesis, the ACC concluded, “[t]his view of the likely mechanism for silica-related lung cancer is widely accepted in the scientific community, including by OSHA's primary source of silica-related health risk estimates, Dr. Kyle Steenland. OSHA appears to share this view as well” (Document ID 2307, Attachment A, p. 54).

The ACC statement regarding acceptance by OSHA and the scientific community is inaccurate. It implies scientific consensus, as well as OSHA's concurrence, that the chronic inflammation from silicosis is the only mechanism by which crystalline silica exposure results in lung cancer. The ACC has over-simplified and neglected the findings of the mechanistic studies that show activation of phagocytic and epithelial cells to be an early cellular response to crystalline silica prior to chronic inflammation (see Document ID 1711, pp. 234-238). As discussed previously, alveolar macrophage activation leads to initial production of ROS and release of cytokine growth factors that could contribute to silica-induced carcinogenicity through both genotoxic and non-genotoxic mechanisms. The early cellular response does not require chronic inflammation and silicosis to be present, as postulated by the ACC. It is possible that the early mechanistic influences that increase cancer risk may be amplified by a later severe chronic inflammation or silicosis, if such a condition develops. However, as Brian Miller, Ph.D., stated “this issue of silicosis being a precursor for lung cancer is unanswerable, given that we cannot investigate for early fibrotic lesions in the living, but must rely on radiographs.” (Document ID 3574, Tr. 31).

In pre-hearing comments the ACC commented, as proof of silicosis being linked to lung cancer, that fibrosis was linked to adenocarcinomas (Document ID 2307, Attachment A, p. 61). This statement is misleading. As explained earlier, silicosis results from stimulation of fibroblast cells that cause lung fibrosis. Adenocarcinomas, a hallmark tumor type in respirable crystalline silica-induced lung cancer, are tumors that arise not from fibroblasts, but exclusively from lung epithelial cells (IARC, 2012, Document ID 1473, pp. 381-389, 392). These tumors may be linked to the genotoxic and non-genotoxic mechanisms that occur prior to fibrosis, not secondary to the fibrotic process itself.

OSHA also received some comments that questioned the existence of a direct genotoxic mechanism. Jonathan Borak, M.D., on behalf of the U.S. Chamber of Commerce, commented, “there is no direct evidence that silica causes cancer by means of a directly DNA-reactive mechanism” (Document ID 2376, p. 21). Dr. Peter Morfeld, on behalf of the ACC, as well as Peter Valberg, Ph.D., and Christopher M. Long, Sc.D., of Gradient Corporation, on behalf of the U.S. Chamber of Commerce, cited a scientific article by Borm et al. (2011, included in Document ID 3573) which reported finding evidence against a genotoxic mechanism and in favor of a mechanism secondary to chronic inflammation (Document ID 3458, pp. 5-7; 4016, pp. 5-6; 4209, p. 51). Borm et al. (2011, included in Document ID 3573) analyzed 245 published studies from 1996 to 2008 identified using the search terms “quartz” and `toxicity” in conjunction with “surface,” “inflammation,” “fibrosis,” and “genotoxicity.” The authors then estimated the lowest dose (in units of micrograms per cell surface area) to consistently induce DNA damage or induce markers of inflammation (e.g., IL-8 upregulation) in in vitro studies. They adjusted the in vitro doses for the lung surface area encountered in vivo and found the crystalline silica dose that produced primary genotoxicity was 60-120 times higher than the dose that produced inflammatory cytokines (Borm et al., 2011, included in Document ID 3573, p. 762). Drs. Valberg and Long concluded that Borm et al. demonstrated that genotoxicity was a secondary response to chronic inflammation, except at very high exposures at which genotoxicity independent of inflammation might occur. They also maintained that lung cancer as a secondary response to chronic inflammation is considered to have a threshold (Document ID 4016, p. 6).

OSHA reviewed the Borm et al. study (2011, Document ID 3889), and notes several limitations. The authors examined the findings from various genotoxic assays (comet assay, 8-OH-dG, micronucleus test) (Borm et al., 2011, 3889, p. 758). They reported that 40 μg/cm² was the lowest dose in vitro to produce significant direct DNA damage from crystalline silica. This genotoxic dose appears to be principally obtained from a study of a specific quartz sample (i.e., DQ12) in a single human alveolar epithelial cell line (i.e., A549 cells), even though Appendix Table 3 cited in vitro studies using other cells (e.g., fibroblasts) and other types of quartz (e.g., MinUsil) that produced direct genotoxic effects at lower doses (Borm et al., 2011, Document ID 3889, pp. 760, 769-770). This is especially pertinent since Borm et al. state that in vitro systems utilizing single-cell cultures are generally much less sensitive than in vivo systems, especially if attempting to determine oxidative stress-induced effects, since many cell culture systems use reagents that can scavenge ROS (Borm et al. 2011, Document ID 3889, p. 760). There was no indication that the authors accounted for this deficiency. They go on to conclude that their work shows a large-scale variation in hazard across different forms of quartz with regard to effects such as DNA breakage (e.g., genotoxicity) and inflammation (Borm et al. 2011, Document ID 3889, p. 762).

The extreme variation in response along with reliance on an insensitive genotoxicity test system could overestimate the appropriate genotoxic dose in human lung cells in vivo. In addition, Borm et al. used the dose sufficient to initiate production of an inflammatory cytokine (i.e., IL-8) in the A549 cell-line as the threshold for inflammation. It is not clear that an early cellular response, such as IL-8 production necessarily reflects a sustained inflammatory response. In summary, OSHA finds inconsistencies in this analysis, leaving some questions regarding the study's conclusion that silica induces genotoxicity only as a secondary response to an inflammation-driven mechanism. While the in vitro dose comparisons in this study fail to demonstrate that genotoxicity is secondary to the inflammatory response, the study findings do indicate that cellular responses to crystalline silica that drive inflammation may also lead to tumorigenesis through both genotoxic and non-genotoxic mechanisms.

Dr. Morfeld, in his hearing testimony on behalf of the ACC, referred to the paper by Borm et al. (2011) as reaching the conclusion that the mechanism of silica-related lung cancer is secondary inflammation-driven genotoxicity. As summarized by the ACC in post-hearing comments, he observed that “there are no crystalline silica particles found in the nucleus of the cells. There is nothing going on with particles in the epithelial cells inside the lung” (Document ID 4209, p. 52). In hearing testimony, however, Dr. Morfeld acknowledged that the Borm paper had limitations on extrapolating from in vitro to in vivo and cited a study by Donaldson et al. (2009), which discussed some of the limitations and the need for caution in extrapolating from in vitro to in vivo (Document ID 3582, Tr. 2076-2077; 3894, pp. 1-2). In considering this testimony, OSHA notes that the Donaldson et al. (2009) study, which includes the same authors as the Borm et al. (2011) study, acknowledged that direct interaction between respirable crystalline silica and epithelial cellular membranes induces intracellular oxidative stress which is capable of being genotoxic (Document ID 3894, p. 3). This is consistent with the OSHA position as well as the most recent IARC reevaluation of the cancer hazard from crystalline silica dust. As IARC stated in its most recent evaluation of the carcinogenicity of respirable crystalline silica under a section on direct genotoxicity and cell transformation (Document ID 1473, section 4.2.2, pp. 391-393):

Reactive oxygen species are generated not only at the particle surface of crystalline silica, but also by phagocytic and epithelial cells exposed to quartz particles. . . . Oxidants generated by silica particles and by the respiratory burst of silica-activated phagocytic cells may cause cellular and lung injury, including DNA damage (Document ID 1473, p. 391).

Given the IARC determination as well as the animal and in vitro studies reviewed herein, OSHA finds that there is no conclusive evidence that silica-related lung cancer only occurs as a secondary response to chronic inflammation, or that silicosis is a necessary prerequisite for lung cancer. Instead, OSHA finds support in the scientific literature for a conclusion that tumors may form through genotoxic as well as non-genotoxic mechanisms that result from respirable crystalline silica interaction with alveolar macrophages and other lung cells prior to onset of silicosis.

4. Hypothesis That Crystalline Silica-Induced Lung Disease Exhibits a Threshold

It is well established that silicosis arises from an advanced chronic inflammation of the lung. As noted above, a common hypothesis is that pathological conditions that depend on chronic inflammation may have a threshold. The exposure level at which silica-induced health effects might begin to appear, however, is poorly characterized in the literature (see Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases). The threshold exposure level required for a sustained inflammatory response is dependent upon multiple pro- and anti-inflammatory factors that can be quite variable from individual to individual and from species to species (Document ID 3896).

Discounting or overlooking the evidence that respirable crystalline silica may be genotoxic in the absence of chronic inflammation, Drs. Valberg and Long commented that crystalline silica follows a threshold paradigm for poorly soluble particles (PSPs). PSPs are defined generally as nonfibrous particles of low acute toxicity, which are not directly genotoxic (ILSI, 2000, Document ID 3906, p. 1). Specifically, Drs. Valberg and Long stated:

Mechanisms whereby lung cells respond to retention of a wide variety of PSPs, including crystalline silica, follow a generally accepted threshold paradigm, where the initiation of a chronic inflammatory response is a necessary step in the disease process, and the inflammatory response does not become persistent until particle retention loads become sufficient to overwhelm lung defense mechanisms. This overall progression from increased but controlled pulmonary inflammation across a threshold exposure that leads to lung damage has been described by a number of investigators (Mauderly and McCunney, 1995; ILSI, 2000; Boobis et al., 2009; Porter et al. 2004) (Document ID 2330, p. 19).

Similarly, Dr. Cox, in his post-hearing comments, discussed his 2011 article describing a quantifiable exposure-response threshold for lung diseases induced by inhalation of respirable crystalline silica (Document ID 4027, p. 29). Dr. Cox hypothesized the existence of an exposure threshold such that exposures to PSPs, which he described as including titanium dioxide, carbon black, and crystalline silica, must be intense enough and last long enough to disrupt normal homeostasis (i.e., normal cellular functions) and overwhelm normal repair processes. Under the scenario he described, a persistent state of chronic, unresolved inflammation results in a disruption of macrophage and neutrophil ability to clear silica and other foreign particles from the lung (Document ID 1470, pp. 1548-1551, 1555-1556).

OSHA disagrees with these characterizations about exposure thresholds because, among other reasons, respirable crystalline silica is not generally considered to be in the class of substances defined as PSPs. Specifically, regarding the comments of Drs. Valberg and Long, OSHA notes that the two cited documents (Mauderly and McCunney, 1995, and ILSI, 2000) summarizing workshops on PSPs did not include crystalline silica in the definition of PSP and the lung “overload” concept, instead highlighting silica's cytotoxic and genotoxic mechanisms. Mauderly and McCunney (1995) stated, “[i]t is generally accepted that the term `overload' should be used in reference to particles having low cytotoxicity, which overload clearance [mechanisms] by virtue of the mass, volume, or surface area of the deposited material (Morrow, 1992)” (p. 3, article cited in Document ID 2330, p. 19). Mauderly specifically cited quartz as a cytotoxic particle that may fall outside this definition (p. 24, article cited in Document ID 2330, p. 19). The International Life Science Institute's (ILSI) Workshop Report (2000) intended only to address particles of “low acute toxicity,” such as carbon black, coal dust, soot, and titanium dioxide (Document ID 3906, p. 1). OSHA believes that the cytotoxic nature of crystalline silica would exclude it from the class of rather nonreactive, non-toxic particles mentioned above. Therefore, the Agency concludes that most scientific experts would not include crystalline silica in the class of substances known as PSPs, nor intend for findings regarding PSPs to be extrapolated to crystalline silica.

During the public hearing, OSHA questioned Dr. Morfeld about the relevance of the rat overload response and whether he considered crystalline silica to be like other PSPs such as carbon black. Dr. Morfeld replied that he was well aware of the literature and indicated that crystalline silica was not considered one of the PSPs (specifically not like carbon black) that these reports reviewed (Document ID 3582, Tr. 2072-2074). OSHA also notes a report of the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC), which was cited by the ACC (Document ID 4209, p. 32) and stated that “particles exhibiting significant surface related (cyto)toxicity like crystalline silica (quartz) and/or other specific toxic properties do not fall under this definition [of PSPs]” (Document ID 3897, p. 5).

Respirable crystalline silica differs from PSPs because it does not require particle overload to induce the same response typical of PSPs. “Overload” refers to the consequence of exposure that results in a retained lung burden of particles that is greater than the steady-state burden predicted from deposition rates and clearance kinetics (Document ID 4174, p. 20). This is a result of a volumetric over-exposure of dust in the lung, which overwhelms macrophage function. Respirable crystalline silica does not operate on this mechanism since macrophage function is inhibited by the cytotoxic nature of respirable crystalline silica rather than a volumetric overload (Oberdorster, 1996, Document ID 3969). Therefore, respirable crystalline silica does not require particle overload to induce the same response. Studies have found that the respirable crystalline silica exposure levels required to induce tumor formation in some animal studies are similar to those observed in human studies, whereas studies involving PSPs tend to show responses at much higher levels of exposure (Muhle et al., 1991, Document ID 1284; Muhle et al., 1995, 0378; Saffiotti and Ahmed, 1995, 1121).

A study by Porter et al. (2004) demonstrated that pulmonary fibrosis induction does not require silica particle overload (Document ID 0410, p. 377). The ACC cited this study in its post-hearing brief, stating, “Porter . . . noted that the response of the rat lung to inhaled crystalline silica particles is biphasic, with a below-threshold phase characterized by increased but controlled pulmonary inflammation” (Document ID 4209, p. 52). OSHA notes that this biphasic response is due in part to the cytotoxic nature of crystalline silica, which disrupts macrophage clearance of silica particles leading to a chronic inflammatory response at less than overload conditions. While there are some mechanistic similarities, OSHA believes that the argument that crystalline silica operates on the basis of lung overload is erroneous and based on false assumptions that ignore toxicological properties unique to crystalline silica, such as cytotoxicity and the generation of intracellular ROS (Porter et al., 2002, Document ID 1114; Porter et al., 2004, 0410). As previously discussed, the generation of ROS could potentially damage cellular DNA by a genotoxic mechanism that may not exhibit a threshold.

OSHA thoroughly reviewed Dr. Cox's 2011 article (Document ID 1470), in which he proposed a threshold for crystalline silica, in its Supplemental Literature Review (Document ID 1711, Attachment 1, pp. 37-39). OSHA concluded that the evidence used to support Cox's assertion that the OSHA PEL was below a threshold for lung disease in humans was not supported by the evidence presented (Document ID 1470, p. 1543; 1711, Attachment 1). Specifically, Cox (2011) modelled a threshold level for respirable crystalline silica using animal studies of PSPs. This approach, according to the ILSI report (2000) and ECETOC report (2013), is clearly not appropriate since the cytotoxic nature of crystalline silica is not consistent with the low-toxicity PSPs (Document ID 3906, p. 1; 3897, p. 5). Dr. Cox (2011) categorized crystalline silica incorrectly as a PSP and ignored the evidence for cytotoxicity and genotoxicity associated with crystalline silica. He further failed to consider or include studies indicating a tumor response at exposure levels below that leading to an excessive chronic inflammatory response, such as Porter et al. (2002) and Muhle et al. (1995) (Document ID 1114; 0378). Thus, OSHA considers the threshold model designed by Dr. Cox (2011, Document ID 1470) and referenced by Drs. Valberg and Long (Document ID 2330) to be contradicted by the best available evidence regarding the toxicological properties of respirable crystalline silica. Although OSHA acknowledges the possible existence of a threshold for an inflammatory response, the Agency believes that the threshold is likely much lower than that advocated by industry representatives such as the ACC and the Chamber of Commerce (see Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases).

OSHA concludes that a better estimate of a threshold effect for inflammation and carcinogenesis was done by Kuempel et al. (2001, Document ID 1082). These researchers studied the minimum human exposures necessary to achieve adverse functional and pathological evidence of inflammation. They employed a physiologically-based lung dosimetry model, included more relevant studies, and considered a genotoxic effect for lung cancer (Kuempel et al., 2001, Document ID 1082; see 1711, pp. 231-232). Briefly, Kuempel et al. evaluated both linear and nonlinear (threshold) models and determined that the average minimum critical quartz lung burden (M_crit) in rats associated with reduced pulmonary clearance and increased neutrophil inflammation was 0.39 mg quartz/g lung tissue. M_crit is based on the lowest observed adverse effect level in a study in rats (Kuempel, 2001, Document ID 1082, pp. 17-23). A human lung dosimetry model, developed from respirable coal mine dust and quartz exposure and lung burden data in UK coal miners (Tran and Buchanan, 2001, Document ID 1126), was then used to estimate the human-equivalent working lifetime exposure concentrations associated with lung doses. An 8-hour time-weighted average (TWA) concentration of 0.036 mg/m³ (36 μg/m³) over a 45-year working lifetime was estimated to result in a human-equivalent lung burden to the average M_crit in rats (Document ID 1082, pp. 24-26). OSHA peer reviewer Gary Ginsburg, Ph.D., summarized, “the Kuempel et al. (2001, 2001b) rat analysis of lung threshold loading and extrapolation to human dosimetry leads to the conclusion that in the median case this threshold is approximately 3 times below the current [now former] OSHA PEL” (Document ID 3574, pp. 23). This estimated threshold would be significantly below the final PEL of 50 μg/m³.

In pre-hearing comments, ACC stated that some health organizations suggested a silicosis-dependent threshold exists for lung cancer (ACC, Document ID 2307, Attachment A, pp. 60-62). Specifically, ACC cited Environment and Health Canada as stating:

Although the mechanism of induction for the lung tumours has not been fully elucidated, there is sufficient supportive mode of action evidence from the data presented to demonstrate that a threshold approach to risk assessment is appropriate based on an understanding of the key events in the pathogenesis of crystalline silica induced lung tumours (pp. 49-51 as cited by ACC, Document ID 2307, p. 62).

In addition to the statement submitted by ACC, Environment and Health Canada also stated that:

While there is sufficient evidence to support key events in a threshold mode of action approach for lung tumours, the molecular mechanism is still not fully elucidated. Also, despite the fact that the effects seen in rats parallel the effects observed in human studies, additional mechanistic studies could further clarify why lung tumours are not seen in all experimental animals . . . Thus, the question of whether silica exposure, in the absence of silicotic response, results in lung tumours remains unanswered.” (pp. 51-52 as cited by ACC, Document ID 2307, pp. 59-61).

It should be noted that the Environment and Health Canada report was to determine general population risk of exposure to respirable crystalline silica as a fraction of PM₁₀. Environment and Health Canada found that levels 0.1-2.1 μg/m³ respirable crystalline silica were sufficiently protective for the general population because they represented a margin of exposure (MOE) 23-500 times lower than the 50 μg/m³ quartz concentration associated with silicosis in humans (pp. 50-51 as cited by ACC, Document ID 2307, pp. 59-61).

A report by Mossman and Glenn (2013) reviewed the findings from several international OEL setting panels (Document ID 4070). The report cites findings from the European Commission's Scientific Committee on Occupational Exposure Limits for respirable crystalline silica. The findings “acknowledged a No Observed Adverse Exposure Level (NOAEL) for respirable crystalline silica in the range below 0.020 mg/m³, but stated that a clear threshold for silicosis could not be identified” (Mossman and Glen, 2013; Document ID 4070, p. 655). The report went on to state that SCOEL (2002) recommended that an OEL should lie below 50 μg/m³ (Document ID 4070, p. 655). Therefore, even if silica-induced lung cancer were limited only to a mechanism that involved an inflammation-dependent threshold, OSHA concludes that exposure threshold would likely be lower than the final PEL.

5. Renal Disease and Autoimmunity

While mechanistic data is limited, other observed health effects from inhalation of respirable crystalline silica include kidney and autoimmune effects. Translocation of particles through the lymphatic system and filtration through the kidneys may induce effects in the immune and renal systems similar to the types of changes observed in the lung (Miller, 2000, Document ID 4174, pp. 40-45). A review of the available literature indicates that respirable crystalline silica most likely induces an oxidative stress response in the renal and immune cells similar to that described above (Donaldson et al., 2009, Document ID 3894).

6. Conclusion

OSHA has reviewed and responded to the comments received on the mechanistic studies of respirable crystalline silica-induced lung cancer and silicosis, as well as comments that the mechanistic data imply the existence of an exposure threshold. OSHA concludes that: (1) Lung cancer likely results from both genotoxic and non-genotoxic mechanisms that arise during early cellular responses as well as during chronic inflammation from exposure to crystalline silica; (2) there is not convincing data to demonstrate that silicosis is a prerequisite for lung cancer; (3) experimental studies in rats are relevant to humans and provide supporting evidence for carcinogenicity; (4) crystalline silica does not behave like PSPs such as titanium dioxide; and (5) any threshold for an inflammatory response to respirable crystalline silica is likely several times below the final PEL of 50 μg/m³. Thus, the best available evidence on this issue supports OSHA's findings that respirable crystalline silica increases the risk of lung cancer in humans, even in the absence of silicosis, and that lung cancer risk can be increased by exposure to crystalline silica at or below the new OSHA PEL of 50 μg/m³.

I. Comments and Responses Concerning Thresholds for Silica-Related Diseases

In this section, OSHA discusses comments focused on the issue of exposure-response thresholds for silica exposure. In the comments received by OSHA on this topic, an exposure-response “threshold” for silica exposure typically refers to a level of exposure such that no individual whose exposure is below that level would be expected to develop an adverse health effect. Commenters referred to thresholds both in terms of concentration and cumulative exposure (i.e., a level of cumulative exposure below which an individual would not be expected to develop adverse health effects). In addition to individual thresholds, some commenters referred to a “population average threshold,” that is, the mean or median value of individual thresholds across a population of workers. There is significant scientific controversy over whether any such thresholds exist for silicosis and lung cancer, as well as the cumulative exposure level or concentration at which a threshold effect may occur and whether certain statistical modeling approaches can be used to identify threshold effects.

OSHA has reviewed the evidence in the record pertaining to thresholds, and has determined that the best available evidence supports the Agency's use of non-threshold exposure-response models in its risk assessments for silicosis and lung cancer. The voluminous scientific record accrued by OSHA in this rulemaking supports lowering the existing PEL to 50 μg/m³. Rather than indicating a threshold of risk that starts above the previous general industry PEL, the weight of this evidence, including OSHA's own risk assessment models, supports a conclusion that there continues to be significant, albeit reduced, risk at the 50 μg/m³ exposure limit. OSHA's evaluation of the best available evidence on thresholds indicates that there is considerable uncertainty about whether there is any threshold below which silica exposure causes no adverse health effects; but, in any event, the weight of evidence supports the view that, if there is a threshold of exposure for the health effects caused by respirable crystalline silica, it is likely lower than the new PEL of 50 μg/m³. Commenters have not provided convincing evidence of a population threshold (e.g., an exposure level safe for all workers) above the revised PEL. In addition, OSHA's final risk assessment demonstrates that achieving this limit—which OSHA separately concludes is overall the lowest feasible level for silica-generating operations—will result in significant reductions in mortality and morbidity from occupational exposure to respirable crystalline silica.

1. Thresholds—General

In the Preliminary Quantitative Risk Assessment (QRA) (Document ID 1711, pp. 275, 282-285), OSHA reviewed evidence on thresholds from a lung dosimetry model developed by Kuempel et al. (2001, Document ID 1082) and from epidemiological analyses conducted by Steenland and Deddens (2002, Document ID 1124). As discussed in the Preliminary QRA, Kuempel et al. (2001) used kinetic lung models for both rats and humans to relate lung burden of crystalline silica and estimate a minimum critical lung burden (M_crit) of quartz above which particle clearance begins to decline and lung inflammation begins to increase (early steps in the process of developing silica-related disease). The M_crit would be achieved by a human equivalent airborne exposure to 36 μg/m³ for 45 years, based on the authors' rat-to-human lung model conversion. Exposures below this level would not lead to an excess lung cancer risk in the average individual, if it were assumed that cancer is strictly a secondary response to persistent inflammation. OSHA notes, however, that if some of the silica-related lung cancer risk occurs as a result of direct genotoxicity from early cellular interaction with respirable silica particles, then this threshold value may not be applicable. Since silicosis is caused by persistent lung inflammation, this exposure level could be viewed as a possible average threshold level for that disease as well (Document ID 1711, p. 284). As 36 μg/m³ is well below the previous general industry PEL of 100 μg/m³ and below the final PEL of 50 μg/m³, the Kuempel et al. study showed no evidence of an exposure-response threshold high enough to impact OSHA's choice of PEL.

Steenland and Deddens (2002, Document ID 1124) examined a pooled lung cancer study originally conducted by Steenland et al. (2001a). They found that a threshold model based on the log of cumulative dose (15-year lag) fit better than a no-threshold model, with the best threshold at 4.8 log mg/m³-days (representing an average exposure of 10 μg/m³ over a 45-year working lifetime). OSHA preliminarily concluded that, in the Kuempel et al. (2001) study and among the studies evaluated by Steenland et al. (2001a) in the pooled analysis, there was no empirical evidence of a threshold for lung cancer in the exposure range represented by the previous and final PELs (i.e., at 50 μg/m³ or higher) (Document ID 1711, pp. 275, 284). Thus, based on these two studies, workers exposed at or below the new PEL of 50 μg/m³ over a working lifetime still face a risk of developing silicosis and lung cancer because their exposure would be above the supposed exposure threshold.

In its prehearing comments, the ACC argued that OSHA's examination of the epidemiological evidence, along with animal studies and mechanistic considerations, “has not shown that reducing exposures below currently permitted exposure levels would create any additional health benefits for workers. OSHA's analysis and the studies on which it relies have not demonstrated the absence of an exposure threshold above 100 μg/m³ for the various adverse health effects considered in the QRA” (Document ID 2307, Attachment A, p. 26; also 2348, Attachment 1, p. 33). According to the ACC, an exposure threshold above OSHA's previous general industry PEL of 100 μg/m³ means that workers exposed below that level will not get sick, negating the need to lower the PEL (Document ID 2307, Attachment A, p. 91).

Members of OSHA's peer review panel for the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711) rejected the ACC's comments as unsupportable. Peer reviewer Mr. Bruce Allen stated: “it is essentially impossible to distinguish between dose-response patterns that represent a threshold and those that do not” in epidemiological data (Document ID 3574, p. 8). Peer reviewer Dr. Kenneth Crump similarly commented:

OSHA is on very solid ground in the [Preliminary QRA's] statement that “available information cannot firmly establish a threshold exposure for silica-related effects” . . . the hypothesis that a particular dose response does not have a threshold is not falsifiable. Similarly, the hypothesis that a particular dose response does have a threshold is not falsifiable (Document ID 3574, p. 17).

Dr. Cox, representing the ACC, agreed with Dr. Crump that “it's impossible to prove a negative, empirically . . . you could never rule out that possibility” of a threshold at a low level of exposure (Document ID 3576, Tr. 402). However, he contended that it is possible to rule out a threshold in the higher-level range of observed exposures based on observed illness: “I think that there are plenty of chemicals for which the hypothesis of a threshold exist[ing] at or above current standards could be ruled out because you see people getting sick at current levels” (Document ID 3576, Tr. 403). Other commenters stated their belief that workers recently diagnosed with silicosis must have had exposures above the previous general industry PEL and, based on this supposition, concluded that OSHA has not definitively proven risk to workers exposed below the previous general industry PEL (Document ID 4224, pp. 2-5; Tr. 3582, pp. 1951-1963).

OSHA agrees with Dr. Cox that observation of workers “getting sick at current levels” can rule out a threshold effect at those levels. As is discussed below, there is evidence that workers exposed to silica at cumulative or average exposure levels permitted under the previous PELs have become ill and died as a result of their exposure. OSHA thus strongly disagrees with any implication from commenters that the Agency should postpone reducing a PEL until it has extensive documentation of sick and dying workers to demonstrate that the current PEL is not sufficiently protective (see Section II, Pertinent Legal Authority, and Section VI, Final Quantitative Risk Assessment and Significance of Risk).

The ACC's and Chamber's comments on this issue essentially argue that the model OSHA used to assess risk was inadequate to assess whether a threshold of risk exists and, if one does exist, at what level (Document ID 2307, Attachment A, pp. 52-65; 2376, pp. 20-22; 2330, pp. 17-21). According to OSHA peer reviewer Dr. Crump, however, the analytical approach taken by OSHA in the Preliminary QRA was appropriate. Considering the inherent limitations of epidemiological data:

an attempt to distinguish between threshold and non-threshold dose responses is not even a scientific exercise . . . The best that can be done is to attempt to place bounds on the amount of risk at particular exposures consistent with the available data, which is what OSHA had done in their risk assessment (Document ID 3574, p. 17).

A further source of uncertainty in investigating thresholds was highlighted by Dr. Mirer, on behalf of the AFL-CIO (Document ID 3578, Tr. 988-989) and by peer reviewer Dr. Andrew Salmon, who stated:

[m]any of the so-called thresholds seen in epidemiological studies represent thresholds of observability rather than thresholds of disease incidence . . . studies (and anecdotal observations) with less statistical power and shorter post-exposure followup (or none) will necessarily fail to see the less frequent and later-appearing responses at lower doses. This creates an apparent threshold which is higher in these studies than the apparent threshold implied by studies with greater statistical power and longer follow-up (Document ID 3574, p. 37).

Peer reviewer Dr. Gary Ginsberg suggested that, recognizing these inherent limitations, OSHA should characterize the body of evidence and argument surrounding thresholds by discussing the following factors related to whether a threshold for silica-related health effects exists at exposure levels above the previous general industry PEL:

the choices relative to the threshold concept for the silica dose response . . . [including] specific dose response datasets that are consistent with a linear or a threshold-type model, if a threshold seems likely, where was it seen relative to the current and proposed PEL, and a general discussion of mechanism of action, measurement error and population variability as concepts that can help us understand silica dose response for cancer and non-cancer endpoints (Document ID 3574, p. 24).

Following Dr. Ginsberg's suggestion, OSHA has, in its final health and risk analysis, considered the epidemiological evidence relevant to possible threshold effects for silicosis and lung cancer. As discussed below, first in “Thresholds—Silicosis and NMRD” and then in “Thresholds—Lung Cancer,” OSHA has carefully considered comments about statistical methods, exposure measurement uncertainty, and variability as they pertain to threshold effects. The discussion addresses the epidemiological evidence with respect to both cumulative and concentration thresholds. For reference, a working lifetime (45 years) of exposure to silica at the previous general industry PEL (100 μg/m³) and the final PEL (50 μg/m³) yield cumulative exposures of 4.5 mg/m³-yrs and 2.25 mg/m³-yrs, respectively. Other sections with detailed discussions pertinent to threshold issues include Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, and Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis.

2. Thresholds—Silicosis and NMRD

OSHA has determined that the studies most relevant to the threshold issue in this rulemaking are those of workers who have cumulative exposures or average exposure concentrations below the levels associated with the previous general industry PEL (100 μg/m³, or cumulative exposure of 4.5 mg/m³-yrs). Contrary to comments that OSHA only relied on studies involving exposures far above the levels of interest to OSHA in this rulemaking, and then extrapolated exposure-response relationships down to relevant levels (e.g., Document ID 2307, Attachment A, pp. 94-95; 4226, p. 2), a number of silicosis studies included workers who were exposed at levels close to or below the previous OSHA PEL for general industry. For example, four of the six cohorts of workers in the pooled silicosis mortality risk analysis conducted by Mannetje et al. (2002) had median cumulative exposures below 2.25 mg/m³-yrs., and three had median silica concentrations below 100 μg/m³ (Mannetje et al., 2002, Document ID 1089, p. 724). Other silicosis studies with significant numbers of relatively low-exposed workers include analyses of German pottery workers (Birk et al., 2009, Document ID 4002, Attachment 2; Mundt et al., 2011, 1478; Morfeld et al., 2013, 3843), Vermont granite workers (Attfield and Costello, 2004, Document ID 0285; Vacek et al., 2011, 1486), and industrial sand workers (McDonald et al., 2001, Document ID 1091; Hughes et al., 2001, 1060; McDonald et al., 2005, 1092). In this section, OSHA will discuss each of them in relationship to whether they suggest the existence of a threshold above 100 μg/m³, the previous PEL for general industry.

a. Mannetje et al. Pooled Study and Related Analyses

Mannetje et al. (2002b, Document ID 1089) estimated excess lifetime risk of silicosis based on six of the ten cohorts that were part of the IARC multi-center exposure-response study (Steenland et al., 2001a, Document ID 0452). The six cohorts were U.S. diatomaceous earth (DE) workers, Finnish granite workers, U.S. granite workers, U.S. industrial sand workers, U.S. gold miners, and Australian gold miners. Together, the cohorts included 18,634 subjects and 170 silicosis deaths. All cohorts except the Finnish granite workers and Australian gold miners had significant numbers of workers with median cumulative and/or average exposures below the levels associated with OSHA's previous general industry PEL. Checking for nonlinearities in their exposure-response model, Mannetje et al. found that a five-knot cubic spline model (which allows for deviations, such as thresholds, from a linear relationship) did not fit the data better than the linear model used in their main analysis. The result of this attempt to check for nonlinearities suggests that there is no threshold effect in the relationship between cumulative silica exposure and silicosis risk in the study. Significantly, NIOSH stated that the results of Mannetje et al.'s analysis “suggest the absence of threshold at the lowest [cumulative] exposure analyzed . . . in fact, the trend for silicosis mortality risk extends down almost linearly to the lowest cumulative exposure stratum”, in which “the average cumulative exposure is the equivalent of 45 years of exposure at 11.1 μg/m³ silica” (Document ID 4233, pp. 34-35). This level is significantly below the new OSHA PEL of 50 μg/m³.

As discussed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, OSHA commissioned Drs. Kyle Steenland and Scott Bartell to examine the potential effects of exposure measurement error on the mortality risk estimates derived from the pooled studies of lung cancer (Steenland et al., 2001, Document ID 0452) and silicosis (Mannetje et al., 2002b, Document ID 1089). Their analysis of the pooled data, using a variety of standard statistical techniques (e.g., regression analysis), also found the data either consistent with the absence of a threshold or inconsistent with the existence of a threshold (Document ID 0469). Thus, neither Mannetje et al. nor Steenland and Bartell's analyses of the pooled cohorts suggested the existence of a cumulative exposure threshold effect; in fact, they suggested the absence of a threshold. Given the predominance in these studies of cohorts where at least half of the workers had cumulative exposures below 4.5 mg/m³-yrs, OSHA believes these results constitute strong evidence against an exposure threshold above the level of cumulative exposure resulting from long-term exposure at the previous PEL of 100 μg/m³.

b. Vermont Granite Workers

As discussed in the Supplemental Literature Review of Epidemiological Studies, Vacek et al. (2011, Document ID 1486) examined exposures from 1950 to 1999 for a group of 7,052 workers in the Vermont granite industry (Document ID 1711, Attachment 1, pp. 2-5). The exposure samples show relatively low exposures for the worker population. For the period 1950 to 2004, Verma et al. (2012), who developed the job exposure matrix used by Vacek et al., estimated that average exposure concentrations in 21 of 22 jobs were below 100 μg/m³, and 11 of the 22 job classes were at 50 μg/m³ or below. The remaining job category, laborer, had an estimated average exposure concentration of exactly 100 μg/m³ (Verma et al., 2011, Document ID 1487, p. 75).

Six of the 5,338 cohort members hired in or after 1940, when Vermont's dust control program was in effect, were identified as having died of silicosis by the end of the follow-up period (Vacek et al., Document ID 1486, p. 314). The frequency of observed silicosis mortality in the population is significant by OSHA standards (1.1 per 1,000 workers), and may be underestimated due to under-reporting of silicosis as a cause of death (see Section V.E, Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality). This observed silicosis mortality shows that deaths from silicosis occurred among workers hired after silica concentrations were reduced below OSHA's previous general industry PEL. It therefore demonstrates that a threshold for silicosis above 100 μg/m³ is unlikely.

In terms of morbidity, Graham et al.'s study of radiographic evidence of silicosis among retired Vermont granite workers found silicosis in 5.7 percent of workers hired after 1940 (equivalent to 57/1,000 workers) (Graham et al., 2004, Document ID 1031, p. 465). OSHA concludes that these studies of low-exposed workers in the Vermont granite industry show significant risk of silicosis—both mortality and morbidity—at concentrations below the previous PELs. These studies also indicate that a threshold at an exposure concentration significantly above the previous PEL for general industry, as posited by industry representatives, is unlikely.

c. U.S. Industrial Sand Workers

In an exposure-response study of 4,027 workers in 18 U.S. industrial sand plants, Steenland and Sanderson (2001) reported that approximately three-quarters of the workers with complete work histories had cumulative exposures below 1.28 mg/m³-yrs, well below the cumulative exposure of 2.25 mg/m³-yrs associated with a working lifetime of exposure at the final PEL of 50 μg/m³ (Document ID 0455, p. 700). The study identified fourteen deaths from silicosis and unspecified pneumoconiosis (~3.5 per 1,000 workers) (Document ID 0455, p. 700), of which seven occurred among workers with cumulative exposures below 1.28 mg/m³-yrs. As with other reports of silicosis mortality, this figure may underestimate the true rate of silicosis mortality in this worker population.

Hughes et al. (2001) reported 32 cases of silicosis mortality in a cohort of 2,670 workers at nine North American industrial sand plants (~12 per 1,000) (Document ID 1060, p. 203). The authors developed a job-exposure matrix based on exposure samples collected by the companies and by MSHA between 1973 and 1994, along with the 1946 exposure survey used by Steenland and Sanderson (2001, Document ID 0455; 2307, Attachment 7, p. 6). Job histories were available for 29 workers who died of silicosis. Of these, fourteen had estimated cumulative exposure less than or equal to 5 mg/m³-yrs, and seven had cumulative exposures less than or equal to 1.5 mg/m³-yrs (Document ID 1060, p. 204). Both studies clearly showed silicosis risk among workers whose cumulative exposures were comparable to those that workers could experience under the final PEL (Document ID 0455, p. 700; 1060, p. 204), indicating that a threshold above this level of cumulative exposure is unlikely.

d. German Porcelain Workers

A series of papers by Birk et al. (2009, Document ID 4002, Attachment 2; 2010, Document ID 1467), Mundt et al. (2011, Document ID 1478), and Morfeld et al. (2013, Document ID 3843) examined silicosis mortality and morbidity in a population of over 17,000 workers in the German porcelain industry. Cohort members' annual average concentrations of respirable quartz dust were reconstructed from detailed work histories and dust measurements collected in the industry from 1951 onward (Birk et al., 2009, Document ID 4002, Attachment 2, pp. 374-375). Morfeld et al. observed 40 silicosis morbidity cases (ILO profusion category 1/1 or greater), and noted that additional follow-up of the cohort might be necessary due to the long latency period of silicosis (2013, Document ID 3843, p. 1032).

Follow-up time is a critical factor for detection of silicosis, which has a typical latency of 20-30 years (see Morfeld et al., 2013, Document ID 3843, p. 1028). As stated in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, the disease latency for silicosis can extend to around 30 years. Follow-up was extremely limited in the German porcelain workers silicosis morbidity analysis, with a mean of 7.5 years of follow up for the study population (Document ID 3843). Despite the limited follow-up time, the cohort showed evidence of silicosis morbidity among low-exposed workers: 17.5 percent of cases occurred among workers whose highest average silica exposure in any year (“highest annual”) was estimated by the authors to be less than 250 μg/m³, and 12.5 percent of cases occurred among workers whose highest annual silica exposure was estimated at less than 100 μg/m³ (Document ID 3843).

The lead author of the study, Dr. Peter Morfeld, testified at the public hearings on behalf of the ACC Crystalline Silica Panel. In his post-hearing comments, Dr. Morfeld stated that “[m]echanistic considerations imply that we should not expect to see a threshold for cumulative exposure” in silicosis, but that the question of whether a threshold concentration level may exist remains (Document ID 4003, p. 3). The study by Morfeld et al. “focused on the statistical estimation of a concentration threshold . . . [and] simultaneously took into account the cumulative exposure to respirable crystalline silica dust as a driving force of the disease” (Document ID 4003, p. 3). Morfeld et al. applied a technique developed by Ulm et al. (1989, 1991) to estimate a concentration threshold. In this method a series of candidate exposure concentration values are subtracted from the estimated annual mean concentration data. Using the recalculated exposure estimates for the study population, regression analyses for each candidate are run to identify the best fitting model, using the Akaike Information Criterion (AIC) to evaluate model fit (Document ID 3843, p. 1029). According to Morfeld, the best fitting model in their study estimated a threshold concentration of 250 μg/m³ (AIC = 488.3) with a 95 percent confidence interval of 160 to 300 μg/m³. A second model with very similar fit (AIC = 488.8) estimated a threshold concentration of 200 μg/m³ with a 95 percent confidence interval of 57 μg/m³ to 270 μg/m³. A third model with a poorer fit (AIC=490.6) estimated a threshold concentration of 80 μg/m³ with a 95 percent confidence interval of 0.2 μg/m³ to 210 μg/m³ (Document ID 3843, Table 3, p. 1031).

In the Final Peer Review Report, Dr. Crump stated that Morfeld et al.'s modeling approach, like “all such attempts statistically to estimate a threshold,” is “not reliable because the threshold estimates so obtained are highly unstable” (Document ID 3574, p. 17). Dr. Morfeld's co-author, Dr. Mundt, stated in the public hearings:

I'll be the first one to tell you there is a lot of imprecision and, therefore, say confidence intervals or uncertainty should be respected, and that the—I'm hesitant to just focus on a single point number like the .25 [250 μg/m³], and prefer that you encompass the broader range that was reported in the Morfeld, on which I was an author and consistently brought this point to the table (Document ID 3577, Tr. 645).

NIOSH submitted post-hearing comments on the analysis in Morfeld et al. (2013). NIOSH pointed out that the exposure measurements in the analysis were based on German dust samplers, which for pottery have been shown to collect approximately twice as much dust as U.S. samplers. Therefore, “when Dr. Morfeld cited 0.15 mg/m³ (150 μg/m³) as the lower 95% confidence limit for the threshold, that would convert to 0.075 mg/m³ (75 μg/m³) in terms of equivalent measurements made with a U.S. sampler” (Document ID 4233, p. 21). Similarly, the U.S. equivalent of each of the other threshold estimates and confidence limits presented in Morfeld et al.'s analysis would be about half the reported exposure levels. NIOSH also commented that Morfeld et al.'s analysis appears to be consistent with both threshold and non-threshold models (Document ID 4233, p. 55). Furthermore, NIOSH observed that Morfeld et al. did not account for uncertainty in the values of one of their model parameters (ε); therefore their reported threshold confidence limits of 0.16-0.30 are too narrow (Document ID 4233, p. 56). More generally, NIOSH noted that Morfeld et al. did not quantitatively evaluate how uncertainty in exposure estimates may have impacted the results of the analysis; Morfeld agreed that he had not performed a “formal uncertainty analysis” (Document ID 4233, p. 58; 3582, Tr. 2078-2079). NIOSH concluded, “it is our firm recommendation to discount results based on the model specified in [Morfeld et al. Eq. 3] . . . including all results related to a threshold” (Document ID 4233, p. 58). OSHA has evaluated NIOSH's comments on the analysis and agrees that the issues raised by NIOSH raise serious questions about Morfeld et al.'s conclusions regarding a silica threshold.

OSHA's greater concern with Dr. Morfeld's estimate of 250 μg/m³ as a threshold concentration for silicosis is the fact that a substantial proportion of workers with silicosis in Dr. Morfeld's study had no estimated exposure above the threshold suggested by the authors; this threshold was characterized by commenters, including the Chamber of Commerce (Chamber), as a concentration “below which the lung responses did not progress to silicosis” (Document ID 4224, Attachment 1, p. 3). This point was emphasized by Dr. Brian Miller in the Final Peer Review Report (Document ID 3574, p. 57) and by NIOSH (Document ID 4233, p. 57). In the study, 17.5 percent of workers with silicosis were classified as having no exposure above Morfeld et al.'s estimated threshold of 250 μg/m³, (Document ID 3843, p. 1031) and 12.5 percent of these workers were classified as having no exposure above 100 μg/m³. OSHA believes the presence of these low-exposed workers with silicosis clearly contradicts the authors' estimate of 250 μg/m³ as a level of exposure below which no worker will develop silicosis (see Document ID 4233, p. 57).

In a post-hearing comment, Dr. Morfeld offered a different interpretation of his results, describing his threshold estimate as a “population average” which would not be expected to characterize risk for all individuals in a population. Rather, according to Dr. Morfeld “we expect to see differences in response thresholds among subjects” (Document ID 4003, p. 5). OSHA agrees with this interpretation, which was similarly expressed in several comments from OSHA's peer reviewers on the subject of thresholds (e.g., Document ID 3574, pp. 13, 21-22). Consistent with its peer reviewers' opinions, OSHA draws the conclusion from the data and discussion concerning population averages that these “differences in response thresholds among subjects” support setting the PEL at 50 μg/m³ in order to protect the majority of workers in the population of employees exposed to respirable crystalline silica. OSHA's review of the Morfeld et al. data on German porcelain workers thus reinforces its view that reducing exposures to this level will benefit the many workers who would develop silicosis at exposure levels below that of the “average” worker.

Dr. Morfeld's discussion of his estimate as a “population average” among workers with different individual responses to silica exposure echoes several comments from OSHA's peer reviewers on the subject of thresholds. In the Final Peer Review Report, Dr. Ginsberg observed that a linear exposure-response model may reflect a distribution of individual “thresholds,” such that “the population can be characterized as having a distribution of vulnerability. This distribution may be due to differences in levels of host defenses that come with differences in age, co-exposure to other chemicals, the presence of interacting background disease processes, non-chemical stressors, and a variety of other host factors” (Document ID 3574, p. 21). Given the number of factors that may influence vulnerability to certain diseases in a population of workers, Dr. Ginsberg continued:

it is logical for OSHA to strongly consider inter-subject variability . . . as the reason for linearly-appearing regression slopes in silica-related non-cancer and cancer studies. This explanation does not imply an artifact [that is, a false appearance of linear exposure-response] but that the linear (or log linear) regression coefficient extending down to low dose reflects the inherent variability in susceptibility such that the effect of concern . . . may occur in some individuals at doses well below what might be a threshold in others (Document ID 3574, pp. 21-22).

Peer reviewer Mr. Bruce Allen agreed that “[i]t makes no sense to discuss a single threshold value . . . Given, then, that thresholds must be envisioned as a distribution in the population, then there is substantial population-level risk even at the mean threshold value, and unacceptably high risk levels at exposures far below the mean threshold.” He further stated:

It is NOT, therefore, inappropriate to model the population-level observations using a non-threshold model . . . In fact, I would claim that it is inappropriate to include ANY threshold models (i.e., those that assume a single threshold value) when modeling epidemiological data. A non-threshold model for characterizing the population dose-response behavior is theoretically and practically the optimal approach (Document ID 3574, p. 13).

OSHA concludes that this German porcelain workers cohort shows evidence of silicosis among workers exposed at levels below the previous PELs, and that continued follow-up of this cohort would be likely to show greater silicosis risk among low-exposed workers due to the short follow-up time. Furthermore, the Chamber's characterization of Dr. Morfeld's result as “a threshold concentration of 250 μg/m³ below which the lung responses did not progress to silicosis” (Document ID 4224, p. 3) is plainly inaccurate, as the estimated exposures of a substantial proportion of the workers with silicosis in the data set did not exceed this level.

e. Park et al. (2002)

The ACC submitted comments on the Park et al. (2002, Document ID 0405) study which examined silicosis and lung disease other than cancer (i.e., NMRD) in a cohort of diatomaceous earth workers. The ACC's comments on this study are discussed in detail in Section V.D, Comments and Responses Concerning Silicosis and Non-Malignant Respiratory Disease Mortality and Morbidity, including comments relating to exposure-response thresholds in this study. Briefly, the ACC claimed that the Park et al. (2002) study is “fully consistent” with Morfeld's estimate of a threshold above the 100 μg/m³ concentration for NMRD, including silicosis, mortality (Document ID 2307, Attachment A, p. 107). However, NIOSH explained in its post-hearing brief that categorical analysis for NMRD indicated no threshold existed at or above a cumulative exposure corresponding to 25 μg/m³ over 40 years of exposure, which is below the cumulative exposure equivalent to the new PEL over 45 years (Document ID 4233, p. 27). Park et al. did not attempt to estimate a threshold below that level because the data lacked the power needed to discern a threshold (Document ID 4233, p. 27). OSHA agrees with NIOSH's assessment, which indicates that, if there is a cumulative exposure threshold for NMRD, including silicosis, it is significantly below the final PEL of 50 μg/m³.

f. Conclusion—Silicosis and NMRD

OSHA concludes that the body of epidemiological literature clearly demonstrates risk of silicosis and NMRD morbidity and mortality among workers who have been exposed to cumulative exposures or average exposure concentrations at or below the levels associated with the previous general industry PEL (100 μg/m³, or cumulative exposure of 4.5 mg/m³-yrs). Thus, OSHA does not agree with commenters who have stated that the previous general industry PEL is fully protective and that reducing it will yield no health benefits to silica-exposed workers (e.g., Document ID 4224, p. 2-5; Tr. 3582, pp. 1951-1963). Instead, the Agency finds that the evidence is at least as consistent with a finding that no threshold is discernible as it is with a finding that a threshold exists at some minimal level of exposure. The best available evidence also demonstrates silicosis morbidity and mortality below the previous PEL of 100 μg/m³, indicating that any threshold for silicosis (understood as an exposure level below which no one would develop disease), if one exists, is below that level. Even if the conclusion reached by Dr. Morfeld that a population average threshold exists above the level of the previous PEL is accurate, there will still be a substantial portion of the population who will develop silicosis from exposures below the identified “threshold.” These findings support OSHA's action in lowering the PEL to 50 μg/m³.

3. Thresholds—Lung Cancer

OSHA's Preliminary QRA and supplemental literature review included several studies that provide information on possible threshold effects for lung cancer. OSHA has determined that the epidemiological studies most relevant to the threshold issue are those with workers who have cumulative exposures or average exposure concentrations below the levels associated with the previous general industry PEL (100 μg/m³, or cumulative exposure of 4.5 mg/m³-yrs). As with the silicosis studies previously discussed, contrary to comments that OSHA only relied on studies involving exposures far above the levels of interest to OSHA in this rulemaking (e.g., Document ID 2307, Attachment A, pp. 94-95; 4226, p. 2), a number of lung cancer studies included workers who were exposed at levels close to or below the previous general industry PEL. Five of the 10 cohorts of workers in the pooled lung cancer risk analysis conducted by Steenland et al. (2001a) had median cumulative exposures below 4.5 mg/m³-yrs (the cumulative level associated with a working lifetime of exposure at the previous general industry PEL); four were also below 2.25 mg/m³-yrs (the cumulative level associated with a working lifetime of exposure at the revised PEL) and three had median silica concentrations below 100 μg/m³ (Document ID 0452, p. 775). Other lung cancer studies with significant numbers of relatively low-exposed workers include analyses of the Vermont granite workers (Attfield and Costello, 2004, Document ID 0285; Vacek et al., 2011, 1486) and industrial sand workers (McDonald et al., 2001, Document ID 1091; Hughes et al., 2001, 1060; McDonald et al., 2005, 1092) described in the previous discussion on silicosis. In addition to the epidemiological studies discussed here, in Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, OSHA discussed studies that have shown direct genotoxic mechanisms by which exposure to crystalline silica at any level, with no threshold effect, may lead to lung cancer.

a. Steenland et al. Pooled Lung Cancer Study and Related Analyse

Steenland et al. (2001a) estimated excess lifetime risk of lung cancer based on a 10-cohort pooled study, which included several cohorts with significant numbers of workers with median cumulative and average exposures below those allowed by the previous general industry PEL (Document ID 0452). Results indicated that 45 years of exposure at 0.1 mg/m³ (100 μg/m³) would result in a lifetime risk of 28 excess lung cancer deaths per 1,000 workers (95% confidence interval (CI) 13-46 per 1,000). An alternative (non-linear) model yielded a lower risk estimate of 17 per 1,000 (95% CI 2-36 per 1,000).

A follow-up letter by Steenland and Deddens (2002, Document ID 1124) addressed the possibility of an exposure threshold effect in the pooled lung cancer analysis conducted by Steenland et al. in 2001. According to Dr. Steenland, “We further investigated whether there was a level below which there was no increase in risk, the so-called threshold. So we fit models that had a threshold versus those that didn't, and we explored various thresholds that might apply” (Document ID 3580, Tr. 1229). Threshold models using average exposure and cumulative exposure failed to show a statistically significant improvement in fit over models without a threshold. However, the authors found that when they used the log of cumulative exposure (a transformation commonly used to reduce the influence of high exposure points on a model), a threshold model with a 15-year lag fit better than a no-threshold model. The authors reported the best threshold estimate at 4.8 log mg/m³-days (Document ID 1124, p. 781), or an average exposure of approximately 10 μg/m³ over a 45-year working lifetime, one-fifth of the final PEL. Dr. Steenland explained what his analysis indicated regarding a cumulative exposure threshold for lung cancer: “we found, in fact, that there was a threshold model that fit better than a no-threshold model, not enormously better but better statistically, but that threshold was extremely low . . . far below the . . . silica standard proposed by OSHA” (Document ID 3580, Tr. 1229).

In response to comments from ACC Panel members Dr. Valberg and Dr. Long that the analysis presented by Steenland et al. showed a clear threshold at a level of cumulative exposure high enough to bear on OSHA's choice of PEL (Document ID 2330, p. 20), Dr. Steenland explained that their conclusion was based on a misreading of an illustration in his study:

[I]f you look at the figure, you see that the curve of the spline [a flexible, nonlinear exposure-response model] starts to go up around four on the log scale of microgram per meter cubed days. And if you transform that from the log to the regular scale, that is quite consistent with the threshold we got when we did a formal analysis using the log transform model [discussed above] (Document ID 3580, Tr. 1255).

The ACC representatives' comments do appear to be based on a misunderstanding of the figure in question, due to an error in Dr. Steenland's 2001 publication in which the axis of the figure under discussion was incorrectly labeled. This error was later corrected in an erratum (Document ID 3580, Tr. 1257; Steenland et al., 2002, Erratum. Cancer Causes Control, 13:777).

In addition, at OSHA's request, Drs. Steenland and Bartell (ToxaChemica, 2004, Document ID 0469) conducted a quantitative uncertainty analysis to examine the effects of possible exposure measurement error on the pooled lung cancer study results (see Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis). These analyses showed no evidence of a threshold effect for lung cancer at the final or previous PELs. Based on Dr. Steenland's work, therefore, OSHA believes that no-threshold models are appropriate for evaluating the exposure-response relationship between silica exposure and lung cancer. Even if commenters are correct that threshold models are preferable, the threshold is likely at a level of cumulative exposure significantly below what a worker would accumulate in 45 years of exposure at the final PEL, and is therefore immaterial to this rulemaking (see Document ID 1124, p. 781).

b. Vermont Granite Workers

In the Preliminary QRA and supplemental literature review, OSHA reviewed several studies on lung cancer among silica-exposed workers in the Vermont granite industry, whose exposures were reduced to relatively low levels due to a program for dust control initiated in 1938-1940 by the Vermont Division of Industrial Hygiene (Document ID 1711, pp. 97-102; 1711, Attachment 1, pp. 2-5; 1487, p. 73). As discussed above, Verma et al. (2012) reported that all jobs in the industry had average exposure concentrations at or below 100 μg/m³—most of them well below this level—in the time period 1950-2004 after implementation of exposure controls (Document ID 1487, Table IV, p. 75).

Attfield and Costello (2004) examined a cohort of 5,414 Vermont granite workers, including 201 workers who died of lung cancer (Document ID 0285, pp. 130, 134). In this study, cancer risk was elevated at cumulative exposure levels below 4.5 mg/m³-yrs, the amount of exposure that would result from a 45-year working lifetime of exposure at the previous PEL. The authors reported elevated lung cancer in all exposure groups, observing statistically significant elevation among workers with cumulative exposures between 0.5 and 1 mg/m³-yrs (p < 0.05), cumulative exposures between 2 and 3 mg/m³-yrs (p < 0.01), and cumulative exposures between 3 and 6 mg/m³-yrs (p < 0.05) (Document ID 0285, p. 135). These findings indicate that a threshold in exposure-response for lung cancer is unlikely at cumulative exposure levels associated with 45 years of exposure at the previous PEL and below.

Vacek et al. (2011) examined a group of 7,052 men, overlapping with the Attfield and Costello cohort, who worked in the Vermont granite industry at any time between January 1, 1947 and December 31, 1998 (Document ID 1486). Like Attfield and Costello, Vacek et al. reported significantly elevated lung cancer (p < 0.01) (Document ID 1486, p. 315). Most of the lung cancer cases in Vacek et al. (305/356) had cumulative exposures less than or equal to 4.1 mg/m³-yrs (Document ID 1486, p. 316), below the cumulative exposure level of 4.5 mg/m³-yrs associated with 45 years of exposure at the previous PEL and below. However, unlike Attfield and Costello, Vacek et al. did not find a statistically significant relationship of increasing lung cancer risk with increasing silica exposure, leading Vacek et al. to conclude that increased lung cancer mortality in the cohort may not have been due to silica exposure (Document ID 1486, p. 312).

The strengths and weaknesses of both studies and the differences between them that could account for their conflicting conclusions were discussed in great detail in Section V.F, Comments and Responses Concerning Lung Cancer Mortality. For the purpose of evaluating the effects of low concentrations of silica exposure, as well as whether a threshold exposure exists, OSHA believes the Attfield and Costello study may merit greater weight than Vacek et al. As discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, OSHA believes Attfield and Costello's choice to exclude the highest exposure group from their analysis likely improved their study's estimate of the exposure-response relationship at lower exposures; by making this choice, they limited the influence of highly uncertain exposure estimates at higher levels and helped to reduce the impact of the healthy worker survivor effect. The Agency acknowledges the strengths of the Vacek et al. analysis as well, including longer follow-up of workers.

In conclusion, OSHA does not find compelling evidence in these studies of Vermont granite workers of a cumulative exposure threshold for lung cancer in the exposure range below the previous general industry PEL. This conclusion is based on the statistically significant elevations in lung cancer reported in both cohorts described above, which were composed primarily of workers whose cumulative exposures were below the level associated with a working lifetime of exposure. However, OSHA acknowledges that a strong conclusion regarding a threshold is difficult to draw from these studies, due to the disagreement between Attfield and Costello and Vacek et al. regarding the likelihood that excess lung cancer among Vermont granite workers was due to their silica exposures.

c. Industrial Sand Workers

OSHA's Preliminary QRA (Document ID 1711, pp. 285-287) evaluated a 2001 case-control analysis of industrial sand workers including 2,640 men employed before 1980 for at least three years in one of nine North American sand-producing plants. One of the sites was a large associated office complex where workers' exposures were lower than those typically experienced by production workers (Hughes et al., 2001, Document ID 1060). A later update by McDonald et al. (2005, Document ID 1091) eliminated one plant, following 2,452 men from the 8 remaining U.S. plants. Both cohorts overlapped with an earlier industrial sand cohort, including 4,626 workers at 18 plants, which was included in Steenland et al.'s pooled analysis (2001a, Document ID 0452). OSHA noted that these studies (Hughes et al., 2001, Document ID 1060; McDonald et al., 2005, 1092; Steenland and Sanderson, 2001, 0455) showed similar exposure-response patterns of increased lung cancer mortality with increased exposure.

In the Final Peer Review Report, Dr. Ginsberg commented on the relevance of the industrial sand cohort studies, which included low-exposed workers with exceptionally well-characterized exposures, for threshold issues:

With respect to the body of silica epidemiology literature, perhaps the case with the least amount of measurement error is of US industrial sand workers wherein many measurements were made with filter samples and SRD determination of crystalline silica and in which there was very careful estimation of historical exposure for both silica and smoking (MacDonald et al. 2005; Steenland and Sanderson 2001; Hughes et al. 2001) (Document ID 3574, pp. 22-23).

OSHA agrees with Dr. Ginsberg's assessment of these studies and has found them to be particularly high quality. Thus, the Agency was especially interested in the studies' findings, which showed that cancer risk was elevated at cumulative exposure levels below 4.5 mg/m³-yrs, the amount of exposure that would result from a 45-year working lifetime of exposure at the previous PEL. OSHA believes these results provide strong evidence against a threshold in cumulative exposure at any level high enough to impact OSHA's choice of PEL. Dr. Ginsberg agrees with OSHA's conclusion (Document ID 3574, p. 23).

d. Other Studies

Comments submitted by the ACC briefly mentioned several epidemiological studies that, they claim, “suggest the existence of a threshold for any increased risk of silica-related lung cancer,” including studies by Sogl et al. (2012), Mundt et al. (2011), Pukkala et al. (2005), Calvert et al. (2003), Checkoway et al. (1997), and Steenland et al. (2001a). OSHA previously reviewed several of these studies in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment, and the Supplemental Literature Review, though not with specific attention to their implications for exposure-response thresholds (Document ID 1711, pp. 139-155; 1711, Attachment 1, pp. 6-12). The studies cited by ACC are discussed below, with the exception of Steenland et al. (2001a), which was previously reviewed in this section.

e. German Porcelain Workers

OSHA reviewed Mundt et al. (2011, Document ID 1478) in its Supplemental Literature Review (Document ID 1711, Attachment 1, pp. 6-12). As discussed there, Mundt et al. examined the risks of silicosis morbidity and lung cancer mortality in a cohort of 17,644 German porcelain manufacturing workers who had participated in medical surveillance programs for silicosis between 1985 and 1987. This cohort was also examined in a previous paper by Birk et al. (2009, Document ID 4002, Attachment 2).

Quantitative exposure estimates for this cohort showed an average annual exposure of 110 μg/m³ for workers hired prior to 1960 and an average of 30 μg/m³ for workers hired after 1960. More than 40 percent of the cohort had cumulative exposures less than 0.5 mg/m³-yrs at the end of follow-up, and nearly 70 percent of the cohort had average annual exposures less than 50 μg/m³ (Mundt et al., 2011, Document ID 1478, pp. 283-284).

The lung cancer mortality hazard ratios (HRs) associated with average annual exposure were statistically significant in two of the four average annual exposure groups: 2.1 (95% CI 1.1-4.0) for average annual exposure group >50-100 μg/m³ and 2.4 (95% CI 1.1-5.2) for average annual exposure group >150-200 μg/m³, controlling for age, smoking, and duration of employment. In contrast, the HRs for lung cancer mortality associated with cumulative exposure were not statistically elevated after controlling for age and smoking.

The authors suggested the possibility of a threshold for lung cancer mortality. However, no formal threshold analysis for lung cancer was conducted in this study or in the follow-up threshold analysis conducted on this population by Morfeld et al. for silicosis (2013, Document ID 4175). Having reviewed this study carefully, OSHA believes it is inconclusive on the issue of thresholds due to the elevated risk of lung cancer seen among low-exposed workers (for example, those with average exposures of 50-100 μg/m³), which is inconsistent with the ACC's claim that a threshold exists at or above the previous PEL of 100 μg/m³, and due to several limitations which may preclude detection of a relationship between cumulative exposure and lung cancer in this cohort. As discussed in the Preliminary QRA, these include: (1) A strong healthy worker effect observed for lung cancer; (2) Mundt et al. did not follow the typical convention of considering lagged exposures to account for disease latency; and (3) the relatively young age of this cohort (median age 56 years old at time of silicosis determination) (Document ID 1478, p. 288) and limited follow-up period (average of 19 years per subject) (Birk et al. 2009, Document ID 4002, Attachment 2, p. 377). Only 9.2 percent of the cohort was deceased by the end of the follow up period. Mundt et al. (2011) acknowledged this limitation, stating that the lack of increased risk of lung cancer was a preliminary finding (Document ID 1478, p. 288).

f. German Uranium Miners

In pre-hearing comments, Dr. Morfeld described a study of 58,677 German uranium miners by Sogl et al. (2012, Document ID 3842; 2307, Attachment 2, p. 11). Dr. Morfeld noted that the study was based on a detailed exposure assessment of respirable crystalline silica (RCS) dust. According to Dr. Morfeld, Sogl et al. “showed that no lung cancer excess risk was observed at RCS dust exposure levels below 10 mg/m³-years” (Document ID 2307, Attachment 2, p. 11). OSHA's review of this publication confirmed that the authors reported a spline function with a single knot at 10 mg/m³-yrs, which Morfeld interprets to suggest a threshold for lung cancer of approximately 250 μg/m³ average exposure concentration for workers exposed over the course of 40 years. However, the authors also noted that an increase in risk below this level could not be ruled out due to strong confounding with radon, resulting in possible over-adjustment (Sogl et al., Document ID 3842, p. 9). That is, because workers with high exposures to silica would also have had high exposures to the lung carcinogen radon, the models used by Sogl et al. may have been unable to detect a relationship between silica and lung cancer in the presence of radon. As described previously, excess lung cancer has been observed among workers with lower cumulative exposures than the Sogl et al. “threshold” in other studies which do not suffer from confounding from potent lung carcinogens other than silica (for example, industrial sand workers), and which are, therefore, likely to provide more reliable evidence on the issue of thresholds. OSHA concludes that the Sogl et al. study does not provide convincing evidence of a cumulative exposure threshold for lung cancer.

g. U.S. Diatomaceous Earth Workers

Checkoway et al. (1997) investigated the risk of lung cancer among diatomaceous earth (DE) workers exposed to respirable cristobalite (a type of silica found in DE) (Document ID 0326; 1711, pp. 139-143). Exposure samples were collected primarily at one of the two plants in the study by plant industrial hygienists over a 40-year timeframe from 1948 to 1988 and used to estimate exposure for each individual in the cohort (Seixas et al., 1997, Document ID 0431, p. 593). Based on 77 deaths from cancer of the trachea, lung, and bronchus, the standardized mortality ratios (SMR) were 129 (95% CI 101-161) and 144 (95% CI 114-180) based on rates for U.S. and local county males, respectively (Document ID 0326, pp. 683-684). The authors found a positive, but not monotonic, exposure-response trend for lung cancer. The risk ratios for lung cancer with increasing quintiles of respirable crystalline silica exposure were 1.00, 0.96, 0.77, 1.26 and 2.15 with a 15-year exposure lag. Lung cancer mortality was thus elevated for workers with cumulative exposures greater than 2.1 mg/m³-yrs, but was only statistically significantly elevated for the highest exposure category (RR = 2.15; 95% CI 1.08-4.28) (Document ID 0326, p. 686). OSHA notes that this highest exposure category includes cumulative exposures only slightly higher than 4.5 mg/m³-yrs, the level of cumulative exposure resulting from a 45-year working lifetime at the previous PEL of 100 μg/m³. OSHA does not believe that the appearance of a statistically significantly elevated lung cancer risk in the highest category should be interpreted as evidence of an exposure-response threshold, especially in light of the somewhat elevated risk seen at lower exposure levels. OSHA believes it is more likely to reflect limited power to detect excess risk at lower exposure levels, a common issue in epidemiological studies which was emphasized by peer reviewer Dr. Andrew Salmon in relation to purported thresholds (Document ID 3574, p. 37).

h. Finnish Nationwide Job Exposure Matrix

OSHA reviewed Pukkala et al. (2005, Document ID 0412) in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711, pp. 153-154). As discussed there, Pukkala et al. (2005) evaluated the occupational silica exposure among all Finns born between 1906 and 1945 who participated in a national population census on December 31, 1970. Follow-up of the cohort was through 1995. Between 1970 and 1995, there were 30,137 cases of incident lung cancer among men and 3,527 among women. Exposure data from 1972 to 2000 was collected by the Finnish Institute of Occupational Health (FIOH). Cumulative exposure categories for respirable quartz were defined as: <1.0 mg/m³-yrs (low), 1.0-9.9 mg/m³-yrs (medium) and >10 mg/m³-yrs (high). For men, over 18 percent of the 30,137 lung cancer cases worked in occupations with potential exposure to silica dust. The cohort showed statistically significantly increased lung cancer among men in the lowest occupationally exposed group (those with less than 1.0 mg/m³-yrs cumulative silica exposure), as well as for men with exposures in the two higher groups (1.0-9.9 mg/m³-yrs and >10 mg/m³-yrs). For women, the cohort showed statistically significantly increased lung cancer among women with at least 1.0 mg/m³-yrs cumulative silica exposure. Given these results, it is unclear why ACC stated that Pukkula's results suggest that “excess risk of lung cancer is mainly attributable to . . . cumulative exposure exceeding 10 mg/m³-years” (Document ID 4209, p. 54). Indeed, Pukkula's analysis appears to show excess risk of lung cancer among men with any level of occupational exposure and among women whose cumulative exposures were quite low (at least equivalent to about 25 μg/m³ over 45 years). It does not support the ACC's contention that lung cancer is seen primarily in workers with exposures greater than 200 μg/m³ (Document ID 4209, p. 54), but rather suggests that any threshold for lung cancer risk would likely be well below 100 μg/m³.

i. U.S. National (27 states) Case-Control Study

As discussed in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711, pp. 152-153), Calvert et al. (2003, Document ID 3890) conducted a case-control study using 4.8 million death certificates from the National Occupational Mortality Surveillance data set. Death certificates were collected from 27 states covering the period from 1982 to 1995. Cases were persons who had died from any of several diseases of interest: Silicosis, tuberculosis, lung cancer, chronic obstructive pulmonary disease (COPD), gastrointestinal cancers, autoimmune-related diseases, or renal disease. Worker exposure to crystalline silica was categorized as no/low, medium, high, or super-high based on their industry and occupation. The authors acknowledged the potential for confounding by higher smoking rates for cases compared to controls, and partially controlled for this by eliminating white-collar workers from the control group in the analysis. Following this adjustment, the authors reported weak, but statistically significantly elevated, lung cancer mortality odds ratios (OR) of 1.07 (95% CI 1.06-1.09) and 1.08 (95% CI 1.01-1.15) for the high- and super-high exposure groups, respectively (Calvert et al., 2003, Document ID 3890, p. 126). Upon careful review of this study, OSHA maintains its position that it should not be used for quantitative risk analysis (including determination of threshold effects) because it lacks an exposure characterization based on sampling. Any determination regarding the existence or location of a threshold based on Calvert et al. (2003) must, therefore, be considered highly speculative.

j. Conclusion—Lung Cancer

In conclusion, OSHA has determined that the best available evidence on the issue of a threshold for silica-related lung cancer does not support the ACC's contention that an exposure-response threshold, below which respirable crystalline silica exposure is not expected to cause cancer, exists at or above the previous general industry PEL of 100 μg/m³. While there are some studies that claim to point to thresholds above the previous general industry PEL, multiple studies contradict this evidence, most convincingly through evidence that cohort members with low cumulative silica exposures suffered from lung cancer as a result of their exposure. These studies indicate that there is either no threshold for silica-related lung cancer, or that this threshold is at such a low level that workers cumulatively exposed at or below the level allowed by the new PEL of 50 μg/m³ will still be at risk of developing lung cancer. Thus, OSHA does not agree with commenters who have stated that the previous general industry PEL is fully protective and that reducing it will yield no health benefits to silica-exposed workers (e.g., Document ID 4224, p. 2-5; Tr. 3582, pp. 1951-1963).

4. Exposure Uncertainty and Thresholds

In his pre-hearing comments, Dr. Cox stated that the observation of a positive and monotonic exposure-response relationship in epidemiological studies “does not constitute valid evidence against the hypothesis of a threshold,” and that OSHA's findings of risk at exposures below the previous PEL for general industry “could be due simply to exposure misclassification” in studies of silica-related health effects in exposed workers (Document ID 2307, Attachment 4, pp. 41-42). His statements closely followed his analyses from a 2011 paper, in which Cox presented a series of simulation analyses designed to show that common concerns in epidemiological analyses, such as uncontrolled confounding, errors in exposure estimates, and model specification errors, can obscure evidence of an exposure-response threshold, if such a threshold exists (Document ID 3600, Attachment 7). Dr. Cox concluded that the currently available epidemiological studies “do not provide trustworthy information about the presence or absence of thresholds in exposure-response relations” with respect to an exposure concentration threshold for lung cancer (Document ID 3600, Attachment 7, p. 1548).

OSHA has reviewed Dr. Cox's comments and testimony, and concludes that uncertainty about risk due to exposure estimation and confounding cannot be resolved through the application of the statistical procedures recommended by Dr. Cox. (Similar comments from Dr. Cox about alleged biases in the studies relied upon are addressed in the next section, where OSHA reaches similar conclusions). A reviewer on the independent peer review panel, Dr. Ginsberg, commented that:

epidemiology studies will always have issues of exposure misclassification or other types of error that may create uncertainty when it comes to model specification. However, these types of error will also bias correlations to the null such that if they were sufficiently influential to obscure a threshold they may also substantially weaken regression results and underestimate the true risk (Document ID 3574, p. 23).

OSHA agrees with Dr. Ginsberg. As discussed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, a “gold standard” exposure sample is not available for the epidemiological studies in the silica literature, so it is not possible to determine the direction or magnitude of the effects of exposure misclassification on OSHA's risk estimates. The silica literature is not unique in this sense. As stated by Mr. Robert Park of NIOSH, “modeling exposure uncertainty as described by Dr. Cox . . . is infeasible in the vast majority of retrospective observational studies. Nevertheless, mainstream scientific thought holds that valid conclusions regarding disease causality can still be drawn from such studies” (Document ID 4233, p. 32).

For the reasons discussed throughout this analysis of the scientific literature, OSHA concludes that, even acknowledging a variety of uncertainties in the studies relied upon, these uncertainties are, for the most part, typical or inherent in these types of studies. OSHA therefore finds that the weight of evidence in these studies, representing the best available evidence on the health effects of silica exposure, strongly supports the findings of significant risk from silicosis, NMRD, lung cancer, and renal disease discussed in this section and in the quantitative risk assessment that follows in the next section (see Benzene, 448 U.S. at 656 (“OSHA is not required to support its finding that a significant risk exists with anything approaching scientific certainty. Although the Agency's findings must be supported by substantial evidence, 29 U.S.C. 655(f), 6(b)(5) specifically allows the Secretary to regulate on the basis of the `best available evidence.' ”)).

5. Conclusion

In summary, OSHA acknowledges that common issues with epidemiological studies limit the Agency's ability to determine whether and where a threshold effect exists for silicosis and lung cancer. However, as shown in the foregoing discussion, there is evidence in the epidemiological literature that workers exposed to silica at concentrations and cumulative levels allowable under the previous general industry PEL not only develop silicosis, but face a risk of silicosis high enough to be significant ( >1 per 1,000 exposed workers). Although the evidence is less clear for lung cancer, studies nevertheless show excess cases of lung cancer among workers with cumulative exposures in the range of interest to OSHA. Furthermore, the statistical model-based approaches proposed in public comments do not demonstrate the existence or location of a “threshold” level of silica exposure below which silica exposure is harmless to workers. The above considerations lead the Agency to conclude that any possible exposure threshold is likely to be at a low level, such that some workers will continue to suffer the health effects of silica exposure even at the new PEL of 50 μg/m³.

There is a great deal of argument and analysis directed at the question of thresholds in silica exposure-response relationships, but nothing like a scientific consensus about the appropriate approach to the question has emerged. If OSHA were to accept the ACC's claim that exposure to 100 μg/m³ silica is safe for all workers (due to a threshold at or above an exposure concentration of 100 μg/m³) and set a PEL at 100 μg/m³ for all industry sectors, and if that claim is in fact erroneous, the consequences of that error to silica-exposed workers would be grave. A large population of workers would remain at significant risk of serious occupational disease despite feasible options for exposure reduction.

J. Comments and Responses Concerning Biases in Key Studies

OSHA received numerous comments and testimony, particularly from representatives of the ACC, regarding biases in the data that the Agency relied upon to conduct its Preliminary Quantitative Risk Assessment (Preliminary QRA). In this section, OSHA focuses on these comments regarding biases, particularly with respect to how such biases may have affected the data and findings from the key peer-reviewed, published studies that OSHA relied upon in its Preliminary QRA.

The data utilized by OSHA to conduct its Preliminary QRA came from published studies in the peer-reviewed scientific literature. When developing health standards, OSHA is not required or expected to conduct original research or wait for better data or new studies (see 29 U.S.C. 655(b)(5); e.g., United Steelworkers v. Marshall, 647 F.2d 1189, 1266 (D.C. Cir. 1980), cert. denied, 453 U.S. 913 (1981)). Generally, OSHA bases its determinations of significant risk of material impairment of health on the cumulative evidence found in a number of studies, no one of which may be conclusive by itself (see Public Citizen Health Research Group v. Tyson, 796 F.2d 1479, 1495 (D.C. Cir. 1986) (reviewing courts do not “seek a single dispositive study that fully supports the Administrator's determination . . . Rather, [OSHA's] decision may be fully supportable if it is based . . . on the inconclusive but suggestive results of numerous studies.”). OSHA's critical reading and interpretation of scientific studies is thus appropriately guided by the instructions of the Supreme Court's Benzene decision that “so long as they are supported by a body of reputable scientific thought, OSHA is free to use conservative assumptions in interpreting the data with respect to carcinogens, risking error on the side of overprotection rather than underprotection” (Industrial Union Dep't v. American Petroleum Inst., 448 U.S. 607, 656 (1980)).

Since OSHA is not a research agency, it draws from the best available existing data in the scientific literature to conduct its quantitative risk assessments. In most cases, with the exception of certain risk and uncertainty analyses prepared for OSHA by its contractor ToxaChemica, OSHA had no involvement in the data generation or analyses reported in those studies. Thus, in calculating its risk estimates, OSHA used published regression coefficients or equations from key peer-reviewed, published studies, but had no control over the actual published data; nor did the Agency have access to the raw data from such studies.

As discussed throughout Section V of this preamble, the weight of scientific opinion indicates that respirable crystalline silica is a human carcinogen that causes serious, life-threatening disease at the previously-permitted exposure levels. Under its statutory mandate, the Agency can and does take into account the potential for statistical and other biases to skew study results in either direction. However, the potential biases of concern to the commenters are well known among epidemiologists. OSHA therefore believes that the scientists who conduct the studies and subject them to peer review before publication have taken the potential for biases into account in evaluating the quality of the data and analysis. As discussed further below, OSHA heard testimony from David Goldsmith, Ph.D., describing how scientists use “absolutely the best evidence they can lay their hands on” and place higher value on studies that are the least confounded by other factors that, if unaccounted for, could contribute to the effect (e.g., lung cancer mortality). (Document ID 3577, Tr. 894-895). Dr. Goldsmith also testified that many of the assertions of biases put forth in the rulemaking docket are speculative in nature, with no actual evidence presented (Document ID 3577, Tr. 901). Thus, while taking seriously the critiques of the “body of reputable scientific thought” OSHA has used to support this final silica standard, the Agency finds no reason, as discussed below, to consider discredited in any material way its key conclusions regarding causation or significant risk of harm.

In his pre-hearing comments, Dr. Cox, on behalf of the ACC, claimed that the Preliminary QRA did not address a number of sources of potential bias:

The Preliminary QRA and the published articles that it relies on do not correct for well-known biases in modeling statistical associations between exposures and response. (These include study, data, and model selection biases; model form specification and model over-fitting biases; biases due to residual confounding, e.g., because age is positively correlated with both cumulative exposure and risk of lung diseases within each age category (typically 5 or more years long); and biases due to the effects of errors in exposure estimates on shifting apparent thresholds to lower concentrations). As a result, OSHA has not demonstrated that there is any non-random association between crystalline silica exposure and adverse health responses (e.g., lung cancer, non-malignant respiratory disease, renal disease) at exposure levels at or below 100 [µg/m³]. The reported findings of such an association, e.g., based on significantly elevated relative risks or statistically significant positive regression coefficients for exposed compared to unexposed workers, are based on unverified modeling assumptions and on ignoring uncertainty about those assumptions (Document ID 2307, Attachment 4, pp. 1-2).

These biases, according to Dr. Cox, nearly always result in false positives, i.e., finding that an exposure-response relationship exists when there really is no such relationship (Document ID 3576, Tr. 380). Although his comments appear to be directed to all published, peer-reviewed studies relied upon by OSHA in estimating risks, Dr. Cox admitted at the hearing that his statements about false positives were based on his review of the Preliminary QRA with relation to lung cancer only, and that he “[didn't] really know” whether the same allegations of bias he directed at the lung cancer studies are relevant to the studies of silica's other health risks (Document ID 3576, Tr. 426). In his comments, Dr. Cox discussed each source of bias in detail; OSHA will address them in turn. The concerns expressed by commenters, including Dr. Cox, about exposure uncertainty—another potential source of bias—are addressed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis.

1. Model Specification Bias

Dr. Cox stated that model specification error occurs when the model form, such as the linear absolute risk model, does not correctly describe the data (Document ID 2307, Attachment 4, p. 21). Using a simple linear regression example from Wikipedia, Dr. Cox asserted that common indicators of goodness-of-fit, including sum of square residuals and correlation coefficients, can be weak in identifying “nonlinearities, outliers, influential single observations, and other violations of modeling assumptions” (Document ID 2307, Attachment 4, pp. 52-53). He advocated for the use of diagnostic tests to check that a model is a valid and robust choice, stating, “[u]nfortunately, OSHA's Preliminary QRA and the underlying papers and reports on which it relies are not meticulous in reporting the results of such model diagnostics, as good statistical and epidemiological practice requires” (Document ID 2307, Attachment 4, p. 21). In his post-hearing brief, Dr. Cox further described these diagnostic tests to include plots of residuals, quantification of the effects of removing outliers and influential observations, and comparisons of alternative model forms using model cross-validation (Document ID 4027, p. 2). He also suggested using Bayesian Model Averaging (BMA) or other model ensemble methods to quantify the effects of model uncertainty (Document ID 4027, p. 3).

OSHA believes that guidelines for which diagnostic procedures should be performed, and whether and how they are reported in published papers, are best determined by the scientific community through the pre-publication peer review process. Many studies in the silica literature did not report the results of diagnostic tests. For example, the Vacek et al. (2009) study of lung cancer and silicosis mortality, which was submitted to the rulemaking record by the ACC to support its position, made no mention of the results of model diagnostic tests; rather, the authors simply stated that models were fitted by maximum likelihood, with the deviance used to examine model fitting (Document ID 2307, Attachment 6, pp. 11-12). As illustrated by this example, authors of epidemiological studies do not normally report the results of diagnostic tests; nor do such authors publish their raw data. Therefore, there is no data readily available to OSHA with which it could perform the diagnostic analysis that Dr. Cox states is necessary. If the suggestion is that no well-conducted epidemiological study that failed to report a battery of diagnostic tests or disclose what they showed should be relied upon for regulatory purposes, there would be virtually no body of scientific study left for OSHA to consider, raising the legal standard for issuing toxic substance standards far above what the Benzene decision requires. Despite this, OSHA maintains that, given the large number of peer-reviewed studies in the published scientific literature on crystalline silica, subjecting each model in each study to diagnostic testing along the lines advocated by Dr. Cox would not fundamentally change the collective conclusions when examining the literature base as a whole. Despite Dr. Cox's criticisms, the scientific literature that OSHA reviewed to draw its conclusions regarding material impairment of health and used in its quantitative risk assessment, constitutes the best available evidence upon which to base this toxic substance standard, in accordance with 29 U.S.C. 655(b) and the Benzene decision and subsequent case law.

Dr. Cox's other suggested approach to addressing model uncertainty, BMA, can be used to construct a risk estimate based on multiple exposure-response models. Unlike BMA, standard statistical practice in the epidemiological literature is to evaluate multiple possible models, identify the model that best represents the observations in the data set, and use this model to estimate risk. In some cases, analysts may report the results of two or more models, along with their respective fit statistics and other information to aid model selection for risk assessment and show the sensitivity of the results to modeling choices (e.g., Rice et al., 2001, Document ID 1118). These standard approaches were used in each of the studies relied on by OSHA in its Preliminary QRA.

In contrast, BMA is a probabilistic approach designed to account for uncertainty inherent in the model selection process. The analyst begins with a set of possible models (M_i) and assigns each a prior probability (Pr[M_i]) that reflects the analyst's initial belief that model M_i represents the true exposure-response relationship. Next, a data set is used to update the probabilities assigned to the models, generating the posterior probability for each model. Finally, the models are used in combination to derive a risk estimate that is a composite of the risk estimates from each model, weighted by each model's posterior probability (see Viallefont et al., 2001, Document ID 3600, Attachment 34, pp. 3216-3217). Thus, BMA combines multiple models, and uses quantitative weights accounting for the analyst's belief about the plausibility of each model, to generate a single weighted-average risk estimate. These aspects of BMA are regarded by some analysts as improvements to the standard approaches to exposure-response modeling.

However, Kyle Steenland, Ph.D., Professor, Department of Environmental Health, Rollins School of Public Health, Emory University, the principal author of a pooled study that OSHA heavily relied upon, noted that BMA is not a standard method for risk assessment. “[Bayesian] model averaging, to my knowledge, has not been used in risk assessment ever. And so, sure, you could try that. You could try a million things. But I think OSHA has correctly used standard methods to do their risk assessment and [BMA] is not one of those standard methods” (Document ID 3580, Tr. 1259).

Indeed, BMA is a relatively new method in risk analysis. Because of its novelty, best practices for important steps in BMA, such as defining the class of models to include in the analysis, and choosing prior probabilities, have not been developed. Until best practices for BMA are established, it would be difficult for OSHA to conduct and properly evaluate the quality of BMA analyses. Evaluation of the quality of available analyses is a key step in the Agency's identification of the best available evidence on which to base its significant risk determination and benefits analysis.

OSHA also emphasizes that, as noted by Dr. Steenland, scientifically accepted and standard practices were used to estimate risk from occupational exposure to crystalline silica (Document ID 3580, Tr. 1259). Thus OSHA has decided that it is not necessary to use BMA in its QRA, and that the standard statistical methods used in the studies it relies upon to estimate risk are appropriate as a basis for risk estimation. OSHA notes that it is possible to incorporate risk estimates based on more than one model in its risk assessment by presenting ranges of risk, a strategy often used by OSHA when the best available evidence includes more than one model, analytical approach, or data set. In its Preliminary QRA, OSHA presented ranges of risks for silica-related lung cancer and silicosis based on different data sets and models, thus further lessening the utility of using more complex techniques such as BMA. OSHA continued this practice in its final risk assessment, presented in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

2. Study Selection Bias

Another bias described by Dr. Cox is study selection bias, which he stated occurs when only studies that support a positive exposure-response relationship are included in the risk assessment, and when criteria for the inclusion and exclusion of studies are not clearly specified in advance (Document ID 2307, Attachment 4, pp. 22-23). Dr. Cox noted the criteria used by OSHA to select studies, as described in the Supplemental Literature Review of Epidemiological Studies on Lung Cancer Associated with Exposure to Respirable Crystalline Silica (Supplemental Literature Review) (Document ID 1711, Attachment 1, p. 29). Dr. Cox, however, claimed that OSHA did not apply these criteria consistently, in that there may still be exposure misclassification or confounding present in the studies OSHA relied upon to estimate the risk of the health effects evaluated by the Agency (Document ID 2307, Attachment 4, pp. 24-25). Similarly, the American Foundry Society (AFS), in its post-hearing brief, asserted that, “No formal process is described for search criteria or study selection” and that OSHA's approach of identifying studies based upon the IARC (1997) and NIOSH (2002) evaluations of the literature “is a haphazard approach that is not reproducible and is subject to bias. Moreover it appears to rely primarily on information that is more than 10 years old” (Document ID 4229, p. 4).

OSHA disagrees with the arguments presented by Dr. Cox and the AFS, as did some commenters. The American Public Health Association (APHA), in its post-hearing brief, expressed strong support for OSHA's study selection methods. Dr. Georges Benjamin, Executive Director, wrote, “APHA recognizes that OSHA has thoroughly reviewed and evaluated the peer-reviewed literature on the health effects associated with exposure to respirable crystalline silica. OSHA's quantitative risk assessment is sound. The agency has relied on the best available evidence and acted appropriately in giving greater weight to those studies with the most robust designs and statistical analyses” (Document ID 2178, Attachment 1, p. 1). Similarly, Dr. Steenland testified that “OSHA has done a very capable job in conducting the summary of the literature” (Document ID 3580, Tr. 1235).

In response to the criticisms by Dr. Cox and the AFS, OSHA notes that the silica literature was exhaustively reviewed by IARC in 1997 and NIOSH in 2002 (Document ID 1062; 1110). As a result, there was no need for OSHA to initiate a new review of the historical literature. Instead, OSHA used the IARC and NIOSH reviews as a starting point for its own review. As recognized by the APHA, OSHA evaluated and summarized many of the studies referenced in the IARC and NIOSH reviews, and then performed literature searches to identify new studies published since the time of the IARC and NIOSH reviews. OSHA clearly described this process in its Review of Health Effects Literature: “OSHA has included in its review all published studies that the Agency deems relevant to assessing the hazards associated with exposure to respirable crystalline silica. These studies were identified from numerous scientific reviews that have been published previously such as the IARC (1997) and NIOSH (2002) evaluations of the scientific literature as well as from literature searches and contact with experts and stakeholders” (Document ID 1711, p. 8). For its Preliminary QRA, OSHA relied heavily on the IARC pooled exposure-response analyses and risk assessment for lung cancer in 10 cohorts of silica-exposed workers (Steenland et al., 2001a, Document ID 0452) and multi-center study of silicosis mortality (Mannetje et al., 2002b, Document ID 1089). As stated in the Review of Health Effects Literature, these two studies “relied on all available cohort data from previously published epidemiological studies for which there were adequate quantitative data on worker exposures to crystalline silica to derive pooled estimates of disease risk” (Document ID 1711, p. 267).

In addition to relying on these two pooled IARC multi-center studies, OSHA also identified single cohort studies with sufficient quantitative information on exposures and disease incidence and mortality rates. As pointed out by Dr. Cox, OSHA described the criteria used for selection of the single cohort studies of lung cancer mortality:

OSHA gave studies greater weight and consideration if they (1) included a robust number of workers; (2) had adequate length of follow-up; (3) had sufficient power to detect modest increases in lung cancer incidence and mortality; (4) used quantitative exposure data of sufficient quality to avoid exposure misclassification; (5) evaluated exposure-response relationships between exposure to silica and lung cancer; and (6) considered confounding factors including smoking and exposure to other carcinogens (Document ID 1711, Attachment 1, p. 29).

Using these criteria, OSHA identified four single-cohort studies of lung cancer mortality that were suitable for quantitative risk assessment; two of these cohorts (Attfield and Costello, 2004, Document ID 0285; Rice et al., 2001, 1118) were included among the 10 used in the IARC multi-center study and two appeared later (Hughes et al., 2001, Document ID 1060; Miller and MacCalman, 2009, 1306) (Document ID 1711, p. 267). For NMRD mortality, in addition to the IARC multi-center study (Mannetje et al., 2002b, Document ID 1089), OSHA relied on Park et al. (2002) (Document ID 0405), who presented an exposure-response analysis of NMRD mortality (including silicosis and other chronic obstructive pulmonary diseases) among diatomaceous earth workers (Document ID 1711, p. 267). For silicosis morbidity, several single-cohort studies with exposure-response analyses were selected (Chen et al., 2005, Document ID 0985; Hnizdo and Sluis-Cremer, 1993, 1052; Steenland and Brown, 1995b, 0451; Miller et al., 1998, 0374; Buchanan et al., 2003, 0306) (Document ID 1711, p. 267).

With respect to Dr. Cox's claim that OSHA did not apply its criteria consistently, on the basis that there may still be exposure misclassification or confounding present, OSHA notes that it selected studies that best addressed the criteria; OSHA did not state that it only selected studies that addressed all of the criteria. Given the fact that some of the epidemiological studies concern exposures of worker populations dating back to the 1930's, there is always some potential for exposure misclassification or the absence of information on smoking. When this was the case, OSHA discussed these limitations in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711). For example, OSHA discussed the lack of smoking information for cases and controls in the Steenland et al. (2001a, Document ID 0452) pooled lung cancer analysis (Document ID 1711, pp. 150-151).

With respect to the AFS's claim that OSHA relied on studies that were more than 10 years old, OSHA again notes that it reviewed, in its Review of Health Effects Literature and its Supplemental Literature Review, the studies in the silica literature and selected the ones that best met the criteria described above (Document ID 1711; 1711, Attachment 1). It would be improper to only select the most recent studies, particularly if the older studies are of higher quality based on the criteria. Furthermore, the studies OSHA relied upon in its Preliminary QRA were published between 1993 and 2009; the claim that OSHA primarily relied on older studies is thus misleading, when the studies were of relatively recent vintage and determined to be of high quality based on the criteria described above. The AFS also suggested that OSHA examine several additional foundry studies of lung cancer (Document ID 2379, Attachment 2, p. 24); OSHA retrieved all of these suggested studies, added them to the rulemaking docket following the informal public hearings, and discusses them in Section V.F, Comments and Responses Concerning Lung Cancer Mortality.

3. Data Selection Bias

A related bias presented by Dr. Cox is data selection bias, which he stated occurs when only a subset of the data is used in the analysis “to guarantee a finding of a positive” exposure-response relationship (Document ID 2307, Attachment 4, p. 26). He provided an example, the Attfield and Costello (2004, Document ID 0285) study of lung cancer mortality, which excluded data as a result of attenuation observed in the highest exposure group (Document ID 2307, Attachment 4, pp. 26-27). Attenuation of response means the exposure-response relationship leveled off or decreased in the highest exposure group. Referring to another study of the same cohort, Vacek et al. (2009, Document ID 2307, Attachment 6; 2011, 1486), Dr. Cox stated, “OSHA endorses the Attfield and Costello findings, based on dropping cases that do not support the hypothesis of an ER [exposure-response] relation for lung cancer, while rejecting the Vacek et al. study that included more complete data (that was not subjected to post hoc subset selection) but that did not find a significant ER [exposure-response] relation” (Document ID 2307, Attachment 4, pp. 26-27).

OSHA believes there are very valid reasons for the observance of attenuation of response in the highest exposure group that would justify the exclusion of data in Attfield and Costello (2004, Document ID 0285) and other studies. This issue was discussed by Gary Ginsberg, Ph.D., an OSHA peer reviewer from the Connecticut Department of Public Health, in his post-hearing comments. Dr. Ginsberg noted that several epidemiological studies have found an attenuation of response at higher doses, with possible explanations including: (1) Measurement error, which arises from the fact that the highest doses are associated with the oldest datasets, which are most prone to measurement error; (2) “intercurrent causes of mortality” from high dose exposures that result in death to the subject prior to the completion of the long latency period for cancer; and (3) the healthy worker survivor effect, which occurs when workers with ill health leave the workforce early (Document ID 3574, p. 24). As discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, OSHA disagrees strongly with Dr. Cox's assertion that data were excluded to ensure a positive exposure-response relationship (Document ID 2307, Attachment 4, p. 26). In addition, as detailed in Section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA calculated quantitative risk estimates for lung cancer mortality from several other studies that did not rely on a subset of the data (Rice et al., 2001, Document ID 1118; Hughes et al., 2001, 1060; Miller and MacCalman, 2009, 1306; ToxaChemica, 2004, 0469; 1711, p. 351). These studies also demonstrated positive exposure-response relationships.

4. Model Selection Bias

Another selection bias presented by Dr. Cox is model selection bias, which he said occurs when many different combinations of models, including alternative exposure metrics, different lags, alternative model forms, and different subsets of data, are tried with respect to their “ability to produce `significant'-looking regression coefficients” (Document ID 2307, Attachment 4, p. 27). This is another aspect of model specification error, as discussed above under model averaging. Dr. Cox wrote:

This type of multiple testing of hypotheses and multiple comparisons of alternative approaches, followed by selection of a final choice based [on] the outcomes of these multiple attempts, completely invalidates the claimed significance levels and confidence intervals reported for the final ER [exposure-response] associations. Trying in multiple ways to find a positive association, and then selecting a combination that succeeds in doing so and reporting it as `significant,' while leaving the nominal (reported) statistical significance level of the final selection unchanged (typically at p=0.05), is a well-known recipe for producing false-positive associations (Document ID 2307, Attachment 4, p. 28).

Dr. Cox further stated that unless methods of significance level reduction (i.e., reducing the nominal statistical significance level of the final selection) are used, the study is biased towards false-positive results (Document ID 2307, Attachment 4, p. 28).

During the informal public hearings, counsel for the ACC asked Mr. Park of NIOSH's Risk Evaluation Branch about this issue, i.e., trying a number of modeling choices, including exposure metrics, log-transformations, lag periods, and model subsets (Document ID 3579, Tr. 149-150). Mr. Park's reply supports the use of multiple modeling choices in the risk assessment as a form of sensitivity analysis:

Investigations like this look at a number of options. They come into the study not totally naïve. They, in fact, have some very strong preference even before looking at the data based on prior knowledge. So cumulative exposure, for example, is a generally very high confidence choice in a metric. Trying different lags is interesting. It helps validate the study because you know what it ought to look like sort of. And in many cases, the choice does not make a lot of difference. So it's kind of a robust test, and similarly, the choice of the final model is not just coming in naïve. A linear exposure response has a lot of biological support in many different contexts, but it could be not the best choice (Document ID 3579, Tr. 150-151).

ACC counsel further asked, “And does one at the end of this process, though, make any adjustment in what you consider to be the statistically significant relationship in light of the fact that you've looked at so many different models and arrangements?” (Document ID 3579, Tr. 151-152). Mr. Park replied, “No, I don't think that's a legitimate application of a multiple comparison question” (Document ID 3579, Tr. 152). OSHA agrees with Mr. Park that significance level reduction is not appropriate in the context of testing model forms for risk estimation, and notes that, in the Agency's experience, significance level reduction is not typically performed in the occupational epidemiology literature. In addition, OSHA notes that, in many of the key studies relied upon by the Agency to estimate quantitative risks, the authors presented the results of multiple models that showed statistically significant exposure-response relationships. For example, Rice et al. (2001) presented the results of six model forms, with all except one being significant (Table 1, Document ID 1118, p. 41). Attfield and Costello (2004) presented the results of their model with and without a 15-year lag and log transformation, with many results being significant (Table VII, Document ID 0285, p. 135). Thus, OSHA concludes that model selection bias is not a problem in its quantitative risk assessment.

Furthermore, OSHA disagrees with Dr. Cox's assertion that modeling choices are used to “produce `significant'-looking regression coefficients” (Document ID 2307, Attachment 4, p. 27). OSHA believes that the investigators of the studies it relied upon in its Preliminary, and now final, QRA made knowledgeable modeling choices based upon the exposure distribution and health outcome being examined. For example, in long-term cohort studies, such as those of lung cancer mortality relied upon by OSHA, most authors relied upon cumulative exposure (mg/m³-yrs or mg/m³-days), i.e., the concentration of crystalline silica exposure (mg/m³) multiplied by the duration of exposure (years or days), as an exposure metric. Consistent with standard statistical techniques used in epidemiology, the cumulative exposure metric may then be log-transformed to account for an asymmetric distribution with a long right tail, or attenuation, and the metric may be lagged by several years to account for the long latency period between the exposure and the development of lung cancer. When investigators use subsets of the data, they typically explain the rationale and the effect of using the subset in the analysis. These choices all have important justifications and are not used purely to produce the authors' desired results, as Dr. Cox suggested (Document ID 2307, Attachment 4, p. 27).

5. Model Uncertainty Bias

Related to model selection bias is Dr. Cox's assertion of model uncertainty bias, which he said occurs when many different models are examined and then one is selected on which to base risk calculations; this approach “treats the finally selected model as if it were known to be correct, for purposes of calculating confidence intervals and significance levels. But, in reality, there remains great uncertainty about what the true causal relation between exposure and response looks like (if there is one)” (Document ID 2307, Attachment 4, pp. 28-29). He further stated that ignoring this bias leads to artificially narrow confidence intervals, which bias conclusions towards false-positive findings. He then cited a paper (Piegorsch, 2013, included in Document ID 3600) describing statistical methods for overcoming this bias by “including multiple possible models in the calculation of results” (Document ID 2307, Attachment 4, p. 29). OSHA concludes this bias is really an extension of model specification error and model selection bias, previously discussed, and maintains that best practices for model averaging have not yet been established, making it difficult for the Agency to conduct and properly evaluate the quality of BMA analyses.

6. Model Over-Fitting Bias

Next, Dr. Cox discussed model over-fitting bias, which he said occurs when the same data set is used both to fit a model and to assess the fit; this “leads to biased results: Estimated confidence intervals are too narrow (and hence lower confidence limits on estimated ER [exposure-response] slopes are too high); estimated significance levels are too small (i.e., significance is exaggerated); and estimated measures of goodness-of-fit overstate how well the model fits the data” (Document ID 2307, Attachment 4, p. 39). He suggested using appropriate statistical methods, such as “k-fold cross-validation,” to overcome the bias (Document ID 2307, Attachment 4, p. 39).

OSHA does not agree that using the same data set to fit and assess a model necessarily results in an over-fitting bias. The Agency understands over-fitting to occur when a model is excessively complex relative to the amount of data available such that there are a large number of predictors relative to the total number of observations available. For survival models, it is the number of events, i.e., deaths, that is relevant, rather than the size of the entire sample (Babyak, 2004, included in Document ID 3600, p. 415). If the number of predictors (e.g., exposure, age, gender) is small relative to the number of events, then there should be no bias from over-fitting. In an article cited and submitted to the rulemaking docket by Dr. Cox, Babyak (2004) discussed a simulation study that found, for survival models, an unacceptable bias when there were fewer than 10 to 15 events per independent predictor (included in Document ID 3600, p. 415). In the studies that OSHA relied on in its Preliminary QRA, there were generally a large number of events relative to the small number of predictors. For example, in the Miller and MacCalman (2009) study of British coal miners, in the lung cancer model using both quartz and coal dust exposures, there was a large number of events (973 lung cancer deaths) relative to the few predictors in the model (quartz exposure, coal dust exposure, cohort entry date, smoking habits at entry, cohort effects, and differences in regional background cause-specific rates) (Document ID 1306, pp. 6, 9). Thus, OSHA does not agree the studies it relied upon were substantially influenced by over-fitting bias. OSHA also notes that k-fold cross-validation, as recommended by Dr. Cox, is not typically reported in published occupational epidemiology studies, and that the studies the Agency relied upon in the Preliminary QRA were published in peer-reviewed journals and used statistical techniques typically used in the field of occupational epidemiology and epidemiology generally.

7. Residual Confounding Bias

Dr. Cox also asserted a bias due to residual confounding by age. Bias due to confounding occurs in an epidemiological study, in very general terms, when the effect of an exposure is mixed together with the effect of another variable (e.g., age) not accounted for in the analysis. Residual confounding occurs when additional confounding factors are not considered, control of confounding is not precise enough (e.g., controlling for age by using groups with age spans that are too wide), or subjects are misclassified with respect to confounders (Document ID 3607, p. 1). Dr. Cox stated in his comments that:

key studies relied on by OSHA, such as Park et al. (2002), do not correct for biases in reported ER [exposure-response] relations due to residual confounding by age (within age categories), i.e., the fact that older workers may tend to have both higher lung cancer risks and higher values of occupational exposure metrics, even if one does not cause the other. This can induce a non-causal association between the occupational exposure metrics and the risk of cancer (Document ID 2307, Attachment 4, p. 29).

The Park et al. (2002) study of non-malignant respiratory disease mortality, which Dr. Cox cited as not considering residual confounding by age, used 13 five-year age groups (<25, 25-29, 30-34, etc.) in the models (Document ID 0405, p. 37). Regarding this issue in the Park et al. (2002) study, in its post-hearing comments, NIOSH stated:

This is a non-issue. The five-year categorization was used only for deriving the expected numbers of cases as an offset in the Poisson analysis using national rates which typically are classified in five-year intervals (on age and chronological time). The cumulative exposures were calculated with a 10-day resolution over follow-up and then averaged across observation time within 50 cumulative exposure levels cross-classified with the five-year age-chronological time cells of the classification table. There would be virtually no confounding between age and exposure [using this approach] (Document ID 4233, p. 33).

OSHA agrees with this assessment, noting that it appears that age groups were adequately constructed to prevent residual confounding. OSHA thus rejects this assertion of residual confounding by age in the Park et al. (2002) study.

8. Summary of Biases

In summary, OSHA received comments and heard testimony on potential biases in the studies upon which it relied for its QRA. The ACC's Dr. Cox, in particular, posited a long list of biases, including model form specification bias, study selection bias, data selection bias, model selection bias, model over-fitting bias, model uncertainty bias, residual confounding bias, and bias as a result of exposure measurement error. OSHA, in this section, has specifically addressed each of these types of bias (except for bias due to exposure estimation error, which is addressed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis).

In addition, OSHA heard testimony that countered the claims of biases and their potential to cause false positive results. When asked about the biases alleged by Dr. Cox and Dr. Long, Dr. Goldsmith testified, “All of these other things, it seems to me, are smoke screens for an inability to want to try and see what the body of evidence really shows” (Document ID 3577, Tr. 895-896). Later in his testimony, when asked about exposure misclassification, Dr. Goldsmith similarly noted, “[a]nd for a lot of the arguments that are being put forward by industry, they are speculating that there is the potential for these biases, but they haven't gotten, [from] my perspective, the actual evidence that this is the case” (Document ID 3577, Tr. 901). Similarly, OSHA has reviewed the record evidence extensively and is not aware of any specific, non-speculative evidence of biases in the studies that it relied upon.

There also is a question of the extent to which Dr. Cox actually reviewed all of the studies that he asserted to be biased. Upon questioning from Anne Ryder, Attorney in the Office of the Solicitor, Department of Labor, Dr. Cox admitted that he had not examined the issue of silica and silicosis, and that his statements about false positives were based on his review of the Preliminary QRA with relation to lung cancer only:

MS. RYDER: . . . You talked a little bit earlier about the false positives that are . . . present with a lot of the studies on lung cancer. And, but I believe, in your comment you didn't say that there are any of those same false positives with studies dealing with silicosis and silica exposure. Is that correct?

DR. COX: I don't think I opined on that. So—and I really haven't looked carefully at the question. I do take it as given that silica at sufficiently high and prolonged exposures causes silicosis. I've not really examined that literature.

MS. RYDER: So you don't think that those studies have the same issues that some of the lung cancer studies have?

DR. COX: I don't really know (Document ID 3576, Tr. 426).

Dr. Cox further testified, regarding the likelihood that the conclusions of the Preliminary QRA for silicosis are correct, “I expect that the evidence is much stronger for silica and silicosis. But I haven't reviewed it, so I can't testify to it” (Document ID 3576, Tr. 427).

OSHA believes this testimony to be inconsistent with some of the broad conclusions in Dr. Cox's pre-hearing written submission to the rulemaking record, in which he claimed that all adverse outcomes in the Preliminary QRA may have been affected by false positives. Dr. Cox concluded in this submission that:

These multiple uncontrolled sources of false-positive bias can generate findings of statistically “significant” positive ER [exposure-response] associations even in random data, or in data for which there is no true causal relation between exposure and risk of adverse health responses. Because OSHA's Preliminary QRA and the studies on which it relies did not apply appropriate technical methods (which are readily available, as discussed in the references) to diagnose, avoid, or correct for these sources of false-positive conclusions, the reported findings of “significantly” positive ER [exposure-response] associations between crystalline silica exposures at and below the current PEL and adverse outcomes (lung cancer, non-malignant lung disease, renal disease) are not different from what might be expected in the absence of any true ER [exposure-response] relations. They therefore provide no evidence for (or against) the hypothesis that a true ER [exposure-response] relation exists. Thus, OSHA has not established that a non-random association exists between crystalline silica exposures at or below the current PEL and the adverse health effects on which it bases its determination of significant risk and calculates supposed health effect benefits (Document ID 2307, Attachment 4, pp. 29-30).

OSHA notes that “non-malignant lung disease” includes silicosis, studies of which Dr. Cox subsequently testified that he did not examine.

In conclusion, the studies relied upon by OSHA for its risk assessment were peer-reviewed and used methods for epidemiology and risk assessment that are commonly used. Dr. Cox provided no study-specific evidence (e.g., data re-analysis) to support his comments that the studies OSHA relied upon were adversely affected by numerous different types of bias. As described above, OSHA recognizes that there are uncertainties associated with the results of the studies relied on for its risk assessment, as is typically the case for epidemiological studies such as these. Nevertheless, as previously stated, OSHA maintains that it has used a body of peer-reviewed scientific literature that, as a whole, constitutes the best available evidence of the relationship between respirable crystalline silica exposure and silicosis, lung cancer, and the other health effects studied by the Agency in promulgating this final rule.

K. Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis

Exposure estimation error, a typical feature of epidemiological studies, occurs when the authors of an exposure-response study construct estimates of the study subjects' exposures using uncertain or incomplete exposure data. Prior to the publication of its Preliminary Quantitative Risk Assessment (Preliminary QRA), the Agency commissioned an uncertainty analysis conducted by Drs. Kyle Steenland and Scott Bartell, through its contractor, ToxaChemica, Inc., to address exposure estimation error in OSHA's risk assessment, and incorporated the results into the Preliminary QRA. After reviewing comments submitted to the record on the topic of exposure estimation error, OSHA maintains that it has relied upon the best available evidence by: (1) Using high-quality exposure-response studies and modeling approaches; (2) performing an uncertainty analysis of the effect of exposure estimation error on the risk assessment results; and (3) further submitting that analysis to peer review. OSHA concludes from its uncertainty analysis that exposure estimation error did not substantially affect the results in the majority of studies examined (Document ID 1711, pp. 299-314).

Furthermore, having carefully considered the public comments criticizing ToxaChemica's uncertainty analysis, OSHA has concluded that it was not necessary to conduct additional analyses to modify the approach adopted by Drs. Steenland and Bartell in the uncertainty analysis. Nor was it necessary to incorporate additional sources of uncertainty in the analysis. Also, given the evidence in the rulemaking record that these estimation errors bias results towards underestimating rather than overestimating the risks from exposure in many circumstances, it is very unlikely that regression coefficients and risk estimates from all of the different studies relied on in the Preliminary QRA were biased upward. Accordingly, OSHA remains convinced that the conclusions of the Agency's risk assessment are correct and largely unaffected by potential error in exposure measurement.

OSHA received significant comments on the topic of exposure estimation error in the studies it relied on in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711). A number of commenters discussed the importance of accounting for exposure estimation error. Dr. Cox, representing the ACC, described exposure estimation error as perhaps the “most quantitatively important” issue in the studies OSHA relied upon (Document ID 2307, Attachment 4, p. 40). Similarly, Christopher M. Long, Sc.D., Principal Scientist at Gradient, representing the U.S. Chamber of Commerce (Chamber), testified that exposure measurement error is a “common source of uncertainty in most occupational and environmental epidemiologic studies” (Document ID 3576, Tr. 298). According to Dr. Long, this type of error can lead to inaccurate risk estimates by creating error in the exposure-response curve derived from a data set and obscuring the presence of a threshold (Document ID 3576, Tr. 300; see Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases, for further discussion on thresholds). Dr. Long further stated that exposure measurement error can lead to over- or under-estimation of risk: “the impact of exposure measurement error . . . can bias either high or low. It can bias towards the null. It can be a source of positive bias.” (Document ID 3576, Tr. 358-359). A bias to the null in an exposure-response model used in a quantitative risk assessment is an underestimation of the relationship between exposure level and the rate of the disease or health effect of interest, and results in underestimation of risk.

OSHA agrees with the assessments of the ACC and the Chamber with respect to the importance of exposure measurement error. Indeed, OSHA peer reviewer, Dr. Gary Ginsberg, in his peer review comments (Document ID 3574, p. 21), and OSHA's risk assessment contractor, Dr. Steenland, in his hearing testimony (Document ID 3580, Tr. 1266-1267), noted the potential for exposure measurement error to bias exposure-response coefficients towards the null. Dr. Steenland explained: “misclassification I would say in general tends to bias things to the null. It's harder to see positive exposure-response trends in the face of misclassification. It depends partly on the type of error. . . . But, on the whole, I would say that exposure measurement tends to bias things down rather than up” (Document ID 3580, Tr. 1266-1267). Fewell et al., the authors of a paper on residual confounding submitted by the ACC, wrote, “It is well recognized that under certain conditions, nondifferential measurement error in the exposure variable produces bias towards the null” (2007, Document ID 3606, p. 646).

Several commenters representing the ACC challenged the methods used in ToxaChemica's uncertainty analysis on the grounds that the analysis failed to adequately address exposure estimation error. In spite of their criticisms, critics were unable to supply better studies than those OSHA used. Indeed, when asked during the hearing, Dr. Long was unable to identify any studies that the Agency could use that acceptably account for the impact of exposure measurement error on exposure-response associations for crystalline silica (Document ID 3576, Tr. 356-357), and none was supplied following the hearings.

Taking into account the record evidence discussed above, OSHA concludes that it is possible for exposure measurement error to lead to either over- or under-estimation of risk and that this issue of exposure measurement error is not specific to the silica literature. It further concludes that industry representatives could not identify, and failed to submit, any published epidemiological studies of occupational disease that corrected for such bias to their satisfaction (Document ID 3576, Tr. 356-357).

Nevertheless, because OSHA agreed that an analysis of exposure estimation error as a source of uncertainty is important, it commissioned the uncertainty analysis discussed above to explore the potential effects of exposure measurement error on the conclusions of OSHA's risk assessment (Document ID 0469). The analysis examined the potential effects of exposure measurement error on the mortality risk estimates derived from the pooled studies of lung cancer (Steenland et al. 2001a, Document ID 0452) and silicosis (Mannetje 2002b, Document ID 1089). This included the effects of estimation error on the detection and location of a possible threshold effect in exposure-response models.

The uncertainty analysis OSHA commissioned from Drs. Steenland and Bartell (2004, Document ID 0469) addressed possible error in silica exposure estimates from: (1) Random error in individual workers' exposure estimates and (2) error in the conversion of dust measurements (typically particle count concentrations) to gravimetric respirable silica concentrations, which could have affected estimates of average exposure for job categories in the job-exposure matrices used to estimate workers' silica exposure. To address possible error in individual workers' exposure estimates, the analysts performed a Monte Carlo analysis, a type of simulation analysis which varies the values of an uncertain input to an analysis (in this case, exposure estimates) to explore the effects of different values on the outcome of the analysis. The Monte Carlo analysis sampled new values for workers' job-specific exposure levels from distributions they believed characterized the exposures of individual workers in each job. In each run of the Monte Carlo analysis, the sampled exposure values were used to calculate new estimates of each worker's cumulative exposures, and the resulting set was used to fit a new exposure-response model.

Similarly, the analysts performed a Monte Carlo analysis to address the issue of uncertainty in conversion from dust to respirable silica exposure, sampling new conversion factors from a normal distribution with means equal to the original conversion factor, calculating new estimates of workers' cumulative exposures, and re-fitting the exposure-response model for each Monte Carlo run. To examine the sensitivity of the model to the joint effects of both error types, the analysts ran 50 Monte Carlo simulations using the sampling procedure for both individual exposures and job-specific conversion factors. They also examined the effects of systematic bias in conversion factors, considering that these may have been consistently under-estimated or over-estimated for any given cohort. They addressed possible biases in either direction, conducting 20 simulations where the true silica content was assumed to be either half or double the estimated silica content of measured exposures.

The results of their analysis indicated that the conclusions of the pooled lung cancer study conducted previously by Steenland et al. (Document ID 0452) and included in OSHA's Preliminary QRA were unlikely to be affected by the types of exposure estimation error examined by Drs. Steenland and Bartell, whose analysis of the underlying data was itself reviewed by OSHA's peer review panel. As explained below, after reviewing comments critical of the uncertainty analysis, OSHA reaffirms its conclusion that workers exposed to silica at the previous PELs are at significant risk of disease from their exposure.

Drs. Long and Valberg, representing the Chamber, commented that Drs. Steenland and Bartell's uncertainty analysis did not address all potential sources of error and variability in exposure measurement, such as possible instrument error; possible sampling error; random variability in exposure levels; variability in exposure levels resulting from changes in worker job functions during work shifts, production process changes, or control system changes; variability in sampler type used; variability in laboratory methods for determining sampling results and laboratory errors; variability in duration of exposure sampling; variability in sampling locations; variability in reasons for sample data collection (e.g., compliance sampling, periodic sampling, random survey sampling); variability in type of samples collected (e.g., bulk samples, respirable dust samples); variation among workers and over time in the size distribution, surface area, recency of fracture, and other characteristics of the particles inhaled; and extrapolation of exposure sampling data to time periods for which sampling data are not available (Document ID 2330, pp. 4-5). OSHA notes that these sources of potential error and variability are common in occupational exposure estimation, and are sources of uncertainty in most epidemiological studies, a point with which Drs. Valberg and Long agree (Document ID 2330, p. 14).

OSHA has determined that its reliance on the best available evidence provided it with a solid, scientifically sound foundation from which to conclude that exposure to crystalline silica poses a significant risk of harm, notwithstanding the various uncertainties inherent in epidemiology generally or potentially affecting any given study and that no studies exist entirely free from the types of data limitations or error and variability Drs. Valberg and Long identified. During the public hearing Dr. Long acknowledged that OSHA had not overlooked studies that he believed adequately addressed the sources of error cited in his comments. He was also unable to provide examples of such analyses in the silica literature, or in any other area of occupational epidemiology (Document ID 3576, Tr. 355-358; see also Document ID 3577, Tr. 641, 648 (testimony of Dr. Kenneth Mundt)). Additionally, Drs. Valberg and Long's critique of Drs. Steenland and Bartell's uncertainty analysis ignores constraints on the available data and reasonable limits on the analysts' ability to investigate the full variety of possible errors and their potential effects on OSHA's risk assessment.

OSHA additionally notes that Dr. Kenneth Crump, an OSHA peer reviewer, in his examination of ToxaChemica's (Document ID 0469) study of exposure uncertainty in the Steenland et al. pooled study, opined that it was sound. He further observed that the “analysis of error conducted by [ToxaChemica] is a very strong effort. The assumptions are clearly described and the data upon [which] they are based appear to be appropriate and appropriately applied.” Dr. Crump was careful to note, however, that “there are questions, as there will always be with such an analysis . . . A major source of error that apparently was not accounted for is in assuming that the average measure of exposure assigned to a job is the true average” (Document ID 3574, pp. 161-162). Dr. Cox referenced Dr. Crump's comment in his own pre-hearing comments, in the context of a discussion on the importance of exposure uncertainty in OSHA's risk analysis (Document ID 2307, p. 40). OSHA addressed this particular criticism in the Review of Health Effects Literature and Preliminary QRA. There, it stated that it is possible that some job exposure estimates were above or below the true average for a job; however, there was no “gold standard” measurement available to appropriately test or adjust for this potential source of error (Document ID 1711, p. xv). The Agency further stated that the uncertainty, or sensitivity, analysis included potential error in job averages, and found that most cohorts in the lung cancer and silicosis mortality pooled studies were not highly sensitive to random or systematic error in job-average exposure estimates (Document ID 1711, pp. 303-314). In his final evaluation of OSHA's response to his comments of 2009, Dr. Crump stated, “I believe that my comments have been fairly taken into account in the current draft and I have no further comments to make” (Document ID 3574, p. 17).

Similarly, Dr. Morfeld, representing the ACC, criticized Drs. Steenland and Bartell for performing only 50 simulations of workplace exposures as part of the uncertainty analysis (Document ID 2307, Attachment 2, p. 10). Peer reviewer Mr. Bruce Allen also remarked that this type of uncertainty analysis typically requires more than 50 simulations (Document ID 3574, p. 114). However, as stated by OSHA in the response to peer review section of the Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 379-400), the results did not appear to change much with an increased number of simulations. Thus, OSHA has concluded that the sensitivity findings would not have changed substantially by running more simulations. Indeed, in the final peer review report conveying his evaluation of OSHA's response to his comments of 2009, Mr. Allen stated that OSHA adequately addressed his comments in the updated risk assessment (Document ID 3574, p. 5).

The overall salient conclusion that OSHA draws from this peer-reviewed analysis is that even in those cohorts where exposure error had some impact on exposure-response models for lung cancer or silicosis, the resulting risk estimates at the previous and new PELs remain clearly significant. Therefore, OSHA continues to rely on, and have confidence in, the risk analysis it had performed. In particular, OSHA concludes that Drs. Steenland and Bartell's modeling choices were based on the best available data from a variety of industrial sources and, through their uncertainty analysis, reached conclusions that survive the ACC and Chamber criticisms of the study methodology. OSHA further concludes that it is not necessary to conduct additional analysis to modify the approach adopted by Drs. Steenland and Bartell or to incorporate additional sources of exposure estimation uncertainty in the analysis.

OSHA also disagrees with other specific criticisms that Drs. Long and Valberg made concerning the uncertainty analysis. Dr. Long testified that “there are no formal analyses conducted to determine the error structures of the three sources of exposure measurement error included in the sensitivity analyses; for example, without any formal analysis, the OSHA assessment simply assumed a purely Berkson type error structure from the assignment of job-specific average exposure levels for individual exposures” (Document ID 3576, 304-305). Dr. Cox expressed a similar concern that

OSHA has not developed an appropriate error model specifically for the exposure estimates in the crystalline silica studies and has not validated (e.g., using a validation subset) that any of the ad hoc error models that they discuss describes the real exposure estimate errors of concern. They have also provided no justification for ToxaChemica's assumption of a log-normal distribution without outliers or mixtures of different distributions . . . and have provided no rationale for the assumption that a=0.8*p (Document ID 2307, Attachment 4, p. 45).

OSHA disagrees with Dr. Long's and Dr. Cox's characterizations, which implies that Drs. Steenland and Bartell did not adequately investigate the patterns of error in the data available to them. As noted in their 2004 report and by Dr. Steenland during the public hearings, ToxaChemica did not have the internal validation data (true exposures for a subset of the data set) that would be required to conduct formal analyses or validation of the error structure within each cohort of the pooled analysis (Document ID 0469, p. 16; 3580, pp. 1229-1231). Such data are not often available to analysts. However, Drs. Steenland and Bartell researched and reviewed worker exposure and dust composition data from several worksites to inform the error structures used in their analyses. For example, their analysis of individual workers' exposure data from the pooled analyses' industrial sand cohort formed the basis of the equation used for the exposure error simulation, which Dr. Cox represented as an assumption lacking any rationale. Drs. Steenland and Bartell also reviewed a number of studies characterizing the distribution of conversion factors across and within jobs at different worksites. OSHA concludes that Drs. Steenland and Bartell made a strong effort to collect data to inform their modeling choices, and that their choices were based on the best available information on error structure.

Dr. Long stated that “another limitation of the [ToxaChemica uncertainty] assessment was its assumption of log-linear . . . types of models, including log linear models with log-transformed exposure variables, and it focused on cumulative measures of silica exposure that obscure both within-person and between-person variability in exposure rates” (Document ID 3576 pp. 305-306). Dr. Long's assertion regarding the choice of exposure models is incorrect, as the sensitivity analysis was not limited to log-linear models. It included models with flexibility to capture nonlinearities in exposure-response, including spline analyses and categorical analyses, and log-transformation of the exposure variable was used only in the lung cancer analysis where it was shown in the original pooled analysis to better fit the data and address issues of heterogeneity between cohorts (Document ID 0469). Drs. Steenland and Bartell found only slight differences between the adjusted exposure-response estimates for each type of model.

Drs. Long and Valberg also contended that the cumulative exposure metric used in the Steenland and Bartell pooled study did not sufficiently allow for examination of the effects of exposure measurement uncertainty on the results of OSHA's risk assessment, because other exposure metrics could be more relevant. OSHA disagrees. As discussed in Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric, cumulative exposure is widely acknowledged by health experts as a driver of chronic diseases such as silicosis and lung cancer, has been found to fit the exposure-response data well in many studies of silicosis and lung cancer in the silica literature, and best fit the exposure-response data in the underlying pooled data sets to which Drs. Steenland and Bartell applied their subsequent uncertainty analyses. Thus, OSHA believes it was appropriate for this investigation of exposure estimation error to focus on the cumulative exposure metric, for reasons including data fit and general scientific understanding of this disease.

Furthermore, Dr. Long's concern that the choice of cumulative silica exposure might “obscure within-person variability in exposure rates” is not well supported in the context of lung cancer and silicosis mortality. Because death from these diseases typically occurs many years after the exposure that caused it, and complete records of past exposures do not typically exist, it is very difficult, using any metric, to trace within-person exposure variability (that is, changes in a person's exposure over time); these factors, not the choice of cumulative exposure metric, make it difficult to address variability in individuals' exposures over time and their effects on risk. OSHA notes that some analysts have explored the use of other exposure metrics in threshold analyses, submitting studies to the record which the Agency has reviewed and discussed in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.

Dr. Long also testified that “[t]here's very little discussion in the OSHA report regarding the potential impacts of exposure measurement error on identification of thresholds . . . [ToxaChemica's 2004 report] noted that exposure-response threshold estimates are imprecise and appear to be highly sensitive to measurement errors” (Document ID 3576 p. 306). Dr. Cox further noted that exposure misclassification can “create the appearance of a smooth, monotonically increasing estimated ER [exposure-response] relation” and shift thresholds to the left (Document ID 2307, Attachment 4, pp. 41-42); that is, create the appearance that a threshold effect occurs at a lower exposure level than would be seen in a data set without exposure misclassification.

In their uncertainty analysis, Drs. Steenland and Bartell estimated an exposure-response threshold for the pooled cohorts in each of the 50 runs conducted for their lung cancer analysis. They defined the “threshold” as the highest cumulative exposure for which the estimated odds ratio was less than or equal to 1.0, reporting a mean value of 3.04 mg/m³-days and median of 33.5 mg/m³-days across the 50 runs (Document ID 0469, p. 15). The authors observed that “[t]hese estimates are somewhat lower than the original estimate (Steenland and Deddens 2002) of a threshold at 121 mg/m³-days (4.8 on the log scale), which translates to about 0.01 mg/m³ [10 µg/m³] over a working 30-year lifetime (considering a 15-year lag), or 0.007 [7µg/m³] over a 45-year lifetime without considering a 15-year lag” (Document ID 0469, p. 15). These exposure levels are about one-fifth the PEL of 50 μg/m³ included in the final standard.

As noted by Dr. Long, the threshold estimates were highly variable across the 50 iterations (SD of 1.64 on the log scale), in keeping with other comments received by OSHA that estimates of exposure-response thresholds based on epidemiological data tend to be highly sensitive to sources of measurement error and other issues common to epidemiological investigations (see Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases). However, the Agency notes that the results of the uncertainty analysis, suggesting a possible cumulative exposure threshold at approximately one-fifth the final 50 μg/m³ PEL, provide no cause to doubt OSHA's determination that significant risk exists at both the previous and the revised PEL.

An additional concern raised by Dr. Cox was based on his misunderstanding that the equation used to characterize the relationship between true and observed exposure in Drs. Steenland and Bartell's simulation, “Exposuretrue = Exposureobserved + E”, concerned cumulative exposure. Dr. Cox stated that the equation is “inappropriate for cumulative exposures [because] both the mean and the variance of actual cumulative exposure received typically increase in direct proportion to duration” (Document ID 2307, Attachment 4, p. 45). That is, the longer period of time over which a cumulative exposure is acquired, the higher variance is likely to be, because cumulative exposure is the sum of the randomly varying exposures received on different days. However, the exposures referred to in the equation are the mean job-specific concentrations recorded in the job-exposure matrix (Exposureobserved) and individuals' actual exposure concentrations from each job worked (Exposuretrue), not their cumulative exposures (Document ID 0469, p. 11). Therefore, Dr. Cox's criticism is unfounded.

Dr. Cox additionally criticized the simulation analysis on the basis that “[t]he usual starting point for inhalation exposures [is] with the random number of particles inhaled per breath modeled as a time-varying (non-homogenous) Poisson process . . . It is unclear why ToxaChemica decided to assume (and why OSHA accepted the assumption) of an underdispersed distribution . . . rather than assuming a Poisson distribution” (Document ID 2307, Attachment 4, pp. 45-46). OSHA believes this criticism also reflects a misunderstanding of Drs. Steenland and Bartell's analysis. While it could be pertinent to an analysis of workers' silica dose (the amount of silica that enters the body), the analysis addresses the concentration of silica in the air near a worker's breathing zone, not internal dose. The worker's airborne concentration is the regulated exposure endpoint and the exposure of interest for OSHA's risk assessment. Thus, the uncertainty analysis does not need to account for the number of particles inhaled per breath.

More broadly, Dr. Cox asserted that the Monte Carlo analysis “is an inappropriate tool for analyzing the effects of exposure measurement error on estimated exposure-response data,” citing a paper by Gryparis et al. (2009) (Document ID 2307, Attachment 4, p. 44). This paper indicates that by randomly simulating exposure measurement error, the Monte Carlo approach can introduce classical error (Document ID 3870, p. 262). Peer reviewer Dr. Noah Seixas similarly commented that “[t]he typical Monte Carlo simulation, which is what appears to have been done, would introduce classical error,” that is, error which is independent of the unobserved variable (in this case, the true exposure value). He explained that, as a result, “the estimated risks [from the simulation analyses] are most likely to be underestimates, or conservatively estimating risk. This is an important aspect of measurement error with significant implications for risk assessment and should not be overlooked.” (Document ID 3574, pp. 116-117). Addressing Dr. Cox's broader point, Dr. Seixas in his peer review stated that the “simulation of exposure measurement error in assessing the degree of bias that may have been present is a reasonable approach to assessing this source of uncertainty” (Document ID 3574, pp. 116). Dr. Crump similarly characterized the uncertainty analysis used in the Steenland and Bartell study as “a strong effort” that “appropriately applied” this method (Document ID 3574, pp. 161-162). In this regard, OSHA generally notes that the advantages and limitations of various methods to address exposure measurement error in exposure-response models is an area of ongoing investigation in risk assessment. As shown by the comments of OSHA's peer reviewers above, there is no scientific consensus to support Dr. Cox's opinion that the Monte Carlo analysis is an inappropriate approach to analyze the effects of exposure measurement error.

In conclusion, through use of high quality studies and modeling, performance of an uncertainty analysis, and submission of the results of that analysis to peer review, OSHA maintains that it has relied upon the best available evidence. In addition, OSHA has carefully considered the public comments criticizing ToxaChemica's uncertainty analysis and has concluded that exposure estimation error did not substantially affect the results in the majority of studies examined (Document ID 1711, pp. 299-314). As a result, it was not necessary to conduct additional analyses modifying the approach adopted by Drs. Steenland and Bartell. Accordingly, OSHA reaffirms its determination that the conclusions of the Agency's risk assessment are correct and largely unaffected by potential error in exposure measurement.

L. Comments and Responses Concerning Causation

As discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, OSHA finds, based upon the best available evidence in the published, peer-reviewed scientific literature, that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, other non-malignant respiratory disease (NMRD), and renal and autoimmune effects. Exposure to respirable crystalline silica causes silicosis and is the only known cause of silicosis. For other health endpoints like lung cancer that have both occupational and non-occupational sources of exposure, OSHA used a comprehensive weight-of-evidence approach to evaluate the published, peer-reviewed scientific studies in the literature to determine their overall quality and whether there is substantial evidence that exposure to respirable crystalline silica increases the risk of a particular health effect. For example, with respect to lung cancer, OSHA reviewed 60 epidemiological studies covering more than 30 occupational groups in over a dozen industrial sectors and concluded that exposure to respirable crystalline silica increases the risk of lung cancer (Document ID 1711, pp. 77-170). This conclusion is consistent with that of the World Health Organization's International Agency for Research on Cancer (IARC), HHS' National Toxicology Program (NTP), the National Institute for Occupational Safety and Health (NIOSH), and many other organizations and individuals, as evidenced in the rulemaking record and discussed throughout this section.

In spite of this, and in addition to asserting that OSHA's Preliminary QRA was affected by many biases, Dr. Cox, on behalf of the ACC, argued that OSHA failed to conduct statistical analyses of causation, which led to inaccurate conclusions about causation. He specifically challenged OSHA's reliance upon the IARC determination of carcinogenicity, as discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, and its use of the criteria for evaluating causality developed by the noted epidemiologist Bradford Hill (Document ID 2307, Attachment 4, pp. 13-14; 4027, p. 28). The Hill criteria are nine aspects of an association that should be considered when examining causation: (1) The strength of the association; (2) the consistency of the association; (3) the specificity of the association; (4) the temporal relationship of the association; (5) the biological gradient (i.e., dose-response curve); (6) the biological plausibility of the association; (7) coherency; (8) experimentation; and (9) analogy (Document ID 3948, pp. 295-299).

Instead, Dr. Cox suggested that OSHA use the methods listed in Table 1 of his 2013 paper, “Improving causal inferences in risk analysis,” which he described as “the most useful study designs and methods for valid causal analysis and modeling of causal exposure-response (CER) relations” (Document ID 2307, Attachment 4, p. 11). Because OSHA did not use these methods, Dr. Cox maintained that the Agency's Preliminary QRA “asserts causal conclusions based on non-causal studies, data, and analyses” (Document ID 2307, Attachment 4, p. 3). He also contended that OSHA “ha[d] conflated association and causation, ignoring the fact that modeling choices can create findings of statistical associations that do not predict correctly the changes in health effects (if any) that would be caused by changes in exposures” (Document ID 2307, Attachment 4, p. 3). He claimed that “[t]his lapse all by itself invalidates the Preliminary QRA's predictions and conclusions” (Document ID 2307, Attachment 4, p. 3). As discussed below, since OSHA's methodology and conclusions regarding causation are based on the best available evidence, they are sound. Consequently, Dr. Cox's contrary position is unpersuasive.

1. IARC Determination

Dr. Cox asserted that OSHA erred in its reliance on the IARC determination of carcinogenicity for crystalline silica inhaled in the forms of quartz or cristobalite. He believed OSHA only relied on the IARC findings because they aligned with the Agency's opinion, noting that the “IARC analysis involved some of the same researchers, same methodological flaws, and same gaps in explicit, well-documented derivations of benefits and conclusions as OSHA's own preliminary QRA” (Document ID 2307, Attachment 4, pp. 13-14). OSHA, however, relied on IARC's determination to include lung cancer in its quantitative risk assessment because it constitutes the best available evidence. For this reason, Dr. Cox's position is without merit and OSHA's findings are supported by substantial evidence in the record and reasonable.

As discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, the IARC classifications and accompanying monographs are well recognized in the scientific community, and have been described by scientists as “the most comprehensive and respected collection of systematically evaluated agents in the field of cancer epidemiology” (Demetriou et al., 2012, Document ID 4131, p. 1273). IARC's conclusions resulted from a thorough expert committee review of the peer-reviewed scientific literature, in which crystalline silica dust, in the form of quartz or cristobalite, was classified as Group 1, “carcinogenic to humans,” in 1997 (Document ID 2258, Attachment 8, p. 210). Since the publication of these conclusions, the scientific community has reaffirmed their soundness. In March of 2009, 27 scientists from eight countries participated in an additional IARC review of the scientific literature and reaffirmed that crystalline silica dust is a Group 1 carcinogen, i.e., “carcinogenic to humans” (Document ID 1473, p. 396). Additionally, the HHS' U.S. National Toxicology Program also concluded that respirable crystalline silica is a known human carcinogen (Document ID 1164, p. 1).

Further supporting OSHA's reliance on IARC's determination of carcinogenicity for its quantitative risk assessment is testimony offered by scientists during the informal public hearings. This testimony highlighted IARC's carcinogenicity determinations as very thorough examinations of the scientific literature that demonstrate that exposure to respirable crystalline silica causes lung cancer. For example, when asked about Dr. Cox's causation claims during the informal public hearings, David Goldsmith, Ph.D., noted that causation was very carefully examined by IARC. He believed that IARC, in its 1997 evaluation of evidence for cancer and silica, “. . . chose . . . the best six studies that were the least confounded for inability to control for smoking or other kinds of hazardous exposures like radiation and asbestos and arsenic . . .” (Document ID 3577, Tr. 894-896). He also believed it “. . . crucial . . . that we pay attention to those kinds of studies, that we pay attention to the kinds of studies that were looked at by the IARC cohort that Steenland did from 2001. That's where they had the best evidence” (Document ID 3577, Tr. 894-896).

Regarding IARC's evaluation of possible biases and confounders in epidemiological studies, as well as its overall determination, Frank Mirer, Ph.D., of CUNY School of Public Health, representing the AFL-CIO, testified:

IARC has active practicing scientists review—I've been on two IARC monographs, but not these monographs, monograph working groups. It's been dealt with. It's been dealt with over a week of intense discussion between the scientists who are on these committees, as to whether there's chance bias in confounding which might have led to these results, and by 1987 for foundries and 1997 for silica, and it's been decided and reaffirmed.

So people who don't believe it are deniers, pure and simple. This is the scientific consensus. I was on the NTP Board of Scientific Counselors when we reviewed the same data. Known to be a human carcinogen. Once you know it's a human carcinogen from studies in humans, you can calculate risk rates (Document ID 3578, Tr. 937).

That OSHA relied on the best available evidence to draw its conclusions was also affirmed by Dr. Cox's inability to provide additional studies that would have cast doubt on the Agency's causal analysis. Indeed, during the informal public hearings, Kenneth Crump, Ph.D., an OSHA peer reviewer from the Louisiana Tech University Foundation, asked Dr. Cox if he could identify “any causal studies of silica that they [OSHA] should have used but did not use?” Dr. Cox responded: “I think OSHA could look at a paper from around 2007 of Brown's, on some of the issues and causal analysis, but I think the crystalline silica area has been behind other particulate matter areas . . . in not using causal analysis methods. So no, I can't point to a good study that they should have included but didn't” (Document ID 3576, Tr. 401-402). In light of the above, OSHA maintains that in relying on IARC's determination of carcinogenicity, its conclusions on causation are rooted in the best available evidence.

2. Bradford Hill Criteria and Causality

Dr. Cox also challenged OSHA's use of Hill's criteria for causation. He claimed that the Bradford Hill considerations were neither necessary nor sufficient for establishing causation, which was his reason for failing to include them in the statistical methods listed in Table 1 of his written comments for objectively establishing evidence about causation (Document ID 4027, p. 28). As explained below, based on its review of the record, OSHA finds this position meritless, as it is unsupported by the best available evidence.

As a preliminary matter, Hill's criteria for causation (Document ID 3948) are generally accepted as a gold standard for causation in the scientific community. Indeed, OSHA heard testimony during the informal public hearings and received post-hearing comments indicating that Dr. Cox's assertion that statistical methods should be used to establish causality is not consistent with common scientific practice. For example, Andrew Salmon, Ph.D., an OSHA peer reviewer, wrote:

The identification of causality as opposed to statistical association is, as described by Bradford Hill in his well-known criteria, based mainly on non-statistical considerations such as consistence, temporality and mechanistic plausibility: the role of statistics is mostly limited to establishing that there is in fact a quantitatively credible association to which causality may (or may not) be ascribed. OSHA correctly cites the substantial body of evidence supporting the association and causality for silicosis and lung cancer following silica exposure, and also quotes previous expert reviews (such as IARC). The causal nature of these associations has already been established beyond any reasonable doubt, and OSHA's analysis sufficiently reflects this (Document ID 3574, p. 38).

Similarly, Kyle Steenland, Ph.D., Professor, Department of Environmental Health, Rollins School of Public Health, Emory University, in response to a question about Dr. Cox's testimony on causation from Darius Sivin, Ph.D., of the UAW Health and Safety Department, stated that the Bradford Hill criteria are met for lung cancer and silicosis:

[M]ost of the Bradford Hill criteria apply here. You know you can never prove causality. But when the evidence builds up to such an extent and you have 100 studies and they tend to be fairly consistent, that's when we draw a causal conclusion. And that was the case for cigarette smoke in lung cancer. That was the case for asbestos in lung cancer. And when the evidence builds up to a certain point, you say, yeah, it's a reasonable assumption that this thing causes, X causes Y (Document ID 3580, pp. 1243-1244).

As a follow-up, OSHA asked if Dr. Steenland felt that the Bradford Hill criteria were met for silica health endpoints. Dr. Steenland replied, “For silicosis or for lung cancer. I had said they're met for both” (Document ID 3580, p. 1262).

Gary Ginsberg, Ph.D., an OSHA peer reviewer, agreed with Dr. Steenland, remarking to Dr. Cox during questioning, “I'm a little dumbfounded about the concern over causality, given all the animal evidence” (Document ID 3576, Tr. 406). Mr. Park from NIOSH's Risk Evaluation Branch, in his question to Dr. Cox, echoed the sentiments of Dr. Ginsberg, stating:

It's ludicrous to hear someone question causality. There's 100 years of research in occupational medicine, in exposure assessment. People here even in industry would agree that silica they say causes silicosis, which causes lung cancer. There's some debate about whether the middle step is required. There's no question that there's excess lung cancer in silica-exposed populations. We look at literature, and we identify what we call good studies. Good studies are ones that look at confounding, asbestos, whatever. We make judgments. If there's data that allows one to control for confounding, that's part of the analysis. If there is confounding that we can't control for, we evaluate it. We ask how bad could it be? There's a lot of empirical judgment from people who know these populations, know these exposures, know these industries, who can make very good judgments about that. We aren't stupid. So I don't know where you're coming from (Document ID 3576, Tr. 410-411).

Indeed, Kenneth Mundt, Ph.D., testifying on behalf of the International Diatomite Producers Association (part of the ACC Crystalline Silica Panel, which included Dr. Cox), and whose research study was the basis for the Morfeld et al. (2013, Document ID 3843) paper that reportedly identified a high exposure threshold for silicosis, also appeared to disagree with Dr. Cox's view of causation. Dr. Mundt testified that while he thought he could appreciate Dr. Cox's testimony, at some point there is sufficiently accumulated evidence of a causal association; he concluded, “I think here, over time, we've had the advantage with the reduction of exposure to see reduction in disease, which I think just makes it a home run that the diseases are caused by, therefore can be prevented by appropriate intervention” (Document ID 3577, Tr. 639-640).

OSHA notes that Dr. Cox, upon further questioning by Mr. Park, appeared to concede that exposure to respirable crystalline silica causes silicosis; Dr. Cox stated, “I do not question that at sufficiently high exposures, there are real effects” (Document ID 3576, Tr. 412). Later, when questioned by Anne Ryder, an attorney in the Solicitor of Labor's office, he made a similar statement: “I do take it as given that silica at sufficiently high and prolonged exposures causes silicosis” (Document ID 3576, Tr. 426). Based upon this testimony of Dr. Cox acknowledging that silica exposure causes silicosis, OSHA interprets his concern with respect to silicosis to be not one of causation, but rather a concern with whether there is a silicosis threshold (i.e., that exposure to crystalline silica must generally be above some level in order for silicosis to occur). Indeed, OSHA peer reviewer Brian Miller, Ph.D., noted in his post-hearing comments that Dr. Cox, when challenged, accepted that silica was causal for silicosis, “but questioned whether there was evidence for increased risks at low concentrations; i.e. whether there was a threshold” (Document ID 3574, p. 31). Thresholds for silicosis are addressed in great detail in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.

Based on the testimony and written comments of numerous scientists representing both public health and industry—all of whom agree that causation is established by applying the Bradford Hill criteria and examining the totality of the evidence—OSHA strongly disagrees with Dr. Cox's claims that the Bradford Hill criteria are inadequate to evaluate causation in epidemiology and that additional statistical techniques are needed to establish causation. OSHA defends its reliance on the IARC determination of 1997 and re-determination of 2012 that crystalline silica is a causal agent for lung cancer. OSHA's own Review of Health Effects Literature further demonstrates the totality of the evidence supporting the causality determination (Document ID 1711). Indeed, other than Dr. Cox representing the ACC, no other individual or entity questioned causation with respect to silicosis. Even Dr. Cox's questioning of causation for silicosis appears to be more of a question about thresholds, which is discussed in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.

3. Dr. Cox's Proposed Statistical Methods

OSHA reviewed the statistical methods provided by Dr. Cox in Table 1 of his 2013 paper, “Improving causal inferences in risk analysis,” (Document ID 2307, Attachment 4, p. 11), and explains below why the Agency did not adopt them. For example, Intervention Time Series Analysis (ITSA), as proposed by Dr. Cox in his Table 1, is a method for assessing the impact of an intervention or shock on the trend of outcomes of interest (Gilmour et al., 2006, cited in Document ID 2307, Attachment 4, p. 11). Implementing ITSA requires time series data before and after the intervention for both the dependent variable (e.g., disease outcome) and independent variables (e.g., silica exposure and other predictors), as well as the point of occurrence of the intervention. Although time-series data are frequently available in epidemiological studies, for silica we do not have a specific “intervention point” comparable to the implementation of a new OSHA standard that can be identified and analyzed. Rather, changes in exposure controls tend to be iterative and piecemeal, gradually bringing workers' exposures down over the course of a facility's history and affecting job-specific exposures differently at different points in time. Furthermore, individual workers' exposures change continually with new job assignments and employment. In addition, in a situation where the intervention really reduces the adverse outcome to a low level, such as 1/1000 lifetime excess risk, ITSA would require an enormous observational database in order to be able to estimate the actual post-intervention level of risk. OSHA believes the standard risk analysis approach of estimating an exposure-response relationship based on workers' exposures over time and using this model to predict the effects of a new standard on risk appropriately reflects the typical pattern of multiple and gradual changes in the workers' exposures over time found in most industrial facilities.

Another method listed in Dr. Cox's Table 1, marginal structural models (MSM), was introduced in the late 1990s (Robins, 1998, cited in Document ID 2307, Attachment 4, p. 11) to address issues that can arise in standard modeling approaches when time-varying exposure and/or time-dependent confounders are present. These methods are actively being explored in the epidemiological literature, but have not yet become a standard method in occupational epidemiology. As such, OSHA faces some of the same issues with MSM as were previously noted with BMA: Published, peer-reviewed studies using this approach are not available for the silica literature, and best practices are not yet well established. Thus, the incorporation of MSM in the silica risk assessment is not possible using the currently available literature and would be premature for OSHA's risk assessment generally.

In addition, in his post-hearing brief, Dr. Cox contended that “[a] well-done QRA should explicitly address the causal fraction (and explain the value used), rather than tacitly assuming that it is 1” (Document ID 4027, p. 4). However, this claim is without grounds. OSHA understands Dr. Cox's reference to the “causal fraction” to mean that, when estimating risk from an exposure-response model, only a fraction of the total estimated risk should be attributed to disease caused by the occupational exposure of interest. The Agency notes that the “causal fraction” of risk is typically addressed through the use of life table analyses, which incorporate background rates for the disease in question. Such analyses, which OSHA used in its Preliminary QRA, calculate the excess risk, over and above background risk, that is solely attributable to the exposure in question. Thus, there is no need to estimate a causal fraction due to exposure. These approaches are further discussed in Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric. Furthermore, nowhere in the silica epidemiological literature has the use of an alternative “causal fraction” approach to ascribing the causal relationship between silica exposure and silicosis and lung cancer been deemed necessary to reliably estimate risk.

4. The Assertion That the Silica Scientific Literature May Be False

Dr. Cox also asserted that the same biases and issues with causation in OSHA's Quantitative Risk Assessment (QRA) were likewise present in the silica literature. He wrote, “In general, the statistical methods and causal inferences described in this literature are no more credible or sound than those in OSHA's Preliminary QRA, and for the same reasons” (Document ID 2307, Attachment 4, p. 30).

The rulemaking record contains evidence that contradicts Dr. Cox's claims with respect to the scientific foundation of the QRA. Such evidence includes scientific testimony and the findings of many expert bodies, including IARC, the HHS National Toxicology Program, and NIOSH, concluding that exposure to respirable crystalline silica causes lung cancer. At the public hearing, Dr. Steenland, Professor at Emory University, testified that the body of evidence pertaining to silica was of equal quality to that of other occupational health hazards (Document ID 3580, pp. 1245-1246). Dr. Goldsmith similarly testified:

Silica dust . . . is like asbestos and cigarette smoking in that exposure clearly increases the risk of many diseases. There have been literally thousands of research studies on exposure to crystalline silica in the past 30 years. Almost every study tells the occupational research community that workers need better protection to prevent severe chronic respiratory diseases, including lung cancer and other diseases in the future. What OSHA is proposing to do in revising the workplace standard for silica seems to be a rational response to the accumulation of published evidence (Document ID 3577, Tr. 865-866).

OSHA agrees with these experts, whose positive view of the science supporting the need for better protection from silica exposures stands in contrast to Dr. Cox's claim regarding what he believes to be the problematic nature of the silica literature. Dr. Cox asserted in his written statement:

Scientists with subject matter expertise in areas such as crystalline silica health effects epidemiology are not necessarily or usually also experts in causal analysis and valid causal interpretation of data, and their causal conclusions are often mistaken, with a pronounced bias toward declaring and publishing findings of `significant' effects where none actually exists (false positives). This has led some commentators to worry that `science is failing us,' due largely to widely publicized but false beliefs about causation (Lehrer, 2012); and that, in recent times, `Most published research findings are wrong' (Ioannadis, 2005), with the most sensational and publicized claims being most likely to be wrong. (Document ID 2307, Attachment 4, pp. 15-16).

Moreover, during the public hearing, Dr. Cox stated that, with respect to lung cancer in the context of crystalline silica, the literature base may be false:

MR. PERRY [OSHA Director of the Directorate of Standards and Guidance]: So as I understand it, you basically think there's a good possibility that the entire literature base, with respect to lung cancer now, I'm talking about, is wrong?

DR. COX: You mean with respect to lung cancer in the context of crystalline silica?

MR. PERRY: Yes, sir.

DR. COX: I think that consistent with the findings of Lauer [Lehrer] and Ioannidis and others, I think that it's very possible and plausible that there is a consistent pattern of false positives in the literature base, yes. And that implies, yes, they are wrong. False positives are false (Document ID 3576, Tr. 423).

The Ioannidis paper (Document ID 3851) used mathematical constructs to purportedly demonstrate that most claimed research findings are false, and then provided suggestions for improvement (Document ID 3851, p. 0696). Two of his suggestions appear particularly relevant to the silica literature: “Better powered evidence, e.g., large studies or low-bias meta-analyses, may help, as it comes closer to the unknown `gold' standard. However, large studies may still have biases and these should be acknowledged and avoided”; and “second, most research questions are addressed by many teams, and it is misleading to emphasize the statistically significant findings of any single team. What matters is the totality of the evidence” (Document ID 3851, pp. 0700-0701). OSHA finds no merit in the claim that most claimed research findings are false. Instead, it finds that the silica literature for lung cancer is overall trustworthy, particularly because the “totality of the evidence” characterized by large studies demonstrates a causal relationship between crystalline silica exposure and lung cancer, as IARC determined in 1997 and 2012 (Document ID 2258, Attachment 8, p. 210; 1473, p. 396).

OSHA likewise notes that there was disagreement on Ioannidis' methods and conclusions. Jonathan D. Wren of the University of Oklahoma, in a correspondence to the journal that published the paper, noted that Ioannidis, “after all, relies heavily on other studies to support his premise, so if most (i.e., greater than 50%) of his cited studies are themselves false (including the eight of 37 that pertain to his own work), then his argument is automatically on shaky ground” (Document ID 4087, p. 1193). In addition, Steven Goodman of Johns Hopkins School of Medicine and Sander Greenland of the University of California, Los Angeles, performed a substantive mathematical review (Document ID 4081) of the Ioannidis models and concluded in their correspondence to the same journal that “the claims that the model employed in this paper constitutes `proof' that most published medical research claims are false, and that research in `hot' areas is most likely to be false, are unfounded” (Document ID 4095, p. 0773).

Christiana A. Demetriou, Imperial College London, et al. (2012), analyzed this issue of potential false positive associations in the field of cancer epidemiology (Document ID 4131). They examined the scientific literature for 509 agents classified by IARC as Group 3, “not classifiable as to its carcinogenicity to humans” (Document ID 4131). Of the 509 agents, 37 had potential false positive associations in the studies reviewed by IARC; this represented an overall frequency of potential false positive associations between 0.03 and 0.10 (Document ID 4131). Regarding this overall false positive frequency of about 10 percent, the authors concluded, “In terms of public health care decisions, given that the production of evidence is historical, public health care professionals are not expected to react immediately to a single positive association. Instead, they are likely to wait for further support or enough evidence to reach a consensus, and if a hypothesis is repeatedly tested, then any initial false-positive results will be quickly undermined” (Document ID 4131, p. 1277). The authors also cautioned that “Reasons for criticisms that are most common in studies with false-positive findings can also underestimate an association and in terms of public health care, false-negative results may be a more important problem than false-positives” (Document ID 4131, pp. 1278-1279). Thus, this study suggested that the false positive frequency in published literature is actually rather low, and stressed the importance of considering the totality of the literature, rather than a single study.

Given these responses to Ioannidis, OSHA fundamentally rejects the claim that most published research findings are false. The Agency concludes that, most likely, where, as here, there are multiple, statistically significant positive findings of an association between silica and lung cancer made by different researchers in independent studies looking at distinct cohorts, the chances that there is a consistent pattern of false positives are small; OSHA's mandate is met when the weight of the evidence in the body of science constituting the best available evidence supports such a conclusion.

M. Comments and Responses Concerning Working Life, Life Tables, and Dose Metric

As discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, OSHA presented risk estimates associated with exposure over a working lifetime to 25, 50, 100, 250, and 500 μg/m³ respirable crystalline silica (corresponding to cumulative exposures over 45 years to 1.125, 2.25, 4.5, 11.25, and 22.5 mg/m³-yrs). For mortality from silica-related disease (i.e., lung cancer, silicosis and non-malignant respiratory disease (NMRD), and renal disease), OSHA estimated lifetime risks using a life table analysis that accounted for background and competing causes of death. The mortality risk estimates were presented as excess risk per 1,000 workers for exposures over an 8-hour working day, 250 days per year, and a 45-year working lifetime. This is a legal standard that OSHA typically uses in health standards to satisfy the statutory mandate to “set the standard which most adequately assures, to the extent feasible, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life.” 29 U.S.C. 655(b)(5). For silicosis morbidity, OSHA based its risk estimates on cumulative risk models used by various investigators to develop quantitative exposure-response relationships. These models characterized the risk of developing silicosis (as detected by chest radiography) up to the time that cohort members (including both active and retired workers) were last examined. Thus, risk estimates derived from these studies represent less-than-lifetime risks of developing radiographic silicosis. OSHA did not attempt to estimate lifetime risk (i.e., up to age 85) for silicosis morbidity because the relationships between age, time, and disease onset post-exposure have not been well characterized.

OSHA received critical comments from representatives of the ACC and the Chamber. These commenters expressed concern that (1) the working lifetime exposure of 45 years was not realistic for workers, (2) the use of life tables was improper and alternative methods should be used, and (3) the cumulative exposure metric does not consider the exposure intensity and possible resulting dose-rate effects. OSHA examines these comments in detail in this section, and shows why they do not alter its conclusion that the best available evidence in the rulemaking record fully supports the Agency's use of a 45-year working life in a life table analysis with cumulative exposure as the exposure metric of concern.

1. Working Life

The Chamber commented that 45-year career silica exposures do not exist in today's working world, particularly in “short term work-site industries” such as construction and energy production (Document ID 4194, p. 11; 2288, p. 11). The Chamber stated that careers in these jobs are closer to 6 years, pointing out that OSHA's contractor, ERG, estimated a 64 percent annual turnover rate in the construction industry. Referring to Section 6(b)(5) of the Occupational Safety and Health (OSH) Act of 1970, the Chamber concluded, “OSHA improperly inflates risk estimates with its false 45-year policy, contradicting the Act, which requires standards based on actual, `working life' exposures—not dated hypotheticals” (Document ID 4194, pp. 11-12; 2288, pp. 11-12).

As stated previously, OSHA believes that the 45-year exposure estimate satisfies its statutory obligation to evaluate risks from exposure over a working life, and notes that the Agency has historically based its significance-of-risk determinations on a 45-year working life from age 20 to age 65 in each of its substance-specific rulemakings conducted since 1980. The Agency's use of a 45-year working life in risk assessment has also been upheld by the DC Circuit (Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1264-65 (D.C. Cir. 1988)) (also see Section II, Pertinent Legal Authority). Even if most workers are not exposed for such a long period, some will be, and OSHA is legally obligated to set a standard that protects those workers to the extent such standard is feasible. For reasons explained throughout this preamble, OSHA has set the PEL for this standard at 50 µg/m³ TWA. In setting the PEL, the Agency reasoned that while this level does not eliminate all risk from 45 years of exposures for each employee, it is the lowest level feasible for most operations.

In addition, OSHA heard testimony and received several comments with accompanying data that support a 45-year working life in affected industries. For example, six worker representatives of the International Union of Bricklayers and Allied Craftworkers (BAC), which represents a portion of the unionized masonry construction industry (Document ID 4053, p. 2), raised their hands in the affirmative when asked if they had colleagues who worked for longer than 40 years in their trade (Document ID 3585, Tr. 3053). Following the hearings, BAC reviewed its International Pension Fund and counted 116 members who had worked in the industry for 40 years or longer. It noted that this figure was likely an understatement, as many workers had previous experience in the industry prior to being represented by BAC, and many BAC affiliates did not begin participation in the Fund until approximately a decade after its establishment in 1972 (Document ID 4053, p. 2).

OSHA heard similar testimony from representatives of other labor groups and unions. Appearing with the Laborers' Health and Safety Fund of North America (LHSFNA), Eddie Mallon, a long-time member of the New York City tunnel workers' local union, testified that he had worked in the tunnel business for 50 years, mainly on underground construction projects (Document ID 3589, Tr. 4209). Appearing with the United Steelworkers, Allen Harville, of the Newport News Shipbuilding Facility and Drydock, testified that there are workers at his shipyard with more than 50 years of experience. He also believed that 15 to 20 percent of workers had 20 to 40 years of experience (Document ID 3584, Tr. 2571).

In addition, several union representatives appearing with the Building and Construction Trades Department (BCTD) of the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO) also commented on the working life exposure estimate. Deven Johnson, of the Operative Plasterers' and Cement Masons' International Association, testified that he thought 45 years was relevant, as many members of his union had received gold cards for 50 and 60 years of membership; he also noted that there was a 75-year member in his own local union (Document ID 3581, Tr. 1625-1626). Similarly, Sarah Coyne, representing the International Union of Painters and Allied Trades, testified that 45 years was adequate, as “we have many, many members who continue to work out in the field with the 45 years” (Document ID 3581, Tr. 1626). Charles Austin, of the International Association of Sheet Metal, Air, Rail and Transportation Workers, added that thousands of workers in the union's dust screening program have been in the field for 20 to 30 years (Document ID 3581, Tr. 1628-1629).

In its post-hearing comment, the BCTD submitted evidence on behalf of the United Association of Plumbers, Fitters, Welders and HVAC Service Techs, which represents a portion of the workers in the construction industry. A review of membership records for this association revealed 35,649 active members with 45 years or more of service as a member of the union. Laurie Shadrick, Safety and Health National Coordinator for the United Association, indicated that this membership figure is considered an underestimate, as many members had previous work experience in the construction industry prior to joining the union, or were not tracked by the union after transitioning to other construction trades (Document ID 4073, Attachment 1b). The post-hearing comment of the BCTD also indicated a trend of an aging workforce in the construction industry, with workers 65 years of age and older predicted to increase from 5 percent in 2012 to 8.3 percent in 2022 (Document ID 4073, Attachment 1a, p. 1). This age increase is likely due to the fact that few construction workers have a defined benefit pension plan, and the age for collecting Social Security retirement benefits has been increasing; as a result, many construction workers are staying employed for longer in the industry (Document ID 4073, Attachment 1a, p. 1). Thus, the BCTD expressed its support for using a 45-year working life in the construction industry for risk assessment purposes (Document ID 4073, Attachment 1a, p. 1).

In addition to BAC and BCTD, OSHA received post-hearing comments on the 45-year working life from the International Union of Operating Engineers (IUOE) and the American Federation of State, County and Municipal Employees (AFSCME). The IUOE reviewed records of the Central Pension Fund, in which IUOE construction and stationary local unions participate, and determined that the average years of service amongst all retirees (75,877 participants) was 21.34 years, with a maximum of 49.93 years of active service. Of these retirees, 15,836 participants recorded over 30 years of service, and 1,957 participants recorded over 40 years of service (Document ID 4025, pp. 6-7). The IUOE also pointed to the testimony of Anthony Bodway, Special Projects Manager at Payne & Dolan, Inc. and appearing with the National Asphalt Pavement Association (NAPA), who indicated that some workers in his company's milling division had been with the company anywhere from 35 to 40 years (Document ID 3583, Tr. 2227, 2228). Similarly, the AFSCME reported that, according to its 2011 poll, 49 percent of its membership had over 10 years of experience, and 21 percent had over 20 years (Document ID 3760, p. 2).

The rulemaking record on this topic of the working life thus factually refutes the Chamber's assertion that “no such 45-year career silica exposures exist in today's working world, particularly in construction, energy production, and other short term work-site industries” (Document ID 4194, p. 11; 2288, p. 11). Instead, OSHA concludes that the rulemaking record demonstrates that the Agency's use of a 45-year working life as a basis for estimating risk is legally justified and factually appropriate.

2. Life Tables

Dr. Cox, on behalf of the ACC, commented that OSHA should use “modern methods,” such as Bayesian competing-risks analyses, expectation-maximization (EM) methods, and copula-based approaches that account for subdistributions and interdependencies among competing risks (Document ID 2307, Attachment 4, p. 61). Such methods, according to Dr. Cox, are needed “[t]o obtain risk estimates . . . that have some resemblance to reality, and that overcome known biases in the naïve life table method used by OSHA” (Document ID 2307, Attachment 4, p. 61). Dr. Cox then asserted that the life table method used in the following studies to estimate mortality risks is also incorrect: Steenland et al. (2001a, Document ID 0452), Rice et al. (2001, Document ID 1118), and Attfield and Costello (2004, Document ID 0285) (Document ID 2307, Attachment 4, pp. 61-63).

OSHA does not agree that the life table method it used to estimate mortality risks is incorrect or inappropriate. Indeed, the Agency's life table approach is a standard method commonly used to estimate the quantitative risks of mortality. As pointed out by Rice et al. (2001), the life table method was developed by the National Research Council's BEIR IV Committee on the Biological Effects of Ionizing Radiations (BEIR), Board of Radiation Effects Research, in its 1988 publication on radon (Document ID 1118, p. 40). OSHA notes that the National Research Council is the operating arm of the National Academy of Sciences and the National Academy of Engineering, and is highly respected in the scientific community. As further described by Rice et al., an “advantage of this [actuarial] method is that it accounts for competing causes of death which act to remove a fraction of the population each year from the risk of death from lung cancer so that it is not necessary to assume that all workers would survive these competing causes to a given age” (Document ID 1118, p. 40). Because this life table method is generally accepted in the scientific community and has been used in a variety of peer-reviewed, published journal articles, including some of the key studies relied upon by the Agency in its Preliminary QRA (e.g., Rice et al., 2001, Document ID 1118, p. 40; Park et al., 2002, 0405, p. 38), OSHA believes it is appropriate here.

Regarding the alternative methods proposed by Dr. Cox, OSHA believes that these methods are not widely used in the occupational epidemiology community. In addition, OSHA notes that Dr. Cox did not provide any alternate risk estimates to support the use of his proposed alternative methods, despite the fact that the Agency made its life table data available in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 360-378). Thus, for these reasons, OSHA disagrees with Dr. Cox's claim that the life table method used by the Agency to estimate quantitative risks was inappropriate.

3. Exposure Metric

In its risk assessment, OSHA uses cumulative exposure, i.e., average exposure concentration multiplied by duration of exposure, as the exposure metric to quantify exposure-response relationships. It uses this metric because each of the key epidemiological studies on which the Agency relied to estimate risks used cumulative exposure as the exposure metric to quantify exposure-response relationships, although some also reported significant relationships based on exposure intensity (Document ID 1711, p. 342). As noted in the Review of Health Effects Literature, the majority of studies for lung cancer and silicosis morbidity and mortality have consistently found significant positive relationships between risk and cumulative exposure (Document ID 1711, p. 343). For example, nine of the ten epidemiological studies included in the pooled analysis by Steenland et al. (2001a, Document ID 0452) showed positive exposure coefficients when exposure was expressed as cumulative exposure (Document ID 1711, p. 343).

Commenting on this exposure metric, the ACC argued that cumulative exposure undervalues the role of exposure intensity, as some studies of silicosis have indicated a dose-rate effect, i.e., short-term exposure to high concentrations results in greater risk than longer-term exposure to lower concentrations at an equivalent cumulative exposure level (Document ID 4209, p. 58; 2307, Attachment A, pp. 93-94). The ACC added that, given that silica-related lung cancer and silicosis may both involve an inflammation-mediated mechanism, a dose-rate effect would also be expected for lung cancer (Document ID 4209, p. 58). It concluded that “assessments of risk based solely on cumulative exposure do not account adequately for the role played by intensity of exposure and, accordingly, do not yield reliable estimates of risk” (Document ID 4209, p. 68). Patrick Hessel, Ph.D., representing the Chamber, pointed to the initial comments of OSHA peer reviewer Kenneth Crump, Ph.D., who stated that “[n]ot accounting for a dose-rate effect, if one exists, could overestimate risk at lower concentrations” (Document ID 4016, p. 2, citing 1716, pp. 165-167).

OSHA acknowledges these concerns regarding the exposure metric and finds them to have some merit. However, it notes that the best available studies use cumulative exposure as the exposure metric, as in common in occupational epidemiological studies. As discussed below, there is also substantial good evidence in the record supporting the use of cumulative exposure as the exposure metric for crystalline silica risk assessment.

Paul Schulte, Ph.D., of NIOSH testified that “cumulative exposure is a standard and appropriate metric for irreversible effects that occur soon after actual exposure is experienced. For lung cancer and nonmalignant respiratory disease, NMRD mortality, cumulative exposure lagged for cancer is fully justified . . . For silicosis risk assessment purposes, cumulative exposure is a reasonable and practical choice” (Document ID 3579, Tr. 127). NIOSH also conducted a simulated dose rate analysis for silicosis incidence with data from a Chinese tin miners cohort and, in comparing exposure metrics, concluded that the best fit to the data was cumulative exposure with no dose-rate effect (Document ID 4233, pp. 36-39). This finding is consistent with the testimony of Dr. Steenland, who stated, “Cumulative exposure, I might say, is often the best predictor of chronic disease in general, in epidemiology” (Document ID 3580, Tr. 1227). OSHA also notes that using a cumulative exposure metric (e.g., mg/m³-yrs) factors in both exposure intensity and duration, while using only an exposure intensity metric (e.g., μg/m³) ignores the influence of exposure duration. Dr. Crump's comment that “[e]stimating risk based on an `incomplete' exposure metric like average exposure is not recommended . . . . [E]xposure to a particular air concentration for one week is unlikely to carry the same risk as exposure to that concentration for 20 years, although the average exposures are the same” also supports the use of a cumulative exposure metric (Document ID 1716, p. 166).

With regard to a possible dose-rate effect, OSHA agrees with Dr. Crump that if one exists and is unaccounted for, the result could be an overestimation of risks at lower concentrations (Document ID 1716, pp. 165-167). OSHA is aware of two studies discussed in its Review of Health Effects Literature and Preliminary QRA that examined dose-rate effects on silicosis exposure-response (Document ID 1711, pp. 342-344). Neither study found a dose-rate effect relative to cumulative exposure at silica concentrations near the previous OSHA PEL (Document ID 1711, pp. 342-344). However, they did observe a dose-rate effect in instances where workers were exposed to crystalline silica concentrations far above the previous PEL (i.e., several-fold to orders of magnitude above 100 μg/m³) (Buchanan et al., 2003, Document ID 0306; Hughes et al., 1998, 1059). For example, the Hughes et al. (1998) study of diatomaceous earth workers found that the relationship between cumulative silica exposure and risk of silicosis was steeper for workers hired prior to 1950 and exposed to average concentrations above 500 µg/m³ compared to workers hired after 1950 and exposed to lower average concentrations (Document ID 1059). Similarly, the Buchanan et al. (2003) study of Scottish coal miners adjusted the cumulative exposure metric in the risk model to account for the effects of exposures to high concentrations where the investigators found that, at concentrations above 2000 µg/m³, the risk of silicosis was about three times higher than the risk associated with exposure to lower concentrations but at the same cumulative exposure (Document ID 0306, p. 162). OSHA concluded that there is little evidence that a dose-rate effect exists at concentrations in the range of the previous PEL (100 µg/m³) (Document ID 1711, p. 344). However, at the suggestion of Dr. Crump, OSHA used the model from the Buchanan et al. study in its silicosis morbidity risk assessment to account for possible dose-rate effects at high average concentrations (Document ID 1711, pp. 335-342). OSHA notes that the risk estimates in the exposure range of interest (25-500 μg/m³) derived from the Buchanan et al. (2003) study were not appreciably different from those derived from the other studies of silicosis morbidity (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1.).

In its post-hearing brief, NIOSH also added that a “detailed examination of dose rate would require extensive and real time exposure history which does not exist for silica (or almost any other agent)” (Document ID 4233, p. 36). Similarly, Dr. Crump wrote, “Having noted that there is evidence for a dose-rate effect for silicosis, it may be difficult to account for it quantitatively. The data are likely to be limited by uncertainty in exposures at earlier times, which were likely to be higher” (Document ID 1716, p. 167). OSHA agrees with Dr. Crump, and believes that it has used the best available evidence to estimate risks of silicosis morbidity and sufficiently accounted for any dose-rate effect at high silica average concentrations by using the Buchanan et al. (2003) study.

For silicosis/NMRD mortality, the ACC noted that Vacek et al. (2009, Document ID 2307, Attachment 6) reported that, in their categorical analysis of the years worked at various levels of exposure intensity, only years worked at >200 µg/m³ for silicosis and >300 µg/m³ for NMRD were associated with increased mortality (Document ID 2307, Attachment A, p. 93, citing 2307, Attachment 6, pp. 21, 23). However, OSHA believes it to be inappropriate to consider these results in isolation from the other study findings, and notes that Vacek et al. (2009) also reported statistically significant associations of silicosis mortality with cumulative exposure, exposure duration, and average exposure intensity in their continuous analyses with univariate models; for NMRD mortality, there were statistically significant associations with cumulative exposure and average exposure intensity (Document ID 2307, Attachment 6, pp. 21, 23).

In addition, OSHA notes that Vacek et al. (2009) did not include both an exposure intensity term and a cumulative exposure term in the multivariate model, after testing for correlation between cumulative exposure and years at particular exposure intensity; such a model would indicate how exposure intensity affects any relationship with cumulative exposure. As Dr. Crump stated in his comments:

To demonstrate evidence for a dose-rate effect that is not captured by cumulative exposure, it would be most convincing to show some effect of dose rate that is in addition to the effect of cumulative exposure. To demonstrate such an effect one would need to model both cumulative exposure and some effect of dose rate, and show that adding the effect of dose rate makes a statistically significant improvement to the model over that predicted by cumulative exposure alone (Document ID 1716, p. 166).

Indeed, both Buchanan et al. (2003, Document ID 0306) and Hughes et al. (1998, Document ID 1059), when examining possible dose-rate effects for silicosis morbidity, specifically included both cumulative exposure and exposure intensity in their multivariate models. Additionally, as described in the lung cancer section of this preamble, the Vacek et al. study may be affected by both exposure misclassification and the healthy worker survivor effect. Both of these biases may flatten an exposure-response relationship, obscuring the relationship at lower exposure levels, which could be the reason why a significant effect was not found at the lower exposure levels in the Vacek et al. (2009, Document ID 2307, Attachment 6) multivariate analysis.

Regarding lung cancer mortality, the ACC pointed out that Steenland et al. (2001a, Document ID 0452) acknowledged that duration of exposure did not fit the data well in their pooled lung cancer study. The ACC indicated that exposure intensity should be considered (Document ID 2307, Attachment A, p. 93; 4209, p. 58, citing 0452, p. 779). OSHA interpreted the results of the Steenland et al. (2001, Document ID 0452) study to simply mean that duration of exposure alone was not a good predictor for lung cancer mortality, where a lag period may be important between the exposure and the development of disease. Indeed, Steenland et al. found the model with logged cumulative exposure, with a 15-year lag, to be a strong predictor of lung cancer (Document ID 0452, p. 779). Additionally, no new evidence of a dose-rate effect in lung cancer studies was submitted to the record.

For these reasons, OSHA does not believe there to be any persuasive data in the record that supports a dose-rate effect at exposure concentrations near the revised or previous PELs. OSHA concludes that cumulative exposure is a reasonable exposure metric on which to base estimates of risk to workers exposed to crystalline silica in the exposure range of interest (25 to 500 μg/m³).

N. Comments and Responses Concerning Physico-Chemical and Toxicological Properties of Respirable Crystalline Silica

As discussed in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711, pp. 344-350), the toxicological potency of crystalline silica is influenced by a number of physical and chemical factors that affect the biological activity of the silica particles inhaled in the lung. The toxicological potency of crystalline silica is largely influenced by the presence of oxygen free radicals on the surfaces of respirable particles; these chemically-reactive oxygen species interact with cellular components in the lung to promote and sustain the inflammatory reaction responsible for the lung damage associated with exposure to crystalline silica. The reactivity of particle surfaces is greatest when crystalline silica has been freshly fractured by high-energy work processes such as abrasive blasting, rock drilling, or sawing concrete materials. As particles age in the air, the surface reactivity decreases and exhibits lower toxicologic potency (Porter et al., 2002, Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al., 1995, 1128). In addition, surface impurities have been shown to alter silica toxicity. For example, aluminum and aluminosilicate clay on silica particles has been shown to decrease toxicity (Castranova et al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini, 1998, 1016; Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998, 1016).

In the preamble to the proposed standard, OSHA preliminarily concluded that although there is evidence that several environmental influences can modify surface activity to either enhance or diminish the toxicity of silica, the available information was insufficient to determine to what extent these influences may affect risk to workers in any particular workplace setting (Document 1711, p. 350). NIOSH affirmed OSHA's preliminary conclusion regarding the silica-related risks of exposure to clay-occluded quartz particles, which was based on what OSHA believed to be the best available evidence. NIOSH stated:

NIOSH concurs with this assessment by OSHA. Currently available information is not adequate to inform differential quantitative risk management approaches for crystalline silica that are based on surface property measurements. Thus, NIOSH recommends a single PEL for respirable crystalline silica without consideration of surface properties (Document ID 4233, p. 44).

Two rulemaking participants, the Brick Industry Association (BIA), which represents distributors and manufacturers of clay brick, and the Sorptive Minerals Institute (SMI), which represents many industries that process and mine sorptive clays for consumer products and commercial and industrial applications, provided comment and supporting evidence that the crystalline silica encountered in their workplace environments presents a substantially lower risk of silica-related disease than that reflected in the Agency's Preliminary QRA.

BIA argued that the quartz particles found in clays and shales used in clay brick are occluded in aluminum-rich clay coatings. BIA submitted to the record several studies indicating reduced toxicity and fibrogenicity from exposure to quartz in aluminum-rich clays (Document ID 2343, Attachment 2, p. 2). It purported that “OSHA lacks the statutory authority to impose the proposed rule upon the brick and structural clay manufacturing industry because employees in that industry do not face a significant risk of material impairment of health or functional capacity” (Document ID 2242, pp. 2-3). BIA concluded that its industry should be exempted from the rule, stating: “OSHA should exercise its discretion to exempt the brickmaking industry from compliance with the proposed rule unless and until it determines how best to take into account the industry's low incidence of adverse health effects from silica toxicity” (Document ID 2242, p. 11).

SMI argued that silica in sorptive clays exists as either amorphous silica or as geologically ancient, occluded quartz, “neither of which pose the health risk identified and studied in OSHA's risk assessment” (Document ID 4230, p. 2). SMI further contended that OSHA's discussion of aged silica “does not accurately reflect the risk of geologically ancient, (occluded) silica formed millions of years ago found in sorptive clays” (Document ID 4230, p. 2). Additionally, SMI noted that clay products produced by the sorptive minerals industry are not heated to high temperatures or fractured, making them different from brick and pottery clays (Document ID 2377, p. 7). In support of its position, SMI submitted to the record several toxicity studies of silica in sorptive clays. It stated that the evidence does not provide the basis for a finding of a significant risk of material impairment of health from exposure to silica in sorptive clays (Document ID 4230, p. 2). Consequently, SMI concluded that the application of a reduced PEL and comprehensive standard is not warranted.

Having considered the evidence SMI submitted to the record, OSHA finds that although quartz originating from bentonite deposits exhibits some biological activity, it is clear that it is considerably less toxic than unoccluded quartz. Moreover, evidence does not exist that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to quartz in bentonite-containing materials and similar sorptive clays. This finding does not extend to the brick industry, where workers are exposed to silica through occluded quartz in aluminum rich clays. The Love et al. study (1999, Document ID 0369), which BIA claimed would be of useful quality for OSHA's risk assessment, shows sufficient cases of silicosis to demonstrate significant risk within the meaning used by OSHA for regulatory purposes. In addition, OSHA found a reduced, although still significant, risk of silicosis morbidity in the study of pottery workers (Chen et al., 2005, Document ID 0985) that BIA put forth as being representative of mortality in the brick industry (Document ID 3577, Tr. 674). These findings are discussed in detail below.

1. The Clay Brick Industry

BIA did not support a reduction in the PEL because although brick industry employees are exposed to crystalline silica-bearing materials, BIA believes silicosis is virtually non-existent in that industry. It contended that silica exposure in the brick industry does not cause similar rates of disease as in other industries because brick industry workers are exposed to quartz occluded in aluminum-rich layers, reducing the silica's toxicity. BIA concluded that “no significant workplace risk for brick workers from crystalline silica exposure exists at the current exposure limit” (Document ID 3577, Tr. 654) and that reducing the PEL would have no benefit to workers in the brick industry (Document ID 2300, p. 2). These concerns were also echoed by individual companies in the brick industry, such as Acme Brick (Document ID 2085, Attachment 1), Belden Brick Company (Document ID 2378), and Riverside Brick & Supply Company, Inc. (Document ID 2346, Attachment 1). In addition, OSHA received over 50 letters as part of a letter campaign from brick industry representatives referring to BIA's comments on the lack of silicosis in the brick industry (e.g., Document ID 2004).

The Tile Council of North America, Inc., also noted that “[c]lay raw materials used in tile manufacturing are similar to those used in brick and sanitary ware manufacturing” and also suggested that aluminosilicates decrease toxicity (Document ID 3528, p. 1). OSHA agrees with the Tile Council of North America, Inc., that their concerns mirror those of the BIA and, therefore, the Agency's consideration and response to BIA also applies to the tile industry.

a. Evidence on the Toxicity of Silica in Clay Brick.

On behalf of BIA, Mr. Robert Glenn presented a series of published and unpublished studies (Document ID 3418), also summarized by BIA (Document ID 2300, Attachment 1) as evidence that “no significant workplace risk for brick workers from crystalline silica exposure exists at the current exposure limit” (Document ID 3577, Tr. 654). Most of these studies, including an unpublished report on West Virginia brick workers (West Virginia State Health Department, 1939), a study of North Carolina brick workers (Trice, 1941), a study of brick workers in England (Keatinge and Potter, 1949), a study of Canadian brick workers (Ontario Health Department, 1972), two studies of North Carolina brick workers (NIOSH, 1978 and NIOSH, 1980), a study of English and Scottish brick workers (Love et al., 1999, Document ID 0369), and an unpublished study commissioned by BIA of workers at 13 of its member companies (BIA, 2006), reported little or no silicosis among the workers examined (Document ID 3418; 3577, Tr. 655-669).

Based on its review of the record evidence, OSHA finds that there are many silica-containing materials (e.g., other clays, sand, etc.) in brick and concludes that BIA's position is not supported by the best available evidence. The analysis contained in the studies Mr. Glenn presents does not meet the rigorous standards used in the studies on which OSHA's risk assessment relies. Indeed the studies cited by Mr. Glenn and BIA do not adequately support their contention that silicosis is “essentially non-existent.” Several studies were poorly designed and applied inappropriate procedures for evaluating chest X-rays (Document ID 3577, Tr. 682-685). Dr. David Weissman of NIOSH underscored the significance of such issues, stating: “It's very important, for example, to use multiple [B] readers [to evaluate chest X-rays] and medians of readings, and it is very important for people to be blinded to how readings are done” (Document ID 3577, Tr. 682). Also problematic was Mr. Glenn's failure to provide key information on the length of exposure or time since the first exposure in any of the studies he presented, which examined only currently employed workers. Information on duration of exposure or time since first exposure is essential to evaluating risk of silicosis because silicosis typically develops slowly and becomes detectable between 10 years and several decades following a worker's first exposure. In the hearing, Dr. Ken Rosenman also noted inadequacies related to silicosis latency, testifying that “we know that silicosis occurs 20, 30 years after . . . first exposure . . . if people have high exposure but short duration, short latency, you are not going to see positive x-rays [even if silicosis is developing] and so it's not going to be useful” (Document ID 3577, Tr. 688-689).

Mr. Glenn acknowledged shortcomings in the studies he submitted for OSHA's consideration, agreeing with Dr. Weissman's points about quality assurance for X-ray interpretation and study design (e.g., Document ID 3577, Tr. 683). In response to Dr. Rosenman's concerns about silicosis latency, he reported that no information on worker tenure or time since first exposure was presented in Trice (1941), Keatings and Potter (1949), Rajhans and Buldovsky (1972), the NIOSH studies (1978, 1980), or Love et al. (1999), and that more than half of the West Virginia brick workers studied by NIOSH (1939) had a tenure of less than 10 years (Document ID 4021, pp. 5-6), a time period that OSHA believes is too short to see development of most forms of silicosis. He suggested that high exposures in two areas of the West Virginia facilities could trigger accelerated or acute silicosis, which could be observed in less than 10 years, if the toxicity of the silica in clay brick was comparable to silica found in other industries (post-hearing comments, p. 5). However, OSHA notes that a cross-sectional report on actively employed workers would not necessarily capture cases of accelerated or acute silicosis, which are associated with severe symptoms that compromise individuals' ability to continue work, and therefore would result in a survivor effect where only unaffected workers remain at the time of study.

Mr. Glenn further argued that the Agency should assess risk to brick workers based on studies from that industry because the incidence of silicosis among brick workers appears to be lower than among workers in other industries (Document ID 3577, Tr. 670). For the reasons discussed above, OSHA does not believe the studies submitted by Mr. Glenn provide an adequate basis for risk assessment. In addition, studies presented did not: (1) Include retired workers; (2) report the duration of workers' exposure to silica; (3) employ, in most cases, quality-assurance practices for interpreting workers' medical exams; or (4) include estimates of workers' silica exposures. Furthermore, Mr. Glenn acknowledged in the informal public hearing that the Love et al. (1999, Document ID 0369) study of 1,925 workers employed at brick plants in England and Scotland in 1990-1991 is the only available study of brick workers that presented exposure-response information (Document ID 3577, Tr. 692). He characterized the results of that study as contradictory to OSHA's risk assessment for silicosis morbidity because the authors concluded that frequency of pneumoconiosis is low in comparison to other quartz-exposed workers (Document ID 4021, p. 2). He also cited an analysis by Miller and Soutar (Document ID 1098) (Dr. Soutar is a co-author of the Love et al. study) that compared silicosis risk estimates derived from Love et al. and those from Buchanan et al.'s study of Scottish coal workers exposed to silica, and concluded that silicosis risk among the coal workers far exceeded that among brick workers (Document ID 3577, Tr. 671). He furthermore concluded that the Love et al. study is “the only sensible study to be used for setting an exposure limit for quartz in brick manufacturing.” (Document ID 3577, Tr. 679).

Based on review of the Love et al. study (Document ID 0369), OSHA agrees with Mr. Glenn's claim that the silicosis risk among workers in clay brick industries appears to be somewhat lower than might be expected in other industries. However, OSHA is unconvinced by Mr. Glenn's argument that risk to workers exposed at the previous PEL is not significant because the cases of silicosis reported in this study are sufficient to show significant risk within the meaning used by OSHA for regulatory purposes (1 in 1,000 workers exposed for a working lifetime).

Love et al. reported that 3.7 percent of workers with radiographs were classified as ILO Category 0/1 (any signs of small opacities) and 1.4 percent of workers were classified as ILO Category 1/0 (small radiographic opacities) or greater. Furthermore, among workers aged 55 and older, the age category most likely to have had sufficient time since first exposure to develop detectable lung abnormalities from silicosis exposure, Love et al. reported prevalences of abnormal radiographs ranging from 2.9 percent (cumulative exposure below 0.5 mg/yr-m³) to 16.4 percent (exposure at least 4 mg/yr-m³) (Love et al. 1999, Document ID 0369, Table 4, p. 129). According to the study authors, these abnormalities “are the most likely dust related pathology—namely, silicosis” (Document ID 0369, p. 132). Given that OSHA considers a lifetime risk of 0.1 percent (1 in 1,000) to clearly represent a significant risk, OSHA considers the Love et al. study to have demonstrated a significant risk to brick workers even if only a tiny fraction of the abnormalities observed in the study population represent developing silicosis (see Benzene, 448 U.S. 607, 655 n. 2). According to the study authors, “the estimated exposure-response relation for quartz suggests considerable risks of radiological abnormality even at concentrations of 0.1 mg/m³ [100 μg/m³] of quartz” (Document ID 0369, p. 132).

OSHA concludes that, despite the possibly lower toxicity of silica in the clay brick industry compared to other forms, and despite the Love et al. study's likely underestimation of risk due to exclusion of retired workers, the study demonstrates significant risk among brick workers exposed at the previous general industry PEL. It also suggests that the silicosis risk among brick workers would remain significant even at the new PEL. Furthermore, OSHA is unconvinced by Mr. Glenn's argument that the Agency should develop a quantitative risk assessment based on the Love et al. study, because that study excluded retired workers and had inadequate worker follow-up. As explained earlier in this section, adequate follow-up time and inclusion of retired workers is extremely important to allow for latency in the development of silicosis. Therefore, OSHA relied on studies including retired workers in its QRA for silicosis morbidity.

Mr. Glenn additionally argued that the risk of lung cancer from silica exposure among brick workers is likely to be lower than among workers exposed to silica in other work settings. Mr. Glenn acknowledged that “there are no published mortality studies of brick workers that look at cause of death or lung cancer death” (Document ID 3577, Tr. 674). However, he stated that “pottery clays are similar to the structural clays used in brickmaking in that the quartz is occluded in aluminum-rich layers of bentonite, kaolinite, and illite,” and that OSHA should consider studies of mortality among pottery workers as representative of the brick industry (Tr. 674). Mr. Glenn cited the Chen et al. (2005) study of Chinese pottery workers, which reported a weak exposure-response relationship between silica exposure and lung cancer mortality, and which appeared to be affected by PAH-related confounding. He concluded that the Chen et al. study “provides strong evidence for aluminum-rich clays suppressing any potential carcinogenesis from quartz” (Document ID 3577, Tr. 675).

OSHA acknowledges that occlusion may weaken the carcinogenicity of silica in the brick clay industry, but does not believe that the Chen et al. study provides conclusive evidence of such an effect. This is because of the relatively low carcinogenic potential of silica and the difficulty involved in interpreting one cohort with known issues of confounding (see Section V.F, Comments and Responses Concerning Lung Cancer Mortality). OSHA also notes, however, that it estimated risks of silicosis morbidity from the cited Chen et al. (2005, Document ID 0985) study, and found the risk among pottery workers to be significant, with 60 deaths per 1,000 workers at the previous PEL of 100 μg/m³ and 20 deaths per 1,000 workers at the revised PEL of 50 μg/m³ (as indicated in Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). Thus, given Mr. Glenn's assertion that pottery clays are similar to the clays used in brickmaking, OSHA believes that while the risk of silicosis morbidity may be lower than that seen in other industry sectors, it is likely to still be significant in the brickmaking industry.

Thus, OSHA concludes that the BIA's position is not supported by the best available evidence. The studies cited by Mr. Glenn to support his contention that brick workers are not at significant risk of silica-related disease do not have the same standards as those studies used by OSHA in its quantitative risk assessment. Furthermore, in the highest-quality study brought forward by Mr. Glenn (Love et al. 1999, Document ID 0369), there are sufficient cases of silicosis to demonstrate significant risk within the meaning used by OSHA for regulatory purposes. Even if the commenters' arguments that silica in clay brick is less toxic were, to some extent, legitimate, this would not significantly affect OSHA's own estimates from the epidemiological evidence of the risks of silicosis.

2. Sorptive Minerals (Bentonite Clay) Processing

SMI asserted that the physico-chemical form of respirable crystalline silica in sorptive clays reduces the toxicologic potency of crystalline silica relative to the forms of silica common to most studies relied on in OSHA's Preliminary QRA. In other words, the risk associated with exposure to silica in sorptive clays is assertedly lower than the risk associated with exposure to silica in other materials. SMI based this view on what it deemed the “best available scientific literature,” epidemiological, in vitro, and animal evidence OSHA had not previously considered. It believed the evidence showed reduced risk from exposure to occluded quartz found in the sorptive clays and that occluded quartz does not create a risk similar to that posed by freshly fractured quartz (Document ID 2377, p. 7). Based on this, SMI contended that the results of OSHA's Preliminary QRA were not applicable to the sorptive minerals industry, and a more stringent standard for crystalline silica is “neither warranted nor legally permissible” (Document ID 4230, p. 1). As discussed below, OSHA reviewed the evidence submitted by SMI and finds that although the studies provide evidence of some biological activity in quartz originating from bentonite deposits, there is not quantitative evidence that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to quartz in bentonite-containing materials and similar sorptive clays.

a. Evidence on the Toxicity of Silica in Sorptive Minerals

SMI submitted a number of studies to the rulemaking record. First, it summarized a retrospective study by Waxweiler et al. (Document ID 3998, Attachment 18e) of attapulgite clay workers in Georgia in which the authors concluded that there was a significant deficit of non-malignant respiratory disease mortality and no clear excess of lung cancer mortality among these workers. It used the study as the basis for its recommendation to OSHA that the study “be cited and that exposures in the industry be recognized in the final rule as not posing the same hazard as those in industries with reactive crystalline silica” (Document ID 2377, p. 10).

Based on its review of the rulemaking record, OSHA concludes that the Waxweiler et al. study is of limited value for assessing the hazard potential of quartz in bentonite clay because of the low airborne levels of silica to which the workers were exposed. The Agency's conclusion is supported by NIOSH's summary of the time-weighted average (TWA) exposures calculated for each job category in Waxweiler et al. (1988, Document ID 3998, Attachment 18e), which were found to be “within the acceptable limits as recommended by NIOSH (i.e., <0.05 mg/m³ [50 μg/m³]) . . . and most were substantially lower” (Document ID 4233, p. 41). It cannot be known to what extent the low toxicity of the dust or the low exposures experienced by the workers each contributed to the lack of observed disease.

SMI also presented a World Health Organization (WHO) document (2005, Document ID 3929), which recognized that “studies of workers exposed to sorptive clays have not identified significant silicosis risk” (Document ID 2377, p. 10). However, although WHO did find that there were no reported cases of fibrotic reaction in humans exposed to montmorillonite minerals in the absence of crystalline silica (Document ID 3929, p. 130), the WHO report does discuss the long-term effects from exposure to crystalline silica, including silicosis and lung cancer. In fact, with respect to evaluating the hazards associated with exposure to bentonite clay, WHO regarded silica as a potential confounder (Document ID 3929, p. 136). Thus, WHO did not specifically make any findings with respect to the hazard potential of quartz in the bentonite clay mineral matrix but instead recognized the hazard presented by exposure to crystalline silica generally.

Additionally, the WHO (Document ID 3929, pp. 114, 118) cited two case/case series reports of bentonite-exposed workers, one demonstrating increasing prevalence of silicosis with increasing exposure to bentonite dust (Rombola and Guardascione, 1955, Document ID 3998, Attachment 18) and another describing cases of silicosis among workers exposed to bentonite dust (Phibbs et al. 1971, Document ID 3998, Attachment 18b). Rombola and Guardascione (1955) found silicosis prevalences of 35.5 and 12.8 percent in two bentonite processing factories, and 6 percent in a bentonite mine. In the factory where the highest exposures occurred, 10 of the 26 cases found were severe and all cases developed with seven or fewer years of exposure, indicating that exposure levels were extremely high (Document ID 4233, p. 42, citing 3998, Attachment 18). Phibbs et al. (1971) reviewed chest x-rays of 32 workers in two bentonite plants, of which x-ray films for 14 indicated silicosis ranging from minimal to advanced. Although the exposure of affected workers to respirable dust or quartz is not known, industrial hygiene surveys conducted in four bentonite plants showed some areas having particle counts in excess of 3 to 11 times the ACGIH particle count limit (Document ID 3998, Attachment 18b, p. 4). This is roughly equivalent to exposure levels between 8 and 28 times OSHA's former general industry PEL of 100 μg/m³ (given that the particle count limit is about 2.5 or more times higher than the gravimetric limit for respirable quartz (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA). Exposures of this magnitude are considerably higher than those experienced by worker cohorts of the studies relied on by OSHA in its Final Risk Assessment and discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA. For example, the median of average exposures reported in the ten cohort studies used by Steenland et al. (2001, Document ID 0684, p. 775) ranged from about one-half to six times the former general industry PEL.

The lack of specific exposure information on bentonite workers found with silicosis, combined with the extraordinary exposures experienced by workers in the bentonite plants studied by Phibbs et al. (1971), make this study, while concerning, unsuitable for evaluating risks in the range of the former and final rule PELs. OSHA notes that the WHO report also concluded that available data were inadequate to conclusively establish a dose-response relationship or even a cause-and-effect relationship for bentonite dust, and that its role in inducing pneumoconiosis remains uncertain.

SMI also presented evidence from animal and in vitro studies that it believes shows that respirable crystalline quartz present in sorptive clays exists in a distinct occluded form, which significantly mitigates adverse health effects due to the physico-chemical characteristics of the occluded quartz. As discussed below, based on careful review of the studies SMI cited, OSHA believes these studies indicate that silica in bentonite clay is of lower toxicologic potency than that found in other industry sectors.

SMI submitted two studies: an animal study (Creutzenberg et al. 2008, Document ID 3891) and a study of the characteristics of quartz samples isolated from bentonite (Miles et al. 2008, Document ID 4173). SMI contended that these studies demonstrate the low toxicity potential of geologically ancient occluded quartz found in sorptive clays (Document ID 2377, pp. 8-9).

Creutzenberg et al. (2008) summarized the findings from a rat study aimed at “characterizing the differences in biological activity between crystalline ground reference quartz (DQ12) and a quartz with occluded surfaces (quartz isolate) obtained from a clay deposit formed 110-112 million years ago” (Document ID 3891, p. 995). Based on histopathological assessment of the lungs in each treatment group, Creutzenberg et al. (2008, Document ID 3891) found that the DQ12 reference quartz group exhibited a significantly stronger inflammatory reaction than the quartz isolate, which showed a slight but still statistically significant inflammatory response compared to the control group. The increased inflammatory response was observed at day 3 but not at 28 or 90 days. Thus, reaction elicited by the quartz isolate, thought to have similar properties to bentonite, was considered by the investigators to represent a moderate effect that did not progress. In light of this, the implications of this study for development of silicosis are unclear.

SMI also cited Miles et al. (2008, Document ID 4173), who studied the mineralogical and chemical characteristics of quartz samples isolated from bentonite, including the quartz isolate used by Creutzenberg et al. (2008) in their animal study. Their evaluation identified several differences in the chemical and physical properties of the quartz isolates and unoccluded quartz that could help explain the observed differences in toxicity (Document ID 4173); these included differences in crystal structure, electrical potential of particle surfaces, and, possibly, differences in the reactivity of surface-free radicals owing to the presence of iron ions in the residual clay material associated with the quartz isolates.

With respect to the two studies just discussed, animal evidence cited by SMI demonstrates that quartz in bentonite induces a modest inflammatory reaction in the lung that does not persist (Creutzenberg et al., 2008, Document ID 3891). Such a reaction is notably different from the persistent and stronger response seen with standard experimental quartz material without surface occlusion (Creutzenberg et al., 2008, Document ID 3891). Physical and chemical characteristics of quartz from bentonite deposits have been shown to differ from standard experimental quartz in ways that can explain its reduced toxicity (Miles et al., 2008, Document ID 4173). However, the animal studies cited by SMI are not suitable for risk assessment since they were short-term (90 days), single-dose experiments.

In sum, human evidence on the toxicity of quartz in bentonite clay includes one study cited by SMI that did not find an excess risk of respiratory disease (Waxweiller et al., Document ID 3998, Attachment 18e). However, because exposures experienced by the workers were low with most less than that of the final rule PEL, the lack of an observed effect cannot be solely attributed to the nature of the quartz particles. Two studies of bentonite workers found a high prevalence of silicosis based on x-ray findings (Rombola and Guardascione, 1955, Document ID 3998, Attachment 18; Phibbs et al., 1971, Document ID 3998, Attachment 18b). Limited exposure data provided in the studies as well as the relatively short latencies seen among cases of severe silicosis make it clear that the bentonite workers were exposed to extremely high dust levels. Neither of these studies can be relied on to evaluate disease risk in the exposure range of the former and revised respirable crystalline silica PELs.

OSHA finds that the evidence for quartz originating from bentonite deposits indicates some biological activity, but also indicates lower toxicity than standard experimental quartz (which has similar characteristics to quartz encountered in most workplaces where exposures occur). For regulatory purposes, however, OSHA finds that the evidence does not exist that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to quartz in sorptive clays at the 100 μg/m³ PEL. Instead, OSHA finds that the record provides no sound basis for determining the significance of risk for exposure to sorptive clays containing respirable quartz. Thus, OSHA is excluding sorptive clays (as described specifically in the Scope part of Section XV, Summary and Explanation) from the scope of the rule, until such time that sufficient science has been developed to permit evaluation of the significance of the risk. However, in excluding sorptive clays from the rule, the general industry PEL, as described in 29 CFR 1910.1000 Table Z-3, will continue to apply.

VI. Final Quantitative Risk Assessment and Significance of Risk

A. Introduction

To promulgate a standard that regulates workplace exposure to toxic materials or harmful physical agents, OSHA must first determine that the standard reduces a “significant risk” of “material impairment.” Section 6(b)(5) of the OSH Act, 29 U.S.C. 655(b). The first part of this requirement, “significant risk,” refers to the likelihood of harm, whereas the second part, “material impairment,” refers to the severity of the consequences of exposure. Section II, Pertinent Legal Authority, of this preamble addresses the statutory bases for these requirements and how they have been construed by the Supreme Court and federal courts of appeals.

It is the Agency's practice to estimate risk to workers by using quantitative risk assessment and determining the significance of that risk based on the best available evidence. Using that evidence, OSHA identifies material health impairments associated with potentially hazardous occupational exposures, and, when possible, provides a quantitative assessment of exposed workers' risk of these impairments. The Agency then evaluates whether these risks are severe enough to warrant regulatory action and determines whether a new or revised rule will substantially reduce these risks. For single-substance standards governed by section 6(b)(5) of the OSH Act, 29 U.S.C. 655(b)(5), OSHA sets a permissible exposure limit (PEL) based on that risk assessment as well as feasibility considerations. These health and risk determinations are made in the context of a rulemaking record in which the body of evidence used to establish material impairment, assess risks, and identify affected worker population, as well as the Agency's preliminary risk assessment, are placed in a public rulemaking record and subject to public comment. Final determinations regarding the standard, including final determinations of material impairment and risk, are thus based on consideration of the entire rulemaking record.

In this case, OSHA reviewed extensive toxicological, epidemiological, and experimental research pertaining to the adverse health effects of occupational exposure to respirable crystalline silica, including silicosis, other non-malignant respiratory disease (NMRD), lung cancer, and autoimmune and renal diseases. Using the information collected during this review, the Agency developed quantitative estimates of the excess risk of mortality and morbidity attributable to the previously allowed and revised respirable crystalline silica PELs; these estimates were published with the proposed rule. The Agency subsequently reexamined these estimates in light of the rulemaking record as a whole, including comments, testimony, data, and other information, and has determined that long-term exposure at and above the previous PELs would pose a significant risk to workers' health, and that adoption of the new PEL and other provisions of the final rule will substantially reduce this risk. Based on these findings, the Agency is adopting a new PEL of 50 μg/m³.

Even though OSHA's risk assessment indicates that a significant risk also exists at the revised action level of 25 μg/m³, the Agency is not adopting a PEL below the revised 50 μg/m³ limit because OSHA must also consider the technological and economic feasibility of the standard in determining exposure limits. As explained in the Summary and Explanation for paragraph (c), Permissible Exposure Limit (PEL), of the general industry/maritime standard (paragraph (d) for construction), OSHA has determined that, with the adoption of additional engineering and work practice controls, the revised PEL of 50 μg/m³ is technologically and economically feasible in most operations in the affected general industrial and maritime sectors and in the construction industry, but that a lower PEL of 25 μg/m³ is not technologically feasible for most of these operations (see Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA) and Chapter IV, Technological Feasibility, of the FEA). Therefore, OSHA concludes that by establishing the 50 μg/m³ PEL, the Agency has reduced significant risk to the extent feasible.

B. OSHA's Findings of Material Impairments of Health

As discussed below and in OSHA's Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 7-229), there is convincing evidence that inhalation exposure to respirable crystalline silica increases the risk of a variety of adverse health effects, including silicosis, NMRD (such as chronic bronchitis and emphysema), lung cancer, kidney disease, immunological effects, and infectious tuberculosis (TB). OSHA considers each of these conditions to be a material impairment of health. These diseases make it difficult or impossible to work and result in significant and permanent functional limitations, reduced quality of life, and sometimes death. When these diseases coexist, as is common, the effects are particularly debilitating (Rice and Stayner, 1995, Document ID 0418; Rosenman et al., 1999, 0421). Based on these findings and on the scientific evidence that respirable crystalline silica substantially increases the risk of each of these conditions, OSHA has determined that exposure to respirable crystalline silica increases the risk of “material impairment of health or functional capacity” within the meaning of the Occupational Safety and Health Act.

1. Silicosis

OSHA considers silicosis, an irreversible and potentially fatal disease, to be a clear material impairment of health. The term “silicosis” refers to a spectrum of lung diseases attributable to the inhalation of respirable crystalline silica. As described more fully in the Review of Health Effects Literature (Document ID 1711, pp. 16-71), the three types of silicosis are acute, accelerated, and chronic. Acute silicosis can occur within a few weeks to months after inhalation exposure to extremely high levels of respirable crystalline silica. Death from acute silicosis can occur within months to a few years of disease onset, with the affected person drowning in his or her own lung fluid (NIOSH, 1996, Document ID 0840). Accelerated silicosis results from exposure to high levels of airborne respirable crystalline silica, and disease usually occurs within 5 to 10 years of initial exposure (NIOSH, 1996, Document ID 0840). Both acute and accelerated silicosis are associated with exposures that are substantially above the previous general industry PEL, although no precise information on the relationships between exposure and occurrence of disease exists.

Chronic silicosis is the most common form of silicosis seen today, and is a progressive and irreversible condition characterized as a diffuse nodular pulmonary fibrosis (NIOSH, 1996, Document ID 0840). Chronic silicosis generally occurs after 10 years or more of inhalation exposure to respirable crystalline silica at levels below those associated with acute and accelerated silicosis. Affected workers may have a dry chronic cough, sputum production, shortness of breath, and reduced pulmonary function. These symptoms result from airway restriction caused by the development of fibrotic scarring in the lower regions of the lungs. The scarring can be detected in chest x-ray films when the lesions become large enough to appear as visible opacities. The result is a restriction of lung volumes and decreased pulmonary compliance with concomitant reduced gas transfer. Chronic silicosis is characterized by small, rounded opacities that are symmetrically distributed in the upper lung zones on chest radiograph (Balaan and Banks, 1992, Document ID 0289, pp. 347, 350-351).

The diagnosis of silicosis is based on a history of exposure to respirable crystalline silica, chest radiograph findings, and the exclusion of other conditions that appear similar. Because workers affected by early stages of chronic silicosis are often asymptomatic, the finding of opacities in the lung is key to detecting silicosis and characterizing its severity. The International Labour Organization (ILO) International Classification of Radiographs of Pneumoconioses (ILO, 1980, Document ID 1063; 2002, 1064) is the currently accepted standard against which chest radiographs are evaluated for use in epidemiological studies, medical surveillance, and clinical evaluation. The ILO system standardizes the description of chest x-rays, and is based on a 12-step scale of severity and extent of silicosis as evidenced by the size, shape, and density of opacities seen on the x-ray film. Profusion (frequency) of small opacities is classified on a 4-point major category scale (0-3), with each major category divided into three, giving a 12-point scale between 0/− and 3/+. Large opacities are defined as any opacity greater than 1 cm that is present in a film (ILO, 1980, Document ID 1063; 2002, 1064, p. 6).

The small rounded opacities seen in early stage chronic silicosis (ILO major category 1 profusion) may progress (through ILO major categories 2 and/or 3) and develop into large fibrotic masses that destroy the lung architecture, resulting in progressive massive fibrosis (PMF). This stage of advanced silicosis is usually characterized by impaired pulmonary function, permanent disability, and premature death. In cases involving PMF, death is commonly attributable to progressive respiratory insufficiency (Balaan and Banks, 1992, Document ID 0289).

Patients with ILO category 2 or 3 background profusion of small opacities are at increased risk, compared to those with category 1 profusion, of developing the large opacities characteristic of PMF. In one study of silicosis patients in Hong Kong, Ng and Chan (1991, Document ID 1106, p. 231) found the risk of PMF increased by 42 and 64 percent among patients whose chest x-ray films were classified as ILO major category 2 or 3, respectively. Research has shown that people with silicosis advanced beyond ILO major category 1 have reduced life expectancy compared to the general population (Infante-Rivard et al., 1991, Document ID 1065; Ng et al., 1992a, 0383; Westerholm, 1980, 0484).

Silicosis is the oldest known occupational lung disease and is still today the cause of significant premature mortality. As discussed further in Section V.E, Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality, in 2013, there were 111 deaths in the U.S. where silicosis was recorded as an underlying or contributing cause of death on a death certificate (NCHS data). Between 1996 and 2005, deaths attributed to silicosis resulted in an average of 11.6 years of life lost by affected workers (NIOSH, 2007, Document ID 1362). In addition, exposure to respirable crystalline silica remains an important cause of morbidity and hospitalizations. National inpatient hospitalization data show that in the year 2011, 2,082 silicosis-related hospitalizations occurred, indicating that silicosis continues to be a significant health issue in the U.S. (Document ID 3577, Tr. 854-855). Although there is no national silicosis disease surveillance system in the U.S., a published analysis of state-based surveillance data from the time period 1987-1996 estimated that between 3,600-7,000 new cases of silicosis occurred in the U.S. each year (Rosenman et al., 2003, Document ID 1166).

It has been widely reported that available statistics on silicosis-related mortality and morbidity are likely to be understated due to misclassification of causes of death (for example, as tuberculosis, chronic bronchitis, emphysema, or cor pulmonale), lack of occupational information on death certificates, or misdiagnosis of disease by health care providers (Goodwin et al., 2003, Document ID 1030; Windau et al., 1991, 0487; Rosenman et al., 2003, 1166). Furthermore, reliance on chest x-ray findings may miss cases of silicosis because fibrotic changes in the lung may not be visible on chest radiograph; thus, silicosis may be present absent x-ray signs or may be more severe than indicated by x-ray (Hnizdo et al., 1993, Document ID 1050; Craighhead and Vallyahan, 1980, 0995; Rosenman et al., 1997, 4181).

Although most workers with early-stage silicosis (ILO categories 0/1 or 1/0) typically do not experience respiratory symptoms, the primary risk to the affected worker is progression of disease with progressive decline of lung function. Several studies of workers exposed to crystalline silica have shown that, once silicosis is detected by x-ray, a substantial proportion of affected workers can progress beyond ILO category 1 silicosis, even after exposure has ceased (e.g., Hughes, 1982, Document ID 0362; Hessel et al., 1988, 1042; Miller et al., 1998, 0374; Ng et al., 1987a, 1108; Yang et al., 2006, 1134). In a population of coal miners whose last chest x-ray while employed was classified as major category 0, and who were examined again 10 years after the mine had closed, 20 percent had developed opacities consistent with a classification of at least 1/0, and 4 percent progressed further to at least 2/1 (Miller et al., 1998, Document ID 0374). Although there were periods of extremely high exposure to respirable quartz in the mine (greater than 2,000 μg/m³ in some jobs between 1972 and 1976, and more than 10 percent of exposures between 1969 and 1977 were greater than 1,000 μg/m³), the mean cumulative exposure for the cohort over the period 1964-1978 was 1.8 mg/m³-yrs, corresponding to an average silica concentration of 120 μg/m³. In a population of granite quarry workers exposed to an average respirable silica concentration of 480 μg/m³ (mean length of employment was 23.4 years), 45 percent of those diagnosed with simple silicosis (i.e., presence of small opacities only on chest x-ray films) showed radiological progression of disease after 2 to 10 years of follow up (Ng et al., 1987a, Document ID 1108). Among a population of gold miners, 92 percent progressed in 14 years; exposures of high-, medium-, and low-exposure groups were 970, 450, and 240 μg/m³, respectively (Hessel et al., 1988, Document ID 1042). Chinese mine and factory workers categorized under the Chinese system of x-ray classification as “suspected” silicosis cases (analogous to ILO 0/1) had a progression rate to stage I (analogous to ILO major category 1) of 48.7 percent, and the average interval was about 5.1 years (Yang et al., 2006, Document ID 1134).

The risk of silicosis carries with it an increased risk of reduced lung function as the disease irreversibly progresses. There is strong evidence in the literature for the finding that lung function deteriorates more rapidly in workers exposed to silica, especially those with silicosis, than what is expected from a normal aging process (Cowie, 1988, Document ID 0993; Hughes et al., 1982, 0362; Malmberg et al., 1993, 0370; Ng and Chan, 1992, 1107). The rates of decline in lung function are greater in those whose disease showed evidence of radiologic progression (Begin et al., 1987, Document ID 0295; Cowie, 1988, 0993; Ng and Chan, 1992, 1107; Ng et al., 1987a, 1108). Additionally, the average deterioration of lung function exceeds that in smokers (Hughes et al., 1982, Document ID 0362).

Several studies have reported no decrease in pulmonary function with an ILO category 1 level of profusion of small opacities but found declines in pulmonary function with categories 2 and 3 (Ng et al., 1987a, Document ID 1108; Begin et al., 1988, 0296; Moore et al., 1988, 1099). However, one study found a statistically significantly greater annual loss in forced vital capacity (FVC) and forced expiratory volume in one second (FEV₁) among those with category 1 profusion compared to category 0 (Cowie, 1988, Document ID 0993). In another study, the degree of profusion of opacities was associated with reductions in several pulmonary function metrics (Cowie and Mabena, 1991, Document ID 0342). Some studies have reported no associations between radiographic silicosis and decreases in pulmonary function (Ng et al., 1987a, Document ID 1108; Wiles et al., 1972, 0485; Hnizdo, 1992, 1046), while other studies (Ng et al., 1987a, Document ID 1108; Wang et al., 1997, 0478) have found that measurable changes in pulmonary function are evident well before the changes seen on chest x-ray. Findings of pulmonary function decrements absent radiologic signs of silicosis may reflect the general insensitivity of chest radiography in detecting lung fibrosis, or may also reflect that exposure to respirable silica has been shown to increase the risk of non-malignant respiratory disease (NMRD) and its attendant pulmonary function losses (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA).

Moreover, exposure to respirable crystalline silica in and of itself, with or without silicosis, increases the risk that latent tuberculosis infection can convert to active disease. Early descriptions of dust diseases of the lung did not distinguish between TB and silicosis, and most fatal cases described in the first half of this century were a combination of silicosis and TB (Castranova et al., 1996, Document ID 0314). More recent findings demonstrate that exposure to silica, even without silicosis, increases the risk of infectious (i.e., active) pulmonary TB (Sherson and Lander, 1990, Document ID 0434; Cowie, 1994, 0992; Hnizdo and Murray, 1998, 0360; teWaterNaude et al., 2006, 0465). Both conditions together can hasten the development of respiratory impairment and increase mortality risk even beyond that experienced by persons with active TB who have not been exposed to respirable crystalline silica (Banks, 2005, Document ID 0291).

Based on the information presented above and in its review of the health literature, OSHA concludes that silicosis remains a significant cause of early death and of serious illness, despite the existence of an enforceable exposure limit over the past 40 years. Silicosis in its later stages of progression (i.e., with chest x-ray findings of ILO category 2 or 3 profusion of small opacities, or the presence of large opacities) is characterized by the likely appearance of respiratory symptoms and decreased pulmonary function, as well as increased risk of progression to PMF, disability, and early mortality. Early-stage silicosis, although without symptoms among many who are affected, nevertheless reflects the formation of fibrotic lesions in the lung and increases the risk of progression to later stages, even after exposure to respirable crystalline silica ceases. In addition, the presence of silicosis increases the risk of pulmonary infections, including conversion of latent TB infection to active TB. Silicosis is not a reversible condition, and there is no specific treatment for the disease, other than administration of drugs to alleviate inflammation and maintain open airways, or administration of oxygen therapy in severe cases. Based on these considerations, OSHA finds that silicosis of any form, and at any stage of progression, is a material impairment of health and that fibrotic scarring of the lungs represents loss of functional respiratory capacity.

2. Lung Cancer

OSHA considers lung cancer, an irreversible and frequently fatal disease, to be a clear material impairment of health (see Homer et al., 2009, Document ID 1343). According to the National Cancer Institute (SEER Cancer Statistics Review, 2006, Document ID 1343), the five-year survival rate for all forms of lung cancer is only 15.6 percent, a rate that has not improved in nearly two decades. After reviewing the record as a whole, OSHA finds that respirable crystalline silica exposure substantially increases the risk of lung cancer. This finding is based on the best available toxicological and epidemiological data, reflects substantial supportive evidence from animal and mechanistic research, and is consistent with the conclusions of other government and public health organizations, including the International Agency for Research on Cancer (1997, Document ID 1062; 2012, Document ID 1473), the HHS National Toxicology Program (2000, Document ID 1417), the CDC's National Institute for Occupational Safety and Health (2002, Document ID 1110), the American Thoracic Society (1997, Document ID 0283), and the American Conference of Governmental Industrial Hygienists (2010, Document ID 0515).

The Agency's primary evidence comes from evaluation of more than 50 studies of occupational cohorts from many different industry sectors in which exposure to respirable crystalline silica occurs, including: Granite and stone quarrying; the refractory brick industry; gold, tin, and tungsten mining; the diatomaceous earth industry; the industrial sand industry; and construction. In addition, the association between exposure to respirable crystalline silica and lung cancer risk was reported in a national mortality surveillance study (Calvert et al., 2003, Document ID 0309) and in two community-based studies (Pukkala et al., 2005, Document ID 0412; Cassidy et al., 2007, 0313), as well as in a pooled analysis of 10 occupational cohort studies (Steenland et al., 2001a, Document ID 0452). Toxicity studies provide supportive evidence of the carcinogenicity of crystalline silica, in that they demonstrate biologically plausible mechanisms by which crystalline silica in the deep lung can give rise to biochemical and cellular events leading to tumor development (see Section V.H, Mechanisms of Silica-Induced Adverse Health Effects).

3. Non-Malignant Respiratory Disease (NMRD) (Other Than Silicosis)

Although many of the stakeholders in this rule have focused their attention on the evidence related to silicosis and lung cancer, the available evidence shows that exposure to respirable crystalline silica also increases the risk of developing NMRD, in particular chronic bronchitis and emphysema. OSHA has determined that NMRD, which results in loss of pulmonary function that restricts normal activity in individuals afflicted with these conditions (see American Thoracic Society, 2003, Document ID 1332), constitutes a material impairment of health. Both chronic bronchitis and emphysema can occur in conjunction with the development of silicosis. Several studies have documented increased prevalence of chronic bronchitis and emphysema among silica-exposed workers even absent evidence of silicosis (see Document ID 1711, pp. 182-192; NIOSH, 2002, 1110; American Thoracic Society, 2003, 1332). There is also evidence that smoking may have an additive or synergistic effect on silica-related NMRD morbidity or mortality (Hnizdo, 1990, Document ID 1045; Hnizdo et al., 1990, 1047; Wyndham et al., 1986, 0490; NIOSH, 2002, 1110). In a study of diatomaceous earth workers, Park et al. (2002, Document ID 0405) found a positive exposure-response relationship between exposure to respirable cristobalite (a form of silica) and increased mortality from NMRD.

Decrements in pulmonary function have often been found among workers exposed to respirable crystalline silica absent radiologic evidence of silicosis. Several cross-sectional studies have reported such findings among granite workers (Theriault et al., 1974a, Document ID 0466; Wallsh, 1997, 0477; Ng et al., 1992b, 0387; Montes II et al., 2004b, 0377), gold miners (Irwig and Rocks, 1978, Document ID 1067; Hnizdo et al., 1990, 1047; Cowie and Mabena, 1991, 0342), gemstone cutters (Ng et al., 1987b, Document ID 1113), concrete workers (Meijer et al., 2001, Document ID 1243), refractory brick workers (Wang et al., 1997, Document ID 0478), hard rock miners (Manfreda et al., 1982, Document ID 1094; Kreiss et al., 1989, 1079), pottery workers (Neukirk et al., 1994, Document ID 0381), slate workers (Surh, 2003, Document ID 0462), and potato sorters exposed to silica in diatomaceous earth (Jorna et al, 1994, Document ID 1071).

OSHA also evaluated several longitudinal studies where exposed workers were examined over a period of time to track changes in pulmonary function. Among both active and retired granite workers exposed to an average of 60 μg/m ³, Graham et al. did not find exposure-related decrements in pulmonary function (1981, Document ID 1280; 1984, 0354). However, Eisen et al. (1995, Document ID 1010) did find significant pulmonary decrements among a subset of granite workers (termed “dropouts”) who left work and consequently did not voluntarily participate in the last of a series of annual pulmonary function tests. This group of workers experienced steeper declines in FEV1 compared to the subset of workers who remained at work and participated in all tests (termed “survivors”), and these declines were significantly related to dust exposure. Thus, in this study, workers who had left work had exposure-related declines in pulmonary function to a greater extent than did workers who remained on the job, clearly demonstrating a survivor effect among the active workers. Exposure-related changes in lung function were also reported in a 12-year study of granite workers (Malmberg, 1993, Document ID 0370), in two 5-year studies of South African miners (Hnizdo, 1992, Document ID 1046; Cowie, 1988, 0993), and in a study of foundry workers whose lung function was assessed between 1978 and 1992 (Hertzberg et al., 2002, Document ID 0358).

Each of these studies reported their findings in terms of rates of decline in any of several pulmonary function measures, such as FVC, FEV₁, and FEV₁/FVC. To put these declines in perspective, Eisen et al. (1995, Document ID 1010) reported that the rate of decline in FEV₁ seen among the dropout subgroup of Vermont granite workers was 4 ml per mg/m³-yrs of exposure to respirable granite dust; by comparison, FEV₁ declines at a rate of 10 ml/year from smoking one pack of cigarettes daily. From their study of foundry workers, Hertzberg et al., reported finding a 1.1 ml/year decline in FEV₁ and a 1.6 ml/year decline in FVC for each mg/m³-yrs of respirable silica exposure after controlling for ethnicity and smoking (2002, Document ID 0358, p. 725). From these rates of decline, they estimated that exposure to the previous OSHA general industry quartz standard of 100 µg/m³ for 40 years would result in a total loss of FEV₁ and FVC that is less than but still comparable to smoking a pack of cigarettes daily for 40 years. Hertzberg et al. also estimated that exposure to the current standard for 40 years would increase the risk of developing abnormal FEV1 or FVC by factors of 1.68 and 1.42, respectively (2002, Document ID 0358, pp. 725-726). OSHA believes that this magnitude of reduced pulmonary function, as well as the increased morbidity and mortality from non-malignant respiratory disease (NMRD) that has been documented in the studies summarized above, constitute material impairments of health and loss of functional respiratory capacity.

4. Renal and Autoimmune Effects

Finally, OSHA's review of the literature reflects substantial evidence that exposure to crystalline silica increases the risk of renal and autoimmune diseases, both of which OSHA considers to be material impairments of health (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA). Epidemiological studies have found statistically significant associations between occupational exposure to silica dust and chronic renal disease (e.g., Calvert et al., 1997, Document ID 0976), subclinical renal changes including proteinurea and elevated serum creatinine (e.g., Ng et al., 1992c, Document ID 0386; Rosenman et al., 2000, 1120; Hotz, et al., 1995, 0361), end-stage renal disease morbidity (e.g., Steenland et al., 1990, Document ID 1125), chronic renal disease mortality (Steenland et al., 2001b, Document ID 0456; 2002a, 0448), and granulomatosis with polyangitis (Nuyts et al., 1995, Document ID 0397). Granulomatosis with polyangitis is characterized by inflammation of blood vessels, leading to damaging granulomatous formation in the lung and damage to the glomeruli of the kidneys, a network of capillaries responsible for the first stage of blood filtration. If untreated, this condition often leads to renal failure (Nuyts et al., 1995, Document ID 0397, p. 1162). Possible mechanisms for silica-induced renal disease include a direct toxic effect on the kidney and an autoimmune mechanism (see Section V.H, Mechanisms of Silica-Induced Adverse Health Effects; Calvert et al., 1997, Document ID 0976; Gregorini et al., 1993, 1032). Steenland et al. (2002a, Document ID 0448) demonstrated a positive exposure-response relationship between exposure to respirable crystalline silica and end-stage renal disease mortality.

In addition, there are a number of studies that show exposure to be related to increased risks of autoimmune disease, including scleroderma (e.g., Sluis-Cremer et al., 1985, Document ID 0439), rheumatoid arthritis (e.g., Klockars et al., 1987, Document ID 1075; Rosenman and Zhu, 1995, 0424), and systemic lupus erythematosus (e.g., Brown et al., 1997, Document ID 0974). Scleroderma is a degenerative disorder that leads to over-production of collagen in connective tissue that can cause a wide variety of symptoms including skin discoloration and ulceration, joint pain, swelling and discomfort in the extremities, breathing problems, and digestive problems. Rheumatoid arthritis is characterized by joint pain and tenderness, fatigue, fever, and weight loss. Systemic lupus erythematosus is a chronic disease of connective tissue that can present a wide range of symptoms including skin rash, fever, malaise, joint pain, and, in many cases, anemia and iron deficiency. OSHA considers chronic renal disease, end-stage renal disease mortality, granulomatosis with polyangitis, scleroderma, rheumatoid arthritis, and systemic lupus erythematosus clearly to be material impairments of health.

C. OSHA's Final Quantitative Risk Estimates

To evaluate the significance of the health risks that result from exposure to hazardous chemical agents, OSHA relies on epidemiological and experimental data, as well as statistical methods. The Agency uses these data and methods to characterize the risk of disease resulting from workers' exposure to a given hazard over a working lifetime at levels of exposure reflecting both compliance with previous standards and compliance with the new standard. In the case of respirable crystalline silica, the previous general industry, construction, and shipyard PELs were formulas that limit 8-hour TWA exposures to respirable dust; the limit on exposure decreased with increasing crystalline silica content of the dust. OSHA's previous general industry PEL for respirable quartz was expressed both in terms of a particle count and a gravimetric concentration, while the previous construction and shipyard employment PELs for respirable quartz were only expressed in terms of a particle count formula. For general industry, the gravimetric formula PEL for quartz approaches 100 µg/m³ of respirable crystalline silica when the quartz content of the dust is about 10 percent or greater. The previous PEL's particle count formula for the construction and shipyard industries is equal to a range of about 250 μg/m³ to 500 μg/m³ expressed as respirable quartz. In general industry, the previous PELs for cristobalite and tridymite, which are forms (polymorphs) of silica, were one-half the PEL for quartz.

In this final rule, OSHA has established a uniform PEL for respirable crystalline silica by revising the PELs applicable to general industry, construction, and maritime to 50 μg/m³ TWA of respirable crystalline silica. OSHA has also established an action level of 25 µg/m³ TWA. In this section of the preamble, OSHA presents its final estimates of health risks associated with a working lifetime (45 years) of exposure to 25, 50, and 100 µg/m³ respirable crystalline silica. These levels represent the risks associated with exposure over a working lifetime to the new action level, new PEL, and previous general industry PEL, respectively. OSHA also presents estimates associated with exposure to 250 and 500 µg/m³ to represent a range of risks likely to be associated with exposure to the former construction and shipyard PELs. Risk estimates are presented for mortality due to lung cancer, silicosis and other non-malignant respiratory disease (NMRD), and end-stage renal disease, as well as silicosis morbidity. These estimates are the product of OSHA's risk assessment, following the Agency's consideration of new data introduced into the rulemaking record and of the numerous comments in the record that raised questions about OSHA's preliminary findings and analysis.

After reviewing the evidence and testimony in the record, OSHA has determined that it is appropriate to base its final risk estimates on the same studies and models as were used in the NPRM (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA). For mortality risk estimates, OSHA used the models developed by various investigators and employed a life table analysis to implement the models using the same background all-cause mortality data and consistent assumption for length of lifetime (85 years). The life table is a technique that allows estimation of excess risk of disease mortality factoring in the probability of surviving to a particular age assuming no exposure to the agent in question and given the background probability of dying from any cause at or before that age (see Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric). Since the time of OSHA's preliminary analysis, the National Center for Health Statistics (NCHS) released updated all-cause mortality background rates from 2011; these rates are available in an internet web-based query by year and 2010 International Classification of Diseases (ICD) code through the Centers of Disease Control and Prevention (CDC) Wonder database ( http://wonder.cdc.gov/udc-icd10.html ). Using these updated statistics, OSHA revised its life table analyses to estimate lifetime risks of mortality that result from 45 years of exposure to respirable crystalline silica. OSHA's final quantitative mortality risk estimates are presented in Table VI-1 below.

For silicosis morbidity risk estimates, OSHA relied on the cumulative risk models developed by investigators of five studies who conducted studies relating cumulative disease risk to cumulative exposure to respirable crystalline silica (see footnotes to Table VI-1). Of these, only one, the study by Steenland and Brown (1995) of U.S. gold miners, employed a life-table analysis. Table VI-1 also presents OSHA's final quantitative estimates of silicosis morbidity risks.

OSHA notes that the updated risk estimates are not substantially different from those presented in the Preliminary QRA; for example, for exposure at the previous general industry PEL approaching 100 μg/m³, the excess lung cancer mortality risk ranged from 13 to 60 deaths per 1,000 workers using the original 2006 background data, and from 11 to 54 deaths per 1,000 workers using the updated 2011 background data. For exposure at the revised PEL of 50 μg/m³, the risk estimates ranged from 6 to 26 deaths per 1,000 workers using the 2006 background data, and 5 to 23 deaths per 1,000 workers using the 2011 background data. Similarly, the updated risk estimates for NMRD are not substantially different; for example, for exposure for 45 working years at the previous general industry PEL approaching 100 μg/m³, the excess NMRD mortality risk, using the Park et al. (2002, Document 0405) model was 83 deaths per 1,000 workers using the original 2006 background data, and 85 deaths per 1,000 workers using the updated 2011 background data. For exposure at the revised PEL of 50 μg/m³, the risk estimate was 43 deaths per 1,000 workers using the 2006 background data, and 44 deaths per 1,000 workers using the 2011 background data.

OSHA also presents in the table the excess lung cancer mortality risk associated with 45 years of exposure to the previous construction/shipyard PEL (in the range of 250 to 500 µg/m³). It should be noted, however, that exposure to 250 or 500 µg/m³ over 45 years represents cumulative exposures of 11.25 and 22.5 mg/m³-yrs, respectively, which are well above the median cumulative exposure for most of the cohorts used in the risk assessment. Estimating excess risks over this higher range of cumulative exposures required some degree of extrapolation, which adds uncertainty. In addition, at cumulative exposures as high as permitted by the previous construction and maritime PELs, silica-related causes of mortality will compete with each other and it is difficult to determine the risk of any single cause of mortality in the face of such competing risks.

OSHA's final risk estimates for renal disease reflect the 1998 background all-cause mortality and renal mortality rates for U.S. males, rather than the 2011 rates used for lung cancer and NMRD, as updated in the previous sections. Background rates were not adjusted for the renal disease risk estimates because the CDC significantly changed the classification of renal diseases after 1998; they are now inconsistent with those used by Steenland et al. (2002a, Document ID 0448), the study relied on by OSHA, to ascertain the cause of death of workers in their study. OSHA notes that the change in classification system, from ICD-9 to ICD-10, did not materially affect background rates for diseases grouped as lung cancer or NMRD. The findings from OSHA's final risk assessment are summarized below.

OSHA notes that the key studies in its final risk assessment were composed of cohorts with cumulative exposures relevant to those permitted by the preceding General Industry PEL (45 years of exposure at 100 μg/m³ equals 4.5 mg/m³-yrs). Table VI-2 provides the reported cumulative exposure information for each of the cohorts of the key studies. Most of these cohorts had mean or median cumulative exposures below 4.5 mg/m³-yrs. Based on this data, OSHA concludes that the cumulative exposures experienced by the cohorts are relevant and reasonable for use in the Agency's final risk assessment.

1. Summary of Excess Risk Estimates for Lung Cancer Mortality

For estimates of lung cancer risk from crystalline silica exposure, OSHA has relied upon studies of exposure-response relationships presented in a pooled analysis of 10 cohort studies (Steenland et al., 2001a, Document ID 0452; ToxaChemica, Inc., 2004, 0469) as well as on individual studies of granite (Attfield and Costello, 2004, Document ID 0543), diatomaceous earth (Rice et al., 2001, Document ID 1118), and industrial sand (Hughes et al., 2001, Document ID 1060) worker cohorts, and a study of coal miners exposed to respirable crystalline silica (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306). OSHA found these studies to have been suitable for use to quantitatively characterize health risks to exposed workers because: (1) Study populations were of sufficient size to provide adequate statistical power to detect low levels of risk; (2) sufficient quantitative exposure data were available over a sufficient span of time to characterize cumulative exposures of cohort members to respirable crystalline silica; (3) the studies either adjusted for or otherwise adequately addressed confounding factors such as smoking and exposure to other carcinogens; and (4) investigators developed quantitative assessments of exposure-response relationships using appropriate statistical models or otherwise provided sufficient information that permits OSHA to do so. OSHA implemented all risk models in its own life table analysis so that the use of background lung cancer rates and assumptions regarding length of exposure and lifetime were consistent across each of the models, and so OSHA could estimate lung cancer risks associated with exposure to specific levels of silica of interest to the Agency.

The Steenland et al. (2001a, Document ID 0452) study consisted of a pooled exposure-response analysis and risk assessment based on raw data obtained for ten cohorts of silica-exposed workers (65,980 workers, 1,072 lung cancer deaths). The cohorts in this pooled analysis include U.S. gold miners (Steenland and Brown, 1995a, Document ID 0450), U.S. diatomaceous earth workers (Checkoway et al., 1997, Document ID 0326), Australian gold miners (de Klerk and Musk, 1998, Document ID 0345), Finnish granite workers (Koskela et al., 1994, Document ID 1078), South African gold miners (Hnizdo et al., 1997, Document ID 1049), U.S. industrial sand workers (Steenland et al., 2001b, Document ID 0456), Vermont granite workers (Costello and Graham, 1988, Document ID 0991), and Chinese pottery workers, tin miners, and tungsten miners (Chen et al., 1992, Document ID 0329). To determine the exposure-response relationship between silica exposures and lung cancer, the investigators used a nested case-control design with cases and controls matched for race, sex, age (within five years), and study; 100 controls were matched for each case. An extensive exposure assessment for this pooled analysis was developed and published by Mannetje et al. (2002a, Document ID 1090).

Using ToxaChemica's study (2004, Document ID 0469) of this pooled data, the estimated excess lifetime lung cancer risk associated with 45 years of exposure to 100 μg/m³ (about equal to the previous general industry PEL) is between 20 and 26 deaths per 1,000 workers. The estimated excess lifetime risk associated with 45 years of exposure to silica concentrations in the range of 250 and 500 μg/m³ (about equal to the previous construction and shipyard PELs) is between 24 and 33 deaths per 1,000. At the final PEL of 50 μg/m³, the estimated excess lifetime risk ranges from 16 to 23 deaths per 1,000, and, at the action level of 25 μg/m³, from 10 to 21 deaths per 1,000.

In addition to the pooled cohort study, OSHA's Final Quantitative Risk Assessment presents risk estimates in Table VI-1 derived from four individual studies where investigators presented either lung cancer risk estimates or exposure-response coefficients. Two of these studies, one on diatomaceous earth workers (Rice et al., 2001, Document ID 1118) and one on Vermont granite workers (Attfield and Costello, 2004, Document ID 0543), were included in the 10-cohort pooled study (Steenland et al., 2001a, Document ID 0452; ToxaChemica Inc., 2004, 0469). The other two were of British coal miners (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009,1306) and North American industrial sand workers (Hughes et al., 2001, Document ID 1060).

Rice et al. (2001, Document ID 1118) presented an exposure-response analysis of the diatomaceous worker cohort studied by Checkoway et al. (1993, Document ID 0324; 1996, 0325; 1997, 0326), who found a significant relationship between exposure to respirable cristobalite and increased lung cancer mortality. From this cohort the estimates of the excess risk of lung cancer mortality are 30, 15, and 8 deaths per 1,000 workers for 45 years of exposure to 100, 50, and 25 μg/m³, respectively. For exposures in the range of the current construction and shipyard PELs over 45 years, estimated risks lie in a range between 72 and 137 excess deaths per 1,000 workers.

Somewhat higher risk estimates are derived from the analysis presented by Attfield and Costello (2004, Document ID 0543) of Vermont granite workers. OSHA's use of this analysis yielded a risk estimate of 54 excess deaths per 1,000 workers for 45 years of exposure to the previous general industry PEL of 100 μg/m³, 22 excess deaths per 1,000 for 45 years of exposure to the final PEL of 50 μg/m³, and 10 excess deaths per 1,000 for 45 years of exposure at the action level of 25 μg/m³. Estimated excess risks associated with 45 years of exposure at the current construction PEL range from 231 to 657 deaths per 1,000.

Hughes et al. (2001, Document ID 1060) conducted a study of industrial sand workers in the U.S. and Canada. Using this study, OSHA estimated cancer risks of 33, 14, and 7 deaths per 1,000 for 45 years exposure to the previous general industry PEL of 100 μg/m³, the final PEL of 50 μg/m³, and the final action level of 25 μg/m³ respirable crystalline silica, respectively. For 45 years of exposure to the previous construction PEL, estimated risks range from 120 to 407 deaths per 1,000 workers.

Miller and MacCalman (2010, Document ID 1306; also reported in Miller et al., 2007, Document ID 1305) presented a study of miners from 10 coal mines in the U.K. Based on this study, OSHA estimated the lifetime lung cancer mortality risk to be 11 per 1,000 workers for 45 years of exposure to 100 μg/m³ respirable crystalline silica. For the final PEL of 50 μg/m³ and action level of 25 μg/m³, the lifetime risks are estimated to be 5 and 3 deaths per 1,000, respectively. The range of risks estimated to result from 45 years of exposure to the previous construction and shipyard PELs is from 33 to 86 deaths per 1,000 workers.

2. Summary of Risk Estimates for Silicosis and Other Chronic Lung Disease Mortality

OSHA based its quantitative assessment of silicosis mortality risks on a pooled analysis conducted by Mannetje et al. (2002b, Document ID 1089) of data from six of the ten epidemiological studies in the Steenland et al. (2001a, Document ID 0452) pooled analysis of lung cancer mortality that also included extensive data on silicosis. Cohorts included in the silicosis study were: U.S. diatomaceous earth workers (Checkoway et al., 1997, Document ID 0326); Finnish granite workers (Koskela et al., 1994, Document ID 1078); U.S. granite workers (Costello and Graham, 1988, Document ID 0991); U.S. industrial sand workers (Silicosis and Silicate Disease Committee, 1988, Document ID 0455); U.S. gold miners (Steenland and Brown, 1995b, Document ID 0451); and Australian gold miners (de Klerk and Musk, 1998, Document ID 0345). These six cohorts contained 18,634 workers and 170 silicosis deaths, where silicosis mortality was defined as death from silicosis (ICD-9 502, n = 150) or from unspecified pneumoconiosis (ICD-9 505, n = 20). Although Mannetje et al, (2002b, Document ID 1089) estimated silicosis risks from a Poisson regression, a subsequent analysis was conducted by Steenland and Bartell (ToxaChemica, 2004, Document ID 0469) based on a case control design. Based on the Steenland and Bartell analysis, OSHA estimated that the lifetime risk of silicosis mortality associated with 45 years of exposure to the previous general industry PEL of 100 μg/m³ is 11 deaths per 1,000 workers. Exposure for 45 years to the final PEL of 50 μg/m³ results in an estimated 7 silicosis deaths per 1,000, and exposure for 45 years to the final action level of 25 μg/m³ results in an estimated 4 silicosis deaths per 1,000. Lifetime risks associated with exposure at the previous construction and shipyard PELs range from 17 to 22 deaths per 1,000 workers.

To study non-malignant respiratory diseases (NMRD), of which silicosis is one, Park et al. (2002, Document ID 0405) analyzed the California diatomaceous earth cohort data originally studied by Checkoway et al. (1997, Document ID 0326). The authors quantified the relationship between exposure to cristobalite and mortality from NMRD. Diseases in this category included pneumoconiosis (which includes silicosis), chronic bronchitis, and emphysema, but excluded pneumonia and other infectious diseases. Because of the broader range of silica-related diseases examined by Park et al., OSHA's estimates of the lifetime chronic lung disease mortality risk based on this study are substantially higher than those that OSHA derived from the Mannetje et al. (2002b, Document ID 1089) silicosis analysis. For the previous general industry PEL of 100 μg/m³, exposure for 45 years is estimated to result in 85 excess deaths per 1,000 workers. At the final PEL of 50 μg/m³ and action level of 25 μg/m³, OSHA estimates the lifetime risk from 45 years of exposure to be 44 and 22 excess deaths per 1,000, respectively. The range of risks associated with exposure at the former construction and shipyard PELs over a working lifetime is from 192 to 329 excess deaths per 1,000 workers.

3. Summary of Risk Estimates for Renal Disease Mortality

OSHA's analysis of the health effects literature included several studies that have demonstrated that exposure to respirable crystalline silica increases the risk of renal and autoimmune disease (see Document ID 1711, Review of Health Effects Literature and Preliminary QRA, pp. 208-229). For autoimmune disease, there was insufficient data on which to base a quantitative risk assessment. OSHA's assessment of the renal disease risks that result from exposure to respirable crystalline silica is based on an analysis of pooled data from three cohort studies (Steenland et al., 2002a, Document ID 0448). The combined cohort for the pooled analysis (Steenland et al., 2002a, Document ID 0448) consisted of 13,382 workers and included industrial sand workers (Steenland et al., 2001b, Document ID 0456), U.S. gold miners (Steenland and Brown, 1995a, Document ID 0450), and Vermont granite workers (Costello and Graham, 1988, Document ID 0991). Exposure data were available for 12,783 workers and analyses conducted by the original investigators demonstrated monotonically increasing exposure-response trends for silicosis, indicating that exposure estimates were not likely subject to significant random misclassification. The mean duration of exposure, cumulative exposure, and concentration of respirable silica for the combined cohort were 13.6 years, 1.2 mg/m³-years, and 70 μg/m³, respectively. There were highly statistically significant trends for increasing renal disease mortality with increasing cumulative exposure for both multiple cause analysis of mortality (p < 0.000001) and underlying cause analysis (p = 0.0007). OSHA's estimates of renal disease mortality risk based on this study are 39 deaths per 1,000 for 45 years of exposure at the previous general industry PEL of 100 μg/m³, 32 deaths per 1,000 for exposure at the final PEL of 50 μg/m³, and 25 deaths per 1,000 at the action level of 25 μg/m³. OSHA also estimates that 45 years of exposure at the previous construction and shipyard PELs would result in a renal disease excess mortality risk ranging from 52 to 63 deaths per 1,000 workers. OSHA acknowledges that the risk estimates for end-stage renal disease mortality are less robust than those for silicosis, lung cancer, and NMRD, and are thus more uncertain.

4. Summary of Risk Estimates for Silicosis Morbidity

OSHA's Final Quantitative Risk Assessment is based on several cross-sectional studies designed to characterize relationships between exposure to respirable crystalline silica and development of silicosis as determined by chest radiography. Due to the long latency periods associated with silicosis, OSHA relied on those studies that were able to contact and evaluate many of the workers who had retired. OSHA believes that relying on studies that included retired workers comes closest to characterizing lifetime risk of silicosis morbidity. OSHA identified studies of six cohorts for which the inclusion of retirees was deemed sufficient to adequately characterize silicosis morbidity risks well past employment (Hnizdo and Sluis-Cremer, 1991, Document ID 1051; Steenland and Brown, 1995b, 0451; Miller et al., 1998, 0374; Buchanan et al., 2003, 0306; Chen et al., 2001, 0332; Chen et al., 2005, 0985). Study populations included five mining cohorts and a Chinese pottery worker cohort. With the exception of a coal miner study (Buchanan et al., 2003, Document ID 0306), risk estimates reflected the risk that a worker will acquire an abnormal chest x-ray classified as ILO major category 1 or greater; the coal miner study evaluated the risk of acquiring an abnormal chest x-ray classified as major category 2 or higher.

For miners exposed to freshly cut respirable crystalline silica, OSHA estimates the risk of developing lesions consistent with an ILO classification of category 1 or greater to range from 120 to 773 cases per 1,000 workers exposed at the previous general industry PEL of 100 μg/m³ for 45 years; from 20 to 170 cases per 1,000 workers exposed at the final PEL of 50 μg/m³; and from 5 to 40 cases per 1,000 workers exposed at the new action level of 25 μg/m³. From the coal miner study of Buchanan et al., (2003, Document ID 0306), OSHA estimates the risks of acquiring an abnormal chest x-ray classified as ILO category 2 or higher to be 301, 55, and 21 cases per 1,000 workers exposed for 45 years to 100, 50, and 25 μg/m³, respectively. These estimates are within the range of risks obtained by OSHA from the other mining studies. At exposures at or above 250 μg/m³ (equivalent to the previous construction and shipyard PELs) for 45 years, the risk of acquiring an abnormal chest x-ray approaches 100 percent. OSHA's risk estimates based on the pottery cohort are 60, 20, and 5 cases per 1,000 workers exposed for 45 years to 100, 50, and 25 μg/m³, respectively, which is generally below the range of risks estimated from the other studies and may reflect a lower toxicity of quartz particles in that work environment due to the presence of aluminosilicates on the particle surfaces (see Section V.N, Comments and Responses Concerning Physico-chemical and Toxicological Properties of Respirable Crystalline Silica); they are still well over OSHA's 1 in a 1,000 workers benchmark for setting standards, however. According to Chen et al. (2005, Document ID 0985), adjustment of the exposure metric to reflect the unoccluded surface area of silica particles resulted in an exposure-response of pottery workers that was similar to the mining cohorts, indicating that the occluded surface reduced the toxic potency of the quartz particles. The finding of a reduced silicosis risk among pottery workers is consistent with other studies of clay and brick industries that have reported finding a lower prevalence of silicosis compared to that experienced in other industry sectors (Love et al., 1999, Document ID 0369; Hessel, 2006, 1299; Miller and Soutar, 2007, 1098) as well as a lower silicosis risk per unit of cumulative exposure (Love et al., 1999, Document ID 0369; Miller and Soutar, 2007, 1098).

D. Significance of Risk and Risk Reduction

In this section, OSHA presents its final findings with respect to the significance of the risks summarized above and the potential of the proposed standard to reduce those risks. Findings related to mortality risk will be presented first, followed by silicosis morbidity risks.

1. Mortality Risks

OSHA's Final Quantitative Risk Assessment described above presents risk estimates for four causes of excess mortality: Lung cancer, silicosis, non-malignant respiratory disease (including silicosis), and renal disease. Table VI-1 above presents OSHA's estimated excess lifetime risks (i.e., to age 85, following 45 years of occupational exposure) of these fatal diseases associated with various levels of respirable crystalline silica exposure allowed under the former PELs and the final PEL and action level promulgated herein. OSHA's mortality risk estimates represent “excess” risks in the sense that they reflect the risk of dying from disease over and above that of persons who are not occupationally exposed to respirable crystalline silica.

Assuming a 45-year working life, as OSHA has done in significant risk determinations for previous standards, the Agency finds that the excess risk of disease mortality related to exposure to respirable crystalline silica at levels permitted by the previous OSHA standards is clearly significant. The Agency's estimate of such risk falls well above the level of risk the Supreme Court indicated a reasonable person would consider unacceptable (Benzene, 448 U.S. 607, 655). For lung cancer, OSHA estimates the range of risk at the previous general industry PEL to be between 11 and 54 deaths per 1,000 workers. The estimated risk for silicosis mortality is 11 deaths per 1,000 workers; however, the estimated lifetime risk for non-malignant respiratory disease (NMRD) mortality, including silicosis, is about 8-fold higher than that for silicosis alone, at 85 deaths per 1,000. This higher estimate for NMRD is better than the estimate for silicosis mortality at capturing the total respiratory disease burden associated with exposure to crystalline silica dust. The former captures deaths related to other non-malignant diseases, including chronic bronchitis and emphysema, for which there is strong evidence of a causal relationship with exposure to silica, and is also more likely to capture those deaths where silicosis was a contributing factor but where the cause of death was misclassified. Finally, there is an estimated lifetime risk of renal disease mortality of 39 deaths per 1,000. Exposure for 45 years at levels of respirable crystalline silica in the range of the previous limits for construction and shipyards results in even higher risk estimates, as presented in Table VI-1. It should be noted that these risk estimates are not additive because some individuals may suffer from multiple diseases caused by exposure to silica.

To further demonstrate significant risk, OSHA compares the risks at the former PELs and the revised PEL for respirable crystalline silica to risks found across a broad variety of occupations. OSHA also compares the lung cancer risk associated with the former PELs and revised PEL to the risks for other carcinogens OSHA regulates. The Agency has used similar occupational risk comparisons in the significant risk determinations for other substance-specific standards.

Fatal injury rates for most U.S. industries and occupations may be obtained from data collected by the Department of Labor's Bureau of Labor Statistics (BLS). Table VI-3 shows annual fatality rates per 1,000 employees for several industries for 2013, as well as projected fatalities per 1,000 employees assuming exposure to workplace hazards for 45 years based on these annual rates. While it is difficult to meaningfully compare aggregate industry fatality rates to the risks estimated in the quantitative risk assessment for respirable crystalline silica, which address one specific hazard (inhalation exposure to respirable crystalline silica) and several health outcomes (lung cancer, silicosis, NMRD, renal disease mortality), these rates provide a useful frame of reference for considering risk from inhalation exposure to crystalline silica. For example, OSHA's estimated range of 5-54 excess lung cancer deaths per 1,000 workers from regular occupational exposure to respirable crystalline silica in the range of 50-100 μg/m³ is roughly comparable to, or higher than, the expected risk of fatal injuries over a working life in high-risk occupations such as mining and construction (see Table VI-3). Regular exposures at higher levels, including the previous construction and shipyard PELs for respirable crystalline silica, are expected to cause substantially more deaths per 1,000 workers from lung cancer alone (ranging from 24 to 657 per 1,000) than result from occupational injuries in most private industry. At the final PEL of 50 μg/m³ respirable crystalline silica, the Agency's estimate of excess lung cancer mortality, from 5 to 23 deaths per 1,000 workers, is still 3- to 15-fold higher than private industry's average fatal injury rate, given the same employment time, and substantially exceeds those rates found in lower-risk industries such as finance and educational and health services. Adding in the mortality from silicosis, NMRD, and renal disease would make these comparisons even more stark.

Because there is little available information on the incidence of occupational cancer across all industries, risk from crystalline silica exposure cannot be compared with overall risk from other workplace carcinogens. However, OSHA's previous risk assessments provide estimates of risk from exposure to certain carcinogens. These risk assessments, as with the current assessment for respirable crystalline silica, were based on animal or human data of reasonable or high quality and used the best information then available. Table VI-4 shows the Agency's best estimates of cancer risk from 45 years of occupational exposure to several carcinogens, as published in the preambles to final rules promulgated since the Benzene decision in 1980.

The estimated excess lung cancer mortality risks associated with respirable crystalline silica at the previous general industry PEL, 11-54 deaths per 1,000 workers, are comparable to, and in some cases higher than, the estimated excess cancer risks for many other workplace carcinogens for which OSHA made a determination of significant risk (see Table VI-4, “Selected OSHA Risk Estimates for Prior and Current PELs”). The estimated excess lung cancer risks associated with exposure to the previous construction and shipyard PELs are even higher. The estimated risk from lifetime occupational exposure to respirable crystalline silica at the final PEL of 50 μg/m³ is 5-23 excess lung cancer deaths per 1,000 workers, a range still higher than the risks from exposure to many other carcinogens regulated by OSHA.

OSHA's risk assessment also shows that reduction of the PELs for respirable crystalline silica to the final level of 50 μg/m³ will result in substantial reduction in risk, although quantitative estimates of that reduction vary depending on the statistical models used. Risk models that reflect attenuation of the risk with increasing exposure, such as those relating risk to a log transformation of cumulative exposure, will result in lower estimates of risk reduction compared to linear risk models. Thus, for lung cancer risks, the assessment based on the 10-cohort pooled analysis by Steenland et al. (2001, Document ID 0455; also 0469; 1312) suggests risk will be reduced by about 14 percent from the previous general industry PEL and by 28-41 percent from the previous construction/shipyard PEL (based on the midpoint of the ranges of estimated risk derived from the three models used for the pooled cohort data). These risk reduction estimates, however, are much lower than those derived from the single cohort studies (Rice et al., 2001, Document ID 1118; Attfield and Costello, 2004, 0543; Hughes et al., 2001, 1060; Miller and MacCalman 2009, 1306). These single cohort studies suggest that reducing the previous PELs to the final PEL will reduce lung cancer risk by more than 50 percent in general industry and by more than 80 percent in construction and shipyards.

For silicosis mortality, OSHA's assessment indicates that risk will be reduced by 36 percent and by 58-68 percent as a result of reducing the previous general industry and construction/shipyard PELs, respectively. NMRD mortality risks will be reduced by 48 percent and by 77-87 percent as a result of reducing the general industry and construction/shipyard PELs, respectively, to the new PEL. There is also a substantial reduction in renal disease mortality risks; an 18-percent reduction associated with reducing the previous general industry PEL and a 38-49 percent reduction associated with reducing the previous construction/shipyard PEL.

Thus, OSHA believes that the final PEL of 50 μg/m³ respirable crystalline silica will substantially reduce the risk of material health impairments associated with exposure to silica. However, even at this final PEL, as well as the action level of 25 μg/m³, the risk posed to workers with 45 years of regular exposure to respirable crystalline silica is greater than 1 per 1,000 workers and is still clearly significant.

2. Silicosis Morbidity Risks

OSHA's Final Quantitative Risk Assessment also characterizes the risk of developing silicosis, defined as developing lung fibrosis detected by chest x-ray. For 45 years of exposure at the previous general industry PEL of 100 μg/m³, OSHA estimates that the risk of developing lung fibrosis consistent with an ILO category 1+ degree of small opacity profusion ranges from 60 to 773 cases per 1,000. For exposure at the previous construction and shipyard PELs, the risk approaches 100 percent. The wide range of risk estimates derived from the underlying studies relied on for the risk assessment may reflect differences in the relative toxicity of quartz particles in different workplaces; nevertheless, OSHA finds that each of these risk estimates clearly represents a significant risk of developing fibrotic lesions in the lung. Exposure to the final PEL of 50 μg/m³ respirable crystalline silica for 45 years yields an estimated risk of between 20 and 170 cases per 1,000 for developing fibrotic lesions consistent with an ILO category of 1+. These risk estimates indicate that the final PEL will result in a reduction in risk by about two-thirds or more, which the Agency finds is a substantial reduction of the risk of developing abnormal chest x-ray findings consistent with silicosis.

One study of coal miners also permitted the agency to evaluate the risk of developing lung fibrosis consistent with an ILO category 2+ degree of profusion of small opacities (Buchanan et al., 2003, Document ID 0306). This level of profusion has been shown to be associated with a higher prevalence of lung function decrement and an increased rate of early mortality (Ng et al., 1987a, Document ID 1108; Begin et al., 1988, 0296; Moore et al., 1988, 1099; Ng et al., 1992a, 0383; Infante-Rivard, 1991, 1065). From this study, OSHA estimates that the risk associated with 45 years of exposure to the previous general industry 100 μg/m³ PEL is 301 cases per 1,000 workers, again a clearly significant risk. Exposure to the final PEL of 50 μg/m³ respirable crystalline silica for 45 years yields an estimated risk of 55 cases per 1,000 for developing lesions consistent with an ILO category 2+ degree of small opacity profusion. This represents a reduction in risk of over 80 percent, again a clearly substantial reduction of the risk of developing radiologic silicosis consistent with ILO category 2+.

3. Sources of Uncertainty and Variability in OSHA's Risk Assessment

Throughout the development of OSHA's risk assessment for silica-related health effects, sources of uncertainty and variability have been identified by the Agency, peer reviewers, interagency reviewers, stakeholders, scientific experts, and the general public. This subsection reviews and summarizes several general areas of uncertainty and variability in OSHA's risk assessment. As used in this section, “uncertainty” refers to lack of knowledge about factors affecting exposure or risk, and “variability” refers to heterogeneity, for example, across people, places, or time. For more detailed discussion and evaluation of sources of uncertainty in the risk assessment and a comprehensive review of comments received by OSHA on the risk assessment, (see discussions provided throughout the previous section, Section V, Health Effects).

As shown in Table VI-1, OSHA's risk estimates for lung cancer are a range derived from a pooled analysis of 10 cohort studies (Steenland et al., 2001a, Document ID 0452; ToxaChemica, Inc., 2004, 0469), a study of granite workers (Attfield and Costello, 2004, Document ID 0543), a study of diatomaceous earth workers (Rice et al., 2001, Document ID 1118), a multi-cohort study of industrial sand workers (Hughes et al., 2001, Document ID 1060), and a study of coal miners exposed to respirable crystalline silica (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306). Similarly, a variety of studies in several different working populations was used to derive risk estimates of silicosis mortality, silicosis morbidity, and renal disease mortality. The ranges of risks presented in Table VI-1 for silica mortality and the other health endpoints thus reflect silica exposure-response across a variety of industries and worker populations, which may differ for reasons such as the processes in which silica exposure occurs and the various kinds of minerals that co-exist with crystalline silica in the dust particles (see discussion on variability in toxicological potency of crystalline silica later in this section). The ranges presented in Table VI-1 do not reflect statistical uncertainty (e.g., 95% confidence intervals) or model uncertainty (e.g., the slope of the exposure-response curve at exposures higher or lower than the exposures of the study population) but do reflect variability in the sources of data for the different studies.

The risks presented in Table VI-1, however, do not reflect variability in the consistency, duration or frequency of workers' exposures. As discussed previously in this section, OSHA's final estimates of health risks represent risk associated with exposure to an 8-hour time weighted average of 25, 50, 100, 250 and 500 μg/m³ respirable crystalline silica. These levels represent the risks associated with continuous occupational exposure over a working lifetime of 45 years to the new action level, new PEL, previous general industry PEL, and the range in exposure (250-500 μg/m³) that approximates the previous construction and shipyard PELs, respectively. OSHA estimates risks assuming exposure over a working life so that it can evaluate the significance of the risk associated with exposure at the previous PELs in a manner consistent with Section 6(b)(5) of the Act, which requires OSHA to set standards that substantially reduce these risks to the extent feasible even if workers are exposed over a full working lifetime. However, while the risk assessment is based on the assumed working life of 45 years, OSHA recognizes that risks associated with shorter-term or intermittent exposures at a given airborne concentration of silica will be less than the risk associated with continuous occupational exposure at the same concentration over a working lifetime. OSHA thus also uses alternatives to the 45-year full-time exposure metric in its projections of the benefits of the final rule (Section VII of this preamble and the FEA) that reflect the reduction in silica-related disease that the Agency expects will result from implementation of the revised standard, using the various estimates of workers' typical exposure levels and patterns.

The remainder of this discussion reviews several general areas of uncertainty and variability in OSHA's risk assessment that are not quantitatively reflected in the risk estimates shown in Table VI-1, but that provide important context for understanding these estimates, including differences in the degree of uncertainty among the estimates. These areas include exposure estimation error, dose-rate effects, model form uncertainty, variability in toxicological potency of crystalline silica, and additional sources of uncertainty specific to particular endpoints, (e.g., the small number of cases in the renal disease analysis), differing conclusions in the literature on silica as a causative factor in renal disease and lung cancer, and reporting error in silicosis mortality and morbidity. These different sources of uncertainty have varying effects that can lead either to under- or over-estimation of risks. OSHA has taken these sources of uncertainty into account in concluding that the body of scientific literature supports the finding that there is significant risk at existing levels of exposure. The Agency is not required to support the finding that a “significant risk exists with anything approaching scientific certainty” (Benzene, 448 U.S. at 656).

a. Exposure Estimation Error

As discussed in Section V, OSHA identified exposure estimation error as a key source of uncertainty in most of the studies and thus the Agency's risk assessment. OSHA's contractor, ToxaChemica, Inc., commissioned Drs. Kyle Steenland and Scott Bartell to perform an uncertainty analysis to examine the effect of uncertainty due to exposure estimation error in the pooled studies (Steenland et al., 2001a, Document ID 0452; Mannetje 2002b, 1089) on the lung cancer and silicosis mortality risk estimates (ToxaChemica, Inc., 2004, Document ID 0469). Drs. Steenland and Bartell addressed two main sources of error in the silica exposure estimates. The first arises from the assignment of individual workers' exposures based either on exposure measurements for a sample of workers in the same job or estimated exposure levels for specific jobs in the past when no measurements were available, via a job-exposure matrix (JEM) (Mannetje et al., 2002a, Document ID 1090). The second arises from the conversion of historically-available dust measurements, typically particle count concentrations, to gravimetric respirable silica concentrations. ToxaChemica, Inc. conducted an uncertainty analysis using the raw data from the IARC multi-centric study to address these sources of error (2004, Document ID 0469).

To explore the potential effects of both kinds of uncertainty described above, ToxaChemica, Inc. (2004, Document ID 0469) used the distributions representing the error in job-specific exposure assignment and the error in converting exposure metrics to generate 50 exposure simulations for each cohort. A study-specific coefficient and a pooled coefficient were fit for each new simulation. The results indicated that the only lung cancer cohort for which the mean of the exposure coefficients derived from the simulations differed substantially from the previously calculated exposure coefficient was the South African gold cohort (simulation mean of 0.181 vs. original coefficient of 0.582). This suggests that the results of exposure-response analyses conducted using the South African cohort are sensitive to error in exposure estimates; therefore, there is greater uncertainty due to potential exposure estimation error in an exposure-response model based on this cohort than is the case for the other nine cohorts in Steenland et al's analysis (or, put another way, the exposure estimation for the other nine cohorts was less sensitive to the effects of exposure measurement uncertainty).

For the pooled analysis, the mean coefficient estimate from the simulations was 0.057, just slightly lower than the previous estimate of 0.060. Based on these results, OSHA concluded that random error in the underlying exposure estimates in the Steenland et al. (2001a, Document ID 0452) pooled cohort study of lung cancer is not likely to have substantially influenced the original findings.

Following the same procedures described above for the lung cancer analysis, ToxaChemica, Inc. (2004, Document ID 0469) combined both sources of random measurement error in a Monte Carlo analysis of the silicosis mortality data from Mannetje et al. (2002b, Document ID 1089). The silicosis mortality dataset appeared to be more sensitive to possible error in exposure measurement than the lung cancer dataset, for which the mean of the simulation coefficients was virtually identical to the original. To reflect this exposure measurement uncertainty, OSHA's final risk estimates derived from the pooled analysis (Mannetje et al., 2002b, Document ID 1089), incorporated ToxaChemica, Inc.'s simulated measurement error (2004, Document ID 0469).

b. Uncertainty Related to Dose-Rate Effects

OSHA received comments citing uncertainty in its risk assessment related to possible dose-rate effects in the silica exposure-response relationships, particularly for silicosis. For example, the ACC commented that extrapolating risks from the high mean exposure levels in the Park et al. 2002 cohort (Document ID 0405) to the much lower mean exposure levels relevant to OSHA's risk assessment contributes uncertainty to the analysis (Document ID 4209, pp. 84-85), because of the possibility that risk accrues differently at different exposure concentrations. The ACC thus argued that the risk associated with any particular level of cumulative exposure may be higher for exposure to a high concentration of respirable crystalline silica over a short period of time than for an equivalent cumulative exposure resulting from exposure to a low concentration of respirable crystalline silica over a long period of time (Document ID 4209, p. 58; 2307, Attachment A, pp. 93-94). These and similar comments on dose-rate effects questioned OSHA's use of workers' cumulative exposure levels to estimate risk, as the cumulative exposure metric does not capture dose-rate effects. Thus, according to the ACC, if there are significant dose-rate effects in the exposure-response relationship for a disease or other health endpoint, use of the cumulative exposure metric could lead to error in risk estimates.

The rationale for OSHA's reliance on a cumulative exposure metric to assess the risks of respirable crystalline silica is discussed in Section V. With respect to this issue of uncertainty related to dose-response effects, OSHA finds limited evidence in the record to either support or refute the effects hypothesized by the ACC. As such, OSHA acknowledges some uncertainty. Furthermore, use of an alternative metric such as concentration would not provide assurance that uncertainties would be mitigated or reduced.

Two studies discussed in OSHA's Review of Health Effects Literature and Preliminary QRA examined dose-rate effects on silicosis exposure-response (Document ID 1711, pp. 342-344). Neither study found a dose-rate effect relative to cumulative exposure at silica concentrations near the previous OSHA PEL (Document ID 1711, pp. 342-344). However, they did observe a dose-rate effect in instances where workers were exposed to crystalline silica concentrations far above the previous PEL (i.e., several-fold to orders of magnitude above 100 μg/m³) (Buchanan et al., 2003, Document ID 0306; Hughes et al., 1998, 1059). The Hughes et al. (1998) study of diatomaceous earth workers found that the relationship between cumulative silica exposure and risk of silicosis was steeper for workers hired prior to 1950 and exposed to average concentrations above 500 µg/m³ compared to workers hired after 1950 and exposed to lower average concentrations (Document ID 1059). Hughes et al. reported that subdivisions for workers with exposure to concentrations below 500 μg/m³ were examined, but that no differences were observed across these groups (Document ID 1059, p. 809). It is unclear whether sparse data at the low end of the concentration range contributed to this finding, as the authors did not provide detailed information on the distribution of exposures in the study population.

The Buchanan et al. (2003) study of Scottish coal miners adjusted the cumulative exposure metric in the risk model to account for the effects of exposures to high concentrations where the investigators found that, at concentrations above 2000 μg/m³, the risk of silicosis was about three times higher than the risk associated with exposure to lower concentrations but at the same cumulative exposure (Document ID 0306, p. 162). Buchanan et al. noted that only 16 percent of exposure hours among the workers in the study occurred at levels below 10 μg/m³ (Document ID 0306, p. 161), and cautioned that insufficient data are available to predict effects at very low concentrations where data are sparse (Document ID 0306, p. 163). However, 56 percent of hours occurred at levels between 10 and 100 μg/m³. Detailed information on the hours worked at concentrations within this range was not provided.

Based on its review of these studies, OSHA concluded that there is little evidence that a dose-rate effect exists at concentrations in the range of the previous PEL (100 μg/m³) (Document ID 1711, p. 344). However, there remains some uncertainty related to dose-rate effects in the Agency's silicosis risk assessment. Even if a dose-rate effect exists only at concentrations far higher than the previous PEL, it is possible for the dose-rate effect to impact model form if not properly accounted for in study populations with high-concentration exposures. This is one reason that OSHA presents a range of risk estimates based on a variety of study populations exposed under different working conditions. For example, as OSHA noted in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 355-356), the Park et al. study is complemented by the Mannetje et al. multi-cohort silicosis mortality pooled study. Mannetje et al.'s study included several cohorts that had exposure concentrations in the range of interest for this rulemaking and also showed clear evidence of significant risk of silicosis mortality at the previous general industry and construction PELs (2002b, Document ID 1089). In addition, OSHA used the model from the Buchanan et al. study in its silicosis morbidity risk assessment to account for possible dose-rate effects at high average concentrations (Document ID 1711, pp. 335-342). OSHA notes that the risk estimates in the exposure range of interest (25-500 μg/m³) derived from the Buchanan et al. (2003) study were not appreciably different from those derived from the other studies of silicosis morbidity (see Table VI-1).

c. Model Form Uncertainty

Another source of uncertainty in OSHA's risk analysis is uncertainty with respect to the form of the statistical models used to characterize the relationship between exposure level and risk of adverse health outcomes. As discussed in Section V, some commenters expressed concern that studies relied on by OSHA may not have considered all potential exposure-response relationships and might be unable to discern differences between monotonic and non-monotonic characteristics (e.g., Document ID 2307, Attachment A, p. 113-114).

OSHA acknowledges that the possibility of error in selection of exposure-response model forms is a source of uncertainty in the silica risk assessment. To address this uncertainty, the Agency included studies in the risk assessment that explored a variety of model forms. For example, as discussed in Section V, the ToxaChemica reanalyses of the Mannetje et al. silicosis mortality dataset and the Steenland et al. lung cancer mortality data set examined several model forms including a five-knot restricted spline analysis, which is a highly flexible model form able to capture a variety of exposure-response shapes (Document ID 0469, p. 50). The ToxaChemica reanalysis addresses the issue of model form uncertainty by finding similar exposure-response relationships regardless of the type of model used.

d. Uncertainty Related to Silica Exposure as a Risk Factor for Lung Cancer

As discussed in Section V, OSHA has reviewed the best available evidence on the relationship between silica exposure and lung cancer mortality, and has concluded that the weight of evidence supports the finding that exposure to silica at the preceding and new PELs increases the risk of lung cancer. However, OSHA acknowledges that not every study in the literature on silica-related lung cancer reached the same conclusions. This variability is to be expected in epidemiology, as there are different cohorts, measurements, study designs, and analytical methods, among other factors. OSHA further acknowledges that there is uncertainty with respect to the magnitude of the risk of lung cancer from silica exposure. In the case of silica, the exposure-response relationship with lung cancer may be easily obscured, as crystalline silica is a comparably weaker carcinogen (i.e., the increase in risk per unit exposure is smaller) than other well-studied, more potent carcinogens such as hexavalent chromium (Steenland et al., 2001, Document ID 0452, p. 781) and tobacco smoke, a common co-exposure in silica-exposed populations.

A study by Vacek et al. (2011) illustrates the uncertainties involved in evaluating risk of lung cancer from silica exposure. This study found no significant association between respirable silica exposure and lung cancer mortality in a cohort of Vermont granite workers (Document ID 1486, pp. 75-81). Some commenters criticized OSHA's preliminary risk assessment for rejecting the Vacek et al. (2011) study and instead relying upon the Attfield and Costello (2004, Document ID 0284) study of Vermont granite workers (Document ID 2307, Attachment A, pp. 36-47; 4209, pp. 34-36). As discussed in detail in Section V, OSHA reviewed the Vacek et al. study and all comments received by the Agency on this issue, and has decided not to reject the Attfield and Costello (2004) study in favor of the Vacek et al. (2011) study as a basis for risk assessment. OSHA acknowledges that comprehensive studies, such as those of Attfield and Costello (2004) and Vacek et al. (2011), in the Vermont granite industry have shown conflicting results with respect to lung cancer mortality (Document ID 0284; 1486). Although OSHA believes that the Attfield and Costello (2004) study is the most appropriate Vermont granite study to use in its QRA, it also relied upon other studies, and that the risk estimates for lung cancer mortality based on those studies (i.e., Document ID 0543, 1060, 1118, 1306) still provide substantial evidence that respirable crystalline silica poses a significant risk of lung cancer to exposed workers.

e. Uncertainty Related to Renal Disease

As discussed in Section V, OSHA acknowledges that there are considerably less data for renal disease mortality than those for silicosis, lung cancer, and non-malignant respiratory disease (NMRD) mortality. Although the Agency believes the renal disease risk findings are based on credible data, the risk findings based on them are less robust than the findings for silicosis, lung cancer, and NMRD.

Based upon its overall analysis of the literature, including the negative studies, OSHA has concluded that there is substantial evidence suggesting an association between exposure to crystalline silica and increased risks of renal disease. This conclusion is supported by a number of case reports and epidemiological studies that found statistically significant associations between occupational exposure to silica dust and chronic renal disease (Calvert et al., 1997, Document ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID 0386), end-stage renal disease morbidity (Steenland et al., 1990, Document ID 1125), end-stage renal disease incidence (Steenland et al., 2001b, Document ID 0456), chronic renal disease mortality (Steenland et al., 2002a, 0448), and granulomatosis with polyangitis (Nuyts et al., 1995, Document ID 0397). However, as discussed in the Review of Health Effects Literature and Preliminary QRA, the studies reviewed by OSHA included a number of studies that did not show an association between crystalline silica and renal disease (Document ID 1711, pp. 211-229). Additional negative studies by Birk et al. (2009, Document ID 1468), and Mundt et al. (2011, Document ID 1478) were reviewed in the Supplemental Literature Review of the Review of Health Effects Literature and Preliminary QRA, which noted the short follow-up period as a limitation, which reduces the likelihood that an increased incidence of renal mortality would have been detected (Document ID 1711, Supplement, pp. 6-12). Comments submitted to OSHA by the ACC additionally cited several studies that did not show a statistically significant association between exposure to crystalline silica and renal disease mortality, including McDonald et al. (2005, Document ID 1092), Vacek et al. (2011, Document ID 2340), Davis et al. (1983, Document ID 0999), Koskela et al. (1987, Document ID 0363), Cherry et al. (2012, article included in Document ID 2340), Steenland et al. (2002b, Document ID 0454), Rosenman et al. (2000, Document ID 1120), and Calvert et al. (2003, Document ID 0309) (Document ID 2307, Attachment A, pp. 140-145).

As discussed in detail in Section V, OSHA concludes that the evidence supporting causality regarding renal risk outweighs the evidence casting doubt on that conclusion, but acknowledges this divergence in the renal disease literature as a source of uncertainty.

OSHA estimated quantitative risks for renal disease mortality (Document ID 1711, pp. 314-316) using data from a pooled analysis of renal disease, conducted by Steenland et al. (2002a, Document ID 0448). The data set included 51 deaths from renal disease as an underlying cause, which the authors of the pooled study, Drs. Kyle Steenland and Scott Bartell, acknowledged to be insufficient to provide robust estimates of risk (Document ID 2307, Attachment A, p. 139, citing 0469, p. 27). OSHA agrees with Dr. Steenland and acknowledges, as it did in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, p. 357), that its quantitative risk estimates for renal disease mortality are less robust than those for the other health effects examined (i.e., lung cancer mortality, silicosis and NMRD mortality, and silicosis morbidity).

f. Uncertainty in Reporting and Diagnosis of Silicosis Mortality and Silicosis Morbidity

OSHA's final quantitative risk assessment includes risk estimates for silicosis mortality and morbidity. Silicosis mortality is ascertained by analysis of death certificates for cause of death, and morbidity is ascertained by the presence of chest radiographic abnormalities consistent with silicosis among silica-exposed workers. Each of these kinds of studies are associated with uncertainties in case ascertainment and use of chest roentgenograms to detect lung scarring due to silicosis.

For silicosis mortality, OSHA's analysis includes a pooled analysis of six epidemiological studies first published by Mannetje et al. (2002b, Document ID 1089) and re-analyzed by OSHA's contractor ToxaChemica (2004, Document ID 0469). OSHA finds that the estimates from Mannetje et al. and ToxaChemica's analyses are likely to understate the actual risk because silicosis is under-reported as a cause of death, as discussed in Sections VC.2.iv and V.E in the context of silicosis disease surveillance systems. To help address this uncertainty, OSHA's risk analysis also included an exposure-response analysis of diatomaceous earth (DE) workers (Park et al., 2002, Document ID 0405), which better captures the totality of silica-related respiratory disease than do the datasets analyzed by Mannetje et al. and ToxaChemica. Park et al.. quantified the relationship between cristobalite exposure and mortality caused by NMRD, which includes silicosis, pneumoconiosis, emphysema, and chronic bronchitis. Because NMRD captures much of the silicosis misclassification that results in underestimation of the disease and includes risks from other lung diseases associated with crystalline silica exposures, OSHA finds the risk estimates derived from the Park et al. study are important to include as part of OSHA's range of estimates of the risk of death from silica-related respiratory diseases, including silicosis. (Document ID 1711, pp. 297-298). OSHA concludes that the range of silicosis and NMRD risks presented in the final risk assessment, based on both the ToxaChemica reanalysis of Mannetje et al.'s silicosis mortality data and Park et al.'s study of NMRD mortality, provide a credible range of estimates of mortality risk from silicosis and NMRD across a range of industrial workplaces. The upper end of this range, based on the Park et al. study, is less likely to underestimate risk as a result of under-reporting of silicosis mortality, but cannot be directly compared to risk estimates from studies that focused on cohorts of workers from different industries.

OSHA's estimates of silicosis morbidity risks are based on studies of active and retired workers for which exposure histories could be constructed and chest x-ray films could be evaluated for signs of silicosis. There is evidence in the record that chest x-ray films are relatively insensitive to detecting lung fibrosis. Hnizdo et al. (1993, Document ID 1050) found chest x-ray films to have low sensitivity for detecting lung fibrosis related to silicosis, compared to pathological examination at autopsy. To address the low sensitivity of chest x-rays for detecting silicosis, Hnizdo et al. (1993, Document ID 1050) recommended that radiographs consistent with an ILO category of 0/1 or greater be considered indicative of silicosis among workers exposed to a high concentration of silica-containing dust. In like manner, to maintain high specificity, chest x-rays classified as category 1/0 or 1/1 should be considered as a positive diagnosis of silicosis. Studies relied on in OSHA's risk assessment typically used an ILO category of 1/0 or greater to identify cases of silicosis. According to Hnizdo et al., they are unlikely to include many false positives (diagnoses of silicosis where there is none), but may include false negatives (failure to identify cases of silicosis). Thus, the use of chest roentgenograms to ascertain silicosis cases in the morbidity studies relied on by OSHA in its risk assessment could lead to an underestimation of risk given the low sensitivity of chest roentgenograms for detecting silicosis.

g. Variability in Toxicological Potency of Crystalline Silica

As discussed in Section V, the toxicological potency of crystalline silica is influenced by a number of physical and chemical factors that affect the biological activity of inhaled silica particles. The toxicological potency of crystalline silica is largely influenced by the presence of oxygen free radicals on the surfaces of respirable particles. These chemically-reactive oxygen species interact with cellular components in the lung to promote and sustain the inflammatory reaction responsible for the lung damage associated with exposure to crystalline silica. The reactivity of particle surfaces is greatest when crystalline silica has been freshly fractured by high-energy work processes such as abrasive blasting, rock drilling, or sawing concrete materials. As particles age in the air, the surface reactivity decreases and exhibits lower toxicologic potency (Porter et al., 2002, Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al., 1995, 1128). In addition, surface impurities have been shown to alter silica toxicity. For example, aluminum and aluminosilicate clay on silica particles has been shown to decrease toxicity (Castranova et al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini, 1998, 1016; Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998, 1016).

In the preamble to the proposed standard, OSHA preliminarily concluded that although there is evidence that several environmental influences can modify surface activity to either enhance or diminish the toxicity of silica, the available information was insufficient to determine to what extent these influences may affect risk to workers in any particular workplace setting (Document 1711, p. 350). OSHA acknowledges that health risks are probably in the low end of the range for workers in the brick manufacturing industry, although the evidence still indicates that there is a significant risk at the previous general industry PEL for those workers. OSHA also acknowledges that there was a lack of evidence for a significant risk in the sorbent minerals industry due to the nature of crystalline silica present in those operations; as a result, it decided to exclude sorptive clay processing from this rule. Furthermore, Dudley and Morriss (2015) raise concerns about the whether the exposures reflected in the historical cohorts used in the risk assessment are sufficiently reflective of rapidly changing working conditions over the last 45 years. However, the risk estimates presented in Table VI-1 are based on studies from a variety of industries, such that the risk ranges presented are likely to include estimates appropriate to most working populations. Thus, in OSHA's view, its significant risk finding is well supported by the weight of best available evidence, notwithstanding uncertainties that may be present to varying degrees in the numerous studies relied upon and the even greater number of studies that the Agency considered.

4. OSHA's Response to Comments on Significant Risk of Material Impairment

OSHA received several comments pertaining to the Agency's determination of a significant risk of material impairment of health posed to workers exposed for a working life to the previous PELs. Although many of these comments were supportive of OSHA's conclusions regarding the significance of risk, others were critical or suggested that OSHA has an obligation to further reduce the risk below that estimated to remain at the revised PEL.

Referring to the previous PELs for respirable crystalline silica, the AFL-CIO commented that “[w]orkers face a significant risk of harm from silica exposure at the current permissible exposure limits,” and that “[t]here is overwhelming evidence in the record that exposure to respirable crystalline silica poses a significant health risk to workers” (Document ID 4204, pp. 10-11). The AFL-CIO noted that OSHA's mortality risk estimates well exceeded the benchmark of 1/1,000 excess risk over a working lifetime of exposure to the previous PELs, and also highlighted the risks of silicosis morbidity (Document ID 4204, p. 13). The AFL-CIO further pointed out that there is no cure for silicosis, and quoted oral testimony from workers at the informal public hearings demonstrating that “[s]ilica-related diseases are still destroying workers' lives and livelihoods” (Document ID 4204, p. 19).

Both the UAW and the Building and Construction Trades Department (BCTD) concurred with the AFL-CIO that the previous PEL needs to be lowered to adequately protect workers. Referring to the previous PEL, the BCTD stated that “[t]he record supports OSHA's determination that exposures at the current PEL present a significant risk” (Document ID 4223, p. 6). Although supportive of OSHA's proposed standard, the UAW also suggested the adoption of a PEL of 25 µg/m³ or lower where feasible (Document ID 2282, Attachment 3, p.1), noting that a PEL set at this level “will significantly reduce workers' exposure to deadly silica dust and prevent thousands of illnesses and deaths every year” (Document ID 2282, Attachment 3, p. 25). Similarly, Charles Gordon, a retired occupational safety and health attorney, commented that the revised PEL “leaves a remaining risk of 97 deaths per 1,000 workers from silicosis, lung cancer, and renal disease combined” (Document ID 4236, p. 2). Again, it should be noted that these risk estimates are not additive because some individuals may suffer from multiple diseases caused by exposure to silica. Instead, OSHA presents risk estimates for each health endpoint.

As discussed above, OSHA acknowledges that there remains a significant risk of material impairment of health at the revised PEL; a further reduction in the PEL, however, is not currently technologically feasible (see Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis, in which OSHA summarizes its assessment of the technological feasibility of the revised PEL). Despite this, the final PEL will provide a very substantial reduction in the risk of material impairment of health to silica-exposed workers, as described in the Benzene decision (Benzene, 448 U.S. at 642).

In contrast to the foregoing comments from labor groups contending that OSHA would be setting the PEL too high if it made a final determination to lower the preceding PELs to 50 µg/m³, critical comments came from industry groups including the American Chemistry Council (ACC), which disagreed with OSHA's determination of a significant risk of material impairment of health at the previous PELs. The ACC stated, “OSHA's assessment of these risks is flawed, and its conclusions that the risks are significant at a PEL of 100 µg/m³ and would be substantially reduced by lowering the PEL to 50 µg/m³ are unsupported” (Document ID 4209, p. 12). The ACC then asserted several “fundamental shortcomings” in OSHA's QRA on which OSHA based its significant risk determination (Document ID 4209, pp. 16-17), including a variety of purported biases in the key studies on which OSHA relied. OSHA addresses the ACC's concerns in detail in Section V of this preamble dealing with the key studies relied upon by the Agency for each health endpoint, as well as separate sections addressing the issues of biases, causation, thresholds, the uncertainty analysis, and the life table and exposure assumptions used in the QRA. As more fully discussed in those sections, OSHA finds these concerns to be unpersuasive. As discussed in Section V, the scientific community and regulators in other advanced industrial societies agree on the need for a PEL of at most 50 µg/m³ based on demonstrated health risks, and OSHA has used the best available evidence in the scientific literature to estimate quantitative risks of silica-related illnesses and thereby reach the same conclusion. OSHA's preliminary review of the health effects literature and OSHA's preliminary QRA were, further, examined by an independent, external peer review panel of accomplished scientists, which lent credibility to the Agency's methods and findings and led to some adjustments in the analysis that strengthened OSHA's final risk assessment. There is, additionally, widespread support for the Agency's methods and conclusions in the rulemaking record. As such, OSHA is confident in its conclusion that there is a significant risk of material impairment of health to workers exposed to respirable crystalline silica at the levels of exposure permitted under the previous PELs and under this final standard, and finds no merit in broad assertions purporting to debunk this conclusion.

In summary, as discussed throughout Section V and this final rule, OSHA concludes, based on the best available evidence in the scientific literature, that workers' exposure to respirable crystalline silica at the previous PELs results in a clearly significant risk of material impairment of health. The serious, and potentially fatal, health effects suffered by exposed workers include silicosis, lung cancer, NMRD, renal disease, and autoimmune effects. OSHA finds that the risk is substantially decreased, though still significant, at the new PEL of 50 µg/m³ and below, including at the new action level of 25 µg/m³. The Agency is constrained, however, from lowering the PEL further by its finding that a lower PEL would be infeasible in many operations across several industries. Given the significant risks faced by workers exposed to respirable crystalline silica under the previously-existing exposure limits, OSHA believes that it is imperative that it issue this final standard pursuant to its statutory mandate under the OSH Act.

VII. Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis

A. Introduction

OSHA's Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA) addresses issues related to the costs, benefits, technological and economic feasibility, and the economic impacts (including impacts on small entities) of this final respirable crystalline silica rule and evaluates regulatory alternatives to the final rule. Executive Orders 13563 and 12866 direct agencies to assess all costs and benefits of available regulatory alternatives and, if regulation is necessary, to select regulatory approaches that maximize net benefits (including potential economic, environmental, and public health and safety effects; distributive impacts; and equity). Executive Order 13563 emphasized the importance of quantifying both costs and benefits, of reducing costs, of harmonizing rules, and of promoting flexibility. The full FEA has been placed in OSHA rulemaking docket OSHA-2010-0034. This rule is an economically significant regulatory action under Sec. 3(f)(1) of Executive Order 12866 and has been reviewed by the Office of Information and Regulatory Affairs in the Office of Management and Budget, as required by executive order.

The purpose of the FEA is to:

• Identify the establishments and industries potentially affected by the final rule;
• Estimate current exposures and the technologically feasible methods of controlling these exposures;
• Estimate the benefits resulting from employers coming into compliance with the final rule in terms of reductions in cases of silicosis, lung cancer, other forms of chronic obstructive pulmonary disease, and renal failure;
• Evaluate the costs and economic impacts that establishments in the regulated community will incur to achieve compliance with the final rule;
• Assess the economic feasibility of the final rule for affected industries; and
• Assess the impact of the final rule on small entities through a Final Regulatory Flexibility Analysis (FRFA), to include an evaluation of significant regulatory alternatives to the final rule that OSHA has considered.

Significant Changes to the FEA Between the Proposed Standards and the Final Standards

OSHA changed the FEA for several reasons:

• Changes to the rule, summarized in Section I of this preamble and discussed in detail in the Summary and Explanation;
• Comments on the Preliminary Economic Analysis (PEA);
• Updates of economic data; and
• Recognition of errors in the PEA.

OSHA revised its technological and economic analysis in response to these changes and to comments received on the NPRM. The FEA contains some costs that were not included in the PEA and updates data to use more recent data sources and, in some cases, revised methodologies. Detailed discussions of these changes are included in the relevant sections throughout the FEA.

The FEA contains the following chapters:

Chapter I. Introduction

Chapter II. Market Failure and the Need for Regulation

Chapter III. Profile of Affected Industries

Chapter IV. Technological Feasibility

Chapter V. Costs of Compliance

Chapter VI. Economic Feasibility Analysis and Regulatory Flexibility Determination

Chapter VII. Benefits and Net Benefits

Chapter VIII. Regulatory Alternatives

Chapter IX. Final Regulatory Flexibility Analysis

Chapter X. Environmental Impacts

Table VII-1 provides a summary of OSHA's best estimate of the costs and estimated benefits of the final rule using a discount rate of 3 percent. As shown, the final rule is estimated to prevent 642 fatalities and 918 silica-related illnesses annually once it is fully effective, and the estimated cost of the rule is $1,030 million annually. Also as shown in Table VII-1, the discounted monetized benefits of the final rule are estimated to be $8.7 billion annually, and the final rule is estimated to generate net benefits of $7.7 billion annually. Table VII-1 also presents the estimated costs and estimated benefits of the final rule using a discount rate of 7 percent.

The remainder of this section (Section VII) of the preamble is organized as follows:

B. Market Failure and the Need for Regulation

C. Profile of Affected Industries

D. Technological Feasibility

E. Costs of Compliance

F. Economic Feasibility Analysis and Regulatory Flexibility Determination

G. Benefits and Net Benefits

H. Regulatory Alternatives

I. Final Regulatory Flexibility Analysis.

B. Market Failure and the Need for Regulation

Employees in work environments addressed by the final silica rule are exposed to a variety of significant hazards that can and do cause serious injury and death. As described in Chapter II of the FEA in support of the final rule, OSHA concludes there is a failure of private markets to protect workers from exposure to unnecessarily high levels of respirable crystalline silica and that private markets, as well as information dissemination programs, workers' compensation systems, and tort liability options, each may fail to protect workers from silica exposure, resulting in the need for a more protective OSHA silica rule.

After carefully weighing the various potential advantages and disadvantages of using a regulatory approach to improve upon the current situation, OSHA concludes that, in the case of silica exposure, the final mandatory standards represent the best choice for reducing the risks to employees. In addition, rulemaking is necessary in this case in order to replace older existing standards with updated, clear, and consistent health standards.

C. Profile of Affected Industries

Introduction

Chapter III of the FEA presents profile data for industries potentially affected by the final silica rule. The discussion below summarizes the findings in that chapter. As a first step, OSHA identifies the North American Industrial Classification System (NAICS) industries, both in general industry and maritime and in the construction sector, with potential worker exposure to silica. Next, OSHA provides summary statistics for the affected industries, including the number of affected entities and establishments, the number of workers whose exposure to silica could result in disease or death (“at-risk workers”), and the average revenue for affected entities and establishments. Finally, OSHA presents silica exposure profiles for at-risk workers. These data are presented by sector and job category. Summary data are also provided for the number of workers in each affected industry who are currently exposed above the final silica PEL of 50 μg/m³, as well as above an alternative PEL of 100 μg/m³ for economic analysis purposes.

The methodological basis for the industry and at-risk worker data presented in this chapter comes from the PEA, the Eastern Research Group (ERG) analysis supporting the PEA (2007a, 2007b, 2008a, and 2008b), and ERG's analytic support in preparing the FEA. The data used in this chapter come from the rulemaking record (Docket OSHA-2010-0034), the technological feasibility analyses presented in Chapter IV of the FEA, and from OSHA (2016), which updated its earlier spreadsheets to reflect the most recent industry data available. To do so, ERG first matched the BLS Occupational Employment Statistics (OES) survey occupational titles with the at-risk job categories, by NAICS industry. ERG then calculated the percentages of production employment represented by each at-risk job title within industry (see OSHA, 2016 for details on the calculation of employment percentages and the mapping of at-risk job categorizations into OES occupations). ERG's expertise for identifying the appropriate OES occupations and calculating the employment percentages enabled OSHA to estimate the number of employees in the at-risk job categories by NAICS industry (Id.).

In the NPRM and PEA, OSHA invited the public to submit additional information and data that might help improve the accuracy and usefulness of the preliminary industry profile; the profile presented here and in Chapter III of the FEA reflects public comment.

Selection of NAICS Industries for Analysis

The technological feasibility analyses presented in Chapter IV of the FEA identify the general industry and maritime sectors and the construction activities potentially affected by the final silica standard.

General Industry and Maritime

Employees engaged in various activities in general industry and maritime routinely encounter crystalline silica as a molding material, as an inert mineral additive, as a component of fluids used to stimulate well production of oil or natural gas, as a refractory material, as a sandblasting abrasive, or as a natural component of the base materials with which they work. Some industries use various forms of silica for multiple purposes. As a result, employers are faced with the challenge of limiting worker exposure to silica in dozens of job categories throughout the general industry and maritime sectors.

Job categories in general industry and maritime were selected for analysis based on data from the technical industrial hygiene literature, evidence from OSHA Special Emphasis Program (SEP) results, and, in several cases, information from ERG site visit reports and public comment submitted into the record. These data sources provided evidence of silica exposures in numerous sectors. While the available data are not entirely comprehensive, OSHA believes that silica exposures in other sectors are quite limited.

The industry subsectors in the overall general industry and maritime application groups that OSHA identified as being potentially affected by the final silica standard are as follows:

• Asphalt Paving Products
• Asphalt Roofing Materials
• Hydraulic Fracturing
• Industries with Captive Foundries
• Concrete Products
• Cut Stone
• Dental Equipment and Supplies
• Dental Laboratories
• Flat Glass
• Iron Foundries
• Jewelry
• Mineral Processing
• Mineral Wool
• Nonferrous Sand Casting Foundries
• Non-Sand Casting Foundries
• Other Ferrous Sand Casting Foundries
• Other Glass Products
• Paint and Coatings
• Porcelain Enameling
• Pottery
• Railroads
• Ready-Mix Concrete
• Refractories
• Refractory Repair
• Shipyards
• Structural Clay

In some cases, affected industries presented in the technological feasibility analysis have been disaggregated to facilitate the cost and economic impact analysis. In particular, flat glass, mineral wool, and other glass products are subsectors of the glass industry described in Chapter IV, Section IV-9, of the FEA, and captive foundries, iron foundries, nonferrous sand casting foundries, non-sand cast foundries, and other ferrous sand casting foundries are subsectors of the overall foundries industry presented in Chapter IV, Section IV-8, of the FEA.

As described in ERG (2008b, Document ID 1365) and updated in OSHA (2016), OSHA identified the six-digit NAICS codes for these subsectors to develop a list of industries potentially affected by the final silica standard. Table VII-2 presents the sectors listed above with their corresponding six-digit NAICS industries. The NAICS codes and associated industry definitions in the FEA are consistent with the 2012 NAICS edition.

Construction

The construction sector is an integral part of the nation's economy, accounting for approximately 4.5 percent of total private sector employment. Establishments in this industry are involved in a wide variety of activities, including land development and subdivision, homebuilding, construction of nonresidential buildings and other structures, heavy construction work (including roadways and bridges), and a myriad of special trades such as plumbing, roofing, electrical, excavation, and demolition work.

Construction activities were selected for analysis based on historical data of recorded samples of construction worker exposures from the OSHA Integrated Management Information System (IMIS) and the National Institute for Occupational Safety and Health (NIOSH). In addition, OSHA reviewed the industrial hygiene literature across the full range of construction activities and focused on dusty operations where silica sand was most likely to be fractured or abraded by work operations. These physical processes have been found to cause the silica exposures that pose the greatest risk of silicosis for workers.

The construction activities, by equipment or task, that OSHA identified as being potentially affected by the final silica standard are as follows:

• Earth drilling
• Heavy Equipment Operators and Ground Crew Laborers—I (Abrading or fracturing silica containing materials or demolishing concrete or masonry structures)
• Heavy Equipment Operators and Ground Crew Laborers—II (Grading and Excavating)
• Hole Drillers Using Handheld or Stand-Mounted Drills
• Jackhammers and Other Powered Handheld Chipping Tools
• Masonry and Concrete Cutters Using Portable Saws—I (Handheld power saws)
• Masonry and Concrete Cutters Using Portable Saws—II (Handheld power saws for cutting fiber-cement board)
• Masonry and Concrete Cutters Using Portable Saws—III (Walk-behind saws)
• Masonry and Concrete Cutters Using Portable Saws—IV (Drivable or ride-on concrete saws)
• Masonry and Concrete Cutters Using Portable Saws—V (Rig-mounted core saws or drills)
• Masonry Cutters Using Stationary Saws
• Millers Using Portable or Mobile Machines—I (Walk-behind milling machines and floor grinders)
• Millers Using Portable or Mobile Machines—II (Small drivable milling machine (less than half-lane))
• Millers Using Portable or Mobile Machines—III (Milling machines (half-lane and larger with cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate))
• Rock and Concrete Drillers—I (Vehicle-mounted drilling rigs for rock and concrete)
• Rock and Concrete Drillers—II (Dowel drilling rigs for concrete)
• Mobile Crushing Machine Operators and Tenders
• Tuckpointers and Grinders—I (Handheld grinders for mortar removal (e.g., tuckpointing))
• Tuckpointers and Grinders—II (Handheld grinders for uses other than mortar removal)

As shown in OSHA (2016) and in Chapter IV of the FEA, these construction activities occur in the following industries and governmental bodies, accompanied by their four-digit NAICS codes:

• 2361 Residential Building Construction
• 2362 Nonresidential Building Construction
• 2371 Utility System Construction
• 2372 Land Subdivision
• 2373 Highway, Street, and Bridge Construction
2379 Other Heavy and Civil Engineering Construction
• 2381 Foundation, Structure, and Building Exterior Contractors
• 2382 Building Equipment Contractors
• 2383 Building Finishing Contractors
• 2389 Other Specialty Trade Contractors
• 2211 Electric Utilities
• 9992 State Government
• 9993 Local Government

Characteristics of Affected Industries

Table VII-3 provides an overview of the industries and estimated number of workers affected by the final rule. Included in Table VII-3 are summary statistics for each of the affected industries, subtotals for construction and for general industry and maritime, and grand totals for all affected industries combined.

The first five columns in Table VII-3 identify the NAICS code for each industry in which workers are routinely exposed to respirable crystalline silica and the name or title of the industry, followed by the total number of entities, establishments, and employees for that industry. Note that, while the industries are characterized by such exposure, not every entity, establishment, and employee in these affected industries engage in activities involving silica exposure.

The next three columns in Table VII-3 show, for each affected industry, the number of entities and establishments in which workers are actually exposed to silica and the total number of workers exposed to silica. The number of affected establishments was set equal to the total number of establishments in an industry (based on Census data) unless the number of affected establishments would exceed the number of affected employees in the industry. In that case, the number of affected establishments in the industry was set equal to the number of affected employees, and the number of affected entities in the industry was reduced so as to maintain the same ratio of entities to establishments in the industry.

As shown in Table VII-3, OSHA estimates that a total of 652,600 entities (586,800 in construction; 65,900 in general industry and maritime), 675,800 establishments (600,700 in construction; 75,100 in general industry and maritime), and 2.3 million workers (2.0 million in construction; 0.3 million in general industry and maritime) would be affected by the final silica rule. Note that only 67 percent of the entities and establishments, and about 21 percent of the workers in affected industries, actually engage in activities involving silica exposure.

The ninth column in Table VII-3, with data only for construction, shows for each affected NAICS construction industry the number of full-time-equivalent (FTE) affected workers that corresponds to the total number of affected construction workers in the previous column. This distinction is necessary because affected construction workers may spend large amounts of time working on tasks with no risk of silica exposure. As shown in Table VII-3, the 2.0 million affected workers in construction converts to approximately 387,700 FTE affected workers. In contrast, OSHA based its analysis of the affected workers in general industry and maritime on the assumption that they were engaged full time in activities with some silica exposure.

The last three columns in Table VII-3 show combined total revenues for all entities (not just affected entities) in each affected industry, and the average revenue per entity and per establishment in each affected industry. Because OSHA did not have data to distinguish revenues for affected entities and establishments in any industry, average revenue per entity and average revenue per affected entity (as well as average revenue per establishment and average revenue per affected establishment) are estimated to be equal in value.

Silica Exposure Profile of At-Risk Workers

The technological feasibility analyses presented in Chapter IV of the FEA contain data and discussion of worker exposures to silica throughout industry. Exposure profiles, by job category, were developed from individual exposure measurements that were judged to be substantive and to contain sufficient accompanying description to allow interpretation of the circumstance of each measurement. The resulting exposure profiles show the job categories with current overexposures to silica and, thus, the workers for whom silica controls would be implemented under the final rule.

Chapter IV of the FEA includes a section with a detailed description of the methods used to develop the exposure profile and to assess the technological feasibility of the final standard. The final exposure profiles take the exposure data that were used for the same purpose in OSHA's PEA and build upon them, using new data in the rulemaking record. The sampling data that were used to identify the affected industries and to develop the exposure profiles presented in the PEA were obtained from a comprehensive review of the following sources of information: OSHA compliance inspections conducted before 2011, OSHA contractor (ERG) site visits performed for this rulemaking, NIOSH site visits, NIOSH Health Hazard Evaluation reports (HHEs), published literature, submissions by individual companies or associations and, in a few cases, data from analogous operations (Document ID 1720, pp. IV-2-IV-3). The exposure profiles presented in the PEA were updated for the FEA using exposure measurements from the OSHA Information System (OIS) that were taken during compliance inspections conducted between 2011 and 2014 (Document ID 3958). In addition, exposure data submitted to the record by rulemaking participants were used to update the exposure profiles. The criteria used for determining whether to include exposure data in the exposure profiles are described in Section IV-2—Methodology in Chapter IV of the FEA. As explained there, some of the original data are no longer used in the exposure profiles based on those selection or screening criteria. OSHA considers the exposure data relied upon for its analysis to be the best available evidence of baseline silica exposure conditions.

Table VII-4 summarizes, from the exposure profiles, the total number of workers at risk from silica exposure at any level, and the distribution of 8-hour TWA respirable crystalline silica exposures by job category for general industry and maritime sectors and for construction activities. Exposures are grouped into the following ranges: Less than 25 μg/m³; ≥ 25 μg/m³ and ≤ 50 μg/m³; > 50 μg/m³ and ≤ 100 μg/m³; > 100 μg/m³ and ≤ 250 μg/m³; and greater than 250 μg/m³. These frequencies represent the percentages of production employees in each job category and sector currently exposed at levels within the indicated range.

Table VII-5 presents data by NAICS code—for each affected general, maritime, and construction industry—on the estimated number of workers currently at risk from silica exposure, as well as the estimated number of workers at risk of silica exposure at or above 25 μg/m³, above 50 μg/m³, and above 100 μg/m³. As shown, an estimated 1,249,250 workers (1,097,000 in construction; 152,300 in general industry and maritime) currently have silica exposures at or above the new action level of 25 μg/m³; an estimated 948,100 workers (847,700 in construction; 100,400 in general industry and maritime) currently have silica exposures above the new PEL of 50 μg/m³; and an estimated 578,000 workers (519,200 in construction; 58,800 in general industry and maritime) currently have silica exposures above 100 μg/m³—an alternative PEL investigated by OSHA for economic analysis purposes.

D. Technological Feasibility

In Chapter IV of OSHA's FEA, OSHA assesses the technological feasibility of the standard in all affected industry sectors and application groups. The analysis presented in this chapter is organized by industry sectors in general industry and maritime and by application groups in the construction industry. Employee exposures were analyzed at the operation, job category or task/activity level to the extent that the necessary data were available. OSHA collected exposure data to characterize current (baseline) exposures and to identify the tasks, operations, and job categories for which employers will need to either improve their process controls or implement additional controls to reduce respirable crystalline silica exposures to 50 µg/m³ or below. In the few instances where there were insufficient exposure data, OSHA used analogous operations to characterize these operations.

The technological feasibility analysis informed OSHA's selection of the rule's permissible exposure limit (PEL) of 50 µg/m³ respirable crystalline silica, consistent with the requirements of the Occupational Safety and Health Act (“OSH Act”), 29 U.S.C. 651 et seq. Section 6(b)(5) of the OSH Act requires that OSHA “set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity” (29 U.S.C. 655(b)(5)). In fulfilling this statutory directive, OSHA is guided by the legal standard expressed by the Court of Appeals for the D.C. Circuit for demonstrating the technological feasibility of reducing occupational exposure to a hazardous substance:

OSHA must prove a reasonable possibility that the typical firm will be able to develop and install engineering and work practice controls that can meet the PEL in most of its operations. . . . The effect of such proof is to establish a presumption that industry can meet the PEL without relying on respirators. . . . Insufficient proof of technological feasibility for a few isolated operations within an industry, or even OSHA's concession that respirators will be necessary in a few such operations, will not undermine this general presumption in favor of feasibility. Rather, in such operations firms will remain responsible for installing engineering and work practice controls to the extent feasible, and for using them to reduce . . . exposure as far as these controls can do so (United Steelworkers of Am, AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1272 (D.C. Cir. 1980)).

Additionally, the D.C. Circuit explained that “[f]easibility of compliance turns on whether exposure levels at or below [the PEL] can be met in most operations most of the time . . . ” (Am. Iron & Steel Inst. v. OSHA, 939 F.2d 975, 990 (D.C. Cir. 1991)); (see Section II, Pertinent Legal Authority).

Consistent with the legal standard described above, Chapter IV of the FEA, which can be found at www.regulations.gov (docket OSHA-2010-0034), describes OSHA's examination of the technological feasibility of this rule on occupational exposure to respirable crystalline silica. The chapter provides a description of the methodology and data used by OSHA to analyze the technological feasibility of the standard, as well as a discussion of the accuracy and reliability of current methods used for the sampling and analysis of respirable crystalline silica. Chapter IV contains OSHA's analyses, for 21 general industry sectors, 1 maritime sector, and 12 construction industry application groups, of the technological feasibility of meeting the rule's requirements for reducing exposures to silica. For each sector and application group, OSHA addresses the extent to which the evidence in the record indicates that engineering and work practice controls can reduce respirable crystalline silica exposures to the PEL or below and maintain them at that level. These individual technological feasibility analyses form the basis for OSHA's overall finding that employees' exposures can be reduced to the rule's PEL or below in most of the affected sectors' operations. Throughout Chapter IV, OSHA describes and responds to issues raised in the comments and testimony it received from interested parties during the comment periods and public hearing OSHA held on the proposed rule. The material below summarizes the detailed discussion and presentation of OSHA's findings contained in Chapter IV of the FEA.

1. Methodology

As noted above, OSHA's technological feasibility analysis for this rule largely involved describing engineering and work practice controls that OSHA concludes can be expected to control respirable crystalline silica exposures to the PEL or below. For this portion of the analysis, OSHA relied on information and exposure measurements from many different sources, including OSHA's inspection database (OSHA Information System (OIS)), OSHA inspection reports, National Institute of Occupational Safety and Health (NIOSH) reports, site visits by NIOSH and OSHA's contractor, Eastern Research Group, Inc. (ERG), and materials from other federal agencies, state agencies, labor organizations, industry associations, and other groups. In addition, OSHA reviewed studies from the published literature that evaluated the effectiveness of engineering controls and work practices in order to estimate the reductions from current, baseline exposures to silica that can be achieved through wider or improved implementation of such controls. Finally, OSHA considered the extensive testimony and numerous comments regarding the feasibility of implementing engineering and work practice controls, including circumstances that preclude the use of controls in certain situations. In total, OSHA's feasibility analysis is based on hundreds of sources of information in the record, constituting one of the largest databases of information OSHA has used to evaluate the feasibility of a health standard.

The technological feasibility chapter of the FEA describes the industry sectors and application groups affected by the rule, and identifies the sources of exposure to respirable crystalline silica for each affected job category or task. The technological feasibility analysis subdivides the general industry and maritime workplaces into 24 industry sectors. General industry sectors are identified primarily based on the type of product manufactured (e.g., concrete products, pottery, glass) or type of process used (e.g., foundries, mineral processing, refractory repair). Where sufficiently detailed information was available, the Agency further divided general industry sectors into specific job categories on the basis of common factors such as materials, work processes, equipment, and available exposure control methods. OSHA notes that these job categories are intended to represent job functions; actual job titles and responsibilities might differ depending on the facility or industry practice.

For the construction industry, OSHA identified application groups based on construction activities, tasks, or equipment that are commonly recognized to create silica exposures; these tasks involve the use of power tools (e.g., saws, drills, jackhammers) or larger equipment that generates silica-containing dust (e.g., milling machines, rock and concrete crushers, heavy equipment used in demolition or earthmoving). The technological feasibility analysis for the construction industry addresses 12 different application groups, defined by common construction tasks or activities. OSHA organized construction workers by application groups, rather than by industry sector or job titles, because construction workers often perform multiple activities and job titles do not always coincide with the sources of exposure; likewise, the same equipment, tool or task may be called by different names throughout construction and its various subspecialties. By organizing construction activities this way, OSHA was able to create exposure profiles for employees who perform the same activities in any segment of the construction industry.

OSHA developed exposure profiles for each sector and application group in order to characterize the baseline exposures and conditions for each operation or task (see sections 4 and 5 of Chapter IV of the FEA). The sample results included in the exposure profiles presented in the Preliminary Economic Analysis (PEA) were obtained primarily from OSHA compliance inspection reports and from NIOSH Health Hazard Evaluation and control technology assessments. Samples were also obtained from state plan case files, contractor site visits, published literature and other sources. To ensure the exposure profiles were based on the best available data, the exposure profiles were updated by removing samples collected prior to 1990 (n = 290), leaving 2,512 samples from exposure profiles presented in the PEA from 1990 through 2007. More recent samples submitted by commenters during the rulemaking (n = 153), primarily from 2009 through 2014, and samples obtained from the OIS database (n = 699) from OSHA compliance inspections from 2011 to 2014 were added to exposure profiles, resulting in a total of 3,364 samples (2,483 for general industry and 881 for construction) in the final exposure profiles. In total, these were obtained from 683 source documents (see Table VII-6).

The exposure profiles characterize what OSHA considers to be the baseline, or current, exposures for each job category or application group. Where sufficient information on control measures was available, the exposure profiles were subdivided into sample results with and without controls and the controls were discussed in the baseline conditions section. OSHA also discusses the sampling results associated with specific controls in the baseline conditions section. In these cases, the exposure profiles include exposures associated with a range of controlled and uncontrolled exposure scenarios.

The exposure profiles include silica exposure data only for employees in the United States. Information on international exposure levels is occasionally referenced for perspective or in discussions of control options. The rule covers three major polymorphs of crystalline silica (i.e., quartz, cristobalite, and tridymite). However, the vast majority of crystalline silica encountered by employees in the United States is in the quartz form, and the terms crystalline silica and quartz are often used interchangeably. Unless specifically indicated otherwise, all silica exposure data, samples, and results discussed in the technological feasibility analysis refer to personal breathing zone (PBZ) measurements of respirable crystalline silica.

In general industry and maritime, the exposure profiles in the technological feasibility analysis consist mainly of full-shift samples, collected over periods of 360 minutes or more (see Table IV-02-G in the FEA). By using this criterion, OSHA ensured that the samples included in the exposure profiles were collected for at least three-quarters of a typical 8-hour shift and therefore captured most activities involving exposure to silica at which the employee spends a substantial amount of time (Document ID 0845, pp. 38-40; see Table IV-02-G in the FEA). Due to the routine nature of most job activities in general industry, OSHA assumed that, for the partial shift samples of less than 480 minutes, the same level of exposure as measured during the sampled portion of the shift continued during the smaller, unsampled portion. OSHA considers the 6-hour (360-minute) sampling duration to be a reasonable criterion for including a sample because it limits the extent of uncertainty about general industry/maritime employees' true exposures, as no more than 25 percent of an 8-hour shift would be unsampled. The sample result is therefore assumed to be representative of an 8-hour time-weighted average (TWA). Moreover, by relying primarily on sampling results 360 minutes or greater, OSHA minimized the number of results included in the profiles reported as below the limit of detection (LOD). The LOD for an analytical method refers to the smallest mass of silica that can be detected on the filter used to collect the air sample. Many laboratories currently report an LOD of 10 μg or lower for quartz samples (Document ID 0666). As discussed in the Methodology section of Chapter IV of the FEA, relying primarily on samples with a duration of 360 minutes or greater allows OSHA to draw the conclusion that any sample results reported as non-detect for silica are at most 16 μg/m³, and well below the action level of 25 μg/m³.

In the construction industry, approximately 43 percent of the sampling data used in the exposure profiles also consisted of samples collected over periods of 360 minutes or more. Most of the samples (approximately 70%, or an additional 27%) in the construction industry exposure profiles were collected over periods of 240 minutes or more (see Table IV-02-G in the FEA). This allows OSHA to draw the conclusion that any sample results reported as non-detect are below the action level of 25 μg/m³ (see Table IV-2-F in the FEA). Construction workers typically spend their shifts working at multiple discrete tasks and do not normally engage in any one task for the entire duration of a shift; these varied tasks can include tasks that generate exposure to respirable crystalline silica (Document ID 0677). Consequently, for construction, OSHA assumed zero exposure during the unsampled portion of the employee's shift unless there was evidence that silica exposures continued for the entire shift. For example, if a sample measured an average of 100 μg/m³ over 240 minutes (4 hours), the result would be recorded as 50 μg/m³ TWA for a full 8-hour shift (480 minutes).

The Construction Industry Safety Coalition (CISC), comprised of 25 trade associations, was critical of several aspects of OSHA's feasibility analysis. CISC objected to the assumption of zero exposure for the unsampled portion of the work shift when calculating 8-hour TWAs for the construction exposure profiles. It claimed that assuming zero exposure underestimated TWA exposure levels when compared with the alternative assumption used for general industry that the exposure level measured during the sampled time period remained at the same level during the unsampled period (Document ID 2319, pp. 21-25). While there would be some uncertainty whichever assumption OSHA used, OSHA concludes that the no-exposure assumption for unsampled portions of a shift produces a more accurate result than the assumption of continued exposure at the same level because of the widely-recognized differences in work patterns between general industry and construction operations. In general industry, most operations are at a fixed location and involve manufacturing processes that remain relatively constant over a work shift. Also, most of the sample durations in general industry were 360 minutes or longer, and therefore were more likely to be representative of 8-hour TWA exposures. In contrast, construction work is much more variable with respect to the location of the work site, the number of different tasks performed, and the duration of tasks performed. As stated above, tasks that generate exposure to respirable crystalline silica in construction are often performed on an intermittent basis (e.g., Document ID 0677).

OSHA's conclusion that the variability in sample durations for the samples taken by OSHA in the construction industry more accurately reflects the variability in exposure duration for these activities thus comports with empirical experience. An assumption that exposure levels during short-term tasks continued for the entire work shift would substantially overestimate the actual 8-hour TWA exposures. The Building and Construction Trades Department, AFL-CIO (BCTD) supported OSHA's assumptions on work patterns, stating “OSHA correctly treated the unsampled time as having `zero exposure' in its technological feasibility assessment” (Document ID 4223, pp. 16-17). Its conclusion was based on research performed by The Center to Protect Workers' Rights, which developed a task-based exposure assessment model for the construction industry that combines air sampling with task observations and task durations in order to assess construction workers' exposure to workplace hazards (Susi, et al., 2000, Document ID 4073, Attachment 8c). This model, when applied to masonry job sites, found that employees spent much of their shifts performing non-silica-generating tasks, both before and after the task involving silica exposure (Document ID 4223, p. 16; 4073, Attachment 3a, pp. 1-2). BCTD indicated that it was reasonable to assume these types of work patterns would be similar for other construction tasks (Document ID 4223, pp. 16-17).

CISC also commented that OSHA did not account for the varying amounts of crystalline silica that could exist in materials being disturbed by employees, and that OSHA did not account for differences in exposure results “due solely to what part of the country the activity took place in” (Document ID 2319, pp. 26-27). OSHA has determined that the sampling data relied on to establish baseline silica exposures are representative of the range of silica content in materials worked on by construction workers. Information on the percent silica content of the respirable dust sampled was available for 588 of the 881 samples used in the exposure profiles for construction tasks. The silica content in these samples ranged from less than 1 percent (non-detect) to 50 percent, with an average silica content of 9.1 percent. Thus, the sample results in the exposure profiles reflect the range in the silica content of the respirable dust sampled by OSHA at construction work sites. Similarly, the exposure profiles contain exposure results from many different construction tasks taken in a variety of locations around the country under different weather conditions. Therefore, OSHA concludes that the exposure data used in the exposure profiles are the best available evidence of actual exposures in construction representing nationwide weather patterns, and that these data reflect the broad range of silica exposures experienced by employees in the construction industry.

Each section in the technical feasibility analysis presented in Chapter IV of the FEA begins with descriptions of the manufacturing or industrial process or construction activity that has potential exposure to respirable crystalline silica, each job category or construction task with exposure, and the major activities and sources of exposure. Exposure profiles based on the available sampling information are then presented and used to characterize the baseline exposures and conditions for each operation or task (including exposure controls currently in use). Based on the profile of baseline exposures, each section next includes a description of additional engineering and work practice controls that can be implemented to reduce employee exposures to at least the rule's PEL. In addition, comments and other evidence in the record relating to the description of the industry sector or application group, the exposure profile and baseline conditions, and the need for additional controls are discussed in each section. Finally, based on the exposure profile and assessment of available controls and other pertinent evidence in the record, each section includes a feasibility determination for each operation, task, or activity, including an overall feasibility determination where more than one operation, task, or activity is addressed in the section.

In particular, OSHA evaluated information and testimony from the record on the effectiveness of engineering and work practice controls and either: (1) Identified controls that have been demonstrated to reduce exposures to 50 μg/m³ or below; or (2) evaluated the extent to which baseline exposures would be reduced to 50 μg/m³ or below after applying the percent reduction in respirable silica or dust exposure that has been demonstrated for a given control in the operation or task under consideration or, in some cases, in analogous circumstances. In some cases, the evidence demonstrates that most exposures are already below the PEL. OSHA considers the evidence relied on in making its feasibility determinations to be the best available evidence on these issues.

For general industry and maritime, the additional engineering controls and work practices identified by OSHA consist of equipment and approaches that are widely available and are already used in many applications. In some cases, the same technology can be transferred or adapted to similar operations in other industry sectors covered under the scope of this rule. Such controls and work practices include implementing and maintaining local exhaust ventilation (LEV) systems with dust collection systems (such as integrated material transfer stations); enclosing a conveyor of silica-containing material or other containment systems; worker isolation; process modifications; dust suppression, systems such as water sprays; and housekeeping. In many cases, a combination of controls is necessary to control exposures to silica. In general industry, enclosed and ventilated equipment is often already in use. For example, most paint and coating production operations have switched from manual transfer of raw materials containing crystalline silica to integrated bag dumping stations equipped with well-ventilated enclosures and bag compactors (e.g., Document ID 0199, pp. 9-10; 0943, p. 87; 1607 p. 10-19; 1720, p. IV-237). Where the evidence shows that a type of control like the material transfer system is already being used in a sector covered by the rule, OSHA is able to conclude that it can be used more widely in that sector as an additional control or can be adapted to other industry sectors for use during similar operations (see sections IV-15 Paint and Coatings, IV-16 Porcelain Enameling, IV-11 Glass, and IV-05 Concrete Products, of the FEA for additional information).

For construction, the exposure controls contained in Table 1 of the rule consist primarily of water-based dust suppression systems, and LEV systems that are integrated into hand tools and heavier equipment. As shown in Chapter IV of the FEA, such systems are commercially available from several vendors. In addition, equipment such as filtered, ventilated booths or cabs and water-based systems for suppressing fugitive dust generated by crushers and heavy equipment are available to control exposures of construction workers to respirable crystalline silica.

OSHA received numerous comments that disputed OSHA's preliminary conclusion in the Notice of Proposed Rulemaking (NPRM) that a PEL of 50 μg/m³ TWA was technologically feasible. These comments addressed two general areas of concern: (1) Whether sampling and analytical methods are sufficiently accurate to reliably measure respirable crystalline silica concentrations at levels around the PEL and action level; and (2) whether engineering and work practice controls can reduce exposures from current levels to the lower levels required to comply with the new standards. These issues and OSHA's technological feasibility findings are discussed in the sections that follow. Much more detail can be found in Chapter IV of the FEA.

2. Feasibility Determination for Sampling and Analytical Methods

As explained in Pertinent Legal Authority (Section II of this preamble to the final rule), a finding that a standard is technologically feasible requires that “provisions such as exposure measurement requirements must also be technologically feasible” (see Forging Indust. Ass'n v. Sec'y of Labor, 773 F.2d 1436, 1453 (4th Cir. 1985)). Thus, part of OSHA's technological feasibility assessment of a new or revised health standard includes examining whether available methods for measuring worker exposures have sufficient sensitivity and precision to ensure that employers can evaluate compliance with the standard and that workers have accurate information regarding their exposure to hazardous substances. Consistent with the Supreme Court's definition of “feasibility”, OSHA finds that it is feasible to measure worker exposures to a hazardous substance if achieving a reasonable degree of sensitivity and precision with sampling and analytical methods is “capable of being done” (Am. Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490, 509-510 (1981)). OSHA also notes that its analysis of the technological feasibility of the sampling and analysis of respirable crystalline silica must be performed in recognition of the fact that, as recognized by federal courts of appeals, measurement error is inherent to sampling (Nat'l Min. Assoc. v. Sec'y, U.S. Dep't of Labor, Nos. 14-11942, 14-12163, slip op. at 55 (11th Cir. Jan. 25, 2016); Am. Mining Cong. v. Marshall, 671 F.2d 1251, 1256 (10th Cir. 1982)). “Since there is no perfect sampling method, the Secretary has discretion to adopt any sampling method that approximates exposure with reasonable accuracy.” Am. Mining Cong. v. Marshall, 671 F.2d at 1256.

Since the late 1960s, exposures to respirable crystalline silica (hereinafter referred to as “silica”) have typically been measured using personal respirable dust samplers coupled with laboratory analysis of the crystalline silica content of the collected airborne dust. The laboratory analysis is usually performed using X-ray diffraction (XRD) or infrared spectroscopy (IR). A colorimetric method of analysis that was used by a few laboratories has now been phased out (Harper et al., 2014, Document ID 3998, Attachment 8, p. 1). OSHA has successfully used XRD analysis since the early 1970s to enforce its previous PELs for crystalline silica, which, for general industry, were approximately equivalent to 100 micrograms per cubic meter (μg/m³) for quartz and 50 μg/m³ for cristobalite and tridymite (and within the range of about 250 μg/m³ to 500 μg/m³ for quartz in construction). There are no other generally accepted methods for measuring worker exposure to respirable crystalline silica.

The ability of current sampling and analytical methods to accurately measure worker exposures to respirable crystalline silica was a subject of much comment in the rulemaking record. In particular, the Chamber of Commerce (Chamber) and American Chemistry Council (ACC) submitted comments and testimony maintaining that existing methods do not measure respirable crystalline silica exposures with sufficient accuracy to support OSHA's proposal in the Notice of Proposed Rulemaking to reduce the PEL to 50 μg/m³ and establish the 25 μg/m³ action level (Document ID 2285; 2288, pp. 17-21; 2307, Attachment A, pp. 198-227; 4209, pp. 129-155; 3436, p. 8; 3456, pp. 18-19; 3460; 3461; 3462; 4194, pp. 17-21). Similar views were expressed by several other rulemaking participants (e.g., Document ID 2056, p. 1; 2085, p. 3; 2174; 2185, pp. 5-6; 2195, Attachment 1, p. 37; 2276, pp. 4-5; 2317, p. 2; 2379, Comments, pp. 28-30; 4224, pp. 11-14; 4232, Attachment 1, pp. 3-24). Specifically, these commenters argue that, due to several asserted sources of error, current sampling and analytical methods do not meet the NIOSH accuracy criterion of ±25 percent (NIOSH Manual of Analytical Methods, http://www.cdc.gov/niosh/docs/95-117/ ). Their arguments include: (1) That there is sampling error attributed to bias against the particle-size selection criteria that defines the performance of the samplers and variation in performance between sampling devices; (2) that the accuracy and precision of the analytical method at the low levels of silica that would be collected at the revised PEL and action level is less than that in the range of the previous PELs for silica, particularly in the presence of interfering substances; and (3) variation between laboratories analyzing comparable samples adds an unacceptable degree of uncertainty. After considering all of the testimony and evidence in the record, OSHA rejects these arguments and, as discussed below, concludes that it is feasible to obtain measurements of respirable crystalline silica at the final rule's PEL and action level with reasonable accuracy.

OSHA is basing its conclusions on the following findings, which are described in detail in this section. First, although there is variation in the performance of respirable dust samplers, studies have demonstrated that, for the majority of work settings, samplers will perform with an acceptable level of bias (as defined by international standards) as measured against internationally recognized particle-size selection criteria that define respirable dust samplers. This means that the respirable dust mass collected by the sampler will be reasonably close to the mass that would be collected by an ideal sampler that exactly matches the particle-size selection criteria. In addition, OSHA finds that the measure of precision of the analytical methods for samples collected at crystalline silica concentrations equal to the revised PEL and action level is only somewhat higher (i.e., somewhat less precise) than that for samples collected at concentrations equal to the previous, higher PELs. Further, the analytical methods can account for interferences such that, with few exceptions, the sensitivity and precision of the method are not significantly compromised. Studies of measurement variability between laboratories, as determined by proficiency testing, have demonstrated a significant decline in inter-laboratory variability in recent years. Improvements in inter-laboratory variability have been attributed to changes in proficiency test procedures as well as greater standardization of analytical procedures among laboratories. Finally, although measurement variability increases at low sample loads compared to sample loads in the range of the former PELs, OSHA finds, based on these studies, that the magnitude of this increase has also declined in recent years.

Several rulemaking participants commented that OSHA's analysis of the feasibility of sampling and analytical methods for crystalline silica was well supported and sound (Document ID 2080, pp. 3-4; 2244, p. 3; 2371, Attachment 1, p. 5; 3578, Tr. 941; 3586, Tr. 3284; 3577, Tr. 851-852; 4214, pp. 12-13; 4223, pp. 30-33). Gregory Siwinski, CIH, and Dr. Michael Lax, Medical Director of Upstate Medical University, an occupational health clinical center, commented that current laboratory methods can measure respirable crystalline silica at the 50 μg/m³ PEL and 25 μg/m³ action level, and that they have measured exposures below the action level (Document ID 2244, p. 3). Dr. Celeste Montforton of the George Washington School of Public Health testified that “[i]ndustrial hygienists, company safety personnel, consultants, and government inspectors have been conducting for decades workplace sampling for respirable silica . . .” and that some governments, such as Manitoba and British Columbia, are successfully collecting and analyzing samples to determine compliance with their occupational exposure limits of 25 μg/m³ (Document ID 3577, Tr. 851-852). Dr. Frank Mirer of the CUNY School of Public Health, formerly with the UAW and on behalf of the AFL-CIO, stated that “[a]ir sampling is feasible at 25 μg/m³ and below for [a] full shift and even for part shift. It was dealt with adequately in the OSHA proposal” (Document ID 3578, Tr. 941).

The ACC, Chamber, and others base their argument that sampling and analytical methods for respirable crystalline silica are insufficiently precise on strict adherence to NIOSH's accuracy criterion of ±25 percent at a 95-percent confidence level for chemical sampling and analysis methods ( http://www.cdc.gov/niosh/docs/95-117/ ). The ACC pointed out that “OSHA standards typically reflect the NIOSH Accuracy Criterion by requiring employers to use a method of monitoring and analysis that has an accuracy of plus or minus 25 percent . . . ,” and cited a number of OSHA standards where the Agency has included such requirements (benzene, 29 CFR 1910.1028; lead (which requires a method accuracy of ±20%), 29 CFR 1910.1025; cadmium, 29 CFR 1910.1027; chromium (VI), 29 CFR 1910.1026) (Document ID 4209, p. 129). However, the NIOSH accuracy criterion is not a hard, bright-line rule in the sense that a sampling and analytical method must be rejected if it fails to meet this level of accuracy, but is rather a goal or target to be used in methods development. Where evidence has shown that a method does not meet the accuracy criterion at the PEL or action level, OSHA has stipulated a less rigorous level of accuracy to be achieved. For example, OSHA's acrylonitrile standard requires use of a method that is accurate to ±35 percent at the PEL and ±50 percent at the action level (29 CFR 1910.1045), and several OSHA standards require that ±35 percent accuracy be obtained at the action level (arsenic, 29 CFR 1910.1018; ethylene oxide, 29 CFR 1910.1047; formaldehyde, 29 CFR 1910.1048; 1,3-butadiene, 29 CFR 1910.1051; methylene chloride, 29 CFR 1910.1052). As discussed below, the precision of the sampling and analytical method for crystalline silica, as currently implemented using OSHA Method ID-142 for X-ray diffraction, is about ±21 percent for quartz and cristobalite.

In the remainder of this section, OSHA first describes available respirable dust sampling methods and addresses comments and testimony related to the performance and accuracy of respirable dust samplers. Following that discussion, OSHA summarizes available analytical methods for measuring crystalline silica in respirable dust samples and addresses comments and evidence regarding analytical method precision, the presence of interfering materials, and reported variability between laboratories analyzing comparable samples.

a. Respirable Dust Sampling Devices

Respirable dust comprises particles small enough that, when inhaled, they are capable of reaching the pulmonary region of the lung where gas exchange takes place. Measurement of respirable dusts requires the separation of particles by size to assess exposures to the respirable fraction of airborne dusts. A variety of different industrial hygiene sampling devices, such as cyclones and elutriators, have been developed to separate the respirable fraction of airborne dust from the non-respirable fraction. Cyclones are the most commonly used size-selective sampling devices, or “samplers,” for assessing personal exposures to respirable dusts such as crystalline silica. The current OSHA (ID-142, revised December 1996, Document ID 0946) and NIOSH (Method 7500, Document ID 0901; Method 7602, 0903; Method 7603, http://www.cdc.gov/niosh/docs/2003-154/pdfs/7603.pdf ) methods for sampling and analysis of crystalline silica specify the use of cyclones.

Although respirable dust commonly refers to dust particles having an aerodynamic diameter of 10 μm (micrometer) or less, it is more precisely defined by the collection efficiency of the respiratory system as described by a particle collection efficiency model. These models are often depicted by particle collection efficiency curves that describe, for each particle size range, the mass fraction of particles deposited in various parts of the respiratory system. These curves serve as the “yardsticks” against which the performance of cyclone samplers should be compared (Vincent, 2007, Document ID 1456). Figure VII-1 below shows particle collection efficiency curves for two particle size selection criteria: The criteria specified in the 1968 American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for respirable dust, which was the basis for the prior OSHA general industry silica PEL, and an international specification by the International Organization for Standardization (ISO) and the Comité Européen de Normalisation (CEN) known as the ISO/CEN convention, which was adopted by ACGIH in 1994 and is the basis for the definition of respirable crystalline silica in the final rule. In addition to the curves, which cover the full range of particle sizes that comprise respirable dust, particle size collection criteria are also often described by their 50-percent respirable “cut size” or “cut point.” This is the aerodynamic diameter at which 50 percent of the particle mass is collected, i.e., the particle size that the sampler can collect with 50-percent efficiency. Particles with a diameter smaller than the 50-percent cut point are collected with an efficiency greater than 50 percent, while larger-diameter particles are collected with an efficiency less than 50 percent. The cut point for the 1968 ACGIH specification is 3.5 μm and for the ISO/CEN convention is 4.0 μm (Lippman, 2001, Document ID 1446, pp. 107, 113).

For most workplace conditions, the change in the criteria for respirable dust in the final rule would theoretically increase the mass of respirable dust collected over that measured under the previous criteria by an amount that depends on the size distribution of airborne particles in the workplace. Soderholm (1991, Document ID 1661) examined these differences based on 31 aerosol size distributions measured in various industrial workplaces (e.g., coal mine, lead smelter, brass foundry, bakery, shielded metal arc [SMA] welding, spray painting, pistol range) and determined the percentage increase in the mass of respirable dust that would be collected under the ISO/CEN convention over that which would be collected under the 1968 ACGIH criteria. Soderholm concluded that, for all but three of the 31 size distributions that were evaluated, the increased respirable dust mass that would be collected using the ISO/CEN convention for respirable dust instead of the 1968 ACGIH criteria would be less than 30 percent, with most size distributions (25 out of the 31 examined, or 80 percent) resulting in a difference of between 0 and 20 percent (Document ID 1661, pp. 248-249, Figure 1). In the PEA, OSHA stated its belief that the magnitude of this effect does not outweigh the advantages of adopting the ISO/CEN convention. In particular, most respirable dust samplers on the market today are designed and calibrated to perform in a manner that closely conforms to the international ISO/CEN convention.

Incorporating the ISO/CEN convention in the definition of respirable crystalline silica will permit employers to use any sampling device that conforms to the ISO/CEN convention. There are a variety of these cyclone samplers on the market, such as the Dorr-Oliver, Higgins-Dewell (HD), GK2.69, SIMPEDS, and SKC aluminum. In the PEA, OSHA reviewed several studies demonstrating that these samplers collect respirable particles with efficiencies that closely match the ISO/CEN convention (Document ID 1720, pp. IV-21—IV-24). In addition to cyclone samplers, there are also personal impactors available for use at flow rates from 2 to 8 L/min that have been shown to conform closely with the ISO/CEN convention (Document ID 1834, Attachment 1). Cyclones and impactors both separate particles by size based on inertia. When an airstream containing particles changes direction, smaller particles remain suspended in the airstream and larger ones impact a surface and are removed from the airstream. Cyclones employ a vortex to separate particles centrifugally, while impactors use a laminar airflow around a flat surface such that particles in the desired size range impact onto the surface.

The current OSHA sampling method for crystalline silica, ID-142, is the method used by OSHA to enforce the silica PELs and is used by some employers as well. It specifies that a respirable sample be collected by drawing air at 1.7 ± 0.2 liters/minute (L/min) through a Dorr-Oliver 10 millimeter (mm) nylon cyclone attached to a cassette containing a 5-μm pore-size, 37-mm diameter polyvinyl chloride (PVC) filter (Document ID 0946). NIOSH sampling and analysis methods for crystalline silica (Method 7500, Method 7602, Method 7603) have also adopted the ISO/CEN convention with flow rate specifications of 1.7 L/min for the Dorr-Oliver 10-mm nylon cyclone and 2.2 L/min for the HD cyclone (Document ID 0901; 0903). Method 7500 also allows for the use of an aluminum cyclone at 2.5 L/min. NIOSH is revising its respirable dust method to include any sampler designed to meet the ISO/CEN criteria (Document ID 3579, Tr. 218).

The devices discussed above, when used at the appropriate flow rates, are capable of collecting a quantity of respirable crystalline silica that exceeds the quantitative detection limit for quartz (the principle form of crystalline silica) of 10 μg for OSHA's XRD method (Document ID 0946). For several scenarios based on using various devices and sampling times (8-hour, 4-hour, and 1-hour samples), OSHA calculated the amount of respirable quartz that would be collected at quartz concentrations equal to the existing general industry PEL, the proposed (and now final) rule's PEL, and the proposed (and now final) rule's action level. As seen in Table IV.3-A, computations show that the 10-mm nylon Dorr-Oliver operated at an optimized flow rate of 1.7 L/min, the aluminum cyclone operated at 2.5 L/min, the HD cyclone operated at 2.2 L/min, and the GK2.69 operated at 4.2 L/min will all collect enough quartz during an 8-hour or 4-hour sampling period to meet or exceed the 10 µg quartz limit of quantification for OSHA Method ID-142. Therefore, each of the commercially available cyclones is capable of collecting a sufficient quantity of quartz to exceed the limit of quantification when airborne concentrations are at or below the action level, provided that at least 4-hour air samples are taken. Table VII-7 also shows that the samplers can collect enough silica to meet the limit of quantification when the airborne respirable silica concentration is below the action level of 25 μg/m³, in one case as low as 5 μg/m³.

A comment from the National Rural Electric Cooperative Association (NRECA) stated that the current OSHA and NIOSH analytical methods require sampling to collect a minimum of 400 liters of air, and that at the flow rates specified for current samplers, sampling would have to be performed for approximately 2.5 to 4 hours; however, this is considerably longer than most construction tasks performed in electrical transmission and distribution work, which tend to last 2 hours or less (Document ID 2365, pp. 2, 6-7). OSHA does not view this discrepancy to be a problem. The minimum sampling times indicated in the OSHA and NIOSH methods contemplate that exposure occurs over most of the work shift. Construction operations frequently involve shorter-term tasks after which there is no further exposure to respirable crystalline silica. In those situations, OSHA often does not itself continue sampling during inspections and does not expect employers to continue sampling when there is no exposure to silica, and considers the sampling result that is obtained from shorter-term task sampling to be sufficient to represent a worker's 8-hour time-weighted-average (TWA) exposure, which can be calculated assuming no exposure for the period of the shift that is not sampled. If the airborne concentration of silica for the task is low, the sampling result would likely be below the limit of quantification. In that case, it would be safe for the employer to assume that the exposure is below the action level.

Transition to ISO-CEN Criteria for Samplers

In the final rule, OSHA is adopting the ISO/CEN particle size-selective criteria for respirable dust samplers used to measure exposures to respirable crystalline silica. Under the ISO/CEN convention, samplers should collect 50 percent of the mass of particles that are 4 μm in diameter (referred to as the cut point), with smaller particles being collected at higher efficiency and larger particles being collected at lower efficiency. Particles greater than 10 μm in diameter, which are not considered to be respirable, are to be excluded from the sample based on the ISO/CEN convention (Document ID 1446, pp. 112-113).

Several rulemaking participants supported OSHA's proposed adoption of the ISO/CEN criteria for respirable dust samplers (Document ID 1730; 1969; 3576, Tr. 290; 3579, Tr. 218-219; 4233, p. 4). For example, a representative of SKC, Inc., which manufactures samplers used to collect respirable crystalline silica, stated that:

Adoption of the ISO/CEN performance standard for respirable dust samplers by OSHA will bring the U.S. regulatory standards in line with standards/guidelines established by other occupational health and safety agencies, regulatory bodies, and scientific consensus organizations around the world. It will also align OSHA performance criteria for respirable dust samplers to that of NIOSH (Document ID 1730, pp. 1-2).

As discussed above, OSHA's previous (and currently enforceable) general industry PEL for crystalline silica was based on a 1968 ACGIH definition, which specified a model with a cut point of 3.5 μm. Based on available studies conducted over 40 years ago, the Dorr-Oliver 10-mm cyclone was thought to perform closely to this specification. As such, it is the sampling device specified in OSHA's respirable dust sampling and analytical methods, including Method ID-142 for respirable crystalline silica (Document ID 0946). For most sizes of respirable particles, the ISO/CEN convention specifies a greater efficiency in particle collection than does the 1968 ACGIH model; consequently, samplers designed to meet the ISO/CEN convention will capture somewhat greater mass of airborne particle than would a sampler designed to the 1968 ACGIH model, with the magnitude of the increased mass dependent on the distribution of particle sizes in the air. For most particle size distributions encountered in workplaces, the increase in dust mass theoretically collected under the ISO/CEN convention compared to the ACGIH model would be 25 percent or less (Soderholm, 1991, Document ID 1661).

Several rulemaking participants commented that moving from the 1968 ACGIH model to the ISO/CEN convention effectively decreased the PEL and action level below the levels intended, since more dust would be collected by samplers that conform to the ISO/CEN convention than by those that conform to the 1968 ACGIH model (Document ID 2174; 2195, p. 30; 2285, pp. 3-4; 2307, Attachments 10, p. 19, and 12, p. 3; 2317, p. 2; 3456, p. 10; 4194, pp. 15-16). For example, the Chamber commented that adopting the ISO/CEN specification “can result in citations for over exposure to quartz dust where none would have been issued prior to the adoption of this convention” (Document ID 2288, p. 16). OSHA disagrees with this assessment because, based on more recent evaluations (Bartley et al., 1994, Document ID 1438, Attachment 2; Lee et al., 2010, 3616; 2012, 3615), the Dorr-Oliver 10-mm cyclone that has been used by the Agency for enforcement of respirable dust standards for decades has been found to perform reasonably closely (i.e., with an acceptable level of bias) to the ISO/CEN specification when operated at the 1.7 L/min flow rate specified by OSHA's existing method. Consequently, OSHA and employers can continue to use the Dorr-Oliver cyclone to evaluate compliance against the final PEL of 50 μg/m³ without having to change equipment or procedures, and thus would not be collecting a greater quantity of dust than before. Furthermore, OSHA notes that other ISO/CEN-compliant samplers, such as the SKC 10-mm aluminum cyclone and the HD cyclone specified in the NIOSH Method 7500, are already widely used by investigators and employers to evaluate exposures to respirable crystalline silica against benchmark standards. Therefore, the change from the ACGIH convention to the ISO/CEN convention is more a continuation of the status quo than a drastic change from prior practice.

Other rulemaking participants argued that moving to the ISO/CEN convention effectively invalidates OSHA's risk and feasibility analyses since the exposure data that underlie these analyses were obtained using devices conforming to the 1968 ACGIH specification. For example, Thomas Hall, testifying for the Chamber, stated that moving to the ISO/CEN convention “would produce a difference in [current] exposure results from . . . historical measurements that have been used in the risk assessments” (Document ID 3576, Tr. 435). Similarly, in its pre-hearing comments, the ACC argued that:

When OSHA conducted technological feasibility studies for attaining the proposed 50 μg/m³ PEL, the Agency based its decisions on samples collected using the current ACGIH method, not the proposed ISO/CEN method. Thus, the switch to the ISO/CEN definition will have two impacts on feasibility. First, it will add uncertainty regarding OSHA's technological feasibility determination because greater reductions in exposure will be required to achieve a 50 μg/m³ PEL measured by the ISO/CEN definition than by the ACGIH definition that OSHA applied. Second, OSHA's use of the ACGIH definition to estimate compliance costs causes the Agency to underestimate the costs of achieving the 50 μg/m³ PEL because OSHA did not account for the additional workers whose exposures would exceed the proposed PEL under the ISO/CEN definition but who would be exposed below the proposed PEL if measured under the ACGIH definition (Document ID 2307, Attachment 8, p. 9).

OSHA rejects these arguments for the following reasons. First, with respect to the risk information relied on by the Agency, exposure data used in the various studies were collected from employer records reflecting use of several different methods. Some studies estimated worker exposures to silica from particle counts, for which the sampling method using impingers does not strictly conform to either the ACGIH or ISO/CEN conventions (e.g., Rice et al., Document ID 1118; Park et al., Document ID 0405; Attfield and Costello, Document ID 0285; Hughes et al., Document ID 1060). Other studies used measurements taken using cyclone samplers and modern gravimetric methods of silica analysis (e.g., Rice et al. and Park et al., data obtained from cyclone pre-separator up through 1988, Document ID 1118, 0405; Hughes et al., data from 10-mm nylon cyclone through 1998, Document ID 1060). OSHA believes it likely that exposure data collected using cyclones in these studies likely conformed to the ISO/CEN specification since flow rates recommended in the OSHA and NIOSH methods were most likely used. The studies by Miller and MacCalman (Document ID 1097) and by Buchanan et al. (Document ID 0306) used exposure measurements made with the MRE 113A dust sampler, which does conform reasonably well with the ISO/CEN specification (Gorner et al., Document ID 1457, p. 47). The studies by Chen et al. (2001, Document ID 0332; 2005, Document ID 0985) estimated worker exposures to silica from total dust measurements that were converted to respirable silica measurements from side-by-side comparisons of the total dust sampling method with samples taken using a Dorr-Oliver cyclone operated at 1.7 L/min, which is consistent with the ISO/CEN convention (see Section V, Health Effects, of this preamble and OSHA's Preliminary Review of Health Effects Literature and Preliminary Quantitative Risk Assessment, Document ID 1711). Thus, it is simply not the case that the exposure assessments conducted for these studies necessarily reflect results from dust samples collected with a device conforming to the 1968 ACGIH particle size-selective criteria, and OSHA finds that no adjustment of OSHA's risk estimates to reflect exposure measurements consistent with the ISO/CEN convention is warranted.

Second, with respect to the feasibility analysis, OSHA relied on exposure data and constructed exposure profiles based principally on measurements made by compliance officers using the Dorr-Oliver cyclone operated at 1.7 L/min, as the Agency has done since Method ID-142 was developed in 1981, well before the 1990 cut-off date for data used to construct the exposure profiles. As explained earlier in the section, recent research shows that the Dorr-Oliver cyclone operated at this flow rate performs in a manner consistent with the ISO/CEN specification. Other data relied on by OSHA comes from investigations and studies conducted by NIOSH and others who used various cyclones that conform to the ISO/CEN specification. Thus, OSHA finds that the exposure profiles being relied on to evaluate feasibility and costs of compliance do not reflect sample results obtained using the 1968 ACGIH model. Instead, the vast majority of sample results relied upon were collected in a manner consistent with the requirements of the final rule. NIOSH supported this assessment, stating that, given the Dorr-Oliver sampler operated at a flow rate of 1.7 L/min conforms closely to the ISO/CEN convention, “there is continuation with historic exposure data” (Document ID 4233, p. 4). For these reasons, OSHA finds that it is appropriate to rely on the feasibility and cost analyses and underlying exposure data without adjustment to account for the final rule's adoption of the ISO/CEN specification for respirable dust samplers.

Sampling Error

Several commenters raised issues concerning the accuracy of respirable dust samplers in relation to the ISO/CEN criteria, asserting that sampling respirable dust is uncertain and inaccurate, and that there are numerous sources of error. Chief among these were Dr. Thomas Hall of Industrial Hygiene Specialty Resources, LLC, testifying for the Chamber, and Paul K. Scott of ChemRisk, testifying for the ACC.

The Chamber's witnesses and others referenced studies showing that all samplers were biased against the ISO/CEN particle-size selection convention. This means that the sampler would collect more or less mass of respirable particulate than would an ideal sampler that exactly conforms to the ISO/CEN convention. OSHA discussed this issue in the PEA, noting that most samplers tend to over-sample smaller particles and under-sample larger particles, compared to the ISO/CEN convention, at their optimized flow rates. This means that, for particle size distributions dominated by smaller particles, the sampler will collect more mass than would be predicted from an ideal sampler that exactly conforms to the ISO/CEN convention. For particle size distributions dominated by larger particles in the respirable range, less mass would be collected than predicted. In the PEA, OSHA evaluated several studies that showed that several cyclone samplers exhibited a bias of 10 percent or less for most particle size distributions encountered in the workplace. Some of these studies found biases as high as ±20 percent but only for particle size distributions having a large mass median aerodynamic diameter (MMAD) (i.e., 20 µm or larger) and narrow distribution of particle sizes (i.e., a geometric standard deviation (GSD) of 2 or less) (Document ID 1720, pp. IV-21—IV-24). Such particle size distributions are infrequently seen in the workplace; for well-controlled environments, Frank Hearl of NIOSH testified that the GSD for typical particle size distributions would be about 2 (Document ID 3579, Tr. 187). Dr. Hall (Document ID 3576, Tr. 502) testified, similarly, that it would be around 1.8 to 3 for well-controlled environments and higher for uncontrolled environments (see also Liden and Kenny, 1993, Document ID 1450, p. 390, Figure 5; Soderholm, 1991,1661, p. 249, Figure 1). Furthermore, a particle size distribution with a large MMAD and small GSD would contain only a very small percentage (< 10%) of respirable dust that would be collected by a sampler optimized to the ISO/CEN criteria (Soderholm, 1991, Document ID 1661, p. 249, Figure 2). According to Liden and Kenny (1993), “samplers will perform reasonably well providing the absolute bias in sampling is kept to within 10 percent . . . this aim can be achieved . . . over the majority of size distributions likely to be found in field sampling” (Document ID 1450, p. 390).

Dr. Hall commented that “sampling results differ depending on the choice of sampler used” and that published evaluations have shown that they “have different collection efficiencies, specifically with respect to particle collection in aerosol clouds with large [MMADs greater than] 10 μm” (Document ID 2285, p. 16). He cited the work of Gorner et al. (2001, Document ID 1457), who noted that the cut points achieved by different samplers varied considerably and that flow rates were optimized to bring their respective cut points closer to the ISO/CEN convention, as evidence that commercial samplers do not provide consistently similar results. However, OSHA interprets the findings of Gorner et al. as actually providing evidence of samplers' consistency with the ISO/CEN convention for most particle size distributions encountered in the workplace. This study, which was reviewed in OSHA's PEA, evaluated 15 respirable dust samplers, most of them cyclones, against 175 different aerosol size distributions and evaluated the bias and accuracy of sampler performance against the ISO/CEN convention. Gorner et al. found that most of the samplers they tested met the international criteria for acceptable bias and accuracy (described by Bartley et al., 1994, Document ID 1438, Attachment 2 and Gorner et al., 2001, 1457); under those criteria, bias is not to exceed 10 percent and inaccuracy is not to exceed 30 percent for most of the size distributions tested (Document ID 1457, pp. 49, 52; Document ID 1438, Attachment 2, p. 254). Gorner et al. concluded that the samplers “are therefore suitable for sampling aerosols within a wide range of particle size distributions” (Document ID 1457, p. 52). Gorner et al. also stated that sampler performance should be evaluated by examining bias and accuracy rather than simply comparing cut points and slopes against the ISO/CEN convention (Document ID 1457, p. 50), as Dr. Hall did in his comments.

The ACC's witness, Mr. Scott, noted several potential sources of sampling error in addition to the conventional 5-percent pump flow rate error that is included in OSHA's estimate of sampling and analytical error (SAE, discussed further in Section IV-3.2.4—Precision of Measurement). These included variation in performance of the same cyclone tested multiple times (estimated at 6 percent) and variation between different cyclones tested in the same environment (estimated at 5 percent) (Document ID 2308, Attachment 6, pp. 7-8). Based on published estimates of the magnitude of these kinds of errors, Mr. Scott estimated a total sampling error of 9.3 percent after factoring in pump flow rate error, inter-sampler error, and intra-sampler error; this would increase the SAE by 4 percent, for example, from 15 to 19 percent at 50 μg/m³ (Document ID 2308, pp. 8-9). This means that, if all sampler error were factored into the SAE, an employer would be considered out of compliance with the PEL for an exposure exceeding 59.5 µg/m³, rather than at 57.5 µg/m³ if only pump error were considered, a difference of only 2 µg/m³ in silica concentration. OSHA therefore concludes that intra- and inter-sampler error of the types described by Mr. Scott do not materially change how OSHA would enforce, or how employers should evaluate, compliance with the final rule PEL.

As described above, many different respirable dust samplers have been evaluated against the ISO/CEN convention for different particle size distributions and, in general, these biases are small for the vast majority of particle size distributions encountered in the workplace. OSHA concludes that Mr. Scott's estimate likely overstates the true total sampling error somewhat because the measurements of sampler bias against the ISO/CEN criteria involve accurately measuring and maintaining consistent pump flow rates during the testing of the samplers; therefore, adding pump flow rate error to estimates of inter- and intra-sampler measurement error is redundant. Furthermore, if an employer relies on a single type of cyclone sampler, as is OSHA's practice, there would be no inter-sampler variability between different field samples. If an employer is concerned about this magnitude of uncertainty, he or she can choose simply to use the same sampling device as OSHA (i.e., the Dorr-Oliver cyclone operated at a flow rate of 1.7 L/min, as specified in Method ID-142) and avoid any potential measurement uncertainties associated with use of different sampling devices.

The American Foundry Society (AFS) commented that the ASTM Standard D4532 for respirable dust sampling includes errors for sampling, weighing, and bias, none of which is included in OSHA's pump flow rate error (Document ID 2379, p. 29). This ASTM standard describes procedures for sampling respirable dust using a 10-mm cyclone, HD cyclone, or aluminum cyclone in a manner identical to that prescribed in the OSHA and NIOSH methods for sampling and analysis of silica. Thus, the kinds of errors identified by AFS are the same as those reflected in Mr. Scott's testimony described above, which, as OSHA has shown, do not result in substantial uncertainties in exposure measurement.

OSHA further observes that the kinds of sampling errors described by rulemaking participants are independent of where the PEL is established and are not unique to silica; these biases have existed since OSHA began using the Dorr-Oliver cyclone to enforce the previous PELs for crystalline silica, as well as many other respirable dust standards, over 40 years ago. OSHA also believes that sampling error within the range quantified by Mr. Scott would be unlikely to change how an employer makes risk management decisions based on monitoring results. One Chamber witness, Gerhard Knutson, President of Knutson Ventilation, testified that the type of cyclone used to obtain exposure measurements for crystalline silica was not typically a consideration in designing industrial ventilation systems (Document ID 3576, Tr. 521-522). Dr. Hall, another Chamber witness, also testified that he has used all three sampling devices listed in the NIOSH Method 7500 and has not historically made a distinction between them, though he might make different decisions today based on the aerosol size distribution encountered in a particular workplace (Document ID 3576, Tr. 522-523). In his pre-hearing submission, Dr. Hall cited the Gorner et al. (2001, Document ID 1457) study as recommending that “rough knowledge of the aerosol size distribution can guide the choice of an appropriate sampling technique” (Document ID 2285, p. 8). OSHA concludes it unlikely that, in most instances, it is necessary to obtain such data to minimize sampling bias for risk management purposes, given the overall magnitude of the bias as estimated by Mr. Scott (i.e., an error of less than 10 percent).

High Flow Samplers

OSHA's PEA also described high-flow samplers, in particular the GK2.69 from BGI, Inc., which is run at a flow rate of 4.2 L/min in contrast to 1.7 L/min for the Dorr-Oliver and 2.5 L/min for the aluminum cyclone. High-flow devices such as this permit a greater amount of dust to be collected in low-dust environments, thus improving sensitivity and making it more likely that the amount of silica collected will fall within the range validated by current analytical methods. For example, a Dorr-Oliver run at 1.7 L/min where the silica concentration is 50 μg/m³ would collect 41 μg of silica over 8 hours, compared to the GK2.69 run at 4.2 L/min, which would collect 101 μg of silica (see Table IV.3-A), well within the validation range of the OSHA method (i.e., the range over which precision is determined, 50 to 160 μg) (Document ID 0946, p. 1). Several rulemaking participants supported OSHA's proposal to permit use of high-flow samplers that conform to the ISO/CEN convention (Document ID 2256, Attachment 3, p. 12; 3578, Tr. 941; 3586, Tr. 3286-3287; 4233, p. 4). For example, William Walsh, representing the American Industrial Hygiene Association (AIHA) Laboratory Accreditation Programs, stated that he could measure concentrations of silica at the 25 μg action level with sufficient precision by using a high-flow device (Document ID 3586, Tr. 3287).

The performance of high-flow samplers has been extensively studied, particularly by Lee et al. (2010, Document ID 3616; 2012, 3615), Stacey et al. (2013, Document ID 3618), and Kenny and Gussman (1997, Document ID 1444). The Kenny and Gussman study, which was reviewed in OSHA's PEA, found the GK2.69 had good agreement with the ISO/CEN convention at the 4.2 L/min flow rate, with a cut point of 4.2 μm and a collection efficiency curve that was steeper than the ISO/CEN (i.e., it was more efficient for smaller particles and less so for larger particles). For particle size distributions up to an MMAD of 25 μm and GSD of 1.5 to 3.5, bias against the ISO/CEN convention was generally between +5 and −10 percent. Bias was greater (−20 percent) for particle size distributions having an MMAD above 10 μm and a low GSD which, according to the authors, are not likely to be encountered (Document ID 1444, p. 687, Figure 7).

The Lee et al. (2010, Document ID 3616; 2012, 3615) and Stacey (2013, Document ID 3618) studies of high-flow sampler performance are the product of a collaborative effort between NIOSH and the United Kingdom's Health and Safety Executive (HSE) that examined the performance of three high-flow samplers; these were the GK2.69, the CIP10-R (Arelco ARC, France), and the FSP10 (GSA, Germany). The FSP10 runs at a flow rate of 10 L/min and the combination of large cyclone and heavy-duty pump may be burdensome for workers to wear. The CIP-10 also runs at 10 L/min and is much smaller and lighter, but uses a collection technology different from cyclones, which may be unfamiliar to users. According to NIOSH, cyclones operating around 4 L/min “offer a current compromise” for obtaining higher flow rates without the need to use larger personal samplers that may be difficult for workers to wear (Document ID 2177, Attachment B, p. 13; 3579, Tr. 163).” For this reason, OSHA's review of these studies focuses on the performance of the GK2.69 cyclone.

Lee et al. (2010, Document ID 3616) tested the GK2.69 against 11 sizes of monodisperse aerosol and found that, at the 4.2 L/min flow rate, the estimated bias against the ISO/CEN convention was positive for all particle size distributions (i.e., the sampler collected greater mass of particulate than would be predicted from an ideal sampler that exactly conformed to ISO/CEN), with a 10-percent efficiency for collecting 10 μm particles, compared to 1 percent for the ISO/CEN convention. The authors estimated a bias of +40 percent for a particle size distribution having a MMAD of 27.5 μm. However, adjustment of the flow rate to 4.4 L/min resulted in biases of less than 20 percent for most particle size distributions and the collection efficiency for 10 μm particles was much closer to the ISO/CEN convention (2.5 percent compared to 1 percent). The authors concluded that, at the higher flow rate, the GK2.69 cyclone met the international standard for sampler conformity to relevant particle collection conventions (European Committee for Standardization, EN 13205, cited in Lee et al., 2010, Document ID 3616), and would provide relatively unbiased measurements of respirable crystalline silica (Document ID 3616, pp. 706, 708, Figure 5(a)).

Lee et al. (2012, Document ID 3615) performed a similar evaluation of the same samplers using coal dust but included analysis of crystalline silica by both XRD and IR. The GK2.69 runs at a flow rate of 4.4 L/min collected somewhat more respirable dust and crystalline silica than would be predicted from differences in flow rates, compared to the 10-mm nylon cyclone, but nearly the same as the Higgins-Dewell cyclone. The authors found that the GK2.69 “showed non-significant difference in performance compared to the low-flow rate samplers” (Document ID 3615, p. 422), and that “the increased mass of quartz collected with high-flow rate samplers would provide precise analytical results (i.e., significantly above the limit of detection and/or the limit of quantification) compared to the mass collected with low-flow rate samplers, especially in environments with low concentrations of quartz . . .” (Document ID 3615, p. 413). Lee et al. concluded that “[a]ll samplers met the [EN 13205] requirements for accuracy for sampling the ISO respirable convention” (Document ID 3615, p. 424).

Stacey et al. (2013, Document ID 3618) used Arizona road dust aerosols to evaluate the performance of high-flow samplers against the Safety In Mines Personal Dust Sampler (SIMPEDS), which is the low-flow sampler used to measure respirable crystalline silica in the U.K. For the GK2.69, use of a flow rate of 4.2 L/min or 4.4 L/min made little difference in the respirable mass collected, and there was closer agreement between the GK2.69 and SIMPEDS sampler when comparing respirable crystalline silica concentration than respirable dust concentration, and the difference was not statistically significant (Document ID 3618, p. 10). According to NIOSH, the findings by Stacey et al. (2013) corroborate those of Lee et al. (2010 and 2012) that the GK2.69 meets the ISO/CEN requirements for cyclone performance and that either the 4.2 L/min or 4.4 L/min flow rate “can be used to meet the ISO convention within acceptable limits” (Document ID 2177, p. 13).

Mr. Scott testified that the high-flow samplers (including the GK2.69) studied by Lee et al., (2010 and 2012), “tended to have a substantial bias towards collecting more respirable particulates than the low-flow samplers, collecting between 12 percent and 31 percent more mass” because high-flow samplers tend to collect a higher proportion of larger particles (Document ID 3582, Tr. 1984). In his written testimony, he noted that Lee et al. (2010) reported a nearly 10-fold higher collection efficiency for 10 μm particles compared to the ISO/CEN standard. However, Mr. Scott's testimony ignores Lee et al.'s findings that the oversampling of larger particles seen at a flow rate of 4.2 L/min was not apparent at the higher 4.4 L/min flow rate and that Lee et al. (2010) concluded that agreement with the ISO/CEN convention was achieved at the higher flow rate (Document ID 3616, pp. 706, 708). In addition, oversampling of larger particles at the 4.2 L/min flow rate was not reported by Lee et al. (2012, Document 3615) or Stacey et al. (2013, Document ID 3618).

Dr. Hall expressed a similar concern as Mr. Scott. He cited Lee et al. (2010) as stating that the GK2.69 would collect significantly more aerosol mass for particle size distributions having an MMAD of more than 6 μm. He also cited Lee et al. (2010 and 2012) for the finding that the GK2.69 collects from 1.8 to 3.84 times as much aerosol mass as the Dorr-Oliver or Higgins-Dewell cyclones (Document ID 2285, p. 12). In his pre-hearing comment, Dr. Hall stated that “[f]or aerosol clouds with a [MMAD] greater than 10 μm, the expected absolute bias can range be (sic) between 20 and 60%” and “the total variability for the method SAE can be as large as 85-90%” (Document ID 2285, pp. 15-16).

OSHA notes that both Dr. Hall and Mr. Scott focus their comments regarding the performance of high-flow samplers on environments where the particle size distribution is characterized by larger particles and small variance (GSD). The findings by Lee et al. (2010) show that, at a flow rate of 4.2 L/min, under this experimental system, there were large positive biases (>20 percent) against the ISO/CEN convention for nearly all particle size distributions having MMAD of 5 to 10 μm (Document ID 3616, pp. 704-706, Figure 3(b)). However, when the flow rate was adjusted to 4.4 L/min, bias exceeding 20 percent was found to occur primarily with particle size distributions having GSDs under 2.0 and MMAD greater than 10 μm (Document ID 3616, p. 707, Figure 5(a)). As discussed above, it is rare to encounter particle size distributions having relatively large MMADs and small GSDs, so the high variability attributed to high-flow samplers by Dr. Hall and Mr. Scott should not be of concern for most workplace settings. Further, sampler performance is considered acceptable if the bias and accuracy over at least 80 percent of the remaining portion of the bias map are within acceptable limits, which are no more than 10 and 30 percent, respectively (Document ID 1457, pp. 49, 52). The Lee et al. studies (2010 and 2012) concluded that the high-flow samplers tested met these international requirements for accuracy for sampling the ISO/CEN convention, and the Stacey et al. (2013) study found that their results compared favorably with those of Lee et al. (2012). Therefore, OSHA finds that the uncertainties characterized by Dr. Hall and Mr. Scott are exaggerated for most workplace situations, and that there is substantial evidence that high-flow samplers, in particular the GK2.69 cyclone, can be used to collect respirable crystalline silica air samples in most workplace settings without introducing undue bias.

Mr. Scott, testifying for the ACC, was of the opinion that, although high-flow samplers have been evaluated by Gorner et al. (2001, Document ID 1457) and Lee et al. (2010, Document ID 3616; 2012, 3615) with respect to their sampling efficiencies as compared to the ISO/CEN convention and their performance compared to low-flow samplers, none of the studies evaluated the accuracy and precision using methods recommended in NIOSH's Guidelines for Air Sampling and Analytical Method Development and Evaluation (1995, http://www.cdc.gov/niosh/docs/95-117/ ) (Document ID 2308, Attachment 6, p. 18). OSHA understands Mr. Scott to contend that the sampler must be tested against a generated atmosphere of respirable crystalline silica and that the precision of the sampling and analytical method must be determined overall from these generated samples.

OSHA does not agree with the implication that, until high-flow samplers have been evaluated according to the NIOSH (1995) protocol, the findings from the studies described above are not sufficient to permit an assessment of sampler performance. The NIOSH Guidelines cited by Mr. Scott state that “[a]n experimental design for the evaluation of sampling and analytical methods has been suggested. If these experiments are not applicable to the method under study, then a revised experimental design should be prepared which is appropriate to fully evaluate the method” ( http://www.cdc.gov/niosh/docs/95-117/ , p. 1). These guidelines contemplate the development of entirely new sampling and analytical methods. Because the analytical portion of the sampling and analytical method for respirable crystalline silica was already fully evaluated before the GK2.69 was developed (Kenny and Gussman, 1997, Document ID 1444), it was only necessary to evaluate the performance of the GK2.69 high-flow sampler. As described above, the studies by Lee et al. (2010, Document ID 3616; 2012, 3615) and Stacey et al. (2013, Document ID 3618) reflect a collaborative effort between NIOSH in the U.S. and HSE in the U.K. to evaluate the performance of high-flow respirable dust samplers. The Lee et al. (2010, 2012) studies were conducted by NIOSH laboratories in Morgantown, West Virginia with peer review by HSE scientists, and the Stacey et al. (2013) study was conducted by HSE at the Health and Safety Laboratory at Buxton in the U.K. Both Lee et al. (2012) and Stacey et al. (2013) concluded that high-flow samplers studied, including the GK2.69, met the EN 13205 requirements for accuracy for sampling against the ISO/CEN convention, demonstrating that results from these two national laboratories compared favorably. OSHA concludes these peer-reviewed studies, performed by NIOSH and HSE scientists, meet the highest standards for effective methods evaluation and therefore does not agree with the suggestion that additional work following NIOSH's protocol is necessary. Comments submitted by NIOSH indicate that the Lee et al. (2010, 2012) and Stacy et al. (2013) studies are sufficient to establish the GK2.69 high-flow sampler as acceptable for sampling respirable crystalline silica under the ISO/CEN convention (Document ID 2177, Attachment B; 4233, p. 4).

URS Corporation, on behalf of the ACC, commented that precision will not be improved by the use of high-flow samplers because filter loadings of interferences will increase along with the amount of crystalline silica; this would, in URS's opinion, necessitate additional sample handling procedures, such as acid washing, that erode precision. URS also argued that such samples may require analysis of multiple peaks and that overall X-ray intensity may be diminished due to increased filter load (Document ID 2307, Attachment 12, p. 3). In its post-hearing brief, the ACC stated that the use of high-volume samplers “in addition to traditional Dorr-Oliver sampler” would reduce inter-laboratory precision (i.e., the extent to which different laboratories achieve similar results for the same sample) due to the use of multiple sampler types (Document ID 4209, p. 154).

OSHA finds that these arguments are unsupported. Although the high-flow sampler will collect more dust than lower-flow samplers in the same environment, the relative proportion of any interfering materials collected to the amount of crystalline silica collected would remain unchanged. Thus, there should be no increased effect from the interfering materials relative to the silica. OSHA recognizes that, to prevent undue interference or diminished X-ray intensity, it is important to keep the dust load on the filter within reasonable limits. Both OSHA and NIOSH methods stipulate a maximum sample weight to be collected (3 mg for OSHA and 2 mg for NIOSH) (Document ID 0946, p. 5; 0901, p. 3), and in the event that excess sample is collected, the sample can be split into portions and each portion analyzed separately (Document ID 0946, p. 5). In environments where using a high-flow sampler is likely to collect more than the maximum sample size, use of a lower-flow sampler is advised. In response to the concern that permitting use of high-flow samplers will affect inter-laboratory variability, OSHA observes that employers are already using a variety of commercially available samplers, such as those listed in the NIOSH Method 7500, to obtain exposure samples; not everyone uses the Dorr-Oliver sampler. Thus, for the final rule, OSHA is permitting employers to use any sampling device that has been designed and calibrated to conform to the ISO/CEN convention, including higher-flow samplers such as the GK2.69. In effect, this is a continuation of well-studied current practice, not an untested departure from it.

b. Laboratory Analysis of Crystalline Silica

Crystalline silica is analyzed in the laboratory using either X-ray diffraction (XRD) or infrared spectroscopy (IR). A third method, colorimetric spectrophotometry, is no longer used (Document ID 3579, Tr. 211; Harper et al., 2014, 3998, Attachment 8, p. 1). This section describes crystalline silica analysis by XRD and IR and responds to comments and testimony on the precision and accuracy of these methods for measuring crystalline silica concentrations in the range of the final rule's PEL and action level. As discussed below, both XRD and IR methods can detect and quantify crystalline silica in amounts collected below the final rule's 25 µg action level.

X-Ray Diffraction

For XRD, a dust sample that has been collected by a sampler is deposited on a silver-membrane filter and scanned by the X-ray beam, where X-rays diffract at specific angles. A sensor detects these diffracted X-ray beams and records each diffracted beam as a diffraction peak. Unique X-ray diffraction patterns are created when the diffraction peaks are plotted against the angles at which they occur. The intensity of the diffracted X-ray beams depends on the amount of crystalline silica present in the sample, which can be quantified by comparing the areas of the diffraction peaks obtained with those obtained from scanning a series of calibration standards prepared with known quantities of an appropriate reference material. Comparing multiple diffraction peaks obtained from the sample with those obtained from the calibration standards permits both quantitative and qualitative confirmation of the amount and type of crystalline silica present in the sample (i.e., quartz or cristobalite). A major advantage of XRD compared with the other techniques used to measure crystalline silica is that X-ray diffraction is specific for crystalline materials. Neither non-crystalline silica nor the amorphous silica layer that forms on crystalline silica particles affects the analysis. The ability of this technique to quantitatively discriminate between different forms of crystalline silica and other crystalline or non-crystalline materials present in the sample makes this method least prone to interferences. Sample analysis by XRD is also non-destructive, meaning that samples can be reanalyzed if necessary (Document ID 1720, pp. IV-26—IV-27).

The OSHA Technical Manual lists the following substances as potential interferences for the analysis of crystalline silica using XRD: Aluminum phosphate, feldspars (microcline, orthoclase, plagioclase), graphite, iron carbide, lead sulfate, micas (biotite, muscovite), montmorillonite, potash, sillimanite, silver chloride, talc, and zircon ( https://www.osha.gov/dts/osta/otm/otm_ii/otm_ii_1.html , Chapter 1, III.K). The interference from other minerals usually can be recognized by scanning multiple diffraction peaks quantitatively. Diffraction peak-profiling techniques can resolve and discriminate closely spaced peaks that might interfere with each other. Sometimes interferences cannot be directly resolved using these techniques. However, many interfering materials can be chemically washed away in acids that do not dissolve the crystalline silica in the sample. Properly performed, these acid washes can dissolve and remove these interferences without appreciable loss of crystalline silica (Document ID 1720, p. IV-27).

The nationally recognized analytical methods using XRD include OSHA ID-142, NIOSH 7500, and MSHA P-2 (Document ID 0946; 0901; 1458). All are based on the XRD of a redeposited thin-layered sample with comparison to standards of known concentrations (Document ID 0946, p. 1; 0901, p. 1; 1458, p. 1). These methods, however, differ on diffraction peak confirmation strategies. The OSHA and MSHA methods require at least three diffraction peaks to be scanned (Document ID 0946, p. 5; 1458, p. 13). The NIOSH method only requires that multiple peaks be qualitatively scanned on representative bulk samples to determine the presence of crystalline silica and possible interferences, and quantitative analysis of air samples is based on a single diffraction peak for each crystalline silica polymorph analyzed (Document ID 0901, pp. 3, 5).

Infrared Spectroscopy

Infrared spectroscopy is based on the principle that molecules of a material will absorb specific wavelengths of infrared electromagnetic energy that match the resonance frequencies of the vibrations and rotations of the electron bonds between the atoms making up the material. The absorption of IR radiation by the sample is compared with the IR absorption of calibration standards of known concentration to determine the amount of crystalline silica in the sample. Using IR can be efficient for routine analysis of samples that are well characterized with respect to mineral content, and the technique, like XRD, is non-destructive, allowing samples to be reanalyzed if necessary. The three principle IR analytical methods for crystalline silica analyses are NIOSH 7602 (Document ID 0903), NIOSH 7603 ( http://www.cdc.gov/niosh/docs/2003-54/pdfs/7603.pdf ), and MSHA P-7 (Document ID 1462); NIOSH Method 7603 and MSHA P-7 were both specifically developed for the analysis of quartz in respirable coal dust. OSHA does not use IR for analysis of respirable crystalline silica.

Interferences from silicates and other minerals can affect the accuracy of IR results. The electromagnetic radiation absorbed by silica in the infrared wavelengths consists of broad bands. In theory, no two compounds have the same absorption bands; however, in actuality, the IR spectra of silicate minerals contain silica tetrahedra and have absorption bands that will overlap. If interferences enhance the baseline measurement and are not taken into account, they can have a negative effect that might underestimate the amount of silica in the sample. Compared with XRD, the ability to compensate for these interferences is limited (Document ID 1720, pp. IV-29—IV-30).

c. Sensitivity of Sampling and Analytical Methods

The sensitivity of an analytical method or instrument refers to the smallest quantity of a substance that can be measured with a specified level of accuracy, and is expressed as either the LOD or the “Limit of Quantification” (LOQ). These two terms have different meanings. The LOD is the smallest amount of an analyte that can be detected with acceptable confidence that the instrument response is due to the presence of the analyte. The LOQ is the lowest amount of analyte that can be reliably quantified in a sample and is higher than the LOD. These values can vary from laboratory to laboratory as well as within a given laboratory between batches of samples because of variation in instrumentation, sample preparation techniques, and the sample matrix, and must be confirmed periodically by laboratories.

At a concentration of 50 µg/m³, the final rule's PEL, the mass of crystalline silica collected on a full-shift (480 minute) air sample at a flow rate of 1.7 L/min, for a total of 816 L of air, is approximately 41 µg (see Table VII-7). At a concentration of 25 µg/m³, the final rule's action level, the mass collected is about 20 µg. The LOQ for quartz for OSHA's XRD method is 10 µg (Document ID 0946; 3764, p. 4), which is below the amount of quartz that would be collected from full-shift samples at the PEL and action level. Similarly, the reported LODs for quartz for the NIOSH and MSHA XRD and IR methods are lower than that which would be collected from full-shift samples taken at the PEL and action level (NIOSH Method 7500, Document ID 0901, p. 1; MSHA Method P-2, 1458, p. 2; NIOSH Method 7602, 0903, p. 1; NIOSH Method 7603, http://www.cdc.gov/niosh/docs/2003-154/pdfs/7603.pdf , p. 1; MSHA Method P-7, 1462, p. 1).

The rule's 50 µg/m³ PEL for crystalline silica includes quartz, cristobalite, and tridymite in any combination. For cristobalite and tridymite, the previous general industry formula PEL was approximately 50 µg/m³, so the change in the PEL for crystalline silica does not represent a substantive change in the PEL for cristobalite or tridymite when quartz is not present. OSHA Method ID-142 (Document ID 0946) lists a 30-µg LOQ for cristobalite; however, because of technological improvements in the equipment, the current LOQ for cristobalite for OSHA's XRD method as implemented by the OSHA Salt Lake Technical Center (SLTC) is about 20 µg (Document ID 3764, p. 10).

That XRD analysis of quartz from samples prepared from reference materials can achieve LODs and LOQs between 5 and 10 µg was not disputed in the record. Of greater concern to several rulemaking participants was the effect of interfering materials potentially present in a field sample on detection limits and on the accuracy of analytical methods at low filter loads when interferences are present. Although the Chamber's witness, Robert Lieckfield of Bureau Veritas Laboratories, did not dispute that laboratories could achieve this level of sensitivity (Document ID 3576, Tr. 485-486), the ACC took issue with this characterization of method sensitivity stating that “the LOQ for real world samples containing interferences is likely to be higher than the stated LOQ's for analytical methods, which are determined using pure NIST samples with no interferences” (Document ID 4209, p. 132). Both Mr. Lieckfield and Mr. Scott testified that the presence of interferences in samples can increase the LOQ and potential error of measurement at the LOQ (Document ID 2259, p. 7; 3460, p. 5).

Mr. Scott (Document ID 2308, Attachment 6, p. 5) cited a laboratory performance study by Eller et al. (1999a, Document ID 1687), in which laboratories analyzing samples with and without interfering materials present reported a range of LOD's from 5 μg to 50 μg. Mr. Scott believed that this study provided evidence that interfering materials present in crystalline silica samples adversely affected laboratories' reported LODs. OSHA disagrees with this interpretation. The Agency reviewed this study in the PEA (Document ID 1720, p. IV-33) and believes that the variability in reported LODs reflected differences in laboratory practices with respect to instrument calibration and quality control procedures. These factors led Eller et al. (1999b, Document ID 1688, p. 24; 1720, p. IV-42) to recommend changes in such practices to improve laboratory performance. Thus, OSHA finds that the variation in reported LODs referred to by Mr. Scott cannot be attributed primarily to the presence of interfering materials on the samples.

The presence of interferences can adversely affect the sensitivity and precision of the analysis, but typically only when the interference is so severe that quantification of crystalline silica must be made from secondary and tertiary diffraction peaks (Document ID 0946, p. 6). However, OSHA finds no evidence that interferences usually present serious quantification problems. First, there are standard protocols in the OSHA, NIOSH, and MSHA methods that deal with interferences. According to OSHA Method ID-142,

Because of these broad selection criteria and the high specificity of the method for quartz, some of the listed interferences may only present a problem when a large amount of interferent is present. . . . Interference effects are minimized by analyzing each sample for confirmation using at least three different diffraction peaks so as to include peaks where the quartz and cristobalite results are in good agreement and where the interferent thus causes no problem. Bulk samples or a description of the process being sampled are useful in customizing a chemical cleanup procedure for any interference found difficult to resolve by software. Even so, the presence of an interference rarely jeopardizes the analysis (Document ID 0946, p. 5).

Software developed by instrument manufacturers and techniques such as acid washing of the sample when interferences are suspected to be present are also useful in resolving interferences. The Chamber's expert witness, Mr. Lieckfield, acknowledged that it was also their practice at his lab to chemically treat samples from the start to remove interfering materials and to analyze multiple diffraction peaks to resolve interferences (Document ID 3576, Tr. 533, 542). According to OSHA's representative from the SLTC, it is “nearly always possible” to eliminate interferences and is it no more difficult to obtain precise measurements when interferences are present than when they are not (Document ID 3579, Tr. 48).

ACC also cites the results of a round-robin performance study that it commissioned, in which five laboratories were provided with crystalline silica samples with and without interfering materials (Document ID 4209, p. 132). These laboratories reported non-detectable levels of silica for 34 percent of the filters having silica loadings of 20 μg or more. However, as discussed below in the section on inter-laboratory variability (Section IV-3.2.5—Measurement Error Between Laboratories), OSHA has determined that this study is seriously flawed and, in particular, that there was systematic bias in the results, possibly due to sample loss. This could explain the high prevalence of reported non-detectable samples by the laboratories, rather than the presence of interferences per se.

Furthermore, OSHA's review of the several hundred inspection reports relied on to evaluate the technological feasibility of the final rule's PEL in many industry sectors does not show that investigators have particular difficulty in measuring respirable crystalline silica concentrations below the PEL. Sections IV-4 and IV-5 of this chapter contain hundreds of exposure measurement results in a wide variety of workplace settings that were detected and reported by a laboratory as being above detectable limits but below the PEL or action level. If, as ACC suggests, interferences have a profound effect on the ability to measure concentrations in this range, many of these samples might have been reported as “less than the LOD,” with the reported LOD in the range of 25 μg to 50 μg. Examination of the exposure data described in Sections IV-4 and IV-5 of this chapter shows clearly that this is not the case (see exposure profiles for Concrete Products, Section IV-4.3; Cut Stone, Section IV-4.4; Foundries (Metal Casting), Section IV-4.8; Mineral Processing, Section IV-4.12; Porcelain Enameling, Section IV-4.14; Ready Mix Concrete, Section IV-4.17; Refractories, Section IV-4.18). In addition, the United Steelworkers reported receiving exposure data from 17 employers with samples in this same range, indicating that sampling of exposures below the final PEL and action level is feasible and already being utilized by employers (Document ID 4214, pp. 12-13; Document ID 4032, Attachment 3).

Therefore, OSHA finds that the presence of interfering substances on field samples will not, most of the time, preclude being able to detect concentrations of respirable crystalline silica in the range of the PEL and action level, and that such instances where this might occur are rare. Accordingly, even when the presence of interfering substances is taken into account, worker exposure is capable of being measured with a reasonable degree of sensitivity and precision.

d. Precision of Measurement

All analytical methods have some random measurement error. The statistics that describe analytical error refer to the amount of random variation in measurements of replicate sets of samples containing the same quantity of silica. This variation is expressed as a standard deviation about the mean of the measurements. The relative standard deviation (RSD), a key statistic used to describe analytical error, is calculated by dividing the standard deviation by the mean for a data set. The RSD is also known as the coefficient of variation (CV).

When random errors are normally distributed, a 95-percent confidence interval can be calculated as X̄ ± (1.96 × CV), where X̄ is the mean. This statistic is termed the “precision” of the analytical method and represents a 2-sided confidence interval in that, for a particular measurement, there is a 95-percent chance that the “true” value, which could be higher or lower than the measurement, lies within the confidence interval. The measure of analytical precision typically also includes a term to represent error in sampler pump flow, which is conventionally taken to be 5 percent. The better the precision of an analytical method, the lower its value (i.e., a method having a precision of 17 percent has better precision than one with a precision of 20 percent).

OSHA also uses a statistic called the Sampling and Analytical Error (SAE) to assist compliance safety and health officers (CSHOs) in determining compliance with an exposure limit. The estimate of the SAE is unique for each analyte and analytical method, and must be determined by each laboratory based on its own quality control practices. At OSHA's Salt Lake Technical Center (SLTC), where analytical methods are developed and air samples taken for enforcement purposes are analyzed, the SAE is based on statistical analysis of results of internally prepared quality control samples. Sampling and analytical components are assessed separately, where CV₁ reflects analytical error that is estimated from the analysis of quality control samples, and CV₂ is the sampling error, assumed to be 5 percent due to variability in sampling pump flow rates that can affect sample air volume. Analytical error is combined with sampling pump error, and the SAE is calculated as a one-sided 95-percent confidence limit with the following formula:

The current SLTC SAE for crystalline silica is approximately 0.17, according to testimony from a representative of SLTC (Document ID 3579, Tr. 95). OSHA uses the SAE in its enforcement of PELs, where the PEL times the SAE is added to the PEL for a substance and compared to a sample result (see Section II, Chapter 1 of the OSHA Technical Manual, https://www.osha.gov/dts/osta/otm/otm_toc.html ). A sample result is considered to have definitively exceeded the PEL if the result is greater than the sum of the PEL and the PEL times the SAE. For example, with the PEL at 50 μg/m³ and an SAE of 17 percent, an air sample result would have to be greater than 58.5 μg/m³ (i.e., 50 + (50 × 0.17)) to be considered to have definitively exceeded the PEL. This policy gives employers the benefit of the doubt, as it assumes that the actual exposure was below the PEL even when the result is above the PEL but below the PEL plus the SAE; the effect is that OSHA does not cite an employer for an exposure above the PEL unless the Agency has obtained a sample measurement definitively above the PEL after accounting for sampling and analytical error.

OSHA's quality control samples, which were prepared and analyzed at SLTC, demonstrate that the XRD method has acceptable precision, even at the low range of filter loads (50 μg). For the period April 2012 through April 2014, SLTC's analysis of 348 quality control samples, with a range of filter loads of about 50 to 250 μg crystalline silica, showed average recovery (i.e., the measurement result as compared to the reference mean value for the sample) of 0.98 with an RSD of 0.093 and precision of 20.8 percent (Document ID 3764, Attachment 1). Among those samples, there were 114 with a target filter load of 50 μg (range of actual filter load was 50 to 51.6 μg); these samples showed an average recovery of 1.00 with an RSD of 0.093 and precision of 20.7 percent (Document ID 3764, Attachment 1). Thus, OSHA's experience with quality control standards shows that the XRD method for quartz is as precise in the low range of method validation as it is over the full range.

The ACC raised several questions regarding OSHA's Method ID-142 and its validation. First, a paper they submitted by Sandra Wroblewski, CIH, of Computer Analytical Solutions notes that OSHA's stated Overall Analytical Error is 26 percent, higher than the 25-percent level “OSHA states is necessary to ensure that a PEL can be feasibly measured,” and that the method had not been validated for cristobalite (Document ID 2307, Attachment 10, pp. 13-14). In addition, the ACC stated that OSHA's method specifies a precision and accuracy validation range of 50-160 µg quartz per sample, above the quantity that would be collected at the PEL and action level (assuming use of a Dorr-Oliver sampler at 1.7 L/min) and that the method has not been tested for validation at a range corresponding to the PEL and action level (Document ID 2307, Attachment 10, p. 14). ACC also argued that OSHA's method does not comply with the Agency's Inorganic Methods Protocol, which requires the CV₁ to be 0.07 or less and the detection limit to be less than 0.1 times the PEL (Document ID 2307, Attachment A, p. 202). The Edison Electric Institute (Document ID 2357, pp. 20-21) and Ameren Corporation (Document ID 2315, p. 2) expressed similar concerns about the detection limit.

While OSHA's published Method ID-142 reports an Overall Analytical Error of 26 percent, OSHA no longer uses this statistic (it is in the process of revising Method ID-142); the Agency provides measures of precision and SAE instead. The Overall Analytical Error, which is described in Method ID-142, published in 1996, included a bias term that is now corrected for in the data used to determine method precision, so there is no longer a need to include a bias term in the estimation of analytical error. As described above, the precision of Method ID-142 is about 21 percent based on recent quality control samples. OSHA's Inorganic Methods Protocol, to which the ACC referred, has been replaced by evaluation guidelines for air sampling methods using spectroscopic or chromatographic analysis, published in 2005 ( https://www.osha.gov/dts/sltc/methods/spectroguide/spectroguide.html ) and 2010 ( https://www.osha.gov/dts/sltc/methods/chromguide/chromguide.html ), respectively. These more recent publications no longer reflect the guidance contained in the Inorganic Methods Protocol, and OSHA's Method ID-142 is consistent with these more recent guidelines. Finally, although the published method did not include validation data for filter loads below 50 μg or data for cristobalite, OSHA has conducted studies to characterize the precision that is achieved at low filter loads for quartz and cristobalite; these studies are in the rulemaking record (Document ID 1670, Attachment 1; 1847, Attachment 1; 3764, pp. 15-16) and are discussed further below.

In comments submitted on behalf of the Chamber, Mr. Lieckfield cited the NIOSH Manual of Analytical Methods, Chapter R, as stating that “current analysis methods do not have sufficient accuracy to monitor below current exposure standards” (Document ID 2259, p. 1). However, this is contradicted by NIOSH's own post-hearing submission, which stated that, although method variability was assessed based on the exposure limits at that time (i.e., 1983, see Document ID 0901, pp. 1, 7), “it was known from an intra-laboratory study that an acceptable variability would likely be at least 20 μg on-filter, and so 20 μg was given as the lower range of the analytical method” (Document ID 4233, p. 3). Furthermore, in Chapter R of NIOSH's Manual, NIOSH goes on to say that the GK2.69 high-flow sampler “has promise for potentially lowering the levels of silica that can be measured and still meet the required accuracy” ( http://www.cdc.gov/niosh/docs/2003-154/pdfs/chapter-r.pdf , p. 265). This chapter was published in 2003, well before the studies by Lee et al. (2010, 2012) and Stacey et al. (2013), discussed above, which demonstrate that the GK2.69 sampler has acceptable performance. NIOSH concluded in its post-hearing comment that “current methods of sampling and analysis for respirable crystalline silica have variability that is acceptable to demonstrate compliance with the proposed PEL and action level” (Document ID 4233, p. 4).

At the time of the proposal, there was little data characterizing the precision of analytical methods for crystalline silica at filter loads in the range of the PEL and action level (i.e., with prepared samples of 40 μg and 20 μg crystalline silica, which are the amounts of silica that would be collected from full-shift sampling at the PEL and action level, respectively, assuming samples are collected with a Dorr-Oliver cyclone at a flow rate of 1.7 L/min). To characterize the precision of OSHA's Method ID-142 at low filter loads, SLTC conducted studies in 2010 and again in 2013 (the latter of which was presented in the PEA; see Document ID 1720, p. IV-35). For these studies, the lab prepared 10 replicate samples each of quartz and cristobalite from NIST standard reference material and determined the precision of the analytical method; a term representing pump flow rate error was included in the precision estimate. In the 2010 test (Document ID 1670, Attachment 1), the precision for quartz loads equating to the PEL and action level was 27 and 33 percent, respectively. For cristobalite loads equating to the PEL and action level, the precision was 23 and 27 percent, respectively. The results from the 2013 test (Document ID 1847, Attachment 1; 3764, pp. 15-16; Document ID 1720, p. IV-35) showed improvement in the precision; for quartz, precision at loads equating to the PEL and action level was 17 and 19 percent, respectively, and for cristobalite, precision at loads equating to the PEL and action level was 19 and 19 percent, respectively. Both the 2010 and 2013 tests were conducted using the same NIST standards, same instrumentation, and same sample preparation method (OSHA Method ID-142) with the exception that the 2013 test used automatic pipetting rather than manual pipetting to prepare the samples (Document ID 1847). OSHA believes it likely that this change in sample preparation reduced variation in the amount of silica loaded onto the filters, which would account for at least some of the increased precision seen between 2010 and 2013 (i.e., imprecision in preparing the samples would make the analytical precision for 2010 appear worse than it actually was). Based on these studies, particularly the 2013 study, OSHA preliminarily determined that the XRD method was capable of accurately measuring crystalline silica concentrations at the PEL and action level.

The ACC believed that OSHA's reliance on the 2013 study was “misplaced” because the results were not representative of “real world” samples that contain interfering minerals that could increase analytical error, and because the studies did not account for inter-laboratory variability (Document ID 4209, pp. 135-137; 2308, Attachment 6, p. 10). The ACC also believed that variability would have been depressed in this study because the samples were analyzed in close temporal proximity by the same analyst and using the same instrument calibration, and the study involved only 10 samples at each filter load (Document ID 4209, pp. 137-138; 2308, Attachment 6, p. 10). The ACC's witness, Mr. Scott, also commented that the study failed to take into account the effect of particle sizes on the analysis of crystalline silica and believed that SLTC's evaluation could not reflect differences in precision between the XRD and IR methods (Document ID 2308, Attachment 6, p. 10).

Despite the criticism that OSHA's investigation involved a small number of samples analyzed at the same time, the results obtained were comparable to OSHA's analysis of quality control samples at somewhat higher filter loads (between 50 and 51.6 μg) analyzed over a two-year period (Document ID 3764, Attachment 1). These results, described above, showed a precision of 20.7 percent, compared to 17 and 19 percent for quartz filter loads of 40 and 20 μg, respectively (Document ID 1847, Attachment 1; Document ID 3764). From these results, OSHA concludes that any effect on analytical error from performing a single study using the same analyst and instrument calibration is modest.

OSHA also concludes that Mr. Scott's argument that particle size effects were not taken into account is without merit. The samples prepared and analyzed in OSHA's study, like any laboratory's quality control samples, use standard materials that have a narrow range in particle size. Although large (non-respirable) size particles can result in an overestimate of crystalline silica content, in practice this is not typically a serious problem with air samples and is more of a concern with analyzing bulk samples. First, as discussed above, respirable dust samplers calibrated to conform to the ISO/CEN convention are collecting respirable particulate and excluding larger particles (Document ID 3579, Tr. 219). In analyzing field samples, OSHA uses microscopy to identify whether larger particles are present and, if they are, the results are reported as a bulk sample result so as not to be interpreted as an airborne exposure (Document ID 3579, Tr. 213). Additionally, OSHA's Method ID-142 calls for grinding and sieving bulk samples to minimize particle size effects in the analysis (Document ID 0946, p. 13). OSHA also notes that the Chamber's witness, Mr. Lieckfield, testified that his laboratory does not check for oversized particles (Document ID 3576, p. 483).

With regard to interferences, as discussed above, there are procedures that have been in place for many years to reduce the effect of interfering materials in the analysis. The presence of interferences does not typically prevent an analyst from quantifying crystalline silica in a sample with reasonable precision. As to the claim regarding XRD versus IR, a recent study of proficiency test data, in which multiple laboratories are provided comparable silica samples, both with and without interfering materials added, did not find a meaningful difference in precision between laboratories using XRD and those using IR (Harper et al., 2014, Document ID 3998, Attachment 8). In addition, as discussed above, NIOSH's and OSHA's measures of precision of the XRD method at low filter loads were comparable, despite differences in equipment and sample preparation procedures. Therefore, OSHA finds that the studies it carried out to evaluate the precision of OSHA Method ID-142 at low filter loads provide a reasonable characterization of the precision of the method for analyzing air samples taken at concentrations equal to the final PEL and action level under the respirable crystalline silica rule.

With respect to the ACC's and Mr. Scott's reference to inter-laboratory variation in silica sample results, OSHA discusses data and studies that have evaluated inter-laboratory variance in analytical results in the next section.

e. Measurement Error Between Laboratories

The sources of random and systematic error described above reflect the variation in sample measurement experienced by a single laboratory; this is termed intra-laboratory variability. Another source of error that affects the reliability of results obtained from sampling and analytical methods is inter-laboratory variability, which describes the extent to which different laboratories may obtain disparate results from analyzing the same sample. Inter-laboratory variability can be characterized by using data from proficiency testing, where laboratories analyze similarly-prepared samples and their results are compared. In practice, however, it is difficult to separate intra- and inter-laboratory variability because each laboratory participating in a proficiency test provides analytical results that reflect their own degree of intra-laboratory variability. Thus, use of proficiency test data to compare performance of laboratories in implementing an analytical method is really a measure of total laboratory variability.

The best available source of data for characterizing total variability (which includes an inter-laboratory variability component) of crystalline silica analytical methods is the AIHA Industrial Hygiene Proficiency Analytical Testing (PAT) Program. The AIHA PAT Program is a comprehensive testing program that provides an opportunity for laboratories to demonstrate competence in their ability to accurately analyze air samples through comparisons with other labs. The PAT program is designed to help consumers identify laboratories that are deemed proficient in crystalline silica analysis.

Crystalline silica (using quartz only) is one of the analytes included in the proficiency testing program. The AIHA PAT program evaluates the total variability among participating laboratories based on proficiency testing of specially prepared silica samples. The AIHA contracts the preparation of its crystalline silica PAT samples to an independent laboratory that prepares four PAT samples in the range of about 50 to 225 μg (Document ID 3586, Tr. 3279-3280) and one blank sample for each participating laboratory per round. Each set of PAT samples with the same sample number is prepared with as close to the same mass of crystalline silica deposited on the filter as possible. However, some variability occurs within each numbered PAT sample set because of small amounts of random error during sample preparation. Before the contract laboratory distributes the round, it analyzes a representative lot of each numbered set of samples to ensure that prepared samples are within ±10 percent (Document ID 3586, Tr. 3276). The samples are distributed to the participating laboratories on a quarterly basis (Document ID 1720, p. IV-36). The PAT program does not specify the particular analytical method to be used. However, the laboratory is expected to analyze the PAT samples using the methods and procedures it would use for normal operations.

The results of the PAT sample analysis are reported to the AIHA by the participating laboratories. For each PAT round, AIHA compiles the results and establishes upper and lower performance limits for each of the four sample results based on the mean and RSD of the sample results. For each of the four samples, a reference value is defined as the mean value from a selected set of reference laboratories. The RSD for each of the four samples is determined from the results reported by the reference labs after correcting for outliers (generally clear mistakes in analysis or reporting, particularly those that are order-of-magnitude errors) (Document ID 4188, p. 2). A participating laboratory receives a passing score if at least three out of the four sample results reported are within 20 percent of the reference mean for the sample (Document ID 3586, Tr. 3291). Two or more results reported by a lab in a given round that are outside the limits results in the lab receiving an unsatisfactory rating. An unsatisfactory rating in 2 of the last 3 rounds results in revocation of the lab's AIHA accreditation for the analysis of crystalline silica. Participation in the PAT program is a prerequisite for accreditation through the AIHA Industrial Hygiene Laboratory Accreditation Program (IHLAP).

In the PEA, OSHA presented PAT results from its SLTC for the period June 2005 through February 2010 (PAT Rounds 160-180) (Document ID 1720, pp. IV-40-41). The mean recovery was 99 percent, with a range of 55 to 165 percent. Eighty-one percent of the samples analyzed over this period were within ±25 percent of the reference mean and the RSD for this set of samples was 19 percent, showing reasonable agreement with the reference mean. OSHA also evaluated PAT data from all participating laboratories for the period April 2004 through June 2006 (PAT Rounds 156-165) (Document ID 1720, pp. IV-37—IV-40). Overall, the mean lab RSD was 19.5 percent for the sample range of 49 to 165 μg. Beginning with Round 161, PAT samples were prepared by liquid deposition rather than by sampling a generated silica aerosol, in order to improve consistency and reduce errors in sample preparation. The improvement was reflected in the results, with the mean lab RSD declining from 21.5 percent to 17.2 percent after the change to liquid deposition, demonstrating the improved consistency between PAT samples.

In the time since OSHA analyzed the PAT data, Harper et al. (2014, Document ID 3998, Attachment 8) evaluated more recent data. Specifically, Harper et al. (2014, Document ID 3998, Attachment 8, p. 3) evaluated PAT test results for the period 2003-2014 (Rounds 152 through 194) and found that variation in respirable crystalline silica analysis has improved substantially since the earlier data from 1990 to 1998 was studied by Eller et al. (1999a, Document ID 1687). A total of 9,449 sample results were analyzed after removing re-test results, results where the method of analysis was not identified, and results that were more than three standard deviations from the reference mean. There was a clear improvement in overall variation in the newer data set compared with that of Eller et al. (1999a, Document ID 1687), with the mean laboratory RSD declining from about 28.7 percent to 20.9 percent (Document ID 3998, Attachment 8, Figure 1). Both the older and newer data sets showed that analytical variation increased with lower filter loadings, but the more recent data set showed a much smaller increase than did the older. At a filter load of 50 μg, the mean lab RSD of the more recent data was less than 25 percent, whereas it was almost 35 percent with the older data set (Document ID 3998, Attachment 8, Figure 1). It was also clear that the change in sample preparation procedure (i.e., from aerosol deposition to liquid deposition starting in Round 161) explained at least some of the improvement seen in the more recent PAT results, with the mean lab RSD declining from 23.6 percent for all rounds combined to 19.9 percent for Rounds 162-194.

Despite the improvement seen with the change in deposition method, it is important to understand that the observed variation in PAT results between labs still reflects some sample preparation error (limited to ±10 percent as explained above), a source of error not reflected in the analysis of field samples. Other factors identified by the investigators that account for the improved performance include the phasing out of the colorimetric method among participating labs, use of more appropriate calibration materials (i.e., NIST standard reference material), calibration to lower mass loadings, stricter adherence to published method procedures, and possible improvements in analytical equipment. There was also only a small difference (2 percent) in mean lab RSD between labs using XRD and those using IR (Document ID 3998, Attachment 8, p. 9). The increase in variance seen with lower filter loads was not affected either by analytical method (XRD vs. IR) or by the composition of interfering minerals added to the matrix (Document ID 3998, Attachment 8, p. 4).

OSHA finds that this study provides substantial evidence that employers will obtain reliable results from analysis of respirable crystalline silica most of the time for the purpose of evaluating compliance with the PEL. From Round 162 through 194 (after the deposition method was changed), and over the full range of PAT data, only about 7 out of the 128 (5 percent) lab RSD values reported were above 25 percent (Document ID 3404, Figure 2). For filter loads of 75 μg or less, only 3 lab RSD values out of about 30 reported, were above 25 percent. As stated above, the mean RSD at a filter load of 50 μg was less than 25 percent and agreement between labs improved substantially compared to earlier PAT data.

Summary data for PAT samples having a target load of less than 62.5 μg were provided by AIHA in a post-hearing comment (Document ID 4188) and compared with the findings reported by Harper et al. (2014, Document ID 3998, Attachment 8). For PAT rounds 155-193 (from 1999 to 2013), there were 15 sets of samples in the range of 41.4 to 61.8 μg distributed to participating laboratories. Lab RSDs from results reported for these samples ranged from 11.2 to 26.4 percent, with an average RSD of 17.1 percent, just slightly above the average RSD of 15.9 percent for all samples across the entire range of filter loads from those rounds. Taken together, the results of the analysis performed by Harper et al. (2014, Document ID 3998, Attachment 8) and the summary data provided by AIHA (Document ID 4188) suggest that sample results from participating labs will be within 25 percent of the crystalline silica filter load most of the time.

In its post hearing comments, the National Stone, Sand & Gravel Association (NSSGA) contended that analytical laboratories cannot provide adequately precise and accurate results of silica samples (Document ID 4232). NSSGA provided a detailed analysis of low-load samples from the same 15 PAT rounds as examined by AIHA (Document ID 4188) and concluded that “employers and employees cannot rely on today's silica sampling and analytical industry for consistently accurate sample results necessary to achieve or surpass compliance requirements” (Document ID 4232, p. 26). The NSSGA compared individual labs' sample results to the reference mean for each sample and found, from the AIHA PAT data, that 76-84 percent of the results were within 25 percent of the reference mean, and the range of results reported by laboratories included clear outliers, ranging from zero to several-fold above the target filter load (Document ID 4232, p. 8, Table 1, rows 1-6). NSSGA concluded from this that “[i]t is of little value to employers that a given lab's results meet the NIOSH Accuracy Criterion while other labs' results cannot, particularly since employers almost certainly won't know which labs fall into which category” (Document ID 4232, p. 10). NSSGA's point appears to be that the outliers in the PAT data erode an employer's ability to determine if they are receiving accurate analytical results, without which they have little ability to determine their compliance status with respect to the PEL or action level. Further, NSSGA suggests that OSHA's analysis of the PAT data, discussed above, is not adequate to demonstrate the performance of an individual laboratory that may be chosen by an employer.

In response to NSSGA's criticism, OSHA points out that its analysis of the PAT data was part of its analysis of technological feasibility in which the Agency's legal burden is to show that employers can achieve compliance in most operations most of the time. It may be an unavoidable fact that lab results may be inaccurate some of the time, but that does not render the standard infeasible or unenforceable. OSHA contends that its analysis has satisfied that burden and nothing in the NSSGA's comments suggests otherwise.

NSSGA further suggests that employers have no means of determining, based on a laboratory's PAT proficiency rating alone, whether that individual laboratory is likely to produce erroneously high or low results. OSHA concurs that selecting a laboratory based on accreditation, price, and turnaround time, as NSSGA suggests (Document ID 4232, p. 5), is common but may be inadequate to determine whether an individual laboratory is capable of producing results of consistently high quality. Employers and their industrial hygiene consultants can, and should, ask additional questions and request additional assurances of quality from the laboratories they consider using. For example, employers can ask to review the laboratory's individual PAT results over time, focusing on and questioning any significant outliers in the laboratory's results. While NSSGA suggests that the PAT results are treated as confidential by the AIHA-PAT program (Document ID 4232, p. 6), there is nothing stopping a laboratory from sharing its PAT data or any other information related to its accreditation with their clients or prospective clients.

Further, laboratories routinely perform statistical analyses of their performance in the context of analyzing known samples they use for equipment calibration, and often perform statistical comparisons among the various technicians they employ. Review of these statistics can shed light on the laboratory's ability to provide consistent analysis. Finally, as employers conduct exposure monitoring over time, and come to understand what results are typically seen in their workplaces, clear outliers should become more identifiable; for example, if employee exposures are usually between the action level and PEL, and a sample result shows an exposure significantly above the PEL without any clear change in workplace conditions or operations, employers should question the result and ask for a reanalysis of the sample. Employers could also request gravimetric analysis for respirable dust against which to compare the silica result to confirm that the silica content of the dust is consistent with past experience. For example, if, over time, an employer's consistent results are that the silica content of respirable dust generated in its workplace is 20 percent silica, and subsequently receives a sample result that indicates a significantly higher or lower silica content, it would be appropriate for the employer to question the result and request reanalysis. Therefore, OSHA rejects the idea that employers are at the mercy of random chance and have to simply accept a high degree of uncertainty in exposure measurements; rather, there are positive steps they can take to reduce that uncertainty.

Results from the AIHA PAT program were discussed at considerable length during the rulemaking proceeding. After considering all of the analyses of PAT data presented by Eller et al. (1999a, Document ID 1687), OSHA in its PEA, and Harper et al. (2014, Document ID 3404), the ACC concluded that “PAT program results indicate that analytical variability as measured by precision is unacceptably high for silica loadings in the range of 50-250 μg” and that the PAT data “provide strong evidence that commercial laboratories will not be able to provide reliable measurements of . . . [respirable crystalline silica] exposures at the levels of the proposed PEL and action level” (Document ID 4209, p. 144). OSHA disagrees with this assessment. First, OSHA's experience over the last 40 years in enforcing the preceding PEL that this standard supersedes is that analytical variability has not been an impediment to successful enforcement of the superseded PEL, and there have been few, if any, challenges to such enforcement actions based on variability. Nor has OSHA been made aware of concerns from employers that they have been unable to evaluate their own compliance with the former PEL or make reasonable risk management decisions to protect workers. In fact, the Chamber's expert, Mr. Lieckfield, admitted that analytical variability for asbestos, another substance that has been regulated by OSHA over the Agency's entire history, “is worse” than that for crystalline silica (Document ID 3576, Tr. 531).

To support its contention that reliably measuring silica at the final rule's PEL and action level is not possible, the ACC cited Harper et al. (2014, Document ID 3998, Attachment 8) as stating that further increases in laboratory variance below the 40-50 μg range would have “implications for the [working] range of the analytical methods,” and that excessive variance might “make it difficult to address for either method” (Document ID 4209, p. 144). However, it is clear from Harper et al. (2014) that this is the basis for the authors' recommendation that the PAT program consider producing samples with filter loads as low as 20 μg to “support the analysis of lower target concentration levels” (Document ID 3404, p. 5). They also identify use of currently available higher-flow-rate sampling devices (discussed above) to increase the collected mass of silica, which would generate field samples in the filter load range currently used in the PAT program.

Finally, the ACC sponsored a performance testing study to assess inter-laboratory variability at crystalline silica filter loads at 40 and 20 μg (i.e., the amount of silica collected at final rule's PEL and action level, respectively, assuming use of a Dorr-Oliver cyclone operated at a flow rate of 1.7 L/min) as well as at 80 μg (i.e., the amount collected at the preceding PEL) (Document ID 2307, Attachment 14; 3461; 3462). The study was blinded in that participating laboratories were not aware that they were receiving prepared samples, nor were they aware that they were involved in a performance study. For this study, each of five laboratories was sent three replicate rounds of samples; each round consisted of three filters prepared with respirable crystalline silica (Min-U-Sil 5) alone, three of silica mixed with kaolin, three of silica mixed with soda-feldspar, and one blank filter. The samples were prepared by RJ Lee Group and sent by a third party to the laboratories as if they were field samples. All laboratories were accredited by AIHA and analyzed the samples by XRD.

The samples were initially prepared on 5 μm PVC filters; however, due to sample loss during preparation, RJ Lee changed to 0.8 μm PVC filters. It should be noted that the 2-propanol used to suspend the Min-U Sil sample for deposition onto the 0.8 μm filter dissolved between 50 and 100 μg of filter material, such that the amount of minerals deposited on the filter could not be verified from the post-deposition filter weights. In addition, two of the labs had difficulty dissolving these filters in tetrahydrofuran, a standard method used to dissolve PVC filters in order to redeposit the sample onto silver membrane filters for XRD analysis. These labs were replaced by two laboratories that used muffle furnaces to ash the filters before redeposition, as did the other three labs originally selected.

Results reported from the labs showed a high degree of both intra- and inter-laboratory variability as well as a systematic negative bias in measured vs. applied silica levels, with mean reported silica values more than 30 percent lower than the deposited amount. Across all laboratories, mean results reported for filter loads of 20, 40, and 80 μg were 13.36, 22.93, and 46.91 μg, respectively (Document ID 2307, Attachment 14, pp. 5-6). In addition, laboratories reported non-detectable results for about one-third of the silica samples (Document ID 2307, Attachment 14, p. 7) and two blank filters sent to the labs were reported to have silica present, in one case an amount of 52 μg (Document ID 2307, Attachment 14, pp. 9-10; 3582, Tr. 1995). Individual CVs for the labs ranged from 20 to 66 percent, up to more than 3 times higher than the CVs reported by OSHA or NIOSH for their respective methods. After examining variability in reported results, the investigators concluded that two-fold differences in filter load could not be reliably distinguished in the concentration range of 25 to 100 μg/m³ (Document ID 2307, Attachment 14, p. 14).

OSHA identifies several deficiencies in this study; these deficiencies are sufficient to discredit the finding that high variability in silica results can be attributed to the inability of the analytical method to accurately measure crystalline silica at filter loads representative of concentrations at the action level and PEL set by this rule. Principally, the loss of filter material during deposition of the samples, combined with the lack of any verification of the actual amount of silica loaded onto the filters, makes it impossible to use the laboratory results to assess lab performance since the amount of silica on the filters analyzed by the labs cannot be known. The large negative bias in lab results compared to the target filter load implies that there was significant sample loss. In addition, the quality control employed by RJ Lee to ensure that filter loads were accurately known consisted only of an analysis of six separately prepared samples to evaluate the recovery from the 0.8 μm PVC filter and two sets of filters to evaluate recovery and test for shipping loss (Document ID 3461, Slides 8, 15, 16; 3582, Tr. 2090-2091). This is in stark contrast to the procedures used by the AIHA PAT program, which verifies its sample preparation by analyzing a statistically adequate number of samples prepared each quarter to ensure that sample variation does not exceed ±10 percent (Document ID 3586, Tr. 3276-3277). RJ Lee's use of the 0.8 μm PVC copolymer filter (Document ID 4001, Attachment 1) is also contrary to the NIOSH Method 7500 (Document ID 0901), which specifies use of the 5 μm PVC filter, and may have introduced bias. As stated at the hearing by Mary Ann Latko of the AIHA Proficiency Analytical Testing Programs, “[a]ny variance from the NIOSH method should not be considered valid unless there's a sufficient quality control data provided to demonstrate the reliability of the modified method” (Document ID 3586, Tr. 3278).

OSHA finds that the AIHA PAT data are a far more credible measure of inter-laboratory variation in crystalline silica measurement than the ACC-sponsored RJ Lee study. Strict procedures are used to prepare and validate sample preparation in accordance with ISO requirements for conformity assessment and competence of testing in calibration laboratories (Document ID 3586, Tr. 3275) and the database includes 200 rounds of silica testing since 2004, with 55 laboratories participating in each round (Document ID 3586, Tr. 3264-3265). By comparison, the RJ Lee study consisted of three rounds of testing among five laboratories.

One of the goals of the RJ Lee study was to conduct a double-blind test so that laboratories would not know they were analyzing prepared samples for proficiency testing; according to Mr. Bailey, a laboratory's knowledge that they are participating in a performance study, such as is the case with the AIHA PAT program, “can introduce bias into the evaluation from the very beginning” (Document ID 3582, Tr. 1989; Document ID 4209, p. 147). However, OSHA doubts that such knowledge has a profound effect on laboratory performance. Accredited laboratories participating in the PAT program undergo audits to ensure that analytical procedures are applied consistently whether samples are received from the field or from the PAT program. According to testimony from Mr. Walsh:

[S]ite assessors [for the AIHA accreditation program] are very sensitive to how PAT samples are processed in the lab. It's a specific area that's examined, and if the samples are processed in any way other than a normal sample, the laboratory is cited as a deficiency (Document ID 3586, Tr. 3299-3300).

Therefore, after considering the evidence and testimony on the RJ Lee study and AIHA PAT Program data, OSHA concludes that the AIHA PAT data are the best available data on which to evaluate inter-laboratory variability in measuring respirable crystalline silica. The data evaluated by Harper et al. (2014) showed that laboratory performance has improved in recent years resulting in greater agreement between labs; mean RSD for the period 2003-2013 was 20.9 percent (Document ID 3998, Attachment 8, Figure 1). In addition, across the range of PAT filter loadings, only about 5 percent of the samples resulted in lab RSDs above 25 percent. At lower filter loads, 75 μg or less, about 10 percent of samples resulted in RSDs above 25 percent Document ID 3998, Attachment 8, Figure 2). OSHA concludes that these findings indicate general agreement between laboratories analyzing PAT samples.

Although laboratory performance has not been broadly evaluated at filter loads below 40 μg, particularly when interferences are present, OSHA's investigations show that the XRD method is capable of measuring crystalline silica at filter loads of 40 μg or less without appreciable loss of precision. The analysis of recent PAT data by Harper et al. (2014, Document ID 3998, Attachment 8) shows that the increase seen in inter-laboratory variation with lower filter loads (e.g., about 50 and 70 μg) is modest compared to the increase in variation seen in the past from earlier PAT data, and the summary data provided by AIHA (Document ID 4188) show that the average lab RSD for samples with low filter loads is only a few percentage points above average lab RSD across the full range of filter loads used in the PAT program since 1999. OSHA finds that the studies of recent PAT data demonstrate that laboratories have improved their performance in recent years, most likely as a result of improving quality control procedures such as were first proposed by Eller et al. (1999b, Document ID 1688, pp. 23-24). Such procedures, including procedures concerning equipment calibration, use of NIST standard reference material for calibration, and strict adherence to published analytical methods, are required by Appendix A of the final standards (29 CFR 1910.1053 and 29 CFR 1926.1153). According to Dr. Rosa Key-Schwartz, NIOSH's expert in crystalline silica analysis, NIOSH worked closely with the AIHA laboratory accreditation program to implement a silica emphasis program for site visitors who audit accredited laboratories to ensure that these quality control procedures are being followed (Document ID 3579, Tr. 153). With such renewed emphasis being placed on tighter procedures for crystalline silica analysis, OSHA finds that exposure monitoring results being received from laboratories are more reliable than was the case in years past and thus are deserving of greater confidence from employers and workers.

f. Conclusion

Based on the record evidence reviewed in this section, OSHA finds that current methods to sample respirable dust and analyze samples for respirable crystalline silica by XRD and IR methods are capable of reliably measuring silica concentrations in the range of the final rule's PEL and action level. This finding is based on the following considerations: (1) Several sampling devices are available that conform to the ISO/CEN specification for particle-size selective samplers with a level of bias and accuracy deemed acceptable by international convention, and moving to the ISO/CEN convention will maintain continuity with past practice, (2) both the XRD and IR methods can measure respirable crystalline silica with acceptable precision at amounts that would be collected by samplers when airborne concentrations are at or around the PEL and action level, and (3) laboratory proficiency data demonstrate that there is reasonable agreement between laboratories analyzing comparable samples most of the time.

There are several sampling devices that can collect respirable crystalline silica in sufficient quantity to be measured by laboratory analysis; some of these include the Dorr-Oliver nylon cyclone operated at 1.7 L/min air flow rate, the Higgins-Dewell cyclones (2.2 L/min), the SKC aluminum cyclone (2.5 L/min), and the GK2.69, which is a high-flow sampler (4.2 L/min). Each of these cyclones can collect the minimum amount of silica necessary, at the PEL and action level, for laboratories to measure when operated at their respective flow rates for at least four hours. In addition, each of these devices (as well as a number of others) has been shown to conform to the ISO/CEN convention with an acceptable bias and accuracy for a wide range of particle-size distributions encountered in the workplace. OSHA used the Dorr-Oliver at a flow rate of 1.7 L/min to enforce the previous PELs for respirable crystalline silica, so specifying the use of sampling devices conforming to the ISO/CEN convention does not reflect a change in enforcement practice. The modest error that is associated with using respirable dust samplers is independent of where the PEL is set, and these samplers have been used for decades both by OSHA, to enforce the preceding silica PEL (and other respirable dust PELs), and by employers in managing silica-related risks. Therefore, OSHA finds that these samplers are capable of and remain suitable for collecting respirable dust samples for crystalline silica analysis.

Both XRD and IR analytical methods are capable of quantifying crystalline silica with acceptable precision when air samples are taken in environments where silica concentrations are around the PEL and action level. OSHA's quality control samples analyzed by XRD over the past few years show the precision to be about 20 percent over the range of filter loads tested (about one-half to twice the former PEL). OSHA conducted studies to characterize the precision of its Method ID-142 at low filter loads representing the amounts that would be captured using the Dorr-Oliver cyclone at the action level and PEL (i.e., 20 and 40 μg, respectively), and found the precision, for quartz and cristobalite, at both 20 and 40 μg to be comparable to the precision at the higher range of filter loads.

Evaluation of data from AIHA's Proficiency Analytical Testing Program shows that results from participating laboratories are in agreement (i.e., within 25%) most of the time. Performance between laboratories has improved significantly in recent years, most likely due to adoption of many of the quality control practices specified by Appendix A of the final standards. Although precision declines as the amount of crystalline silica in samples declines, the rate of decline in precision with declining mass is less today than for prior years. OSHA expects that increasing emphasis on improved quality control procedures by the AIHA laboratory accreditation program (Document ID 3579, Tr. 153), the requirement in the final rule for employers to use laboratories that use XRD or IR analysis (not colorimetric) and that are accredited and conform to the quality control procedures of Appendix A of the final standards, and increased market pressure for laboratories to provide reliable results are likely to improve agreement in results obtained by laboratories in the future.

Inter-laboratory variability has not been well characterized at filter loads below 50 μg, which is slightly more than would be collected by a Dorr-Oliver cyclone sampling a silica concentration at the PEL over a full shift. However, OSHA concludes that the studies conducted by SLTC show that acceptable precision can be achieved by the XRD method for filter loads obtained by collecting samples with the Dorr-Oliver and similar devices at the action level and PEL. If employers are concerned about the accuracy that their laboratory would achieve at filter loads this low, samplers with higher flow rates could be used to collect an amount of silica that falls within the working range of the OSHA method and within the range of filter loads currently used by the PAT program (i.e., 50 μg or more). For example, either the aluminum cyclone or HD will collect at least 50 µg or more of silica where concentrations are around the PEL, and the GK2.69 will collect a sufficient quantity of crystalline silica where concentrations are at least at the action level.

Based on the information and evidence presented in this section, OSHA is confident that current sampling and analytical methods for respirable crystalline silica provide reasonable estimates of measured exposures. Employers should be able to rely on sampling results from laboratories meeting the specifications in Appendix A of the final standards to analyze their compliance with the PEL and action level under the new silica rule; employers can obtain assurances from laboratories or their industrial hygiene service providers that such requirements are met. Similarly, employees should be confident that those exposure results provide them with reasonable estimates of their exposures to respirable crystalline silica. Thus, OSHA finds that the sampling and analysis requirements under the final rule are technologically feasible.

3. Feasibility Findings for the Final Permissible Exposure Limit of 50 μg/m³

In order to demonstrate the technological feasibility of the final PEL, OSHA must show that engineering and work practices are capable of reducing exposures to the PEL or below for most operations most of the time. Substantial information was submitted to the record on control measures that can reduce employee exposures to respirable crystalline silica, including but not limited to LEV systems, which could include an upgrade of the existing LEV or installation of additional LEV; process enclosures that isolate the employee from the exposure; dust suppression such as wet methods; improved housekeeping; and improved work practices. Substantial information was also submitted to the record on the use of respiratory protection; while OSHA does not, as a rule, consider the use of respirators when deciding whether an operation is technologically feasible, it does, when it finds a particular operation or task cannot achieve the PEL without respiratory protection, require appropriate respirator use as a supplementary control to engineering and work practice controls, when those controls are not sufficient alone to meet the PEL.

OSHA finds that many engineering control options are currently commercially available to control respirable dust (e.g., Document ID 0199, pp. 9-10; 0943, p. 87; 1607, p. 10-19; 1720, p. IV-237; 3791, p. iii; 3585, p. 3073; 3585, p. 3072). These controls will reduce employees' exposures to respirable crystalline silica when the employees are performing the majority of tasks that create high exposures. OSHA's finding is based on numerous studies, conducted both in experimental settings in which the tools, materials and duration of the task are controlled by the investigator, and in observational field studies of employees performing their normal duties in the field. As detailed in Chapter IV of the FEA, more than 30 studies were submitted to the docket that report substantial reductions in exposure when using controls compared with uncontrolled situations. The specific reports that OSHA relied upon to estimate the range of reductions that can be achieved through the implementation of engineering controls are discussed in greater detail in the relevant sections of the technological feasibility analyses.

Table VII-8 lists the general industry sectors included in the technological feasibility analysis and indicates the numbers of job categories in each sector for which OSHA has concluded that the final PEL of 50 μg/m³ is technologically feasible (see Chapter IV of the FEA). As this table shows, OSHA has determined that the final rule's PEL is feasible for all general industry sectors for the vast majority of operations in these affected industry sectors (87 out of 90). For only three general industry job categories, OSHA has concluded that exposures to silica will likely exceed the final rule's PEL even when all feasible controls are fully implemented; therefore, supplemental respiratory protection will be needed in addition to those controls to ensure that employees are not exposed in excess of the PEL for those three categories. Specifically, supplemental use of respiratory protection may be necessary for abrasive blasting operations in the concrete products industry sector, cleaning cement trucks in the ready mix concrete industry sector, and during abrasive blasting operations in shipyards. In addition, in foundries, while finding that compliance with the standard is overall feasible for all job categories, OSHA recognizes that supplemental use of respiratory protection may be necessary for the subset of employees who infrequently perform refractory lining repair; for the small percentage of shakeout operators, knockout operators, and abrasive blasters who work on large castings in circumstances where substitution to non-silica granular media is not feasible; and for maintenance operators performing refractory patching where reduced silica refractory patching products cannot be used.

OSHA has determined that some engineering controls are already commercially available for the hydraulic fracturing industry, and other controls that have demonstrated promise are currently being developed. OSHA recognizes, however, that engineering controls have not been widely implemented at hydraulic fracturing sites, and no individual PBZ results associated with controls have been submitted to the record.

The available information indicates that controls for dust emissions occurring from the sand mover, conveyor, and blender hopper have been effective in reducing exposures. KSW Environmental reported that a commercially-available control technology reduced exposures in one test with all 12 samples below the NIOSH recommended exposure limit (REL) of 50 μg/m³ (Document ID 4204, p. 35, Fn. 21). KSW Environmental also stated that four additional customer tests resulted in 76 PBZ samples, all below 100 μg/m³ (Document ID 4204, p. 35, Fn. 21). Another manufacturer of a similar ventilation system (J&J Bodies) reported that there was significantly less airborne dust during the loading of proppant onto the sand mover when its dust control system was used. This dust control system was used at 10 different hydraulic fracturing sites with reportedly good results (Document ID 1530, p. 5).

These findings indicate that, with good control of the major dust emission sources at the sand mover and along the conveyor to the blender hopper, exposures can be reduced to at least 100 μg/m³. Use of other dust controls, including controlling road dust (reducing dust emissions by 40 to 95 percent), applying water misting systems to knock down dust released from partially-enclosed conveyors and blender hoppers (reducing dust emissions by more than half), providing filtered booths for sand operators (reducing exposure to respirable dust by about half), reducing drop height at transfer points and hoppers, and establishing regulated areas, will further reduce exposures to 50 μg/m³ or below. Additional opportunities for exposure reduction include use of substitute proppant, where appropriate, and development and testing of dust suppression agents for proppant, such as that developed by ARG (Document ID 4072, Attachment 35, pp. 9-10). OSHA anticipates that once employers come into compliance with the preceding PEL, the additional controls to be used in conjunction with those methodologies to achieve compliance with the PEL of 50 μg/m³ will be more conventional and readily available.

Therefore, OSHA finds that the PEL of 50 μg/m³ can be achieved for most operations in the hydraulic fracturing industry most of the time. As shown in Table IV.4.22-B of the FEA, this level has already been achieved for almost one-third of all sampled workers (and nearly 1 in 5 sand fracturing workers, the highest exposed job category). OSHA expects that the growing availability of the controls needed to achieve the preceding PEL, along with further development of emerging technologies and better use and maintenance of existing controls, will reduce exposures to at or below the PEL for the remaining operations.

The American Petroleum Institute (API), the Marcellus Shale Coalition (MSC), and Halliburton questioned whether the analysis of engineering controls presented in the PEA was sufficient to demonstrate the technological feasibility of reducing exposures to silica at hydraulic fracturing sites to levels at or below 50 μg/m³, in part because the analysis did not include industry-specific studies on the effectiveness of dust controls but largely relied instead on research from other industries (Document ID 2301, Attachment 1, pp. 29, 60-61; 2302, pp. 4-7; 2311, pp. 2-3). These stakeholders argued that OSHA needed to do significantly more data collection and analysis to show that the PEL of 50 μg/m³ is feasible for hydraulic fracturing operations.

OSHA sought additional information on current exposures and dust control practices. Throughout the NPRM and hearings, OSHA, as well as other stakeholders, requested additional information on exposures and engineering controls (Document ID 3589, Tr. 4068-4070, 4074-4078, 4123-4124; 3576, Tr. 500, 534). Submissions to the record indicate that significant efforts are currently being made to develop more effective dust controls specifically designed for hydraulic fracturing (Document ID 1530; 1532; 1537; 1538; 1570; 4072, Attachments 34, 35, 36; 4204, p. 35, Fn. 21). However, industry representatives provided no additional sampling data to evaluate the effectiveness of current efforts to control exposures. Thus, NIOSH and OSHA provided the only detailed air sampling information for this industry, and summary data were provided by a few rulemaking participants (Document ID 4204, Attachment 1, p. 35, Fn. 21; 4020, Attachment 1, p. 4).

When evaluating technological feasibility, OSHA can consider engineering controls that are under development. Under section 6(b)(5) of the OSH Act, 29 U.S.C. 655(b), OSHA is not bound to the technological status quo and can impose a standard where only the most technologically advanced companies can achieve the PEL even if it is only some of the operations some of the time. Lead I (United Steelworkers of Am., AFL-CIO-CLC v. Marshall, 647 F.2d 1189 (D.C. Cir. 1980)); Am. Iron & Steel Inst. v. OSHA, 577 F.2d 825 (3d Cir. 1978). Relying on these precedents, the D.C. Circuit reaffirmed that MSHA and OSHA standards may be “technology-forcing” in Kennecott Greens Creek Min. Co. v. MSHA, 476 F.3d 946, 957, 960 (D.C. Cir. 2007), and that “the agency is `not obliged to provide detailed solutions to every engineering problem,' but only to `identify the major steps for improvement and give plausible reasons for its belief that the industry will be able to solve those problems in the time remaining.' ” Id. (finding that MSHA provided “more than enough evidence,” including “identif[ying] several types of control technologies that are effective at reducing . . . exposure,” to conclude that the industry could comply with the two-year implementation date of a technology-forcing standard) (citing Nat'l Petrochemical & Refiners Ass'n v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002)).

OSHA concluded that these technologies will enable the industry to comply within five years. OSHA has described technologies that have been developed and tested, and that have demonstrated that the PEL is obtainable. These technologies have been developed to reduce exposures to the preceding PEL, but some of them appear also to have the capability to reduce some exposures to the PEL of 50 µg/m³. KSW Environmental has provided data that indicate exposures can be achieved at or below the PEL (Document ID 1570, p. 22; 4204, Attachment 1, p. 35, Fn. 21; 4222, Attachment 2, p. 6), and NIOSH has presented concepts of “mini-bag houses” that can be retrofitted on existing equipment (Document ID 1537, p. 5; 1546, p. 10). SandBox Logistics, LLC, has developed a shipping container for bulk transport of sand specifically designed for hydraulic fracturing operations that eliminates the need for sand movers, a major source of exposure to silica at fracturing sites (Document ID 3589, Tr. 4148). OSHA views these and other advanced controls discussed above as on the “horizon,” but not currently widely available for operational use (Am. Fed'n of Labor & Cong. of Indus. Organizations v. Brennan, 530 F.2d 109, 121 (3d Cir. 1975)). Once they are deployed, as explained fully in Chapter IV of the FEA, more conventional adjustments and additional controls can be used with them to lower exposures to the new PEL or below.

Evidence in the record shows widespread recognition of silica exposure hazards on hydraulic fracturing sites and industry's efforts to address them primarily through the efforts of the National Service, Transmission, Exploration & Production Safety (STEPS) network's Respirable Silica Focus Group. The STEPS network initiated action to address exposure to silica at hydraulic fracturing sites in 2010, when NIOSH first conducted air sampling and then publicized the severity of hazardous silica exposures as part of its Field Effort to Assess Chemical Exposures in Gas and Oil Workers (Document ID 1541). Recognition of silica exposures in the industry well above the preceding PEL of 100 µg/m³ prompted the development of engineering controls to reduce exposures to silica. While some companies in the hydraulic fracturing industry are able to obtain and implement controls to comply with the preceding PEL (e.g., Document ID 4204, Attachment 1, p. 35, Fn. 21), the technology is not currently widely available. Given the progress that has been made since 2010, OSHA concluded that these technologies will become more widely available and enable the industry to comply with the final PEL within five years. As noted by Kenny Jordan, the Executive Director of the Association of Energy Service Companies (AESC), his organization's participation on the National Occupational Research Agenda (NORA) NIOSH Oil and Gas Extraction Council enabled members to be “at the forefront of building awareness of the silica at the well site issue, particularly among those working in fracking operations” (Document ID 3589, Tr. 4059). In the five years since that time, the substantial progress in controlling silica exposures at fracking sites described above has occurred.

In June 2012, the STEPS network, in which AESC and many other industry, educational and regulatory entities participate, launched a respirable silica focus group to spread awareness, better characterize on-site silica exposures, and facilitate and evaluate the development of engineering controls (Document ID 3589, Tr. 4059; 1537). This enabled several manufacturers of engineering controls, such as KSW Environmental (formerly Frac Sand Dust Control and Dupre) who had developed a working model in 2009 (Document ID 1520), to collaborate and share information on various engineering controls. As a consequence, the silica control field has grown significantly during this period, including the development, testing and, in some cases, deployment of new technologies, including those from KSW Environmental, J&J Truck Bodies, SandBox Logistics, and NIOSH's baghouse. For example, John Oren, the co-inventor of the SandBox Logistics technology, said it had taken his company only three years to develop the product and make it commercially available (Document ID 3589, Tr. 4148). OSHA concludes that an additional five years will be more than enough time for these and other firms to complete development and increase manufacturing and sales capacity, and, simultaneously, for hydraulic fracturing employers to test, adopt and adapt these emerging technologies to their workplaces. Indeed, in light of the progress that has already been made, it may be more accurate to call the standard “market-accelerating” than “technology-forcing.”

During the rulemaking, API touted the efforts of this industry to develop technology to protect workers against the hazards of silica (Document ID 4222, Attachment 2, p. 9). OSHA agrees with API that these efforts have been noteworthy and that more time is warranted to allow for continued development, commercialization, and implementation of these innovative technologies. OSHA is confident that with the innovation displayed by this industry to date, the hydraulic fracturing industry can further reduce worker exposures to the PEL if sufficient time is provided. Therefore, OSHA is providing an extra three years from the effective date of the standard—for a total of five years—to implement engineering controls for the hydraulic fracturing industry. OSHA concludes that this is ample time for this highly technical and innovative industry to come into compliance with the final PEL. This is consistent with, but longer than, the time frame OSHA granted for implementation of engineering controls for hexavalent chromium, where OSHA provided four years to allow sufficient time for some industries to coordinate efforts with other regulatory compliance obligations as well as gain experience with new technology and learn more effective ways to control exposures (71 FR 10100, 10372, Feb. 28, 2006). Thus, with the extra time provided for this industry to come into compliance, OSHA finds that the final PEL of 50 µg/m³ is feasible for the hydraulic fracturing industry.

In the two years leading up to the effective date, the hydraulic fracturing industry will continue to be subject to the preceding PEL in 29 CFR 1910.1000 (Table Z). In order to meet the preceding PEL of 100 µg/m during this interim period, such compliance will include adoption of the new engineering controls discussed above as they become widely available for field use.²⁵ As a result, OSHA expects many exposures in hydraulic fracturing to be at or near the 50 µg/m³ level ahead of the five-year compliance date due to the expected efficacy of this new technology. Thus, with the extra time provided for this industry to come into compliance, OSHA finds that the standard is feasible for most workers in the Hydraulic Fracturing industry most of the time.

OSHA has determined that a PEL of 50 µg/m³ is technologically feasible for the maritime industry. Although it is not feasible to reduce painters' exposures to 50 µg/m³ when conducting abrasive blasting operations most of the time without the use of respirators, evidence in the record demonstrates that it is feasible to reduce painters' helpers' exposure to 50 µg/m³ most of the time with HEPA-filtered vacuums. As noted in Chapter IV of the FEA, workers in the maritime industry may also be exposed during foundry activities; as explained in FEA Chapter IV. Section 4.8.4—Captive Foundries, OSHA has determined that it is feasible to reduce exposures during most operations in captive foundries to 50 µg/m³, most of the time. The record evidence indicates that shipyard foundries face similar issues controlling silica as other typical small foundries (e.g., cleaning the cast metal) and that shipyard foundries cast items in a range of sizes, from small items like a ship's plaque to large items like the bow structure for an aircraft carrier (Document ID 1145; 3584, Tr. 2607). OSHA did not receive comments indicating that foundries in shipyards would require any unique controls to reduce exposures, and therefore believes that exposures in shipyard foundries can also be reduced to 50 µg/m³ in most operations, most of the time. Accordingly, OSHA has determined that 50 µg/m³ is feasible for most silica-related activities performed in the maritime industry.

Even if captive foundries are excluded from consideration, OSHA considers the standard to be feasible for shipyards with the use of respirators by painters doing abrasive blasting. OSHA recognizes that, consistent with its hierarchy of controls policy for setting methods of compliance, respirator use is not ordinarily taken into account when determining industry-wide feasibility. Neither this policy nor the “most operations most of the time” formulation for technological feasibility is meant to place OSHA in a “mathematical straitjacket” (Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607, 655 (1980) (“Benzene”) (stated with respect to the “significant risk” finding, which the Supreme Court recognized is “based largely on policy considerations” (Benzene, 448 U.S. at 655 n.62)). No court has been confronted with a situation where an industry has two operations (or any even number), of which one can achieve the PEL through engineering controls and the other (or exactly half) can achieve it most of the time only with the use of respirators. However, the same court that formulated the “most operations most of the time” standard “also noted that `[i]nsufficient proof of technological feasibility for a few isolated operations within an industry, or even OSHA's concession that respirators will be necessary in a few such operations, will not undermine' a showing that the standard is generally feasible” (Amer. Iron & Steel Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991) (Lead II), (quoting United Steelworkers of Am. AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1272 (D.C. Cir. 1980) (“Lead I”)). It further recognized the intended pragmatic flexibility of this standard by stating that “[f]or example, if `only the most technologically advanced plants in an industry have been able to achieve [the standard]—even if only in some of their operations some of the time,' then the standard is considered feasible for the entire industry” (Lead II, 939 F. 2d at 980 (quoting Lead I, 647 F.2d at 1264)). In this instance, OSHA has determined that it makes sense to treat painters performing abrasive blasting in shipyards as an outlier for which the PEL established for all other covered industries is feasible, even conceding that respirators will be necessary. If abrasive blasting were the predominant activity that occurs in shipyards, there might be justification to set a separate, higher PEL for shipyards. But as in construction (for which supplemental respirator use is also contemplated for abrasive blasting operations), abrasive blasting is one of many activities that occurs; substitution of non-silica blasting materials is an option in many cases; few, if any, painters spend entire days or weeks doing blasting operations and thus needing respirators for the duration; and lowering the standard from 250 µg/m³ to 50 µg/m³ does not threaten the economic viability of the industry. Under these circumstances, OSHA concludes that it may find the standard feasible for shipyards rather than raise the PEL for this single industry because it can only achieve the uniform PEL with respirators or, alternatively, not be able to revise the previous PEL of 250 µg/m³ at all.

Table VII-9 lists the construction application groups included in the technological feasibility analysis and indicates the numbers of tasks in each application group. As this table shows, OSHA has determined that the rule's PEL is feasible for the vast majority of tasks (19 out of 23) in the construction industry. For those construction tasks listed in Table 1 of paragraph (c) of the construction standard, OSHA has determined that the controls listed on Table 1 are either commercially available from tool and equipment manufacturers or, in the case of jackhammers, can be fabricated from readily available parts. Therefore, OSHA has determined that these control requirements are technologically feasible and will, with few exceptions, achieve exposures of 50 μg/m³ or less most of the time. Furthermore, Table 1 in paragraph (c) of the standard for construction acts as a “safe harbor” in the sense that full and proper implementation of the specified controls satisfies the employer's duty to achieve the PEL, and the employer is under no further obligation to do an exposure assessment or install additional, non-specified controls. Thus, OSHA finds the operations listed in Table 1 to be technologically feasible for the vast majority of employers who will be following the table.

Where available evidence indicates that exposures will remain above this level after implementation of dust controls (see Chapter IV of the FEA), Table 1 requires that respiratory protection be used. OSHA has determined that available engineering and work practice controls cannot achieve exposure levels of 50 μg/m³ or less for only two activities: Handheld grinders used to remove mortar (i.e., tuckpointing) and dowel drilling in concrete. For a few other activities, OSHA concludes that respiratory protection will not generally be needed unless the task is performed indoors or in enclosed areas, or the task is performed for more than four hours in a shift. Table 1 requires use of respiratory protection when using handheld power saws indoors or outdoors more than four hours per shift; walk-behind saws indoors; dowel drills in concrete; jackhammers or handheld powered chipping tools indoors or outdoors more than four hours per shift; handheld grinders for mortar removal; and handheld grinders for uses other than mortar removal when used indoors for more than four hours per shift.

OSHA has also evaluated the feasibility of three application groups that do not appear on Table 1: Underground construction, drywall finishing work, and abrasive blasting. For these operations, employers will be subject to the paragraph (d) requirements for alternative exposure control methods. Due in part to the complexity of excavating machines, dust controls, and the ventilation systems required to control dust for underground operations, OSHA decided not to include underground construction and tunneling operations in Table 1 of paragraph (c) of the construction standard. Nonetheless, OSHA has determined that the PEL is technologically feasible in underground construction because exposures can be reduced to 50 µg/m³ or less most of the time. Drywall finishing work was not included on Table 1 because silica-free drywall compounds are commercially available and can be used to eliminate exposure to silica when finishing drywall. In contrast to underground construction and drywall finishing, OSHA decided that abrasive blasting was not suited to the Table 1 approach because employers have several options in the control measures they can implement when abrasive blasting based on their particular application. For example, substitution to low-silica agent, use of wet blasting and process enclosures are all possible control options for abrasive blasting operations. Therefore, OSHA does not specify a specific control for abrasive blasting suitable for all applications, unlike the entries on Table 1 for tuckpointing and dowel drilling, where LEV is the only option accompanied by required supplemental respirator use. Furthermore, OSHA has existing requirements for abrasive blasting under the ventilation standard for construction (29 CFR 1926.57). In certain situations, that standard requires abrasive blasting operators to use abrasive blasting respirators approved by NIOSH for protection from dusts produced during abrasive blasting operations (29 CFR 1926.57(f)(5)(i) through (iii)). That standard also includes specifications for blast-cleaning enclosures (29 CFR 1926.57(f)(3)), exhaust ventilation systems (29 CFR 1926.57(f)(4)), air supply and air compressors (29 CFR 1926.57(f)(6)), and operational procedures (29 CFR 1926.57(f)(7)). OSHA also has similar requirements for abrasive blasting under the general industry standard (29 CFR 1910.94). Therefore, OSHA expects that respiratory protection will be required to be used during blasting operations under the paragraph (d) approach that employers must follow when employees are doing this task.

The American Chemistry Council's (ACC's) Crystalline Silica Panel contended that OSHA did not demonstrate that the proposed standard would be technologically feasible in all affected industry sectors because OSHA had failed to account for day-to-day environmental variability in exposures (Document ID 4209, Attachment 1, p. 97). ACC noted that OSHA enforces PELs as never-to-be-exceeded values and that an employer can be cited based on a single measurement even if most exposures on most days are below the PEL. Therefore, they stated that to be “reasonably confident of complying with OSHA's proposed PEL of 50 μg/m³, the long-term average exposure in most workplaces likely would have to be maintained at a level below 25 μg/m³ (or even below 20 μg/m³)” (Document ID 4209, p. 97; 2307, Attachment A, pp. 23-24, 160). Representatives from the American Foundry Society (AFS) and the Asphalt Roofing Materials Association (ARMA) made similar arguments (Document ID 2291, p. 5; 3584, Tr. 2654-2655; 3580, Tr. 1282-1284, 1289).

OSHA recognizes the existence of exposure variability due to environmental factors that can affect employee exposures, especially in the construction industry where work sites and weather conditions can change on a daily basis. OSHA has acknowledged this in past rulemakings where the same issue was raised (e.g., benzene, 52 FR 34534; asbestos, 53 FR 35609; lead in construction, 58 FR 26590; formaldehyde, 57 FR 22290; cadmium, 57 FR 42102; and chromium (VI), 71 FR 10099). However, not all exposure variation is due to random environmental factors; rather, many high exposures are the result of predictable causes that the employer can readily identify and address in efforts to improve exposure control. Several studies were submitted to the docket that used multivariate statistical models to identify factors associated with increased exposure to silica during various construction activities (Document ID 3608, 3803, 3956, 3998 Attachment 5h). These studies reported that as much as 80 percent of the variability in respirable quartz exposures could be attributed to various exposure determinants included in the models, clearly indicating that not all variability in exposure is uncontrollable. This was also attested to at the hearing by Dr. Frank Mirer:

Exposures go up and down not by magic but by particular conditions, differences in work methods, differences in control efficiency, differences in adjacent operations (Document ID 3578, Tr. 971).

OSHA concludes from the evidence in the record that the consistent use of engineering controls will reduce exposure variability. By improving or adding effective controls and work practices to reduce employee exposures to the PEL or below, employers will reduce exposure variability, and this reduction will provide employers with greater confidence that they are in compliance with the revised PEL. OSHA does, however, acknowledge that exposure controls cannot entirely eliminate variability. Some day-to-day variability in silica exposure measurements may remain, despite an employer's conscientious application and maintenance of all feasible engineering and work practice controls. Nonetheless, the legal standard for finding that a PEL is technologically feasible for an industry sector is whether most employers can implement engineering and work practice controls that reduce exposures to the PEL or below most of the time. As explained in Section XV, Summary and Explanation, in situations where exposure measurements made by OSHA indicate that exposures are above the PEL, and that result is clearly inconsistent with an employer's own exposure assessment, OSHA will use its enforcement discretion to determine an appropriate response. Moreover, for the vast majority of construction employers (and some general industry or maritime employers doing tasks that are “indistinguishable” from Table 1 tasks and choose to comply with the construction standard), full compliance with Table 1 will eliminate the risk that an employer will be subject to citation for exposures above the PEL, even when the employer has instituted all feasible controls that normally or typically maintain exposures below the PEL.

OSHA also received a number of general comments on the feasibility of wet methods and LEV, as well as comments on challenges faced when employing these dust control strategies in specific work settings. In general industry, several commenters indicated for specific industries that there was no one control that could obtain the PEL of 50 μg/m³ (Document ID 2264, p. 36). CISC was also critical of several aspects of OSHA's feasibility analysis. CISC commented that OSHA failed to consider exposures from secondary or adjacent sources and that OSHA should factor this into its analysis (Document ID 2319, p. 30; 4217, p. 13). Dr. Mirer also stated that many employees' silica exposures are due to dust released from adjacent operations, but indicated that if these dust releases are controlled, the exposures of workers in adjacent areas will be substantially reduced (Document ID 4204, p. 104). In many industries, OSHA has shown that all sources of respirable crystalline silica should be controlled and that often a combination of controls may be needed to address potential sources of silica. Additionally, addressing each source of exposure also reduces exposures in adjacent areas, thus mitigating the concern about secondary exposures expressed by both industry and union stakeholders.

Other commenters addressed the use of water on construction sites; several commenters asserted that it is not always possible for employers to use water for dust suppression. For example, in its post-hearing submission, CISC discussed what it believed to be “significant obstacles” to using wet dust suppression technologies on construction sites. Such obstacles include freezing weather, which contraindicates water use, and a lack of running water onsite, which requires employers to deliver water, a practice which, according to CISC, is both “costly and time consuming” (Document ID 4217, pp. 18-19). However, many other participants commented that these barriers can be overcome. For example, Phillip Rice, of Fann Contracting, Inc., uses water trucks to haul water to sites and includes the cost of doing so in his bids. He added that “when someone says they can't get water on their project there is something wrong” (Document ID 2116, Attachment 1, p. 33). Representatives of the International Union of Bricklayers and Allied Craftworkers pointed out that water is essential for work in the masonry trades and without it, no mortar can be mixed to set materials (Document ID 3585, Tr. 3059-3060). They testified that, in their experience, it was rare to work on sites that did not have water or electricity available, but when they do, they bring in water trucks and gas-powered generators to run saws (Document ID 3585, Tr. 3061-3063). With respect to weather conditions, heated water or heated shelters can be used if construction work is being performed in sub-freezing temperatures (Document ID 3585, Tr. 3095-3096).

These comments and testimony indicate that the vast majority of the barriers to wet dust suppression raised by CISC have already been overcome in various construction settings. However, OSHA recognizes that there will be limited instances where the use of wet dust suppression is not feasible, particularly where its use can create a greater hazard. For example, water cannot be used for dust control in work settings where hot processes are present due to the potential for steam explosions (Document ID 2291, p. 13; 2298, p. 3), nor can it be used safely where it can increase fall hazards, such as on a roof (Document ID 2214, p. 2). Nevertheless, OSHA finds that many employers currently use wet dust suppression, that there are many commercially available products with integrated water systems for dust suppression, and that these products can be used in most work settings to control exposures to respirable crystalline silica. In the limited cases where dust suppression is not feasible, OSHA discusses the use of alternative controls such as local exhaust ventilation and the supplemental use of respiratory protection, as needed.

Some commenters questioned whether OSHA had adequately considered the difficulties in complying with the PEL for maintenance activities. The National Association of Manufacturers, for example, quoted one of its members, who stated:

[t]here are occasional conditions where maintenance cleaning is performed inside conveyor enclosures where the enclosure is ordinarily a part of the dust control systems. This is just one example of where a control would have to be breached in order to properly maintain it as well as the operating equipment. It is simply not technically feasible to establish engineering controls for all possible maintenance activities (Document ID 2380, Attachment 2, p. 1).

OSHA has addressed maintenance activities in each sector's technological feasibility analysis, but the standard itself acknowledges the difficulties of some maintenance activities. Paragraph (g)(1)(ii) of the standard for general industry and maritime (paragraph (e)(1)(ii)(B) in construction) requires respiratory protection “where exposures exceed the PEL during tasks, such as certain maintenance and repair tasks, for which engineering and work practice controls are not feasible” (see the Summary and Explanation section on Respiratory Protection for more information).

CISC submitted comments suggesting that the technological feasibility analysis was incomplete because it did not cover every construction-related task for which there is the potential for exposure to silica dust. It listed more than 20 operations, including cement mixing, cutting concrete pavers, demolishing drywall or plaster walls/ceilings, overhead drilling, demolition of concrete and masonry structures, and grouting floor and wall tiles, that it stated OSHA must examine in order to establish feasibility, in addition to the application groups already covered by OSHA's analysis (Document ID 2319, pp. 19-21). CISC asserted that, because of the many types of silica-containing materials used in the construction industry, as well as the presence of naturally occurring silica in soil, additional data collection and analysis by OSHA should be conducted before promulgating a final rule (Document ID 2319, pp. 25-26; 4217, p. 3).

As explained in the NPRM, OSHA's analysis for construction focuses on tasks for which the available evidence indicates that significant levels of respirable crystalline silica may be created, due primarily to the use of powered tools or large equipment that generates visible dust. OSHA notes that many of the examples of tasks for which CISC requested additional analysis are tasks involving the tools and equipment already covered in this feasibility analysis. For example, overhead drilling is addressed in section IV-5.4 Hole Drillers Using Handheld or Stand-Mounted Drills, and the demolition of concrete and masonry structures is addressed in section IV-5.3 Heavy Equipment Operators. In other cases, such as for concrete mixing, there are no sampling data in the record to indicate that the task is likely to result in 8-hour TWA exposures above the action level. Exposure can occur when cleaning dried cement, and the feasibility of control measures to reduce exposures when cleaning out the inside of cement mixers is discussed in section IV-4.17 Ready Mix Concrete. Other tasks listed by CISC involve working with wet or intact concrete, which is unlikely to result in 8-hour TWA exposures above the action level. Further, CISC did not submit to the record any air monitoring data to support its assertion that these activities result in significant exposures. Therefore, OSHA has not added these additional activities to the feasibility analysis.

4. Feasibility Findings for an Alternative Permissible Exposure Limit of 25 μg/m³

In the NPRM, OSHA invited comment on whether it should consider a lower PEL because it determined there was still significant risk at the proposed PEL of 50 μg/m³ (78 FR 56288, September 12, 2013). OSHA has determined that the rule's PEL of 50 μg/m³ is the lowest exposure limit that can be found to be technologically feasible based on the rulemaking record. Specifically, OSHA has determined that the information in the rulemaking record either demonstrates that the proposed alternative PEL of 25 μg/m³ would not be achievable for most of the affected industry sectors and application groups or the information is insufficient to conclude that engineering and work practice controls can consistently reduce exposures to or below 25 μg/m³. Therefore, OSHA cannot find that the proposed alternative PEL of 25 μg/m³ is achievable for most operations in the affected industries, most of the time.

The UAW submitted comments and data to the record, maintaining that a PEL of 25 μg/m³ is technologically feasible. As evidence, it submitted exposure data from a dental equipment manufacturing plant and two foundries (Document ID 2282, Attachment 3, pp. 7-8; 4031, pp. 3-8) showing that exposures to silica in these establishments were consistently below 25 μg/m³ TWA. However, OSHA cannot conclude that exposure data from three facilities is representative of the wide array of facilities affected by the rule or sufficient to constitute substantial record evidence that a PEL of 25 μg/m³ is technologically feasible in most operations most of the time.

Although available exposure data indicate that exposures below 25 μg/m³ have already been achieved for most employees in some general industry sectors and construction application groups (e.g., dental laboratories, jewelry, and paint and coatings in general industry, and drywall finishers and heavy equipment operators performing excavation in construction), the relatively low exposures can be attributed to the effective control of the relatively small amounts of dust containing silica generated by employees in these industries and application groups. Further extrapolation to other sectors or groups with higher baseline exposures or more challenging control situations is not warranted, however.

For most of the industries and application groups included in this analysis, a review of the sampling data indicates that an alternative PEL of 25 μg/m³ cannot be achieved with engineering and work practice controls. OSHA finds that engineering and work practice controls will not be able to consistently reduce and maintain exposures to an alternative PEL of 25 μg/m³ in the sectors that use large quantities of silica containing material, including foundries (ferrous, nonferrous, and non-sandcasting), concrete products, and hydraulic fracturing, or have high energy operations, such as jackhammering and crushing machines.

For instance, in the ferrous foundry industry, the baseline median exposure in the profiles exceeds 50 μg/m³ for 6 of the 12 job categories analyzed: Sand system operators, shakeout operators, abrasive blasting operator, cleaning/finishing operators, maintenance operators, and housekeeping employees. OSHA concluded that engineering and work practice controls can reduce TWA exposures to 50 μg/m³ or less for most of these operations most of the time. However, because large amounts of silica-containing sand is transported, used, and recycled to create castings, OSHA cannot conclude that available controls can reduce exposures to or below 25 μg/m³ in any step of the production process. Additionally, high energy operations in foundries can create concentrations of respirable silica above 25 μg/m³. For example, the shakeout process is a high energy operation using equipment that separates castings from mold materials by mechanically vibrating or tumbling the casting. The dust generated from this process causes elevated silica exposures for shakeout operators and often contributes to exposures for other employees in a foundry. The effectiveness of dust controls on shakeout operations was demonstrated at three foundries that implemented various dust controls in the shakeout area (e.g., shakeout enclosure added, ventilation system improved, conveyors enclosed and ventilated); full-shift samples taken by or for OSHA measured exposures for shakeout operators ranging from less than or equal to 13 μg/m³ to 41 μg/m³ (Document ID 1365, pp. 2-51; 1407, p. 20; 0511, p. 2). These readings were obtained in foundries that had made a systematic effort to identify and abate all sources of dust emission with the establishment of an abatement team consisting of an engineer, maintenance and production supervisors, and employees. TWA exposures for the shakeout operators were reduced to less than 50 μg/m³, but two of the four measurements in this well-controlled facility exceeded 25 μg/m³ (see Chapter IV 4.8.1 of the FEA). Other industry sectors that use substantial quantities of crystalline silica as a raw material include refractories, glass products, mineral processing, structural clay and cement products. OSHA finds that the available evidence on exposures at facilities in these industries in which controls have been implemented indicates most exposures are typically between 25 μg/m³ and 50 μg/m³.

For other general industry sectors, OSHA has insufficient data to demonstrate that engineering and work practice controls will reduce exposures to or below 25 μg/m³ most of the time (see Chapter IV of the FEA). For example, it is not evident that exposures can be reduced to 25 μg/m³ for four out of five jobs analyzed in the pottery sector, for two out of three job categories in the structural clay sector, and for two jobs in the porcelain enameling sector.

OSHA has also determined that application groups in construction that use large quantities of silica containing material or involve high energy operations will not be able to consistently achieve 25 μg/m³ (e.g. tuck pointing/grinding and rock and concrete drilling). These operations cause employees to have elevated exposures even when available engineering and work practice controls are used. Examples include using jackhammers during demolition of concrete and masonry structures, grinding concrete surfaces, using walk-behind milling machines, operating rock and concrete crushers, and using portable saws to cut concrete block. For instance, jackhammering is a high energy operation and OSHA finds that when employees perform this operation for four hours or less in a shift, most employees using jackhammers outdoors experience levels at or below 50 μg/m³ TWA but not reliably at or below 25 μg/m³. The use of portable cut-off saws (a type of handheld power saw) is also a high energy operation that can lead to exposures over 25 μg/m³. Due to energy applied to the material being cut from the rapid rotation of the circular blade, the dust generated can be difficult to control; available data indicate that exposures will often exceed 25 μg/m³ TWA, even when the portable cut-off saw is used with water for dust suppression. Evidence in the record indicates that, for most of the other construction operations examined, use of feasible engineering and work practice controls will still result in frequent exposures above 25 μg/m³. For other tasks in construction application groups, OSHA has insufficient data to demonstrate that engineering and work practice controls will reduce exposures to or below 25 μg/m³ most of the time (see Chapter IV of the FEA).

Therefore, OSHA concludes that 50 μg/m³ as an 8-hour TWA is the lowest feasible exposure limit that the record demonstrates can be applied to most general industry, maritime, and construction operations without the excessive use of respirators. OSHA also concludes that it would hugely complicate both compliance and enforcement of the rule if it were to set a PEL of 25 μg/m³ for a minority of industries or operations where it would be technologically feasible and a PEL of 50 μg/m³ for the remaining industries and operations where technological feasibility at the lower PEL is either demonstrably unattainable, doubtful or unknown. OSHA is not under a legal obligation to issue different PELs for different industries or application groups, but may exercise discretion to issue a uniform PEL if it determines that the PEL is technologically feasible for all affected industries (if not for all affected operations) and that a uniform PEL would constitute better public policy (see Section II, Pertinent Legal Authority (discussing the chromium (VI) decision)). In declining to lower the PEL to 25 μg/m³ for any segment of the affected industries, OSHA has made that determination here.

E. Costs of Compliance

Overview

This section assesses the costs to establishments in all affected industry sectors of reducing worker exposures to silica to an 8-hour time-weighted average (TWA) permissible exposure limit (PEL) of 50 μg/m³—or, alternatively, for employers in construction to meet the Table 1 requirements—and of complying with the standard's ancillary requirements. This cost assessment is based on OSHA's technological feasibility analysis presented in Chapter IV of the FEA; analyses of the costs of the standard conducted by OSHA's contractor, Eastern Research Group; testimony during the hearings; and the comments submitted to the docket as part of the rulemaking process.

OSHA estimates that the standard will have a total cost of $1,029.8 million per year in 2012 dollars. Of that total, $370.8 million will be borne by the general industry and maritime sectors, and $659.0 million will be borne by the construction sector. Costs originally estimated for earlier years in the PEA were adjusted to 2012 dollars using the appropriate price indices. In general, all employee and supervisor wages (loaded) were from the 2012 BLS OES (Document ID 1560); medical costs were inflated to 2012 dollars using the medical services component of the Consumer Price Index; and, unless otherwise specified, all other costs were inflated using the GDP Implicit Price Deflator (Document ID 1666).

All costs were annualized using a discount rate of 3 percent, which—along with 7 percent —is one of the discount rates recommended by OMB. Annualization periods for expenditures on equipment are based on equipment life, while there is a 10-year annualization period for one-time costs. Note that the benefits of the standard, discussed in Section VII.G of this preamble and in Chapter VII of the FEA, were annualized over a 60-year period to reflect the time needed for benefits to reach steady-state values. Therefore, the time horizon of OSHA's complete analysis of this rule is 60 years. Employment and production in affected industries are being held constant over this time horizon for purposes of the analysis. All non-annual costs are estimated to repeat every ten years over the 60-year time horizon, including one-time costs that recur because of changes in operations over time or because of new entrants that must comply with the standard. Table VII-10 shows, by affected industry in the sectors of general industry and maritime, annualized compliance costs for all establishments, all small entities (as defined by the Small Business Act and the Small Business Administration's (SBA's) implementing regulations; see 15 U.S.C. 632 and 13 CFR 121.201), and for all very small entities (those with fewer than 20 employees). Table VII-11 similarly shows, by affected industry in construction, annualized compliance costs for all entities, all small entities, and all very small entities. Note that the totals in these tables and all other tables in this chapter, as well as totals summarized in the text, may not precisely sum from underlying elements due to rounding.

OSHA's exposure profile, presented in Chapter III of the FEA, represents the Agency's best estimate of current exposures (i.e., baseline exposures). Except for compliance with Table 1 in construction, OSHA did not attempt to determine the extent to which current exposures in compliance with the new silica PEL are the result of baseline engineering controls or the result of other circumstances leading to low exposures. This information is not needed to estimate the costs of (additional) engineering controls needed to comply with the new PEL, but it is relevant to estimate the costs of complying with Table 1 in construction.

For both construction and general industry/maritime, the estimated costs for the silica rule represent the additional costs necessary for employers to achieve full compliance with the new standard, assuming that all firms are compliant with the previous standard. Thus, the estimated costs do not include any costs necessary to achieve compliance with previous silica requirements, to the extent that some employers may not be fully complying with previously-applicable regulatory requirements. OSHA almost never assigns costs for reaching compliance with an already existing standard to a new standard addressing the same health issues. Nor are any costs associated with previously-achieved compliance with the new requirements included.

Because of the severe health hazards involved, as well as current OSHA regulation, the Agency expects that the estimated 11,640 abrasive blasters in the construction sector and the estimated 3,038 abrasive blasters in the maritime sector are currently wearing respirators as required by OSHA's abrasive blasting provisions (29 CFR 1915.154 (referencing 29 CFR 1910.134)). Furthermore, an estimated 264,761 workers, including abrasive blasters, will need to use respirators at least once during a year to achieve compliance with the new silica rule in construction, and, based on the NIOSH/BLS respirator use survey (NIOSH/BLS, 2003, Document ID 1492), an estimated 56 percent of construction employees whose exposures are high enough that they will need respirators under the new rule currently use such respirators. OSHA therefore estimates that 56 percent of affected construction employees already use respirators in compliance with the respirator requirements of the final silica rule.

Other than respiratory protection, OSHA did not assume baseline compliance with any other ancillary provision, even though some employers have reported that they currently monitor silica exposure, provide silica training, and conduct medical surveillance.

The remainder of this chapter is organized as follows. First, unit and total costs by provision are presented for general industry and maritime and for construction. Following that, the chapter concludes with a summary of the estimated costs of the rule for all affected industries.

1. Engineering Controls

a. General Industry and Maritime

The engineering control section in Chapter V of the FEA covers OSHA's estimates of engineering control costs for general industry and maritime sectors. Oil and natural gas fracturing operations are addressed separately because OSHA used a different methodology to estimate engineering control costs for this application group. This section will address OSHA's overall methodology, the methodology for each category of costs (such as ventilation, housekeeping, conveyors), issues specific to small entities, and issues specific to the hydraulic fracturing industry. Within each of these discussions, this section summarizes the methodology used in the PEA to estimate engineering control costs, summarizes and responds to the comments on the PEA, and summarizes the changes made to the methodology used in the PEA for the FEA. Finally, the chapter presents OSHA's final estimates of engineering control costs.

Introduction

The PEA's technological feasibility analysis identified the types of engineering controls that affected industries or sectors would need in order to control worker exposures to at or below the proposed PEL of 50 μg/m³. Through its contractor, Eastern Research Group (ERG), OSHA generated cost estimates for those controls using product and technical literature, equipment vendors, industrial engineers, industrial hygienists, and other sources, as relevant to each item. Wherever possible, objective cost estimates from recognized technical sources were used. Specific sources for each estimate were presented with the cost estimates.

Table V-4 of the PEA provided a list of possible controls on an industry-by-industry basis and included details on control specifications and costs. The basic information for the types of controls needed was taken from the PEA's technological feasibility analysis. The following discussion explains how OSHA developed and used these estimates to prepare the aggregate costs of engineering controls presented in the PEA.

In developing engineering control cost estimates for the PEA, OSHA made a variety of estimates about the size or scope of the engineering or work practice changes necessary to reduce silica exposures in accordance with the proposed rule. In some cases, OSHA estimated that employers would need to install all new engineering controls. In other cases, though, employers were expected to only need to add additional ventilation capacity or improve maintenance for existing equipment. In these cases, the costs were based on judgments of the amount of incremental change (either additional capacity or additional maintenance work) required per year. These estimates of the size or scope of the necessary engineering or work practice changes reflected representative conditions for the affected workers based on technical literature (including National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluations), judgments of knowledgeable consultants and industry observers, and site visits. A detailed list of the specific costing assumptions and information sources for each control, grouped by job category or industry sector, was shown in PEA Appendix V-A, Table V-A-1.

In order to estimate costs in a consistent manner, OSHA, in the PEA, estimated all costs on an annualized basis. For capital costs, OSHA calculated the annualized capital cost, using a three percent discount rate over the expected lifetime of the capital item. The capital costs for long-lasting capital items (such as ventilation system improvements) were annualized over ten years. OSHA estimated that, in the general industry and maritime sectors, any capital expenditure would also entail maintenance costs equal to ten percent of the value of the capital investment annually.

General Methodology

General Methodology: Per-Worker Basis and Treatment of Overexposures for Cost Calculations

PEA Estimates

OSHA, in the PEA, estimated control costs on a per-worker basis. Costs were related directly to the estimates of the number of workers needing controls (i.e., workers exposed over 50 μg/m³). OSHA divided engineering control costs into two categories: (1) Those only needed by establishments with employees exposed to levels of silica that exceeded the preceding general industry PEL of 100 μg/m³; and (2) those applicable to all establishments where workers were exposed to levels of silica above the proposed PEL (whether just above 50 μg/m³ or also above 100 μg/m³). It should be noted that the maritime sector has been subject to a different preceding PEL of 250 μg/m³. The PEA estimates were presented in the PEA cost analysis tables. The overwhelming majority of the costs (90 percent of all engineering control costs and 85 percent of costs associated with meeting the preceding PEL of 100 μg/m³) were associated with the second category (controls applicable to all establishments with exposures above the proposed or preceding PEL). Because OSHA is not accounting for the costs of controls necessary to reach the preceding PEL, the PEA focused on controls that may be needed to meet the new PEL. OSHA derived per-worker costs by examining the controls needed for each job category in each industry and dividing the cost of that control by the number of workers whose exposures would be reduced by that control. OSHA then multiplied the estimated per-worker control cost by the number of workers exposed between the proposed (new) PEL of 50 μg/m³ and the preceding PEL of 100 μg/m³. The numbers of workers in this category were based on the exposure profiles for at-risk occupations developed in the technological feasibility analysis in Chapter IV of the PEA and the estimates of the number of workers employed in these occupations were developed in the industry profile in Chapter III of the PEA. The exposure profile information was determined to be the best available data for estimating the need for incremental controls on a per-worker basis.

In general, in the PEA, OSHA inferred the extent to which exposure controls were already in place from the distribution of overexposures among the affected workers. Thus, if most exposures in a facility were above the preceding PEL, OSHA broadly interpreted this as a sign of limited or no controls, and if most exposures were below the proposed (new) PEL of 50 μg/m³, this would be indicative of having adequate controls in place. OSHA calculated the costs of controls per exposed worker in each job category and assigned this cost to the total number of employees exposed between the proposed (new) PEL and the preceding PEL. For example, if a control cost $1,000 per year and covered 4 employees, the cost per employee would be $250 per year. If 100 employees in the job category were exposed between the preceding and proposed (new) PEL, then the total costs would be $250 times 100 employees or $25,000. No costs were estimated for employees currently exposed above the preceding PEL or below the proposed (new) PEL.

OSHA determined that multiple controls would be needed for almost all jobs in general industry in order reduce exposures from baseline conditions to meeting the proposed (new) PEL of 50 μg/m³. Some of these controls cover a group of workers, while others might be individualized (such as daily housekeeping by each individual worker).

Comments on the Per-Worker Basis and Proportionality of Costs

URS, speaking for the American Chemistry Council (ACC), argued that OSHA's approach underestimated the costs of controls because it based costs on controls per worker instead of controls per facility (Document ID 2307, Attachment 8, p. 4). Since OSHA did not provide a distribution of exposures by facility or provide facility-specific information, URS used data in the record to create its own models to account for facility size. URS described its approach as follows:

URS created three statistical binomial distributions of overexposed workers, one for each of the three facility sizes, using OSHA's estimate of the percentage of over-exposed workers for that job. The result was a binomial distribution curve indicating the percentage of overexposed workers for each job category for each size-specific “model facility.”

For each binomial distribution, the peak of the distribution curve centers on the average number of overexposed workers per facility for that job description according to OSHA's estimate (Document ID 2307, Attachment 8, p. 7).

In taking this approach, URS erroneously assumed that the distribution of overexposed workers per facility was random, as evidenced by its use of a binomial distribution to approximate overexposures per facility within each of three facility sizes (Document ID 2307, Attachment 8, p. 7). Examination of the spreadsheet URS provided shows that this approach approximately doubles the number of controls needed and, and for this reason, doubles the total cost of engineering controls (Document ID 2307, Attachment 26, Table 2A, URS Summary Worksheet).

OSHA disagrees with URS's implicit conclusion that overexposures are random across facilities. It is not reasonable to assume that controls have no relation to exposure level as this approach assumes. As will be discussed later in the context of OSHA's treatment of the preceding PEL, the data underlying the exposure profile show that establishments with low exposures are much more likely to have controls in place than those with very high exposures.

URS then assumed that if one worker in a job category is overexposed, then all controls listed by OSHA will be needed (Document ID 2307, Attachment 25, Engineering Costs). URS did not dispute that multiple controls would be needed for almost all jobs in general industry in order reduce exposures from baseline conditions to meeting the proposed (new) PEL of 50 μg/m³. The existence of multiple controls weakens the theory suggested by URS—that all controls are needed if even one worker is exposed at levels above the PEL—because as explained above, some controls are individualized while some protect groups of workers.

The best possible approach to what engineering controls are needed might differ based on whether: (1) There are no controls for a job category in place at all and most workers are overexposed by a large margin; or (2) only some workers in a job category are overexposed by a small margin (i.e., a set of controls is already in place).

In the first case, the most common approach would be to apply a relatively full set of controls, as explained in OSHA's technological feasibility analysis. This might start with enclosures and local exhaust ventilation (LEV), but, if exposures are high and the establishment is very dusty, it might also include initial cleaning or the introduction of ongoing routine housekeeping. In these situations, in which most employees are overexposed, OSHA estimated that the full set of controls listed in the technological feasibility analysis would be applied and, in these cases, there would be little difference in the results obtained using OSHA's approach and the results obtained using the approach suggested by URS.

However, the approach to controlling silica exposures that OSHA believes to be typical when establishments are faced with the second situation would be quite different, and therefore different from what URS expected. Commenters from both labor (Document ID 4204, p. 40) and industry (Document ID 1992, p. 6) pointed out that when there are controls in place or only some workers are overexposed, the first step is to examine work practices. The AFL-CIO noted that exposures can be controlled through work practices, repositioning ventilation systems, and controlling fugitive emissions (carryover from adjacent silica emitting processes) (Document ID 4204, p. 40). Implementing these types of changes can be inexpensive. The principal cost of improving work practices may only be training or retraining workers in appropriate work practices. OSHA's proportional cost approach in the PEA may therefore overestimate costs for situations in which overexposures can be corrected with work practice changes because the Agency will have included costs for engineering controls when, in fact, none will be needed. The URS approach will always include the costs of all controls for a job category in any facility where anyone in a job category is overexposed, and will thus yield even higher estimates.

As described in Chapter IV, Technological Feasibility, of the FEA, and summarized below, in situations in which there are LEV systems in place but the PEL is still not being met, employers would typically try many things short of removing the entire system and replacing it with a system with greater air flow velocities (and thus greater capacity and cost). The incremental solutions to controlling silica exposures include minor design modification of existing controls, better repair and maintenance of existing controls, adding additional LEV capacity to existing systems, improving housekeeping, modifying tools or machinery causing high levels of emissions, and reducing cross contamination.

Some worksites might require a slightly different and readily modified design. For example, an OSHA special emphasis program inspection of a facility in the Concrete Products industry discovered that installing a more powerful fan motor, installing a new filter bag for the bag-filling machine LEV, and moving hoods closer to the packing operator's position reduced respirable dust exposure by 92 percent, to 11 μg/m³ (Document ID 0126, pp. 7-8). In an assessment of the Asphalt Roofing industry, NIOSH recommended repair and servicing of existing process enclosures and ventilation systems to eliminate leaks and poor hood capture but did not indicate that entirely new systems would need to be installed (Document ID 0889, pp. 12-13; 0891, pp. 3 and 11; 0890, p.14; 0893, p. 12).

In other cases, better equipment repair and maintenance procedures can be the key to meeting the PEL when there are already controls in place. For example, as described in Chapter IV of the FEA, in the Concrete Products industry, OSHA obtained a sample of 116 μg/m³ for a material handler who operated a forklift to transport product between stations. The inspector noted that there were leaks in the silo bin chute and that some controls were not fully utilized. The report indicated that dust generated by various other processes in the facility was a contributing factor to the forklift operator's high level of exposure. In this case, the first course of action for the employer would be to correct the deficiencies in the existing systems. Similarly, at a site visit in the Paint and Coating industry, ERG monitored mixer operators' exposures and obtained results below the limit of detection while workers emptied 50-pound bags of powder into hoppers when dust control systems were working properly. These values are 95 percent lower than the 263 μg/m³ obtained during another shift, at the same plant, when the dust control systems malfunctioned (Document ID 0199, p. 9).

In other cases, as pointed out by a foundry commenter, adding LEV capacity to existing systems for silica emissions not yet subject to any LEV control can be a good strategy for lowering exposures (Document ID 1992, p. 6). In one foundry, NIOSH investigators recommended installation of LEV over the coater and press areas, enclosure of the coating process, and/or repair and servicing of existing process enclosures and ventilation systems to eliminate leaks and poor hood capture (Document ID 0889, pp. 12-13; 0891, pp. 3 and 11; 0890, p. 14; 0893, p. 12).

Various combinations of improved housekeeping, initial cleaning, and switching to High-Efficiency Particulate Air (HEPA) vacuums can also help employers meet the PEL. In the Structural Clay industry, professional cleaning in a brick manufacturing facility removed “several inches” of dust from floors, structural surfaces and equipment (Document ID 1365, pp. 3-19-3-20; 0571). These changes alone led to a dramatic decrease in exposures, by as much as 90 percent, to below 50 μg/m³, for materials handlers. Similar results were observed for grinding operators (Document ID 0571). In one NIOSH evaluation, operators in a grinding area where good housekeeping practices were being implemented had substantially lower exposures than operators in a grinding room where the housekeeping practices were poor. The grinding room referred to as the “C plant” had 2 to 3 inches of settled dust on the floor and had an exposure result of 144 μg/m³. Grinding operators at the grinding room referred to as the “B plant,” where dust had been cleaned up, had substantially lower exposures (24 μg/m³) (Document ID 0235, pp. 6-7).

Good housekeeping also increases the useful life of equipment. As discussed in Chapter IV of the FEA, dust clogs machines and reduces their useful life. As an example, regulating cotton dust was acknowledged to increase productivity by reducing down time. It also increased the useful life of looms (Document ID 2256, Attachment 4, p. 11). The Agency predicts that this is likely to be the case with silica controls as well. Dust being properly captured at the source can also result in cost savings in housekeeping activities because less dust needs to be cleaned up when it is captured at the source and not allowed to spread (Document ID 2256, Attachment 4, p. 11).

In specific situations, there are a variety of other controls that may be useful. As discussed in the Technological Feasibility chapter of the FEA, Simcox et al. (1999) (Document ID 1146) found that Fabricators in the Cut Stone industry had a mean exposure of 490 μg/m³, which was reduced 88 percent to 60 μg/m³ when dry grinding tools used on granite were replaced or modified to be water-fed. Similar reductions were found at other facilities when wet grinding, polishing, and cutting methods were adopted (Document ID 1365, p. 11-20; 1146, p. 579). In the technological feasibility chapter, OSHA examined the work practices of cut stone splitters and chippers and found that a combination of wetting the floor at appropriate times, modifying ventilation directly from the top of the saws, and retrofitting splitting stations with LEV reduced exposures from a mean of 117 μg/m³ to a mean of 18 μg/m³, an 85 percent reduction (Document ID 1365, p. 11-22; 0180).

Finally, in situations where there is cross contamination, employers may achieve the PEL for some workers without implementing any controls specific to that job category. As pointed out by the AFL-CIO, when this occurs, OSHA's costs may be overestimated (Document ID 4204, Attachment 1, p. 105).

These examples show that in many situations, where there are already controls in place, or where exposures are only slightly above the PEL, the PEL can be met by a variety of mechanisms short of installing an entirely new set of controls. Since the record shows that, frequently, exposures can be controlled without installing new engineering controls, OSHA's approach of estimating costs based on the proportion of the workers exposed above the PEL is much more likely to be accurate than estimates based on URS's suggestion that all controls are needed whenever one worker is exposed above the PEL.

The URS facility-based approach would require taking the costs of newly installing a full set of controls even if only one worker is exposed above the PEL. This approach assumes that (1) the existing exposure levels in a given facility have been achieved without the use of any controls; and (2) existing controls cannot be improved upon for less than the cost of installing an entirely new system of controls. These assumptions are unsupported by the URS comments and the nature of exposure control, as discussed above.

OSHA, therefore, rejects URS's approach and is maintaining its per-worker basis for calculating costs for the FEA. Based on the evidence presented in this section, the Agency concludes that OSHA's proportional approach of assigning control costs to each worker based on the cost per worker of a complete set of controls is a better approach to commonly encountered exposure situations than to assume that any reading above the PEL triggers the need for a complete set of controls.

The AFL-CIO argued that OSHA's proportional approach resulted in an over-estimation of costs because it involved adding costs for the exposed occupation wherever there was an overexposure, even when the overexposure was primarily or solely the result of cross contamination. The AFL-CIO recommended that OSHA “identify operations which are unlikely to [generate] silica emissions, or background and bystander exposure measurements, and subtract those measured exposure levels from those operations which do emit silica” (Document ID 4204, Attachment 1, pp. 31-32). OSHA has routinely included the elimination of cross contamination as a component of the controls needed for some job categories. As discussed in Chapter IV of the FEA, OSHA also believes that other controls will still be needed for many job categories in which cross contamination is common and as long as these additional controls are needed, overall costs will not decline as a result of controlling cross contamination. However, OSHA agrees that there may be situations in which correcting cross contamination alone would be sufficient. In this case, the commenter is right that OSHA may sometimes overestimate costs.

General Methodological Issues—Comments on Costs Associated With Exposures Over the Preceding PEL

Many commenters argued that OSHA should have attributed the costs of reaching the preceding PEL of 100 μg/m³ to this standard (Document ID 2307, Attachment 8b, p. 16; 2195, p. 33; 1819, p. 2; 2375, Attachment 2, p. 65; 2307, Attachment 1, p. 2; 2379, Attachment 2, p. 9). For example, Stuart Sessions of Environomics, commenting on behalf of the ACC, stated that of the workers currently exposed over 50 μg/m³, two-thirds are exposed over 100 μg/m³, and that OSHA erred in excluding the costs of reducing those exposures to 100 μg/m³ (Document ID 2307, Attachment C, pp. 2-3).

OSHA's preliminary initial regulatory flexibility analysis (PIRFA) for the 2003 Small Business Advocacy Review (SBAR) panel included benefits and costs associated with future compliance with existing silica requirements on the basis that the rule would help improve compliance with the existing silica rules (OSHA, 2003a and 2003b) (Document ID 1685 and 0938, respectively). Upon further consideration, OSHA determined that a more fair and accurate measure of the benefits and costs of the proposed rule was to begin the analysis with a baseline of full compliance with existing requirements; OSHA has retained this approach for the final rule. The Agency offers three reasons in support of this approach. First, the obligation to comply with the preceding silica PEL is independent of OSHA's actions in this rulemaking. The benefits and costs associated with achieving compliance with the preceding silica rules are a function of those rules and do not affect the choice of PEL. The question before the Agency was whether to adopt new rules, and its analysis focused on the benefits and costs of those new rules. Second, the Agency's longstanding policy is to assume 100 percent compliance for purposes of estimating the costs and benefits of new rules, and to assume less than full compliance with the existing OSHA rules would be inconsistent with that policy. Finally, assuming full compliance with the existing rules is in keeping with standard OSHA practice in measuring the incremental effects of a new rule against pre-existing legal obligations. Reliance on costs that assume full compliance with both the preceding and proposed (new) OSHA rules makes it easier to compare the two regulatory schemes.

Some commenters also disagreed with the way OSHA attributed costs to employers whose workers were being exposed to silica at levels greater than the preceding PEL of 100 μg/m³ (Document ID 3251, p. 2; 3296, p. 2; 3333, p. 2; 3373, p.2; 2503, p.2; 2291, p. 16; 4209, p. 111). These commenters argued that OSHA did not attribute any costs to reaching 50 μg/m³ to employers whose employees were exposed above 100 μg/m³. They argued that OSHA instead assumed that the costs and controls necessary to reach 100 μg/m³ would also be sufficient to reach a level of 50 μg/m³, and as discussed above, that OSHA did not account for those costs because reducing exposures to the preceding PEL of 100 μg/m³ was already required before this rulemaking. The American Foundry Society (AFS) argued that OSHA reduced costs by two-thirds “under the logic that employers must comply with the current PEL and the proposal does not add any existing obligation” (Document ID 2379, Appendix 1, p. 10). AFS added that OSHA's underestimation of costs in this manner was particularly severe because OSHA used outdated data that showed more employees with exposures over 100 μg/m³, whereas more recent data would show fewer employees with exposures above 100 μg/m³ and more with exposures between 50 and 100 μg/m³. Had OSHA used this updated data, in AFS's estimation, the Agency would have identified more employers needing to install additional engineering controls and thus there would be additional costs that were not accounted for in the PEA (Document ID 2379, Attachment 3, pp. 9-10). ACC made a similar point, saying that as a result of OSHA's methodology, “the exposure reduction costs for the estimated 81,000 workers now exposed above 100 μg/m³ are not taken into account by OSHA on either a full cost basis or an incremental cost basis” (Document ID 2308, Attachment 9, pp. 2-3).

In addition URS, among others, argued that “OSHA fails to account for the non-linear costs associated with each incremental reduction in silica concentrations,” meaning that URS believed that it is more costly to achieve additional reductions in exposure as exposures are lowered. For example, according to URS's contention, it would be more costly to reduce exposures from 75 μg/m³ to 50 μg/m³ than from 125 μg/m³ to 100 μg/m³ (Document ID 2308—Attachment 8, p. 11; 2291, p. 16; 4209, p. 11; 2307, Attachment 2, pp. 181-182; 2379, Attachment 2, p. 9; 3487, p. 13).

OSHA has several responses to these criticisms. In response to the criticism that OSHA overestimated the number of workers with exposure levels above 100 μg/m³ as a result of using outdated data, the Agency has updated the exposure profile used to develop the final analysis of costs. This update is described previously in Chapters III and IV of the FEA. As a result of this update, OSHA found that, in the aggregate, the percentage of workers in general industry and maritime exposed to silica levels between 50 μg/m³ and 100 μg/m³ rose from 33 percent as estimated in the PEA to 42 percent. And, as the commenters noted would be the case, the percentage exposed at levels above 100 μg/m³ fell from 67 percent to 58 percent. OSHA has updated this analysis to incorporate these data and has estimated costs for these additional workers whose exposures fall between 50 μg/m³ and 100 μg/m³. The revised distribution also shows that of those workers with exposures above the new PEL, 41 percent are exposed between the new PEL and the preceding general industry PEL with an average exposure level of 70 μg/m³, 29 percent are exposed between the preceding PEL and 250 μg/m³ with an average exposure level of 156 μg/m³, and 30 percent are exposed above 250 μg/m³ with an average exposure level of 485 μg/m³. Where an industry submitted more recent exposure data or information about exposure distributions within their industry, OSHA was able to show that its final exposure distribution was roughly equivalent (see Chapter IV of the FEA).

The technological feasibility analysis (presented in Chapter IV of the FEA) describes the controls necessary for reducing exposures from the highest levels observed in an industry's exposure profile to the new PEL. In all application groups except two (asphalt paving products and dental laboratories), the highest observed exposures were above the preceding PEL. With the exception of hydraulic fracturing, the technological feasibility analysis did not distinguish between the controls necessary to meet the preceding general industry PEL of 100 μg/m³ and those necessary to meet the new general industry PEL of 50 μg/m³. Instead, the technological feasibility analysis simply listed the controls necessary for those employers whose employees had the highest baseline exposures to significantly reduce exposures and, in most operations, meet the new PEL.

It was not necessary for OSHA to distinguish between controls necessary to achieve the preceding PEL and those necessary to achieve the new PEL in order to demonstrate the technological feasibility of achieving a PEL of 50 μg/m³. Such a distinction would have been difficult because, from a baseline of uncontrolled exposures, the controls necessary to meet the preceding and new PELs are difficult to distinguish. For example, if there are two different controls necessary to fully meet the new PEL, then it is logically possible that two different establishments may achieve an exposure level at or below the preceding PEL in different ways. One establishment may have excellent housekeeping but poorly maintained LEV. Another may have well maintained LEV but poor housekeeping. For individual cases, there is not a simple demarcation of which controls of the total set of controls are necessary to achieve the new PEL when only the exposure level and not the controls already in place are known. Nor, as discussed above, is it the case that a control, once installed, will always provide identical protection. Two otherwise equal facilities may have the same installed controls but different exposure levels because of the quality of the maintenance of the system.

For the purposes of costing engineering controls for general industry and maritime in the PEA, OSHA assigned all of the costs for meeting a PEL of 50 μg/m³—including the costs of controls necessary to meet the preceding PEL of 100 μg/m³—to all workers with exposure levels between 50 μg/m³ and 100 μg/m³. However, OSHA assigned no costs in the PEA to employees whose exposures exceeded the preceding PEL. This approach would be accurate for both those above and below the preceding PEL only if the exact same controls would be needed to control exposures in both situations and these controls would always yield an exposure level below the preceding PEL. However, as discussed in the previous section on proportionality of costs, OSHA has determined that this is not typically the case. There exist multiple kinds of controls and the actual application and operation of the control can differ. The approach applied in the PEA applied more controls than will typically be needed where exposures are below the preceding PEL and thus overestimates costs in these situations, but then assigns no costs for achieving the new PEL where exposures are above the preceding PEL. In the latter situation, it can reasonably be expected that, in most cases, some costs would be incurred to meet the new PEL even after the preceding PEL is met and therefore the PEA methodology underestimated costs in those situations. Although these over- and under-estimates are partially offsetting, OSHA acknowledges that any over-estimates of cost do not necessarily offset the potential under-estimates of costs.

OSHA has therefore decided to adopt an approach to the estimation of costs different from that adopted in the PEA. In the FEA, OSHA relied on data available in the rulemaking record to both correct the overestimate of costs for those below the preceding PEL and, as many industry commenters urged, estimate the costs necessary to meet the preceding PEL as well as the new PEL for those above the preceding PEL.

To be clear, these data still do not enable OSHA to distinguish between the exact controls needed to get from uncontrolled exposures to the preceding PEL and those needed to get from the preceding PEL to the new PEL on an industry-by-industry and occupation-by-occupation basis. However, the data do enable OSHA to show that the majority of the costs of controlling silica exposures are incurred in order to reduce exposures from uncontrolled levels to the preceding PEL. OSHA will then assume that 50 percent of the costs incurred will be to implement the controls necessary to get from the uncontrolled situation to the preceding PEL and 50 percent to implement the controls necessary to go from the preceding PEL to meeting the new PEL. If, in fact, a majority of the costs are incurred in order to reduce exposures to the preceding PEL, the assumption that attributes 50 percent of costs to going from the preceding PEL to the new PEL will overestimate the true costs for establishments with exposures at the preceding PEL or between the preceding PEL and the new PEL.

In order to assess whether the majority of the costs are necessary to meet the preceding PEL, OSHA first examined what kinds of exposures are associated with the uncontrolled situations that served as the starting point for the estimates of needed controls in the technological feasibility analysis. The average level of exposure across all of general industry for employees with exposure exceeding the preceding PEL is over 300 μg/m. Thus, on average, across all industries the uncontrolled situation involves high levels of exposure, commonly more than 3 times the preceding PEL.

In general, to reduce exposures from over 2.5 times the preceding PEL to the preceding PEL, employers would have to implement some measure or measures, and those measures would be the ones that provide the greatest reduction in silica exposures and therefore control most of the silica exposures in the facility. In most cases this will be a working LEV system or some form of worker isolation. Measures like improved housekeeping cannot reduce exposures from the levels observed in uncontrolled exposure situations to the preceding PEL. OSHA reviewed industry-by-industry and occupation-by-occupation cost estimates for engineering controls and found that, on average 63 percent of the costs were for LEV, 23 percent were for housekeeping, and 16 percent were for other controls, most commonly wet methods (based on OSHA, 2016). In many cases, where wet methods were applicable, wet methods represented the majority of the costs and there were not significant LEV costs. As a result, 79 percent of the costs of controls, on average, are attributable to either wet methods or LEV. The combination of LEV or wet methods with some improvement in housekeeping (though not the improvements necessary to meet the new PEL) will constitute the majority of costs for virtually all occupational categories. Some improvement in housekeeping will typically also be required to meet even the preceding PEL. While employers can probably meet the preceding PEL with less than ideally maintained LEV systems, improvements in maintenance will not reverse the conclusion that the majority of the costs are incurred to meet the preceding PEL. This is the case because on average 63 percent of engineering control costs are necessary to reach the preceding PEL and some housekeeping costs will also be necessary, leaving a significant percentage of expenditures above 50 percent of the costs available for improved maintenance.

To confirm the findings of this cost-spreadsheet-based analysis of where the majority of the costs are incurred, OSHA reviewed industries where good data are available on controls in both uncontrolled situations and situations with exposures between the new and the preceding PEL. OSHA examined the exposures and controls in eight ferrous sand casting foundry facilities. In these eight facilities, four had relatively few workers exposed above 50 μg/m³, and the other 4 had many exposures over 100 μg/m³. OSHA found that those facilities with most exposures over 100 μg/m³ generally had little or no LEV (relying instead on general ventilation), poor housekeeping, no enclosures for workers, and poor maintenance. The foundries where silica dust was better controlled generally had working LEV systems, good housekeeping that kept surfaces free of silica dust, and good maintenance practices. This indicates that LEV and some housekeeping are essential to meeting the preceding PEL. OSHA also examined data on all exposures with control descriptions. These data showed that exposures above 250 μg/m³ occurred in uncontrolled situations or situations in which controls, though installed, were not in use. In situations where exposures were between the preceding and new PELs, most exposures showed some controls in place, normally LEV, but not all controls recommended. In some cases there were no controls in place. These generally represented situations in which exposures were much lower than the typical uncontrolled situations and such facilities would not normally need the full controls necessary to go from very high levels of exposure to the new PEL (See Exhibit: Descriptions of Control, available in Docket OSHA-2010-0034 at www.regulations.gov ).

Based on these findings, OSHA determined that the majority of costs are incurred in order to implement controls necessary to get from an uncontrolled situation to the preceding PEL. However, OSHA developed cost estimates for engineering controls based on the conservative assumption that 50 percent of the total costs of going from an uncontrolled situation to the new PEL is incurred in order to reach the preceding PEL and the remaining 50 percent are incurred to reach the new PEL. For example, in the cut stone industry 63 percent of those exposed above the new PEL are also above the preceding PEL and 37 percent are below the preceding PEL but above the new PEL. The total cost to the cut stone industry of going from uncontrolled exposure to the new PEL is $17.7 million. With OSHA's assumption that half of the costs of going from an uncontrolled situation to the new PEL is incurred in order to reach the preceding PEL, then the cost for those employers with employees exposed above the preceding PEL would be 63 percent of $17.5 million times 0.5, which equals $5.5 million. The cost for those below the preceding PEL would be 37 percent of $17.7 million times 0.5, which equal $3.3 million. The total cost of going from the preceding PEL to the new PEL in the cut stone industry is therefore the sum of these two calculations: $8.8 million. This will overestimate the costs of reaching the new PEL, given the majority of the costs are incurred to implement controls necessary to reach the preceding PEL.

As presented in more detail below, this approach results in a total annualized cost estimate for general industry and maritime engineering controls of $225 million. Fortunately, this cost estimate is not highly sensitive to the allocation percentage chosen. Each decrement of 5 percentage points changes the engineering control costs by approximately 5.5 percent. Thus, for example, if 65 percent of the costs are necessary to go from the preceding PEL to the new PEL, then the annualized cost estimate for engineering controls would rise to $261 million per year.

Accounting for Costs of Downtime

Some commenters suggested that OSHA failed to account for the downtime that installing engineering controls or performing an initial through cleaning would require (e.g., Document ID 2368, p. 13 for engineering controls; Document ID 2379, Attachment 2, p. 16 for initial thorough cleaning).

Almost all firms need downtime occasionally in order to perform general maintenance, inventory, or other tasks. In the final rule, OSHA has extended the compliance date for general industry from one year to two years. This will allow almost all employers to schedule work that might require downtime to install, improve, or maintain controls that they determine are necessary to meet the new PEL or to perform the initial thorough cleaning at times when they would already need scheduled downtime for other purposes. Therefore, OSHA has determined that there will be no additional costs incurred for downtime in order for employers to install engineering controls or to perform the initial thorough cleaning.

Technological Change

One commenter, Dr. Ruth Ruttenberg, testifying for the AFL-CIO, argued that OSHA had overestimated costs by failing to consider technological change:

Technological improvements—both engineering and scientific—are constantly occurring, especially when the pressure of a pending or existing regulation provide a strong incentive to find a way to comply at a lower cost. . . . These improvements are well-documented following the promulgation of rules for vinyl chloride, coke ovens, lead, asbestos, lock-out/tag-out, ethylene oxide, and a host of others (Document ID 2256, Attachment 4, p. 2).

Dr. Ruttenberg recognized that OSHA, in the PEA, already predicted some “technological and cost-saving advances with silica,” such as expanding the use of automated processes and developing more effective bag seals, but criticized OSHA for not accounting for those cost savings in its analysis:

Technological improvements are as sure a reality—based on past experience and academic research—as overestimation of cost and underestimate of benefits are in an OSHA regulatory analysis. More than 40 years of OSHA history bear this out (Document ID 2256, Attachment 4, p. 3).

When promulgating health standards, OSHA generally takes an approach in which cost estimates and economic feasibility analyses are based on the technologies specified in the technological feasibility analysis. This is a conservative approach to satisfying OSHA's legal obligations to show economic and technological feasibility. As a result, the Agency does not account for some factors that may reduce costs, such as technological changes that reduce the costs of controls over time and improvements in production that reduce the number of employees exposed. As pointed out in the PEA, and from the examples described in the “Total Cost Summary” at the end of this chapter, some past experience suggests that these factors tend to result in OSHA's costs being overestimated. OSHA considers the primary purpose of the cost estimate to be to provide a basis for evaluating the economic feasibility of the rule, and OSHA has determined that for this rulemaking, feasibility is most accurately demonstrated by using an approach that does not account for the potential impacts of future technological changes.

General Methodological Issues: Number of Workers Covered by a Control PEA Estimates

The cost calculations in the PEA included estimates of the number of workers whose exposures are controlled by each engineering control. Because working arrangements vary within occupations and across facilities of different sizes, there are no definitive data on how many workers are likely to be covered by a given set of controls. In many small facilities, especially those that might operate only one shift per day, some controls will limit exposures for only a single worker. Also, small facilities might have only one worker in certain affected job categories. More commonly, however, and especially in the principal production operations, several workers are likely to derive exposure reductions from each engineering control.

The PEA relied on case-specific judgments of the number of workers whose exposures are controlled by each engineering control (see Table 3-3 in ERG, 2007b, Document ID 1608). The majority of controls were estimated to benefit four workers, based on the judgment that there is often multi-shift work and that many work stations are shared by at least two workers per shift. The costs of some types of equipment that protect multiple employees, such as HEPA vacuums, were spread over larger groups of employees (e.g., six to eight workers). In the PEA, the average number of workers affected represented an average across all establishments, large and small.

Comments and Responses

Some commenters questioned OSHA's estimate of the number of workers whose exposures could be controlled per newly added or enhanced control. OSHA's PEA most commonly estimated that four workers would have their exposures reduced for each new or enhanced engineering control. Dr. Ronald Bird, testifying for the Chamber of Commerce, argued that OSHA's estimates were simply arbitrary assumptions (Document ID 2368, p. 14). Stuart Sessions, testifying for the ACC, argued that the use of a single standard crew size of four led OSHA to underestimate costs and economic impacts for smaller establishments, at which, he argued, “there are virtually never as many as four overexposed workers in any job category, and it is simply impossible that one application of a package of controls in this situation could protect as many as 4 overexposed workers on average” (Document ID 4231, Attachment 1, p. 6).

The approach OSHA used was intended to represent the average number of employees affected by a given set of controls. Larger establishments may have more than four workers whose exposures are reduced by a single control, and smaller establishments may have fewer than four. However, OSHA agrees that this approach may result in an underestimate of costs for the smallest establishments. Because it is particularly important to consider the costs to the smallest establishments, OSHA has reduced the number of employees whose exposures are reduced per control by half for establishments with fewer than twenty employees, so that in those small establishments a given control is assumed to reduce exposures for two workers instead of four as assumed in the PEA. Because larger establishments may have greater numbers of employees whose exposures are reduced per control, this change may result in an overall overestimation of costs. (In the PEA, the overestimation of costs for larger facilities was partially offset by the underestimation of costs for smaller establishments. This is no longer the case in the FEA.) OSHA nevertheless believes the revised approach used in the FEA is better than the approach used in the PEA for purposes of capturing economic impacts on smaller establishments, even though it may result in aggregate costs being overestimated.

Variability

Some commenters argued that both OSHA's technological feasibility and cost analyses were flawed because OSHA neglected to address the day-to-day variability of exposure measurements. By failing to address the issue of variability, these commenters argued, OSHA grossly underestimated the costs of engineering controls. These commenters reported that silica exposures would have to be controlled to levels considerably lower than the proposed (new) PEL in order to account for the variation in exposures across jobs and from day to day (e.g., Document ID 2307, Attachment 2, p. 202; 2308, Attachment 7, p. 2; 2308, Attachment 8, p. 6; 2379, Attachment 4, p. 1; 2291, p. 11; 2195, pp. 26-27; 2503, p. 2; 2222, Attachment 1, p. 1). For example, in response to a written question about the activities in which employers were able to achieve the proposed (new) PEL “most of the time,” AFS objected to the premise of the question, noting that “[s]everal foundries have received citations for exposures above the current PEL on operations or tasks for which the proposed PEL is achieved most of the time” (Document ID 2379, Appendix 1, p. 18). AFS argued that OSHA's non-compliance model of enforcement requires employers to reduce average exposures to half the PEL in order to have confidence that exposures will never exceed the PEL (Document ID 2379, Appendix 2, p. 29). The Asphalt Roofing Manufacturing Association (ARMA) made a similar point and said that the majority of asphalt roofing plants operated by its members have some exposures over the PEL of 50 μg/m³, even if it's a “relatively small incidence” (Document ID 2291, p. 11).

Both AFS and ARMA offered estimates of the magnitude of this variability by measuring the statistical variance of exposures. AFS stated that to assure 84 percent confidence in compliance with the preceding PEL, the mean exposures in some specific jobs in specific foundries would need to be below half that PEL, and that the “mean level necessary to achieve the 95 percent confidence of compliance could not be determined but is significantly below one half the PEL” (Document ID 2379, Appendix 1, p. 23).

ARMA examined the distribution of silica exposures in over 1,300 samples from 57 asphalt roofing facilities. These data showed that even though the median exposures for all jobs were below the new action level of 25 μg/m³, a total of 9 percent of all samples were above the new PEL of 50 μg/m³ (Document ID 2291, p. 5, Table 1). ARMA also provided an estimate of the “lowest strictly achievable level” (meaning a level not to be exceeded more than 5 percent of the time) which varied by job classification from 67 to 310 μg/m³ (Document ID 2291, p. 9, Table 2).

One serious problem with the ARMA analysis is that the discussions of variability and the estimates of mathematical variance are based on results either from different facilities with potentially different levels of controls or from all job categories within one facility. The key issue for assessing the importance of variability is the variance within a given job category in a specific establishment with specific controls. The methodology employed is such that even if individual job categories or individual facilities had no variance, pooling data across facilities would create variance.

ARMA estimated that sufficiently controlling variation would require investment in capture vents, duct work, and dust collection systems costing up to $2.1 million each in initial costs per manufacturing line (Document ID 2291, p. 12). AFS did not provide a cost estimate solely for sufficiently controlling variation.

The AFL-CIO disagreed with industry's arguments and instead argued that the best way to reduce variability was not simply to add additional engineering controls because, as explained earlier in the discussion of URS's comments on the per-worker cost basis, overexposures are not random:

The worker-to-worker variation is explainable and controllable: Workers use different methods, they may take different positions relative to ventilation systems, they may use different work practices, and they may be subject to fugitive emissions (carryover from adjacent silica emitting processes). These differences in conditions can be observed by the industrial hygienist collecting the air sample, compared to exposure levels, and changed. Day-to-day variation for the same worker is caused by variation in materials, ventilation systems, production rate, and adjacent sources showing such variation. Sometimes these variations can be large, based on breakdowns of ventilation, process upsets and blowouts (Document ID 4204, p. 40).

OSHA's enforcement policies are discussed in Chapter IV of the FEA and in this preamble. Variability of exposures is potentially a cost issue when there are technologically feasible controls that have costs not otherwise accounted for that could further reduce environmental variability. If it is not technologically feasible to reduce variability then there will be no further costs. For example, if an employer has installed all feasible controls, there are no additional costs for engineering controls because there are no additional controls to purchase, regardless of variability. On the other hand, an employer who has a median exposure level of 80 percent of the PEL with frequent excursions above and who could feasibly reduce variability would be required to do so.

As noted above, those (AFS, ARMA) who argued that OSHA had underestimated costs by failing to account for exposure variability, in general, assumed that the best approach to reducing variability would be to increase the levels of LEV to reduce the average exposure level to half of the PEL or less, without examining the origin of the variability.

OSHA agrees with the AFL-CIO that variability in exposure is likely controllable by examining the origins of the variability. One origin is poor work practices. To improve work practices, employers could observe work practices when monitoring takes place; determine which work practices are associated with high exposures; and modify those work practices found to lead to high exposures. Variability can also be the result of a failure of controls not functioning properly, either resulting from sudden failures or from gradual deterioration of performance over time. The latter can be prevented by good maintenance.

Both in its cost assessment for the proposal and in the modifications made for this final rule, OSHA has taken account of the costs necessary to reduce unusual and exceptionally high exposure levels and thus reduce some sources of variation. As discussed in the cost of ancillary provisions, OSHA has estimated costs for exposure monitoring that include the time for observation of the worker. OSHA has also estimated costs for training to assure good work practices, and has increased the estimated length of training in general industry to ensure that the time is sufficient for training on work practices. In this section, OSHA has costed LEV, LEV maintenance, and the need for replacement LEV to assure that the LEV will function properly. OSHA has therefore already accounted for a variety of costs associated with steps that can be taken to reduce variability in exposures.

Substitution of Low- or Non-Silica Inputs

PEA Estimate

For several industries, employers might lower silica exposures by substituting low- or non-silica inputs for existing inputs. While this option can be an extremely effective method for controlling silica exposures in many industries, OSHA did not cost this option in the PEA. OSHA determined that there were often complicating factors that restricted the potential for broad substitution of non-silica-containing inputs for silica-containing inputs throughout the affected industries. It is possible that the same product quality cannot be maintained without using silica. Some products made with substitute ingredients were judged to be inferior in quality and potentially not viable in the market. In addition, a substitute silica ingredient might introduce adverse health risks of its own. Further, in several instances, the availability of reasonably inexpensive alternative non-silica ingredients was well known but the alternative was not selected as a control option by most firms. In light of these concerns, OSHA decided not to include the option of non-silica substitutes in estimating the cost of the proposed rule.

Comments and Responses on Substitution

Some commenters complained that OSHA's analysis did not account for the costs of substitution (Document ID 2264, Attachment 1, p. 27; 2379, Attachment 2, p. 6; 3485, p. 25; 3487, p. 17).

OSHA considered the comments on the issue but has decided to adhere to the approach taken in the PEA. OSHA did not take account of the costs of substituting other substances for silica, because, while such substitution might have substantial benefits and avoid the need for engineering controls, OSHA determined that, in most situations, substitution is not the least costly method of achieving the proposed or new PEL (Document ID 2379, Attachment 2, p. 6). As a result, OSHA's final cost analyses do not account for the possibility that firms would choose to substitute for substances other than silica. To the extent that substitutes are the least costly solution in some situations, OSHA has overestimated the costs.

Cost of Air Quality Permit Notification

The Agency received comments suggesting that foundries and other manufacturing plants would be required by the Environmental Protection Agency (EPA), or other federal or state environmental authorities, to incur an administrative cost to ensure their systems are compliant with relevant EPA regulations. Commenters expressed concern that the permitting process itself could be a major undertaking, made worse by difficult compliance deadlines. Given that the final rule provides extra time for planning and permitting, OSHA has examined the potential impacts of the new rule and finds that the commenters are overstating the potential for such costs. The argument for significant permitting costs was typically combined (e.g., Document ID 2379, Appendix 3) with an argument that the Agency underestimated the amount of ventilation required to comply with the final rule; comments on ventilation requirements are dealt with in great detail elsewhere in this chapter.

Upon investigation, while OSHA agrees that it would be appropriate to recognize an administrative burden with respect to the interfacing environmental regulations, the Agency believes that many of the commenters' concerns were overstated. First, many control methods needed to comply with the final rule will not require alterations to existing ventilation systems. As discussed earlier in Chapter V of the FEA, work practices, housekeeping and maintenance are important components in controlling exposures; in many cases existing ventilation, as designed and permitted with the environmental authority, is adequate, but needs to be maintained better. In addition, most establishments, particularly smaller ones, will continue to have particulate emissions levels that fall below the level of EPA permit requirements. In the case of large facilities that do not, the changes will be on a sufficiently small scale that they will not require elaborate repermitting, but will only require minor incremental costs for notifying the environmental authorities, or in some cases, submitting a “minor” permit (see http://www2.epa.gov/nsr and http://www2.epa.gov/title-v-operating-permits ). Taking into account the preceding silica PEL and the estimate that baghouses will capture 99 percent of silica emissions (Document ID 3641, p. VII-19), OSHA concludes that it is unlikely that facilities will encounter a need for significant air permit modifications.

The Agency recognizes, however, that there will be minor incremental costs for notifying environmental authorities. While many establishments in the United States may have no requirement to do so, the Agency has conservatively assumed that all establishments with twenty or more employees in most industries will need to dedicate a certain amount of time to preparing a one-time notification to environmental authorities to ensure that their air permits accurately reflect current operating conditions. OSHA has determined that small establishments would generally lack the large scale industrial facilities requiring permits, and that the few that might require such permits would be balanced out by the likely inclusion of medium establishments that do not actually require permits for their emissions. The industries excluded were those that generally lack large scale industrial facilities, or that do not produce a concentrated, as opposed to diverse or unconsolidated, emission source. The excluded industries were hydraulic fracturing, shipyards, dental equipment and labs, jewelry, railroads, and landscaping.

To allow for adequate administrative time for creating and submitting the notification, at those facilities that could potentially incur costs, OSHA allocated 20 hours to establishments with 20 to 499 employees and 40 hours to establishments with 500 or more employees. A manager's loaded hourly wage rate of $74.97 was applied to estimate the cost to employers (BLS, OES, 2012, Document ID 1560). The costs per establishment were estimated at approximately $1,500 per medium establishment and $3,000 per large establishment. Because both new permit applications and permit modifications are minor administrative chores, OSHA's cost estimates are sufficient to cover either case.

Costs for Specific Engineering Controls

Ventilation Costs

PEA Estimates

In the PEA, OSHA determined that at many workstations, employers needed to improve ventilation to reduce silica exposures. The cost of ventilation enhancements estimated in the PEA generally reflected the expense of ductwork and other equipment for the immediate workstation or individual location and, potentially, the cost of incremental capacity system-wide enhancements and increased operating costs for the heating, ventilation, and air conditioning (HVAC) system for the facility.

In considering the specific ventilation enhancements for given job categories the PEA estimated the type of LEV and the approximate quantity in cubic feet per minute (cfm) of air flow required to reduce worker exposures.

To develop generally applicable ventilation cost estimates for the PEA, a set of workstation-specific and facility-wide ventilation estimates were defined using suggested ventilation approaches described in the American Conference of Governmental Industrial Hygienists (ACGIH) Industrial Ventilation Manual, 24th edition (Document ID 1607). With the assistance of industrial hygienists and plant ventilation engineering specialists, workstation estimates of cfm were derived from the ACGIH Ventilation Manual, and where not covered in that source, from expert judgements for the purpose of costing LEV enhancements (Document ID 1608, p. 29).

Over a wide range of circumstances, ventilation enhancement costs, which included a cost factor for HEPA filters and baghouses, where needed, varied from roughly $9 per cfm to approximately $18 per cfm (Document ID 1608, p. 29). Because of a lack of detailed data to estimate the specific ventilation installation costs for a given facility, an estimate of the likely average capital cost per cfm was used and applied to all ventilation enhancements. Based on discussions with ventilation specialists, $12.83 per cfm was judged to be a reasonable overall estimate of the likely capital costs of ventilation enhancements (Document ID 3983, p. 1).

OSHA applied the per-cfm capital cost estimate to estimated cfm requirements for each workstation. By using the unit value of $12.83 per cfm, the cost estimates for each ventilation enhancement included both the cost of the LEV enhancement at the workstation and the contribution of the enhancement to the overall facility ventilation system requirements. That is, each ventilation enhancement at a workstation was expected to generate costs to the building's general ventilation system either by requiring increased capacity to make up for the air removed by the LEV system or to filter the air before returning it to the workplace.

For operating costs, engineering consultants analyzed the costs of heating and cooling system operation for 12 geographically (and therefore, climatologically) diverse U.S. cities. The analysis, presented in Table 3-2 in the ERG report (Document ID 1608, p. 30), showed the heating and cooling British Thermal Unit (BTU) requirements for 60-hours-a-week operation (12 hours a day, Monday through Friday) or for a continuous 24-hour-a-day, year-round operation, with and without recirculation of plant air. Facilities that recirculate air have much lower ventilation system operating costs because they do not need to heat or cool outside air to comfortable inside temperatures.

In the PEA, ventilation operating costs were based on a weighted average of the costs of four operating scenarios: (1) No recirculated air, continuous operation; (2) no recirculated air, operating 60 hours per week; (3) recirculated HEPA filtered air, continuous operation; and (4) recirculated HEPA filtered air, operating 60 hours per week. These scenarios were chosen to reflect the various types of operating system characteristics likely to be found among affected facilities. The weights (representing the share of total facilities falling into each category) and operating costs per cfm for each of these scenarios are shown below in Table VII-11-1:

The national average annual operating cost per cfm was estimated to be $2.22. This estimate was a weighted average of the operating costs for facilities that recirculate air and those that require make-up air. The operating costs for HEPA-filter recirculated air were estimated at $0.50 per cfm for facilities operating 60 hours per week and $1.40 per cfm for those continuously operating 24 hours per day. The operating costs for facilities that do not recirculate air were $5.78 per cfm for those operating 60 hours per week and $15.55 per cfm for those operating continuously. In generating these estimates, it was judged that 80 percent of facilities would recirculate airflow and 20 percent would not, and that 75 percent within each group operate for 12 hours per day on weekdays, with the remainder operating continuously, year-round, for 24 hours a day.

OSHA also added a maintenance factor to the operating cost estimates, which was 10 percent of the capital cost investments of $12.83 per cfm for ventilation systems. As a result, the total annual costs per cfm, excluding annualized capital costs, were estimated to be $3.50 (weighted average operating costs of $2.22 plus annual maintenance costs of 10 percent of $12.83).

Underlying the cost results was the assumption that, over the course of the proposed one-year compliance period for engineering controls, employers would schedule installation of ventilation to minimize disruption of production, just as they would with any modification to their plants.

Comments and Responses on Local Exhaust Ventilation Issues: Need for a Complete New System

Local exhaust ventilation represents one of the major costs associated with engineering controls in both the PEA and in the FEA. Commenters raised issues both about OSHA's PEA estimates of the unit costs of LEV and about the adequacy of OSHA's estimates of the volume of LEV that would be needed to adequately control silica exposures.

URS, testifying on behalf of ACC, argued that any firm that would be utilizing LEV to meet a PEL of 50 μg/m³ would need to remove any existing LEV and install an entirely new LEV system. Thus, in URS's estimation, there would be no incremental addition of LEV. In a discussion of the URS approach during OSHA's informal public hearings, OSHA asked the URS representative to confirm that his organization commented that when a majority of workers are exposed over the PEL, the existing controls must be replaced instead of enhanced:

MR. BURT: I want to be sure I understand what that's saying. Let's say you encountered a situation in which there were four workers. Two were exposed at 35, two at 60. You would scrap all of the controls and start over again. That's what it seems to be saying.

[. . .]

MR. WAGGENER: [Y]es, that they would need to be replaced with a more adequate system (Document ID 3582, Tr. 2109-2110).

OSHA's examination of the spreadsheets URS provided documenting its independently developed cost estimates shows that, in all cases where any employee in an establishment was exposed above 50 μg/m³, URS assumed that the employer would need to install a complete new LEV system and included the costs for installing and operating this entirely new system (Document ID 2308, Attachment 8, pp. 13-14).

John Burke from OSCO Industries took a different approach to the question that better illustrates the options that OSHA believed to be available when it developed the PEA estimates:

A single large dust collector is probably already handling the exhausting of the entire sand conditioning system. Most likely all the pick-up points referenced in the economic analysis already have suction being applied and yet there is still an overexposure. What do you do and how much is that going to cost? If the sand system operator is overexposed then you could first evaluate work practices controls. If work practice controls are unsuccessful and additional suction is needed, that suction is going to be very expensive! If your environmental operating permit allows it you may be able to tweak the performance of the dust collector. There may be some things you can do to tweak the capacity of your existing dust collector to bring it up to exactly its permitted air volume or you might have to enlarge your dust collector (Document ID 1992, p. 6).

OSHA agrees with Mr. Burke. As discussed above, there are usually a wide variety of ways to improve existing controls before removing and reinstalling an LEV system. As a result, OSHA finds the URS approach unrealistic and likely to significantly overestimate costs.

Comments and Responses on the Volume of Controls Needed

One commenter, URS, questioned OSHA's estimates of the volume of additional LEV that would be needed to comply with the standard. URS, testifying for ACC, reported that OSHA's estimates in the PEA were too low as compared to the recommendations in Table 6-2 of the ACGIH Ventilation Manual (28th Edition). They criticized OSHA's estimates saying that OSHA routinely underestimated required capture velocities by at least a factor of two for particles with high (conveyor loading, crushing) or very high (grinding, abrasive blasting, tumbling) energies of dispersion (Document ID 2308, Attachment 8, pp. 12 and 14). URS said that “the capture velocities for LEV systems in OSHA's models were often based on the minimum recommended velocity,” that OSHA's estimated additional LEV was too low because “the ACGIH capture velocity values used by OSHA were first developed and published many years ago” and were not sufficient to control dust to the levels OSHA is now proposing, and that “the velocity values used in OSHA's cost model are most likely undersized by a factor of 2 or more” (Document ID 2308, pp. 11-12). Other than its own supposition, URS did not identify an alternative source for OSHA to use as the basis for estimates of ventilation capacity necessary to control silica exposures.

In response to these comments, and in order to determine whether ACGIH recommendations had changed between the 24th edition (which OSHA used to develop estimates in the PEA) and the more recent 28th edition, OSHA checked its estimated volumes against those in the more recent ACGIH Ventilation Manual (Chapter 13 in the 28th edition (Document ID 3883)). In the 24th edition of the Manual, ACGIH provided a single recommendation for ventilation capacity rather than a range. In the PEA, OSHA adopted this recommendation and did not choose a value from within a range of values. The 28th edition of the Manual provides more flexibility in system design and specification and incorporates a recommended range. However, OSHA determined that the ventilation capacity estimates did not change between the 24th edition of the Manual and the 28th edition. In most cases, OSHA's estimated volumes were identical to those recommended by ACGIH. The exceptions were situations in which ACGIH provided no recommendation (in which case OSHA relied on recommendations of industrial hygienists), and situations in which the technological feasibility analysis recommended additional volumes of LEV capacity above what employers were typically using. In the latter situations, OSHA estimated that an additional 25 percent of the ACGIH specification would be necessary to adequately control silica exposures (See Exhibit: Comparison of OSHA CFM Volumes to ACGIH Values, available in Docket OSHA-2010-0034 at www.regulations.gov ).

URS argued that silica was different from other substances LEV might be applied to in ways that would call for higher volumes of ventilation (Document ID 2308, Attachment 8, p. 14). However, in all cases involving silica (such as shake-out stations), the ACGIH Manual recommended the volumes used by OSHA and criticized by URS.

OSHA's estimates of the ventilation capacity necessary to control silica exposures relied on a detailed set of recommendations provided by ACGIH while URS simply asserted that these values are “most likely undersized by a factor of 2 or more” without providing additional evidence to support this (Document ID 2308, Attachment 8, p. 12). Based on these findings, OSHA has determined that the ACGIH recommendations constitute the best available evidence and has maintained the estimates of ventilation capacity from the PEA for the FEA.

Comments Providing Alternative Ventilation System Cost Estimates

Other commenters provided much higher costs than OSHA's estimates but without providing any background to allow OSHA to put those costs in context. It is difficult for OSHA to evaluate a cost estimate without information on the size of the facility, the estimated volume of air, and the exposure levels before and after the LEV was installed.

The Interlocking Concrete Pavement Institute (ICPI) commented that OSHA underestimated compliance costs because “[o]ne ICP manufacturer reported that it could cost $150,000 to acquire and install highly efficient vacuum and water dust-control systems” and other manufacturers reported similarly high costs (Document ID 2246, p. 11). At the public hearings, OSHA sought clarification on the assumptions underlying the ICPI cost estimate, and the ICPI representative stated that $150,000 was a mid-range estimate. The representative also confirmed that this was the cost of an entirely new system:

MR. BLICKSILVER: [D]oes this actually represent the incremental cost associated with complying with OSHA's proposed rule? . . . Or is this an overall cost for dust control in these manufacturing plants?

MR. SMITH: The latter (Document ID 3589, Tr. 4407-4409).

In a follow-up verbal exchange, OSHA requested that ICPI analyze its survey data to produce median values for the range of cost estimates and submit their analysis as a post-hearing comment (Document ID 3589, Tr. 4409). However, no ICPI comments appeared in the record following the Institute's testimony at the hearings.

Similarly, OSHA asked Mr. Tom Slavin, testifying for AFS, for additional information from AFS on the many cost estimates for individual foundries that it had included in its comments:

MR. BURT: You provide many examples of cost to specific foundries of specific activities. I would like to suggest that those can be most useful if we have data on the size of the firm in question, the type of foundry if that's appropriate, and what they were trying to accomplish with this effort.

Were they at 400 and trying to get to 100, at 100 trying to get lower? Something that puts it in context would again make these many, many helpful quotes much more useful.

Size is just critical, just because of the fact that when we don't know whether we're talking about 20 or 200 people in a foundry really affects what you want to do with those cost estimates. And that one's relatively simple, size of firm, type of foundry if you have it, what they were trying to do with that effort (Document ID 3584, Tr. 2773-2774).

Later in the exchange, OSHA requested information on “the components of [AFS's estimated cost per cfm of additional ventilation] that would be capital cost, installation cost, and then any other operating costs you have” (Document ID 3584, Tr. 2784). OSHA received no response to this request.

Unfortunately, it is almost impossible for OSHA to make use of commenters' estimates of costs or volume of LEV systems without information on the size of the facility and on what the resulting system accomplished in terms of reducing exposure levels. OSHA consistently requested this kind of information, but did not receive it. As shown in the discussion of alternative estimates of costs by small entity representatives during the SBAR Panel (discussed below), even estimates that appear higher than OSHA's average costs can be consistent with those costs when the full context for the estimates is examined.

Comments and Responses on Unit Cost per CFM

Many commenters thought that OSHA's unit costs for ventilation were too low. With respect to the annualized value of the capital costs plus operating and maintenance costs of $5.33 that OSHA used in the PEA, AFS stated:

The PEA uses an annual cost factor of $5.33 for ventilation, including ducting and bag house operation [...] is far below foundry experience. A group of foundry ventilation managers and ventilation experts estimated the annual cost per CFM at $20 for exhaust alone and another $6-10 for makeup air critical to achieving the lower PEL. The cost to meet the new U.S. Environmental Protection Agency (EPA) dust loading criteria increases the exhaust annual cost to $25 per CFM. Any new installation would be expected to design to the new criteria even if not yet required to do so for that specific jurisdiction (Document ID 2379, Appendix 3, p. 9).

URS, commenting on behalf of ACC, estimated the annualized cost of LEV to be $27 per cfm, and increased OSHA's original estimate of capital costs from $12.83 to $22 per cfm for the purpose of URS's cost estimate (Document ID 2308, Attachment 8, pp. 13-14).

Many other commenters from industry suggested unit costs for additional LEV. For example, AFS provided independent estimates of annualized costs of $20 to $25 per cfm and URS estimated $22 to $27 capital costs per cfm (Document ID 2379, Appendix 1, p. 45; 2308, Attachment 8, p. 14; 2379, Appendix 2, p. 13; 2503, p. 2; 2119, Attachment 3, p. 4; 2248, p. 8; 3490, p. 3; 3584, Tr. 2779).

OSHA agrees that there can be a wide range of both capital and operating costs associated with LEV. Capital costs will vary according to such factors as the exact nature of the ventilation (including the design of the slot, hood, or bagging station), the volume of materials to be handled by the ventilation, and the length of the ductwork necessary. OSHA also would like to clarify that, as shown in OSHA's spreadsheets (OSHA, 2016), where there are major structural changes associated with a control, such as automation, a new bagging station, or conveyor closure, these costs are estimated over and above the basic capital costs of LEV. Annual operating costs vary according to climate, hours of operation, and the extent to which air is recirculated. To examine these possible costs, OSHA reviewed the thoroughly documented LEV costs presented in its Final Economic Analysis for the Occupational Exposure to Hexavalent Chromium Standard (Document ID 3641). In that FEA, OSHA's estimates of the capital costs for LEV (updated to 2012 dollars) averaged more than $20 per cfm when major work station changes, such as automated bag slitting stations, were included in the cost of LEV. Ordinary additional LEV without major workstation changes was estimated to have an average capital cost of $9 per cfm in 2012 dollars. Operating costs in that rulemaking were estimated to be somewhat higher than estimated here, but combined annualized costs (capital plus operating costs) were approximately the same (See Exhibit: Analysis of LEV Costs from Hex Chrome, available in Docket OSHA-2010-0034 at www.regulations.gov ).

OSHA agrees that the capital costs of some kinds of LEV that involve significant workstation modifications or even automation can exceed $20 per cfm, but finds an average of $13.34 (in 2012 dollars) per cfm in capital costs to be reasonable given that some kinds of LEV installation can cost as little as $3 to $5 per cfm. OSHA also finds the operating cost estimates used in the FEA to be a reasonable average across a very wide variety of circumstances.

Housekeeping and Dust Suppression Costs

PEA Costs

For a number of occupations, the technological feasibility analysis in the PEA indicated that improved housekeeping practices were needed to reduce silica exposures. The degree of incremental housekeeping depended upon how dusty the operations were and the appropriate equipment for addressing the dust problem. The incremental costs for most such occupations reflected labor associated with additional housekeeping efforts. Because incremental housekeeping labor was required on virtually every work shift by most of the affected occupations, the costs of housekeeping in the PEA were significant. The PEA also estimated that employers would need to purchase HEPA vacuums and to incur the ongoing costs of HEPA vacuum filters. The time needed for such housekeeping varied from five to twenty minutes per affected worker per day. Appendix V-A in the PEA provided detailed specifications on the application of housekeeping and other dust-suppression controls in each occupational category and the sources of OSHA's unit cost data for such controls.

For some indoor dust suppression tasks, it was assumed that dust suppression mixes—often sawdust-based with oil or other material that adheres to dust and allows it to be swept up without becoming airborne—were spread over the areas to be swept. For these products, estimates were made of usage rates and the incremental times necessary to employ them in housekeeping tasks.

For outdoor dust suppression, the PEA determined that workers must often spray water over storage piles and raw material receiving areas. The methods by which water is provided for these tasks can vary widely, from water trucks to available hoses. It was judged that most facilities would make hoses available for spraying and that spraying requires a materials-handling worker to devote part of the workday to lightly spray the area for dust control.

The PEA did not include any costs for thorough cleaning designed to remove accumulated dust, either as a one-time cost or as an annual cost.

Comments and Responses on Costs of Routine Housekeeping and Initial Cleaning

Commenters had a number of issues with respect to how OSHA treated the costs of housekeeping, including the time and equipment needed for vacuuming, the need for professional floor to ceiling cleaning, and the costs of the ban on dry sweeping.

Comments and Responses on Costs of Routine Housekeeping

With respect to the use of HEPA vacuums, AFS commented that due to the volume of sand involved, foundries often use vacuum systems that cost $45,000 instead of the $3,500 estimated by OSHA in the PEA (Document ID 4229, Attachment 1, p. 23). Several commenters reported that HEPA semi-mobile central vacuum systems cost more than $40,000 to purchase and cost approximately $4,000 per year to maintain, and that sweeping compound costs approximately $4,000 per year (Document ID 2384, p. 7; 2114, Attachment 1, p. 4). Several others noted that acquiring HEPA vacuums and employee time for vacuuming would be expensive (Document ID 2301, Attachment 1, p. 74; 3300, pp. 4-5; 2114, Attachment 1, p. 4).

OSHA's costs are for improved housekeeping, beyond the necessary tasks related to dealing with the large volumes of sand used in foundries. For this final rule, OSHA estimates the costs of additional housekeeping as those necessary for overexposed workers to spend 10 minutes vacuuming their immediate work areas with a 15-gallon HEPA vacuum. It is possible that a large firm may find a dust handling system or a semi-mobile central vacuum system less expensive than having individual workers equipped with smaller capacity HEPA vacuums spend additional time performing housekeeping on each shift.

With respect to the shipbuilding sector, OSHA found that it had not accounted for the costs of HEPA vacuums for abrasive blasting helpers. OSHA has added costs for the vacuums, but not for the time spent performing housekeeping as the vacuums replace dry sweeping.

As to the possible costs of the ban on dry sweeping, OSHA has modified this prohibition in ways that should avoid significant costs in situations where dry sweeping is the only effective method of housekeeping.

Comments and Responses on Costs of Initial Cleaning

URS, testifying for ACC, questioned OSHA's omission of “professional cleaning” from its cost models for some industries, noting that professional cleaning was identified in the PEA as necessary for some industries to achieve the PEL (Document ID 2308, Attachment 8, p. 12). URS also provided estimates of the cost of professional cleaning:

Based on communications with several industries, URS estimates that a thorough annual professional cleaning will cost about $1.00 per square foot of the facility process operations area.

. . . A professional cleaning can take several days to accomplish [. . .] For square footage, URS assumed 20,000 square feet for very small facilities, 50,000 square feet for small facilities, and 200,000 square feet for large facilities (Document ID 2308, Attachment 8, p. 24).

Initial thorough facility cleaning and rigorous housekeeping are supplemental controls and work practices addressed in the technological feasibility analysis for the following application groups: Concrete Products, Pottery, Structural Clay, Mineral Processing, Iron Foundries, Nonferrous Sand Foundries, and Captive Foundries. OSHA failed to include the costs of a thorough initial cleaning in the PEA, but has developed estimates of these costs for the FEA in response to the URS comment. The final standard sets the performance objective of achieving the PEL using engineering controls, work practices, and where necessary, respiratory protection, and, with respect to facility cleaning and housekeeping, the rule does not mandate that firms hire outside specialists. To estimate the final costs for initial thorough facility cleaning, OSHA first developed an analysis of average production floor space in square feet for two plant sizes based on data on plant floor space and employment for individual facilities reported in various NIOSH control technology and exposure assessment field studies (OSHA examined Document ID 215; 216; 268; 1373; 1383; 3786; 3996; and 4114. The analysis is in Exhibit: Analysis of Plant Floor Space, available in Docket OSHA-2010-0034 at www.regulations.gov ).

For the purpose of estimating cleaning costs, OSHA characterized establishments with fewer than twenty employees as very small establishments, and characterized establishments with twenty or more employees as larger establishments.

OSHA determined, based on a review of the data in the NIOSH field studies, that production floor space averages 725 square feet per employee (See Exhibit: Analysis of Plant Floor Space).

For very small establishments with fewer than 20 employees, OSHA used an average of 7 employees per establishment. For larger establishments, OSHA used an average of 80 employees. (These estimates of the number of employees are based on OSHA (2016), which shows that the average number of employees for establishments with fewer than 20 employees is 7 employees and that the average number of employees for establishments with more than 20 employees is 80 employees.) Based on these parameters, OSHA's floor space model found that the typical floor space for very small establishments is 5,075 square feet and for larger establishments is 58,000 square feet.

ERG spoke with a representative of an upper-Midwestern firm specializing in the industrial cleaning of foundries and related facilities (Document ID 3817, p. 2). According to that representative, cleaning costs depend on numerous factors, such as the distance to the facility that needs to be cleaned, the size and number of machines and pieces of equipment present, the types of required cleaning activities, and the presence of confined spaces. The representative described one of his company's clients as a sand-casting foundry that produces 42,000 tons of gray and ductile iron castings per year in a 210,000 square foot facility. According to the representative, a crew of two technicians cleans the facility every 2 to 3 weeks at a cost of $2,200 to $3,500 per cleaning, which requires one day, or roughly $0.01 to $0.02 per square foot in 2014 dollars.

For the FEA, OSHA is estimating, based on data from the ERG field interviews, that it will take 4 to 5 days to perform a one-time initial cleaning (remove all visible silica dust) and that if the same facility is cleaned every 2 to 3 weeks it will take 1 day to clean it. At a cost of $0.02 per day per square foot, and using a cleaning duration of 5 days, OSHA calculated a cost of $0.15 per square foot in 2012 dollars for an initial thorough cleaning. This value is derived from inflating the 2003 estimate of $0.10 per square foot ($0.02 per day per square foot over 5 days) to 2012 dollars, which raised the cost to $0.12 per square foot. OSHA also allowed for an additional allotment of 25 percent of the estimated cost of $0.12 per square foot (in 2012 dollars) to ensure that the cleaning was sufficiently thorough to achieve compliance, increasing the total from $0.12 to $0.15. OSHA judges that this is a reasonable average for the range of facilities to be covered, especially given that some annual cleaning is probably already occurring at most facilities and therefore the full cost of cleaning would not be attributable to this rule. The costs here are applied to represent an incremental cleaning beyond that employed for normal business purposes.

As discussed earlier in this chapter, URS, an engineering consultant to ACC, estimated that a thorough annual professional cleaning will cost about $1.00 per square foot of a facility's process operations area. URS provided no specific reference for that unit estimate other than that it communicated with industry representatives (Document ID 2308, Attachment 8, p. 24). The data OSHA used to develop its cost estimates are based on interviews with a company that provides housekeeping services rather than companies that may or may not have purchased such services. OSHA's estimated costs for a thorough initial cleaning are over five times the costs of a thorough cleaning where there is just few weeks' worth of accumulated dust. Greater accumulations during an initial cleaning do not mean that the initial cleaning will cost 50 times the cost of a more basic/regular cleaning, as much of the cost of the initial cleaning will be due to the time spent going over the entire facility with the appropriate cleaning devices—a cost that is fixed by area and not by accumulation. OSHA therefore rejects the URS unit estimate of $1.00 per square foot as not representative of a typical cost for initial thorough facility cleaning, particularly for firms that choose to use in-house resources. Nonetheless, OSHA acknowledges that unique circumstances may create higher unit costs than the value OSHA is using in the FEA. OSHA also acknowledges that the cost of cleaning per square foot probably declines as facility size increases (Document ID 4231, p. 4). The paucity of data on square footage for the affected facilities, however, did not allow for further modeling of cleaning costs.

For this final analysis of costs for initial thorough facility cleaning, OSHA estimated that an upfront, one-time, extensive servicing (using vacuum and wash equipment) to rid the production area of respirable crystalline silica during plant turnaround or other downtime would cost $0.15 per square foot (including the additional allowance to ensure a sufficiently thorough cleaning) or $0.02 when annualized at 3 percent for 10 years, and OSHA applied that unit cost along with the average production floor space discussed above in OSHA's cost model (725 square feet per employee) to derive final costs for facility cleaning by application group. For the seven affected application groups, OSHA estimates that annualized initial thorough facility cleaning costs will range from just under $45,000 for Nonferrous Sand Foundries to $488,000 for Concrete Products. Across all seven affected application groups, OSHA estimates that annualized costs for initial thorough facility cleaning will total $2.8 million.

Conveyor Covers

The technological feasibility analysis in the PEA recommended reducing silica exposures by enclosing process equipment, such as conveyors, particularly where silica-containing materials were transferred (and notable quantities of dust can become airborne), or where dust is generated, such as in sawing or grinding operations. For the PEA, OSHA estimated the capital costs of conveyor covers as $20.73 (updated to 21012 dollars) per linear foot, based on Landola (2003, Document ID 0745) (as summarized in footnote a in Table V-3 of the PEA). OSHA estimated that each work crew of four affected workers would require 100 linear feet of conveyors. OSHA, based on ERG's estimates, calculated maintenance costs as 10 percent of capital costs. Based on the technological feasibility analysis, OSHA also included the cost of LEV on the vents of the conveyors for the structural clay, foundry, asphalt roofing, and mineral processing application groups, but not for the glass and mineral wool application groups.

URS commented that OSHA underestimated the length of conveyors by using 100 linear feet in its estimate, and suggested that the estimate of 200 feet that it used as the basis for its estimates was still an underestimation for some foundries (Document ID 2307, Attachment 26, Control Basis and Control Changes tabs). URS maintained OSHA's estimate of $20.73 per linear foot in its own calculations. However, it appears that URS did not understand that OSHA estimated 100 linear feet of conveyors for every 4 workers, not 100 linear feet of conveyors for an entire affected establishment. Further, the URS comment indicated that 100 linear feet was an underestimate for “medium and large foundries.” But because OSHA's estimate of 100 linear feet is for every four workers, OSHA actually estimated much longer conveyor lengths for larger facilities with more workers. OSHA has determined that its estimate of 100 linear feet for every four workers at a cost of $20.73 per linear foot is a reasonable approach for estimating the costs of conveyor covers.

Selected Control Options That Are Not Costed

Consistent with ERG's cost model, in the PEA OSHA chose not to estimate costs for some control options mentioned in the accompanying technological feasibility analysis in Chapter IV of the PEA. In these cases, OSHA judged that other control options for a specific at-risk occupation were sufficient to meet the PEL. AFS identified several control options for which OSHA did not estimate costs:

• Substitution of non-silica sand (V-A-51)
• Pneumatic sand handling systems (V-A-51)
• Didion drum to clean scrap for furnace operators (V-A-52)
• Non-silica cores and core coatings (V-A-52)
• Professional cleaning costs and associated downtime (V-A-52)
• Physical isolation of pouring areas (V-A-52)
• Modify ventilation system to reduce airflow from other areas (V-A-52)
• Automation of a knockout process (V-A-53)
• Automated abrasive blast pre-cleaning of castings for finishing operators (V-A-54)
• Wet methods (V-A-54)
• Low silica refractory (V-A-55) (Document ID 2379, p. 16)

Just because a control is mentioned in the technological feasibility analysis does not mean that OSHA has determined that its use is required—only that it represents a technologically feasible method for controlling exposures. The Agency developed cost estimates based on the lowest cost combination of controls that allows employers to move from an uncontrolled situation to meeting the new PEL. OSHA did not include the costs for possible controls that were either more expensive or were not necessary to achieve the PEL. OSHA (2016) describes in detail which controls were considered necessary to achieve the PEL. OSHA continues in the FEA to exclude costs for these kinds of more expensive possible controls.

Railroads

In its preliminary estimates, OSHA inadvertently applied the preceding general industry PEL of 100 μg/m³ in its analysis of the railroad industry. Silica exposures among railroad employees, however, result from ballast dumping, which is track work that is generally subject to OSHA's construction standard and covered by the preceding construction PEL of 250 μg/m³ (see discussion of railroads in Chapter III, Industry Profile). As a result, OSHA has changed its conclusion that there would be no incremental costs for railroads to meet the new PEL. OSHA has reassigned all costs previously assigned to meeting the preceding PEL to being incremental costs of meeting the new PEL. Although the railroad activities affected by the new silica rule will typically constitute construction work, OSHA has categorized all compliance costs for railroads with general industry costs under NAICS 482110 because the railroad industry is predominantly engaged in non-construction work and its NAICS code is not typically classified as a construction code.

Costs of Engineering Controls for Hydraulic Fracturing in the PEA

Both in the PEA and in the FEA, OSHA presented the methods of estimating the costs of controlling silica exposures during hydraulic fracturing separately from the engineering control costs for all other portions of general industry because there are some fundamental differences in the methodology OSHA used, and thus in the comments OSHA received on that methodology. In the PEA, OSHA began its analysis of hydraulic fracturing in the standard way of examining the set of engineering controls available to control employee exposures to silica. Unlike the way OSHA handled the rest of general industry, however, for hydraulic fracturing OSHA identified precisely which controls were necessary to go from current levels of exposure to the preceding general industry PEL of 100 μg/m³ and then what further controls would be necessary to go from the preceding general industry PEL of 100 μg/m³ to the new PEL of 50 μg/m³. OSHA took a different approach for this sector because the data available for this industry, as a result of an extensive set of site visits, were adequate to make this type of determination. OSHA determined that a combination of wet methods, partial enclosure, and LEV controls would be sufficient to meet a PEL of 100 μg/m³ for hydraulic fracturing. OSHA then determined that LEV controls at thief hatches and operator enclosures would be sufficient to reduce exposures during hydraulic fracturing from 100 μg/m³ to 50 μg/m³. The costs of these additional engineering controls were shown in Tables A-14, A-15, and A-16 for large, medium, and small fleets, respectively, in the PEA (the full derivation of the results in these tables can be found in ERG, 2013, Document ID 1712).

As discussed in the Industry Profile section of the FEA (Chapter III), the basic unit for analysis for this industry is the fleet rather than the establishment. Rather than allocating costs according to the proportion of workers above a given exposure level, as was done for the rest of general industry, for hydraulic fracturing the controls applied per fleet were judged to reduce the exposures of all workers associated with the fleet.

Public Comments on OSHA's Preliminary Cost Estimates for Engineering Controls in Hydraulic Fracturing

General Methodology

Though there were extensive comments on OSHA's estimates of engineering control costs for hydraulic fracturing, no commenter objected to the differences in methodology compared to OSHA's treatment of the other general industry sectors (as outlined above). Halliburton Energy Services, Inc. commented that OSHA's analysis “lacks data” (Document ID 4211, p. 5). As discussed in Chapter IV Technological Feasibility, OSHA agrees that there is limited experience with many possible controls. For this reason, OSHA has allowed this industry an extended compliance deadline of five years before they have to meet the new PEL with engineering controls. However, OSHA does not agree that this adds significant uncertainty to the costs analysis. The costs of the controls OSHA has examined, and especially those needed to go from the preceding general industry PEL to the new PEL can readily be ascertained. It is possible that the cost of some controls that have not yet been tested and that OSHA has not costed could be much lower than the costs OSHA estimated in the PEA and in the FEA.

Compliance Rate

In the joint comments submitted by the American Petroleum Institute and the Independent Petroleum Association of America (API/IPAA or “the Associations”), the Associations disagreed with OSHA's estimated current compliance rate for the use of engineering controls. In the PEA, OSHA estimated a compliance rate of ten percent for engineering controls in this industry. In their comments the Associations said that “ERG assumed that 10% of all hydraulic fracturing firms already utilize: (1) Baghouse controls; (2) caps on fill ports; (3) dust curtains; (4) wetting methods; and (5) conveyor skirting systems” (Document ID 2301, p. 40, fn. 148).

While OSHA used a compliance rate of ten percent for all of these controls, it is not meant to represent that all prescribed controls are used in ten percent of firms. OSHA's compliance rates take into account that some well sites, as documented in Chapter IV of the FEA, were observed to be using a variety of controls that reduce dust levels, and as a result, those firms will not need to implement as many additional controls in order to achieve the new PEL. Further, as noted in Chapter IV of the FEA, the industry is constantly installing additional controls to reduce silica exposures. Thus the Agency sees no reason to change its estimate of current compliance. In any case, removing the assumption would make only a ten percent difference to the cost estimates, which would not be a change of large enough magnitude to threaten OSHA's conclusion that compliance with the final rule is economically feasible for the hydraulic fracturing industry.

Maintenance Costs

In the PEA, OSHA estimated that the life of most capital equipment would be ten years, and that maintenance and operating costs would range from ten to thirty percent of capital costs per year (ten percent being most common).

API/IPAA argued that the hostile, sandy environment of the well site shortens the useful life of equipment and increases maintenance costs. The Associations estimated that the useful life of equipment ranges from 5 years to 7.5 years and that annual operating and maintenance costs range from 10 percent to 25 percent of capital costs. While OSHA agrees that the oilfield environment is challenging and dusty, there is no evidence in the record that these environments are more challenging than other industrial settings where equipment lives of 10 years and operating and maintenance costs of 10 to 30 percent have been used as reasonable estimates.

Cost of Specific Controls

Dust Booths

In the PEA, OSHA estimated that there would need to be one dust booth for each sand moving machine, and that this would result in one dust booth for small fleets, three for medium fleets, and five for large fleets. In critiquing OSHA's cost analysis for hydraulic fracturing, API/IPAA disagreed with OSHA's estimates that only sand mover operators would need to utilize dust control booths in order to achieve the new PEL (Document ID 2301, p. 69). API/IPAA suggested that instead there would need to be one booth per affected worker and that only one worker could utilize a given booth. In the Associations' estimate this would mean that there would need to be 3, 8 and 12 booths for small, medium, and large fleets, respectively (Document ID 2301, Attachment 4, Dust Booths, row 9).

As discussed in the technological feasibility chapter of the FEA, OSHA agrees that workers other than sand mover operators will need to use dust booths. However, OSHA does not agree that a booth can only accommodate a single person. These booths are places of refuge and are not assigned to specific individuals. The technological feasibility chapter in the FEA determined that dust booths can accommodate more than one person per booth. Because OSHA agrees that more employees than sand mover operators will need booths, OSHA has raised its estimates of booths needed by size class from 1, 4, and 5 booths to 3, 6, and 8 booths. While this estimate of the number of booths is lower than that recommended by API/IPAA, OSHA finds that these booths can accommodate 2 persons per booth and thus can accommodate more workers than API/IPAA suggested.

In the PEA, OSHA estimated the transportation costs for booths as $37.25 per booth. API/IPAA disagreed. The Associations argued that a cost of $513 for a small fleet, which would only have one booth, would be more appropriate (Document ID 2301, p. 69). Most of the difference between API/IPAA's cost estimate for deploying dust control booths and OSHA's estimate is attributable to the fact that the Associations presented their cost per fleet and OSHA presented its cost per booth. API/IPAA applied their estimate of the number of booths necessary at these worksites when deriving their estimate and they estimated about six times as many booths being necessary as OSHA did. However, after further examination of this cost, OSHA determined that the standard per-mile shipping rate that it used to estimate transportation costs in the PEA was applied incorrectly. This resulted in an estimate of transportation costs for booths in the PEA that was too low. OSHA has determined that the cost to transport dust booths presented by the Associations more completely captured the costs associated with transporting these booths. For the FEA, OSHA has accepted the Associations' per-fleet transportation cost of $513 for each booth and applied the cost to the Agency's estimate of the number of booths necessary to control silica exposures on well sites.

Water Misting

In the PEA, OSHA estimated that water misting system would be needed to control residual emissions from some releases from sand moving systems. These water misting systems were estimated to cost $60,000 per fleet to purchase and an additional 20 percent of the purchase cost for installation. API/IPAA incorrectly assumed that these water misting systems were intended to control all dust emission from truck traffic and other sources (Document ID 2301, pp. 69-70). This was not the case—dust suppression for truck and other traffic was costed at a much higher rate separately from water misting.

OSHA's cost estimates for misting systems were based on conversations with a mining dust control specialist who indicated the price and efficacy of available water misting systems (Document ID 1571). While API/IPAA disagreed with OSHA's costs, they did not offer any data to show an alternative cost, instead simply carrying OSHA's estimate for water misting systems forward in their analysis to arrive at their cost estimate (Document ID 2301, Attachment 3, Water Misting, cells K:O6 and J8). OSHA has determined that the equipment that formed the basis for its cost estimates in the PEA may not be durable enough to stand up to the wear from frequent loading, unloading, and transportation. Therefore, the Agency, based on its own judgement, has increased the estimated cost of a water misting system by 33 percent in order to account for the need for a more durable system. Based on this, OSHA's final cost analysis for hydraulic fracturing includes costs of $79,800 per fleet to purchase the equipment plus installation costs of $15,960 for installation (20 percent of the purchase price) for water misting equipment to control residual dust emissions from sand moving systems.

Costs of Transportation

In developing the costs for hydraulic fracturing firms to comply with this rule in the PEA, it was determined that the baghouse controls that are commercially available are integrated into sandmover units and therefore should not present any logistical difficulties for transportation purposes. However, in examining the costs to transport, assemble, and disassemble the control equipment, API/IPAA noted potential difficulties in adding baghouse controls to sandmovers, which are often nearly at weight limits for road movement (Document ID 2301, p. 71).

OSHA's determination about integrated units has not changed since the PEA. The existence of integrated units is further discussed in Chapter IV of the FEA, Technological Feasibility. OSHA notes that sandmover units are not the heaviest items transported by hydraulic fracturing firms, so the additional weight associated with baghouse controls would be insignificant in this context. These firms are highly experienced in moving the heavy, bulky equipment needed on well sites and including additional controls on this equipment is not expected to create a situation that exceeds the capabilities of these firms.

Containerized Systems

Commenting on OSHA's analysis of the cost of controls for hydraulic fracturing, API/IPAA expressed concern that OSHA was considering requiring the use of containerized systems. The Associations stated that these systems would be economically infeasible for small fleets and raised questions about whether these systems would be sufficient to allow fleets using them to achieve the PEL (Document ID 4222, p. 7). Neither in the PEA nor the FEA has OSHA's cost analysis reflected the use of containerized systems, nor does OSHA require their use. Instead, containerized systems represent a possible technological change that could potentially reduce the costs of silica control. OSHA has in no way quantitatively tried to estimate the effects of this possible reduction.

Conveyor Skirting

In the PEA, OSHA found that conveyor skirting systems with appropriate LEV would be needed to meet the new PEL, and included the cost of such controls in the incremental costs associated with the new PEL. As discussed in Chapter IV, Technological Feasibility, in the FEA, however, OSHA now finds that these conveyor skirting systems will be needed to meet the preceding PEL, but not to further lower exposures to the new PEL, so OSHA is not including costs for these controls as incremental costs associated with achieving the new PEL. As a result, the FEA does not include costs for conveyor skirting systems and LEV.

Dust Suppression—Control of Dust Generated From Traffic

On the other hand, dust suppression to control silica emissions generated by truck traffic, estimated in the PEA as necessary only to meet the preceding PEL, has now been determined to be necessary to meet the new PEL (see Chapter IV, Technological Feasibility in the FEA). As a result, in the FEA OSHA added the costs of dust suppression to control silica dust generated by truck traffic to the estimated incremental costs of meeting the new PEL. OSHA estimates that dust suppression is more expensive in the aggregate than conveyor skirting systems with appropriate LEV.

OSHA made two additional changes to the costs of dust suppression from the PEA to the FEA. First, OSHA accepted the unit costs for dust suppression application provided by API/IPAA (Document ID 2301, Attachment 3, Dust Suppression). This unit cost is somewhat lower than the original estimate that OSHA adopted in the PEA (Document ID 1712). This seems reasonable to OSHA based on the costs of the most commonly used dust suppression materials. Second, OSHA has determined that these controls will be utilized to reduce exposures for ancillary support workers and remote/intermittent workers, 50 percent of whom work in situations that currently have exposures below the new PEL (as shown in the exposure profile in the section on hydraulic fracturing in Chapter IV, of the FEA, technological feasibility). As a result, instead of assigning dust suppression costs for all wells (as in the PEA), OSHA determined in the FEA that dust suppression costs would be incurred by 50 percent of wells. This aligns with a view that, in many cases, natural conditions (silica content of soils, dustiness, wetness and/or climate) are such that dust suppression is not needed.

Small Business Considerations

Small Business Regulatory Enforcement Fairness Act (SBREFA) Comments on Compliance

Costs in General Industry and Maritime

Before publishing the NPRM, OSHA received comment on the accuracy of its unit costs through the Small Business Advocacy Review (SBAR) Panel process.

The Small Entity Representatives (SERs) who participated in the 2003 SBAR Panel process on OSHA's draft standards for silica provided many comments on the estimated compliance costs OSHA presented in the Preliminary Initial Regulatory Flexibility Analysis (PIRFA) for general industry and maritime (Document ID 0938).

In response to the SERs' comments, OSHA carefully reviewed its cost estimates and evaluated the alternative estimates and methodologies suggested by the SERs. OSHA updated all unit costs presented in the PIRFA to reflect the most recent cost data available and inflated all costs to 2009 dollars prior to publication of the proposed rule. However, the Agency generally determined that the control cost estimates in the PIRFA were based on sound methods and reliable data sources.

For the PEA, OSHA reviewed the SERs' cost estimates for small entities in the foundry and structural clay industries. Given that those SERs did not report their own sizes, the Agency could not compare their estimates to the estimates in the PEA. OSHA concluded that the compliance costs reported by the SERs in general industry that did provide size data were not incompatible with OSHA's own estimates of the costs of engineering controls to comply with the PEL. As discussed above, for the FEA, OSHA has halved the number of workers assumed to be covered by each control for most controls in establishments with fewer than twenty employees, which results in a doubling of the engineering control costs for these establishments.

Comments and Responses on Costs for Small Establishments

Stuart Sessions, testifying on behalf of ACC, argued that OSHA had underestimated costs to small establishments for two reasons: (1) Small establishments may have higher exposures and therefore many need to spend more money installing controls to reduce those exposures; and (2) costs to small establishments may involve diseconomies of scale—whereby smaller facilities would have to pay more per unit to procure and install systems—that OSHA had not accounted for (Document ID 4231, Attachment 1, pp. 2-4).

With respect to the issue about small establishments having higher exposures—the commenter simply asserted that this is the case without providing any evidence to support the claim. Mr. Sessions speculated that smaller businesses have a “lesser ability to afford compliance expenditures and lesser ability to devote management attention to compliance responsibilities” (Document ID 4231, Attachment 1, p. 2). While it is possible that very small establishments may not have the same controls already in place as large establishments, as asserted by the commenter, this does not necessarily mean that very small establishments will have higher exposures. Small and very small establishments typically only have one shift per day, so fewer shifts are being worked where there is a potential for exposure. They also may spend more time on activities not involving silica exposures. For example, a small art foundry that produces one or two castings a week will simply spend proportionally less time on activities that lead to silica exposure than a large production foundry.

With respect to the issue of diseconomies of scale, OSHA has taken this phenomenon into account in its cost estimates in the FEA. First, in order to provide a conservative estimate of costs for the purposes of determining the impacts on very small employers, OSHA has revised what Mr. Sessions called “the most inappropriate of OSHA's assumptions” (Document ID 4231, Attachment 1, p. 6). In the PEA, OSHA estimated that a single control would reduce the exposures of four workers. For the FEA, OSHA has revised its estimates so that the number of workers whose exposures are reduced by a control are half that used in the PEA for establishments with fewer than 20 employees—reducing the number of workers covered by a control from four to two. OSHA made this adjustment even though there are ways in which small establishments may have lower costs per cfm than larger establishments. For capital costs, a major element of cost per cfm is the length of ductwork. Within the same industry, the length of ductwork will be much shorter in smaller establishments. For operating costs per cfm, length of operating time is a key element of costs.

OSHA has continued to estimate that the exposures of four employees whose exposures would be reduced per control for establishments with more than twenty employees (even though it is likely that more than four workers have their exposures reduced per control in the largest establishments). This effectively means that very large establishments with hundreds of employees have been modeled as if their costs were equivalent to that of several 20-40 person establishments combined. Far from neglecting diseconomies of scale, in an effort to be conservative and adequately account for the challenges faced by smaller establishments, OSHA has instead neglected to account for economies of scale in larger establishments.

Mr. Sessions calculated some higher overall costs for smaller establishments (Document ID 4231, Attachment 1, pp. 6-10). However, these costs are critically dependent on the assumptions already addressed and rejected by OSHA, such as that exposures are random and that any exposures require that all possible controls be installed to control those exposures.

Final Control Costs

Unit Control Costs

Methodology

For the FEA, OSHA used unit costs developed in the PEA for specific respirable crystalline silica control measures from product and technical literature, equipment vendors, industrial engineers, industrial hygienists, and other sources, as relevant to each item. Some PEA estimates were modified for the FEA based on comments in the record, and all costs were updated to 2012 dollars. Specific sources for each estimate are presented with the cost estimates. Wherever possible, objective cost estimates from recognized technical sources were used. Table V-4 in the FEA provides details on control specifications and data sources underlying OSHA's unit cost estimates.

Summary of Control Costs for General Industry and Maritime

Table V-5 in the FEA summarizes the estimated number of at-risk workers and the annualized silica control costs for each application group. Control costs in general industry and maritime for firms to achieve the PEL of 50 μg/m³ level are expected to total $238.1 million annually. As shown, application group-level costs exceed $15.0 million annually for concrete products, hydraulic fracturing, iron foundries, railroads, and structural clay.

Table V-6 in the FEA shows aggregate annual control costs in general industry and maritime by NAICS industry. These costs reflect the disaggregation of application group costs among the industries that comprise each group (see Table III-1 in Chapter III of the FEA on the profile of affected industries.)

b. Control Costs in Construction

In both the PEA and the FEA, OSHA determined that employers, in order to minimize exposure monitoring costs, would select appropriate controls from Table 1. The final estimate for control costs, however, includes Table 1 control costs for a larger number of employees than in the PEA. For the purpose of estimating control costs in the PEA, OSHA examined all of the employers with employees engaged in Table 1 tasks but judged that only a subset of those employers (those with workers exposed above the proposed silica PEL) would require additional engineering controls. For this final rule, OSHA has judged, for costing purposes, that all of the construction employers with employees performing any task covered in Table 1 will adopt the engineering controls for that task as specified in Table 1. Thus, in the FEA, OSHA took the more conservative approach—which may result in an overestimate of costs—of identifying the cost of controls for all employers with employees engaged in Table 1 tasks, not just the subset of employers with employees exposed above the PEL. However, as discussed in Chapter III of the FEA, OSHA did adjust control costs to reflect the 44 percent of workers in construction currently exposed at or below the PEL who are estimated to be in baseline compliance with the Table 1 requirements.

OSHA is also likely overestimating the cost of controls for another reason. If the employer is able to demonstrate by objective data, or other appropriate means, that worker exposures would be below the action level under any foreseeable conditions, the employer would be excluded from the scope of the final rule. These employers would not require additional controls. OSHA did not have sufficient data to identify this group of employers and did not try to reduce the costs to reflect this group, so OSHA's estimate of costs is therefore overestimated by an amount equal to the costs for those employers engaged in covered construction tasks but excluded from the scope of the rule.

A few tasks involving potentially hazardous levels of silica exposure are not covered in Table 1. Employers would have to engage in exposure monitoring for these tasks pursuant to paragraph (d) and use whatever feasible controls are necessary to meet the PEL specified in paragraph (d)(1). For example, tunnel boring and abrasive blasting are not covered by Table 1 and are therefore addressed separately in this cost analysis. Although several commenters identified various other activities that they believed were not covered by Table 1 that could result in crystalline silica exposure over the PEL (Document ID 2319, pp. 19-21; 2296, pp. 8-9), some of these activities were simply detailed particularized descriptions of included activities. For example, overhead drilling is addressed in the FEA, Chapter IV-5.4 Hole Drillers Using Handheld or Stand-Mounted Drills, and the demolition of concrete and masonry structures is addressed in the FEA, Chapter IV-5.3 Heavy Equipment Operators. For the remainder, the available exposure data did not indicate that these activities resulted in a serious risk of exposure to respirable crystalline silica (see FEA, Chapter III Industry Profile, Construction, Public Comments on the Preliminary Profile of Construction and Summary and Explanation, Scope and Application); furthermore, these other activities could be addressed using the controls identified in the FEA. Because OSHA did not have sufficient data to identify a significant number of silica exposures above the PEL of 50 μg/m³ for these activities, the Agency did not include costs for controlling silica exposures during these activities. Nevertheless, to the extent that employers find it necessary to implement controls for any activity that OSHA did not explicitly include in this analysis, the FEA shows that those controls are clearly economically feasible.

The control costs for the construction standard are therefore based almost entirely on the tasks and controls specified in Table 1. Most of the remainder of this section is devoted to explaining the manner in which OSHA estimated the costs of applying appropriate engineering controls to construction activities as required by Table 1 of the final standard. These costs are generated by the application of known dust-reducing technology, such as the application of wet methods or ventilation systems, as detailed in the technological feasibility analysis in Chapter IV of the FEA. These costs are discussed first, and, following that, the control costs for tasks not specified in Table 1 are separately estimated.

OSHA revised Table 1 between the PEA and the FEA. The entries included in the table have been modified with some tasks being added and some being removed. In addition, the methods of controlling exposures that Table 1 requires for certain tasks have changed in response to comments and additional analysis. Excluding changes to respirator requirements, which are addressed elsewhere in this preamble, significant and substantive revisions to Table 1 that have the potential to impact control costs include:

• New entries on Table 1—

○ Handheld power saws for cutting fiber-cement board (with blade diameter of 8 inches or less)

○ Rig-mounted core saws and drills

○ Dowel drilling rigs for concrete

○ Small drivable milling machines (less than half-lane)

○ Large drivable milling machines (half-lane and larger for cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate)

○ Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials.

○ Heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing, abrading, or fracturing silica-containing materials

• Removed entry for drywall finishing from Table 1
• Revised entries on Table 1—

○ Drivable saw entry revised to permit outdoor use only.

○ Portable walk-behind or drivable masonry saws divided into two entries—walk-behind saws and drivable saws.

○ Handheld drills entry revised to include stand-mounted drills and overhead drilling.

○ Combined entries for vehicle-mounted drilling rigs for rock and vehicle-mounted drilling rigs for concrete.

○ Milling divided into three tasks—walk-behind milling machines and floor grinders; small drivable milling machines (less than half-lane); and large drivable milling machines (half-lane and larger with cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate).

○ Heavy equipment used during earthmoving divided into two tasks—(1) heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials, and (2) use of heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing, abrading, or fracturing silica-containing materials.

○ Revised crushing machines entry to require equipment designed to deliver water spray or mist for dust suppression and a ventilated booth or remote control station.

In addition to the new and revised tasks in Table 1, some of the controls and specifications required by Table 1 were revised for this final rule, including removal of “Notes/Additional Specifications” from individual Table 1 entries and addition of substantive paragraphs after the table. Those revisions include:

• Revised or newly required controls/specifications for Table 1 tasks—

○ Revised requirement to operate and maintain tools/machine/equipment in accordance with manufacturer's instructions to minimize dust emissions.

○ Revised specifications for dust collectors to require they provide at least 25 cubic feet per minute (cfm) of air flow per inch of blade/wheel diameter (for some, but not all entries that include a dust collection system as a control method).

○ Revised specification for dust collectors to require they provide the air flow recommended by the tool manufacturer, or greater, and have a filter with 99 percent or greater efficiency and a filter-cleaning mechanism (for some, but not all entries that include a dust collection system as a control method). The entries for handheld grinders for mortar removal (i.e., tuckpointing) and handheld grinders for uses other than mortar removal require a cyclonic pre-separator or filter-cleaning mechanism.

○ Revised requirement for tasks indoors or in enclosed areas to provide a means of exhaust as needed to minimize the accumulation of visible airborne dust (paragraph (c)(2)(i)).

○ Added requirement for wet methods to apply water at flow rates sufficient to minimize release of visible dust (paragraph (c)(2)(ii)).

○ Revised specifications for enclosed cabs to require that cabs: (1) Are maintained as free as practicable from settled dust; (2) have door seals and closing mechanisms that work properly; (3) have gaskets and seals that are in good condition and working properly; (4) are under positive pressure maintained through continuous delivery of fresh air; (4) have intake air that is filtered through a filter that is 95% efficient in the 0.3-10.0 μm range (e.g., MERV-16 or better); and (5) have heating and cooling capabilities (paragraph (c)(2)(iii)).

○ Added requirement to operate handheld grinders outdoors only for uses other than mortar removal, unless certain additional controls are implemented.

○ Added wet methods option for use of heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing, abrading, or fracturing silica-containing materials.

○ Added requirement to use wet methods when employees outside of the cab are engaged in tasks with heavy equipment used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials.

• Removed controls/specifications for Table 1 tasks—

○ Removed requirements to change water frequently to avoid silt build-up in water.

○ Removed requirements to prevent wet slurry from accumulating and drying.

○ Removed requirements to operate equipment such that no visible dust is emitted from the process.

○ Removed local exhaust dust collection system option and requirement to ensure that saw blade is not excessively worn from the entry for handheld power saws.

○ Removed requirement to eliminate blowing or dry sweeping drilling debris from working surface from the entry for handheld and stand-mounted drills (including impact and rotary hammer drills).

○ Removed additional specifications for dust collection systems for vehicle-mounted drilling rigs for concrete (e.g., use smooth ducts and maintain duct transport velocity at 4,000 feet per minute; provide duct clean-out points; install pressure gauges across dust collection filters; activate LEV before drilling begins and deactivate after drill bit stops rotating).

○ Removed requirements to operate grinder for tuckpointing flush against the working surface and to perform the work against the natural rotation of the blade.

○ Removed dust collection system option and requirement to use an enclosed cab from crushing machines.

These and other changes to Table 1 are discussed in detail in Section XV: Summary and Explanation of this preamble. While Table 1 has changed with regard to the tasks included and the control methods required, OSHA's methodology used to estimate the costs of controls for the construction industry has remained basically the same as that explained in detail in the PEA, with steps added (and explained in the following discussion) to address cost issues raised during the comment period and the updates and revisions to Table 1. OSHA summarizes the methodology in the following discussion, but the PEA includes additional details about the methodology not repeated in the FEA.

OSHA adopted the control cost methodology developed by ERG (2007a, Document ID 1709) for the PEA and subsequently for the FEA. In order to provide some guidance on that cost methodology, OSHA itemizes below the three major steps, with sub-tasks, used to estimate control costs in construction, with two additional steps added for the FEA to estimate the number of affected workers by industry and equipment category (numbered Step 3) and to estimate control costs for self-employed persons (numbered Step 5)—tables referenced below are in Chapter V of the FEA:

• Step 1: Baseline daily costs, relative costs of controls, and labor share of value

○ Use RSMeans (2008, Document ID 1331) estimates to estimate the baseline daily cost for every representative job associated with each silica equipment category (Table V-30) and unit labor and equipment costs (Table V-31).

○ Use vendors' equipment prices and RSMeans estimates to estimate the unit cost of silica controls (Table V-32), and estimate the productivity impact for every silica control and representative job, to be added to the cost of the control applied to a particular job (Table V-33).

○ Use the costs from Tables V-32 and V-33 to calculate the incremental productivity impact, labor cost, and equipment cost for each representative job when controls are in place (Table V-34).

○ Using Tables V-30 and V-34, calculate the percentage incremental cost of implementing silica controls for each representative job (Table V-35).

○ Calculate the weighted average incremental cost (in percentage terms) and labor share of total costs for each silica job category (outdoors and indoors estimated separately) using the assumed distribution of associated representative jobs (Tables V-36a and V-36b).

• Step 2: Total value of activities performed in all Table 1 silica equipment categories

○ Match BLS Occupational Employment Statistics OES occupational classifications for key and secondary workers with the labor requirements for each equipment category (Table V-37) and estimate the full-time-equivalent (FTE) number of employees by key and secondary occupations working on each silica task (Tables V-38a and V-38b).

○ Based on the distribution of occupational employment by industry from OES, distribute the full-time-equivalent employment totals for each equipment category by NAICS construction industry (Table V-39).

• Step 3: Total affected employment by industry and equipment category

○ Disaggregate construction industries into four distinct subsectors based on commonality of construction work (Table V-40a) and then estimate the percentage of affected workers by occupation, equipment category, and construction subsector (Table V-40b).

○ Use the percentage of affected workers by occupation, equipment category, and construction subsector (Table V-40b) to obtain total affected employment by occupation (Table V-41) and total affected employment by industry and task (Table V-42).

• Step 4: Aggregate silica control costs (not including self-employed persons)

○ Using the FTE employment totals for each task by NAICS construction industry (Table V-39) and the mean hourly wage data from OES, adjusted for fringe benefits, calculate the annual labor value of each Table 1 silica activity by NAICS construction industry (Table V-43).

○ Using the labor share of value calculated for each activity performed in a silica-related equipment category (Table V-43), estimate the total value of each Table 1 equipment/task category by industry (Table V-44).

○ Estimate the distribution of silica work by equipment type, duration of activity, and location of activity (Table V-45).

○ Multiply the total value of Table 1 construction activities requiring controls (Table V-44) by the percentage incremental cost associated with the controls required for each activity that uses equipment in each equipment category (Tables V-36a and V-36b) and weighted by the percentage of tasks performed outdoors and indoors/within an enclosed space (Table V-45), to calculate the total control costs, adjusted for baseline compliance, by Table 1 equipment category and industry (Table V-46).

○ Calculate engineering control costs for silica-generating construction activities not covered in Table 1 (Tables V-47a and V-47b).

○ Combine the control costs for Table 1 construction activities (Table V-46) and the control costs for construction activities not covered in Table 1 (Tables V-47a and V-47b) to calculate the total control costs by equipment category and construction industry (Table V-48).

• Step 5: Adjust aggregate silica control costs to include self-employed persons

○ Use data from the BLS Current Population Survey to estimate the ratio of the number of self-employed persons to the number of employees by occupation (Table V-49) and then redo the estimation after restricting self-employed persons to just those occupations covered by OSHA that potentially involve exposure to hazardous levels of respirable crystalline silica (Table V-50).

○ Multiply the FTE rate for each occupation (from Tables V-38a and V-38b) by the number of self-employed workers and employees in that occupation (from Table V-50) to obtain the ratio of FTE self-employed persons to FTE employees and then reduce that ratio to reflect only self-employed persons working on a multi-employer worksite where the work of the self-employed person cannot be isolated in time or space (Table V-51).

○ Increase the earlier estimate of control costs by equipment category and industry (Table V-48) by the adjusted FTE ratio of self-employed workers (Table V-40) to calculate total control costs by equipment category and industry with self-employed persons included (Table V-52).

Baseline Costs of Representative Jobs

Baseline Job Safety Practices

OSHA's cost estimates address the extent to which current construction practices incorporate silica dust control measures. Thus, OSHA's baseline reflects such safety measures as are currently employed. To the limited extent that silica dust control measures are already being employed, OSHA has reduced the estimates of the incremental costs of silica control measures to comply with the new PEL. As discussed in Chapter III of the FEA and summarized in Tables III-A-1 and III-A-2, OSHA estimates that 44 percent of workers with exposures currently below the new PEL are using the controls required in Table 1.

Representative Jobs

Unlike the situation with the general industry/maritime standard, OSHA does not have extensive data identifying the number of employees engaged in Table 1 tasks or the duration of their exposure to respirable crystalline silica during those tasks. Therefore, ERG developed a model based on “representative jobs” for the purposes of identifying the control costs necessary to comply with Table 1. Using RSMeans Heavy Construction Cost Data (RSMeans, 2008, Document ID 1331), which is a data source frequently used in the construction industry to develop construction bids, ERG (2007a, Document ID 1709) defined representative jobs for each silica-generating activity described in the feasibility analysis. These activities and jobs are directly related to the silica-related construction activities described in the technological feasibility chapter of the FEA. ERG (2007a, Document ID 1709) specified each job in terms of the type of work being performed (e.g., concrete demolition), the makeup of the crew necessary to do the work, and the requisite equipment. For example, for the impact drilling activity, ERG defined three representative jobs for various types of demolition work. For each job, ERG derived crew composition and equipment requirement data from the RSMeans (2008,Document ID 1331) guide and then calculated the per-day baseline cost from the labor rates, equipment charges, material costs, and overhead and profit markups presented in the cost estimating guide.

Table V-30 of the FEA shows the specifications for each representative job and the associated daily labor, equipment, and material costs. Table V-31 of the FEA provides a summary of the labor rates and equipment charges used to estimate the daily cost of each representative construction job in Table V-30 of the FEA. Note that the data on hourly wages with overhead and profit in Table V-31 of the FEA, obtained from RSMeans (2008, Document ID 1331), are employed here to be consistent with other RSMeans cost parameters to estimate the baseline costs of representative jobs. The RSMeans estimates are published for the purpose of helping contractors formulate job bids, so ERG relied on that data as an indicator of the amount of labor and time that would be required for each of the representative jobs in the cost model developed for this analysis. These RSMeans estimates are later used only to determine two ratios: The labor share of the costs of representative construction jobs and the percentage increase in the cost of each representative job due to the addition of controls to comply with the final rule. Everywhere else in the cost chapter, when the actual wages were important to the calculations and are expressed as fixed amounts and not just ratios, OSHA used 2012 BLS wage data, which include fringe benefits but not overhead and profit.

SBREFA Panel Comments on Cost Methodology for Construction

Prior to the publication of the PEA, one SBREFA commenter criticized the methodology for estimating engineering control costs on the grounds that while RSMeans estimates were used to establish the marginal costs of new controls (as a percentage of baseline costs), average wage rates (including fringe benefits) from the BLS Occupational Employment Statistics Survey, 2000, were used to calculate the value of at-risk tasks without providing a justification for not using RSMeans wage data (Document ID 0968, p. 13). Since BLS wage rates are significantly lower than the RSMeans rates used by ERG in earlier parts of the analysis, the commenter argued that this would significantly lower the base to which the marginal cost factors are applied to estimate compliance costs (Id.). This SBREFA commenter further argued that the RSMeans estimates are likely to be on the high end of estimated wages because they only cover unionized labor and are therefore likely to lead to high estimates of impacts. The commenter then recommended that more appropriate indexed labor wage costs be computed and used consistently throughout the analysis (Document ID 0968, p. 14).

First, the commenter's concern is misplaced because the choice of the RSMeans estimates source does not skew the results in the manner suggested by the commenter; nor does it even have a significant impact on the cost analysis. The RSMeans estimates were used only to develop the ratio of costs for the representative jobs to the total labor cost and then to determine the incremental compliance costs as a percentage of the total and the share (percentage) of estimate value with controls accounted for by labor. Because the RSMeans estimates are organized by project cost to assist contractors in bid planning, that data set is the logical choice for this purpose over BLS data, which provides wage data but does not provide comparable costs for projects. Dividing project labor value by the labor share of project value yields an estimate of total project value.

The absolute level of the RSMeans wage and equipment cost levels do not directly affect the resultant aggregate compliance costs. While lower wage rates would lower the baseline costs of the representative jobs, it does not follow that control costs as a percent of baseline costs would also be lower. In fact, if lower wage rates are combined with the same equipment costs, the equipment part of incremental control costs would be a higher percentage of total baseline costs. Only the labor share (percentage) of baseline costs, along with the incremental compliance costs as a percent of baseline costs, are taken from the analysis of representative costs and used in the subsequent estimation of aggregate costs. The absolute levels of the wage rates and equipment costs taken from RSMeans do not directly enter the aggregate cost analysis.

Second, OSHA notes that the BLS wage data, on which the aggregate compliance costs are based, are obtained from a statistically valid, national survey of employment and compensation levels and are the best available data characterizing national averages of wages by detailed occupation. For some of the reasons the commenter noted, OSHA believes that the BLS wage estimate provides a more accurate reflection of average wages.

Another set of SBREFA commenters criticized OSHA's cost estimation methodology, arguing that fundamental errors resulted in serious underestimates of the costs of engineering controls. The commenters asserted without any significant explanation that the task-by-task incremental cost estimates (shown in Table V-23 of the PIRFA, Document ID 1720, p. 749) should have been multiplied by two factors: (1) “The ratio of the RSMeans labor rate to the BLS wage and benefits rate,” and (2) the inverse of the “percentage in key occupations working on task” from Table V-26 (also in the PIRFA, Document ID 1720, p. 766). Under this approach, the commenters argued that “the cost of PEL controls for brickmasons, blockmasons, cement masons and concrete finishers performing grinding and tuckpointing would be approximately seventy-two (72.0) times the ERG estimate, and . . . the cost of PEL controls for drywall finishing (at the 50 μg/m³ PEL) would be approximately 7.2 times the ERG estimate” (Document ID 0004).

The rationalization for these calculations was not provided, and OSHA found these conclusions without merit. The incremental control costs shown in Table V-34 of the FEA were based on RSMeans estimates for labor and equipment costs. As shown in Table V-34, these cost estimates, after adjustments for productivity impacts, are used to calculate the percentage increase in baseline costs associated with each control. The RSMeans-based cost estimates shown in Table V-34 are also used to estimate the share of total baseline task/project costs accounted for by labor requirements. The averages of the percentage increase due to incremental control costs and the labor share (percentage) of total baseline costs are shown in Table V-37 of the FEA. These two percentages are used to extrapolate the aggregate control costs associated with each task. This extrapolation was based on (1) the full-time-equivalent employment in key and secondary occupations associated with each task, and (2) the value of the labor time as measured by the BLS occupational wage statistics, adjusted for fringe benefits.

OSHA provided similar responses in the PEA and requested comment on its responses to the SBREFA comments, but received none (see PEA, p. V-131).

The same set of SBREFA commenters further argued that OSHA's analysis contained five more “fundamental errors” (Document ID 0004). First, the commenters asserted that OSHA's calculations understate the actual cost because they are based on old data (1999 or 2000 data from RSMeans rather than RSMeans 2003 data). OSHA used the most recent available data at the time the initial preliminary analysis was completed and subsequently updated those data for the PEA (and the FEA) using RSMeans estimates from 2008 (Document ID 1331). However, as noted previously, the RSMeans estimates do not directly determine the absolute level of aggregate compliance costs, but rather the labor share (percentage) of project costs and incremental compliance costs as a percentage of baseline costs. This aspect of the analysis received no further comment and has been retained for the FEA.

Second, the commenters asserted that there is no information to “suggest much less substantiate the premise that the exposure monitoring data in Tables 3-1 and 3-2 [in the ERG (2007a) report, Document ID 1709)] (even if they were properly collected and analyzed) are in any way representative of current workplace exposures across the country” (Document ID 0004). In response, OSHA points out that the profiles used to estimate the numbers of workers exposed in excess of each PEL option were, in fact, based on the extensively documented technological feasibility analysis with many of the data points in the exposure profiles being taken from the findings of OSHA inspections (and based on ERG, 2007a, Document ID 1709). OSHA is tasked with using the best available evidence to develop the analyses, and the data in the exposure profile represent the best available evidence on current workplace exposures to respirable crystalline silica. More importantly, for estimating the cost of controls, Table 1 in the final rule is intended to be the default option for protecting workers performing covered tasks, regardless of actual exposure level. The FEA reflects this, while recognizing that a sizable minority of workers with exposures below the PEL have limited their exposures by using such controls currently.

Third, the commenters claimed that there is “is no information to suggest much less substantiate the premise that the exposure monitoring data in Tables 3-1 and 3-2 (even if they were representative of current workplace exposures) are in any way representative of the non-existent, theoretical jobs artificially created by the FTE [full-time equivalent] analysis so as to justify their use as the foundation for Table 4-12” (Document ID 0004). However, OSHA notes that the representative jobs on which the cost analysis is based were designed to correspond directly to the tasks assessed in the technological feasibility analysis. Furthermore, Table 4-12 in ERG (2007a, Document ID 1709) was derived directly from Table 3-2 and is independent of the “FTE analysis.”

Fourth, the commenters argued that a more logical and appropriate methodology would assume that all FTEs were exposed above the PEL in the absence of controls, and the commenter could find “no justification, and substantial support to the contrary, for an approach that artificially condenses actual exposures into far more highly concentrated exposures (by condensing all at-risk task hours into FTEs) and then [assumes] that, despite the impact of this change, the grab bag of exposure monitoring described in ERG Tables 3-1, 3-2 and 4-12 represents these FTEs” (Document ID 0004). The commenters asserted that the effect in ERG (2007a, Document ID 1709) of “first multiplying total project costs by the FTE percentage (from Table 4-8) and then by the `Percentage of Workers Requiring Controls' from Table 4-12 (and then by the average `Total Incremental Costs as % of Baseline Costs' by job category from Table 4-7) results in an unjustified double discounting of exposed workers in the incremental cost calculation” (Document ID 0004).

OSHA disagrees. The Agency notes that ERG (2007a, Document ID 1709) used the exposure profiles from the industry profile to estimate the number of full-time equivalent workers that are exposed above the PEL. In other words, this exposure profile is applicable if all exposed workers worked full time only at the specified silica-generating tasks. The actual number exposed above the PEL is represented by the adjusted FTE numbers (see Table 4-22 in ERG, 2007a, Document ID 1709). The adjusted FTE estimate takes into account that most workers, irrespective of occupation, spend some time working on jobs where no silica contamination is present. The control costs (as opposed to some program costs) are independent of the number of workers associated with these worker-days. OSHA noted in the PEA that the thrust of the comment about “double discounting” was unclear, but the commenters did not respond with clarification. Nothing is “discounted” in the estimation of aggregate control costs.

Finally, the SBREFA commenters argued that the “application of the FTE analysis to the additional equipment costs is based on the wholly unfounded assumption, contrary to actual experience, that this additional equipment could be used with perfect efficiency (i.e., never idle) so that it is only at a particular site during the time the at-risk tasks are being performed” (Document ID 0004). In response, OSHA notes that its analysis does in fact assume some efficiency with respect to the use of additional equipment required for controls. However, many of the equipment costs are based on monthly equipment rental rates provided by RSMeans that already embody some degree of idleness over the course of a year (see ERG, 2007a, Table 4-3, Document ID 1709). In other cases, daily equipment costs were directly estimated based on equipment purchase costs, annualization factors, and assumed operating and maintenance costs. OSHA did receive further comment on the issue following the publication of the PEA (Document ID 4217, pp. 84-88), and, in response, the Agency developed prorated ownership costs (equivalent to twice the rental rates) for control equipment for tradespersons performing tasks involving short-term, intermittent silica work.

Public Comment on Engineering Control Costs in Construction

Having already incorporated comments from small business in the SBREFA panel process, the Agency produced revised estimates for the PEA in support of the proposed silica rule. In the PEA, OSHA requested comments from rulemaking participants on the Agency's preliminary estimate of control costs in construction. Below are comments representative of the prominent issues that raised concerns.

The most broad-based critique of the construction cost analysis came from the Construction Industry Safety Coalition (CISC), and its consultant Environomics (Document IDs 2319, 2320, and 4217). Several of their arguments regarding underestimation of costs related to an undercount of the affected construction population (for example, they believed OSHA should have accounted for the cost to control silica exposures for plumbers). OSHA agrees in part that there were some occupations—plumbers, plumber helpers, electricians, electrician helpers, roofers, roofer helpers, terrazzo workers and finishers, and sheet metal workers—that likely have exposure and should be included in this analysis, as they do perform some activities covered by Table 1. These are discussed in FEA Chapter III, Industry Profile.

Owning Versus Renting Engineering Controls in Construction

OSHA also received comments regarding the availability of control equipment. In its post-hearing brief, CISC commented:

In the Agency's cost analysis, it has also made the entirely impractical assumption that controls (e.g., wet methods, LEV) for the tools that construction workers use in performing tasks that generate respirable silica need to be available only during the exact duration while a dusty task is performed. The CISC estimates costs instead to provide control equipment on an “always available” basis to workers who engage in dusty tasks. Control equipment must be available whenever a worker may need to perform an at-risk task, and not for only the very limited duration when the at-risk task is actually being performed. Costs for the engineering controls required to meet the reduced PEL in the proposed rule will be far higher than OSHA estimates (Document ID 4217, p. 29).

While OSHA agrees that CISC's argument has merit, during hearing testimony CISC's representative acknowledged that its estimates did not initially take into account the economic life of a control. This is reflected in the following conversation between CISC's Stuart Sessions and OSHA's Robert Stone:

MR. STONE: So returning to the methodology for costing, you pretty much used our numbers and you used our, presumably, like you mentioned the dust shroud that has a one-year life and, therefore, after one year, you take the cost again the second year, is that right? And the third year, and so on? Okay. I think this is perhaps a problem with the way you've done your analysis. We used basically FTEs, full-time equivalents. You're using three percent of the time let's say for plumbers, as an example, you're applying it to three crews, all right? At the end of one year, you're having them buy another dust shroud. And my view . . . they will have used nine percent of the economic life of the dust shroud. Now, you can argue I'd make an adjustment because we estimate 150-[day construction work-year] use of it, for full-time use. This would suggest, though, that after one year, you will have used one-sixth of the life of that dust shroud and an employer is not going to throw it out. It's still functional. He'll use it for the next five years. He'll use it for six years. Any views on that?

* * *

MR. SESSIONS: Yes. That's a good point, and I hadn't thought about that.

MR. STONE: Okay, thank you. A related point is actually the same issue. It would be operating in maintenance costs. You're—it's going to be one-sixth of our original estimate, but I don't think you've made that adjustment.

MR. SESSIONS: Correct. (Document ID 3580, Tr. 1501-1502).

After the hearing discussion, CISC revised its methodology, noting:

After additional thought and discussion about this issue with several construction tradespeople, we . . . concluded that useful life is a function of both how often the tool and controls are used, but also how long they sit in the construction worker's truck and get bounced around going from job site to job site (even when they are not used), and how often they are taken out of the truck and returned to the truck (even when they are only set up then taken down at the job site but not actually used). Thus useful life will increase if a tool sits idle for some percentage of the time when it is available, but useful life will not increase to the same proportional extent as the decrease in usage. We assumed in the example in workbook Tab # X2B that using the tool and equipment 1/4 as often will double its useful life (Document ID 4217, p 89).

OSHA agrees with this updated methodology and has adopted CISC's approach—essentially assuming one-half of the usage life over which to amortize the purchased control equipment—for jobs that typically involve intermittent short-term exposure. The jobs for which the Agency assumed a half-life of the control equipment were: (1) Hole drillers using hand-held or stand-mounted drills—for electricians, plumbers, carpenters, and their helpers, and for sheet metal workers; and (2) handheld power saws for carpenters and their helpers. Note that OSHA's adoption of this updated approach resolves CISC's criticism that OSHA had not accounted for productivity decreases from controls not being available when the worker needs to use them for short-term or intermittent silica jobs.

For all other construction jobs (i.e., those not itemized above involving intermittent short-term exposure), OSHA did not adopt CISC's approach but instead (as in the PEA) used the market-derived rental rate for control equipment without either doubling the rental rate to take into account “down-time” or requiring purchase of the control equipment. There are several reasons OSHA retained its PEA approach for these jobs in the final rule:

• In most cases, an employer's own/rent decision for control equipment will be determined by the own/rent decision for the construction equipment (including construction tools) to which the control equipment will be applied. If the employer rents/owns the construction equipment, the employer will rent/own the control equipment. The major exception would be if a particular piece of control equipment could be applied to many types of construction equipment. An example might be a dust collector. In that situation, the employer might find it economic to rent the construction equipment and own the control equipment. But, in that case, the purchased control equipment will not be sitting idle.
• Construction equipment is sufficiently expensive that employers, as a general matter, will not find it economically efficient to have it sitting idle. That is why employers so frequently rent construction equipment. Of course, employers that do only one type of construction job all year (or those that are sufficiently large that they work on that particular type of construction job all year) will find it economic to own the construction equipment—as well as the control equipment—but then the control equipment will not be sitting idle.
• In light of permit requirements and other job-planning requirements, in almost all cases, the employer will have advance knowledge of the details of the construction job (as opposed to, sometimes, repair work in general industry). This knowledge would include the construction equipment—and controls—required to perform the job. In fact, employers will often schedule construction jobs precisely to avoid having construction equipment sitting idle. In other words, the typical employer—and certainly the competent employer—won't come to the job site unprepared, needing to leave the job site to obtain rental equipment or controls.
• The construction sector is a significant component of the U.S. economy. There is a large, competitive construction equipment/control rental market in place to serve it. In most places, employers should be able to obtain needed construction equipment/controls in a timely manner under terms similar to those estimated here.

For the aforementioned reasons, OSHA believes that the ownership-versus-rental cost issue, except in the case of construction jobs that involve intermittent short-term exposure, is somewhat of a red herring. The difference in amortized cost should be negligible, given that employers will choose to own or rent based on whichever is the lower-cost alternative. In fact, because rental costs are typically somewhat higher than amortized ownership costs, OSHA may have overestimated compliance costs for those employers who purchase control equipment.

Self-Employed Persons

CISC, and its contractor Environomics, claimed in their comments that OSHA had omitted the costs of compliance by sole proprietors (typically self-employed persons) (Document ID 4217, p. 80). The inclusion of such costs and the circumstances under which they would arise are discussed in Chapter III of the FEA. In the FEA OSHA has accounted for costs associated with controlling employee exposures from sole proprietor activities. The actual self-employment data and the estimated effect on employer costs are presented at the end of this section on engineering control costs in construction.

Full Cost vs. Incremental Cost

Prior to the PEA, a participant in the SBREFA process noted that while OSHA established the total incremental cost for each silica control method (summarized for the final rule in Table V-35 of the FEA), the cost estimates were based on the application of a single control method. The commenter argued that there may be cases where two or more control methods would have to be applied concurrently to meet the exposure limits (Document ID 0968, p. 14). In response, OSHA noted in the PEA that for each task, specified control options correspond to the control methods described in the technological feasibility analysis in Chapter IV (of the PEA). These methods reflected the choices laid out in Table 1 of the proposed rule; they were also presented in Table V-25 in the PEA along with OSHA's calculation of the weighted average proportion of project costs attributable to labor and the incremental control costs as a percentage of baseline project cost.

Throughout the comment period, CISC reiterated its pre-PEA objections to OSHA's methodology of estimating incremental costs instead of the “full” compliance costs, which CISC defined as including the costs for employers to meet their existing duty to comply with OSHA's old PEL (CISC claims employers of “nearly 60,000 workers” were not in compliance with OSHA's preceding standard and would have OSHA attribute the costs of compliance with the preceding standard to the costs of this rule) (Document ID 4217, p. 33):

In our view, OSHA has made two errors in the approach it has taken:

• First, the “full” compliance costs for reducing worker exposures from their current levels to below the proposed new PEL are the conceptually correct costs to estimate when assessing economic feasibility, not the “incremental” costs for reducing exposures to below the proposed new PEL from a starting point assuming compliance with the current PEL. In practice, employers will face the full costs, not the lesser incremental costs, and the economic feasibility assessment should consider whether employers can afford these full costs, not the hypothetical and lower incremental costs.
• Second, OSHA has made a conceptual error in the Agency's methodology for estimating compliance costs * * * Insofar as OSHA omits all costs for [employees with exposures >250 µg/m³]—failing to estimate the costs to reduce their exposures all the way down below 50 µg/m³ instead of only to below 250 µg/m³—OSHA estimates costs that fall short of the incremental costs of the Proposed Standard that the Agency aims to estimate. (Document ID 4217, pp. 96-97)

Both arguments are now largely moot because in the FEA almost all of the construction engineering control costs are based on compliance with Table 1 and encompass all employees engaged in the Table 1 tasks, regardless of their current level of exposure. OSHA has included the full incremental—and full total—costs for all employers in construction who have workers who are performing tasks listed on Table 1, even those workers with exposures currently above 250 µg/m³.

CISC's arguments for the construction sector are now only relevant to the very few tasks not covered by Table 1, such as tunnel boring. OSHA therefore addresses CISC's arguments in the context of those few tasks.

The first argument is that employers who are not in compliance with the preceding PEL of 250 µg/m³ will have to incur costs to achieve that PEL in addition to the costs they will incur to reach the new PEL of 50 µg/m³. As laid out in the PEA, OSHA rejects this position, as this is inappropriate for estimating economic feasibility among firms making a good faith effort to comply with the existing silica rule. Employers who had a legal obligation to comply with OSHA's preceding PEL but failed to do so are not excused from their previous obligation by the new rule; nor can the fulfillment of a pre-existing duty be fairly re-characterized as a new duty resulting from a new rule. But this issue is not limited to construction, and a more complete discussion is presented in the general industry engineering control cost section in the FEA.

The second argument can be dismissed on similar grounds. CISC's argument appears to assume that employers will incur different costs for different controls necessary to reduce exposures from above 250 µg/m³ down to 250 µg/m³, and from 250 µg/m³ down to 50 µg/m³. In many cases, however, the same controls needed to bring exposures below 250 µg/m³ will also bring exposures to 50 µg/m³ or below, so there would be no cost associated with the new rule. To the extent that separate controls are required to reduce exposures down from 250 µg/m³ to 50 µg/m³, OSHA does account for the costs for those controls.

General Comments on Cost Methodology

James Hardie Building Products commissioned Peter Soyka of Soyka & Company LLC to perform an evaluation of the PEA. While Mr. Soyka's comments cover many aspects of the analysis and overlap with those of other commenters, some were relatively unique.

In one place, Mr. Soyka questions the entire method of analyzing jobs from the level of workers and their tasks. He expressed concern about both what he termed the failure to capture the cost to the establishment, as well as the need for workers to have controls available (Document ID 2322, Attachment G, p. 165). OSHA did not, however, ignore other costs for establishments. Elements of these costs are dealt with at the establishment level for some ancillary provisions of the standard, and are discussed later in this chapter. The second element, regarding the availability of controls for certain occupations, mirrors concerns raised by Environomics and CISC, and has been dealt with above.

Elsewhere in his comments, Mr. Soyka states that “OSHA should develop revised unit costs that consider the full array of elements that affect what a business charges its customers for a unit of time expended.” Such unit costs,” he submitted, “would include direct labor, fringe benefits, overhead, SG&A, and a reasonable allowance for profit (e.g., the typical cost of capital found in a specific industry or overall)” (Document ID 2322, Attachment G, p. 182). The approach put forward in the PEA and in the FEA incorporates fringe labor costs. OSHA has provided a sensitivity analysis of the effects of including other cost elements in the sensitivity analysis section of the FEA. As noted elsewhere, for the FEA the Agency recognizes that the labor productivity effect of adopting certain controls is accompanied by a loss of productivity in equipment under certain circumstances; that additional cost has been incorporated in the FEA. The National Association of Home Builders (NAHB) faulted the costing of engineering controls in the PEA on several grounds, including several very similar to those raised by Mr. Soyka and addressed earlier. NAHB also stated that OSHA has not considered the “unique nature of construction, in that sites are not fixed in nature, and that equipment may need to be moved between several sites in a single day” or the “compliance costs for cleanup of the jobsites” (Document ID 2296, p. 38). Both are addressed in the FEA as opportunity costs or housekeeping costs.

Other Aspects of Unit Costs

Following publication of the NPRM, a representative of petrochemical employers, the American Fuel and Petrochemical Manufacturers, raised concerns about retrofitting and clean-up costs that it claimed were improperly omitted from OSHA's analysis of engineering controls in construction:

OSHA claims “[t]he estimated costs for the proposed silica standard rule include the additional costs necessary for employers to achieve full compliance.”[ ] Yet it fails to consider the additional costs of retrofitting existing equipment to comply with Table 1 in Section 1926.1053 (Table 1). In addition to acquiring new engineering controls not previously implemented, many employers will have to modify pre-existing equipment to come into compliance (e.g., outfitting the cab of a heavy equipment bulldozer with air conditioning and positive pressure). Table V-3, found in OSHA's complete PEA, begins to address these costs by enumerating the capital and operating costs for the engineering controls required by Table 1. But it does not account for the ancillary costs of retrofitting those controls, including the cost of retrofitting the equipment itself as well as the lost time the facility may absorb in doing so.

OSHA also fails to account for the clean-up costs associated with the natural by-products from Table 1's required engineering controls. For example, many of the engineering controls require the use of wet methods or water delivery systems. [ ] Employers will incur costs from removing (from the clean-up process itself and lost time) excess water to prevent ice or mold from developing. Yet these costs go unaccounted for in the PEA (Document ID 2350, pp. 6-7).

In the FEA, the Agency does not include any specific cost for retrofitting equipment. The record indicates that almost universally employers either already have equipment with the required controls available for use (e.g., wet method for saw), or the equipment allows for the easy addition of a control (e.g., shroud for HVAC). Furthermore, most equipment is portable and/or handheld and is relatively inexpensive with a useful life of two years or less. As a result, it would simply not make economic sense to retrofit the equipment when it would be less expensive to replace it. In addition, most other types of relevant construction equipment—heavier and drivable—generally have a useful life of ten years or less; control-ready equipment of this type has been on the market for years and is typically already in use. Thus, OSHA did not estimate any retrofitting costs. While some employers might still retain pieces of earth-moving equipment that do not have a cab that complies with Table 1, equipment with a cab is the industry standard for both purchase and rental. As discussed in this chapter in the context of productivity, the implication is that the market has shifted to heavy equipment with cabs even in the absence of a silica standard. In addition, in final Table 1 OSHA has reduced the number of tasks that require equipment with enclosed cabs to just a single task: Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials or used during demolition activities involving silica-containing materials. For the odd piece of old, cab-less heavy equipment which does not conform to the requirements of Table 1, individual employers have the choice of renting the required equipment to perform that single task, or simply using the cab-less equipment only on non-silica tasks (thereby ceding the one silica-abrading construction task to employers that have more up-to-date equipment). In short, the requirement to use a cab when performing Table 1 tasks is not a requirement to retrofit all existing equipment that might conceivably be used for a Table 1 task.

Regarding the question of clean-up costs, the commenter treats the issue as if there were no clean-up costs associated with generating silica currently. As discussed in the Environmental Impact Analysis (Section XIV of this preamble) and in the discussion of productivity impacts later in this section, there was substantial comment to the record indicating that in many, if not most, situations, the controls associated with reducing silica exposure will lead to a net decrease in the amount of time required for cleanup after a job. While OSHA is not attempting to quantify any potential cost savings, the record likewise does not support attributing additional costs to cleanup.

Specific Industry/Equipment Category Cost Comments

Crushing Machines

William Turley, executive director of the Construction & Demolition Recycling Association (CDRA), broadly described the impacts he anticipated for his industry.

Recyclers who crush materials for reentry into the economic mainstream as aggregate products would appear to have to do all of the following:

• Purchase and install climate-controlled enclosures or cabs for all crusher operators;
• Install crusher baghouses for particulate emission reduction;
• Enclose conveyor belts—a measure unprecedented in our industry;
• Install effectively designed and maintained water spraying equipment;
• Impose full-shift use of respirators for all quality control hand pickers working on processing lines;
• Establish and implement emission testing protocols and procedures to ensure compliance with the PEL;
• Implement medical surveillance programs for all employees engaged in material crushing activities; and
• Achieve a “no visible emissions” standard, which frankly is both unattainable and utterly unreasonable.

To the best of our knowledge, no recycler in the United States has a system even resembling the above. The cost of such systems will unquestionably threaten the economic viability of construction & demolition debris recyclers across the Country. It must also be pointed out that the industry has an exceptionally diverse composition of larger operators with higher economic margins and small operations with limited capabilities to capitalize the type of equipment called for in this rulemaking (Document ID 2220, pp. 2-3).

The final silica rule does not require all the above steps. OSHA expects that crushing machines will be used for construction/demolition activities, as discussed in detail in the Summary and Explanation of the standard. As such, OSHA anticipates that employers engaged in the recycling operation would follow Table 1 and would not need to conduct exposure monitoring.

For crushing machines, OSHA removed the “no visible emissions” requirement and the requirement for enclosed cabs, both of which had been in the proposed Table 1. Employers are now required to use a spray system and comply with manufacturer instructions. Also, there is no requirement to enclose conveyor belts or install crusher baghouses. Instead, employees must use a remote control station or ventilated booth that provides fresh, climate-controlled air to the operator. For the FEA, OSHA added the cost of a ventilated booth for the use of crushing machines in construction/demolition activities. Most crushing machines are already equipped with movable controls that will allow operation of the machine from inside the booth, so no additional equipment modifications will be required for most machines. Crushers available for purchase or rental are also typically equipped with a water spray system, so OSHA has not assessed any incremental cost for sprayers.

Homebuilding—Roofing

The National Roofing Contractors Association (NRCA) objected to OSHA's preliminary cost estimates for controls used to limit silica exposure in roofing operations, claiming that OSHA's preliminary estimate of an average of $550 per year for firms that employ 20 workers or fewer (covering the majority of roofing contractors) had significantly underestimated the cost of specialized saws that would be required for roofing equipment. In support of the argument that OSHA had underestimated costs, NRCA identified costs for retrofitting portable saws with integrated dust collection systems along with specialized vacuums equipped with HEPA filters (Document ID 2214 p. 4).

The task of cutting most roofing materials would fall under “Handheld power saws (any blade diameter)” in Table 1, and the final version of Table 1 does not allow for the dust collection methods described, so the majority of costs quoted by NAHB are not relevant. Instead, the final version of Table 1 requires that the employer use wet methods. Second, the estimate of $550 a year in costs to very small employers was an estimated average across all affected establishments with fewer than 20 employees, not just roofing operations in homebuilding. Questions of small business impact or economic feasibility for the roofing industry are dealt with Chapter VI of the FEA.

The comments submitted by consultant Peter Soyka on behalf of James Hardie Building Products (“Hardie”) presented a table of typical devices with engineering controls involved in fiber cement cutting and an un-sourced range of costs for the retail prices of those types of devices and their controls (Document ID 2322, p. 13).

Hardie's inclusion of a table of retail prices for the purchase of equipment with controls suggests there may have been a misunderstanding of the nature of OSHA's cost methodology—it is not based on purchasing entirely new pieces of equipment, but making sure the equipment has the controls necessary to comply with Table 1. To the extent commenters submitted estimates addressing the latter question, OSHA has taken them into consideration in its final estimates.

Asphalt Milling

Fann Contracting, Inc. acknowledged that the availability of equipment with built-in controls is rising. However, the commenter suggested that OSHA's preliminary assessment of the design specifications and costs for the engineering controls identified in Table 1 of the proposed rule had under-counted the amount of milling machines and other paving-related equipment that the commenter believed would still require additional retrofits to enclosed cabs (sealing cracks, adding air conditioning, upgrading to HEPA filters, etc.) to satisfy the requirements in Table 1 (Document ID 2116, pp. 6-7).

Table 1 in the final rule does not require a cab for milling machines or any of the equipment identified by the commenter for paving purposes, so the commenter's concerns are not relevant. Table 1 only requires cabs for “(xvii) Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials,” and specifies it as an option for “(ix) Vehicle-mounted drilling rigs for rock and concrete.” Table 1 requires employers to use wet methods to control dust emissions from milling machines. These costs have been accounted for in the cost analysis.

Drywall Finishing

A SBREFA commenter raised questions about the availability of silica-free joint compound for drywall finishing (Document ID 0004). In the PEA, OSHA relied on NIOSH studies showing that silica-free joint compounds had become readily available in recent years (see ERG, 2007a, Section 3.2) (Document ID 1709). The cost model for the PEA assumed that 20 percent of drywall finishing jobs would continue to use conventional joint compound. Based on additional information, OSHA has determined that all commercially available joint compounds have no, or very low amounts of, silica and do not pose a risk to workers from respirable crystalline silica (Document ID 2296, pp. 32, 36; 1335, p. iii) and has therefore not included drywall finishing in Table 1 or taken any costs for this task (see Section XV. Summary and Explanation of the Standards, Specified Exposure Control Methods for more information).

Number of Days Controls Are Used Annually

Whether equipment, and the relevant controls, are rented or purchased, the effective annual cost of the equipment is based on the assumed number of days per year that it would be used. In the PEA, OSHA had estimated rental of the equipment for 150 days during each 365-day period. Based on comments received from industry representatives during the 2003 SBAR Panel process (Docket ID 0968), this estimate had been reduced from an average of 250 days in the Preliminary Initial Regulatory Flexibility Analysis (PIRFA). This reduced workday estimate presumably reflected winter weather slowdown in many parts of the country, as well as general weather conditions (such as rain) that can interfere with many construction processes, and resulted in 2/3 higher daily rental rates for control equipment.

However, Environomics, in developing its own cost estimates, assumed that control equipment would be used for 250 days a year, without an articulated rationale for departing from the estimate provided during the SBAR Panel process (Document ID 4023, Attachment 2, X2B-Hole Drilling Unit Costs, Cell P:Q44). More importantly, Environomics selectively and inconsistently applied 250 days only to the frequency of usage but not to the daily rate (which OSHA had based on 150 days of usage). To see why it is a problem to apply a different number of days to the same daily rate, consider a piece of control equipment, with a one-year life, known to cost $1,500. Using a 150-day construction work-year, OSHA would estimate a daily rate for the control equipment of $10 ($1,500/150 days in the construction work-year). The annual cost for that control would be $1,500 ($10 multiplied by 150 days). Using the same example, Environomics would keep OSHA's daily rate of $10 (amortized over 150 days) but apply it to a 250-day calendar to arrive at an annual cost of $2,500—where the one-year cost of the equipment was known to be $1,500. In short, the selective 250-day methodology Environomics used results in an overestimation of costs by 67 percent.

Accordingly, OSHA has decided to retain the 150-day construction work year based on the best available evidence, and the Agency has consistently applied that work-year throughout the cost analysis developed in the FEA for construction. (General industry and maritime work is typically less affected by weather, so a separate work-year number of days is used for those calculations).

Unit Control Costs

In developing the cost estimates in the FEA, OSHA defined silica dust control measures for each representative job (see ERG (2007a, Document ID 1709). Generally, these controls involve either a water-spray approach (wet method) or a dust collection system to capture and suppress the release of respirable silica dust. Wet-method controls require a water source (e.g., tank) and hoses. The size of the tank varies with the nature of the job and ranges from a portable water tank (unspecified capacity) costing $15.50 a day to a 10,000 gallon water tank with an engine-driven discharge, costing $168.38 a day. Depending on the type of tool being used, dust collection methods entail vacuum equipment, including a vacuum unit and hoses, and either a dust shroud or an extractor. The capacity of the vacuum depends on the type and size of tool being used. Some equipment, such as concrete floor grinders, comes equipped with a dust collection system and a port for a vacuum hose. The estimates of control costs for those jobs using dust collection methods also include the cost for HEPA filters.

The unit costs for most control equipment are based on price information collected from manufacturers and vendors. In some cases, control equipment costs were based on data from RSMeans (2008) on equipment rental charges (Document ID 1331). Table V-32 of the FEA shows the general unit control equipment costs and the assumptions that OSHA used to estimate the costs for specific types of jobs.

For each job identified as needing engineering controls, OSHA estimated the annual cost of the appropriate controls and translated this cost to a daily charge, based on an assumed use of 150 days per year (30 weeks), as explained earlier. The only exceptions were engineering controls expected to be used for short-term, intermittent work. For these controls, consistent with the CISC methodology that OSHA adopted, carpenters and other occupational groups were estimated to purchase this control equipment, and for costing purposes, OSHA amortized the equipment over its “half-life”—that is, over 75 days rather than 150 days (effectively doubling the daily capital costs of the equipment). Accordingly, Table V-32 of the FEA shows separate daily cost estimates, for regular and for infrequent use, for a dust extraction kit and for a 10-15 gallon vacuum with a HEPA filter.

Incremental Labor Costs and Productivity Impacts in Construction

In addition to incremental equipment costs, OSHA estimated in the PEA the incremental labor costs generated by implementing silica dust controls. These labor costs were generated by: (1) The extra time needed for workers to set up the control equipment; (2) potential reductions in productivity stemming from use of the controls; (3) additional time to service vacuum dust control equipment; and (4) additional housekeeping time associated with or generated by the need to reduce exposures. All additional labor costs related to the use of controls were subsumed into a single additional labor productivity impact estimate for each of the representative job categories. Except where otherwise noted, the productivity impact described is negative, meaning that the addition of the control is expected to reduce productivity. To develop estimates of the labor productivity impacts of the dust control equipment that would be required as a result of the proposed standard, ERG interviewed equipment dealers, construction contractors, industry safety personnel, and researchers working on construction health topics.

In part, because most silica dust controls are not yet the norm in construction, knowledge about the impact of dust controls on productivity was uneven and quite limited. More precisely, few individuals that ERG interviewed were in any position to compare productivity with and without controls and the literature on this topic appears deficient in this regard. Overall, telephone contacts produced a variety of opinions on labor productivity effects, but very few quantitative estimates. Of all the sources contacted, equipment rental agencies and construction firms estimated the largest (negative) productivity impacts. Some equipment vendors suggested that there are positive productivity effects from control equipment due to improved worker comfort (from the reduction in dust levels). Others suggested that the use of dust collection equipment reduces or eliminates the need to clean up dust after job completion. Comments to the record, discussed below, closely mirrored this preliminary information.

The estimation of labor productivity effects is also complicated by the job- and site-specific factors that influence silica dust exposures and requirements for silica dust control. Potential exposures vary widely with hard-to-predict characteristics of some specific work tasks (e.g., characteristics of materials being drilled), environmental factors (e.g., wet or dry conditions, soil conditions, wind conditions), work locations (e.g., varying dust control and dust cleanup requirements for inside or outside jobs), and other factors. Generalizations about productivity impacts, therefore, are hampered by the range of silica dust control requirements and work circumstances.

After considering the existing evidence OSHA concluded that labor productivity impacts are often likely to occur and accounted for them in the PEA analysis. In the PEA, depending on the general likelihood of productivity impacts for each activity, OSHA used a productivity impact ranging from zero to negative five percent of output. After considering the many comments advocating for both increasing and decreasing the productivity impact estimates, OSHA has concluded that the estimates in the PEA were approximately correct and has retained the PEA estimates for the FEA. The comments and factors influencing each selection are described in the following discussion.

SBREFA Panel Comments on Productivity Impacts

In response to the SBREFA Panel, the Reform OSHA Coalition commented on the estimates of the impact of exposure control equipment on productivity during construction operations. This SBREFA commenter noted that the estimates of the productivity impact of using additional control measures were based on interviews with dealers, contractors, and researchers working on construction health topics and expressed its opinion that it was not clear how this “purely qualitative analysis [was translated] into productivity [impact] rates . . . . ” (Document ID 0968, p. 14). The commenter indicated that engineering control compliance costs would be sensitive to the ultimate choice of productivity impact measures (Id.).

OSHA responded to these comments in the PEA as part of the discussion of the basis for OSHA's productivity estimates. OSHA summarizes the responses to SBREFA comments here for the convenience of the reader. As described in the PEA, ERG's research revealed little substantive, quantitative evidence about the magnitude of the productivity impacts of the controls, and in some cases, the direction of the impacts (positive or negative) appeared to depend on the specific nature of the job. OSHA's estimates in the preliminary analysis reflected ERG's best professional judgment about the likely magnitude of these impacts. Some of the estimates may be conservative because under some scenarios for certain tasks the productivity impacts could be significantly smaller than those shown in Table V-23 of the PEA. In some scenarios the productivity impact may even be positive.

The same commenter also expressed a concern that even though “silica is not now considered a hazardous waste,” OSHA had not analyzed the impact of the proposed rule on disposal of “[silica-]contaminated” wastes such as “filters of dust control vacuums and contaminated water discharge” (Document ID 0968, p. 28). The commenter asserted that disposal issues are “acute on the construction site where a means to readily dispose of such material or water is not available” (Id.). The comment was somewhat puzzling because the comment was premised on the fact that there is not currently any “hazardous” classification for such waste that would trigger special disposal duties, and the commenter did not explain why any additional costs would be incurred beyond normal disposal practices. OSHA did not identify any new areas of cost in its Environmental Impacts analysis presented in the FEA, and finds no evidence that employers will be required to incur additional environmental costs as a result of this rule, other than some potential permit-modification notification costs addressed in the discussion of engineering control costs for general industry in the FEA. The incremental disposal costs resulting from dust collected in vacuums, discarded filters, and other sources in construction are therefore likely to be de minimis. An analysis of wet methods for dust controls suggests that in most cases the amount of slurry discharge is not sufficient to cause a runoff to storm drains or surface water.

Public Comment on Productivity Impacts in Construction

OSHA invited comment on the productivity impacts—positive and negative—resulting from the introduction of controls to limit exposure to silica. In the discussion below, OSHA reviews comments supporting both negative productivity impacts and positive productivity impacts. The comments supporting negative productivity impacts include assertions that OSHA underestimated the negative productivity impact of complying with the silica rule, failed to include a productivity impact on equipment, and failed to include a fixed productivity impact. OSHA considered those comments before concluding that it will generally retain the approach it used in the PEA, with the exception of selectively adding additional costs for productivity impacts on equipment in response to a point raised by CISC. OSHA will also explain separately why it is not calculating any productivity impact for two specific activities: (1) Use of cabs for earthmoving equipment, and (2) drywall installation.

Public Comments Suggesting That OSHA Underestimated the Productivity Impacts Associated With Engineering Controls

The Interlocking Concrete Pavement Institute reported that “converting from in-place paver cutting to wet cutting and/or vacuum systems could induce a 50 percent productivity penalty,” but did not otherwise substantiate that claim beyond noting that it was a survey response from one of its members (Document ID 2246, Attachment 1, p. 3).

Mr. Soyka, in the comments prepared for Hardie, critiqued OSHA's estimates of the productivity impact on construction operations as “far too small” and urged OSHA to adjust productivity-loss estimates based on empirical data “if available” (Document ID 2322, Appendix G, pp. 14-15 and 21-22). However, the commenter did not clearly identify any such empirical data in the comments. The only labor-based engineering control cost alternative offered by the commenter that resembled “empirical data” is the addition of a seven-hour penalty per job that was “based on a JHI time-motion study” apparently conducted exclusively in a single industry (new home construction) and comprised of data from just the JHI study (Document ID 2322, Appendix G, Attachment A, p. A-8). OSHA could not determine whether it would actually supply new “empirical evidence” that would warrant a change from the preliminary estimate because the study was not submitted into the record. The commenter cites “James Hardie Building Products, Inc., undated, pg. 15,” which appears to align with an entry in the list of references to an undated “James Hardie Labor Efficiency Manual,” but that manual was not submitted into the record.

Mr. Soyka recommended that OSHA use time-motion studies to derive the estimated productivity impacts.

[. . . F]ew [of the productivity penalties estimated by OSHA] are supported by actual data (e.g., time-motion studies). OSHA should apply a more conservative approach that considers how work flow and task completion are likely to be affected by newly required changes to existing practices as well as entirely new activities (Document ID 2322, Appendix G).

In addition, Mr. Soyka developed an alternative cost model that included additional productivity impacts that OSHA did not include. In this model Mr. Soyka “assumed that wherever possible, company owners in the residential construction industry will outsource their compliance obligations to specific subcontractors . . . providing the products and services that might generate significant amounts of silica dust” (Document ID 2322, Appendix G, p. 26). In this scenario, Mr. Soyka determined that the employer would require “the subcontractor to relocate its work location outside the house(s) being constructed to a distance sufficient to ensure that silica dust concentrations remained minimal inside and around the house(s)” and that “relocating the materials and work giving rise to silica dust generation [. . .] would add substantially to the time required to complete the associated tasks” (Document ID 2322, Appendix G, p. 30). He accounted for this additional time by increasing the productivity impact on the specialty subcontractors to seven hours per job, “based upon time-motion studies conducted by James Hardie (James Hardie Building Products, Inc., undated, pg. 15)” (Document ID 2322, Appendix G, p. 31).

Mr. Soyka's model also included a productivity impact for “wearing respirators to account for fatigue and adverse impacts on employee-to-employee communication” (Document ID 2322, Appendix G, p. 32).

OSHA fundamentally disagrees with the Mr. Soyka's assumptions. Mr. Soyka's assumption that all silica-generating tasks need to be removed from the homebuilding site results from a misunderstanding of OSHA's statement that “[i]n response to the proposed rule, many employers are likely to assign work so that fewer construction workers perform tasks involving silica exposure; correspondingly, construction work involving silica exposure will tend to become a full-time job for some construction workers” (FR, 2013, at 56357) (Document ID 2322, Appendix G, p. 25). OSHA did not mean that silica-generating tasks will be subcontracted out and that subcontractors will be forced to perform these tasks off-site. Rather, the Agency was acknowledging that construction employers would likely consolidate the responsibilities for performing silica-generating tasks to as few workers as possible in order to limit exposures to peripheral workers.

As mentioned previously, the “time-motion studies” performed by James Hardie, compiled in an unpublished reference, were not provided for public inspection. Moreover, the description of how those data were used in developing the model suggests that Mr. Soyka's relevant assumptions are not based on time-motion studies of how long it actually takes to perform specific tasks with controls added. Rather, it appears that Mr. Soyka assumed inflated times to perform the tasks, based on a misunderstanding of what the proposed rule required; in any case, it is not descriptive of the requirements for the final rule. Mr. Soyka's suggested approach contrasts with the estimates provided by CISC/Environomics, which accepted the limitations of the analytical exercise and agreed with most of the estimates in the PEA regarding the “variable” productivity effect.

Moreover, it should be noted that aside from weighing the possible competing forces on productivity in the course of a shift (e.g., more time for set up vs. less time required for clean-up), there is also a short-run/long-run phenomenon over a longer period as the standard comes into use. There may be a short learning curve until workers determine the most efficient way to perform a job when controls are introduced (Document ID 3581, p. 1700); in some cases the effect may be relatively larger until the method of performing a job is reconceptualized. Mr. Sokya criticizes OSHA for not recognizing “the dynamic nature of construction” (Document ID 2322, Appendix G, p. 19), but one obvious aspect of the dynamic nature of construction is that employers will be constantly adapting to changing circumstances and trying to find ways to perform the job in the most cost-effective manner. In short, the Agency believes that a time-motion study of a particular task is neither necessary to determine approximately what the effect will be in the short-run, nor would it allow OSHA to determine what the long-run cost of integrating the controls will be.

CISC and its consultant Environomics, as well as some other commenters, questioned OSHA's productivity-loss estimates associated with the required controls. CISC/Environomics claimed that overall OSHA “underestimated productivity losses associated with performing tasks using the prescribed controls by an amount roughly equal to the average equipment intensity of about 42 percent” (Document ID 2320, p. 29). CISC/Environomics reported that this underestimation came largely from OSHA failing to account for what they termed “fixed productivity impacts” and for productivity impacts to equipment. Both of these concerns are discussed below.

In its post-hearing brief, CISC/Environomics presented the results from a questionnaire and interviews conducted with employers and knowledgeable tradespeople; the results included a finding that “the variable penalty percentages [. . .] were the same as or slightly larger than those that OSHA had estimated” (Document ID 4217, p. 92). CISC/Environomics did not submit the questionnaire or the answers received, nor the details of the interviews, to the record so OSHA could not fully evaluate the findings or compare them to its own findings. Based on the available summary information it appears that, while CISC and OSHA's estimates for variable productivity costs were nearly identical, it is not clear that CISC's estimates took current compliance into account. CISC stated that its members felt that “something greater than zero variable productivity penalty should be estimated for masons using portable saws controlled with wet methods [. . .] and for heavy equipment operations using enclosed cabs and HEPA filters” (Document ID 4217, pp. 92-93). OSHA acknowledges that there would be a productivity impact to comply with the requirements of the silica rule relative to using no controls for those activities. However, as shown in Chapter III of the FEA, Industry Profile, OSHA has found high levels of baseline compliance with the provisions of the rule for those activities. As is standard in OSHA's costing methodology, only costs above and beyond those incurred under current standards are attributable to the final rule.

In addition, CISC argued that OSHA should take higher productivity impacts because “in some fraction of these instances [(where controls would be required)], the controls are hellaciously difficult to use” (Document ID 3580, Tr. 1321). The testimony goes on to give examples of such difficulties such as when “building houses where the utilities are not yet in and the water is not yet in,” when working in places where power is not readily available such as in parking garages or on scaffolding, and when doing work that requires wet methods outdoors in extremely cold temperatures (Document ID 3580, Tr. 1321-1322). A different commenter, the National Utility Contractors Association, similarly criticized OSHA's estimates for excluding additional water-transportation costs: “there is not always a water supply available which would require trucking large volumes of water to the job site which adds additional costs.” (Document ID 3729, p.3)

Given the fact that the majority of the silica-generating equipment requiring controls under this standard—such as tuckpointing grinders and concrete drilling equipment—require electricity, OSHA does not find merit in applying any productivity impact simply because the controls for those tools may also need electricity. If the employer can find a way to power the equipment, it can also power the controls when necessary. Similarly, employers must commonly transport water to worksites without it for cleanup and sanitation purposes, and OSHA's technological feasibility analysis explains why the amount of water required to generate the spray mist is not typically very significant. Although it seems plausible that wet methods would occasionally be used outdoors by some employers in weather cold enough to freeze the water mist used to control the silica dust, this is far from a common construction occurrence. Moreover, it is not entirely clear from the record that freezing mist would decrease productivity. OSHA's estimates of productivity impacts is intended to represent an average across all situations, and the tiny fraction of time wet methods will need to be used outdoors in extremely cold weather should not skew the average productivity impact.

CISC/Environomics stated that there should also be a productivity impact on equipment rental or use as well as for the additional labor to operate that equipment longer. Environomics reported that a complete cost estimate of productivity loss would include not only the additional labor time required, but also the cost of having to rent equipment for a longer period of time.

. . . Simply put, a productivity penalty for labor will translate to a productivity penalty for equipment. For example, if due to a labor productivity loss, the labor time required to complete a job increases from eight hours to eight hours and 15 minutes, the equipment time required for job completion will also increase to eight hours and 15 minutes. Additional equipment rental costs will be incurred for the additional 15 minutes, or equipment owned by the employer will be delayed for use on another job by 15 minutes (Document ID 2320, p. 29).

This concern was reiterated both in its hearing testimony (Document ID 3580, Tr.1323) and in its post-hearing brief where Environomics stated that “OSHA's analysis should add an equipment component to the costs associated with whatever productivity penalty is incurred in performing a construction task using the Table 1 controls” (Document ID 4217, p. 91). OSHA agrees, in part, and recognizes that there can be a productivity impact for equipment (as well as for labor) for many tasks when there is a cost created by having to extend the rental time of the equipment.

In the PEA, OSHA had estimated the labor productivity impacts associated with engineering controls to reduce silica exposure. For the FEA, the Agency has added a parallel cost for the equipment portion of the cost for a number of equipment categories. These are itemized in Table V-34 of the FEA. For example, for Task 15 (Demolition of concrete slabs, mesh-reinforcing, up to 3″deep), there is estimated to be a 2 percent labor increase related to maintaining wet methods for dust suppression. In the original Means estimates, it was estimated that approximately 70 percent of the costs of the task were labor-related, divided between an operator and a laborer. This 2 percent additional cost is estimated to amount to $9.39 in added labor cost for an equipment operator and $7.84 for a laborer, or a total labor productivity cost per job of $17.23. For the FEA, OSHA is adding an additional cost item of $7.58 to reflect an opportunity cost, in the form of a prospective extended equipment rental cost, raising the total incremental estimated cost to $24.81 per task. As with the other construction engineering control costs, this additional cost item is task-specific.

While OSHA judged that equipment productivity can be impacted negatively by the new rule for many tasks, there are two general categories for which the Agency determined that there would be no impact on equipment productivity. The first broad category is short-term, intermittent work in which the equipment and control are often idle. An example would be a plumber drilling holes in concrete. The equipment and control are sufficiently inexpensive (relatively speaking) that the construction employer or trade contractor (or possibly even the tradesperson) would typically own rather than rent the equipment and control. As discussed elsewhere in the FEA, OSHA determined that certain tradespersons, such as plumbers, electricians, and their helpers, are more likely to purchase their equipment, rather than renting it. OSHA estimated the cost of purchasing control equipment at twice the rental cost.

The second category of tasks for which the Agency did not assess any equipment productivity impact is the group of tasks in which there is not a fixed ratio of labor to capital (capital in this case including rental costs). For example, as explained in the following unit cost discussion, Task 10 (as detailed in Table V-34 of the FEA) involves performing earthmoving as a heavy equipment operation task. In this case, while extra time by a laborer would be required to tend to the application of wet methods, such application would be done simultaneously with actually performing the earth-moving task. Thus, while wet methods for Task 10 would require an added labor cost (itemized as a “productivity” cost), it would not actually slow down the operation so as to require the longer period of use of the equipment that would impose an equipment impact.

CISC/Environomics also argued that part of the productivity effect was fixed and would therefore need to be accounted for separately. This fixed component, CISC/Environomics reported, would be “typically involving activities such as initial set-up and final take-down and clean-up of the control equipment, [which] often occur at the beginning and end of a job or work shift” (Document ID 4217, p. 90, see also 2320, p. 28; 3580, Tr. 1320). This would mean that shorter jobs would have a relatively larger percentage loss in productivity.

Other commenters did not agree that there would be costs related to set up. During the hearings, Deven Johnson, of the Operative Plasterers' and Cement Masons' International Association, testified that the concrete grinding “tools that are on the market today come integral with the capture device[. . .] The hose is attached to the grinder already. The electrical cord is attached to the motor already. [. . .] You simply plug it in and start using it [. . .] there's no setup time” and that for “a walk-behind concrete diamond-bladed saw for cutting slabs, the setup time is, make sure there's gas in it and . . . hook a water hose up to it and turn the water on” (Document ID 3581, Tr. p. 1699). During the hearing, Manafort Brothers described a wheel-based machine used to suppress dust during demolition operations, which was simply wheeled onto the worksite and hooked up to a water supply and electrical source (Document ID 3583, Tr. 2430), and the Building Trades Construction Department (BCTD) of the AFL-CIO submitted an extensive list of available tools that included the controls required by the rule that would require little or no set up (Document ID 4073, Attachment 4a).

Based on the evidence in the record, OSHA determined that any time needed to set up the engineering controls required by this rule is adequately accounted for in the productivity impacts the Agency has included, particularly in light of the fact that OSHA is not making any adjustment to account for productivity improvements that are likely to result from this rule (see the discussion of comments identifying productivity improvements later in this section). Environomics' inclusion of both a “fixed” productivity impact as well as a “variable” productivity impact, without recognizing offsetting productivity benefits identified by other commenters', results ins a significant overestimate of the productivity impact.

Public Comments Suggesting That OSHA had Overestimated the Productivity Impacts Associated With Engineering Controls

BCTD strongly disagreed with CISC's estimates about productivity decreases resulting from the rule, stating in their post-hearing brief:

[a]ll that [CISC] offered to support these significant increases [in the productivity impact] is an explanation of how its approach to calculating productivity differs from OSHA's and a few examples, such as:

So in the case of the carpenters with the dust extraction equipment on the drill and the HEPA vacuum, the carpenter takes a little bit longer to do his hole-drilling task because he's got to attach the equipment to the drill. He's got to attach the hose to the HEPA vacuum. He's got to walk over before he drills and he's got to turn on the HEPA vacuum. Then after he drills, he's got to turn off the HEPA vacuum. He's got to periodically empty the HEPA vacuum. He's got to worry about the vacuum hose from the drill to the vacuum getting kinked and all that sort of thing. So the job takes a little bit longer. Tr:1317-18.

CISC offered no evidence that its analytical approach is more accurate than OSHA's. Moreover, this description of how its hypothetical carpenter would deploy control technology assumes the employer would select the most cumbersome and inefficient technique available, rather than taking advantage of the range of more suitable and less costly tools that are readily available on the market. See, e.g., Ex. 4073, Att.7a (ROI: hand-held drill with integrated dust collection) (Document ID 4223, pp. 55-56).

BCTD also took exception to the fact that “CISC acknowledged that `there may be a productivity net gain in terms of cleanup from using a control,' Tr:1319 (Sessions), [but did] not appear to have taken potential gains into consideration when estimating its lost productivity cost” (Document ID 4223 pp. 55).

Dr. Ruth Ruttenberg highlighted the various areas where the PEA may have overestimated the negative productivity effect of engineering controls in construction. She stated that the assumption of a negative impact on productivity

. . . is yet another example of OSHA erring on the side of being conservative in cost estimates. Despite the fact that some who were interviewed suggested there could be a positive impact on productivity, OSHA's PEA assessed anywhere from 0 percent to a 5 percent penalty in productivity loss as a result of OSHA compliance with the proposed silica rule. (PEA, p. V-123-124) The impact of an assumption of lost productivity can be profound, and OSHA acknowledges this: “. . . the magnitude of the productivity impacts can substantially change the estimate of the overall cost increase associated with controls” (PEA, p. V-131).

Despite the fact that OSHA leaves likely productivity increases out of its calculations, it does point to opportunities to increase productivity with dust control. [. . .]

Limiting dust increases visibility for workers. (PEA, p. V-126) Vacuum systems speed up drilling because continuous removal of drill cuttings from the hole, reduce the need for workers to periodically stop and clean. (PEA, p. V-128) And the list goes on. OSHA's cost estimates are conservative, and high, when it comes to productivity impact (Document ID 2256-A4, p. 7).

Productivity Improvements

In addition to comment that the productivity loss due to this rule would be minimal, OSHA also received considerable comment to the record that the controls would improve productivity in a number of ways the Agency had not factored in—for example by reducing clean-up time by capturing dust at the source, improving worker comfort and morale, and encouraging innovation.

Productivity Improvements—Reduced Clean-Up Time

Testimony at the public hearings by the International Union of Bricklayers and Allied Craftworkers on the experience by union members with engineering controls suggested that use of controls may boost productivity by reducing the amount of dust that needs to be cleaned up during a given shift. The following is a hearing dialogue between Chris Trahan of BCTD, and Sean Barrett of the International Union of Bricklayers and Allied Craftworkers:

MS. TRAHAN: [. . .] In your experience is there any productivity gains or benefits that you can describe?

MR. BARRETT: I can. These machines, when running correctly, when [. . .] the vacs are regulated, the filters are running good. You can run that machine until 3 o'clock in the afternoon, shut it off, and go home. [. . .] If [the machine is] not [running correctly], you constantly got to keep going back and cleaning up what you already did. You're losing productivity. And over the course of [. . .] a month you're talking 40 man-hours. You're talking a—paying a guy for a week. It's—that's not the case at all [if dust controls are functioning]. You would actually increase productivity by having the right equipment there and not have people have to keep coming back or jimmy-rig little things to try to get by. Just do it the way it was designed, and you'll get a lot farther. . . . (Document ID 3585, Tr. 3055-3057).

Deven Johnson of the Operative Plasterers' and Cement Masons' International Association elaborated on the potential time savings of some of the new engineering controls:

Walter Jones of the Laborer's Health and Safety Fund testified that, for some tasks, reducing or eliminating the need to clean up after a job can dramatically increase productivity, in this case by one-third:

We had the Bricklayers here a few days ago and they were talking about their ability to work till 3:00, because they did not have to clean up. Instead, when they use non-dust controlling or capturing devices, they would have to stop right after lunch in order to begin cleaning up. So we're looking at adding a few more hours to the workday. So to me, in my mind, they're way more productive (Document ID 3589, Tr. 4246).

Joel Guth, President of iQ Power Tools and a mason contractor, testified that he had been able to document the savings in clean-up time.

In certain industries we've been able to measure the time savings from cleaning up the silica dust [. . .] It saves them one to two to three hours a day in cleanup time because they don't have to wash down the house or wash the windows or wash the bushes where they're inherently dry cutting (Document ID 3585, Tr. 2981).

Scott Schneider, CIH, Director of Occupational Safety and Health. Laborer's Health and Safety Fund of North America, discussed how engineering controls contribute to a more productive workplace:

When you control the dust and you don't have—you're not breathing it into your lungs, but you're also not spraying it all over the construction site, all over the sidewalk, and you have to clean it up, there's a lot of other costs involved in not controlling. So I think we're going to realize those benefits by implementing the standard (Document ID 3589, Tr. 4277).

Productivity Improvements—Improved Worker Comfort

OSHA also heard a good deal of testimony suggesting that productivity will be improved through the use of engineering controls due to improving the working conditions for workers.

Mr. James Schultz of Wisconsin Coalition of Occupational Safety and Health described the physiological and practical benefits of introducing or enhancing engineering controls:

I think if you would work in the work environment that was less dust or hopefully dust free, it would definitely increase the amount of productivity just because so much of the time you're spending wiping the dust off your brow because it's falling into your eyes or something like that. Even if you have the respirator, it still interferes with your vision and things like that. So a cleaner environment would definitely be more productive just because [. . .], you spend less time trying to think about how you can protect yourself from this hazard, and I know myself, after working in the place for many years, I've started to have breathing problems and so if you can eliminate those breathing problems, if you can breathe freely, you're also going to be much more productive because you're not going to stop because you have [to] wheeze or go stand outside to get some fresh air for awhile or those types of things (Document ID 3586, Tr. 3253-3254).

Deven Johnson, mentioned previously, testified about the human effect of controlling silica as well:

Another thing is, an individual who is working in an environment where [. . .] he or she is constantly bombarded with concrete dust all day long, your productivity drops as you get more and more miserable as the day goes on. Commonsense would dictate, if you're not blasting me in the face with dust and sand and silica for eight hours a day, that I'm going to feel physically better and I'm not going to be as tired and exhausted and pissed off as I normally would be at the end of the day. Your productivity goes up[. . .]. (Document ID 3581, Tr. 1594-1595).

Mr. Javier Garcia Hernandez, from National Council for Occupational Safety and Health/Equality State Policy Center/Laborsafe, testified on the cognitive factors that affect productivity, and why engineering controls should aid productivity:

. . . as a construction worker, I highly believe that we're more productive when we are protected[. . . .]. We spend less energy focusing on how to protect ourselves. Just imagine you're working in a roomful of dust and you're just trying to either close your eyes or cover your mouth so the less you breathe. So you're constantly thinking about how to breathe less dust but if you have the respirator or the wet, the controlled area, whether it is water or respiratory protection, you're much more productive because our mind is less occupied in how to protect ourselves and we spend that time that we would have spent protecting ourselves working (Document ID 3586, Tr. 3248-49).

Todd Ward, a bricklayer, testified that workers have some awareness of the hazards of dry cutting blocks and that

. . . when [workers] on the job [are] dry cutting they know—it affects morale as well when they know [. . .] they have some safeguards and they're protecting their lungs. So there is an increased productivity when you have a good morale then on the job (Document ID 3585, Tr. 3057).

Productivity Improvements—Innovation

OSHA received comments on the fact that OSHA standards often lead to innovation.

The Laborers' Health and Safety Fund of North America pointed out that “[j]ust about every OSHA standard has had a look-back that has shown [that] industry has innovated to meet the new standard” and continued, saying that “[w]e believe a new OSHA standard with a lower PEL will spur innovation in the construction industry to meet the challenge” (Document ID 3589, pp. 4183-4184).

Charles Gordon observed that “reality is that the new technology will increase productivity faster, so that the actual costs will be much less than predicted” (Document ID 3855, Tr. 3815).

Conclusions Regarding Productivity Impacts

In summary, while some commenters have asserted that OSHA has underestimated the productivity penalties of using engineering controls in construction, other evidence in the record suggests that the aggregate net productivity effect of implementing engineering controls could either be neutral, or possibly positive. In the absence of detailed quantitative data on these various potentially offsetting effects, OSHA has conservatively chosen to retain its percentage estimates from the PEA, while adding some additional productivity impacts that will increase not only labor costs but also equipment costs.

There is one exception: OSHA has removed the productivity impact that it had included in the PEA for drywall installers. As explained in the unit cost discussion, the Agency has determined from the record that there is no economic reason why drywall installers would now use silica-based drywall installation—the U.S. market has shifted entirely to a silica-free compound (Document ID 2287, p. 38; 2296, Attachment 1, p. 30; 1335, pp. 3-4, 7, 10). Therefore, there is no longer a logical basis for a assigning a productivity loss to workers performing this task.

Table VII-12 summarizes the labor productivity estimates. As discussed previously, while empirical quantitative data are quite limited on productivity, it is possible to gauge the relative productivity impacts across the principal control options. For example, OSHA judged that there are no productivity impacts for certain controls, such as mobile crushing machines. On the other hand, OSHA found that the controls required for tuckpointers and grinders may result in additional time being spent setting up and maintaining controls over the course of a workday. In Table V-34 of the FEA, productivity impacts, or “lost production time,” are shown by task and are factors in OSHA's estimate of incremental cost per day.

As discussed, OSHA has retained most of its original estimates of the productivity effects from the PEA. In some cases, however, Table 1, which forms the basis for the equipment categories listed in Table VII-12, was changed from the PEA in response to comment. (see Methods of Compliance in this preamble for further discussion on the changes to Table 1). In other cases, OSHA received clarification on the manner of exposure and added elements to Table VII-12, but did not adjust the productivity impact. For example, OSHA received very specific comments on tasks involving portable masonry saws used to cut fiber cement materials (e.g., “Hardie board”), and this is reflected in specific descriptions in Table 1 and in Table VII-12, but the estimated productivity impact for “masonry cutting using portable saws” remains the same. Similarly, the Table 1 task that included “heavy equipment operations” in the proposed rule has been broken out into two groups: (1) Heavy equipment operators and ground crew laborers used for activities such as grading and excavating that will not involve demolition or other uses that will abrade or fracture silica-containing materials; and (2) heavy equipment operators and ground crew laborers involved in demolition or the abrading or fracturing of silica-containing materials. These two categories are now estimated to have productivity impacts of two and three percent, respectively.

Productivity Impact Estimates, by Equipment Category

Rock and Concrete Drilling

This equipment category includes the following Table 1 tasks:

• Dowel drilling rigs for concrete; and
• Vehicle-mounted drilling rigs for rock and concrete

This equipment category covers a range of drilling activities using truck-mounted and similar drilling equipment, such as quarry drills and crawler-type drills. Dust control requires the use of either a dust collection system or wet drilling methods. Studies of the effectiveness of available dust collection systems have not addressed performance issues, but ERG judged that their use does not affect drilling productivity. While workers must service the dust control equipment during the workday, this activity generally does not affect the rate of drilling, except perhaps for short-duration jobs. The wet drilling methods are integrated into drilling equipment and also should not adversely affect the drilling rate. Thus, OSHA estimates that there will be no lost production time for these tasks.

Tuckpointers and Grinders

This equipment category includes the following Table 1 tasks:

• Handheld grinders for mortar removal (i.e., tuckpointing); and
• Handheld grinders for uses other than mortar removal

According to ERG's search of the literature, grinding tools can be retrofitted with dust control shrouds that connect to a vacuum system (Buser, 2001 & 2002, Document ID 0577). Studies on the use of these controls indicate that extra time is required to install the shroud and periodically clean, empty, or replace the vacuum drums, filters, or bags. The estimated time to install the shroud may be as short as five minutes, although some types of shrouds take longer to install. Once installed, however, the shroud can be left in place for the work at that location, so this activity need not take place at the initiation of each grinding job.

For interior jobs and for exterior work that requires site cleanup of grinding debris, the additional work time required to use a vacuum system might be partially offset by savings in the time required to seal work areas (to prevent dust migration) and to clean the work area after task completion. Overall, clean-up times will vary depending on the size of the job site, the quantity of grinding debris, and the strength and capacity of the vacuum.

Grinding without a dust-control shroud can generate clouds of dust that might impair a worker's views of the grinding area. Whereas metal shrouds also block the view of the grinding area, plastic shrouds allow workers a view of the work area. Some contractors have noted, however, that use of shrouds does not allow for the precision required for certain tasks, such as grinding an inside corner (Lattery, 2001, Document ID 0777).

For exterior jobs where cleanup is not required and where the work area is not sealed, the use of vacuum equipment is likely to decrease productivity for the amount of time required for servicing the vacuum collectors. If, for example, five minutes were required to empty the vacuums every two hours, production time would decline about 4 percent, due simply to dumping the accumulated dust.

At some construction sites, vacuums have been used during the grinding process, but without shrouds. In these cases, one worker typically holds the vacuum nozzle near the grinding tool, which another worker operates. Switching to shrouds with a direct vacuum attachment would eliminate the need for this assistant and is a more productive operation.

Manufacturers and vendors cited other benefits from using the shroud-vacuum systems. Because dust does not build up on and clog the surface of the grinding wheel, the wheels last longer, resulting in an approximate 40 percent savings on the grinding discs (Eurovac, 2001, Document ID 0688). Another source contacted by ERG estimated that shrouds can increase the abrasive life of a grinding wheel by more than 500 percent (Buser, 2001 & 2002, Document ID 0577). In this regard, workers would spend slightly less time replacing wheels over the life of the equipment.

OSHA concluded that while the productivity impacts of vacuum systems can sometimes be partly offset by other factors, net productivity impacts are likely to remain negative. For exterior work, productivity is clearly lower when workers use a vacuum system. Overall, based on ERG's research, OSHA's final cost estimates include a 5 percent impact for lost production time associated with grinding operations in construction. This productivity impact is identical to the impact estimated for this activity in the PEA.

For a tuckpointing project, NIOSH researchers examined the use of vacuum system controls at a large college building complex (Gressel et al., 1999, Document ID 0718). Workers used a shroud-vacuum system with an integral impeller and a fabric dust collection bag. This system required emptying the collection bags about once an hour. The authors reported some problems caused by blocking and kinking of the hose and occasional separations of the hose from the tool. Some of these problems can be attributed to the design of the dust control system and might be rectified by future design innovations. Overall, the vacuum control systems appeared to reduce worker output.

Manufacturers and vendors contacted by ERG estimated that polyurethane shroud-vacuum systems with tuckpointing equipment, similar to those used with hand-held grinders, actually enhance productivity. Among the reasons provided for productivity improvements were: (1) Fewer workers were required; (2) cleanup times were reduced; (3) workers had improved visibility of the work surface; and (4) blades last longer (Buser, 2001 & 2002, Document ID 0577; Caperton, 2002, Document ID 0580; Eurovac, 2001, Document ID 0688; Nash and Williams, 2000, Document ID 0829). These observations on productivity applied to tuckpointers with 2- to 8-inch diameter wheels. In addition, positive effects on worker productivity have also been reported for shrouds that fit on 5-inch and 7- to 8-inch (18-lb) tuckpointers with integrated dust-collection systems since equipment without integrated dust-collection systems require that an additional worker be present to continually vacuum dust away from the work area (Document ID 0577). On the equipment that can be used with the tuckpointers with 5- to 8-inch wheels, an impeller inside the tool housing pushes dust down a hose into a reusable dust-collection bag (Document ID 0577). One vendor estimated that the operational productivity of these tools is no different from that of the same tool without dust control capability. Workers would still be required to periodically empty dust bags, although other clean-up time might be somewhat reduced (Document ID 0580). Because tuckpointing work is almost exclusively exterior work, however, clean-up is often not required.

Based on the considerations for hand-held grinding tools discussed above and the findings from the NIOSH tuckpointing study, OSHA judged in the PEA that use of a vacuum system during tuckpointing operations would impose, on average, a 5 percent negative productivity impact. Based on these findings and because manufacturer optimism about any positive productivity impacts has not been documented in controlled studies, OSHA included the same 5 percent negative productivity impact for tuckpointing tasks in the FEA.

Heavy Equipment Operators and Ground Crew Laborers

This activity includes the following Table 1 tasks:

• Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition; and
• Heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing or abrading or fracturing silica-containing materials

The control method proscribed in the proposed silica standard was to enclose and ventilate the operator's cab. The requirement for an enclosed cab is only retained in the final standard with respect to the use of heavy equipment used to abrade or fracture silica-containing materials or used during demolition. Final Table 1 allows employers to control dust from heavy equipment used for other purposes (e.g., grading or excavating) by using wet methods.

Using an enclosed cab on heavy construction equipment will not require maintenance beyond the general maintenance necessary to maintain the integrity of the cab enclosure. Therefore, OSHA estimated in the PEA that no productivity loss will be incurred for this control.

In the case of heavy equipment operations, CISC/Environomics estimated that there would be a one percent productivity penalty for enclosed cabs, due to communication issues and the need to unclog HEPA filters (Document ID 4217, p. 93). For several reasons OSHA is not persuaded that the factors CISC cites would result in a net productivity loss for enclosed cabs on heavy equipment.

First, it is not clear that communication issues are being created by setting some minimal standards for enclosed cabs. Information supplied in the record indicates that there are alternate means of communication beyond shouting from the cab to the front-line workers outside the cab, including hand signals (Document ID 3583, Tr. 2441) and existing wireless communication systems (Document ID 0805, p. 4; 2262, p. 28). Many of these work environments are noisy, which seems to make alternate means of communication desirable, if not required.

Second, it appears that it may be more economical and desirable for workers to operate in a climate-controlled cab and that equipment with enclosed cabs has become standard in the construction industry. In fact, OSHA has determined that relevant heavy equipment currently comes with an enclosed cab as standard equipment (Document ID 3813, 3814, 3815, 3816), and in pricing construction jobs, RS Means included a cab as a standard equipment (meaning that it was already included in the equipment cost, not an added engineering control). In any case, the fact that cabs are standard suggests that potential buyers do not view the presence of a cab to be undesirable. While Environomics acknowledged this possibility at the hearings, their judgment remained that there would be a net productivity loss (without providing information on how these offsetting considerations were being incorporated) (Document ID 3580, Tr. 1434-1435). While OSHA is not persuaded that the evidence in the record supports Environomics conclusions, their argument is largely moot. Any productivity impact would result only from the addition of new controls, but enclosed cabs appear to have become standard on the relevant equipment, meaning that in most cases employers would not have the option of using open cabs even if OSHA's new rule was not in effect. Thus, there can be no productivity impact attributed to the requirement for a cab.

Although OSHA is not including any productivity impact to account for enclosed cabs, final Table 1 requires water, or other dust suppressants, during specified heavy equipment operations in order to protect workers outside the cab and as an alternative method of protecting operators for activities that do not involve silica abrading or fracturing. OSHA has therefore, as indicated in Table VII-12, added a 2 percent productivity impact for heavy equipment tasks involving grading and excavating, and 3 percent during demolishing, abrading or fracturing silica-containing materials. OSHA judged that the abrading, fracturing, and demolition-related tasks tend to be relatively dustier, and would therefore require relatively more labor to administer.

Hole Drilling Using Handheld or Stand-mounted Drills

This equipment category includes the Table 1 task “handheld and stand-mounted drills (including impact and rotary hammer drills).”

This category includes workers in the construction industry who use handheld drills to create clearly defined holes for attachments (e.g., anchors, bolts, hangers) or for small openings for utility pass-throughs in concrete and other silica-containing construction materials. Workers use common electric drills, pneumatic drills, handheld core drills, stand-mounted drills, rotary drills, rotary hammers, percussion hammer drills, or other impact drills to drill holes. With regard to core drills, only small, handheld core drills with bits up to a few inches in diameter are included in this category. This discussion does not address the use of portable and mobile hole saws used to produce large holes or openings. That equipment is covered in the discussion of Masonry and Concrete Cutters Using Portable Saws.

Handheld and rig-mounted drills can be equipped with local exhaust ventilation to effectively capture dust generated when drilling small diameter holes. Larger core drills, also referred to as core saws, are more frequently used with water as a coolant to extend the service life of the drill bit, as well to suppress dust.

One rock-drill manufacturer asserts that use of vacuum systems speeds drilling by continuously removing the drill cuttings from the hole, making it unnecessary for workers to periodically stop drilling to accomplish this task (Atlas-Copco, 2001, Document ID 0542). On the other hand, the connection and servicing of the vacuum equipment requires incremental work that could reduce productivity. If the construction project at hand involves interior work, this impact might be offset by reductions in the time necessary for cleanup (i.e., interior work would require cleanup, while exterior drilling probably would not). In the PEA, OSHA applied a 2 percent productivity impact where this task is performed and did not receive comment suggesting that this estimate was too low, so OSHA retains the same 2% productivity impact in estimating compliance costs in the FEA.

Jackhammers and Other Powered Handheld Chipping Tools

This equipment category includes the Table 1 task “Jackhammers and handheld powered chipping tools.”

Silica exposures generated during pavement breaking, concrete demolition, and other concrete work using jack hammers and other handheld powered chipping tools (including pavement breakers and other similar tools) are controlled through the use of wet or dry methods.

Regarding wet methods, because the work area generally cannot be presoaked effectively (i.e., dust is generated once impact drillers break through the surface), OSHA judged that adequate dust control requires a constant spray of water to the work area. Thus, dust control requires that a water sprayer be mounted onto the jackhammer (or that a mobile sprayer be set up that can move along with the work). Alternatively, a crew member can use a water hose to spray and wet the concrete and asphalt surfaces being broken, although the associated productivity loss could be substantial, and, for that reason, OSHA believes that construction firms would likely try to avoid that approach.

However, OSHA judged that the incremental productivity impact from the spraying activity is modest because various crew members could occasionally be enlisted to keep the water spray directed in the correct location. Further, because of the interactive nature of the various crew member activities, the time to move the water sprayer is unlikely to affect the overall crew output. In addition, incremental cleanup costs generally would not be significant since most drilling projects are performed outside. Nevertheless, to allow for some incremental work related to supplying water and positioning the spray when wet methods are used, as was the case in the PEA, for the FEA OSHA estimated a 3 percent productivity impact for this equipment category when wet methods are used.

A separate, higher, productivity impact was defined for use of dry methods for activities where jackhammers and other handheld powered chipping tools are used. Dry methods are somewhat less flexible and require a shroud for the close capture of dust as it is generated during operations. Workers also periodically have to empty the vacuum bags in which the dust accumulates. Thus, as discussed above with respect to the use of a shroud for grinding and tuckpointing, these controls are judged to generally have a greater productivity impact during operations and, consistent with the PEA, OSHA assigned a 5 percent productivity impact to use of this control method for this equipment category.

Masonry and Concrete Cutters Using Portable Saws

This equipment category includes the following Table 1 tasks:

• Handheld power saws (any blade diameter);
• Handheld power saws for cutting fiber-cement board (with blade diameter of 8 inches or less);
• Rig-mounted core saws or drills;
• Walk-behind saws; and
• Drivable saws

Drivable saws and walk-behind saws have an integrated water tank, and the sawing is almost always done wet (see FEA Chapter IV, Technological Feasibility). Wet sawing keeps the blade from overheating, with the water acting as coolant. Rig-mounted core saws used to drill larger diameter holes in concrete are typically used with water as a coolant to extend the service life of the bit, as well as to suppress dust.

As has been noted, most portable hand-held concrete saws are designed with wet-sawing capability (see Chapter IV, Technological Feasibility of the FEA). These saws have a water hookup for a hose attachment, but might also be used for dry cutting. (Dry-cut diamond blades for dry cutting are available; these are made especially so that the tips do not separate during dry cutting.)

A construction equipment distributor judged that there are no operational productivity advantages for dry cutting, as opposed to wet cutting (Healy, 2002, Document ID 0726). Wet cutting, however, requires access to water (water line or pressurized tank), and some time is needed to connect the equipment (although OSHA received a number of comments saying that this hook up is very simple and not time consuming—see “Public comments suggesting that OSHA underestimated the productivity impacts associated with engineering controls” earlier in this section for more detail). In addition, the water hose hookup may be cumbersome and interfere with the work (Healy, 2002, Document ID 0726). For these reasons, as was estimated in the PEA, for the FEA, OSHA assigned a cost of 2 percent in lost production time for equipment in this category.

For the final rule, the Agency has clarified in Table 1 that hand-held circular saws with a blade diameter of eight inches or less specially designed for cutting fiber cement board can be used outdoors without respiratory protection, when equipped with a local exhaust ventilation. The productivity impact for this group is also estimated at 2 percent because, although it does not have an impact on job performance, it involves some set-up time and incremental maintenance.

Masonry Cutters Using Stationary Saws

This equipment category includes the Table 1 task “Stationary masonry saws.” Stationary saws for masonry, brick, and tile cutting come equipped with water systems for wet cutting, which is the conventional, baseline control method for this type of work. Some modest incremental time is needed to provide for and connect the water supply and to maintain the water nozzles and spray system. This incremental time was the basis for OSHA to estimate a 2 percent cost in lost production, both in the PEA and in the FEA.

Millers Using Portable or Mobile Machines

This equipment category includes the following Table 1 tasks:

• Walk-behind milling machines and floor grinders;
• Small drivable milling machine (less than half-lane);
• Large drivable milling machines (half-lane and larger with cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate)

The activities performed using equipment in this category range from cold planing and cleaning of asphalt to surface planing or grinding of concrete. In large-scale projects, such as street resurfacing, baseline practices are judged to control silica dust exposures. No additional controls would be needed, and therefore no negative productivity impacts are expected.

While some grinding machines designed for milling concrete surfaces have built-in dust collection or wet-method systems, others must be attached to external vacuum equipment. ERG reviewed the available literature and found no evidence that the grinding operation is slowed when such vacuum equipment is attached. Nevertheless, workers must devote some time to setting up equipment, changing vacuum bags or barrels, and cleaning filters. On the other hand, using an LEV system to capture dust as it is generated reduces the time required for cleaning up the settled dust from the surfaces following completion of the grinding task. OSHA estimated in the PEA that there would be a 2 percent productivity impact for milling using wet methods and a 5 percent productivity impact when using LEV systems. These estimates have been retained for the FEA.

Mobile Crushing Machine Operators and Tenders

This equipment category comprises the Table 1 task “Crushing machines.”

OSHA projected in the PEA that there would be no productivity impact for this equipment category. The Table 1 requirements for this machinery have changed in the final rule, but OSHA's conclusion that there will be no productivity impact remains the same. Final Table 1 requires employers to protect employees through a combination of sprayers and requiring the operator to operate the machinery from within a ventilated booth or at a remote control station. Once installed, the sprayer systems will be part of the crushing machine operation and will not impact production rates. For the purpose of the economic analysis of this rule, OSHA has accounted for additional costs for use of the ventilated booth. Because the booth can be located close to the machinery, there would not be productivity loss from the operator having to travel to a different location for operation. In most cases the booth can be set up quickly once at each location, so in most cases there will not be any significant productivity loss associated with the use of the booth.

Baseline and Incremental Unit Control Costs

Table V-34 in the FEA, and presented as Table VII-13 in this section, summarizes the control method and costs per day for each representative construction job. These costs include incremental equipment costs and indirect labor costs due to productivity impacts (decreases in productivity associated with the use of the control equipment).

Note that the only silica tasks in Table V-34 of the FEA considered to have short-term infrequent work where the employee would own the equipment are Task 11: Hole drilling using hand-held or stand-mounted drills and Task 18: Masonry cutting using portable saws—II. Note also that all the indoor tasks in Table V-34 of the FEA have an additional daily control equipment cost of $1.67 for a fan.

Table V-35 of the FEA summarizes the baseline costs and incremental control costs from Tables V-30 and V-34, of the FEA, respectively, for each representative silica-related job in OSHA's silica construction cost analysis. The control cost (defined as incremental control costs per day) are shown in Table V-35 of the FEA as a percentage of the baseline daily job costs. As the incremental control costs were obtained from Table V-34, they are just the sum of additional labor and equipment costs associated with the use of silica controls, including the labor and equipment productivity impacts of the use of the silica controls.

As is evident from Table V-35 of the FEA, these incremental control costs can range from 0.3 percent to 7.8 percent of the baseline job cost. The magnitude of the productivity impacts can substantially change the estimate of the overall cost increase associated with the silica dust controls.

Table V-36a of the FEA presents the weighted average of control costs by task category for outdoor tasks. OSHA defined “weights” for each job category (column “Relative Frequency Within Categories”) based on the projected relative applicability of the controls and/or tasks within each category (as determined in the technological feasibility analysis in Chapter IV of the FEA). These percentages did not change from the PEA except for the two tasks that have each been further partitioned into multiple tasks in the final rule: Heavy construction operators and masonry cutters using portable saws. Heavy equipment operators are subdivided into tasks that involve fracturing, abrading, or demolishing silica-containing materials such as masonry or concrete, that require use of wet methods whenever workers other than the equipment operator are present, and tasks that involve use of heavy equipment for earthmoving and excavation of soil, that require wet methods only as necessary to minimize fugitive dust. Masonry cutters using portable saws are subdivided into five categories: (1) Handheld power saws such as cutoff saws; (2) handheld power saws for cutting fiber-cement board with blade diameters of less than eight inches; (3) walk-behind saws; (4) drivable saws; and (5) rig-mounted core saws. Wet methods are specified as a control method for all use of portable saws except for handheld power saws for cutting fiber-cement board, for which LEV rather than use of water to suppress dust is required. The labor cost as a percentage of project costs—which, as subsequently shown, is a critical factor in calculating the total value of all silica-generating construction activities—is derived from Table V-30 of the FEA.

Table V-36b of the FEA presents the weighted average of control costs by task category for tasks indoors or in enclosed areas (“indoor tasks”). The procedures are identical to those used in Table V-36a of the FEA, and the only difference is that the total incremental costs as a percentage of baseline costs are higher due to the addition of the cost of a fan for indoor tasks.

Once the total value of all silica-generating construction activity is calculated for each task, as shown in Table V-44 of the FEA, the incremental costs associated with each task category as a percentage of baseline costs (from Tables V-36a and V-36b of the FEA) will determine the costs that the engineering control requirements in the final construction standard add to the costs of construction activity—that is, the incremental costs of the resulting reduction in silica exposure.

Aggregate “Key” and “Secondary” Labor Costs for Representative Projects

To estimate aggregate labor costs or value for each equipment category, OSHA first matched OES occupational classifications with the labor requirements for each equipment category (e.g., hole drillers using hand-held or stand-mounted drills). These matching occupations are shown in Table V-37 of the FEA. In order to estimate the percentage of time during each work day that workers spend on activities using equipment in the relevant categories, OSHA designated some occupations as “key” and others as “secondary.” The key field in Table V-37 is set to “1”, if a key occupation and to “0” if a secondary one. Even those employees who are engaged in tasks on Table 1 typically spend only a portion of their workdays engaged in silica-generating tasks, so the distinction between “key” and “secondary” is needed in order to estimate the amount of time workers participate in silica-generating tasks. In the preliminary and final cost analyses, OSHA applied ERG's occupation designation, as explained in greater detail below. OSHA requested comment on the designations of “key” and “secondary” designations in the PEA, but did not receive any comments challenging those designations.

“Key” occupations refer to the worker or workers on each crew who perform the principal silica-generating activity using the equipment in each equipment category. For each equipment category, ERG estimated the overall percentage of time that workers in key occupations devote to the activity.

Other “secondary” crew members (e.g., first-line supervisors/managers and construction laborers) were estimated in terms of their ratio to the number of key workers required for given task areas. The secondary crew ratios range from 0 percent (no one in a secondary occupation engaged in silica-generating tasks) to 300 percent (three times the number of secondary occupation workers, in relation to the number of key workers, exposed to silica-generating tasks). As noted above, OSHA used these percentages and ratios to estimate (on an annual basis) the amount of time these employees are using relevant equipment to engage in work that causes silica exposures. The estimate of the percentage of time performing the silica-generating activity can be viewed in terms of the full-time-equivalent (FTE) employees engaged in work that utilizes equipment in each equipment category. These estimates and the corresponding ratios for secondary workers are shown in Table V-37 of the FEA.

For the key occupations, OSHA was able to obtain some data with which to estimate the proportion of time workers perform activities using silica-generating equipment. For the secondary occupations, such estimates were generally not possible. Thus, the participation of secondary occupations in silica-generating activities was defined based on their relationship to the key occupations. This participation is defined by their presence in the job crews, as shown in Table V-30 of the FEA. To illustrate the need for this approach, consider the difficulty in predicting how often construction foremen of all types are present during activities where silica-generating equipment is used. BLS data, for example, provide only a total number of foremen, but no information about how they might spend their time. It is reasonable to forecast, however, using the job-crew definitions, that foremen will be present in some proportion to the number of workers in key occupations using jackhammers and other powered handheld chipping tools, rock and concrete drillers, and other silica-generating equipment. OSHA presented these data in the PEA and requested comments, but did not receive any on this aspect of the analysis. Therefore, OSHA is retaining its estimates from the PEA, except as noted.

For some activities, the crew size and composition vary among the jobs defined in the equipment category. In those cases, OSHA used ERG determinations as to the most representative crew composition and used that crew model to define the ratio of secondary to key occupations (ERG, 2007a, Document ID 1709).

The estimates of the number of FTE employees engaged in activities using silica-generating equipment are one of many factors that influence the final cost estimates. There are few data, however, on the breakdown of time spent by construction workers in various activities. The following discussion presents the basis for the time-on-task estimates for the key occupations as included in the PEA and the FEA (except where noted). OSHA presented most of these estimates for public comment in the PEA but did not receive any comments challenging them.

Rock and Concrete Drillers

A review of NIOSH reports covering rock and concrete drillers showed that over 75 percent of driller time was spent on actual drilling (NIOSH 1992a, Document ID 0911, NIOSH 1992b, Document ID 0910, NIOSH 1995, Document ID 0907) and is supported by updated data in NIOSH, 1999b (Document ID 0220). Therefore, for the PEA and FEA, OSHA used 75 percent as the best indication of the time spent using dust-generating equipment for workers in this category.

Tuckpointers and Grinders

Grinding and tuckpointing are only two of the numerous jobs performed by brickmasons, cement masons, and their helpers. Workers in those trades are much more frequently performing bricklaying, cement work, and masonry construction. Where tuckpointers and grinders are being used, a review of the OSHA Special Emphasis Program reports revealed that the time spent using tuckpointers and grinders varied widely (see the technological feasibility analysis for this activity in Chapter IV of the FEA). In both the PEA and in the FEA, OSHA used ERG's estimate that 2.5 percent of the time for workers in each of the applicable occupations would be spent on using this equipment.

Heavy Equipment Operators and Ground Crew Laborers

For the final rule, heavy equipment operators and ground crew laborers were split into two categories in Table 1 based on how the heavy equipment and utility vehicles are being used, which reflects distinctions added in the final rule. This equipment is considered to either be used a) to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during the demolition of concrete or masonry structures; or b) for tasks such as grading and excavating but not including: demolition of concrete or masonry structures or abrading or fracturing silica-containing materials.

ERG estimated that workers using heavy equipment to abrade or fracture silica-containing materials or for demolition devoted only 2.5 percent of their time, on an FTE-equivalent basis, to doing this work.

Key workers in the companion group using heavy equipment for grading and excavating often spend the bulk of their work shift on the equipment itself, engaged in construction work. OSHA Inspection Reports and other documentation consistently show that heavy equipment operators perform their tasks for more than 7 hours per shift (OSHA SEP Inspection Reports 122212079, 116179359; Greenspan, et al., 1995; NIOSH HETA 93-0696-2395, 1999; NIOSH, 1999b; NIOSH ECTB 233-120, 1999c.). Nevertheless, the heavy equipment operator occupational category also includes operators of such equipment as pile drivers, cranes, and air compressors that are not generally associated with silica dust generation. For the PEA, OSHA used ERG's estimate of 75 percent for operating engineers and 50 percent for excavating and loading machine and dragline operators in this category to estimate the number of heavy equipment operators performing silica-generating activities. OSHA did not receive any comment on these estimates and therefore has retained their substance for the FEA.

Hole Drilling Using Handheld or Stand-Mounted Drills

While many workers might occasionally be assigned to drill holes in concrete, this equipment category represents a very small part of the activities of the occupational groups performing this work. ERG judged that carpenters, electricians, plumbers, sheet metal workers, and helpers (construction laborers) spend one percent of their time drilling holes in silica-containing materials in the affected industries. OSHA presented this estimate in the PEA and did not receive comment or alternate estimates and has therefore retained the estimate for the FEA.

Jackhammers and Other Powered Handheld Chipping Tools

OSHA estimated in the PEA that in the key occupation of construction laborers, relatively few use equipment in this category. In developing the estimate of time spent using equipment in this category for the PEA, ERG examined a snapshot of construction activities from the BLS publication, Injuries to Construction Laborers (BLS, 1986, Document ID 0559). That source presents a survey of injured construction workers and includes questions about their activities at the time they were injured. The survey indicated that 3 percent of construction workers were using jackhammers at the time they were injured. ERG judged that, while the survey was not intended to characterize typical construction activities, and a survey of injured workers introduces considerable potential bias into the observations, this estimate was useful as an observation of representative construction activities. ERG also judged that, because jackhammers are heavier, more cumbersome, and more powerful than much construction equipment, workers are probably injured more frequently while using jackhammers, on average, than when using all other construction equipment. Thus, the 3 percent figure is likely to be an upper bound of the amount of time spent using jackhammers and other powered handheld chipping tools. In the absence of other data, OSHA used ERG's estimate that 3 percent of laborers are using this equipment for the PEA. The Agency received no additional data or comment on this estimate and has therefore retained this estimate for the FEA.

Masonry and Concrete Cutters Using Portable Saws—I

The key occupations using portable saws to cut masonry and concrete, namely brickmasons, blockmasons, stonemasons, and their helpers, spend, on average, a small share of their time cutting these materials with portable saws. In Table 1, OSHA notes three types of portable saws: (1) Hand-held saws, (2) walk-behind saws, and (3) drivable saws. Each of those is encompassed in this analysis, although small-diameter handheld saws are addressed separately. According to OSHA and NIOSH reports, the workers in these occupations perform multiple masonry activities and might engage in cutting for only a small portion of their shift (OSHA SEP Inspection Report 300646510; NIOSH, 1999a) (Document ID 0084). Another glimpse of this activity can be gleaned from the BLS injury report for construction laborers, where 3 percent of workers were injured while breaking up or cutting concrete, asphalt, brick, rocks, etc. For each of the applicable occupations, OSHA estimated in the PEA that 10 percent of the workers' time would be spent using the equipment in this category. The Agency received no comment on this estimate and has therefore retained this estimate for the FEA.

Masonry and Concrete Cutters Using Portable Saws—II—Small Diameter Saws for Cutting Fiber-Cement Board

The task of using handheld power saws for cutting fiber-cement board (with blade diameter of 8 inches or less) was separated out in Table 1 in the final rule to recognize portable saws used for cutting cement fiberboard or cement fibersiding as a potential source of silica-containing dust. OSHA judged that portable saws would be used by carpenters or their helpers to cut fiber-cement board and that, on average, they would spend 2.5 percent of their time using equipment in this category to cut the referenced materials.

Masonry Cutters Using Stationary Saws

As noted earlier, OSHA and NIOSH surveillance publications report that saw operators perform multiple masonry cutting activities and might engage in cutting silica-containing materials for only a small portion of their shift (OSHA SEP Inspection Report 300646510; NIOSH, 1999a). For the PEA, OSHA used ERG's estimate that workers in mason occupations spend 10 percent of their time cutting silica-containing materials with stationary saws. The Agency received no comment on this estimate and has therefore retained this estimate for the FEA.

Millers Using Portable or Mobile Machines

In the PEA, ERG identified two key occupation groups where millers are using portable or mobile machines: (1) Cement masons and (2) paving, surfacing, and tamping equipment operators. In response to comments (see Document ID 3585, Tr. 3036; 4220, p. 9; 3756, Attachment 1), for the FEA, OSHA added a third key occupation group: Terrazzo workers and finishers. Milling using this equipment represents a small share of the overall job duties of these applicable key occupations: In the PEA OSHA judged that 5 percent of all work for the first two occupation groups is spent using this equipment, and OSHA is retaining that estimate in the FEA because there were no comments challenging that estimate. OSHA estimates that terrazzo workers use the equipment about half as much as the other two occupation groups, so OSHA estimates that 2.5 percent of all work time spent by terrazzo workers and finishers will be spent using this equipment.

Rock Crushing Machine Operators and Tenders

According to information collected from ERG communication and OSHA SEP inspection reports, rock crushing machine operators spend most, if not all, of their shifts at and around the rock crushing process (Polhemus, 2000, Document ID 0958; Haney, 2001, Document ID 0721; OSHA SEP Inspection Report 2116507, Document ID 0186; OSHA SEP Inspection Report 300441862, Document ID 0030). OSHA estimated in the PEA that this occupational group spends 75 percent of its time using rock crushing machines and did not receive any comment on the estimate. OSHA has retained this estimate for the FEA.

Tunnel Boring

Underground workers perform both tunnel work and other types of construction work. The majority of these underground tasks still fall under Table 1 and have been accounted for elsewhere in the appropriate construction task analysis. However, a small amount of silica-generating underground construction work outside the scope of Table 1, primarily in tunnel boring, is expected to occur. The cost of engineering controls for this activity (to comply with the new PEL) is presented after the total engineering control costs to comply with Table 1 are presented.

SBREFA Panel Comments on Key and Secondary Occupations

As stated in the comments during the Silica SBREFA process, one SBREFA commenter was “unable to reconcile ERG's statement that ‘the amount of time . . . grinders and tuck-pointers perform grinding ranges widely, from about 1 hour per shift up to a full 8-hour shift (or longer)’ [see the discussion on technological feasibility in Chapter IV of the FEA] with the 2.5% estimate in Table 4-8 [in the ERG report (2007a); Table V-26 in the PEA]” (Document ID 0004; 1709). The commenter also asserted that masonry cutters use stationary saws approximately 20 to 30 percent of their working time (rather than 10 percent), and that masonry cutters use portable saws approximately 5 percent of their working time (rather than 10 percent) (Document ID 0004).

In response, OSHA reiterated in the PEA that Table V-26 of the PEA showed the estimates of the full-time-equivalent number of workers in key and secondary occupations using equipment to perform silica-generating tasks. These occupations are taken from the BLS Occupational Employment Survey classification system and are much broader than the “masonry cutter” category referred to by the commenter, implying a lower percentage of time devoted to tasks involving masonry cutting.

OSHA did not receive further comment on this explanation. Therefore, OSHA has not changed these estimates in the FEA. For each occupation the estimates in Table V-37 of the FEA are meant to reflect the typical or average amount of a worker's time (over a year) devoted to the listed tasks.

FTE At-Risk Employment by Task Category

Tables V-38a and V-38b of the FEA provide estimates, by occupation, of the full-time-equivalent (FTE) number of key and secondary workers, respectively, for each task category, using the percentages and ratios from Table V-37 of the FEA. These tables are relatively direct compilations from previous tables with adjustments needed, in a few cases, to assure that the industry-specific FTE occupational totals did not exceed the total occupational employment for any industry.

Table V-39 of the FEA shows the corresponding estimates by NAICS code for the construction industry.

OSHA distributed FTE at-risk workers across NAICS codes according to the combination of task categories and occupational (key and secondary) categories (from BLS, 2012, Document ID 1560) derived and updated by ERG for each industry group (ERG, 2007a, Document ID 1709).

Overall, a full-time equivalent of 374,003 workers is estimated to use equipment to perform work on silica-containing materials in construction, ranging from 1,135 FTEs for rock crushing machine operators and tenders to 198,585 FTEs for heavy equipment operators and ground crew laborers (grading and excavating).

Total At-Risk Employment

In the PEA, OSHA used a relatively crude approach to convert the estimated number of FTE affected construction workers to the number at-risk construction workers. There, OSHA used a multiplier of 2 or 5, depending on the industry, to convert the number of FTEs to the number of at-risk workers (in Table V-37 of the PEA).

OSHA received several comments regarding the analysis used in the PEA as being too simplistic. Joseph Liss challenged OSHA's methodology:

Even though OSHA estimates the number of workers needing training for silica exposure under the proposed rule by multiplying full-time equivalents by a factor of either 2 or 5, depending upon the sub-industry, the multiplicative factor for training purposes is likely to be much higher. For example, while paving, surfacing, and tamping operators spend a total of only 5% of their time on tasks exposed to silica, as estimated by ERG, it is not unlikely that many of the 51,857 workers in that industry sub-group will do silica-exposed work at some point, and, thus, require training. There are 823,737 construction laborers, and ERG estimated that 3% of their time is spent on silica-exposed work, but the severe turnover in that industry means firms may need to train many of those workers in silica safety procedures and health effects. OSHA estimates the nation's 575,000 residential construction workers spend 5% of their time on construction work and uses a multiplicative factor of two, thus assuming that only 10% of those workers require training and exposure monitoring. Costs may increase if the number of workers exposed increases, since OSHA requires training for all newly hired workers as well as all initial training for all workers exposed to silica (citations omitted) (Document ID 1950, p. 9).

Additionally, the Construction Industry Safety Coalition (CISC) submitted calculations to arrive at their own results of at-risk workers. They note:

These percentages represent our quick judgement across both the key occupations and the secondary occupations that OSHA identifies as participating in the crew when the at-risk task is performed. If we had more time, we would like to make this judgement more carefully (Document ID 4032, Tab 6).

For the FEA, in response to comments, OSHA refined its process, as described below, to allow for a more nuanced approach to estimating the number of affected workers. As a result of this revised approach, the ratio of the estimated number of at-risk construction workers to the estimated number of FTE-affected construction workers increased from approximately three to one in the PEA to over five to one in the FEA. OSHA first assigned each of the affected NAICS construction industries to one of four subsectors in order to account for likely differences among specific industries with respect to the frequency with which silica-generating equipment is used. These subsectors are shown in Table V-40a of the FEA. Note that non-construction industries doing construction work—state and local governments and electric utilities—are included in Subsector 3.

Second, because at-risk workers do not necessarily specialize in jobs that use equipment that generates silica-containing dust, ERG independently estimated the number of “affected” workers based on judgments of the share of workers in each occupation that would likely ever perform these tasks. These judgments were also made on a subsector-by-subsector basis. In most cases, costs for program requirements (but not for engineering controls) are based on the numbers of affected workers performing each task in a given industry. The estimated share of affected workers for the key occupations, taking into account the specific construction subsector and task, is shown in Table V-40b of the FEA.

Using the FTE rates, secondary ratios, and affected rate parameters displayed in Table V-37 of the FEA, OSHA calculated, in Table V-39 of the FEA, that there are an estimated 374,003 FTEs affected by the rule. Table V-41 of the FEA converts these FTEs to 2.02 million affected construction workers disaggregated by occupation based on 2012 County Business Pattern (CBP) total employment of 2.93 million in affected occupations in construction industries. Thus, as shown in Table V-41 of the FEA, about 68.9 percent of construction workers in affected occupations will be affected by the final rule. Table V-42 of the FEA shows the same estimated number of affected workers, but disaggregated by NAICS industries and equipment category. There are an estimated 13.45 million workers total in the affected industries, meaning that about 15 percent of the workers in these industries are affected by the final rule. That percentage is misleading, however, because almost 7.7 million of total employment in affected industries (almost 60 percent) are employed in state and local governments, of which only 2 percent are affected by the final rule. When these public workers are removed, approximately 32 percent of the construction workers in affected private industries are affected by the final rule.

All of the above statistics do not include the estimated 11,640 at-risk abrasive blasters working in construction industries. Also, because some occupations are associated with the use of more than one equipment category, the “affected” totals are constrained to be less than or equal to the industry total for each at-risk occupation.

Labor Cost and Total Value of Work Performed Using Silica Exposure-Generating Equipment

To derive labor costs and project value for construction work done using the specified equipment where occupational exposure to silica is found, OSHA multiplied the mean hourly wage, as reported by OES (BLS, 2012, Document ID 1560), for each affected occupation within each affected industry, by 2,000 hours. Then, to derive the total value of annual wages expended for work done using specified equipment to perform silica exposure-generating activities, OSHA multiplied that product by the number of affected full-time-equivalent employees. These estimates were then inflated to adjust for fringe benefits. These loaded-wage costs, totaled by industry and equipment category, are summarized in Table V-43 of the FEA as the annual labor value (or labor cost) of silica-generating projects. Overall, OSHA estimated the labor value of all silica-generating construction work performed with the specified equipment to be $21.8 billion annually.

OSHA then converted the labor values for each industry and task category from Table V-43 of the FEA to the total project value by dividing by the labor share of project costs. This conversion is possible because the labor share for each task category equals the labor value divided by project value, so dividing the labor value by the labor share generates an estimate of project value. The corresponding estimates of total project value for each industry and equipment category are shown in Table V-44 of the FEA. Overall, OSHA estimated the value of silica-generating construction work performed with the specified equipment at $41.2 billion. The values for specific equipment categories ranged from $136.2 million for rock crushing machine operators and tenders to $28.0 billion for heavy construction equipment operations-II.

The value of work performed using the specified equipment was then summed by NAICS industry to derive the total value of at-risk projects, a base from which OSHA calculated control costs associated with compliance with Table 1 or the final PEL.

Aggregate Control Costs in Construction To Comply With Table 1 or the New PEL

For the final rule, OSHA revised Table 1 to include separate engineering control and respirator requirements for tasks indoors or in enclosed areas (“indoor tasks”) to provide a means of exhaust as needed to minimize the accumulation of visible airborne dust. As a result, indoor tasks will have an additional cost to reflect use of control equipment (e.g., a fan or “blower”) providing a means of exhaust as needed to minimize the accumulation of visible airborne dust. These additional indoor costs were included in Table V-34 of the FEA. However, to properly reflect these costs in the aggregate control costs in construction, OSHA had to add an additional methodological step. OSHA's Office of Technological Feasibility helped to develop estimates of the distribution of silica-related work disaggregated by the type of control equipment used, the duration of the task, and the location of the task (i.e., indoors or outdoors). The resulting distribution of silica-related work, which is later used to weight costs by the percentage of tasks performed indoors or outdoors, is displayed in Table V-45 of the FEA.

To derive estimates in Table V-46 of the FEA of aggregate incremental compliance costs to meet final Table 1, the total value of construction work using the specified equipment and requiring controls (in Table V-44 of the FEA) was multiplied by the percentage of incremental cost associated with the controls required for each equipment category (in Tables V-36a and V-36b of the FEA), weighted by the percentage of work using each type of equipment performed outdoors and indoors (in Table V-45 of the FEA), and reduced by the percentage of baseline compliance.

As indicated in Table V-46 of the FEA, OSHA estimates that the incremental compliance costs for engineering controls (excluding tunnel boring and abrasive blasting) will total $386.4 million for construction work performed using the specified equipment affected by the final standard.

Control Costs for Construction Tasks Not Under Table 1

Abrasive Blasting

In the PEA, OSHA estimated that some abrasive blasting crews were not currently using all feasible engineering controls and added costs for wet methods for them to achieve the proposed PEL. OSHA did not receive comments on the PEA estimates of engineering control costs for abrasive blasting crews and has retained the same methodology to estimate costs for the FEA.

Consistent with what was done in the PEA, Table V-47a of the FEA presents the unit costs and analytical assumptions applied in OSHA's cost analysis of controlling silica exposures during abrasive blasting operations. As shown in the table, after accounting for the number of affected workers, crew size, daily output, blasting cost per square foot, number of blasting days per year, and the percentage of crews using sand, OSHA estimates that baseline annual costs for sand blasting total $126.7 million. As in the PEA, ERG estimated that the incremental cost for wet blasting is 30 percent of baseline costs and that 50 percent of crews currently use wet methods. Therefore, the annual costs to comply with the final standard by using wet methods during sand blasting are expected to total $19.0 million, or $2,366 per worker for the approximately 8,033 workers exposed to silica dust.

Distributing these annualized costs by industry, OSHA estimates that employers in NAICS 238200, Building Finishing Contractors, will incur compliance costs of $12.1 million annually, while firms in NAICS 238900, Other Specialty Trade Contractors, will incur compliance costs of $6.9 million annually.

Tunnel Boring

Tunnel boring is not included on Table 1 of the final rule. An employer engaged in tunnel boring must comply with the PEL of 50 μg/m³ specified in § 1926.1153(d). Employers in tunnel boring must already comply with the ventilation and dust suppressant requirements in subpart S of Part 1926 (Underground construction), which would have allowed those employers to meet the previous PEL of 250 μg/m³. Therefore, OSHA calculates the additional controls necessary to reduce exposures from the preceding PEL to the new PEL of 50 μg/m³.

In most cases, employers are able to reduce exposures to the preceding PEL by providing suction at the drill head, removing the dust as soon as it is generated. The technological feasibility chapter of the FEA demonstrates that employers can do so by extending the existing suction controls as the drill head progresses. There are limits on these extensions, however, and the amount of worker exposure can increase if the suction is not extended frequently enough to keep it at the drill head. This extension does not require additional machinery, but it is likely to require the employer to invest more labor time to extend the suction device more frequently to meet the new PEL than previously necessary to meet the preceding PEL. OSHA has estimated in Table V-47 of the FEA the control costs for tunnel boring using the same cost methodology applied in the PEA (see Tables V-21 and V-24 in the PEA) to calculate the incremental cost as a percentage of baseline control costs (0.013%). The rest of the calculations in Table V-47 reflect 2012 data on the number of affected FTE tunnel workers and 2012 hourly wage rates. The resulting estimate of annualized incremental control costs for tunnel boring is about 0.02 million.

Table V-48 of the FEA adds the abrasive blasting and the tunnel boring control costs in construction to the control costs for Table 1 tasks presented in Table V-46 of the FEA.

Adjustment for Self-Employed Workers on a Multi-Employer Worksite

The OSH Act provides authority for OSHA to regulate employers for the protection of their employees. Because sole proprietors without employees, referred to as “self-employed workers” for the purposes of this discussion, are not “employers” under the Act, OSHA cannot require them to comply with the silica standard. On a multi-employer worksite, however, their silica activities could expose employees protected by the Act to respirable crystalline silica.

Employers must still protect their employees from exposure to silica in accordance with the standard, whether it is generated by work performed by their own employees or by the work performed by a sole proprietor not regulated by the Act (see the summary and explanation of the written exposure control plan requirements in paragraph § 1926.1153(g)(1)(iv)). Under OSHA's multi-employer citation policy (CPL 02-00-124), employers of workers who may be exposed to silica are considered “exposing employers” who have a duty to protect their employees, even from hazards they do not correct themselves. However, the controlling employer, the employer in overall charge of the worksite or project, also has a duty to exercise reasonable care to prevent and detect violations of the silica standard on the multi-employer worksite. The silica standard does not limit the means by which either employer may fulfill this duty, and in many cases the issue may be resolved if the work schedule does not place the self-employed worker in the same area of the worksite at the same time as employees, thereby avoiding the need for additional measures.

As discussed in Chapter III of the FEA, CISC requested that the Agency account for the costs arising from self-employed workers separately based on the theory that self-employed workers will use the controls necessary to comply with Table 1 to reduce exposures to others when working on a multi-employer worksite where employees are present (Document ID 4217, p. 80). CISC identified several reasons why this might happen, including self-interested recognition of “Table 1 specifications as the safe way to perform their work”; demands by construction general contractors that anyone working on their site, whether self-employed or not, conform to regulatory requirements; and demands by nearby employers that their employees “not suffer increased silica exposures from inappropriate practices by self-employed workers.”

While these are not costs that OSHA typically includes in its analysis, OSHA recognizes that Table 1 is unique among OSHA standards, and that it is possible that controlling employers on a multi-employer construction worksite may assume some costs of engineering controls—either by providing the controls or by reimbursing the self-employed persons for the costs of the controls through increased fees—when they cannot resolve the issue through simple scheduling choices. Therefore, OSHA is estimating the additional cost of the engineering controls in that scenario.

In order to estimate the number of self-employed persons in construction, CISC's contractor, Environomics, Inc., took the following approach:

The U.S. Census Bureau, in Revised 2008 Nonemployer Statistics Reflecting 2009 Methodology Changes, provides information on the number of self-employed individuals (“nonemployers”) working in each of the 4-digit construction industries (total of 2.52 million self-employed construction workers), but no further information on the occupations of these self-employed workers. In order to estimate the number of self-employed workers in each of the various at-risk construction occupations that OSHA identified and that we added, we simply assumed that these 2.52 million “nonemployers” are distributed among occupations within each construction NAICS in the same proportion as employed workers are distributed among occupations within the NAICS (Document ID 4217, p. 80).

Note that the Census data that Environomics used provides detail on self-employed persons by 4-digit NAICS construction industries but not by occupation. Hence, in the absence of occupational data, Environomics simply assumed that the number of self-employed persons by occupation was proportional to the number of employees by occupation—which implies that the ratio of the number of self-employed persons to employees was the same for each occupation. Using this database and approach, Environomics estimated that the ratio of self-employed persons to employees for all occupations affected by the rule was 40.1 percent (1,811,009 self-employed relative to 4,519,889 employees). Based on the full-time-equivalent (FTE) number of workers—which, in OSHA's estimation methodology, determines the amount of engineering control equipment used—Environomics calculated that the ratio of FTE self-employed persons to FTE employees for all occupations affected by the rule was 35.7 percent.

Having reviewed the Environomics self-employment analysis, OSHA has concluded that the occupation of the self-employed persons is a much more relevant factor for estimating costs than the 4-digit construction industry in which self-employed persons work. Therefore, for its analysis, OSHA has chosen to rely on data from the 2013 BLS Current Population Survey, with the goal of estimating the ratio of the number of self-employed persons to the number of employees by occupation. Table V-49 of the FEA presents data from the 2013 BLS Current Population Survey with the focus on the ratio of the self-employed to the non-self-employed (i.e., employees). Note that this table includes many occupations that do not involve silica exposure (e.g., boilermakers, paperhangers, glaziers) and others that are not covered by OSHA (e.g., mining machine operators; roof bolters, mining—covered by MSHA).

Table V-50 of the FEA presents the same data as shown in Table V-49 of the FEA, but restricted to just those occupations where OSHA estimated that workers are potentially exposed to hazardous levels of respirable crystalline silica. One thing that is immediately obvious in this table is the very wide variation from occupation to occupation in the ratio of the self-employed to the employed, with the ratio ranging from 0 percent to 47.53 percent. This wide variation is clearly incompatible with the assumption made by Environomics that the ratio of the number of self-employed to employees is the same for all occupations. Table V-50 of the FEA also shows that average ratio of self-employed to employees over all construction occupations involving silica exposure (when the ratio is allowed to vary by occupation) is 22.82 percent when weighted by the number of employees (as compared to 40.1 percent as estimated by Environomics).

As noted above, in OSHA's methodology, the amount of engineering control equipment used is based on the FTE number of workers. In Table V-51 of the FEA, OSHA multiplied the FTE rate for each occupation (from Tables V-38a and V-38b of the FEA) by the number of self-employed workers and employees in that occupation (from Table V-48 of the FEA). As shown in Table V-51 of the FEA, there are an estimated 69,461 FTE self-employed workers in at-risk occupations, relative to the total of 377,913 FTE employees in at-risk occupations. In other words, the number of at-risk FTE self-employed workers is 18.38 percent of the number of at-risk FTE employees (as compared to 35.7 percent as estimated by Environomics).

The analysis of the number of self-employed persons conducted by Environomics stopped at this point. However, as OSHA explained in Chapter III of the FEA, self-employed workers are not required to comply with the final rule and are only likely to do so in two situations: (1) Where self-employed workers are generating silica dust while working in a multi-employer construction worksite such that their activities could expose the employees of others, and (2) where the host employer (or competent person) is unable to schedule the self-employed worker's activities or location so as to prevent the exposure or overexposure of other, covered workers. OSHA does not have data on the likelihood of either of these two conditions. OSHA judges that self-employed workers work at multi-employer construction sites at the same times as others a minority of their worktime, and work even less frequently within the same area such that covered employees could be exposed. Nevertheless, OSHA is conservatively estimating here that they do so 50 percent of the time. OSHA also judges that the host contractor (with the assistance of the competent person) would be able to schedule the self-employed workers' activities or location so as to prevent the exposure or overexposure of other, covered workers a majority of the time. This makes sense because self-employed workers would often be used on multi-employer sites when they possess special skills not otherwise available onsite. Therefore, their work frequently could be performed at a different time or location from the other work. In any case, for costing purposes, OSHA is conservatively estimating that the work of self-employed persons cannot be isolated in time or space so as to prevent the exposure or overexposure of other, covered workers 50 percent of the time that those self-employed workers are on the multi-employer worksite.

Based on these estimates, OSHA calculates that only 25 percent of the at-risk work of self-employed workers would meet the conditions in which a host or controlling employer would incur engineering control costs to mitigate the exposures to employees on the site. At the bottom of Table V-51 of the FEA, OSHA has accordingly reduced the number of FTE self-employed workers using equipment to perform silica-dust-producing work relative to the number of FTE at-risk employees to 25 percent of the earlier estimate of 18.38 percent. OSHA therefore concludes that the number of FTE at-risk self-employed workers imposing costs on host employers is equal to 4.60 percent of the number of FTE at-risk employees. This result is shown at the bottom of Table V-51 of the FEA.

Finally, in Table VII-13, OSHA increased the estimates of the control costs for work performed using the specified equipment in construction presented in Table V-48 of the FEA by 4.60 percent to include the engineering control costs that would be incurred by host or controlling employers to control the exposures caused by self-employed workers. This increases the annualized cost of engineering controls needed in construction to comply with the final rule from $405.5 million to $423.4 million.

2. Respiratory Protection

OSHA's cost estimates assume that implementation of the recommended silica controls prevents workers in general industry and maritime from being exposed over the PEL in most cases. Specifically, based on its technological feasibility analysis, OSHA expects that the engineering controls are adequate to keep silica exposures at or below the PEL for an alternative PEL of 100 μg/m (introduced for economic analysis purposes). For the new 50 μg/m³ PEL, OSHA's feasibility analysis suggests that the controls that employers use, either because of technical limitations or imperfect implementation, might not be adequate in all cases to ensure that worker exposures in all affected job categories are at or below 50 μg/m³.

For the FEA, OSHA estimates that respirators will be required: (1) For all workers that the Agency's technological feasibility analysis has determined will require respirator use; and (2) for ten percent of the remaining workers currently exposed above 50 μg/m³ at covered workplaces.

This is a change in methodology from the PEA, where OSHA estimated the percentage of workers requiring respirators in an industry as either (1) or (2), whichever was larger. The Agency believes that the FEA formula, which results in higher estimates of respirator usage, is more accurate in that it reflects the combined effects of (1) and (2) whereas the earlier methodology did not. The number of workers that the FEA estimates will need respirators is presented in Table V-13 in the FEA.

In the PEA, OSHA concluded that all maritime workers engaged in abrasive blasting were already required to use respirators under existing OSHA standards and, therefore, maritime establishments would incur no additional costs for maritime workers to use respirators as a result of this final rule. However, for the FEA, OSHA has determined from its earlier technological feasibility analysis that only abrasive blasting operators, but not abrasive blasting helpers, are already required to use respirators under existing OSHA standards. The Agency, therefore, has added respirator costs for abrasive blaster helpers in maritime (half of all the abrasive blaster workers) as a result of this final rule.

For construction, employers whose workers are exposed to respirable silica above the proposed PEL were assumed to adopt the appropriate task-specific engineering controls and, where required, respirators prescribed in Table 1 and paragraph (g)(1) in the final standard. Respirator costs in the construction industry have been adjusted to take into account OSHA's estimate (consistent with the findings from the NIOSH Respiratory Survey, 2003, Document ID 1492) that 56 percent of establishments in the construction industry are already using respirators that would be in compliance with the final silica rule.

OSHA used respirator cost information from a 2003 OSHA respirator study to estimate the annual cost of $367 (general industry) or $286 (construction) for disposable filtering facepiece respirators, $520 (general industry) or $409 (construction) for a half-mask, non-powered, air-purifying respirator and $644 (general industry) or $533 (construction) per year (in 2012 dollars) for a full-face non-powered air-purifying respirator (ERG, 2003, Document ID 1612). These unit costs reflect the annualized cost of respirator use, including accessories (e.g., filters), training, fit testing, and cleaning where relevant.

The PEA estimated that (with the exception of workers who are entering regulated areas) all workers in general industry and construction who need respirators with an assigned protection factor (APF) of 10 would use non-disposable, half-face respirators. The FEA estimates that in general industry half of the workers who need respirators will use half-face elastomeric respirators and half will use disposable N95 respirators. This is because, as clarified in the final rule, both disposable and non-disposable respirators are available with an APF of 10, and, with each type of respirator offering certain advantages, OSHA accordingly estimates that about half of the employees in general industry and maritime will prefer the ease of use of disposable respirators while the other half will prefer the durability of non-disposable respirators. For the construction sector, the FEA estimates that 10 percent of workers needing respirators will use elastomeric half-face respirators and 90 percent will use disposable N95 respirators. This is because very few workers in construction engage in tasks requiring respirator use full-time. Under those circumstances, disposable respirators are both more convenient to use and much less expensive than reusable respirators.

In addition to bearing the costs associated with the provision of respirators, employers will incur a cost burden to establish respirator programs. OSHA projects that this expense will involve an initial 8 hours for establishments with 500 or more employees and 4 hours for all other firms. After the first year, OSHA estimates that 20 percent of establishments would revise their respirator program every year, with the largest establishments (500 or more employees) expending 4 hours for program revision, and all other employers expending 2 hours for program revision. Consistent with the findings from the NIOSH Respiratory Survey (2003) (Document ID 1492), OSHA estimates that 56 percent of establishments in the construction industry that would require respirators to achieve compliance with the final PEL already have a respirator program. OSHA further estimates that 50 percent of firms in general industry and all maritime firms that would require respirators to achieve compliance already have a respirator program.

3. Exposure Assessment

OSHA developed separate cost estimates for (1) initial monitoring or any exposure monitoring at hydraulic fracturing sites and (2) scheduled monitoring at fixed sites (which excludes hydraulic fracturing). Costs under (2) were estimated to be lower because the exposure monitoring is expected to be of shorter duration (possibly obviating an overnight stay) and could be conducted by a lower-cost Industrial Hygienist (IH) or IH technician rather than by a CIH. Based on the comments received in the record, OSHA decided to significantly increase its estimate from $500 (in the PEA) to $2,500 for an IH consultant to perform initial exposure monitoring or to perform at sites that have not previously been well characterized. In the construction sector, the $2,500 cost estimate for IH services applies to all exposure monitoring since the worksite is not fixed and has not been previously characterized. OSHA estimates that the IH periodic exposure monitoring costs would be approximately $1,250, or half of the $2,500 estimate. These IH monitoring costs would cover 2, 6, and 8 personal breathing zone (PBZ) samples per day for small, medium, and large establishments, respectively.

For initial monitoring or any exposure monitoring at hydraulic fracturing sites, the total unit cost of an exposure sample is estimated to range from $487 to $1,425 (depending on establishment size). For periodic monitoring in general industry and maritime, excluding hydraulic fracturing sites, the total unit cost of an exposure sample is estimated to range from $328 to $796 (depending on establishment size).

Tables V-14 and V-61 in the FEA shows the unit costs and associated assumptions used to estimate exposure assessment costs. Unit costs for exposure sampling include direct sampling costs, the costs of productivity losses, and recordkeeping costs, and, depending on establishment size, range from $328 to $1,421 per sample in general industry and maritime and from $488 to $1,425 per sample in construction.

For costing purposes, based on OSHA (2016), OSHA estimated that there are four workers per work area. OSHA interpreted the initial exposure assessment in general industry and maritime as requiring first-year testing of at least one worker in each distinct job classification and work area who is, or may reasonably be expected to be, exposed to airborne concentrations of respirable crystalline silica at or above the action level.

For periodic monitoring, the final standard provides employers an option of assessing employee exposures either under a performance option (paragraph (d)(2)) or a scheduled monitoring option (paragraph (d)(3)). For the performance option, the employer must assess the 8-hour TWA exposure for each employee on the basis of any combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica. For the scheduled monitoring option (termed the “periodic” monitoring option in the proposal), the employer must perform initial monitoring to assess the 8-hour TWA exposure for each employee on the basis of one or more (PBZ) air samples that reflect the exposures of employees on each shift, for each job classification, in each work area. Where several employees perform the same job tasks on the same shift and in the same work area, the employer may sample a representative fraction of these employees in order to meet this requirement. In representative sampling, the employer must sample the employee(s) who are expected to have the highest exposure to respirable crystalline silica. Under the scheduled monitoring option, requirements for periodic monitoring depend on the results of initial monitoring. If the initial monitoring indicates that employee exposures are below the action level, no further monitoring is required. If the most recent exposure monitoring reveals employee exposures to be at or above the action level but at or below the PEL, the employer must repeat monitoring within six months of the most recent monitoring. If the most recent exposure monitoring reveals employee exposures to be above the PEL, the employer must repeat monitoring within three months of the most recent monitoring. OSHA used the fixed schedule option under the frequency-of-monitoring requirements to estimate, for costing purposes, that exposure monitoring will be conducted (a) twice a year where initial or subsequent exposure monitoring reveals that employee exposures are at or above the action level but at or below the PEL, and (b) four times a year where initial or subsequent exposure monitoring reveals that employee exposures are above the PEL.

As required under paragraph (d)(4) of the final rule, employers must reassess exposures whenever a change in the production, process, control equipment, personnel, or work practices may reasonably be expected to result in new or additional exposures at or above the action level, or when the employer has any reason to believe that new or additional exposures at or above the action level have occurred. In response to comments, OSHA increased its estimate from 15 percent to 25 percent of the share of workers whose initial exposure or subsequent monitoring was at or above the action level would undertake additional monitoring.

Changes from the proposed to the final rule have resulted in a significant reduction in OSHA's estimate of the annual number of samples taken by construction employers. For the final rule, employers following Table 1 are not required to engage in initial or subsequent exposure monitoring for those construction workers engaged in tasks on Table 1. Therefore, OSHA only estimated scheduled semi-annual exposure monitoring (for expected exposures at or above the action level but at or below the PEL) and scheduled quarterly exposure monitoring costs (for expected exposures above the PEL) for those operations are not listed on Table 1. In addition, OSHA estimated that some small fraction of employers—1 percent—will choose to conduct initial sampling to investigate the possibility that exposures are so low (below the action level) that Table 1 need not be followed.

A more detailed description of unit costs, other unit parameters, and methodological assumptions for exposure assessments is presented in Chapter V of the FEA.

4. Medical Surveillance

Paragraph (i) of the final standard requires the employer to make medical surveillance available for each employee occupationally exposed to respirable crystalline silica at or above the action level of 25 μg/m³ for 30 days or more per year. ERG (2013) assembled information on representative unit costs for initial and periodic medical surveillance (Document ID 1712). Separate costs were estimated for current employees and for new hires as a function of the employment size (i.e., 1-19, 20-499, or 500+ employees) of affected establishments. Table V-16 in the FEA presents ERG's unit cost data and modeling assumptions used by OSHA to estimate medical surveillance costs.

In accordance with paragraph (i)(2) of the final standard, the initial medical examination will consist of (1) a medical and work history, (2) a physical examination with special emphasis on the respiratory system, (3) a chest x-ray interpreted and classified according to the International Labour Office (ILO) International Classification of Radiographs of Pneumoconiosis by a NIOSH-certified B Reader, (4) a pulmonary function test administered by a spirometry technician with a current certificate from a NIOSH-approved course, (5) testing for latent tuberculosis (TB) infection, and (6) any other tests deemed appropriate by the PLHCP. In accordance with paragraph (i)(3) of the final standard, the contents of the periodic medical examinations are the same as those for the initial examination, with the exception that testing for latent tuberculosis infection is not required.

As shown in Table V-16 in the FEA, the estimated unit cost of the initial health screening for current employees in general industry and maritime ranges from approximately $415 to $435 and includes direct medical costs, the opportunity cost of worker time (i.e., lost work time, evaluated at the worker's 2012 hourly wage, including fringe benefits) for offsite travel and for the initial health screening itself, and recordkeeping costs. The variation in the unit cost of the initial health screening is due entirely to differences in the percentage of workers expected to travel offsite for the health screening. In OSHA's experience, the larger the establishment the more likely it is that the selected PLHCP would provide the health screening services at the establishment's worksite. OSHA estimates that 20 percent of establishments with fewer than 20 employees, 75 percent of establishments with 20-499 employees, and 100 percent of establishments with 500 or more employees would have the initial health screening for current employees conducted onsite.

The unit cost components of the initial health screening for new hires in general industry and maritime are identical to those for existing employees with the exception that the percentage of workers expected to travel offsite for the health screening would be somewhat larger (due to fewer workers being screened annually, in the case of new hires, and therefore yielding fewer economies of onsite screening). OSHA estimates that 10 percent of establishments with fewer than 20 employees, 50 percent of establishments with 20-499 employees, and 90 percent of establishments with 500 or more employees would have the initial health screening for new hires conducted onsite. As shown in Table V-16 in the FEA, the estimated unit cost of the initial health screening for new hires in general industry and maritime ranges from approximately $417 to $437.

The unit costs of medical surveillance in construction were derived using identical methods. As shown in Table V-63 of the FEA, the estimated unit costs of the initial health screening for current employees in construction range from approximately $429 to $467; the estimated unit costs of the initial health screening for new hires in construction range from $433 to $471.

In accordance with paragraph (h)(2) of the final standard, the initial medical examination will consist of (1) a medical and work history, (2) a physical examination with special emphasis on the respiratory system, (3) a chest x-ray interpreted and classified according to the International Labour Office (ILO) International Classification of Radiographs of Pneumoconioses by a NIOSH-certified B Reader, (4) a pulmonary function test administered by a spirometry technician with a current certificate from a NIOSH approved course, (5) testing for latent tuberculosis (TB) infection, and (6) any other tests deemed appropriate by the physician or licensed health care professional (PLHCP). In accordance with paragraph (h)(3) of the final standard, the contents of the periodic medical examinations are the same as those for the initial examination, with the exception that testing for latent tuberculosis infection is not required.

The estimated unit cost of periodic health screening also includes direct medical costs, the opportunity cost of worker time, and recordkeeping costs. As shown in Table V-16 in the FEA, these triennial unit costs in general industry and maritime vary from $415 to $435. For construction, as shown in Table V-63 in the FEA, the triennial unit costs for periodic health screening vary from roughly $429 to $467. The variation in the unit cost (with or without the chest x-ray and pulmonary function test) is due entirely to differences in the percentage of workers expected to travel offsite for the periodic health screening. OSHA estimated that the share of workers traveling offsite, as a function of establishment size, would be the same for the periodic health screening as for the initial health screening for existing employees.

OSHA estimated a turnover rate of 75 percent in general industry and maritime and 40 percent in construction, based on estimates of the separations rate (layoffs, quits, and retirements) provided by the Bureau of Labor Statistics (BLS, 2012). However, not all new hires would require initial medical testing. As specified in paragraph (h)(2) of the final rule, employees who had received a medical examination that meets the requirements of this section within the previous three years would be exempt from undergoing a second “initial” medical examination. OSHA estimates that 25 percent of new hires in general industry and maritime and 60 percent of new hires in construction would be exempt from the initial medical examination.

Although OSHA believes that some affected establishments in construction currently provide some medical testing to their silica-exposed employees, there was significant testimony in the record that many employers would at least have to make changes to their existing practices in order to comply with the new standard. Therefore, for costing purposes, the Agency assumed no current compliance with the health screening requirements of the rule.

OSHA requested information from interested parties on the current levels and the comprehensiveness of health screening in general industry, maritime, and construction. Although testimony in the record indicated that current medical surveillance programs exist to a limited extent among affected employers (see Chapter V, Costs of Compliance) for costing purposes for the rule, OSHA has conservatively assumed no current compliance with the health screening requirements.

Finally, OSHA estimated the unit cost of a medical examination by a pulmonary specialist for those employees found to have signs or symptoms of silica-related disease or are otherwise referred by the PLHCP. OSHA estimates that a medical examination by a pulmonary specialist costs approximately $335 for workers in general industry and maritime and $364 for workers in construction. This cost includes direct medical costs, the opportunity cost of worker time, and recordkeeping costs. In all cases, OSHA anticipates that the worker will travel offsite to receive the medical examination by a pulmonary specialist (see Chapter V in the FEA for a full discussion of OSHA's analysis of medical surveillance costs under the final standard).

5. Familiarization Costs and Costs of Communication of Silica Hazards to Employees

OSHA did not estimate any employer familiarization costs in the PEA in support of the proposed rule. OSHA's rationale for not including familiarization costs in the PEA was that there was already an existing silica standard in place and, therefore, the Agency expected that any familiarization costs for a revised silica standard would be negligible.

However, several commenters on the proposed rule argued that employers will need to spend time to become familiar with the requirements of the final rule; that the employer time spent is the direct result of the final rule itself; and, therefore, that OSHA should include employer familiarization costs as part of the costs of the final rule.

OSHA found the comments in support of including some familiarization costs persuasive and the Agency has now concluded that employers will need to spend some time to understand the ancillary provisions and the other new and revised components of the final rule and to determine what actions they must take in order to comply. OSHA estimated that 8 hours would be spent on familiarization in its 2012 update to the Hazard Communication Standard (see 77 FR 17637-17638 (March 26, 2012)) and believes that this is a reasonable estimate of familiarization time for a typical firm for this final silica rule.

For the silica rule OSHA used the number of employees as a proxy for the level of familiarization that would be needed. Accordingly, OSHA has reduced the average of 8 hours of familiarization time for establishments with fewer employees and increased it significantly for establishments with a larger number of employees: 4 hours per covered employer with fewer than 20 employees; 8 hours per covered employer with 20 to 499 employees; and 40 hours per covered employer with 500 or more employees. These estimates represent average familiarization times; it is expected that some establishments will spend less time on familiarization than estimated here (e.g.,, if worker exposure never meets or exceeds the action level) and some will spend more time on familiarization than estimated here. The annualized costs per establishment range from $19 to $189 for establishments in general industry and maritime and from $21 to $207 for establishments in construction.

The final standard requires two forms of hazard communication to employees: Paragraph (j)(1) notes that employers must include respirable crystalline silica in their existing hazard communication programs required by the hazard communication standard (HCS) (29 CFR 1910.1200), and paragraph (j)(3) requires that employers must provide employees with specific information and training. As specified in paragraph (j)(3)(i) of the final rule and the HCS, training is required for all employees in general industry and maritime are covered by the standard. This requirement applies to newly hired workers who would require training before starting work, workers who change jobs within their current workplace or are assigned new tasks or exposure protection, and any covered worker an employer believes needs additional training. Thus OSHA has estimated a one-time training cost for existing employees as well as recurring training costs to account for new hires.

OSHA estimated separate costs for initial training of current employees and for training new hires. Given that new-hire training might need to be performed frequently during the year, OSHA estimated a smaller class size for new hires. OSHA anticipates that training, in accordance with the requirements of the final rule, will be conducted by in-house safety or supervisory staff with the use of training modules or videos and will last, on average, one hour. OSHA judged that establishments could purchase sufficient training materials at an average cost of $2.10 per worker, encompassing the cost of handouts, video presentations, and training manuals and exercises. Included in the cost estimates for training are the value of worker and trainer time as measured by 2012 hourly wage rates (to include fringe benefits). OSHA also developed estimates of average class sizes as a function of establishment size. For initial training, OSHA estimated an average class size of 5 workers for establishments with fewer than 20 employees, 10 workers for establishments with 20 to 499 employees, and 20 workers for establishments with 500 or more employees. For new hire training, OSHA estimated an average class size of 2 workers for establishments with fewer than 20 employees, 5 workers for establishments with 20 to 499 employees, and 10 workers for establishments with 500 or more employees.

The unit costs of training are presented in Tables V-22 (for general industry/maritime) and V-69 (for construction) in the FEA. Based on ERG's work, OSHA estimated the annualized cost (annualized over 10 years) of initial training per current employee at between $3.39 and $4.10 and the annual cost of new-hire training at between $30.90 and $47.05 per employee in general industry and maritime, depending on establishment size. For construction, OSHA estimated the annualized cost of initial training per employee at between $4.21 and $4.99 and the annual cost of new hire training at between $38.14 and $55.76 per employee, depending on establishment size.

OSHA recognizes that many affected establishments currently provide training on the hazards of respirable crystalline silica in the workplace. In the PEA OSHA estimated that 50 percent of affected establishments already provide such training. However, some of the training specified in the final rule requires that workers be familiar with the training and medical surveillance provisions in the rule.

The Agency reviewed its baseline training estimates in light of comments in the record decided to take a more conservative approach to estimating current compliance with the training provisions in the final rule. Therefore, for the FEA, OSHA assumed no baseline respirable crystalline silica training (other than that already required under the HCS) and that a full hour of training, on average, will be required for all covered workers. This removal of baseline respirable crystalline silica training in estimating training costs has the effect, by itself, of increasing the effective training costs in the FEA relative to the PEA by 33 percent (from an average training time, per employee, of 45 minutes to 60 minutes). OSHA recognizes that this change may lead to an overestimation of training costs for some employers.

6. Regulated Areas

Paragraph (e)(1) of the final standard requires employers in general industry and maritime to establish a regulated area wherever an employee's exposure to airborne concentrations of respirable crystalline silica is, or can reasonably be expected to be, in excess of the PEL. Paragraph (e)(2)(i) requires employers to demarcate regulated areas from the rest of the workplace in a manner that minimizes the number of employees exposed to respirable crystalline silica within the regulated area. Paragraph (e)(2)(ii) requires employers to post signs at all entrances to regulated areas bear the legend specified in paragraph (j)(2) of the standard. Under paragraph (e)(3), employers must limit access to regulated areas and under paragraph (e)(4), employers must provide each employee and designated employee representative entering a regulated area with an appropriate respirator (in accordance with paragraph (g) of the standard) and require each employee and designated employee representative to use the respirator while in a regulated area.

Based on OSHA (2016), OSHA derived unit cost estimates for establishing and maintaining regulated areas to comply with these requirements and estimated that one area would be necessary for every eight workers in general industry and maritime exposed above the PEL. Planning time for a regulated area is estimated to be an initial seven hours of supervisor time (initial cost of $282.67 in 2012 dollars), and one hour for changes annually (at a cost of $40.38 in 2012 dollars); material costs for signs and boundary markers (annualized at $66.93 in 2012 dollars); and costs of $526 annually for two disposable respirators per day to be used by authorized persons (other than those who regularly work in the regulated area) who might need to enter the area in the course of their job duties. Tables V-25 in the FEA shows the cost assumptions and unit costs applied in OSHA's cost model for regulated areas in general industry and maritime. Overall, OSHA estimates that each regulated area would, on average, cost employers $666 annually in general industry and maritime.

7. Written Exposure Control Plans

A written exposure control plan provision was not included in the silica proposal, and no costs for a written exposure control plan were estimated in the PEA. Paragraph (f)(2) in the final standard for general industry and paragraph (g) in the final standard for construction specify the following requirements for a written exposure control plan: (i) A description of the tasks in the workplace that involve exposure to respirable crystalline silica; (ii) a description of the engineering controls, work practices, and respiratory protection used to limit employee exposure to respirable crystalline silica for each task; (iii) a description of the housekeeping measures used to limit employee exposure to respirable crystalline silica; and (iv) for construction, a description of the procedures used to restrict access to work areas, when necessary, to minimize the number of employees exposed to respirable crystalline silica and their level of exposure, including exposures generated by other employers or sole proprietors.

In the FEA, Table V-27 shows the unit costs and assumptions for written exposure control plans in general industry and Tables V-72 and V-74 show, respectively the unit costs for developing and implementing written exposure control plans in construction.

Unit costs for a written exposure control plan were calculated based on establishment size, and the Agency assumed, for costing purposes, that a supervisor will develop and update the written exposure control plan for each establishment, spending 1 hour for establishments with fewer than 20 employees, 4 hours for those establishments with between 20 and 499 employees, and 16 hours for those establishments with 500 or more employees. OSHA estimated that 1 hour would be sufficient for very small establishments because there is, on average, barely more than 1 worker covered by the standard per very small establishment in general industry and maritime.

OSHA further determined that the additional supervisory time needed to review and evaluate the effectiveness of the plan, and to update it as necessary, will also vary by establishment size. OSHA estimated 0.5 hours for establishments with fewer than 20 employees, 2 hours for those with between 20 and 499 employees, and 8 hours for those with 500 or more employees to perform the annual review and update. The Agency expects that no other labor or materials will be required to implement the plan, so the sole cost for this provision is the time it will take to develop, review, and update the plan.

In the context of general industry or maritime activities in permanent facilities, the implementation of the written exposure control plan will not typically involve significant time or effort above existing operations. In construction, however, employers may be faced with new costs to implement the written exposure plan as they move from site to site. OSHA has therefore included costs for implementation, in addition to the costs for development of the plan, for construction activities. The plan must be implemented by a “competent person,” and OSHA has addressed the additional costs for training the competent person after the discussion of the general implementation costs.

Paragraph (g)(4) requires the employer to designate a competent person to implement the exposure control plan, and restrict access to work areas, when necessary, to minimize the number of employees exposed to respirable crystalline silica and their level of exposure, including exposures generated by other employers or sole proprietors. The competent person has two broad options to restrict access to work areas when necessary: (1) Notifying or briefing employees, or (2) direct access control. The direct access control component is similar to the written access control plan included in the PEA, which OSHA has replaced with the written exposure control plan in the final rule. While the requirements for the written exposure control plan are more performance-oriented and thus should provide more flexibility for employers and reduce the cost of compliance, OSHA has estimated the costs of these options using, where appropriate, comparable components of the regulated area and written access control plan costs estimated in the PEA.

For the employee notification or briefing option, OSHA estimated that, on average, it will take the competent person 15 minutes (0.25 hours) per job to revise the briefing plan, that each job will last 10 work-days, and that there are 150 construction working days in a year (Document ID 1709, p. 4-6). OSHA further estimated that it will take the competent person 6 minutes (0.1 hours) to brief each at-risk crew member (where an at-risk crew member could be an employee, a contractor, a subcontractor, or other worker under the control of the competent person) and that each crew consists of 4 at-risk workers. As shown in Table V-74 in the FEA, the annual cost of the job briefing option is $105.25 per at-risk crew member.

For the direct access control option, OSHA estimated that, on average, it will take the competent person 15 minutes (0.25 hours) per job to revise the plan concerning direct access control and, again, that each job will last 10 work-days and that there are 150 construction working days in a year. Thus, OSHA estimates that, on average, each employer would implement a direct access control 15 times per year over a total of 3.75 hours per year.

OSHA also added the cost of signage and tape for constructing physical barriers: 100 feet of hazard tape (per job) and three warning signs. These costs are all displayed in Table V-74 in the FEA. As also shown there, the annualized cost of the direct access control option is $71.40 per at-risk crew member.

As discussed in the Summary and Explanation section of this preamble concerning the written exposure control plan, restricting access is necessary where respirator use is required under Table 1 or when an exposure assessment reveals that exposures are in excess of the PEL, or in other situations identified by the competent person. On the other hand, when exposure to respirable crystalline silica is being successfully contained by engineering controls and work practices specified in Table 1 and no respirator use is required by Table 1, implementation of access control procedures is not required.

OSHA assumed that, in restricting access, half the time employers would use the briefing option and the other half of the time they would use direct access control. Consequently, as shown in Table V-74, the annualized cost of restricting access to work areas is $88.33 per at-risk crew member.

As specified in paragraph (g)(4) of the final standard, a competent person must carry out the responsibilities of implementing the written exposure control plan. As defined in the standard, “competent person” means an individual who is capable of identifying existing and foreseeable respirable crystalline silica hazards in the workplace and who has authorization to take prompt corrective measures to eliminate or minimize them, as well as has the knowledge and ability necessary to fulfill the responsibilities set forth in paragraph (g) of the standard. OSHA has utilized the competent person provision in other construction standards, such as 1926.1127, Cadmium, and 1926.1101, Asbestos, so the Agency expects that there is widespread familiarity with both the concept and the responsibilities of competent person in the construction sector. As in other OSHA construction rules, a major purpose of the competent person provision in this final silica standard is to identify who has the responsibility for inspections of the job sites, materials, and equipment. Thus, OSHA expects that most employers will have training programs in place to produce competent persons, and the cost of training someone will only be a relatively small marginal increase in the overall training cost. For that reason, the Agency expects that many employees designated as competent persons will undergo some training for the position. OSHA is estimating that each competent person will, on average, undergo two hours of training—in addition to the one hour of silica training estimated for all construction employees. OSHA does not anticipate any additional costs beyond training costs to be associated with the requirement that a competent person implement the written exposure control plan.

While the competent person provision does not specify a training requirement, the competent person is required to possess the knowledge and skills to perform the functions required by the standard. For that reason, the Agency expects that many employees designated as competent persons will undergo some training for the position. OSHA estimates that, on average, there will be 1 competent person for each establishment with fewer than 20 employees, 5 competent persons for each establishment with 20-499 employees, and 10 competent persons for each establishment with 500 or more employees.

OSHA expects that competent persons will be trained by a supervisor, presumably one who went through the process to become familiar with the requirements of the respirable crystalline silica standard, or by a combination of supervisory and/or technical staff that are familiar with the operation of the engineering controls. While the competent persons are not required to be supervisors and some of the staff providing the training may not be supervisors, OSHA is using a supervisor's wage to estimate the costs for time spent by both the trainers and the trainees in order to provide the upper cost limit, realizing that the cost for establishments who do not designate supervisors as the competent person will be lower. OSHA estimated that the total cost per establishment to train a competent person in construction will range from $21 to $114 (see Chapter V in the FEA for a full discussion of OSHA's analysis of costs for written exposure control plans under the final standard).

8. Combined General Industry/Maritime Control, Respirator, and Program Costs

Table VII-14 shows that the estimated combined costs for employers in the general industry and maritime sectors to comply with the final silica rule are approximately $370.8 million annually. These costs include $238.1 million annually for engineering controls and $10.5 million annually for respirators to meet the final PEL of 50 μg/m³. The remaining $122.2 million annually are to meet the ancillary provisions of the final rule. These ancillary annual costs consist of $79.6 million for exposure monitoring; $29.7 million for medical surveillance; $6.0 million for familiarization and training; $2.6 million for regulated areas; and $4.1 million for the written exposure control plan.

Table V-B-1 in Appendix V-B in the FEA presents estimated compliance costs by NAICS industry code and program element for small business entities (as defined by the Small Business Act and the Small Business Administration's implementing regulations; see 15 U.S.C. 632 and 13 CFR 121.201) in general industry and maritime, while Table V-B-2 in the FEA presents estimated compliance costs, by NAICS code and program element, for very small entities (fewer than twenty employees) in general industry and maritime.

9. Combined Construction Control, Respirator, and Program Costs

Table VII-15 summarizes the engineering control costs, respirator costs, and program costs of the rule for the construction sector. Annualized compliance costs in construction are expected to total $659.0 million, of which $423.4 million are for engineering controls, $22.4 million are for respirators, and $213.2 million are to meet the ancillary provisions of the rule. These ancillary annual costs consist of $16.5 million for exposure monitoring; $66.7 million for medical surveillance; $89.9 million for familiarization and training; and $40.1 million for the written exposure control plan.

Table V-B-1 in Appendix V-B in the FEA presents estimated compliance costs by NAICS industry code and program element for small entities (as defined by the Small Business Administration) in construction, while Table V-B-2 in the FEA presents estimated compliance costs, by NAICS code and program element, for very small entities (fewer than twenty employees) in construction.

10. Total Cost Summary

As shown in Table VII-16, annualized compliance costs associated with the rule are expected to total $1,030 million. Table VII-16 also provides total annualized costs for general industry, maritime, and construction separately, by major provision or program element included in the rule. This table shows that engineering control costs represent 64 percent of the costs of the standard for all three affected industry sectors: general industry, maritime, and construction. Considering other leading cost categories, costs for exposure assessment and medical surveillance represent, respectively, 30 percent and 15 percent of the costs of the standard for general industry and maritime; costs for training and familiarization and medical surveillance represent, respectively, 14 percent and 10 percent of the costs of the standard for construction.

While the costs presented here represent the Agency's best estimate of the costs to industry of complying with the rule under static conditions (that is, using existing technology and the current deployment of workers), OSHA recognizes that actual costs could be somewhat higher or lower, depending on the Agency's possible overestimation or underestimation of various cost factors. In Chapter VII of the FEA, OSHA provides a sensitivity analysis of its cost estimates by modifying certain critical unit cost factors. Beyond this sensitivity analysis, OSHA notes that its cost estimates do not reflect the possibility that, in response to the rule, industry may find ways to reduce compliance costs.

This could be achieved in three ways. First, in construction, 36 percent of the estimated costs of the rule (all costs except engineering controls) vary directly with the number of workers exposed to silica. However, as shown in Table III-5 in the FEA, more than five times as many construction workers will be affected by the rule as will the number of full-time-equivalent construction workers necessary to do the work. This is because most construction workers currently doing work involving silica exposure perform such tasks for only a portion of their workday. In response to the rule, many employers are likely to assign work so that fewer construction workers perform tasks involving silica exposure; correspondingly, construction work involving silica exposure will tend to become a full-time job for some construction workers. Were this approach fully implemented in construction, the actual cost of the rule would decline because employers would have to comply with the ancillary provisions of the final rule for fewer workers. However, these workers would be subject to the full protections of the final rule.

Second, industry could demonstrate that certain construction activities result in exposures below the action level under any foreseeable conditions—in which case, workers engaged only in those silica-generating activities would not be subject to the requirements of the final rule. For example, an employer could make this demonstration by using objective data developed for short-term, intermittent tasks involving limited generation of silica dust. In estimating the costs for this final rule, however, OSHA included all costs, including ancillary costs as appropriate, associated with short-term intermittent silica tasks.

Third, the costs presented here do not take into account the possible development and dissemination of cost-reducing compliance technology in response to the rule. One possible example is the development of safe substitutes for silica sand in activities such as abrasive blasting operations, repair and replacement of refractory materials, foundry operations, and in the railroad transportation industry. Another is expanded use of automated processes which would allow workers to be isolated from the points of operation that involve silica exposure (such as tasks between the furnace and the pouring machine in foundries and at sand transfer stations in structural clay production facilities). Yet another example is the further development and use of bags with valves that seal effectively when filled, thereby preventing product leakage and worker exposure (for example, in mineral processing and concrete products industries). Probably the most pervasive and significant technological advances, however, will likely come from the integration of compliant control technology into standard production equipment. Such advances would both increase the effectiveness and reduce the costs of silica controls when compared to retrofitted production equipment. Possible examples include local exhaust ventilation (LEV) systems attached to portable tools used by grinders and tuckpointers; enclosed operator cabs equipped with air filtration and air conditioning in industries that mechanically transfer silica or silica-containing materials; and machine-integrated wet dust suppression systems used, for example, in road milling operations.

OSHA has decided not to include in its analysis any possible cost-reducing technological advances or worker specialization because the technological and economic feasibility of the rule can easily be demonstrated using existing technology and employment patterns. However, OSHA believes that actual costs, which will incorporate any future developments of this type, will likely be lower than those estimated here.

a. Costs Under Alternative PEL (100 μg/m³) Scenario

Appendix V-C in the FEA presents, for analytical purposes, costs for an alternative PEL of 100 μg/m³. Total annualized compliance costs under this alternative are $649.3 million. Table V-C-1 displays costs for general industry, maritime, and construction by each program element. Table V-C-2 shows total costs by NAICS industry code for all affected general industry and maritime establishments, for business entities in general industry and maritime defined as small by the Small Business Administration, and for very small business entities in general industry and maritime (those with fewer than twenty employees). Table V-C-3 shows total costs by NAICS industry code for all affected construction establishments, for business entities in construction defined as small by the Small Business Administration, and for very small business entities in construction (those with fewer than twenty employees).

b. Costs Under Alternative Discount Rates

An appropriate discount rate is needed to reflect the timing of costs after the rule takes effect and to allow conversion to an equivalent steady stream of annualized costs.

c. Alternative Discount Rates for Annualizing Costs

Following OMB (2003) guidelines (Document ID 1493), OSHA has estimated the annualized costs of the rule using separate discount rates of 3 percent and 7 percent. Consistent with the Agency's own practices in recent proposed and final rules, OSHA has also estimated, for benchmarking purposes, undiscounted costs—that is, costs using a zero percent discount rate.

d. Summary of Annualized Costs Under Alternative Discount Rates

In addition to using a 3 percent discount rate in its main cost analysis, OSHA estimated compliance costs, in Appendix V-D in the FEA, using alternative discount rates of 7 percent and zero percent. Table V-D-1 and V-D-2 in Appendix V-D present total costs at a 7 percent discount rate for both (1) all employers by major industry category and program element, and (2) affected employers by NAICS industry code and employment size class (all establishments, small entities, and very small entities). Tables V-D-3 and V-D-4 present the same breakdowns of total costs estimated at a zero percent discount rate.

As shown in Appendix V-D, the choice of discount rate has only a minor effect on total annualized compliance costs, with annualized costs increasing from 1,030 million using a three percent discount rate to $1,056 million using a seven percent discount rate, and decreasing to $1,012 million using a zero percent discount rate.

e. Time Distribution of Costs

OSHA analyzed the stream of (unannualized) compliance costs, by industry sector, for the first ten years after the rule takes effect under the simplifying assumption that no provisions of the rule are phased in. As shown in Table VII-16, total compliance costs are expected to peak in Year 1 at more than $1.5 billion. After that, costs are estimated to decline and remain relatively flat after the initial set of capital and program start-up expenditures has been incurred. Costs are projected to rise somewhat in Year 4 as a result of the triennial medical examinations and in Year 6 because of a second cycle of control equipment purchases in construction for short-term, intermittent work. Thereafter there are fluctuations but no strong trend. OSHA notes that the differences between costs for Year 1 and costs for subsequent years are narrower than might otherwise be the case due to (1) the expectation that, in the construction sector, a large percentage of control equipment will be rented (leading to constant annual expenses for the rented control equipment) rather than purchased as capital in Year 1; and (2) the expectation that the only engineering controls needed in the maritime sector will be wet methods, which do not require capital expenditures. On the other hand, the ancillary provisions are expected to have a relatively large number of initial costs (mainly labor rather than capital) in Year 1.

F. Economic Feasibility Analysis and Regulatory Flexibility Determination

Chapter VI of the FEA presents OSHA's analysis of the economic impacts of its final silica rule on affected employers in general industry, maritime, and construction. The discussion below summarizes the findings in that chapter.

As a first step, the Agency explains its approach for achieving the two major objectives of its economic impact analysis: (1) To establish whether the final rule is economically feasible for all affected industries, and (2) to determine if the Agency can certify that the final rule will not have a significant economic impact on a substantial number of small entities. Next, this approach is applied to industries with affected employers in general industry and maritime and then to industries with affected employers in construction. Finally, OSHA examines the employment effects of the silica rule. This includes a review of estimates of employment effects that commenters provided and a summary of a report prepared for the Agency by Inforum—a not-for-profit corporation (based at the University of Maryland) specializing in the design and application of macroeconomic models of the United States (and other countries)—to estimate the industry and aggregate employment effects of the silica rule.

Many commenters questioned OSHA's preliminary conclusions concerning economic feasibility, but did so for reasons that OSHA has responded to in previous chapters.

A variety of commenters raised issues concerning industries with possible silica exposure that were not covered in the Preliminary Economic and Initial Regulatory Feasibility Analysis (PEA). A full discussion of these comments and of industries added is provided in the FEA.

Many commenters questioned why OSHA used no data after 2006 (see comments by the Brick Industry Association (BIA) (Document ID 2300, p. 5), the American Fuel & Petrochemical Manufacturers (AFPM) (Document ID 2350, p. 6), the Belden Brick Company (Document ID 3260, p. 3), Basalite Concrete Products, LLC (Document ID 2083, p. 1), SBG Consulting (Document ID 2222, p. 1), Acme Brick (Document ID 2182, p. 4), Erie Bronze & Aluminum (Document ID 1780, p. 1), Calstone (Document ID 3391, p. 2), the Chamber of Commerce (Document ID 1782, p. 1), the Mason Contractors Association of America (MCAA) (Document ID 1767, p. 2), Scango Consulting LLC d.b.a. Capitol Hardscapes (Document ID 2241, p. 3), the National Concrete Masonry Association (NCMA) (Document ID 3585, p. 2944), the American Road and Transportation Builders Association (ARTBA) (Document ID 2245, p. 4), and the Construction Industry Safety Coalition (CISC) (Document ID 4217, Attachment 1, pp. 4 and 49-52)). As discussed in Chapter III of the FEA, OSHA is using revenue data from 2012 and profit data averaged across the years 2000 through 2012. The revenue data from 2012 represent a reasonable choice because this year was neither a peak growth year nor a recession year and was the most up-to-date data available at the time this analysis was developed. The range of years for profits assures the use of profit rates from throughout the business cycle—including two recessions and two sustained growth periods.

One commenter questioned OSHA's sources and methodology for estimating revenues (Document ID 2308, Attachment 9, pp. 7-8 and 14-16). This commenter questioned the methodology used to update revenue estimates between Economic Census years. This is no longer an issue as OSHA is using 2012 Economic Census data and using 2012 as the base year for the analysis. Therefore, there is no need for a methodology to update Economic Census revenues.

OSHA also received criticism on the choice of the data source and the methodology for estimating profits of the construction industry. These include comments from the National Association of Home Builders (NAHB) and the CISC (Document ID 2296, Attachment 1, pp. 20-22; 2308, Attachment 9, pp. 7-12).

Stuart Sessions, submitting on behalf of the CISC, criticized OSHA for using the Internal Revenue Service's (IRS) Corporation Source Book (CSB) as the source for industry profits since those data are only presented at the four-digit NAICS level instead of the five- or six-digit NAICS level. Mr. Sessions recommended that OSHA use an alternative data source for profit data and recommended Bizminer or RMA (Document ID 4231, Attachment 1, pp.12-13). OSHA investigated these sources and determined that these data were private data sources and that their publishers would not allow the data to be made publicly available. These other sources of profit data also suffered from the disadvantage of not representing adequate and random samples of the affected industries. A further discussion on this issue appears in Chapter III of the FEA.

In the PEA, OSHA used IRS data to calculate profit rates as the ratio of net income to total receipts (with the numerator including only firms with positive net income and the denominator including firms with and without net income) by NAICS industry. In response to comments criticizing this ratio as an inappropriate method to calculate industry profitability (Document ID 2308, Attachment 9, pp. 11-12; 4209, pp. 115-116), OSHA has revised the way that estimated profits are calculated. In the FEA, OSHA calculates profit rates using the method recommended by Mr. Sessions, which is discussed more fully in Chapter III. This method includes unprofitable firms and divides the “net income” from all firms (profitable and unprofitable) by total receipts from all firms (profitable and unprofitable), resulting in somewhat lower profit rates.

Similarly, Mr. Sessions criticized OSHA for using data that he believed were at a level that was too aggregated to show economic impacts of the costs of the rule accurately (Document ID 2319, Attachment 1, p. 71). The Portland Cement Association likewise disagreed with OSHA's presentation of costs as averages across industries. It said that “a more focused explanation of individual plant and facility costs is relevant to those industries with significant compliance responsibilities” (Document ID 2284, p. 6). OSHA's data sources for profile data are presented in Chapter III of the FEA. In general, OSHA has disaggregated industries to the extent that the source data will allow.

The most common criticism of OSHA's preliminary conclusions on economic feasibility was that the conclusions were based on costs that were underestimated or inaccurate (e.g., Document ID 2023, p. 1; 2299, p. 15; 2379, Attachment 3, pp. 2 and 10; 2388, pp. 2 and 10; 2296, Attachment 1, p. 17; 2116, Attachment 1, p. 22; and 3378, Attachment 2). For example, Wayne D'Angelo of the American Petroleum Institute (API) and the Independent Petroleum Association of America (IPAA) (API/IPAA or “the Associations”) critiqued OSHA's feasibility analysis for the hydraulic fracturing industry, stating that OSHA had not met its obligations due to inaccurate cost data and an industry profile that, they asserted, did not “reasonably represent the typical firms in the various segments of the industry, given varying operations, exposure levels, and processes” (Document ID 2301, Attachment 1, pp. 62-63).

OSHA responded to comments on its preliminary cost estimates in Chapter V of the FEA. In the aggregate, OSHA increased its cost estimate by approximately 46 percent, in part, as a result of changes in cost estimates made in response to comments and, in part, as a result of changes in the rule.

Some commenters argued that OSHA had not adequately considered the possibility that smaller establishments might have higher costs or that the costs have a greater impact on small businesses (Document ID 4231, Attachment 1, p. 11; 2379, Attachment 2, p. 7; 3582, Tr. 2107-2109; 2203, p. 1; 2351, p. 8; 3433, p. 9; 3580, Tr. 1398). As discussed in Chapter V, OSHA has made a number of changes to the costs analysis to reflect higher costs for small establishments.

1. Analytic Approach

a. Economic Feasibility

The Court of Appeals for the D.C. Circuit has long held that OSHA standards are economically feasible so long as their costs do not threaten the existence of, or cause massive economic dislocations within, a particular industry or alter the competitive structure of that industry. American Iron and Steel Institute. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991); United Steelworkers of America, AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1265 (D.C. Cir. 1980); Industrial Union Department v. Hodgson, 499 F.2d 467, 478 (D.C. Cir. 1974).

In practice, the economic burden of an OSHA standard on an industry—and whether the standard is economically feasible for that industry—depends on the magnitude of compliance costs incurred by establishments in that industry and the extent to which they are able to pass those costs on to their customers. That, in turn, depends, to a significant degree, on the price elasticity of demand for the products sold by establishments in that industry.

The price elasticity of demand refers to the relationship between the price charged for a product and the demand for that product: The more elastic the relationship, the less an establishment's compliance costs can be passed through to customers in the form of a price increase and the more it has to absorb compliance costs in the form of reduced profits. When demand is inelastic, establishments can recover most of the variable costs of compliance (i.e., costs that are highly correlated with the amount of output) by raising the prices they charge; under this scenario, if costs are variable rather than fixed, profit rates are largely unchanged and the industry remains largely unaffected. Any impacts are primarily on those customers using the relevant product. On the other hand, when demand is elastic, establishments cannot recover all compliance costs simply by passing the cost increase through in the form of a price increase; instead, they must absorb some of the increase from their profits. Commonly, this will mean reductions both in the quantity of goods and services produced and in total profits, though the profit rate may remain unchanged. Other things being equal, higher fixed costs mean that the optimal scale of the typical establishment will be larger than it would be if fixed costs were lower. This in turn means that, where there are higher fixed costs, there will be fewer plants for the same level of production. Whether an increase in fixed costs results in closures of existing plants depends on several factors. If demand regularly increases (such as due to economic growth) or the industry regularly experiences plant closures, the optimal scale may be arrived at by reduced entry rather than premature closures. If plants are not part of a simple homogeneous market, it may not be possible to shift the scale of production. For example, if a plant provides foundry products to others in the same city, it may not be able to readily expand its scale of production. In general, “[w]hen an industry is subjected to a higher cost, it does not simply swallow it; it raises its price and reduces its output, and in this way shifts a part of the cost to its consumers and a part to its suppliers,” in the words of the court in American Dental Association v. Secretary of Labor (984 F.2d 823, 829 (7th Cir. 1993)).

The court's summary is in accord with microeconomic theory. In the long run, firms can remain in business only if their profits are adequate to provide a return on investment that ensures that investment in the industry will continue. As technology and costs change, however, the long-run demand for some products naturally increases and the long-run demand for other products naturally decreases. In the face of additional compliance costs (or other external costs), firms that otherwise have a profitable line of business may have to increase prices to stay viable. Increases in prices typically result in reduced quantity demanded, but rarely eliminate all demand for the product. Whether this decrease in the total production of goods and services results in smaller output for each establishment within the industry, or the closure of some plants within the industry; a reduced number of new establishments entering the industry; or a combination of the three, is dependent on the cost and profit structure of individual firms within the industry.

If demand is perfectly inelastic (i.e., the price elasticity of demand is zero), then the impact of compliance costs that are 1 percent of revenues for each firm in the industry would result in a 1 percent increase in the price of the product, with the quantity demanded constant. (This outcome would hold in the long run, regardless of type of costs, but in the short run would hold with certainty only if compliance costs are strictly variable.) Such a scenario represents an extreme case, but might be observed in situations in which there were few if any substitutes for the product in question, or if the products of the affected sector account for only a very small portion of the revenue or income of its customers. Under this scenario, both profits and output of the industry would be unaffected, but customers would be worse off.

If the demand is perfectly elastic (i.e., the price elasticity of demand is infinitely large), then no increase in price is possible and before-tax profits would be reduced by an amount equal to the costs of compliance (net of any cost savings—such as reduced workers' compensation insurance premiums—resulting from the final standard) if the industry attempted to maintain production at the same level. Under this scenario, if the costs of compliance are such a large percentage of profits that some or all plants in the industry could no longer operate with the hope of an adequate return on investment, then some or all of the firms would close. Similarly, if compliance costs are fixed, such costs may result in premature closures or reduced entry into the market in some circumstances.

A commonly discussed intermediate case would be a price elasticity of demand of one. In this scenario, if the costs of compliance amount to 1 percent of revenues, then production would decline by 1 percent and prices would rise by 1 percent. (As before, this outcome would hold in the long run, regardless of type of costs, but in the short run would hold with certainty only if compliance costs are variable.) Under this scenario, and if marginal costs of the regulation fall proportionally with output, then industry revenues would remain the same, with somewhat lower production, but with similar profit rates. Customers would, however, receive less of the product for their (same) expenditures, and firms would have lower total profits; this, as the court described in Am. Dental Ass'n v. Sec'y of Labor, 984 F.2d 823 (7th Cir. 1993), is the more typical case.

A decline in output as a result of an increase in price may occur in a variety of ways: Individual establishments could each reduce their levels of production; some marginal plants could close; or, in the case of an industry with high turnover of establishments, new entry may be delayed until demand equals supply. In many cases a decrease in overall output for an industry will be a combination of all three kinds of reductions. Which possibility is most likely depends on the rate of turnover in the industry and on the form that the costs of the regulation take.

When turnover in an industry is high, or an industry is expanding rapidly, then the key issue is the long run costs as determined by the cost of entry into the industry. For example, if there is annual turnover in an industry of ten percent per year, and a price elasticity of one, then a single year without new entry would result in a price rise of ten percent. Such a rise would be more than enough to compensate existing employers for a cost increase of one percent of revenues. If the costs are variable costs (i.e., costs that vary with the level of production at a facility), then economic theory suggests that any reductions in output will take the form of reductions in output at each affected facility, with few, if any, plant closures. If the costs of a regulation primarily take the form of fixed costs (i.e., costs that do not vary with the level of production at a facility), and assuming perfect competition, then reductions in overall output are more likely to can only take the form of plant closures or delays in new entry. Most of the costs of this regulation, as estimated in Chapter V of the FEA, are variable costs. Almost all of the major costs of program elements, such as medical surveillance and training, will vary in proportion to the number of employees (which is a rough proxy for the amount of production). Exposure monitoring costs will vary with the number of employees, but do have some economies of scale to the extent that a larger firm need only conduct representative sampling rather than sample every employee. The costs of engineering controls in construction also vary by level of production because almost all necessary equipment can readily be rented and the productivity costs of using some of these controls vary proportionally to the level of production. Finally, the costs of operating engineering controls in general industry (the majority of the annualized costs of engineering controls are in general industry) vary by the number of hours the establishment works, and thus vary by the level of production and are not fixed costs in the strictest sense.

This leaves two kinds of costs that are, in some sense, fixed costs—capital costs of engineering controls in general industry and certain initial costs that new entrants to the industry will not have to bear.

Fixed costs in the form of capital costs of engineering controls in general industry and maritime due to this standard are relatively small as compared to the total costs, representing less than 21 percent of total annualized costs and approximately $1,019 per year per affected establishment in general industry.

There are some initial fixed costs in the sense that they might only be borne by firms in the industry today. For example, costs for general training not currently required and initial costs of medical surveillance may not be borne by establishments new to the industry to the extent they can hire from a workforce that may have already had this training and/or initial medical surveillance. An initial thorough facility cleaning is not a cost a new establishment would need to bear. These costs will disappear after the initial year of the standard and thus would be difficult to pass on. These costs, however, represent less than two percent of total costs and less than $58 per affected establishment. These initial fixed costs that may be borne by firms in the affected industries today, together with capital costs, give a total fixed cost of approximately 22 percent of total annual costs.

Because the remaining three-fourths of the total annual costs are variable, OSHA expects it is somewhat more likely that reductions in industry output resulting from the increase in costs associated with this rule will be met by reductions in output at each affected facility rather than as a result of plant closures or reduced new entry. However, closures of some marginal plants or poorly performing facilities are always possible. To determine whether a rule is economically feasible, OSHA begins with two screening tests to consider minimum threshold effects of the rule under two extreme cases: (1) All costs are passed through to customers in the form of higher prices (consistent with a price elasticity of demand of zero), and (2) all costs are absorbed by the firm in the form of reduced profits (consistent with an infinite price elasticity of demand).

In the former case, the immediate impact of the rule would be observed in increased industry revenues. While there is no hard and fast rule, in the absence of evidence to the contrary, OSHA generally considers a standard to be economically feasible for an industry when the annualized costs of compliance are less than a threshold level of one percent of annual revenues. Retrospective studies of previous OSHA regulations have shown that potential impacts of such a small magnitude are unlikely to eliminate an industry or significantly alter its competitive structure, particularly since most industries have at least some ability to raise prices to reflect increased costs and, as shown in the FEA, normal price variations for products typically exceed three percent a year. Of course, OSHA recognizes that even when costs are within this range, there could be unusual circumstances requiring further analysis.

In the latter case, the immediate impact of the rule would be observed in reduced industry profits. OSHA uses the ratio of annualized costs to annual profits as a second check on economic feasibility. Again, while there is no hard and fast rule, in the absence of evidence to the contrary, OSHA generally considers a standard to be economically feasible for an industry when the annualized costs of compliance are less than a threshold level of ten percent of annual profits. In the context of economic feasibility, the Agency believes this threshold level to be fairly modest, given that normal year-to-year variations in profit rates in an industry can exceed 40 percent or more. OSHA's choice of a threshold level of ten percent of annual profits is low enough that even if, in a hypothetical worst case, all compliance costs were upfront costs, then upfront costs would still equal 88.5 percent of profits using a three percent discount rate (see section Normal Year-to-Year Variations in Prices and Profit Rates below) and thus would be affordable from profits alone without the need for an employer to resort to credit markets. If the threshold level were first-year costs of ten percent of annual profits, firms could even more easily expect to cover first-year costs at the threshold level out of current profits without having to access capital (including credit markets) markets and otherwise being threatened with short-term insolvency.

In general, it is usually the case that firms would be able to pass on some or all of the costs of the rule to their customers in the form of higher prices. OSHA therefore will tend to give much more weight to the ratio of industry costs to industry revenues than to the ratio of industry costs to industry profits. However, if costs exceed either the threshold percentage of revenue or the threshold percentage of profits for an industry, or if there is other evidence of a threat to the viability of an industry because of the standard, OSHA will examine the effect of the rule on that industry more closely. Such an examination would include market factors specific to the industry, such as normal variations in prices and profits, international trade and foreign competition, and any special circumstances, such as close domestic substitutes of equal cost, which might make the industry particularly vulnerable to a regulatory cost increase.

The preceding discussion focused on the economic viability of the affected industries in their entirety. However, even if OSHA found that a final standard did not threaten the survival of affected industries, there is still the question of whether the industries' competitive structure would be significantly altered. For example, if the annualized costs of an OSHA standard were equal to ten percent of an industry's annual profits, and the price elasticity of demand for the products in that industry were equal to one, then OSHA would not expect the industry to go out of business. However, if the increase in costs were such that most or all small firms in that industry would have to close, it could reasonably be concluded that the competitive structure of the industry had been altered. For this reason, OSHA also examines the differential costs by size of establishment.

Public Comments on OSHA's Approach to Economic Feasibility

Some commenters were concerned that reductions of profits of less than ten percent could still represent major losses to an employer. For example, one commenter said:

The proposed rule states that in no cases will the amount of revenue or profits exceed 8.8% noting that this number is easily passed to consumers in the form of increased product and service costs. For a rule as specific and slight as one affecting only silica dust inhalation, a reduction in profits by 8.8% should give the government pause (Document ID 2189, p. 1).

Another commenter expressed similar concerns about a reduction in profits of 4.8 percent (Document ID 1882, Attachment 1, p. 2). OSHA is not dismissive of losses in profits of less than ten percent. However, such losses need to be weighed against the OSH Act's objectives of occupational safety and health. For purposes of assessing economic feasibility, OSHA needs to be concerned with major dislocating effects on entire industries, which will not be the result of relatively small changes in profits. Further, as will be discussed below, these costs can likely be passed on to consumers.

API/IPAA, while disagreeing with OSHA's cost estimates, acknowledged that OSHA's use of the rules of thumb of ten percent of profits or one percent of revenues has been upheld in court (Document ID 2301, Attachment 1, pp. 62-63).

Some commenters were also concerned that OSHA's screening analysis methodology did not give adequate consideration to upfront costs (Document ID 2379, Attachment 3, p. 39; 2119, Attachment 3, p. 22). As will be discussed below, OSHA's choice of a threshold level of ten percent of annual profits is low enough that even if, in a hypothetical worst case, all compliance costs were upfront costs, then upfront costs would still equal 88.5 percent of profits and thus would be affordable from profits alone without needing to resort to credit markets. (If the cost exceeds 100 percent of profits then the company would have to borrow to pay the balance. Otherwise the firm will not have to borrow but could finance the cost internally.)

While not specifically addressed to the issue of the screening analysis, Mr. Sessions provided some estimates of how various percentage cost increases might interact with demand and supply elasticities to produce estimates of declines in total industry output. His estimates show that the decline in total revenues (and, in this situation, total production) associated with increased costs of one percent of revenues ranges from zero to 0.83 percent of total production (the range depending on the elasticities of supply and demand, with the highest impact on total revenues associated with a very unlikely price elasticity of ten) (Document ID 4231, Attachment 1, p. 31). Even the largest decline in revenues would result in only a 0.83 percent decline in revenues, which would not represent a major dislocation of any affected industry. While OSHA does not necessarily endorse this particular approach to calculating changes in total revenue for given percentage change in costs, the calculation confirms OSHA's general view that increases of less than one percent of costs do not render a standard economically infeasible.

After reviewing these comments, OSHA has decided to retain its screening test of ten percent of profits and one percent of revenues as levels below which significant dislocation of an industry is extremely unlikely.

b. Regulatory Flexibility Screening Analysis

The Regulatory Flexibility Act (RFA), Public Law 96-354, 94 Stat. 1164 (codified at 5 U.S.C. 601), requires Federal agencies to consider the economic impact that a final rulemaking will have on small entities. The RFA states that whenever an agency “promulgates a final rule under section 553 of this title, after being required by that section or any other law to publish a general notice of proposed rulemaking, the agency shall prepare a final regulatory flexibility analysis” (FRFA). 5 U.S.C. 604(a). Pursuant to section 605(b), in lieu of an FRFA, the head of an agency may certify that the final rule will not have a significant economic impact on a substantial number of small entities. A certification must be supported by a factual basis. If the head of an agency makes a certification, the agency shall publish such certification in the Federal Register at the time of publication of general notice of final rulemaking or at the time of publication of the final rule. 5 U.S.C. 605(b). Thus, if OSHA cannot issue the required certification, it must prepare a FRFA.

OSHA makes its determination about whether it can issue the required certification by applying screening tests to consider minimum threshold effects of the rule on small entities. These screening tests are similar in concept to those OSHA described above to identify minimum threshold effects for the purposes of demonstrating economic feasibility and are discussed below.

There are, however, two differences. First, for each affected industry, the screening tests are applied, not to all establishments, but to small entities (defined as “small business concerns” by the Small Business Administration (SBA)) and also to very small entities (as defined by OSHA as small businesses with fewer than 20 employees). Second, although OSHA's regulatory flexibility screening test for revenues also uses a minimum threshold level of annualized costs equal to one percent of annual revenues, OSHA has established a minimum threshold level of annualized costs equal to five percent of annual profits for the average small entity or very small entity (rather than the ten percent threshold applicable for general economic feasibility screening). The Agency has chosen a lower minimum threshold level for the profitability screening analysis and has applied its screening tests to both small entities and very small entities in order to ensure that certification will be made, and an FRFA will not be prepared, only if OSHA can be highly confident that a final rule will not have a significant economic impact on a substantial number of small entities or very small entities in any affected industry.

OSHA has prepared separate regulatory flexibility screening tests for general industry, maritime, and construction.

2. Impacts in General Industry and Maritime

In this section, OSHA will determine whether (1) the rule is economically feasible for all affected industries in general industry and maritime, and (2) the Agency can certify that the rule will not have a significant economic impact on a substantial number of small entities in general industry and maritime. OSHA concludes that the rule is economically feasible, but the Agency is unable to certify that it will not have a significant economic impact on a substantial number of small entities.

a. Economic Feasibility Screening Analysis: All Establishments

Earlier chapters of the FEA identified the general industry and maritime sectors potentially affected by the final rule; presented summary profile data for affected industries, including the number of affected entities and establishments, the number of at-risk workers, and the average revenue for affected entities and establishments; and developed estimates, by affected industry, of the costs of the rule. The economic impacts of the final rule on general industry and maritime are driven, in part, by the costs of additional dust control measures, respirators, and silica program activities needed to comply with the rule.

To determine whether the final rule's projected costs of compliance would threaten the economic viability of affected industries; OSHA first compared, for each affected industry, annualized compliance costs to annual revenues and profits per (average) affected establishment. The results for all affected establishments in all affected industries in general industry and maritime are presented in Table VII-18, using annualized costs per establishment for the PEL of 50 μg/m³. Shown in the table for each affected industry are total annualized costs, the total number of affected establishments, annualized costs per affected establishment, annual revenues per establishment, the profit rate, annual profits per establishment, annualized compliance costs as a percentage of annual revenues, and annualized compliance costs as a percentage of annual profits.

The annualized costs per affected establishment for each affected industry were calculated by distributing the industry-level (incremental) annualized compliance costs among all affected establishments in the industry, where annualized compliance costs reflect a three percent discount rate. The annualized cost of the rule for the average establishment in all of general industry and maritime is estimated to be $4,939 in 2012 dollars. It is clear from Table VII-18 that the estimates of the annualized costs per affected establishment in general industry and maritime vary widely from industry to industry. These estimates range from $220,558 for NAICS 213112 (Support Activities for Oil and Gas Operations) and $57,403 for NAICS 331511 (Iron Foundries) to $304 for NAICS 621210 (Offices of Dentists) and $377 for NAICS 324121 (Asphalt Paving Mixture and Block Manufacturing).

Table VII-18 also shows that, within the general industry and maritime sectors, there are no industries in which the annualized costs of the final rule exceed 1 percent of annual revenues and there are eight industries in which the annualized costs of the rule exceed ten percent of annual profits and none where annualized costs exceed one percent of annual revenues. NAICS 213112 (Support Activities for Oil and Gas Operations), has the highest cost impact as a percentage of revenues, of 0.56 percent. NAICS 327120 (Clay Building Material and Refractories Manufacturing) has the highest cost impact as a percentage of profits, of 31.08 percent. For all affected establishments in general industry and maritime, the estimated annualized cost of the rule is, on average, equal to 0.06 percent of annual revenue and 2.43 percent of annual profits.

The industries with costs that exceed ten percent of profits are: NAICS 327110—Pottery, Ceramics, and Plumbing Fixture Manufacturing, 31 percent; NAICS 327120—Clay Building Material and Refractories Manufacturing, 31 percent; NAICS 327991—Cut Stone and Stone Product Manufacturing, 24 percent; NAICS 327390—Other Concrete Product Manufacturing, 17 percent; NAICS 327999—All Other Miscellaneous Nonmetallic Mineral Product Manufacturing, 16 percent; NAICS 327332—Concrete Pipe Manufacturing, 13 percent; NAICS 327331 Concrete Block and Brick Manufacturing, 13 percent; and NAICS 327320 Ready-Mix Concrete Manufacturing, 10 percent.

b. Normal Year-to-Year Variations in Prices and Profit Rates

The United States has a dynamic and constantly changing economy in which an annual percentage changes in industry revenues or prices of one percent or more is common. Examples of year-to-year changes in an industry that could cause such variations in revenues or prices include increases in fuel, material, real estate, or other costs; tax increases; and shifts in demand.

Methodology

To demonstrate the normal year-to-year variation in prices for all the manufacturers in general industry and maritime affected by the rule, OSHA developed in the FEA year-to-year producer price indices and year-to-year percentage changes in producer prices, by industry, for the years 2004 through 2014. As shown in Table VI-3 in the FEA, for the combined affected manufacturing industries in general industry and maritime over the 12-year period, the average change in producer prices was 2.7 percent a year. For the industries in general industry and maritime with the largest estimated potential annual cost impact as a percentage of revenue—NAICS 213112—Support Activities for Oil and Gas Operations, 0.56 percent; and NAICS 327991—Cut Stone and Stone Product Manufacturing, 0.42 percent—the average annual changes in producer prices in these industries over the 12-year period were, respectively, 3.8 percent, and 0.5 percent.

Based on these data, it is clear that the potential cost impacts of the final rule in general industry and maritime are all well within normal year-to-year variations in prices in those industries. The maximum cost impact of the rule as a percentage of revenue in any affected industry is 0.56 percent, while the average annual change in producer prices for affected industries was 2.7 percent for the period 2004 through 2014 (changed from 1998 to 2009 in the PEA). Furthermore, even a casual examination of Table VI-3 of the FEA reveals that annual changes in producer prices in excess of five or even ten percent are possible without threatening an industry's economic viability. Thus, OSHA concludes that the potential price impacts of the final rule would not threaten the economic viability of any industries in general industry and maritime.

Changes in profit rates are also subject to the dynamics of the U.S. economy. A recession, a downturn in a particular industry, foreign competition, or the increased competitiveness of producers of close domestic substitutes are all easily capable of causing a decline in profit rates in an industry of well in excess of ten percent in one year or for several years in succession.

To demonstrate the normal year-to-year variation in profit rates for all the manufacturers in general industry and maritime affected by the rule, OSHA in the FEA developed Table VI-4 and Table VI-5, which show, respectively, year-to-year profit rates and year-to-year percentage changes in profit rates, by industry, for the years 2000 through 2012. For the combined affected manufacturing industries in general industry and maritime over the thirteen-year period, OSHA calculated an average change in profit rates of 138.5 percent a year (average for all industries calculated from the per-NAICS averages shown in Table VI-5 in the FEA). For the industries in general industry and maritime with the largest estimated potential annual cost impacts as a percentage of profit—NAICS 327120—Clay Building Material and Refractories Manufacturing, 31 percent; NAICS 327110—Pottery, Ceramics, and Plumbing Fixture Manufacturing, 31 percent; and NAICS 327991—Cut Stone and Stone Product Manufacturing, 24 percent—the average annual percentage changes in profit rates in these industries over the 13-year period were, respectively, 951 percent, 951 percent, and 113 percent.

One complicating factor is that the annualized costs of the rule, if absorbed in lost profits, would involve not just a temporary loss of profits but a longer term negative effect on profits relative to the baseline. To address this issue, the Agency compared the effect of a longer term reduction in profits to much larger reductions in profits but over shorter periods. Assuming a three-percent discount rate, the Agency determined a ten percent decline in profit rates relative to the original baseline, which remains constant at that lower level over a ten-year period, would be equivalent to:

• An 88.5 percent decline in profit rates for one year;
• a 44.5 percent decline in profit rates that remains constant at the lower level for two years; or
• a 30 percent decline in profit rates that remains constant at the lower level for three years.

An examination of Table VI-5, for the thirteen year period from 2000 to 2012, clearly shows that short-run changes in average industry profit rates of the above magnitudes have occurred on numerous occasions in general industry and maritime, without threatening the economic viability of the affected industries. For this reason, OSHA is confident that potential profit rate impacts of ten percent or less as a result of the rule would not threaten the economic viability of the affected industries in general industry and maritime.

A longer-term loss of profits in excess of ten percent a year could be more problematic for some affected industries and might conceivably, under sufficiently adverse circumstances, threaten an industry's economic viability. In OSHA's view, however, affected industries would generally be able to pass on most or all of the costs of the final rule in the form of higher prices rather than bear the costs of the final rule in reduced profits. In other words, the demand for the goods and services produced by affected industries in general industry and maritime do not appear to be perfectly elastic or close to it. While there are substitutes for these products, there are no perfect substitutes that would lead the price elasticity to be extremely high. As a result, the demand for quantities of brick and structural clay, vitreous china, ceramic wall and floor tile, other structural clay products (such as clay sewer pipe), and the various other products manufactured by affected industries would not significantly contract in response to a 0.48 percent (or lower) price increase for these products. It is of course possible that such price changes will result in some reduction in output, and the reduction in output might be met through the closure of a small percentage of the plants in the industry. However, the only realistic circumstance under which an entire industry would be significantly affected by small price increases would be the availability in the market of a very close or perfect substitute product not subject to OSHA regulation. The classic example, in theory, would be foreign competition. In the following discussion OSHA examines the threat of foreign competition for affected U.S. establishments in general industry and maritime and concludes that it is unlikely to threaten the viability of any affected industry.

Public Comments on Year-to-Year Variations in Prices and Profit Rates

The American Chemistry Council (ACC) stated, with respect to a similar analysis in the PEA, that short-term volatility within an industry sector is of little value in projecting what will happen when a new regulation resets the baseline for profits and revenue because OSHA is comparing short-term changes to long-term changes (Document ID 2307, Attachment 2, p. 196). Another commenter made the similar point that year-to-year fluctuations cannot be compared to long-term changes (Document ID 2308, Attachment 9, p. 7).

OSHA first examines the issue of changes in prices over time. Such changes, on the whole, represent pass through of changes in costs, since profits are not continually rising. These changes in costs are not “fluctuations” with upward and downward shifts in prices. For almost all industries these changes in costs are continuing upward shifts that average each year much larger changes than the maximum price change any industry will need to incur in order to comply with the silica rule.

For variations in profits, these are indeed fluctuations and profits do indeed both rise and fall. However, if, as the commenters argue only long-term average profits matter, then we could reach the very counterintuitive result that there should be no excess plant closures during recessions. This is not the case because long-term profits are, in fact, nothing more than a prediction and the present value of long term profits will be different at the beginning than at the end of a recession. Recognizing these timing effects is why OSHA examined the annualized value of losses in profits associated with the recession beginning 2008 and compared it to the annualized value of the loss in profits as result of costs of this standard. While temporary and permanent losses are different, the use of discounting enables us to compare short- and long-term losses.

c. International Trade Effects

The magnitude and strength of foreign competition is an important factor in determining the ability of firms in the U.S. to pass on (part or all of) the costs of the rule in the form of higher prices for their products. If firms are unable to do so, they must absorb the costs of the rule out of profits, possibly resulting in the business failure of individual firms or even, if the cost impacts are sufficiently large and pervasive, causing significant dislocations within an affected industry.

As in the PEA, OSHA in the final economic analysis examined how likely such an outcome is. The analysis there included a review of trade theory and empirical evidence and the estimation of impacts. Throughout, the Agency drew on ERG (2007c) (Document ID 1710), which was prepared specifically to help analyze the international trade impacts of OSHA's final silica rule. A summary of the FEA results is presented below.

OSHA focused its analysis on eight of the industries likely to be most affected by the final silica rule and for which import and export data were available. OSHA combined econometric estimates of the elasticity of substitution between foreign and domestic products, Annual Survey of Manufactures data, and assumptions concerning the values for key parameters to estimate the effect of a range of hypothetical price increases on total domestic production. In particular, OSHA estimated the domestic production that would be replaced by imported products and the decrease in exported products that would result from a 1 percent increase in prices—under the assumption that firms would attempt to pass on all of a 1 percent increase in costs arising from the final rule. The sum of the increase in imports and decrease in exports represents the total loss to industry attributable to the rule. These projected losses are presented as a percentage of baseline domestic production to provide some context for evaluating the relative size of these impacts.

The effect of a 1 percent increase in the price of a domestic product is derived from the baseline level of U.S. domestic production and the baseline level of imports. The baseline ratio of import values to domestic production for the eight affected industries ranges from 0.04 for iron foundries to 0.547 for ceramic wall and floor tile manufacturing—that is, baseline import values range from 4 percent to more than 50 percent of domestic production in these eight industries. OSHA's estimates of the percentage reduction in U.S. production for the eight affected industries due to increased domestic imports (arising from a 1 percent increase in the price of domestic products) range from 0.013 percent for iron foundries to 0.237 percent for cut stone and stone product manufacturing.

OSHA also estimated the baseline ratio of U.S. exports to consumption in the rest of the world for the sample of eight affected industries. The ratios range from 0.001 for other concrete manufacturing to 0.035 percent for nonclay refractory manufacturing. The estimated percentage reductions in U.S. production due to reduced U.S. exports (arising from a 1 percent increase in the price of domestic products) range from 0.014 percent for ceramic wall and floor tile manufacturing to 0.201 percent for nonclay refractory manufacturing.

The total percentage change in U.S. production for the eight affected industries is the sum of the loss associated with increased imports and the loss resulting from reduced exports. The total percentage reduction in U.S. production arising from a 1 percent increase in the price of domestic products range from a low of 0.085 percent for other concrete product manufacturing to a high of 0.299 percent for porcelain electrical supply manufacturing.

These estimates suggest that the final rule would have only modest international trade effects. It was previously hypothesized that if price increases resulted in a substantial loss of revenue to foreign competition, then the increased costs of the final rule would have to come out of profits. That possibility has been contradicted by the results reported in this section. The maximum loss to foreign competition in any affected industry due to a 1 percent price increase was estimated at approximately 0.3 percent of industry revenue. Because, as reported earlier in this section, the maximum cost impact of the final rule for any affected industry would be 0.56 percent of revenue, this means that the maximum loss to foreign competition in any affected industry as a result of the final rule would be 0.2 percent of industry revenue —which would hardly qualify as a substantial loss to foreign competition. This analysis cannot tell us whether the resulting change in revenues will lead to a small decline in the number of establishments in the industry or slightly less revenue for each establishment. However it can reasonably be concluded that revenue changes of this magnitude will not lead to the elimination of industries or significantly alter their competitive structure.

Based on the Agency's preceding analysis of economic impacts on revenues, profits, and international trade, along with the discussion of industry concerns below, OSHA concluded that the annualized costs of the final rule are below the threshold level that could threaten the economic viability of any industry in general industry or maritime. OSHA further noted that while there would be additional costs (not attributable to the final rule) for some employers in general industry and maritime to come into compliance with the new silica standard, these costs would not affect the Agency's determination of the economic feasibility of the final rule.

Public Comment on International Trade Effects

Foundries

The following comments discuss the loss of business to foreign competition in the foundry industry. The comments have been grouped together by issue and are followed by OSHA's response. The first group of commenters used impact numbers from an alternative cost model to discuss the loss of business to foreign competition.

The United States Chamber of Commerce (“the Chamber”) stated that additional costs of the rule's ancillary provisions along with engineering controls will result in reduced competitiveness relative to foreign foundries (Document ID 2288, pp. 27-28). The Chamber also critiqued OSHA's inability to determine feasibility because of a lack of data to analyze economic impacts across facilities by age, design, operations, condition and region (Document ID 2288, pp. 29-30).

In the comments above, the negative economic effect of losing business to foreign competition is based on an alternative cost model report prepared for the American Foundry Society (AFS) by Environomics. This report is addressed in the Engineering Control Costs section in Chapter V of the FEA, where OSHA concluded that the costs in that report were inflated. Because these inflated costs also underpin the Chamber's claim that the rule will reduce competitiveness with foreign foundries, OSHA does not accept that claim. In response to the Chamber's criticism of OSHA's data sources, the Agency notes that Chapter III, the section on Survey Data and OSHA Economic Analyses, discusses why it was infeasible to collect and compile a full-scale national survey of the kinds of baseline conditions and practices that the Chamber of Commerce urged OSHA to consider.

The following comments from foundry firms and associations address foreign competition in metalcasting from China and India along with the inability to pass the cost on to their customers.

AFS submitted comments that the metalcasting industry would lose business to foreign competition as follows:

Many foundries have closed in recent years with foreign competition assuming much of that business. Five of the eleven identifiable foundries used in the PEA to support OSHA's assertion of feasibility have closed. Because castings are the starting point of many manufacturing processes, loss of foundry jobs also means loss of other manufacturing jobs.

The U.S. metalcasting industry is made up of 1,978 facilities, down from 2,170 five years ago. This reduction can be attributed to the recession, technological advancements, foreign competition and tightening regulations (Document ID 2379, Attachment 3, p. 42; 4035, p. 5).

The Indiana Cast Metals Association concurred with these comments and also suggested that other industries would also be negatively impacted if U.S. foundries shut down (Document ID 2049, p. 1). The Ohio Cast Metals Association submitted two comments stating that the rule will increase costs and undermine the Ohio-based metalcasting industry's ability to compete in the global marketplace:

[The silica rule] will significantly increase costs, slow down or eliminate hiring, reduce the number of foundry jobs and undermine our industry's ability to compete in the global marketplace. For some foundries, the rulemaking could be the final straw that destroys their business.

. . . Over the past two decades Ohio foundries along with other manufacturers throughout the United States have faced tremendous international competition from China, Brazil, and India and many foundries have closed and thousands of employees have lost their jobs during this period. To suggest that Ohio foundries can just pass on the tremendous costs associated with compliance with the proposed silica rule with “minimal loss of business to foreign competition” indicates that the individuals performing this analysis were driven by other agendas or misinformed (Document ID 2119, Attachment 3, pp. 1-2).

Grede Holdings L.L.C. submitted a comment expressing its view that it would be difficult for foundries to pass the cost of compliance to the customer because of international competition, and that the number of foundries in the U.S. has dropped by more than half since 1980, going from 4,200 foundries to 2,050 foundries (Document ID 2298, p. 3).

Sawbrook Steel submitted two comments voicing concern that the implementation of the regulation will cause jobs to move overseas, resulting in a shrinking of the domestic casting manufacturing (Document ID 2227, p. 2; 1995, p. 1).

In the comments above, businesses and associations state that the costs of the rule will be too high and they will lose business to foreign competition. The chief advantage of foreign imports to downstream users, as reported to the U.S. International Trade Commission (ITC) during an investigation they conducted into the competitive conditions in the U.S. foundry market, is their low pricing. Respondents to the investigations said the cost of foreign produced products ranged from ten percent to forty percent less than the cost of U.S. products (Document ID 0753, table 5-60, p. 5-53 as referenced in Document ID 1710, pp. 5-4). U.S. producers have responded to competition with a broad array of initiatives, such as implementing lean manufacturing, improving customer service, and increasing automation (Document ID 0753, pp. 10-14 and 10-15). According to the ITC study:

The use of technology may also be influenced by the type of castings produced and relative wage rates. Low-value, low-quality castings, for example, generally require a lower level of technology and relatively more semi-skilled labor than foundries producing more complex castings. To lower labor costs, foundries in developed countries with higher wage rates may install more automation and technological improvements, whereas foundries in developing countries with relatively lower wage rates may substitute labor for relatively high-cost capital investments (Document ID 0753, p. 2-11).

Before addressing issues on international competition for metalcasters, it should be noted that all foundry industries affected by this rule are below the ten percent cost to profit threshold and one percent cost to revenue threshold. This means that even if the argument that costs cannot be passed on were to be correct, the loss in profits would be less than ten percent and unlikely to effect the feasibility of the industry. Further the costs to be passed on would require less than one percent price increases. In general, metalcasters in the U.S. have shortened lead times, improved productivity through computer design and logistics management, provided expanded design and development services to customers, and provided a higher quality product than foundries in China and other nations where labor costs are low (Document ID 0753, p. 3-12). All of these measures, particularly the higher quality of many U.S. metalcasting products and the ability of domestic foundries to fulfill orders quickly, are substantial advantages for U.S. metalcasters that may outweigh the very modest price increases projected in Tables VI-3 and VI-4 of the FEA (Document ID 1710, p. 5-4). According to the ITC study, quality was the number one purchasing decision factor for the majority of purchasers, with price and lead times ranking lower, and U.S. metalcasters are able to deliver that quality (Document ID 0753, p. 4-5). The ITC report noted:

Certain purchasers noted that when inventory management and complex manufacturing skills are required, U.S. foundries excel. U.S. foundries were also cited by responding U.S. purchasers as manufacturing with a low defect (rejection) rate. (Id.)

Purchaser responses to the ITC's survey stated that some U.S. foundries are also completely inoculated against foreign competition, even if the prices of U.S. foundry products rise:

As noted in questionnaire responses, certain purchasers are committed to buying solely U.S.-made castings. One U.S. foundry official noted that if downstream customers require castings to be made in the United States, then U.S. foundries are guaranteed that business. This situation often occurs when foundries supply castings for federally funded operations, such as construction projects (Document ID 0753, p. 4-5).

Foundries in China and India, while expanding their capacities, are also faced with rising domestic demand due to their own rapidly expanding domestic industrial economies, which affect their ability to fulfill export demand (Document ID 0753, p. 5-16). ERG's research noted a growth in U.S. foundry exports, which could help to offset some of the foreign imports entering the U.S. market. According to one report cited by ERG, U.S. foundry exports were roughly equivalent to 53 percent of the imports (Document ID 1710, p. 5-5).

ERG's research also provided some evidence that the combination of U.S. and foreign demand for metalcasting may outstrip the supply to such a degree that, even if the U.S. foundries operated at full capacity, their maximum output would fail to meet the demand from the U.S. and foreign markets (Document ID 1710, p. 5-5). The U.S. foundry industry is unlikely to face any significant economic impacts if there is ample demand and a limited supply because such a condition makes it easier to pass along any costs of the rule.

Tile Production

The following comments discuss the difficulties of competing with foreign tile producers followed by OSHA's response.

Tile Council of North America (TCNA) noted the import price sensitivity between domestic tile and imported tile as follows:

The low cost of imported tile places an enormous burden on U.S. tile manufacturers to maintain current pricing to remain competitive. According to the latest data collected by TCNA, the average price per square foot of U.S. tile shipments is $1.43. The average price per square foot of Chinese imports is $0.86. With Chinese imports 60% less expensive than U.S. tile in what is an extremely price-competitive market, OSHA's claim that “any price increases would result in minimum loss of business to foreign competition” strains credulity.

To illustrate the tremendous import/price sensitivity between domestic tile and imports, we note the increase in imports from Peru as a result of a bilateral free trade agreement between Peru and the United States eliminating duty on tile from Peru. Although only amounting to a price change of 4—5 cents per square foot, from 2008, the year before the bilateral agreement to the end of 2011, tile imports from Peru into the United States grew by 59%. This illustrates how even a small change in price due to modest increases in operating costs and raw material costs pose an existential threat to the tile manufacturing industry.

The import sensitivity of domestic tile manufacturing operations is well known by the United States International Trade Commission (USITC) and the office of the United States Trade Representative (USTR). The assertion made by OSHA that cost increases will not result in lost market share to foreign competition is in direct conflict with information known by USITC and the USTR and contrary to established public policy (as reflected in existing Free Trade Agreements) and industry testimony.

Contrary to the assertion made by OSHA, the marginal price increases anticipated by required conformance to the rule as proposed would make the domestic tile manufacturing industry highly uncompetitive threatening the very viability of this import-sensitive industry (Document ID 2363, p. 9).

The National Tile Contractors Association also questioned OSHA's preliminary determination that the tile industry could pass on most or all costs through higher prices, calling the claim “wildly erroneous”:

Implementation of the proposed rule's requirements would increase both production and installation costs, and would put pressure on consumer prices. At a time when U.S. consumption of ceramic tile is more than 25% below its peak level (2006), this is a serious concern. The U.S. market is already flooded with lower quality, lower priced imports from many countries that likely do not respect the health, safety, and rights of workers. The low cost of imported tile places an enormous burden on U.S. tile manufacturers to maintain current pricing to remain competitive (Document ID 2267, p. 8).

Dal-Tile echoed the TCNA comments regarding the inability to pass costs onto the customer (Document ID 2147, p. 3).

OSHA does not dispute the commenters' information indicating that Chinese and Peruvian tile are significantly cheaper than U.S. tile, but that point actually undercuts their claim that a small change in the price of U.S. tile would place an “enormous burden” on U.S. tile manufacturers. The commenters note that Chinese tile is already available in the U.S. at just over half the price of U.S. tile. If the market was actually as sensitive as the commenters suggest, and the Chinese tile was competing for the same market share as U.S. tile, under the commenter's logic the U.S. tile industry would have already gone out of business. But that has not happened, suggesting that U.S. tile manufacturers have been able to identify customers for whom the tile price is not the predominant factor. Likewise, the example of Peruvian tile demonstrates only that the lower-priced imported tile is sensitive to small price changes. The commenter provides no evidence that the Peruvian tile is competing for the same customers as the U.S. tile industry.

In summary, the TCNA's argument that cost increases will result in lost market share to foreign competition is unconvincing because it is not clear that there is a strong relationship between the price of the foreign tile and the price of the U.S. tile. One likely cause for this disconnect is that, as TCNA notes, the market is “already flooded with lower quality, lower priced” imports (Document ID 2363, p. 8), suggesting that tile from China, Peru, and the other lower-priced foreign importers are of a lower quality that may be targeted at a different customer base than the higher-quality U.S. tile. This perception that tile from China and other low-cost tile producing countries may be of lower quality produces an imperfect substitution scenario and adds to the inelasticity of demand for domestic tiles, enabling producers to pass some of the costs on to the consumer.

On the other end of the tile price range are the Italian tiles. Italy and China are the top countries of origin for tiles imported into the U.S., but tiles from these countries command very different prices. In terms of general tile products, one source indicates that the average prices of tiles imported by the U.S. in 2012 were $20.20 to $20.90 per square meter for Italian tiles and between $8.30 and $8.70 per square meter for Chinese tiles imported by the U.S., a significant price difference that could be explained by a difference in quality. TCNA stated above that the average price of tile from China is $0.86 per square foot or $9.25 (10.76 × 0.86) per square meter. TCNA's average price of American tile is $1.43 per square foot or $15.39 (10.76 × 1.43) per square meter (Document ID 2363, p. 9), which shows the U.S. producers to be supplying a mid-priced product. Although Italy is also a major source of tile imports in the U.S. despite their higher price, the commenters did not suggest that an increase in U.S. tile prices would cause the U.S. to lose market share to the Italian tile; nor did the commenters suggest that lower-priced U.S. tile could be exported to dominate the Italian market. The implication is, again, that different customers are willing to pay different prices for different quality tile.

Using price as an indicator of quality, the tile market can be segmented into three categories: Low quality, mid-grade, and high quality. The U.S. tile industry has located a niche between the lowest quality/lowest priced tile and the highest quality/highest priced tile. While it is possible that a few tile firms that produce very low-quality or very high-quality tile may be negatively impacted by an increase in the price of their tile, OSHA concludes that the majority of firms would not experience a significant negative economic impact. This is along with the fact that the increase in price from this rule is expected to be minimal. TCNA commented that the average price per square foot of U.S. tile shipments is $1.43. The cost to revenue ratio for NAICS 327122 Ceramic Wall and Floor Tiles is 0.35 percent, meaning this final rule will increase the average cost of U.S. tile by five hundredths of a cent (or $0.0005 per square foot). It is therefore fair to say this extremely modest increase in the average price of U.S. tile would not have a significant economic impact on the U.S. tile industry as a whole.

Brick Industry

During the public hearing Belden Tri-State Building Materials stated that the brick industry has foreign competition, mostly from Canada, and some from Mexico (particularly in Texas, Oklahoma or Arkansas), and Germany (Document ID 3586, Tr. 3457). They indicated that their competition includes not only imported brick but also “other cladding materials like vinyl siding and HardiePlank,” but the competition from imported brick is typically “more expensive brick” because of “innovations in Europe that we just haven't caught up to, different sizes, different colors, different processes” (Id.).

Acme Brick Company representatives indicated in testimony that oversees competition was virtually nonexistent because it is “hard to get that across the ocean economically” and noted that they generally locate their production facilities strategically to be near their markets because “[p]roduction costs really are about a third of the cost of the brick when we have them close . . . [The] farther away [the bricks come from]—there are some distinctions in the quality or the makeup of a brick” (Document ID 3577, Tr. 736).

This testimony indicates to OSHA that international competitors will not be able to take advantage of any potential price increases made by U.S. producers in the U.S. domestic brick market. The brick making industry will therefore be able to pass on most, if not all, of the costs of complying with the rule.

Hydraulic Fracturing

To determine the economic impacts for most industries, OSHA used the Census Bureau's Statistics of U.S. Businesses to estimate revenues on a six-digit NAICS basis but these revenue data were not sufficiently precise to isolate the hydraulic fracturing component from the larger industry (NAICS 213112). As a result, instead of using data from the Economic Census, revenues for hydraulic fracturing firms were based on estimated utilization rates and per stage revenues. As discussed in Chapter III of the FEA, Profile of Affected Industries, the data on this industry have been updated to reflect the comments in the record and the best data available in 2012. The cost to profit percentage for the hydraulic fracturing industry estimated in the FEA is 7.67 percent (below OSHA's ten percent threshold) for fleets of all sizes. The ratio of costs to revenues for hydraulic fracturing firms in the FEA is estimated to be 0.54 percent for all establishments in the industry, 0.17 percent for small entities and 0.24 percent for very small entities. Although the costs as a percent of revenue increased for all establishments, the impacts still remain well below the one percent threshold.

However, these estimates are based on the state of the industry in the base year of 2012 supplemented with data provided in comments to the proposed rule in 2013 and early 2014. When the PEA was published in 2006, the price of oil fluctuated between $70 and $80 a barrel. During the years following the publication of the PEA the price of oil has had some large fluctuations. Before the recession of 2008 the price of oil peaked at $146 per barrel but dropped to $44 dollars per barrel during the economic downturn in 2008. As the price of oil steadily increased during 2009, there was an influx of money invested in the hydraulic fracturing industry. The FEA uses revenue data from 2012 when the price per barrel fluctuated between $90 and $100. However, in the fourth quarter of 2014, the price of oil dropped to $49 per barrel. The price of oil in 2015 has oscillated between approximately $45 and $60 per barrel. Because of this major change in the industry since the record closed in 2012, OSHA has supplemented its feasibility analysis with more current data.

The Structure of the Hydraulic Fracturing Industry

Hydraulic fracturing nearly doubled U.S. oil production from 5.6 million barrels a day in 2010 to a rate of 9.3 million barrels a day in 2015. Up until the drop in oil prices during the fourth quarter of 2014, the expected annual increase in production was one million barrels. The economics of hydraulic fracturing wells is much different than conventional wells. The marginal cost of producing a barrel of oil from a conventional well for large oil producing countries is around $15 to $30. Therefore, the owners of conventional wells continue to produce even as the price per barrel decreased from $100 to $40, and would remain in business at costs down to $30. The traditional oil drilling business is driven by marginal costs, not costs spent to drill the well. This means that supply is inelastic relative to demand. This has not been true for the hydraulic fracturing industry.

Hydraulic fracturing wells have a very short life compared to conventional wells. For example, a well in the Bakken region straddling Montana and North Dakota may start out producing 1,000 barrels a day then decline to 280 barrels at the beginning of year two. By year three, more than half of the reserves will be depleted. Therefore, to generate revenue, producers need to constantly drill new wells. In this sense, hydraulic fracturing wells are more like gold or silver mines than conventional oil production. The recent drop in oil prices has caused a series of bankruptcies and closures across the oil industries. Although there was a reduction in the number of rigs from about 1,600 to 800, hydraulic fracturing still accounted for 4.6 million barrels a day out of a total of 9.4 million barrels or 49 percent of total oil produced in February 2015. Hydraulic fracturing also accounted for 54 percent of natural gas output.

The Energy Information Administration (EIA) projects the Brent crude oil price will average $40 a barrel in 2016 and $50 a barrel in 2017. However, EIA expects crude oil prices to rise in future years, rising to over $70 per barrel by 2020 and to $100 per barrel by 2028. EIA's crude oil price forecast remains subject to significant uncertainties as the oil market moves toward balance and could continue to experience periods of heightened volatility. Thus, industry implementation of OSHA's engineering control requirements, which are not required until five years after the effective date of the rule, may come during a period of much higher and rising energy prices. In any case, the price increase required by this rule is a very small fraction of the fluctuation in energy prices during the past several years.

However, the possibility that oil prices are not going to increase in the near future has spurred a new wave of innovation in energy exploration. Now that prices have dropped to around $50 a barrel, companies are focusing on efficiency and getting the most petroleum for the least amount of money. With the effective date of this rule on the horizon, it is possible that some of this innovation will lead to technologies that not only increase efficiency but reduce worker exposures to silica at the same time.

Through the application of new technology OSHA believes that, even in a lower price environment, hydraulic fracturing entrepreneurs will be able to implement the controls required by this final rule without imposing significant costs, causing massive economic dislocations to the hydraulic fracturing industry, or imperiling the industry's existence. Big oil-field-services like Haliburton Co. and Schlumberger Ltd. report that they have witnessed customers concentrating on using technology such as lasers and other high-tech equipment and data analytics before they drill to make sure new wells deliver the most crude for the investment cost. The application of this new technology as well as fiber-optic tools that help monitor a well during hydraulic fracturing to make sure that it's working as well as possible and new techniques to stimulate microbes already present that attach themselves to bits of oil, essentially breaking it up and making it easier for the crude to flow through rock have had positive quantitative results. Productivity at some “super-fracking” wells has increased 400-600 barrels a day per rig from just a few years ago. Drilling efficiency in some areas has increased as much as 26 percent in a single year while the time to drill and fracture a well has come down from an average of 32 days in 2008 to now only about half that time: 14-16 days from start to finish and in some cases even less. These increased efficiencies result in significant cost savings. Also, the lower demand by hydraulic fracturing companies for equipment rental, trucking, and labor has caused a decrease in their prices, reducing the overall cost of hydraulic fracturing.

Although the drop in the price of oil has caused an initial reduction in hydraulic fracturing operations, the application of recently developed technology to new wells has increased per well production. One expert was quoted in Fortune magazine as saying “[t]here tailing off in U.S. drilling activity, but I expect continued development drilling in major new areas, particularly the Bakken, even at $50 (a barrel).” In the Bakken region in 2015 the decrease in oil production resulting from the reduction of rigs was substantially offset by increases in new well oil production per rig. There are reasons to believe in the continuance of tight oil growth. An analysis by IHS shows that most of the potential U.S. tight oil capacity additions in 2015 have a break-even price in the range of $50 to $69 per barrel. Continued productivity gains, such as improvements in well completion and downspacing, also support the continuation of U.S. production growth at lower prices. Based on these advances, it is plausible that hydraulic fracturing shale operations may achieve break-even costs of $5-$20 per barrel.

A sign of the ongoing effectiveness of upgrades in efficiency in the hydraulic fracturing business is evident in the projections for U.S. crude production. The EIA's Annual Energy Outlook for 2015 has projected that the U.S. is on track to hit reach a record for crude output at 10.6 million barrels a day in 2020.

While the economic conditions faced by the hydraulic fracturing industry have changed significantly since the publication of the proposed rule, this discussion shows that there is significant reason to believe that this rule will not have a significant impact on the hydraulic fracturing industry. Advancements in technology and the application of new efficient drilling methods continue to increase the per-rig production capacity of new-well oil drilling rigs while lowering the costs of operating these rigs. These technological changes increase the energy recovered through hydraulic fracturing, and thus the value of fracturing services, without increasing the costs per well associated with controlling silica exposures. Further, the demand for fracturing services will depend, in part, on energy prices. The costs associated with complying with the silica rule are a minor issue by comparison. Thus, OSHA's conclusion that this rule is economically feasible for the hydraulic fracturing industry has not changed.

Railroads

In the PEA, OSHA did not include any estimates of costs as percentage of revenues or as a percentage of profits for railroads. This was due to the fact that the standard sources of economic statistics that were used for data on revenues and employment for all other affected industries do not include railroads. The Association of American Railroads (AAR) expressed concern about the impact of the rule on small railroads (although not on larger railroads), but did not provide any estimates or analysis, or suggest that OSHA use any specific sources to conduct such an analysis. For the FEA, OSHA did examine costs as percentage of revenues and profits for the railroad industry as a whole using supplemental information from sources typically relied on by the industry.

For the FEA, OSHA estimated that 16,895 workers in the rail transportation industry (NAICS 4821; “railroads”) will be covered by the final standard, including 7,239 workers employed as Ballast Dumpers and 9,656 workers employed as Machine Operators (for the purposes of this analysis, OSHA assumed that the machine operators would be conducting at least some work outside of the cab of the equipment). The Agency estimated that compliance costs for railroads will total $16.6 million, or $980 per affected worker.

Based on these estimates, OSHA judged that the final rule is feasible for railroads because combining supplemental data from BLS and the Association of American Railroads for the estimated 105 rail transportation establishments in NAICS 4821 with a reported revenue of $72.9 billion, the cost-to-revenue impacts are an estimated 0.02 percent and cost-to-profit impacts are an estimated 0.4 percent. In addition, the per-worker cost for railroads ($980) is lower than the average per-worker cost ($1,231) across all affected NAICS industries in general industry and for 2000-2012, the average profit rate for rail transportation, 6.2 percent, was significantly higher than the average profit rate for all affected NAICS industries throughout general industry (3.4 percent).

The AAR noted that small railroads had not been covered in the Initial Regulatory Flexibility Analysis (Document ID 2366, p. 4). The commenter is correct that OSHA did not examine small entities in this sector but has done so for the FEA using supplemental information on railroads.

In 2012, 574 U.S. freight rail establishments, employing 181,264 workers, operated on roughly 169,000 miles of track. The Surface Transportation Board in the U.S. Department of Transportation classifies railroads into three groups based on annual revenues:

• Class I for freight railroads defined as railroads with annual operating revenues above $467.1 million ($2013)
• Class II, includes some regional railroads, defined as railroads each with operating revenues between $37.4 million and $467.1 million ($2013)
• Class III for all other freight rail operations (including smaller regional, short-line, switching, and terminal).

In 2013, in addition to the seven Class I freight railroad systems, there were 21 regional railroads (line-haul railroads operating at least 350 miles of road and/or earning revenue between roughly $40 million and the Class I threshold), and over 500 local railroads (line-haul or short-line railroads smaller than regional railroads). Among the 567 railroads that fell below the Class I revenue threshold, 11 qualified as Class II and the remainder (556, including 10 regional railroads) qualified as Class III (FRA, 2015). Class III railroads are typically local short-line railroads serving a small number of towns and industries or hauling cars for one or more larger railroads. Many Class III railroads were once branch lines of larger railroads or abandoned portions of main lines.

In 2012, employment within 546 local railroad companies totaled 12,293 workers and employment within 21 regional railroads totaled 5,507 workers. Line Haul Railroads are classified in NAICS 482111 and entities within this industry with 1,500 or fewer workers are classified as small by SBA size standards. Local/Short Line Railroads are classified in NAICS 482112 and entities within this industry with 500 or fewer workers are classified as small by the SBA size standard. For 2012, OSHA estimated that all 567 Class II and Class III railroads (combined total of 17,800 workers) qualified as small entities according to the SBA definitions.

In a recent study prepared for Congress, the Federal Railroad Administration reported that in 2013, 546 Local/Short Line Railroads employed 12,293 workers and earned $2.6 billion in revenue. OSHA estimates that of the 16,895 affected employees throughout rail transportation, 1,146 employees of Short-Line railroads are affected by the final rule. According to the BLS Quarterly Census of Employment and Wages, on average 32 establishments were identified within NAICS 482112, Short-Line Railroads (an establishment can operate more than one railroad). Therefore, if all 546 Class III railroads are controlled by 32 establishments, OSHA estimates that revenue per establishment is approximately $81.3 million.

OSHA estimated that compliance costs for rail transportation will total $16,562,059. Therefore, if costs per affected worker ($980 per worker) are apportioned to the establishments operating Short-Line Railroads, OSHA estimates that costs for these local railroads will total $1.1 million, or roughly $35,100 per establishment. As noted above, annual revenues among Short-Line rail operations total approximately $2.6 billion, or $81.3 million per establishment. Applying the industry-wide profit rate of 6.23 percent for NAICS 4821, OSHA estimated that profits per establishment in NAICS 482112 are $5.1 million. Therefore, OSHA estimates that impacts measured as costs as a percent of revenues will not exceed 0.04 percent, and that impacts measured as costs as a percent of profits will not exceed 0.69 percent. Thus, OSHA concludes that the silica standard will not impose a significant impact on a substantial number of small entities in rail transportation and therefore will not threaten the competitive structure or viability of small entities in NAICS 482110.

d. Economic Feasibility Screening Analysis: Small and Very Small Businesses

The preceding discussion focused on the economic viability of the affected industries in their entirety. Even though OSHA found that the final standard did not threaten the survival of these industries, there is still the possibility that the competitive structure of these industries could be significantly altered.

To address this possibility, OSHA followed its normal rulemaking procedure for examining the annualized costs per affected small entity and per very small entity for each affected industry in general industry and maritime. Again, OSHA used its typical minimum threshold level of annualized costs equal to one percent of annual revenues—and, secondarily, annualized costs equal to ten percent of annual profits—below which the Agency has concluded that the costs are unlikely to threaten the survival of small entities or very small entities or, consequently, to alter the competitive structure of the affected industries.

Compliance costs for entities with fewer than 20 employees were estimated, in many cases, using a derived compliance cost per employee. Assuming costs to be equally distributed among all employees, OSHA estimated the compliance cost per employee by dividing total costs for each NAICS by the number of employees. OSHA then multiplied the compliance cost per employee with the ratio of the average number of employees per entity with fewer than 20 employees. Similarly, compliance costs per small entity were estimated from the product of compliance costs per employee and the average number of employees in entities within the SBA classification for the given NAICS. However, some compliance costs, such as some engineering control costs, were modified to reflect diseconomies of scale for very small establishments.

As shown in Table VII-19 and Table VII-20, the annualized cost of the final rule is estimated to be $2,967 for the average small entity in general industry and maritime and $1,532 for the average very small entity in general industry and maritime. These tables also show that the only industry in which the annualized costs of the final rule for small entities exceed one percent of annual revenues is NAICS 213112 (Support Activities for Oil and Gas Operations), which is estimated to be 1.29 percent. There are two industries for very small entities exceeding one percent of annual revenues—NAICS 213112 (Support Activities for Oil and Gas Operations), 2.09 percent and NAICS 327110 (Pottery, Ceramics, and Plumbing Fixture Manufacturing), 1.21 percent.

Small entities in nine industries in general industry and maritime are estimated to have annualized costs in excess of ten percent of annual profits; NAICS 327110: Pottery, Ceramics, and Plumbing Fixture Manufacturing (38.6 percent); NAICS 327120: Clay Building Material and Refractories Manufacturing (33.6 per cent); NAICS 327991: Cut Stone and Stone Product Manufacturing (24.7 percent); NAICS 327999: All Other Miscellaneous Nonmetallic Mineral Product Manufacturing (20.9 percent); NAICS 327390: Other Concrete Product Manufacturing (18.6 percent); NAICS 213112: Support Activities for Oil and Gas Operations (18.2 percent); NAICS 327332: Concrete Pipe Manufacturing (14.5 percent); NAICS 327331: Concrete Block and Brick Manufacturing (13.1 percent); and NAICS 327320: Ready-Mix Concrete Manufacturing (11.5 percent).

Very small entities in sixteen industries are estimated to have annualized costs in excess of ten percent of annual profit: NAICS 327110: Pottery, Ceramics, and Plumbing Fixture Manufacturing (90.6 percent); NAICS 327120 Clay Building Material and Refractories Manufacturing (58.5 percent); NAICS 327999: All Other Miscellaneous Nonmetallic Mineral Product Manufacturing (51.1 percent); NAICS 327991: Cut Stone and Stone Product Manufacturing (30.8 percent); NAICS 213112: Support Activities for Oil and Gas Operations (29.5 percent); NAICS 327390: Other Concrete Product Manufacturing (29.2 percent); NAICS 327212: Other Pressed and Blown Glass and Glassware Manufacturing (22.7 percent); NAICS 327332: Concrete Pipe Manufacturing (22.1 percent); NAICS 327211: Flat Glass Manufacturing (20.4 percent); NAICS 327331: Concrete Block and Brick Manufacturing (19.5 percent); NAICS 327993: Mineral Wool Manufacturing (17.4 percent); NAICS 327992: Ground or Treated Mineral and Earth Manufacturing (16.3 percent); NAICS 327320: Ready-mix Concrete Manufacturing (15.9 percent); NAICS 331513: Steel Foundries (except investment) (12.3 percent); NAICS 331524: Aluminum Foundries (except die-casting) (11.3 percent); and NAICS 331511: Iron Foundries (10.0 percent).

In general, cost impacts for affected small entities or very small entities will tend to be somewhat higher, on average, than the cost impacts for the average business in those affected industries. That is to be expected. After all, smaller businesses typically suffer from diseconomies of scale in many aspects of their business, leading to lower revenue per dollar of cost and higher unit costs. Small businesses are able to overcome these obstacles by providing specialized products and services, offering local service and better service, or otherwise creating a market niche for themselves. The higher cost impacts for smaller businesses estimated for this rule generally fall within the range observed in other OSHA regulations for which there is no record of major industry failures.

In allocating the share of costs to very small entities, OSHA did not have direct information about how many very small entities were engaged in silica-related activities. Instead, OSHA assumed that the affected employees would be distributed among entities of different size according to each entity size class's share of total employment. In other words, if 15 percent of employees in an industry worked in very small entities (those with fewer than 20 employees), then OSHA assumed that 15 percent of affected employees in the industry would work in very small entities. However, in reality, OSHA anticipates that in industries with foundries, none of the entities with fewer than 20 employees have foundries or, if they do, that the impacts are much smaller than estimated here.

SBREFA Comments on Impacts on General Industry and Maritime

In this section, OSHA reviews comments addressing economic impacts in general industry and maritime that were submitted during the SBREFA process prior to the PEA. OSHA addressed these comments in the PEA that was made available for public comment, but OSHA did not receive comments specifically addressing its responses to the SBREFA recommendations. OSHA is reprinting its responses here for the convenience of the reader.

SERs from foundries stated that there had been a long-run decline in the number of foundries in the United States, with the industry under continued pressure from foreign competitors and the need to meet new domestic regulations. The total expense of the draft standard and inability to meet lower PELs would pressure more U.S. foundries out of business, continuing an historical trend in this industry, SERs said. The variability in the foundry products and small open-area production plants would make meeting lower PELs difficult and costly. Many smaller foundries would be put out of business, the SERs said, and many jobs lost in the industry. “Twenty percent of profits is a great deal to spend on engineering controls with questionable results . . . . [t]he economics of the foundry industry today are not pretty,” one SER said. And another: “The cost of meeting the standard will be very difficult . . . . A PEL of 50 would put us out of business.” OSHA found in this FEA that costs as percentage of profits for even very small foundries would not rise to a level of 20 percent.

SERs from the brick industry stated that meeting the provisions of the draft proposed standard, particularly with a lower PEL, would be very tough for their competitive, low margin industry. Similarly, a SER from the pre-cast concrete industry said, “The problem is not putting the company out of business, but that the price of products will increase.” OSHA found that because bricks face limited foreign competition, a very small change in the price of bricks would not affect the viability of the industry.

Other SERs (industrial sand, molding powders, refractory concrete) noted that the impact of the standard on them, particularly if the PEL is lowered, would entail substantial costs, but indirect effects could be significant as well since their major customers (foundries) could be negatively impacted, too. “Refractory companies are going out of business with the foundries,” one SER said. OSHA has concluded that foundries will not, in general go out of business.

e. Regulatory Flexibility Screening Analysis

To determine if the Assistant Secretary of Labor for OSHA can certify that the final silica standard for general industry and maritime will not have a significant economic impact on a substantial number of small entities, the Agency has developed screening tests to consider minimum threshold effects of the final standard on small entities. The minimum threshold effects for this purpose are annualized costs equal to one percent of annual revenues and annualized costs equal to five percent of annual profits applied to each affected industry. (OSHA uses five percent as a threshold for significant impacts on small entities rather than the ten percent used for potentially serious impacts on industries in order to assure that small entity impacts will always receive special attention.) OSHA has applied these screening tests both to small entities and to very small entities. For purposes of certification, the threshold level cannot be exceeded for affected small entities or very small entities in any affected industry. Table VII-19 and Table VII-20 show that, in general industry and maritime, the annualized costs of the final rule exceed one percent of annual revenues for small entities and very small entities in one industry. These tables also show that the annualized costs of the final rule exceed five percent of annual profits for small entities in 15 industries and for very small entities in 25 industries. OSHA is therefore unable to certify that the final rule will not have a significant economic impact on a substantial number of small entities in general industry and maritime and must prepare a Final Regulatory Flexibility Analysis (FRFA). The FRFA is presented in Section VII.I of this preamble.

3. Impacts in Construction

a. Economic Feasibility Screening Analysis: All Establishments

To determine whether the final rule's estimated costs of compliance would threaten the economic viability of affected construction industries, OSHA used the same data sources and methodological approach that were used earlier in this section for general industry and maritime. OSHA first compared, for each affected construction industry, annualized compliance costs to annual revenues and profits per (average) affected establishment. The results for all affected establishments in all affected construction industries are presented in Table VII-21, using annualized costs per establishment for the final PEL of 50 μg/m³.

The annualized cost of the rule for the average establishment in construction, encompassing all construction industries, is estimated at $1,097 in 2012 dollars. The estimates of the annualized costs per affected establishment range from $4,811 for NAICS 237300 (Highway, Street, and Bridge Construction) and $4,463 for NAICS 237100 (Utility System Construction) to $364 for NAICS 236100 (Residential Building Construction) and $360 for NAICS 221100 (Electric Utilities).

Table VII-21 shows that the annualized costs of the rule do not exceed one percent of annual revenues or 10 percent of annual profits for any affected construction industry. NAICS 238100 (Foundation, Structure, and Building Exterior Contractors) has both the highest cost impact as a percentage of revenues, of 0.12 percent, and the highest cost impact as a percentage of profits, of 3.66 percent. For all affected establishments in construction, the estimated annualized cost of the final rule is, on average, equal to 0.05 percent of annual revenue and 1.52 percent of annual profit. These are well below the minimum threshold levels of 1 percent and 10 percent, respectively.

Therefore, even though the annualized costs of the final rule incurred by the construction industry as a whole are roughly twice the combined annualized costs incurred by general industry and maritime, OSHA concludes, based on its screening analysis, that the annualized costs as a percentage of annual revenues and as a percentage of annual profits are below the threshold level that could threaten the economic viability of any of the construction industries. OSHA therefore finds that the final rule is economically feasible for each of the industries engaged in construction activities. OSHA further notes that while there would be additional costs (not attributable to the final rule) for some employers in construction industries to come into compliance with the preceding silica standard, these costs would not affect the Agency's determination of the economic feasibility of the final rule.

Below, OSHA provides additional information to further support the Agency's conclusion that the final rule would not threaten the economic viability of any construction industry.

b. Normal Year-to-Year Variations in Profit Rates

As previously noted, the United States has a dynamic and constantly changing economy in which large year-to-year changes in industry profit rates are commonplace. A recession, a downturn in a particular industry, foreign competition, or the increased competitiveness of producers of close domestic substitutes are all easily capable of causing a decline in profit rates in an industry of well in excess of 10 percent in one year or for several years in succession.

To demonstrate the normal year-to-year variation in profit rates for all the establishments in construction affected by the final rule, OSHA presented data in the FEA on year-to-year profit rates and year-to-year percentage changes in profit rates, by industry, for the years 2000-2012. For the combined affected industries in construction over the 13-year period, the average change in profit rates was 63.09 percent a year. If the three worst years are excluded, there is still substantial variation in profits, far larger than the change in profits that would be necessary if the costs of this rule cannot be passed on.

These data indicate that even if the annualized costs of the final rule for the most significantly affected construction industries were completely absorbed in reduced annual profits, the magnitude of reduced annual profit rates is well within normal year-to-year variations in profit rates in those industries and does not threaten their economic viability. Of course, a permanent loss of profits would present a greater problem than a temporary loss, but it is unlikely that all costs of the final rule would be absorbed in lost profits. Given that, as discussed in Chapter VI of the FEA, the overall price elasticity of demand for the outputs of the construction industry is fairly low and that almost all of the costs estimated in Chapter V of the FEA are variable costs, the data and economic theory suggest that most firms will see small declines in output rather than that any but the most extremely marginal firms would face any real risk of closure. Many parts of the construction industry have already absorbed much more drastic changes in profit without evidence of industry collapse or major change.

Market Structure and Market Impacts in the Construction Industry

At a conceptual level, the market-determined output of the construction industry depends on the intersection of demand and supply curves. Incremental compliance costs of the rule (which are almost entirely variable costs) shift the construction supply curve upward. The net effect is an increase in the price for construction activities and a reduction in the level of activity (with the magnitude of this effect depending on the price elasticity of demand). Lower levels of activity mean less construction work, a reduction in the number of construction establishments, and a concomitant reduction in construction employment. The greater the price elasticity of demand and the greater the increase in marginal costs, the larger will be the reduction in equilibrium output. In terms of prices, the greater the price elasticity of demand, the smaller the increase in prices will be for a given increment to marginal costs, and the larger the reduction in output.

Increasing the cost of construction project activities that generate silica exposures has two effects on the demand for these activities. First, increasing the cost of silica-related jobs relative to the costs of other construction inputs might result in substitution away from this type of work. Architects, building designers, and contractors might be more likely to choose building methods and materials that eliminate or reduce the need to perform silica-related jobs. For example, pre-cast concrete structures that require a relatively high level of concrete finishing work would become more expensive relative to other building technologies. Contractors and others could reduce the cost impact of the standard by switching to other building methods unaffected by the silica rule when the alternative would result in lower cost than would compliance with the rule. The magnitude of these impacts will depend on the feasibility, characteristics, and relative expense of alternative technologies.

Second, some of the increase in the cost of silica-generating activities will increase the marginal cost of construction output and cause the construction supply curve to shift upward, resulting in a higher price for each quantity produced. The magnitude of the impact of the cost increases due to the silica rule on the supply relationship will depend on the size of the cost increases and the importance of silica-generating activities in the overall cost of construction projects. If the silica-generating activities are a small portion of the overall cost of construction then the supply curve shift will be smaller when compared to a shift in the supply curve from silica-generating activity that is a large portion of the overall cost of construction. If, for example, there is a one percent increase in the costs of a silica generating activity and the silica generating activity constitutes only one percent of the costs of a building, then the total increase in the cost of the building will be an almost unobservable 0.01 percent. Magnitude of shifts in derived demand for a service used in making another product are determined by the price change for the final product, not the price change for the service itself.

In practice, if one considers the costs of the final rule relative to the size of construction activity in the United States, it is clear that the price and profit impacts of the final rule on construction industries must be quite limited. The annualized cost of the final rule would be equal to approximately 0.1 percent of the value of annual construction activity in the U.S. Moreover, construction activity in the U.S. is not subject to any disadvantage from foreign competition—any foreign firms performing construction activities in the United States would be subject to OSHA regulations.

c. Impacts by Type of Construction Demand

The demand for construction services originates in three independent sub-sectors: residential building construction, nonresidential building construction, and nonbuilding construction.

Residential Building Construction: Residential building demand is derived from the household demand for housing services. These services are provided by the stock of single and multi-unit residential housing units. Residential housing construction represents changes to the housing stock and includes construction of new units and modifications, renovations, and repairs to existing units. A number of studies have examined the price sensitivity of the demand for housing services. Depending on the data source and estimation methodologies, these studies have estimated the demand for housing services at price elasticity values ranging from -0.40 to -1.0, with the smaller (in absolute value) less elastic values estimated for short-run periods (Glennon, 1989, Document ID 0707; Mayo, 1981, Document ID 0794). In the long run, it is reasonable to expect the demand for the stock of housing to reflect similar levels of price sensitivity.

Many of the silica-generating construction activities affected by the rule are not widely used in single-family construction or renovation. This assessment is consistent with the cost estimates that show relatively low impacts for residential building contractors. (See Table VI-9 of the FEA—the costs as a percent of revenues for Residential Building Construction are estimated to be 0.03 percent and the costs as a percent of profits are estimated to be 1.29 percent). Multi-family residential construction might have more substantial impacts, but, based on Census data, this type of construction represents a relatively small share of net investment in residential buildings.

Nonresidential Building Construction: Nonresidential building construction consists of industrial, commercial, and other nonresidential structures. As such, construction demand is derived from the demand for the output of the industries that use the buildings. For example, the demand for commercial office space is derived from the demand for the output produced by the users of the office space. The price elasticity of demand for this construction category will depend, among other things, on the price elasticity of demand for the final products produced, the importance of the costs of construction in the total cost of the final product, and the elasticity of substitution of other inputs that could substitute for nonresidential building construction. ERG (2007c) found no studies that attempted to quantify these relationships (Document ID 1710). But given the costs of the final rule relative to the size of construction spending in the United States, the resultant price or revenue effects are likely to be quite small as well.

Nonbuilding Construction: Nonbuilding construction includes roads, bridges, and other infrastructure projects. Utility construction (power lines, sewers, water mains, etc.) and a variety of other construction types are also included. A large share of this construction (63.8 percent) is publicly financed (ERG, 2007a, Document ID 1709). For this reason, a large percentage of the decisions regarding the appropriate level of such investments is not made in a private market setting. The relationship between the costs and price of such investments and the level of demand might depend more on political considerations than the factors that determine the demand for privately produced goods and services.

While a number of studies have examined the factors that determine the demand for publicly financed construction projects, these studies have focused on the ability to finance such projects (e.g., tax receipts) and socio-demographic factors (e.g., population growth) to the exclusion of cost or price factors. In the absence of budgetary constraints, the price elasticity of demand for public investment is therefore probably quite low. On the other hand, budget-imposed limits might constrain public construction spending. If the dollar value of public investments were fixed, a price elasticity of demand of 1 would be implied and any percentage increase in construction costs would be offset with an equal percentage reduction in investment (measured in physical units), keeping public construction expenditures constant.

Public utility construction comprises the remainder of nonbuilding construction. This type of construction is subject to the same derived-demand considerations discussed for nonresidential building construction, and for the same reasons, OSHA expects the price and profit impacts to be quite small.

SBREFA Comments on Impacts on the Construction Industry

In this section OSHA reviews comments addressing economic impacts in construction that were submitted during the SBREFA process prior to the PEA. OSHA addressed these comments in the PEA that was made available for public comment, but did not receive comments specifically addressing its responses to the SBREFA recommendations. OSHA is reprinting its responses here for the convenience of the reader.

One commenter believed that OSHA had ignored the range of profitability among businesses, and thus did not adequately recognize that the average percentage reduction in profits could mean bankruptcy for those firms struggling to stay afloat. The Agency's approach to economic feasibility is designed to address the overall health of industries in compliance with legal precedent, which permits OSHA to find a regulation economically feasible even though it may close some marginal firm. In most years, ten percent or more of construction firms exit the industry (See U.S. Census Bureau Business Dynamics Statistics, available at http://www.census.gov/ces/dataproducts/bds/data_firm.html ). The slight acceleration of the closure of such firms is not the kind of economic impact that would make a regulation economically infeasible.

The commenter also asserted that OSHA ignored the cost of credit and that this also varies across businesses. OSHA believes that the cost of credit is not an important issue in this case because OSHA's analysis demonstrates that, in most cases, upfront costs can usually be met from cash flow. Earlier in this chapter, OSHA noted that its choice of a threshold level of ten percent of annual profits for economic feasibility determinations is low enough that even if, in a hypothetical worst case, all compliance costs were upfront costs, then upfront costs would still equal 88.5 percent of profits and thus would be affordable from profits alone without needing to resort to credit markets. As shown in Table VI-12 of the FEA, all industries' costs are a very small percentage of profits, assuring that even upfront costs can be met from profits without resorting to credit markets. Further, a firm that is having trouble meeting upfront costs can rent the appropriate tools without incurring any upfront capital investment costs.

A SER asserted that the impact of the rule would be “catastrophic” for the concrete cutting industry. One SER maintained that the rule would be both economically and technologically infeasible for the specialty trade concrete cutting industry (Document ID 0937, p. 69). The Small Business Advocacy Review (SBAR) Panel recommended that OSHA thoroughly review the economic impacts, and develop a more detailed economic feasibility analysis for certain industries (Document ID 0937, p. 69). OSHA believes that the analyses in this chapter and in Chapter IX of the FEA address the SER's comments and the SBAR Panel recommendations.

Concrete cutting is undertaken for such purposes as grooving for projects such as highways, bridges, and sidewalks along with repairing these structures when they become operationally unsound. These contracts are bid on by firms who will all fall under the final silica rule, so there is no economic disadvantage between firms caused by the silica rule. Because the silica rule only applies in areas subject to OSHA jurisdiction, there is no foreign competition that would not also be subject to the silica standard. The cutting industry also works on runways and parking lots along with homebuilders for smaller projects. The demand for these products are relatively inelastic and not subject to foreign competition, enabling these companies to pass most of the costs of this final rule onto their consumers. Based on these analyses, OSHA disagrees that the rule would be “catastrophic” or economically infeasible for the concrete cutting industry.

d. Economic Feasibility Screening Analysis: Small and Very Small Businesses

The preceding discussion focused on the economic viability of the affected construction industries in their entirety. However, even though OSHA found that the silica standard did not threaten the survival of these construction industries, there is still the possibility that the industries' competitive structures could be significantly altered.

To address this possibility, OSHA examined the annualized costs per affected small and very small entity for each affected construction industry. Table VII-22 and Table VII-23 show that in no construction industries do the annualized costs of the final rule exceed one percent of annual revenues or 10 percent of annual profits either for small entities or for very small entities. Therefore, OSHA concludes, based on its screening analysis, that the annualized costs as a percentage of annual revenues and as a percentage of annual profits are below the threshold level that could threaten the competitive structure of any of the construction industries.

e. Differential Impacts on Small Entities and Very Small Entities

Below, OSHA provides some additional information about differential compliance costs for small and very small entities that might influence the magnitude of differential impacts for these smaller businesses.

The distribution of impacts by size of business is affected by the characteristics of the compliance measures. For silica controls in construction, the dust control measures consist primarily of equipment modifications and additions made to individual tools, rather than large, discrete investments, such as might be applied in a manufacturing setting. As a result, compliance advantages for large firms through economies of scale are limited. It is possible that some large construction firms might derive purchasing power by buying dust control measures in bulk. However, given the simplicity of many control measures, such as the use of wet methods on machines already manufactured to accommodate controls, such differential purchasing power appears to be of limited consequence.

The greater capital resources of large firms will give them some advantage in making the relatively large investments needed for some control measures. For example, cab enclosures on heavy construction equipment or foam-based dust control systems on rock crushers might be particularly expensive for some small entities with an unusual number of heavy equipment pieces. Nevertheless, where differential investment capabilities exist, small construction firms may also have the capability to achieve compliance with lower-cost measures, such as by modifying work practices. In the case of rock crushing, for example, simple water spray systems can be arranged without large-scale investments in the best commercially available systems.

In the program area, large firms might have a slight advantage in the delivery of training or in arranging for health screenings. This phenomenon has been accounted for in the analysis that OSHA provides.

f. Regulatory Flexibility Screening Analysis

To determine if the Assistant Secretary of Labor for OSHA can certify that the final silica standard for construction will not have a significant economic impact on a substantial number of small entities, OSHA applies the same screening analysis to construction as it does for general industry, as discussed earlier in that section for the same reasons: annualized costs equal to one percent of annual revenues and annualized costs equal to five percent of annual profits applied to each affected industry. OSHA has applied these screening tests both to small entities and to very small entities. For purposes of certification, the threshold levels cannot be exceeded for affected small or very small entities in any affected industry.

Table VII-22 and Table VII-23 show that in no construction industries do the annualized costs of the final rule exceed one percent of annual revenues or five percent of annual profits either for small entities or for very small entities. However, as previously noted in this section, OSHA is unable to certify that the final rule will not have a significant economic impact on a substantial number of small entities in general industry and maritime and must prepare a Final Regulatory Flexibility Analysis (FRFA). The FRFA is presented in Section VII.I of this preamble.

4. Employment Impacts on the U.S. Economy

The discussion below on employment impacts of the silica rule on the U.S. economy is divided into three parts: (1) a brief summary of the employment impacts of the proposed silica rule (based on an analysis performed for OSHA by its subcontractor, Inforum, in 2011, Document ID 1701) that the Agency included in the PEA in support of the silica proposal; (2) a review of estimates provided by commenters on the employment effects of the silica proposal; and (3) a summary of a recent analysis of the employment effects of the final silica rule that Inforum performed for OSHA, followed by a critique of the commenters' analysis of employment effects relative to Inforum's analysis.

a. Inforum Analysis of Employment Effects Prepared for Silica Proposal

In October 2011, OSHA directed Inforum to run its macroeconomic model to estimate the employment impacts of the costs of the proposed silica rule. Inforum ran the model for the ten-year period 2014-2023 and reported its annual and cumulative employment and other macroeconomic results. While employment effects varied from year to year and from industry to industry, a key Inforum result was that the proposed silica rule cumulatively would generate an additional 8,625 job-years over the period 2014—2023, or an additional 862.5 job-years annually, on average, over the period. A fuller discussion of Inforum's macroeconomic model and the results of its analysis can be found in Chapter VI of the PEA in support of OSHA's silica proposal and in the Inforum report itself (Inforum, 2011, Document ID 1701).

b. Estimates by Commenters on Employment Effects of the Silica Proposal

Three commenters on the silica proposal—the National Federation of Independent Business (NFIB) with the NFIB Research Foundation; the American Chemistry Council (ACC) with Stuart Sessions of Environomics, Inc.; and the Construction Industry Safety Coalition (CISC) with Environomics, Inc.—provided or reported estimates of the employment effects of the proposed silica rule. These commenter estimates are summarized below.

The NFIB Research Foundation performed a study (Document ID 2210, Attachment 2) to estimate the employment and other macroeconomic effects of OSHA's proposed rule, using the Agency's own estimates of the annualized compliance costs of the proposed rule for affected employers of approximately $637 million in 2009 dollars. The study modeled (a) anticipated employer costs due to the proposed rule, (b) changes to private sector demand, and (c) changes to state and local government spending associated with the proposed rule, and then forecast their effects using NFIB's Business Size Impact Module (BSIM) to run a simulation. The BSIM is a dynamic, multi-region model based on the Regional Economic Models, Inc. (REMI) structural economic forecasting and policy analysis model, which integrates input-output, computable general equilibrium, econometric, and economic geography methodologies. Costs were estimated by five size classes of firms. It was noted that the annualized compliance costs of the proposed rule:

. . . also represent new demand for private sector goods and services for firms who assist businesses affected by the new PEL in complying with the proposed rule. In the BSIM, this new demand for goods and services provided by the private sector acts as a countervailing force to any negative impact on employers the new annualized compliance costs may have (Document ID 2210, Attachment 2, p. 8).

The summary findings of the NFIB Research Foundation study included an overall loss of 27,000 jobs and lost output of over $72 billion in the long run, with at least half the loss expected to occur in the small business sector.

The American Chemistry Council (ACC) (Document ID 4209-A1) reported on Mr. Sessions's post-hearing brief (Document ID 4231), which provided estimates of the economic and employment impacts of the general industry costs to comply with the proposed silica rule and, in addition, criticized Inforum's estimates of the employment effects of the proposed silica rule (Inforum, 2011, Document ID 1701).

Mr. Sessions estimated economic impacts based on the URS Corporation estimates of $6.131 billion as the cost of the proposed silica rule on 19 general industry sectors (Document ID 4209-1, pp. 102-103). (Note that the analysis does not include the construction sector and is more than 50 times higher than OSHA's general industry cost estimate in the proposal). The economic impacts were estimated in two analytical steps: (1) estimate the impact of the proposed regulation's compliance costs on the value of output of the affected industries; and (2) estimate how the expected changes in output will reverberate throughout the economy, using IMPLAN—a well-known input-output model of the U.S. economy.

The first step was achieved by estimating the amount of cost pass-through of the compliance costs, using a supply elasticity of 1.0, and then estimating the demand response to this price increase assuming a demand elasticity of -1.5. This results in a decline in industry revenue equal to about 20 percent of annualized compliance costs, which—given URS's estimates of compliance costs—is equal to $1.23 billion per year. Again using the IMPLAN model, the corresponding estimated employment effect is 18,000 lost jobs annually (5,400 direct effect; 5,000 indirect effect; and 7,500 induced effect) and a loss in economic output/GDP of more than $1.6 billion per year.

Additionally, Mr. Sessions reviewed Inforum's analysis of the employment impacts of the proposed rule. He asserted that OSHA had supplied Inforum with year-by-year compliance costs that were only 53 percent of the annualized costs that OSHA had estimated in the PEA so that Inforum's projections of employment effects would be seriously underestimated:

OSHA estimates the cost of the Proposed Standard to be $658 million per year in 2009 dollars on an annualized basis, excluding the hydraulic fracturing industry. Assuming a 7%/year discount rate, this annual cost, continuing forever as OSHA estimates it will, is equivalent to a present value cost of $9.4 billion dollars in the initial year of compliance. For comparison with this figure, I calculate (also assuming a 7% discount rate) that the present value in the first year for the ten-year schedule of compliance costs shown in Inforum's Table 1 is only $5.0 billion [italics added] (Document ID 4231).

In reviewing the above procedures, OSHA concludes that Mr. Sessions has misinterpreted his own calculations. The annualized value of an infinite series of costs (i.e., continuing forever) discounted at 7 percent is equal to 0.07 (the annualization factor) x the present value (PV). Hence, the annualized cost of Mr. Session's present value of $9.4 billion should equal $658 million. Now, OSHA provided a stream of costs for 10 years, not forever. The annualization factor for annualized costs incurred over ten years using a 7 percent discount rate is equal to 0.1424. Therefore, the PV of OSHA's costs given to Inforum should be $658 million/0.1424, or about $4.6 billion. Mr. Sessions only confused issues by using first-year costs (which is irrelevant to his exercise) rather than annualized costs. So, there is nothing in Mr. Sessions's calculations that would suggest that OSHA had provided Inforum with seriously incomplete costs. However, just to make sure, OSHA and ERG also reviewed the year-by-year proposal cost data given to Inforum (for Inforum, 2011, Document ID 1701) and found nothing amiss.

The Construction Industry Safety Coalition, submitted a late comment on the silica proposal (CISC, 2015), which contains estimates prepared by Environomics, Inc. (Environomics, 2015) of the employment impacts of the proposed silica rule on the construction sector (Document ID 4242). This late comment, including the contained Environomics study, has been excluded from OSHA decision-making consideration, but is presented here for informational purposes only.

The employment effects estimated by Environomics (2015) reflect annual costs to construction industries of $4.9 billion, which includes almost $3.9 billion of direct compliance costs to construction employers and another $1.05 billion of costs passed through from general industry (as a result of the silica rule for general industry) to the construction industry (Document ID 4242). Environomics used the IMPLAN model to translate the estimated $4.9 billion annual cost of the silica rule into more than 52,700 lost jobs related to the construction industry. These job losses would consist of about 20,800 in construction; 12,180 additional jobs lost in industries that supply materials, products, and services to the construction industry; and nearly 20,000 further jobs lost when those who lose their jobs in construction and supplier industries no longer have earnings to spend (i.e., “induced” jobs). Furthermore, Environomics argued that “(t)hese job figures are expressed on a full-time equivalent basis. Given the number of part-time and seasonal jobs in construction, the number of actual workers and actual jobs affected will be much more than 52,700” (Environomics, 2015, Document ID 4242, p. 2).

c. Inforum Analysis of Employment Effects of the Final Silica Rule

In December 2015, OSHA directed Inforum to run its macroeconomic model to estimate the industry and aggregate employment impacts on the U.S. economy of the cost of OSHA's final silica rule. The Agency believes that the specific model of the U.S. economy that Inforum uses—called the LIFT (Long-term Interindustry Forecasting Tool) model—is particularly suitable for this work because it combines the industry detail of a pure input-output model (which shows, in matrix form, how the output of each industry serves as inputs in other industries) with macroeconomic modeling of demand, investment, and other macroeconomic parameters. The Inforum model can thus both trace changes in particular industries through their effect on other industries and also examine the effects of these changes on aggregate demand, imports, exports, and investment, and in turn determine net changes to Gross Domestic Product (GDP), employment, prices, etc.

Using industry-by-industry compliance cost estimates provided by OSHA, Inforum employed the LIFT model of the U.S. economy to compute the industry-level and macroeconomic impacts expected to follow implementation of the silica standard. The general methodology was to embed the compliance costs into the industry price functions of the LIFT model, solve the equations of the model with the additional costs included in the calculations, and then compare the simulation to a baseline scenario which did not include the additional costs. Enforcement of the rule was assumed to start in 2017 in construction and in 2018 in general industry and maritime (with enforcement of engineering control requirements for hydraulic fracturing activities beginning in 2021). The timing of the compliance costs reflected the phased-in enforcement of the rule, and the LIFT model results were calculated over a ten-year horizon, that is, through 2026.

The most significant Inforum result is that the final silica rule cumulatively generates an additional 9,500 job-years over the period 2017-2026, or an additional 950 job-years annually, on average, over the period (Inforum, 2016). It should be noted, however, that these results vary significantly from year to year. For example, in 2017, the first year in which the silica final rule would be in effect and when most capital costs for control equipment would be incurred, an additional 21,100 job-years would be generated as a result of the silica rule. Then, through 2026, the change in job-years relative to the baseline ranges from a high of 19,600 (in 2019) to a low of −17,300 (in 2020). Inforum emphasized that all of these estimated job-year impacts of the silica rule, both positive and negative, should be viewed as negligible—relative to total U.S. employment of between 157 and 168 million workers during the time period under consideration and not statistically different from an estimate of 0 job-years (that is, that the silica rule would have no job impact).

The employment impacts of the silica rule would also vary significantly from industry to industry and from sector to sector. For example, for the period 2017-2026, the construction industry would, on average, gain 4,260 job-years annually while the rest of the U.S. economy would, on average, lose 3,310 job-years annually. Again, relative to total employment in the construction sector of about 10 million workers and employment in the rest of the U.S. economy of about 150 million workers over the 10-year period, these employment impacts should be considered negligible. For a fuller discussion of OSHA's estimate of the employment and other macroeconomic impacts of the silica rule, see Inforum (2016).

One obvious question is why the employment impacts of the silica rule would be positive in construction and negative elsewhere. There seem to be two major reasons. One is that, as reflected in the Inforum model, there is little foreign competition in U.S. construction and the price elasticity of demand in construction is extremely low relative to demand for products in most other industries. Hence, output and employment would be expected to decline minimally in response to any price increase if employers in construction pass on the costs of the silica rule. Second, and probably more important, in OSHA's view, compliance with many of the provisions in the silica rule is relatively labor-intensive, often requiring the application of additional labor in the regulated firms themselves. Examples would include time spent for training, medical surveillance, and activities to meet the PEL (such as setting up and using control equipment and performing housekeeping tasks). The increased labor required to produce a unit of output in regulated firms would tend to increase employment in those industries (holding output constant). This is particularly true in construction, where compliance with the PEL would be much more labor-intensive—both because engineering controls in construction are typically mobile and require more worker activity and because housekeeping and other worker actions are expected to play a larger role in achieving compliance with the PEL. By comparison, engineering control equipment in general industry/maritime is usually in a fixed location (eliminating the need for workers to move the equipment) and worker actions would play a smaller role in achieving compliance with the PEL.

Finally, OSHA turns to a critique of the commenters' analysis of employment effects of the proposed silica rule relative to Inforum's analysis of employment effects of the final silica rule. This critique reflects comments provided in the Inforum report (Inforum, 2016).

The NFIB Research Foundation Analysis: Although the NFIB Research Foundation study (Document ID 2210, Attachment 2) reported that careful attention was given to the analysis of costs and their attribution by firm size, it doesn't offer much information on how the BSIM model works or how the results were obtained. “From what is generally known about the REMI model upon which it is based, the general mechanism is probably the sequence of (1) increased costs leading to (2) increased output price leading to (3) reduced demand and therefore jobs” (Inforum, 2016, p. 8). The study does acknowledge that the costs also represent new private sector demand for firms that assist affected employers in complying with the new PEL, but the purported positive impacts of this private sector demand are not visible in the study. Presumably the reported impacts are net effects that combine the negative effects from the increased prices and reduced demand of the affected sectors with the stimulus from spending on the supplying sectors; however, that is not clear, and the stimulus is not quantified. In Inforum's analysis (Inforum, 2016), these effects are explicitly considered, both for intermediate goods and services as well as investment.

Another important difference from Inforum's analysis is that the NFIB study did not attempt to quantify the additional jobs created in the affected industries. In Inforum's LIFT model, these were captured as changes in labor productivity. For several industries, especially construction, although the industry does experience increased costs, it must also hire more workers to comply with the silica rule. The additional jobs required in the affected industries are not discussed or apparently modeled in the NFIB study. In summary, it seems that the counteracting influences due to intermediate and investment related purchases from other industries, and the job-creating expenditures in the affected industries were not, in fact, captured in the study.

The CISC and ACC Studies: These two studies are being critiqued together because they both rely on costs many times higher than OSHA's estimates and because they both made projections using the IMPLAN model.

What accounts for the difference between LIFT simulations and the CISC and ACC estimates? There are several factors at play:

Probably most importantly, CISC's estimate starts with annual compliance costs for the construction industry that are nearly 7 times larger than OSHA's estimates for the construction industry (only) ($4.1 billion vs. an average of over $600 million, both in 2012 dollars). Meanwhile, the ACC study estimates costs for general industry that are more than 16 times larger than OSHA's estimates for the final rule ($6.1 billion in 2009 dollars versus $359 million in 2012 dollars. Moreover, the CISC and ACC studies assumes that the same annualized cost estimates are imposed each year, whereas the OSHA cost estimates vary over the 10 year time period, with peak costs occurring in the first year.

Neither the CISC nor the ACC application of the IMPLAN model accounted for the increase in demand for capital equipment and intermediate goods and services needed to comply with the proposed silica rule. Thus, the employment and income boosting impacts of these expenditures are not captured in their analysis. In contrast, Inforum's methodology uses an explicit price function where annual compliance costs by industry change commodity prices in proportion to their share of total annual gross costs. In turn, price changes affect production and employment through a dynamic general equilibrium framework. Demand and supply price elasticities in the LIFT model are composites of several sets of empirically estimated functions for final demand, exports, imports, and price mark-ups. Furthermore, the parameters of these functions vary by type of product according to the econometric estimation.

At OSHA's request, Inforum made a separate run using the LIFT model in the absence of the final silica rule for the construction industry but with the final silica rule for general industry and maritime. The purpose of this run was to calculate the indirect effects (only) of the final silica rule for general industry and maritime on prices and employment in the construction industry (Inforum, 2016). This LIFT simulation estimated that the final silica rule for general industry and maritime indirectly increased prices in the construction industry by an average of .005 percent. The direction, if not the magnitude of this effect, is consistent with the CISC/Environomics results (Environomics, 2015, Document ID 4242). This led to a modest decline in construction output and construction jobs. As shown in Table 9 of the Inforum report (Inforum, 2016), the decline in jobs varied from +290 to −940 a year over the period 2017 to 2026, with a cumulative job impact of −4.8 thousand jobs over the 10-year period. Again, it should be emphasized that this separate run was made in the absence of the final silica rule for the construction industry.

The IMPLAN model is static and cannot compute employment and output impacts over time, and it cannot show how the economy evolves to cope with changes in costs. In order to extrapolate over ten years, the authors simply multiply the first year effects by 10. The results are implausible for a dynamic economy as the full static one-year impact is unlikely to be the average impact over the course of several years. At least theoretically, the economy contains powerful forces pushing it towards full employment equilibrium. Therefore, most changes to output and employment due to cost or demand shocks tend to be neutralized through time. That is, most impacts, negative or positive, will approach zero over the long term. Indeed, Inforum's LIFT model produces dynamic results that vary from year to year, which is consistent with fluctuations in the state of the economy and with short and long term expenditure effects. It shows how the employment is reallocated among industries and how the economy eventually will return to the baseline, or potential, level of employment.

While the IMPLAN study places the regulatory analysis within the context of the overall economy, it does not take full advantage of the framework. For instance, given data for gross output in the base year it is possible to compute the industry price effect so that the revenue shocks can be judged relative to a price elasticity of demand. Instead, the study employs an unrealistically large construct of a 5 to 1 compliance cost to revenue loss. Finally, the IMPLAN model's inability to model the long-term properties of the economy severely undermines the study's conclusion of long term cost to the economy.

G. Benefits and Net Benefits

In this section, OSHA discusses the benefits and net benefits of the final silica rule. To set out an approach to estimate the benefits, the Agency will, in the following sections, estimate the number of silica-related diseases prevented as a result of the rule, estimate the timing of the potentially avoided diseases, monetize their economic value, and discount them. Taking into account the estimated costs of the final rule, presented in Chapter V of the FEA, OSHA will then estimate the net benefits and incremental benefits of the rule. Finally, the Agency will assess the sensitivity of the estimates to changes in various cost and benefit parameters.

This section presents OSHA's quantitative estimates of what rule-induced benefits would be under certain assumptions. OSHA acknowledges that these estimates are heavily influenced by the underlying assumptions, and also that the long time frame of this analysis (60 years) is a source of uncertainty. The assumptions underlying these estimates of deaths and morbidity avoided will be discussed in detail as they appear in the remainder of this chapter, but the major ones are as follows:

• The exposure profile and other industrial profile data presented in Chapter III of the FEA reflect both current conditions and future conditions (extending over the next sixty years);
• To separate the effects of this new rule from the effects of compliance with existing standards, it is assumed that any workers currently exposed above the preceding PEL are exposed to levels of silica that exactly meet the preceding PEL;
• The rule will result in workers being exposed at the new PEL but will never reduce exposures below the new PEL;
• Workers have identical exposure tenures (45 years, except where otherwise noted);
• The effects of baseline respirator use on risk are ignored; and
• The assumptions inherent in developing the exposure-response functions discussed in Section VI, presented in Table VI-1 of this preamble, are reasonable throughout the exposure ranges relevant to this benefits analysis. (The reasonableness of these assumptions is discussed in Section VI.)

The first two assumptions are also the basis for the cost analysis in Chapter V of the FEA. The basis for the last assumption is discussed in greater detail in Section VI of this preamble and will be briefly reviewed in this section. It bears emphasis, however, that the sources of data for OSHA's benefits analysis are the same as those used in the Quantitative Risk Assessment (Section VI of this preamble) and the technological feasibility analysis in Chapter IV of the FEA.

While OSHA did not quantify the benefits of the ancillary provisions, consistent with the statute (29 U.S.C. 655(b)(7), section 6(b)(7)), the Agency finds that these provisions are beneficial and necessary in order for the standard to be fully and correctly implemented and for the full benefits of the rule to be realized. On the whole, OSHA intends the requirements for training on control measures, housekeeping, and other ancillary provisions of the rule to apply where those measures are used to limit exposures. Without effective training on use of engineering controls, for example, it is unreasonable to expect that such controls will be used properly and consistently. The ancillary provisions found in the rule are generally standard and common throughout OSHA regulations.

The provision requiring exposure assessment in general industry is integral to determining the engineering controls and work practices needed to control employee exposure to the new PEL, to evaluate the effectiveness of the required engineering and work practice controls, and to determine whether additional controls must be instituted. In addition, monitoring is necessary to determine which respirator, if any, must be used by the employee, and it is also necessary for compliance purposes.

The requirement for regulated areas in general industry and maritime serves several important purposes including alerting employees to the presence of respirable crystalline silica at levels above the PEL, restricting the number of people potentially exposed to respirable crystalline silica at levels above the PEL, and ensuring that those who must be exposed are properly protected. Similarly, the competent person requirement in the construction standard will protect bystanders by restricting access to work areas only when necessary, benefiting those bystanders through reduced exposures.

Written exposure control plans provide a systematic approach for ensuring proper function of engineering controls and effective work practices that can prevent overexposures from occurring. OSHA expects a written exposure control plan will be instrumental in ensuring that employers comprehensively and consistently protect their employees.

The medical surveillance provisions have the potential to protect workers through the early detection of silica-related illnesses and will enable employees to take actions in response to information about their health status gleaned from medical surveillance. Additionally, by requiring medical surveillance to general industry and maritime workers exposed at or above the action level, OSHA provides an incentive for employers to further reduce exposures, where possible, to avoid incurring the costs of medical surveillance.

1. Estimates of the Number of Avoided Cases of Silica-Related Disease

For reasons described in detail in this preamble, OSHA has adopted a PEL of 50 μg/m³ in its silica standards covering general industry, maritime, and construction, along with an alternative method of compliance (Table 1) in construction. Analogous to the estimates in the PEA, OSHA has calculated estimates of the benefits associated with the PEL of 50 μg/m³ for respirable crystalline silica, and corresponding Table 1 in construction, by applying the dose-response relationships developed in OSHA's quantitative risk assessment (QRA) to exposures at or below the preceding PELs.

a. Exposure Profiles

OSHA determined exposure levels at or below the preceding PELs by first developing an exposure profile of current exposures for industries with workers exposed to respirable crystalline silica, using OSHA inspection and site-visit data, and then applying this exposure profile to the total current worker population. The industry-by-industry exposure profile is presented in Chapter III of the FEA.

Because OSHA relied solely on measurement of airborne exposures, respirator use may result in lower baseline exposures inside the respirator than would be indicated by the airborne exposures measurements. The extent to which this affects OSHA's benefits calculations depends on the extent to which there was baseline respirator use in the risk assessment studies OSHA relied on and how these studies accounted for respirator use, if they did so at all. OSHA reviewed the risk assessment studies it is relying on as well as earlier studies that described the source of exposure data for each cohort and how exposures were estimated for cohort members to determine whether respirator use was accounted for. OSHA found that the overwhelming majority of studies did not mention either respirator use or how they accounted for respirator use, even though many took place in time periods and at exposures levels where some respirator use could have been expected. Some studies accounted for use of “dust controls” but did not state whether these “dust controls” included respirator use. Two studies (Rando et al. 2001, Document ID 0415), whose exposure estimates for North American industrial sand workers were used by Hughes et al. (2001, Document ID 1060), and Dosemeci et al. (1993), whose exposure estimates for Chinese mine and pottery workers were modified and used by Chen et al. (2001, Document ID 0332; 2005, Document ID 0985), mention adjusting exposure estimates to account for respirator use, but did not discuss in detail how these adjustments were calculated. Most studies OSHA relied on, directly or indirectly, cover long periods of time, over which respirator use varied. Most cover some time after OSHA set a general industry PEL of approximately 100 μg/m³ and required the use of a respirator if that exposure level was exceeded. In summary, OSHA does not know the extent of respirator use in the risk assessment studies relied on for the benefits analysis, nor how they might differ from current respirator use. As a result, OSHA is unable to accurately adjust its estimates to account for baseline respirator use.

OSHA also is not able to quantify the effectiveness of respirator use. (OSHA regulations provide for assigned protection factors, but these are based on ideal conditions rather than real world conditions.) It is thus difficult to know how to correct for possible respirator use. As will be discussed below, OSHA estimates benefits relative to a baseline characterized by compliance with the preceding PEL. The preceding PEL in construction and maritime is approximately 250 μg/m³. If respirators have a protection factor of five, then they would be equivalent to the new PEL of 50 μg/m³ if fully effective at 250 μg/m³. In general industry there is a preceding PEL of approximately 100 μg/m³. If respirators have a protection factor of two, then they would be equivalent to the new PEL of 50 μg/m³, if fully effective. Beyond this, OSHA does not have the data to quantify the effects of respirator use because it is well known that in actual practice in work settings, respirators are not always as protective as the assigned protection factors would indicate. For the purpose of estimating the health benefits of the final rule, exposures above the relevant preceding PELs were set at the relevant preceding PEL; for purposes of comparing the effects of the preceding and the new standards, the analysis thus assumes full compliance with both, without taking baseline respirator use into account.

By applying the dose-response relationships from the literature to estimates of exposures at or below the preceding PELs across industries, it is possible to estimate the number of cases of the following diseases expected to occur in the worker population given exposures at or below the preceding PELs (the “baseline”):

• fatal cases of lung cancer,
• fatal cases of non-malignant respiratory disease (NMRD) (including silicosis),
• fatal cases of end-stage renal disease, and
• cases of silicosis morbidity.

Non-fatal cases of lung cancer, NMRD and end-stage renal disease were not estimated. In that respect, the estimates of the benefits are understated. However, OSHA's benefits calculations do not, for example, factor in any impact on the rule's implementation of the following aspect of the Agency's enforcement approach: As a general matter, where compliance with a standard's requirement clearly creates a new hazard, employers can raise a defense that compliance with the requirement is not feasible, and OSHA would work with the employer to implement an alternative means of protection that does not create a serious hazard.

In a comment suggesting that some reductions in exposures (and thus some benefits) were not included in OSHA's analysis, Dr. Ruth Ruttenberg noted that “OSHA/ERG did not consider stomach cancer, autoimmune disease, and other cancer and non-cancer health effects of silica exposure” (Document ID 2256, Attachment 4, p. 11). These potential benefits were not quantified, for the PEA or FEA, because the Agency does not, at this time, have sufficient exposure-response data to perform a quantitative risk assessment for these illnesses. The Health Effects and Significance of Risk section of this preamble contain a more detailed discussion of these potential silica-related health effects that were not quantified.

b. OSHA's Method for Using Risk Models and Exposure Profile To Estimate Cases Avoided as a Result of the Rule

The core of OSHA's methodology for benefits analysis is to calculate the number of estimated premature deaths and illness cases avoided as a result of the new rule. To do this, OSHA estimates the expected number of mortality and morbidity cases expected to occur under the assumption that the preceding PEL is being met (i.e., those workplaces where the preceding PEL is currently exceeded are set equal to the preceding PEL), and then subtract the expected number of mortality and morbidity cases estimated to occur with the new rule in place. OSHA then estimates the numbers of disease cases and deaths that would result after the new standard goes into effect (i.e., assuming full compliance in that no worker will be exposed in excess of the new PEL). For this purpose, OSHA assumes all exposures above the new PEL are reduced to the new PEL of 50 μg/m³. The difference between these estimates represents the numbers of disease cases and deaths that the Agency estimates would be avoided as a result of issuing the new standard. That is, this approach focuses on calculating estimates derived from eliminating those exposures between the preceding PEL and the new PEL. As explained later, these estimated mortality and morbidity cases avoided are then monetized to comprise the benefits (in dollar terms) of the rule.

By focusing on exposures between the preceding PEL (even for workers exposed above the preceding PEL) and the new PEL exclusively, and ignoring the possibility that workers' exposures are reduced below the new PEL, OSHA's calculations will have a tendency toward underestimation. Some exposures may be reduced to below the new PEL of 50 μg/m³ as a result of engineering controls that do more than needed. Also, some exposures below the new PEL of 50 μg/m³ may be reduced further due to “bystander effects,” by which those already exposed below the new PEL but working near other exposed workers would have their exposures reduced further.

In order to estimate the number of deaths prevented, OSHA uses a lifetime risk model, which is a mathematical framework that explicitly follows workers from the beginning of their work lives until retirement. Workers are assumed to start work at age 20 and work continuously until age 65, resulting in a 45-year work life, and then assumed to live another 15 years post-retirement, or until age 80. This estimate is useful because the OSH Act requires OSHA to examine exposures for an entire working life. Shorter job tenures will be discussed further below.

Using this model, OSHA calculates the workers' cumulative workplace exposures to silica, and estimates the probability of their dying each year from silica-related diseases. The model also establishes the background probability of the workers' dying from non-silica-related causes. The increase in the workers' probability of dying due to cumulative silica exposure in the workplace is added to this background probability. As will be explained in more detail later, the difference in these probabilities is used to form the basis for estimating the number of illnesses and deaths due to silica exposures as they currently exist and the estimated number of illnesses and deaths that would be avoided when the standard is fully in effect, assuming full compliance.

The background, age-specific survival probabilities are based on the current (2011) U.S. (male) population, the latest year for which age-specific all-cause mortality statistics are available. The exposure-response functions for different diseases, which relate cumulative silica exposure and increased probabilities of respective disease endpoints, are drawn from specific studies discussed in this preamble, Section VI—Final Quantitative Risk Assessment and Significance of Risk. Estimates of the number of cases of silicosis prevented by the new standard were also based on cumulative risk models taken from several morbidity studies, but were not used in life table analyses as was done for mortality (see Section VI of this preamble, Final Quantitative Risk Assessment and Significance of Risk). The exposure levels used in the model cover the U.S. exposure profile as presented in Table III-9 in Chapter III Industry Profile of the FEA. OSHA's exposure profiles for general industry and maritime and for construction contain the estimated numbers of employees exposed within specific bands of exposure levels: below 25 μg/m³, 25 to 50 μg/m³, and above 50 μg/m³ (in bands of 50 μg/m³ to 100 μg/m³, 100 μg/m³ to 250 μg/m³, and above 250 μg/m³, whenever any of these bands are above the preceding PEL, OSHA lowered the estimate for the band to the preceding PEL).

The results in Table III-9 in the FEA represent average daily exposures in the risk model for general industry and maritime. In construction, occupational exposure is commonly intermittent (i.e., not occurring every workday), necessitating an adjustment to accurately estimate these workers' cumulative exposure and risk. Workers in the construction sector perform a multitude of tasks, only some of which involve silica exposure. OSHA's estimated exposure levels represent the 8-hour time-weighted average of exposure on days when workers perform tasks involving silica exposures. However, to account for the fact that, in most affected construction occupations, workers do not do such tasks every day, the cumulative exposure estimate for these workers needed to be adjusted. To account for this intermittent exposure, the risk model uses an adjustment factor which estimates the percentage of days in which a worker will typically perform tasks that generate silica exposures. These adjustment factors are generally based on the proportion of time workers perform silica-generating activities along with associated work crew sizes. So, for example, if, on average, a group of workers is estimated to spend 20 percent of its time performing tasks involving silica exposure, the model multiplies the base exposure level—the exposure that the group of workers is estimated to have based on the exposure profile—by this 20 percent. In the Agency's model, this adjustment factor is calculated as the total number of full time equivalent days that affected employees spend on silica-related tasks divided by total affected employment as shown in Chapter III of the FEA. For all construction occupations other than hole drillers using hand-held drills, OSHA calculated an FTE adjustment factor of 28 percent that was derived from the exposure profile. Hole drillers using hand-held drills have a large number of employees and an extremely low adjustment factor as compared to all other occupations. Because the risk models are nonlinear, averaging such disparate groups together provides unrepresentative results and therefore, this occupation has its risk calculated separately. For hole drillers using hand-held drills, OSHA calculated an adjustment factor of 3.5 percent.

In order to calculate the number of expected and avoided cases for each health outcome, OSHA assumes that all workers whose exposures fall within a band are exposed the same and assigns the average of all individual exposure observations within the relevant band (i.e., the mean exposure) as the single point estimate within each band. This point estimate of exposure is then used with the associated risk estimate for each health outcome, which is multiplied by the estimated number of workers exposed within the exposure band to calculate the number of workers who experience that health outcome in the absence of the new rule. For workers currently exposed above the new PEL, OSHA assumes that their post-rule exposures will be lowered to the new PEL of 50 µg/m³. This reflects the fact that the Agency is taking no benefits for reducing exposure above the previous PELs to the previous PELs. The analysis starts from a baseline of the previous PELs. A similar calculation is then performed at these new exposure levels for these currently overexposed workers: The numbers of workers exposed within each exposure band of the post-rule exposure profile is then multiplied by the associated risk estimates for each health outcome to yield estimates of the numbers of disease cases and fatalities that will occur after the standard is implemented. Finally, subtracting this post-implementation number of deaths and disease cases from those estimated under baseline (pre-rule) conditions yields an estimate of the number of deaths and illness cases averted due to the standard.

As an example, Table VII-23-1 presents the summary calculations for a risk model that produces one estimate of the number of lung cancer deaths avoided by the revised standard for workers in general industry if they were all exposed to silica for 45 years (this uses the ToxaChemica 2004 risk model of lung cancer deaths avoided).

In Table VII-23-1, the total General Industry population at risk for excess lung cancer is 291,019. There are 142,071 workers in the range of silica exposure of below 25 µg/m, 51,377 workers exposed between 25 and 50 µg/m, etc. The “Model Exposure Level-Baseline” row provides the mean exposure level within each range, which is the point estimate of exposure for which the associated lifetime risk estimate is used to estimate the number of lung cancer deaths that occur among workers exposed within each exposure range. For example, from the exposure profile, the mean exposure for workers in General Industry who are exposed below 25 µg/m is 14 µg/m, and the risk of lung cancer for all workers in this exposure band is calculated from this average exposure of 14 µg/m. Though the exposure profile includes 28,297 workers exposed in the range of 100-250 µg/m and 28,443 workers exposed above 250 µg/m, to estimate the number of baseline lung cancer deaths, those workers' exposure levels are set at the preceding PEL of 100 µg/m. In this example, estimated benefits due to the new PEL do not include any benefits to workers for their exposures being reduced to the preceding PEL; only those benefits associated with the exposure levels being reduced from the preceding PEL or lower to the new PEL are included in the estimates. The row labeled “Model Exposure Level-50 PEL” shows the expected exposures among workers that result after the standard is promulgated. Exposures of workers exposed below 50 µg/m are expected to remain unchanged while the exposures of all workers who are currently exposed above 50 µg/m are expected to be reduced to the new PEL of 50 µg/m.

Table VII-23-1 also presents the estimated excess risk of lung cancer per 1,000 workers for each exposure band and the number of lung cancer deaths that would occur among workers exposed within each exposure band for 45 years. For example, among workers exposed within the lowest exposure band, the lifetime risk model estimates an increased risk of lung cancer above the background mortality risk of 14.7 deaths per 1,000 workers at a constant exposure to 14 µg/m³ silica for 45 years. Multiplying this risk estimate by the number of workers at risk in that exposure band (142,071) yields an estimated 2,084 lung cancer deaths. Doing the same across the various baseline exposure level bands results in an estimated baseline total of 5,021 lung cancer deaths due to exposure to silica for the population of workers at risk. The table shows similar estimated lung cancer risks and estimated numbers of deaths in the post-standard scenario. For all workers whose baseline 45-year exposures are at or above 50 µg/m³, the estimated risk of lung cancer associated with exposure at the new PEL of 50 µg/m³ is 19.0 per 1,000 workers. Multiplying this risk by the number of workers exposed to silica at levels between 50 and 100 µg/m³ (41,596), for example, yields an estimated 776 deaths occurring in this group for the post-standard scenario. Doing the same for each exposure band for the post-standard scenario and summing across all exposure bands, the number of estimated excess lung cancer deaths post-standard is 4,858. The next two rows show the difference between the baseline and the post-standard scenarios, both for lung cancer death risks (“differential lung cancer death rate”) and numbers of deaths (“lung cancer deaths averted”). The final total number of lung cancer deaths averted is 163. Dividing by the analytic time horizon of 45 years results in about 4 annual deaths averted.

The preceding example assumes a constant exposure level each year for 45 years. Elsewhere in this chapter, OSHA examines what would happen if the day-to-day exposure remains the same but job tenure is shorter. In order to have a valid comparison, OSHA compares each scenario to what is estimated to happen over 45 years. All job tasks, and hence cumulative exposure, do not change with decreased job tenure; they are just spread over more workers. Thus, if OSHA were to examine a job tenure of 25 years, almost twice as many workers would be exposed for almost half as long as for the 45-year assumption. With a strictly proportional (linear) risk function the benefits of having half the exposure for twice the number of workers would exactly offset each other and final benefits would be the same. Hence the net effect of such changes is directly related to non-linearities in the various lifetime risk models.

c. Results for Cases Avoided

OSHA received a number of comments concerning the Agency's preliminary risk assessment and discussion of the health effects of silica in this preamble to the proposed rule. Those comments are discussed in detail in Sections V (Health Effects) and VI (Final Quantitative Risk Assessment and Significance of Risk) of this preamble to the final rule.

OSHA examined the various lung cancer risk models presented in its QRA to estimate the benefits of lowering the PEL. As can be inferred from Table VI-1 of the Final QRA, the ToxaChemica, Inc. (2004, Document ID 0469) log-linear model estimated the lowest estimate of lung cancer cases avoided from lowering the PEL to 50 or 100 μg/m³, whereas the Attfield and Costello (2004, Document ID 0543) model estimated the highest number of lung cancer cases avoided. The remainder of the studies indicated an intermediate reduction in risk. OSHA used the ToxaChemica 2004 (log-linear model) and Attfield and Costello studies to characterize a range of estimated lung cancer reduction, acknowledging that neither of these estimates captures the full range of uncertainty associated with the models and data used.

Table VII-24 shows the range of modeled estimates for the number of avoided fatal lung cancers for PELs of 50 μg/m³ and 100 μg/m³ for the scenario in which workers are uniformly exposed to silica for 45 years. At the final PEL of 50 μg/m³, the modeling approach yields estimates of 2,921 to 8,246 lung cancers prevented over the lifetime of the worker population, with a midpoint estimate of 5,584 fatal lung cancers prevented. This is the equivalent of between 65 and 183 cases avoided annually, with a midpoint estimate of 124 cases avoided annually, given a 45-year working life of exposure.

Following Park (2002, Document ID 0405), as discussed in the Agency's QRA, OSHA's estimation model suggests that the final PEL of 50 μg/m would, in the scenario in which workers are uniformly exposed to silica for 45 years, prevent 14,606 fatalities over the lifetime of the worker population from non-malignant respiratory diseases arising from silica exposure. This is equivalent to 325 fatal cases prevented annually. Some of these fatalities would be classified as silicosis, but most would be classified as other pneumoconiosis and chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis and emphysema. That is one reason why we would expect this estimate to exceed the count based solely on death certificates (for instance, in 2013, CDC's count based on state-provided vital records is 111 deaths annually from silicosis in the United States).

Certain commenters argued that the recent CDC count of silicosis mortality from death certificates is evidence that OSHA's benefits were overestimated.

Some commenters, such as the American Chemistry Council and Faten Sabry, Ph.D., representing the Chamber of Commerce, argued—based on the numbers of silicosis-related deaths recorded in recent years reported in mortality surveillance data—that OSHA overestimated the estimated benefits of the standard (Document ID 2263, p. 57; 3729, p. 1; 2288, Appendix 6; 4209, pp. 3-4). Dr. Sabry stated that the 52 deaths reported by the CDC in 2010 where silicosis was identified as an underlying cause of death were considerably fewer than the number of silicosis-related deaths that OSHA claimed would be avoided once the proposed standard becomes fully implemented. Dr. Sabry concluded, “[s]o, by OSHA's calculation, reducing the PEL to 50 µg/m³ will prevent more silicosis-related deaths than actually occur in the United States today—which suggests that OSHA's risk assessment is faulty” (Document ID 2288, Appendix 6). The National Utility Contractors Association (NUCA) made the same argument when it asserted: “OSHA predicts that this proposed rule will prevent approximately 600 silica related deaths per year, but the CDC is recording less than 100 deaths per year” (Document ID 3729, p. 1). The National Federation of Independent Business also argued that OSHA estimated 375 prevented cases of silicosis that would have led to deaths, but the CDC reported only about 150 deaths per year where silicosis was the underlying cause or a contributing factor, causing OSHA to overestimate lives saved due to the standard by about 150 percent (Document 2210, Attachment 1, p. 3).

OSHA disagrees that the silicosis mortality surveillance data alone provides evidence that OSHA has overstated the quantitative benefits of the rule. OSHA derived its benefits estimates from exposure data presented in the Industry Profile chapter of the FEA and from its quantitative risk assessment, which is based on epidemiological data that quantify relationships between exposure and disease risk. OSHA relied on these estimates to estimate the number of silicosis-related deaths and illnesses that would occur absent a revised standard and the number of deaths that would be avoided by promulgation of such a standard. From this analysis, OSHA estimated that 325 deaths from silicosis and other non-malignant lung disease and 918 silicosis morbidity cases are estimated to be avoided annually once the full effects of the standards are realized. The 52 deaths cited by Dr. Sabry appears to refer to only the number of deaths with silicosis coded as the “underlying” cause of death on death certificates, and does not include deaths coded with silicosis as a “contributing” cause. Combined with the deaths where silicosis is coded as a “contributing” cause, in this case 49, CDC/NIOSH reported a total of 101 deaths where silicosis was either an underlying cause of death or a contributing cause of death.

OSHA's model does not only count fatalities related to silicosis. OSHA's estimate of the impact of exposure to respirable crystalline silica includes deaths from other diseases (lung cancer, non-malignant respiratory disease such as chronic bronchitis and emphysema, and end-stage renal disease) that, according to scientific evidence, can be caused by exposure to respirable crystalline silica (Document ID 1711; 2175, p. 2). OSHA also estimated, based on the Park study discussed previously, that 325 cases of fatal non-malignant respiratory diseases associated with exposure to silica, including, but not limited to silicosis, that would be prevented annually due to the final standard. Thus, OSHA's estimates of the numbers of deaths prevented that are due to non-malignant respiratory disease are not comparable to surveillance statistics that only capture silicosis as a cause of death. Furthermore, Dr. Sabry's comments are primarily focused on the hydraulic fracturing industry, which only recently became a major source of silica exposure, where most of the effects of current exposures will likely not be seen for a number of years, underlining why this analysis of past trends is not instructive for epidemiological estimates.

In response to NUCA's comparison of OSHA's estimate of 679 deaths avoided to the estimate of fewer than 100 deaths from the surveillance data, the Agency again points out that the model accounts for causes of death other than those resulting from silicosis and therefore reported to CDC/NIOSH in the surveillance data. Therefore, NUCA's comparison is faulty because focusing exclusively on silicosis mortality fails to capture silicosis morbidity, as well as mortality and morbidity resulting from other diseases related to silica exposure, including lung cancer, other non-malignant respiratory disease such as chronic bronchitis and emphysema, and renal disease (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1).

George Kennedy of the National Utilities Contractor's Association makes a similar “apples and oranges” error in his comment:

OSHA predicts that this rule will prevent approximately 600 silica-related deaths per year. But how is this possible if the CDC is reporting less than 100? (Document ID 3583, p. 2240)

Mr. Kennedy's comment is based on comparing CDC counts of documented silicosis fatality cases, but this count is not a report on all silica-related deaths. The Agency's articulated need for the standard, however, is based on the finding that silica exposure results in an array of adverse, mutually independent health endpoints. In contrast, the CDC estimate deals with a small part of the overall health risk from silica exposure.

As also discussed in the Agency's QRA, OSHA finds that workers with higher cumulative exposures to silica are at elevated risk of lung cancer, end-stage renal disease, and non-malignant respiratory diseases. Based on the midpoint of the lower high-end estimate (Attfield and Costello, 2004, Document ID 0543) and a higher low-end estimate (ToxaChemica log-linear model, Document ID 0469), OSHA's estimation model estimates that the new PEL of 50 μg/m³ would, in the scenario in which workers are uniformly exposed to silica for 45 years prevent 5,584 cases of lung cancer, or about 124 cases annually upon reaching “steady state” (see later discussion of this concept) in 60 years. Based on Steenland, Attfield, and Mannetje (2002, Document ID 1089), OSHA's estimation model estimates that the final PEL would prevent 8,689 cases of end-stage renal disease, or about 193 cases annually in steady state. And based on Park (2002, Document ID 0405), OSHA's estimation model estimates that the new PEL would prevent 14,606 cases of non-malignant respiratory diseases (including silicosis) over the lifetime of 45 cohorts' worth of worker population, or about 325 cases annually in steady state, of which 2,970 (66 annually) are attributable to diagnosed cases of silicosis, based on Mannetje (2002, Document ID 1089).

Combining the three major fatal health endpoints—lung cancer, non-malignant respiratory diseases, and end-stage renal disease—OSHA's modeling approach yields estimates that the new PEL would prevent between 26,216 and 31,541 premature fatalities over the lifetime of the current worker population, with a midpoint estimate of 28,879 fatalities prevented. This is the equivalent of between 583 and 701 premature fatalities avoided annually, with a midpoint estimate of 642 premature fatalities avoided annually, given a 45-year working life of exposure.

In addition, the final silica rule is estimated to prevent a large number of cases of silicosis morbidity. Table VII-25 is designed to compare available estimates of actual silicosis cases to the estimates generated by OSHA exposure profile and models. The first set of rows compares present estimates of 2/1 and the second set of rows estimates of 1/0 cases of silicosis generated by various risk models using OSHA's exposure profile. Going across, the first columns are for a tenure length of 45 years, the second set for a tenure length of 13 years. Then below in the second panel, the final set of rows is based on Rosenman, et al. (2003, Document ID 1166) estimates of actual silicosis cases, generated with an alternative modeling approach. To be consistent with OSHA's jurisdiction, OSHA revised Rosenman's estimate to remove workers not in OSHA's jurisdiction, such as miners. The lower panel, based on Rosenman, et al. (Document ID 1166), shows, assuming 45 years of exposure, that between 2,700 and 5,475 new cases of silicosis, at an ILO x-ray rating of 1/0 or higher, are estimated to occur annually at current exposure levels as a result of silica exposure at establishments within OSHA's jurisdiction (i.e., excluding miners). The various models OSHA used yield estimates of between 836 and 8,011 cases, assuming 45 years of exposure and between 393 and 10,107 cases assuming 13 years of exposure at an ILO x-ray rating of 1/0 or higher. OSHA's risk models for morbidity using OSHA's exposure profile are thus somewhat consistent with epidemiologically based estimates of silicosis cases though some are a bit over the epidemiological estimates. When a job tenure of 13 years is assumed, the table shows that for most models, as compared to the 45 year job tenure analysis, the results are a lower numbers of cases, while other models yield estimates of cases within the range estimated by Rosenman for U.S. workers other than miners (who are outside OSHA's jurisdiction.) There are, however, exceptions. The estimated number of cases for some models falls below Rosenman's estimates. On the other hand, two models show an increased number of cases which are above the range of Rosenman's estimates. This is a result of very high rates of cases expected to occur in persons exposed at levels above the preceding PELs. Since OSHA does not estimate benefits to workers exposed at levels above the preceding PELs, any estimated increase in cases among such workers will not affect OSHA's benefits analysis.

A number of commenters took issue with the general idea that silicosis is an occupational health problem for workers whose exposures to silica did not exceed the preceding PELs. These commenters typically pointed to the significant decline in the number of silicosis deaths reported by the CDC in the last few decades.

OSHA does not find these comments persuasive. As explained in depth in the Health Effects and Risk Assessment sections of this preamble, while the Agency welcomes any apparent decline in silicosis cases, the Agency has substantial evidence that significant risk remains at preceding PELs. The commenters do not account for the undercounting of silicosis deaths from death certificates, as demonstrated by Rosenman (Document ID 1166] and others; nor do they address other health endpoints beyond fatal silicosis. Although the decline in reported cases may indicate the Agency's success up to this point in reducing the incidence of silicosis, it cannot be taken as an absolute measure of how many silica-related disease cases currently exist in the population. Most silicosis cases are not fatal—given that the total cases of silicosis have apparently remained largely constant, fewer silicosis fatalities may mean that more individuals are living with silicosis for longer periods while ultimately dying of other causes.

While OSHA has estimated morbidity from silicosis, it has not attempted to estimate the number of morbidity cases from these other health endpoints. Including these other endpoints would increase estimates of the number of overall cases avoided.

As summarized in Table VII-25, OSHA expects that, in the scenario in which workers are uniformly exposed to silica for 45 years, the silica rule will eliminate the majority of 1/0, 1/1, and 1/2 silicosis cases. However, the Agency has not included the elimination of these less severe silicosis cases in its estimates of the monetized benefits and net benefits of the final rule. Instead, as shown above in Table VII-24, OSHA focused its morbidity-only benefits and related net benefits analysis exclusively on the number of silicosis cases reaching the more severe levels of 2/1 and above (moderate-to-severe silicosis, using the ILO method for assessing severity). As discussed in the Agency's QRA, OSHA estimates that the new PEL of 50 μg/m for the current worker population would, in the scenario in which workers are uniformly exposed to silica for 45 years, prevent 41,293 cases of moderate-to-severe silicosis (2/1 or more) over a working life, or about 918 cases prevented annually.

As previously discussed, OSHA based its estimates of reductions in the number of silica-related diseases using estimates that reflect a working life of constant exposure for workers who are employed in a respirable crystalline silica-exposed occupation for their entire working lives, from ages 20 to 65. In other words, these estimates reflect an assumption that workers do not enter or exit jobs with silica exposure mid-career or switch to other exposure groups during their working lives. While the Agency is legally obligated to examine the effect of exposures from a 45-year working lifetime of exposure, for purely informational purposes, the Agency also alternatively examined the effect of assuming that workers are exposed to silica for three other tenure lengths: 25, 13, and 6.6 working years (see Table VII-26a through Table VII-26c for number of cases and Table VII-28a through Table VII-28d for monetary benefits for all four tenure levels).

Table VII-26a presents cases for a worker exposed for 25 years. While each individual worker is estimated to have less cumulative exposure under the 25-years-of-exposure assumption, in fact 56 percent (25/45) as much, the effective exposed population over time is proportionately increased (due to the turnover of workforce for a constant number of jobs, and hence total exposure), over the same time period. A comparison of Table VII-26a to Table VII-24, reflecting exposures over 25 working years versus 45 working years, shows variations in the number of estimated prevented cases by health outcome. Estimated prevented cases of fatal end-stage renal disease are higher in the 25-year model, whereas cases of fatal non-malignant respiratory disease and silicosis morbidity are lower. In the case of lung cancer, the effect varies by model, with a decrease in the Attfield and Costello, 2004 higher estimate (Document ID 0543) and an increase in the ToxaChemica, 2004 lower estimate (Document ID 0469). Looking at overall totals, the midpoint estimate of the number of avoided fatalities under the new PEL of 50 μg/m³ is 642 for 45 years, increasing to 772 for 25 years. For total morbidity, there instead is a decrease: from 918 cases avoided for 45 years down to 443 cases avoided for 25 years, Table VII-26b presents results for 13 years of exposure. For a 13 year job tenure, the midpoint for the number of fatalities avoided is 982 while the total number morbidity cases avoided is 246. Finally, Table VII-26c presents the results for 6.6 years of exposure. In this scenario, the midpoint for the number of fatalities avoided is 1,382 and the total number of morbidity cases avoided is 194. Looking across the tenure results shows that midpoint mortality significantly increases with lower tenure, while total morbidity has a large decrease with lower tenure.

A commenter, Joseph Liss, objected to the Agency's approach of simultaneously increasing the estimated exposed population—not because it was technically incorrect, but because it makes it harder to see the difference in risk to a particular exposed population (Document ID 1950, pp. 16-19).

OSHA reported in the PEA that in the construction industry, which has an unusually high rate of job turnover compared to other industries, BLS data show that the mean job tenure with one's current employer is 6.6 years (BLS, 2010a, Document ID 1620), and the median age of construction workers in the U.S. is 41.6 years (BLS, 2010b, Document ID 1672). OSHA further noted that BLS does not have data on occupational tenure within an industry, but that the Agency would expect that job tenure in the construction occupations as a whole would be substantially greater than the job tenure with a worker's current employer. None of the commenters disagreed. Furthermore, many workers may return to the construction industry after unemployment or work in another industry. Job tenure with the current employer, however, is longer in the other industries affected by the silica rule (BLS, 2010a, Document ID 1620).

Dr. Ronald Bird, submitting a comment on behalf of the U.S. Chamber of Commerce—as well as an unaffiliated commenter, Joseph Liss—suggested that OSHA's estimates of disease cases prevented from 45 years of silica exposure is unrepresentative of the typical tenure of workers affected by the standard, particularly in construction (Document ID 2368, p. 18; Document ID 1950, pp. 15-19). Dr. Bird suggested that workers will routinely change occupations in the course of their lifetime. From a probabilistic standpoint, he calculated that workers would, on average, likely work in an occupation for less than six years. The comments directly from the Chamber of Commerce go further, to say that “[n]o such 45-year career silica exposures exist in today's working world . . .” (Document ID 2288, p. 11).

The article (Rytina, 1983, Document ID 2368) that Dr. Bird cited for his data on occupational turnover provides data that refute the assumptions of Dr. Bird's model. While Dr. Bird assumes that occupational turnover is constant without regard to age or length of occupational experience, the Rytina article states:

Not surprisingly, occupational mobility rates declined sharply with age . . . The rate for workers age 35-44 was less than one fourth as high as that for workers 18 and 19 years of age. * * * [O]ccupational change among older workers occurs less frequently because of attachments to a particular occupation or the risks of losing income, job security, and pension rights, which might accompany an occupational shift (Rytina, 1983, Document ID 2368, p. 5).

Furthermore, the Rytina article shows that among workers 45 to 54 years of age, 16.5 percent of workers have been in the same occupation for 25 years or more, and among workers 55 and older, 32.9 percent have been in the same occupation for 25 years or more. By comparison, Dr. Bird's model suggests that, regardless of age, no more than 13 percent of workers will remain in a given occupation for more than 20 years.

Two commenters also provided evidence of the average tenures of their workers that is contrary to Dr. Bird's estimates. The National Industrial Sand Association (NISA) noted, “many NISA member company employees work at their workplaces for all or much of their worklives. In 2004, a study calculated the mean tenure for NISA member company employees fitting the definition of the study's cohort to be 19.7 years” (Document ID 2195, p. 19). Southern Company, an electric utility, noted that it “has approximately 8000 employees in job titles performing activities with potential exposures to silica-containing materials. The average tenure for these employees is 17 years; 37% of these employees have over 20 years work experience” (Document ID 2185, p. 3).

Other commenters provided evidence to refute the Chamber of Commerce claim that that 45-year career silica exposures no longer exist in today's working world (Document ID 2288, p. 11). During the public hearing, participants on a panel comprised of members of the International Union of Bricklayers and Allied Craftworkers (BAC) were asked if they had colleagues who had worked longer than forty years in their trade. All six of the participants affirmed that they did (Document ID 3585, Tr. 3053). Further, several labor groups submitted evidence of lengthy worker tenure. The BAC noted that:

A review of our International Pension Fund records documented 116 individuals who have worked for 40 years or more. We consider this figure to understate the work lives of Fund participants because many of these individuals had previous work experience in the construction industry before being represented by BAC. In additional, we believe this figure understates the number of participants with work lives of 45 years, because the Fund was established in 1972 and it was not until roughly a decade later that even half of BAC affiliates had commenced participation in the Fund (Document ID 4053, Attachment 1, p. 2).

Similarly, The United Association of Plumbers, Fitters, Welders, and HVAC Service Techs, submitted that “a review of membership records documented 35,649 active members who have worked 45 years or more while they have been a member of the union.” They also concur with the BAC statement that the number may be understated given previous work experience (Document ID 4073, Attachment 3, p. 1). And the International Union of Operating Engineers' Central Pension Fund found the average operating engineer has over 20 years of service in the trade with a range up to 49.93 years (Document ID 4025, Attachment 1, pp. 6-7).

Dr. Bird also objected to OSHA's approach of using a single representative exposure to measure lifetime exposure. He states: “If exposures are variable over the course of a year, the lifetime exposure pattern is contrary to OSHA's assumption and the benefits from the proposed reduction in the PEL would be considerably less” (Document ID 2368, p. 19). Dr. Bird apparently faults the Agency for not considering the possibility that future exposures may be lower than those observed on a given day. However, it is equally plausible that a worker's future exposures may be higher than on the day they were observed by OSHA. The single-day exposure data is the best available data in the record for those workers, and the Agency does not find any persuasive evidence in this record to suggest an obvious bias to characterizing exposure from a single day rather over the course of consecutive days.

Paragraph (i)(2)(v) of the general industry and maritime standard and paragraph (h)(2)(v) of the construction standard also contain specific provisions for diagnosing latent tuberculosis (TB) in the silica-exposed population and thereby reducing the risk of TB being spread to the population at large. OSHA currently lacks good methods for quantifying these benefits. Nor has the Agency attempted to assess benefits directly stemming from enhanced medical surveillance in terms of reducing the severity of symptoms from the illnesses that do result from present or future exposure to silica. Dr. Ruth Ruttenberg, an economist representing the AFL-CIO, noted this as a source of the underestimation of the benefits in her comments (Document ID 2256, Attachment 4, pp. 9-12). However, no commenters suggested how to quantify these effects.

OSHA's risk estimates are based on application of exposure-response models derived from several individual epidemiological studies as well as the pooled cohort studies of Steenland et al. (2001, Document ID 0492) and Mannetje et al. (2002, Document ID 1089). OSHA recognizes that there is uncertainty around any of the point estimates of risk derived from any single study. In its preliminary risk assessment (summarized in Section VI of this preamble), OSHA has made efforts to characterize some of the more important sources of uncertainty to the extent that available data permit. This specifically includes characterizing statistical uncertainty by reporting the confidence intervals around each of the risk estimates (presented in the Preliminary Quantitative Risk Assessment, Document ID 1711); by quantitatively evaluating the impact of uncertainties in underlying exposure data used in the cohort studies; and by exploring the use of alternative exposure-response model forms. OSHA finds that these efforts reflect much, but not necessarily all, of the uncertainties associated with the approaches taken by investigators in their respective risk analyses. However, for reasons explained in Section VI of this preamble, OSHA concludes that characterizing the risks and benefits as a range of estimates derived from the full set of available studies, rather than relying on any single study as the basis for its estimates, better reflects the uncertainties in the estimates and more fairly captures the range of risks likely to exist across a wide range of industries and exposure situations.

Section VI of this preamble provides a more complete discussion of the source of uncertainty in the risk assessment functions used in this benefits analysis. The sources of uncertainty include the degree to which OSHA's risk estimates reflect the risk of disease among workers with widely varying exposure patterns. Some workers are exposed to fairly high concentrations of crystalline silica only intermittently, while others experience more regular and constant exposure. Risk models employed in the quantitative assessment are based on a cumulative exposure metric, which is the product of average daily silica concentration and duration of worker exposure for a specific task. Consequently, these models assume the same risk for a given cumulative exposure regardless of the pattern of exposure, reflecting a worker's long-term average exposure without regard to intermittencies or other variances in exposure. That is, the use of the cumulative exposure metric in these models assumes that there are no significant dose-rate effects in the relationship between silica exposure and risk.

Possible dose-rate effects in the silica exposure-response relationships, particularly for silicosis. OSHA's reliance on a cumulative exposure metric to assess the risks of respirable crystalline silica is discussed in Section V of this preamble. Uncertainty with respect to the form of the statistical models used to characterize the relationship between exposure level and risk of adverse health outcomes is discussed in Section VI.

In its quantitative risk assessment, OSHA used the exposure-response models from the best available evidence (i.e., the key studies discussed at length in Section V, Health Effects and Section VI, Final Quantitative Risk Assessment and Significance of Risk) to estimate risks for 45 years of exposure to the previous PELs, revised PEL, and the action level. When examining the risk estimates specifically for silicosis mortality and morbidity in Table VI, one interesting observation is the apparent difference in the exposure-response relationship for these two endpoints. For example, for 45 years of exposure to the action level (25 μg/m), there would be an estimated 4 deaths from silicosis and 21 cases of silicosis (with chest X-ray ILO category of 2/1 or greater) per 1,000 workers; at the previous PEL (100 μg/m), there would be an estimated 11 deaths from silicosis and 301 cases of silicosis per 1,000 workers. In other words, nearly 20 percent of silicosis cases are estimated to be fatal at the relatively low exposure of 25 μg/m but only about 4 percent are estimated to be fatal at the relatively high exposure of 100 μg/m. Moreover, as noted previously, morbidity and mortality estimates change in opposite directions in response to varying the assumption about workers' total length of exposure. Although this issue was not explicitly raised in the rulemaking record, OSHA notes and addresses it here.

OSHA attributes this apparent difference in the exposure-response relationships for silicosis mortality and morbidity to several factors. First, the silicosis mortality study (ToxaChemica, 2004, Document ID 0469) defined deaths using death certificate data, in which silicosis or unspecified pneumoconiosis was recorded as the underlying cause of death. In contrast, the silicosis morbidity study (Buchanan et al., 2003, Document ID 0306) defined silicosis cases using data from chest x-rays showing radiographic opacities. These radiographic signs of silicosis represent an early endpoint that is very different from silicosis death as the underlying cause of death. Such disparate endpoints are alone one reason why OSHA does not believe that the exposure-response curves should necessarily be proportional.

In addition, as discussed in Section V.E, Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality, silicosis is well-known to be underreported on death certificates in that deaths due to silicosis could have been reported as tuberculosis or chronic obstructive pulmonary disease (Document ID 1089, pp. 724-725; 1030; 3425, p. 2; 3577, Tr. 855, 867; 4204, p. 17; 2175, p. 3; 3577, Tr. 772). Also, silica-exposed workers are at risk for other silica-related diseases, including lung cancer and renal disease, as well as other non-exposure-related causes of death such that many workers who contract silicosis will not ultimately die from silicosis. Therefore the reported silicosis deaths at any level are the lowest possible number of such deaths. Workers with higher cumulative exposures are also likely to be older, and therefore may have a higher rate of other conditions that could have been listed on death certificates. Furthermore, as discussed in Section VI, OSHA's risk assessment required some degree of extrapolation at high doses (e.g., 45 years of exposure to 250 and 500 μg/m³ respirable crystalline silica) that result in cumulative exposures not experienced by many of the cohort members studied. Thus, OSHA attributes the apparent non-proportionality in the exposure-response curves for silicosis mortality and morbidity to these factors. It is possible nonetheless, that future research may shed additional light on this topic.

d. Estimating a Stream of Benefits Over Time

Risk assessments in the occupational environment are generally designed to estimate the risk of an occupationally related illness over the course of an individual worker's lifetime. As previously discussed, the current occupational exposure profile for a particular substance for the current cohort of workers can be matched up against the expected profile after the final standard takes effect, creating a “steady state” estimate of benefits. However, in order to annualize the benefits for the period of time after the silica rule takes effect, it is necessary to create a timeline of benefits for an entire active workforce over that period.

There are various approaches for modeling the workforce. As explained below, OSHA uses a model that considers the effect of lowering exposures for the entire working population. At one extreme, however, one could assume that all of the relevant silica exposures will occur after the standard goes into effect and none of the benefits occurs until after the worker retires, or at least 45 years in the future. In the case of lung cancer, that period would effectively be 60 years, since the 45 years of exposure must be added to a 15-year latency period during which it is assumed that lung cancer does not develop. At the other extreme, one could assume that the benefits occur immediately, or at least immediately after a designated lag. Neither extreme reflects the reality that silica-related diseases that this standard aims to reduce significantly occur at various times during and after the working lives of these populations of workers, with the majority of cases occurring sometime after the typical worker is middle aged. Indeed, based on the various risk models (as detailed in model life tables in Appendix A to the QRA), which reflect real-world experience with development of disease over an extended period of time; it appears that the actual pattern occurs at some point between these two extremes.

The model OSHA uses, therefore, is one that considers the effect of lowering exposures for the entire working population. This population-based approach does not simply follow the pattern of the risk assessments, which are based in part on life tables, and observe that typically the risk of the illness grows gradually over the course of a working life and into retirement. While this would be a good working model for an individual exposed over a working life, it is not very descriptive of the exposed population as a whole. In the latter case, in order to estimate the benefits of the standard over time, OSHA considers that workers currently being exposed to silica are going to vary considerably in age. Since the health risks from crystalline silica exposure depend on a worker's cumulative exposure over a working lifetime, the overall benefits of the final standard will phase in over several decades, as the cumulative exposure gradually falls for all age groups, until those now entering the workforce reach retirement and the annual stream of silica-related illnesses reaches a new, significantly lowered “steady state.” However, the beneficial effects of the rule begin in the near term and increase over time until that “steady state” is reached; and, for a given level of cumulative exposure, the near-term impact of the final rule will be greater for workers who are now middle-aged or older, compared to younger workers with similar current levels of cumulative exposure. This conclusion follows from the structure of the relative risk models used in this analysis and the fact that the background mortality rates for diseases such as lung cancer, chronic obstructive pulmonary disease and renal disease increase with age.

In order to characterize the magnitude of benefits before the steady state is reached, OSHA created a linear phase-in model to reflect the potential timing of benefits. Specifically, OSHA estimated that, for all non-cancer cases, while the number of cases of silica-related disease would gradually decline as a result of the final rule, they would not reach the steady-state level until 45 years had passed. The reduction in cases in any given year in the future was estimated to be equal to the steady-state reduction (the number of cases in the baseline minus the number of cases in the new steady state) times the ratio of the number of years since the standard was implemented and a working life of 45 years; in other words, the number of non-malignant silica-relates cases of disease avoided is assumed to increase in direct proportion to the number of years the standard is in effect until year 45, at which point the numbers hold steady. This formulation also assumes that the number of workers is constant over the entire time frame. Expressed mathematically:

N_t = (C−S) × (t/45),

where N_t is the number of non-malignant silica-related diseases avoided in year t; C is the current annual number of non-malignant silica-related diseases; S is the steady-state annual number of non-malignant silica-related diseases; and t represents the number of years after the final standard takes effect, with t≤45.

In the case of lung cancer, the function representing the decline in the number of cases as a result of the final rule is similar, but there would be a 15-year lag before any reduction in cancer cases would be achieved. Expressed mathematically, for lung cancer:

L_t = (C_m−S_m) × ((t-15)/45),

where 15 ≤t ≤60 and L_t is the number of lung cancer cases avoided in year t as a result of the final rule; C_m is the current annual number of silica-related lung cancers; and S_m is the steady-state annual number of silica-related lung cancers.

This model was extended to 60 years for all the health effects previously discussed in order to incorporate the 15-year lag, in the case of lung cancer, and a 45-year working life. OSHA also has estimated the benefits using other job tenures. For this purpose, OSHA examined scenarios for the same number of years—60 years—but with the work force restarting exposure whenever the first job tenure cycle was complete.

OSHA also has estimated the benefits using other job tenures. For this purpose, OSHA examined scenarios for the same number of years—60 years—but with the work force restarting exposure whenever the first job tenure cycle was complete.

In order to compare costs to benefits, OSHA assumes that economic conditions remain constant and that annualized costs will continue for the entire 60-year time horizon used for the benefits analysis (as discussed in Chapter V of the FEA). OSHA invited comments on this assumption in the PEA, for both the benefit and cost analysis. OSHA was particularly interested in what assumptions and time horizon should be used instead and why. The Agency did not receive any comments on this point.

2. Monetizing the Benefits

OSHA also estimates the monetary value of health and longevity improvements of the type associated with the final silica rule. These estimates are for informational purposes only because OSHA cannot use benefit-cost analysis as a basis for determining the PEL for a health standard. The Agency's methodology for monetizing benefits is based on both the relevant academic literature and on the approaches OSHA and other regulatory agencies have taken in the past for similar regulatory actions.

In explaining OSHA's methodology for monetizing health and longevity improvements, OSHA relied on a 45 year occupational tenure. Later, OSHA discusses monetization under alternative occupational tenures of 25, 13 and 6.6 years.

a. Placing a Monetary Value on Individual Silica-Related Fatalities Avoided

To estimate the monetary value of the reductions in the number of silica-related fatalities, OSHA relied, as OMB recommends in its Circular A-4, on estimates developed from the willingness of affected individuals to pay to avoid a marginal increase in the risk of fatality. While a willingness-to-pay (WTP) approach clearly has theoretical merit, it should be noted that an individual's willingness to pay to reduce the risk of fatality would tend to underestimate the total willingness to pay, which would include the willingness of others—particularly the immediate family—to pay to reduce that individual's risk of fatality.

For estimates using the willingness-to-pay concept, OSHA relies on existing studies of the imputed value of fatalities avoided based on the theory of compensating wage differentials in the labor market. These studies rely on certain critical assumptions for their estimates, particularly that workers understand the risks to which they are exposed and that workers have legitimate choices between high- and low-risk jobs. Actual labor markets only imperfectly reflect these assumptions. A number of academic studies, as summarized in Viscusi and Aldy (2003, Document ID 1220), have shown a correlation between higher job risk and higher wages, suggesting that employees demand monetary compensation in return for a greater risk of injury or fatality. The estimated trade-off between lower wages and marginal reductions in fatal occupational risk—that is, workers' willingness to pay for marginal reductions in such risk—yields an imputed value of an avoided fatality: the willingness-to-pay amount for a reduction in risk divided by the reduction in risk.

OSHA has used this approach in many recent proposed and final rules (see 69 FR 59305 (Oct. 4, 2004) and 71 FR 10099 (Feb. 28, 2006), the preambles for the proposed and final hexavalent chromium rule). Limitations to this approach (see Hintermann, Alberini and Markandya, (2010, Document ID 0739)), have been examined in a recent WTP analysis, by Kniesner et al. (2012, Document ID 3819), using panel data to examine the trade-off between fatal job risks and wages. This article addressed many of the earlier econometric criticisms by controlling for measurement error, endogeneity, and heterogeneity. Accordingly, OSHA views this analysis as buttressing the estimates in Viscusi and Aldy (2003, Document ID 1220), which the Agency is continuing to rely on for the FEA.

OSHA received several comments on the use of willingness-to-pay measures and estimates based on compensating wage differentials. For example, Peter Dorman, Professor of Economics, Evergreen State College, Eric Frumin of Change to Win, and Dr. Ruth Ruttenberg, representing the AFL-CIO, in addition to critiquing the academic studies used to develop the willingness-to-pay measure, cited the absence of effective labor markets for capturing a wage differential for hazardous work (Document ID 2260, Attachment 1; 2372, Attachment 1, pp. 4-15; 2256, Attachment 4, p. 9). OSHA acknowledges that there has been an absence of a wage premium for risk in certain labor markets, and cites this absence in Chapter II of the FEA as an example of market failure. Nonetheless, while the Agency agrees that the absence of a wage premium for risk demonstrates the need for regulatory intervention in the labor market, it does not, in itself, invalidate the use of the willingness-to-pay approach for the informational purposes for which OSHA calculates benefits, so long as there are some reasonably well-functioning parts of the labor market that can be used to estimate the willingness to pay for some subset of workers. OSHA finds that there are such sections of the labor market.

Several studies indicate that there are enough functional parts of the labor market to allow for some quantification of the risk, typically expressed as the value of a statistical life (VSL), a possible measure of willingness to pay. For example, Viscusi and Aldy (2003) conducted a meta-analysis of studies in the economics literature that use a willingness-to-pay methodology to estimate the imputed value of life-saving programs and found that each fatality avoided was valued at approximately $7 million in 2000 dollars. For the PEA, the Agency used the GDP Deflator (U.S. BEA, 2010) to convert this estimate to $8.7 million in 2009 dollars for each fatality avoided. For the FEA, the base year has been further updated to 2012 using the GDP Deflator (U.S. BEA, 2013), yielding an estimate of $9.0 million per fatality avoided.

There are a number of factors that could influence the value of a statistical life (VSL) calculation in different labor markets, but for the purpose of its analysis OSHA has identified methods for normalizing the risk between markets. For example, in Kniesner, Viscusi, and Ziliak (2010, Document ID 0767), the authors addressed the issue of the heterogeneity of the VSL approach among various labor markets by developing analytical tools (quantile regressions) for differentiating by income. For the purpose of quantifying the effects of income growth over time on the value of a statistical life, OSHA relies on their data, which generally show that VSL increases with increased worker income (as banded by quartile). Despite potential weaknesses in the VSL approach, Executive Order 12866 recommends monetization of regulatory benefits (including increases in longevity), and the Agency concludes this constitutes the best available method for this purpose.

b. Placing a Monetary Value on Individual Non-Fatal Silica-Related Diseases Avoided

In addition to the benefits that are based on the imputed value of fatalities avoided, workers also place a value on occupational injuries or illnesses avoided, which reflect their willingness to pay to avoid monetary costs (for medical expenses and lost wages) and quality-of-life losses as a result of occupational illness. Silicosis, lung cancer, and renal disease can be totally disabling and adversely affect individuals for years or even decades in non-fatal cases, or before ultimately proving fatal. Because monetary measures of the willingness to pay for avoiding these illnesses are rare and difficult to find OSHA has included a range based on a variety of estimation methods.

Consistent with Buchanan et al. (2003), OSHA estimated the total number of moderate to severe silicosis cases prevented by the final rule, as measured by 2/1 or more severe x-rays (based on the ILO rating system). However, while radiological evidence of moderate to severe silicosis is evidence of significant material impairment of health, placing a precise monetary value on this condition is difficult, in part because the severity of symptoms may vary significantly among individuals. For that reason, in the PEA, as well as in the FEA, the Agency has employed a broad range of valuation, which should encompass the range of severity these individuals may encounter. Using the willingness-to-pay approach, discussed in the context of the imputed value of fatalities avoided, OSHA has estimated a range in valuations (updated and reported in 2012 dollars) that runs from approximately $64,000 per case—which reflects estimates developed by Viscusi and Aldy (2003, Document ID 1220), based on a series of studies primarily describing simple accidents—to upwards of $5.2 million per case—which reflects estimates developed by Magat, Viscusi, and Huber (1996, Document ID 0791) for non-fatal cancer. The latter number is based on an approach that applies a willingness-to-pay value to avoid serious illness that is calibrated relative to the value of an avoided fatality. OSHA (2006, Document ID 0941) previously used this approach in the FEA supporting its hexavalent chromium final rule, and EPA (2003, Document ID 0657) used this approach in its Stage 2 Disinfection and Disinfection Byproducts Rule concerning regulation of primary drinking water. EPA used the study by Magat, Viscusi & Huber (1996, Document ID 0791) on the willingness to pay to avoid nonfatal lymphoma and chronic bronchitis as a basis for valuing a case of nonfatal cancer at 58.3 percent of the value of a fatal cancer. OSHA's estimate of $5.2 million in 2012 dollars for an avoided case of non-fatal cancer is based on this 58.3 percent figure.

There are several benchmarks for valuation of health impairment due to silica exposure, using a variety of techniques, which provide a number of mid-range estimates between OSHA's high and low estimates of $5.2 million and $64,000. For example, EPA (2008) recently estimated a cost of approximately $460,000, in 2008 dollars, per case of chronic bronchitis, which OSHA (2009) used as the basis for comparison with less severe lung impairments from diacetyl exposure. Another approach is to employ a cost-of-injury model. Combining estimates of productivity losses (i.e., lost wages, fringe benefits, and household production), medical costs (including hospitalizations), and loss of quality-of-life components, Miller (2005), using an enhanced cost-of-injury model, estimated the average silicosis disease cost the equivalent of $335,000 in 2012 dollars).

Miller (2005) also estimated the morbidity costs of several different pneumoconioses other than silicosis and found the other cases to be even more costly to society than silicosis. While the full costs of renal disease are less well known, the medical costs alone of dealing with end-stage renal disease run over $64,000 annually per patient (Winkelmayer, 2002). This suggests that a more comprehensive analysis of the direct costs of renal disease, as well as for the various lung impairments, would produce an estimate well above the $64,000 estimate of injuries in Viscusi and Aldy (2003). Moreover, several studies (e.g., Alberini and Krupnick, 2000) have found that the cost of injury approach tends to significantly underestimate the true economic cost of an injury or illness, relative to the willingness to pay approach, which includes quality of life impacts and psychic costs as well as medical costs and lost income. In this way, looking only at specific elements of this valuation, such as a workers compensation payouts (to the extent they can be linked to a specific employer in a timely manner), would dramatically underestimate the cost of the illness to society.

Thus, the various studies presented in Chapter VII of the FEA suggest that the imputed value of avoided morbidity associated with silica exposure, both for cases preceding death and for non-fatal cases, ranges between $64,000 and $5.2 million, depending in part on the model used to compute the value and in part on the severity and duration of the case. OSHA considers this wide range of estimates is descriptive of the value of preventing morbidity associated with moderate-to-severe silicosis, as well as the morbidity preceding mortality due to other causes enumerated here—lung cancer, lung diseases other than cancer, and renal disease. OSHA is therefore applying these values to monetize cases of avoided silica-related morbidity. OSHA has included these estimates of silicosis morbidity throughout the analysis. For mortality, OSHA has included the midpoints of $64,000 and $5.2 million ($2.63 million) for all mortality cases. The high and low estimates in the remainder of this document for mortality not only reflect different point estimates, but different levels for the morbidity effect.

Public Comment on Valuing Non-Fatal Cases of Silicosis

OSHA requested public input on the issue of valuing the cost to society of non-fatal cases of moderate-to-severe silicosis, as well as the morbidity associated with other related diseases of the lung, and with renal disease. A number of commenters did not directly provide quantitative estimates of the cost of silicosis or other silica-related health effects, but provided qualitative descriptions of the heavy burden to health, work, and family life incurred by having silicosis.

For example, Alan White, of the United Steelworkers Local Union 593, who developed silicosis after working in a foundry for 16 years as a general helper, described the practical implications of developing silicosis:

First of all, for me, there was the growing problem of being out of breath sooner than I used to. That's a difficult situation for a competitor, especially since I didn't know why. Then, I received a big surprise during the conversation with the first doctor when I found out that I have silicosis and that I will lose my job. He and the other doctors all agreed that the diagnosis is silicosis. Watching your wife and other loved ones cry as they figure out what silicosis is was a big hit and then, shortly afterward, there was the radical pay cut from a transfer out of the foundry to a department where I knew nothing because I chose my health over money . . . There are also difficulties outside of work and issues for me to look forward to in the future. Walking while talking on a cell phone is very exhaustive, as well as walking up the stairs from my basement to my second floor apartment. I have increasing difficulty on my current job. Certain irritants like air fresheners, potpourri and cleaners make home life increasingly difficult and I was told that it's downhill from here for both work and home life (Document ID 3477, p. 2).

Mr. White also described how the foundry went to considerable expense to hire people to do the job he previously had done, including the costs to the foundry for mistakes made by the trainees replacing him. Such personnel costs to the employer would not be captured by either the willingness-to-pay approach or cost-of-injury approach.

In addition to questioning the underlying willingness to pay approach, at least one commenter indicated various ways in which the approach employed by OSHA would tend to underestimate the economic benefits of the rulemaking. Dr. Ruttenberg argued that the WTP approach does not include costs to third parties of silica-related illnesses and injuries, starting with a number of government programs:

In its Preliminary Economic Analysis, OSHA says that it wants public input on the issue of valuing the cost to society of non-fatal cases of moderate-to severe silicosis, as well as the morbidity associated with other related diseases of the lung, and with renal disease. (PEA, p. VII-15) This is a key request because adding such societal costs can double the benefits of preventing these diseases. In an article by a lawyer and two economists looking at the social cost of dangerous products, Shapiro, Ruttenberg, and Leigh argue that a large economic burden is borne by private insurance, government programs, the business community and the victims and their families. Those affected by occupational exposures, such as silica, may become eligible for a range of cash or in-kind assistance. Such programs may include unemployment compensation, food stamps, Medicaid, Medicare, State Children's Health Insurance Program (SCHIP), Temporary Assistance for Needy Families (TANF), Social Security Disability, and Old Age, Survivors and Disability Insurance. There are also costs for use of military hospitals and clinics (Document ID 2256, Attachment 4, pp. 9-10) (citations omitted).

Part of the cost of the injury or fatality may be borne in substantial part by the victim's family:

There is another group of costs that can easily double, or even triple, the direct and indirect totals. These are social and economic impacts that are also caused by an incident. They often involve third-party payments, or stress on the victim or his/her family members. The financial pressures on a family can include the need for a caregiver, need for additional income from children or spouse to fill the gap between previous earnings and workers compensation, or psychotherapy for family members to cope with harsh new realities. When children lose their chance at college and higher future earnings, the impact can be hundreds of thousands of dollars (Document ID 2256, Attachment 4).

Dr. Ruttenberg pointed to an existing Department of Transportation study, which suggested that only a fraction of the economic cost of motor vehicle accidents was actually borne by the victim, with the remainder of the costs split between governmental bodies, insurers, and other parties (Document ID 2256, Attachment 4, p. 11).

The Center for Progressive Reform argued that there is value to reducing economic inequities created by occupational illnesses related to silica exposure:

The proposal's implications for fair treatment of workers also deserve more attention. The proposed standards would benefit a population comprising mostly construction workers (more than 85% of the total affected population). This is an industry that is a bastion for middle class workers and those striving to attain middle class status. It is also an industry that employs a significant number of foreign-born and non-union workers, groups who typically have limited power to negotiate improved working conditions. Ensuring that these workers' health is better protected against the hazards of silica exposure is an important step toward reducing socioeconomic inequality, given the linkages between individual health and social mobility. Other federal agencies, including the National Highway Traffic Safety Administration (NHTSA) and Department of Justice (DOJ), have gone so far as to argue that equity and other non-monetizable benefits are sufficient to justify rules for which the monetized costs far outweigh the monetized benefits. (As with the OSH Act, the authorizing statutes under which NHTSA and DOJ were acting do not require cost-benefit analysis, much less require the agencies to produce rules with monetized benefits that outweigh monetized costs) (Document ID 2351, p. 7) (citations omitted).

The Agency recognizes that, as with third party effects, there are aspects of economic equity issues related to occupational injury, illness, and mortality that merit attention for policy making. As noted previously, however, the OSH Act requires that OSHA policy for toxic substances be ultimately determined by issues of risk and feasibility, as opposed to cost-benefit criteria.

The Agency requested public input on the issue of valuing the cost to society of non-fatal cases of moderate to severe silicosis, as well as the morbidity associated with other related diseases of the lung, and with renal disease. The final benefits analysis summarized below and discussed in greater detail in the FEA incorporates OSHA's response to public comment.

c. Adjusting Monetized Benefits To Reflect Rising Future Value

In the PEA, OSHA suggested, provided estimates, and requested comment on adjusting future values of illness and mortality prevention to account for changes in real income over time. Ronald White of the Center for Effective Government favored integrating this element into the monetized benefits analysis (Document ID 2341, p. 3). No commenters argued against it. For the reasons provided in the PEA and described below, the Agency is adopting this approach and has used it to develop its primary benefits estimates.

OSHA's estimates of the monetized benefits of the final rule are based on the imputed value of each avoided fatality and each avoided silica-related disease. As previously discussed, these, in turn, are derived from a worker's willingness-to-pay to avoid a fatality (with an imputed value per fatality avoided of $9.0 million in 2012 dollars) and to avoid a silica-related disease (with an imputed value per disease avoided of between $64,000 and $5.3 million in 2012 dollars). Two related factors suggest that these values will tend to increase over time and help to better identify the amount that a worker would be willing to pay to avoid a fatality.

First, economic theory and empirical evidence from the relevant studies indicate that the value of reducing life-threatening and health-threatening risks—and correspondingly the willingness of individuals to pay to reduce these risks—will increase as real per capita income increases. With increased income, an individual's health and life becomes more valuable relative to other goods because, unlike other goods, they are without close substitutes. Expressed differently, as income increases, consumption will increase but the marginal utility of consumption will decrease. In contrast, added years of life (in good health) are, in the model of Hall and Jones (2007, Document ID 0720), not subject to the same type of diminishing returns and, indeed, may be viewed as the ultimate good.

Second, real per capita income has broadly been increasing throughout U.S. history, including during recent periods. For example, for the period 1950 through 2000, real per capita income grew at an average rate of 2.31 percent a year (Hall and Jones, 2007, Document ID 0720), although real per capita income for the recent 25 year period 1983 through 2008 grew at an average rate of only 1.3 percent a year (U.S. Census Bureau, 2010, Document ID 1621). More important is the fact that real U.S. per capita income is estimated to grow significantly in future years. The Annual Energy Outlook (AEO) estimates, prepared by the Energy Information Administration (EIA) in the Department of Energy (DOE), estimates an average annual growth rate of per capita income in the United States of 2.7 percent for the period 2011-2035. The U.S. Environmental Protection Agency prepared its economic analysis of the Clean Air Act using the AEO estimates. OSHA concludes that it is reasonable to use the same AEO estimates employed by DOE and EPA, and correspondingly estimates that per capita income in the United States will increase by 2.7 percent per year over the 60-year period in the analysis for this silica rule. OSHA, as discussed below, will not use this value combined with the best estimate of income elasticity. Instead OSHA derives a lower combined measure of the adjustment that combines income elasticity and rate of economic growth. Further, OSHA analyzes the sensitivity of the results to this assumption later in this chapter.

On the basis of the predicted increase in real per capita income in the United States over time and the expected resulting increase in the value of avoided fatalities and diseases, OSHA has adjusted its estimates of the benefits of the final rule to reflect the anticipated increase in their value over time. This type of adjustment has been supported by EPA's Science Advisory Board (EPA, 2000b, Document ID 0652) and applied by EPA. OSHA accomplished this adjustment by modifying benefits in year i from [B_i] to [B_i * (1 + k)ⁱ], where “k” is the estimated annual increase in the magnitude of the benefits of the final rule.

What remains is to estimate a value for “k” with which to increase benefits annually in response to annual increases in real per capita income, where “k” is equal to (1 + g) * (η), “g” is the expected annual percentage increase in real per capita income, and “η” is the income elasticity of the value of a statistical life. Probably the most direct evidence of the value of “k” comes from the work of Costa and Kahn (2003, 2004). They estimate repeated labor market compensating wage differentials from cross-sectional hedonic regressions using census and fatality data from the Bureau of Labor Statistics for 1940, 1950, 1960, 1970, and 1980. In addition, with the imputed income elasticity of the value of life on per capita GNP of 1.7 derived from the 1940-1980 data, they then predict the value of an avoided fatality in 1900, 1920, and 2000. Given the change in the value of an avoided fatality over time, it is possible to estimate a value of “k” of 3.4 percent a year from 1900-2000; of 4.3 percent a year from 1940-1980; and of 2.5 percent a year from 1980-2000.

Other, more indirect evidence comes from estimates in the economics literature on the income elasticity of the value of a statistical life. Viscusi and Aldy (2003, Document ID 1220) performed a meta-analysis on 49 wage-risk studies and concluded that the confidence interval upper bound on the income elasticity did not exceed 1.0 and that the point estimates across a variety of model specifications ranged between 0.5 and 0.6. Applied to a long-term increase in per capita income of about 2.7 percent a year, this would suggest a value of “k” of about 1.5 percent a year.

More recently, Kniesner, Viscusi, and Ziliak (2010, Document ID 0767), using panel data quintile regressions, developed an estimate of the overall income elasticity of the value of a statistical life of 1.44. Applied to a long-term increase in per capita income of about 2.7 percent a year, this would suggest a value of “k” of about 3.9 percent a year.

Based on the preceding discussion of these three approaches for estimating the annual increase in the value of the benefits of the final rule and the fact that the estimated increase in real per capita income in the United States has flattened in recent years and could remain so, OSHA has selected a conservative value for “k” of approximately 2 percent a year over the next 60 years.

Thus, based on the best current thinking and data on willingness to pay and its relationship to income elasticity as income increases, OSHA concludes that a 2 percent increase in benefits per year, as measured by a corresponding anticipated increase in VSL, is a reasonable, mid-range estimate. However, OSHA recognizes the uncertainties surrounding these estimates and has subjected them to sensitivity analysis, as discussed below.

Accordingly, OSHA concludes that the rising value, over time, of health benefits is a real phenomenon that should be taken into account in estimating the annualized benefits of the final rule. Table VII-4, in the following section, and the monetized benefits estimates that follow it, show estimates of the monetized benefits of the silica rule with this adjustment integrated into the valuation. OSHA provides a sensitivity analysis of the effects of this approach later in this chapter.

d. The Monetized Benefits of the Final Rule

Table VII-27 presents the estimated annualized (over 60 years, using a 0 percent discount rate) benefits from each of these components of the valuation, and the range of estimates, based on risk model uncertainty (notably in the case of lung cancer), and the range of uncertainty regarding valuation of morbidity. As shown, the full range of monetized benefits, undiscounted, for the final PEL of 50 µg/m runs from $7.3 billion annually, in the case of the lowest estimate of lung cancer risk and the lowest valuation for morbidity, up to $19.3 billion annually, for the highest of both. Note that the value of total benefits is more sensitive to the valuation of morbidity (ranging from $7.9 billion to $18.5 billion, given estimates at the midpoint of the lung cancer models) than to the lung cancer model used (ranging from $12.5 to $13.8 billion, given estimates at the midpoint of the morbidity valuation).

This result comports with the very wide range of valuation for morbidity. At the low end of the valuation range, the total value of benefits is dominated by mortality ($7.7 billion out of $7.9 billion at the case frequency midpoint), whereas at the high end the majority of the benefits are related to morbidity ($11.2 billion out of $18.7 billion at the case frequency midpoint). Also, the analysis illustrates that most of the morbidity benefits are related to silicosis cases that are not ultimately fatal. At the valuation and case frequency midpoint of $13.3 billion, $7.7 billion in benefits are related to mortality, $2.0 billion are related to morbidity preceding mortality, and $3.5 billion are related to morbidity not preceding mortality.

3. Discounting of Monetized Benefits

As previously noted, the estimated stream of benefits arising from the final silica rule is not constant from year to year, both because of the 45-year delay after the rule takes effect until all active workers obtain reduced silica exposure over their entire working lives and because of, in the case of lung cancer, a 15-year latency period between reduced exposure and a reduction in the probability of disease. An appropriate discount rate is needed to reflect the timing of benefits over the 60-year period after the rule takes effect and to allow conversion to an equivalent steady stream of annualized benefits.

a. Alternative Discount Rates for Annualizing Benefits

Following OMB (2003) guidelines (Document ID 1493], OSHA has estimated the annualized benefits of the final rule using separate discount rates of 3 percent and 7 percent. Consistent with the Agency's own practices in recent final and final rules, OSHA has also estimated, for benchmarking purposes, undiscounted benefits—that is, benefits using a zero percent discount rate.

The “appropriate” or “preferred” discount rate to use to monetize health benefits is a controversial topic, which has been the source of scholarly economic debate for several decades. However, in simplest terms, the basic choices involve a social opportunity cost of capital approach or social rate of time preference approach. OSHA analyzes the benefits of this rule under both approaches.

The social opportunity cost of capital approach reflects the fact that private funds spent to comply with government regulations have an opportunity cost in terms of foregone private investments that could otherwise have been made. The relevant discount rate in this case is the pre-tax rate of return on the foregone investments (Lind, 1982b, pp. 24-32) (Document ID 1622).

The rate of time preference approach is intended to measure the tradeoff between current consumption and future consumption, or in the context of the final rule, between current benefits and future benefits. The individual rate of time preference is influenced by uncertainty about the availability of the benefits at a future date and whether the individual will be alive to enjoy the delayed benefits. By comparison, the social rate of time preference takes a broader view over a longer time horizon—ignoring individual mortality and the riskiness of individual investments (which can be accounted for separately).

A usual method for estimating the social rate of time preference is to calculate the post-tax real rate of return on long-term, risk-free assets, such as U.S. Treasury securities (OMB, 2003, Document ID 1493). A variety of studies have estimated these rates of return over time and reported them to be in the range of approximately 1-4 percent.

OMB Circular A-4 (2003) recommends using discount rates of 3 percent (representing the social rate of time preference) and 7 percent (a rate estimated using the social cost of capital approach) to estimate benefits and net benefits (Document ID 1493). Ronald White of the Center for Effective Government endorsed the use of a 3 percent discount rate—since it “appropriately reflects a social rate of time preference approach consistent with recommendations for benefits evaluation by the U.S. Environmental Protection Agency” (Document ID 2341, pp. 3-4). Charles Gordon argued for a 0 percent discount rate:

The economic literature indicates that the social discount rate should be 2 percent or 3 percent. But I believe the social discount rate should be zero, because if you were asked the question, do you want yourself saved from crystalline silica exposure . . . or do you want your son to be saved from crystalline silica death 20 years from now, you could not answer that question. You could not give a preference (Document ID 3588, Tr. 3789-90).

In acknowledgement of OMB Circular A-4 (2003, Document ID 1493), OSHA presents benefits and net benefits estimates using discount rates of 3 percent (representing the social rate of time preference) and 7 percent (a rate estimated using the social cost of capital approach). The weight of the evidence favors using a discount rate of 3 percent or less, and that 3 percent is one of the options permitted by OMB, the Agency is using a 3 percent discount rate to display its primary estimates of benefits under the social rate of time preference method.

b. Summary of Annualized Benefits Under Alternative Discount Rates

Table VII-28a through Table VII-28d presents OSHA's estimates of the sum of the annualized benefits of the final rule, under various occupational tenure assumptions, using alternative discount rates of 0, 3, and 7 percent, with a breakout between construction and general industry/maritime, with each table presenting these results for a different tenure level. All of these benefits calculations reflect willingness-to-pay values that, as previously discussed, increase in real value at 2 percent a year.

Given that the stream of benefits extends out 60 years, the value of future benefits is highly sensitive to the choice of discount rate. As previously established in Table VII-27, the undiscounted benefits (i.e., using the 0 percent discount rate) for the scenario in which workers are uniformly exposed to silica for 45 years range from $7.3 billion to $19.3 billion annually. In Table VII-28a, for 45 years tenure, using a 3 percent discount rate, the annualized benefits range from $4.8 billion to $12.6 billion. Using a 7 percent discount rate, the annualized benefits range from $2.7 billion to $6.9 billion. As can be seen, going from undiscounted benefits (with a midpoint of $13.3 billion) to benefits calculated at a 7 percent discount rate (with a midpoint of $4.8 billion) has the effect of cutting the annualized benefits of the final rule by 64 percent.

Comparing across tenure levels for representative benefits, Table VII-28a for 45 years tenure has total benefits at the midpoint estimate of $8.7 billion at a 3 percent discount rate and $4.8 billion at 7 percent discount rate. Table VII-28b for 25 years tenure has total benefits at the midpoint estimate of $10.0 billion at a 3 percent discount rate and $5.5 billion at 7 percent discount rate. Table VII-28c for 13 years tenure has total benefits at the midpoint estimate of $12.3 billion at a 3 percent discount rate and $6.8 billion at 7 percent discount rate. Finally, Table VII-28d for 6.6 years tenure has total benefits at the midpoint estimate of $16.1 billion at a 3 percent discount rate and $9.0 billion at 7 percent discount rate.

4. Estimates of Net Benefits of the Final Rule

OSHA has estimated as shown in Table VII-29, the monetized and annualized net benefits of the final rule (with a PEL of 50 µg/m³ in general industry/maritime and construction and Table 1 governing almost all controls in Construction), based on the benefits model and costs previously presented in this chapter and in Chapter V of the FEA. Net benefits are the difference between benefits and costs.

Table VII-29 shows net benefits using alternative discount rates of 0, 3, and 7 percent for benefits and costs, including the previously discussed adjustment to monetized benefits to reflect increases in real per capita income over time.

As previously noted, the OSH Act requires the Agency to set standards based on eliminating significant risk to the extent feasible. An alternative criterion of maximizing net (monetized) benefits may result in very different regulatory outcomes. Thus, this analysis of estimated net benefits has not been used by OSHA as the basis for its decision concerning the choice of a PEL or of ancillary requirements for the final silica rule. Instead, it is provided pursuant to Executive Orders 12866 and 13563. OSHA has used the 45 year occupational tenure in its main analysis. OSHA has also examined other possible tenures and provided the results. The occupational tenure results are such the benefits are higher the shorter the occupational tenure. Examination of shorter tenure would actually increase the net benefits because more workers are exposed to silica, albeit for a shorter time each.

Table VII-29 also shows results of estimates of annualized net benefits for an alternative PEL of 100 µg/m³. Under this regulatory alternative, the PEL would be changed from 50 µg/m³ to 100 µg/m³ for all industries covered by the final rule, and the action level would be changed from 25 µg/m³ to 50 µg/m³ (thereby keeping the action level at one-half of the PEL). The ancillary provisions of the standard, such as the medical surveillance provisions, would remain the same in this alternative as in this final rule, but would be impacted by factors such as changes in respirator use and effects on other provisions such as medical surveillance. For example, in the construction sector where medical surveillance requirements are triggered by respirator use, a reduction in respirator use would result in a decrease in the costs associated with medical surveillance. Under this alternative, OSHA determined in the PEA that Table 1 requirements for respirator use would be eliminated and that only abrasive blasters and some underground construction workers, which are not included in Table 1, would be required to wear respirators. However, the number of mortalities and morbidities would rise if workers were exposed to higher levels of silica. OSHA did not receive comment on its analysis of this alternative.

As previously noted in this summary, the choice of discount rate for annualizing benefits has a significant effect on annualized benefits. The same is true for net benefits. For example, the net benefits using a 7 percent discount rate for benefits are considerably smaller than the net benefits using a 0 percent discount rate, declining by more than half to two-thirds under all scenarios. (Conversely, as noted in Chapter V of the FEA, the choice of discount rate for annualizing costs has only a very minor effect on annualized costs.)

The estimates of net benefits in Table VII-29 show that:

• While the net benefits of the final rule vary considerably—depending on the choice of discount rate used to annualize benefits and on whether the calculated benefits are in the high, midpoint, or low range—benefits exceed costs for the 50 μg/m³ PEL in all scenarios that OSHA considered (i.e., the highest estimate for costs is lower than the lowest estimate for benefits).
• The Agency's best estimate of the net annualized benefits of the final rule—using a uniform discount rate for both benefits and costs of 3 percent—and cognizant of the uncertainties inherent in the analysis, is between $3.8 billion and $11.6 billion, with a midpoint value of $7.7 billion.
• The alternative of a 100 μg/m³ PEL has lower net benefits under all assumptions, relative to the 50 μg/m³ PEL. However, for this alternative PEL, benefits were also found to exceed costs in all scenarios that OSHA considered.

One commenter, the Mercatus Institute, argued that the benefits for the proposed rule were overestimated due to OSHA's assumption of full compliance, and that this simultaneously underestimated costs, since the cost of complying with existing rules is assumed away. This commenter stated that the Agency should not assume that firms will necessarily comply with the Agency's rules and the benefits estimates should therefore be lower (Document ID 1819, p. 9). OSHA makes three points in response. First, the argument is logically inconsistent—if the Agency did not assume full compliance with the previous PELs and assumes compliance with the new PEL, as Mercatus advocates, it is true that the estimated costs would increase, but so would the estimated benefits. Second, the logic for the Mercatus Institute's argument seems to be undercut by the Mercatus Institute's own observation that the Agency has had success in reducing silicosis, which suggests that in the long run, at least, firms actually do comply with OSHA rules (Document ID 1819, pp. 4-5). Finally, as discussed in the engineering controls section of Chapter V of the FEA, the Agency has determined that the best way for it to calculate costs and benefits is to estimate the incremental costs and benefits of the standard by assuming full compliance. OSHA also emphasizes that the compliance assumption applies to both costs and benefits so that the comparison of one to the other is not necessarily unduly weighted in either direction (an exception would be the counterfactual scenario in which extremely high non-compliance by a few employers changed benefits estimates substantially but cost estimates only slightly).

Estimates of Incremental Benefits of the Final Rule

Incremental costs and benefits are those that are associated with increasing the stringency of the standard. A comparison of incremental benefits and costs provides an indication of the relative efficiency of the final PEL and the alternative PEL. Again, OSHA has conducted these calculations for informational purposes only and has not used this information as the basis for selecting the PEL for the final rule.

Tables VII-30A and VII-30B show result of estimates of the costs and benefits of reducing exposure levels from the preceding PELs of approximately 250 µg/m (for construction and maritime) and 100 µg/m (for general industry) to the final rule PEL of 50 µg/m and to the alternative PEL of 100 µg/m, using the alternative discount rates of 3 and 7 percent. These tables also introduce a second alternative PEL. Under this second alternative standard, addressed in Tables VII-30A and VII-30B, the PEL would be lowered from 50 µg/m to 25 µg/m for all industries covered by the final rule, while the action level would remain at 25 µg/m (because of difficulties in accurately measuring exposure levels below 25 µg/m). For the construction sector under this second alternative, Table 1 requirements would also be modified to include respiratory protection for all workers covered under Table 1 (because all exposures for Table 1 activities are assumed to be above 25 µg/m), and all these covered workers would be subject to the medical surveillance provision.

Table VII-30A breaks out costs by provision and benefits by type of disease and by morbidity/mortality, while Table VII-30B breaks out costs and benefits by major industry sector or construction task sector. As Table VII-30A shows, at a discount rate of 3 percent, a PEL of 50 µg/m³, relative to a PEL of 100 µg/m³, imposes incremental costs of $381 million per year; incremental benefits of $4.3 billion per year, and additional net benefits of $3.9 billion per year. The final PEL of 50 µg/m³ also has higher net benefits than 100 µg/m³ either at a 3 percent or 7 percent discount rate.

Table VII-30B continues this incremental analysis but with breakdowns between construction and general industry/maritime. As shown, both sectors show strong positive net benefits, which are greater for the final PEL of 50 µg/m³ than the alternative of 100 µg/m³.

The estimates in Tables VII-30A and VII-30B indicate that, across all discount rates, there are net benefits to be achieved by lowering exposures from the preceding PEL (250 μg/m or 100 μg/m) to 100 μg/m and then, in turn, lowering them further to 50 μg/m and then to 25 μg/m, and the lower the PEL, the greater the net benefits. Net benefits decline across all incremental changes in PELs as the discount rate for annualizing benefits increases. The incremental net benefit of reducing the PEL from 100 μg/m³ to 50 μg/m³ is greater than the incremental net benefit of reducing the PEL from 50 μg/m³ to 25 μg/m³ under both the 3 percent discount rate and the 7 percent discount rate.

However, the majority of the benefits and costs that OSHA estimates for the final rule (PEL of 50 μg/m³) are from the initial effort to lower exposures from the preceding PEL of 250 μg/m³ in both construction and maritime to 100 μg/m³, as shown in the 100 μg/m³ column and the Incremental Costs/Benefits column between the 100 μg/m³ column and the 50 μg/m³ column in Table VII-30A. The majority of the costs and benefits attributable to lowering exposures to 100 μg/m³ are in the construction industry. OSHA did not estimate any costs or benefits for general industry employers lowering exposures to an alternative of 100 μg/m³ because the preceding PEL was already 100 μg/m³, but a relatively small amount of costs and benefits would be attributed to maritime employers lowering exposures to the alternative of 100 μg/m³ from the preceding PEL of 250 μg/m³. Because a single standard would cover both general industry and maritime employers, those costs and benefits are grouped together in Table VII-30A and VII-30B.

In addition to examining alternative PELs, OSHA also examined alternatives to other provisions of the standard. These alternatives are discussed in the following Chapter VIII of the FEA: Regulatory Alternatives.

5. Sensitivity Analysis

In this section, OSHA presents the results of two different types of sensitivity analysis. In the first type of sensitivity analysis, OSHA made a series of isolated changes to individual cost and benefit input parameters in order to determine their effects on the Agency's estimates of annualized costs, annualized benefits, and annualized net benefits. In the second type of sensitivity analysis—a so-called “break-even” analysis—OSHA also investigated isolated changes to individual cost and benefit input parameters, but with the objective of determining how much they would have to change for annualized costs to equal annualized benefits.

Again, the Agency has conducted these calculations for informational purposes only and has not used these results as the basis for selecting the PEL for the final rule.

a. Analysis of Isolated Changes to Inputs

The methodology and calculations underlying the estimation of the costs and benefits associated with this rulemaking are generally linear and additive in nature. Thus, the sensitivity of the results and conclusions of the analysis will generally be proportional to isolated variations a particular input parameter. For example, if the estimated time that employees need to travel to (and from) medical screenings is doubled, the corresponding labor costs double as well.

OSHA evaluated a series of such changes in input parameters to test whether and to what extent the general conclusions of the economic analysis held up. OSHA first considered changes to input parameters that affected only costs and then changes to input parameters that affected only benefits. Each of the sensitivity tests on cost parameters had only a very minor effect on total costs or net costs. Much larger effects were observed when the benefits parameters were modified; however, in all cases, net benefits remained significantly positive. On the whole, OSHA found that the conclusions of the analysis are reasonably robust, as changes in any of the cost or benefit input parameters still show significant net benefits for the final rule. The results of the individual sensitivity tests are summarized in Table VII-31A and B and are described in more detail below.

OSHA has tailored the sensitivity analysis to examine issues raised by commenters, particularly with respect to costs. (For more detail, see Chapter V of the FEA.) For each alternative, the estimated cost increase is equivalent to the estimated decrease in net benefits (except for minor rounding discrepancies). For instance, in the first example of sensitivity testing, when OSHA doubled the estimated portion of the affected self-employed population from 25 to 50 percent, and estimates of other input parameters remained unchanged, Table VII-31A shows that the estimated total costs of the final rule increased by $17.9 million annually, or by about 1.7 percent, while estimated net benefits also declined by $17.9 million, from $7,657 million to $7,639 million annually.

In the second example, OSHA doubled the estimated familiarization time needed to understand the requirements of the new standard relative to OSHA's best estimate, which ranged from 4 to 40 hours depending on establishment size (see Chapter V for more detail). As shown in Table VII-31A, if OSHA's estimates of other input parameters remained unchanged, the total estimated costs of the final rule increased by $16.0 million annually, or by about 1.5 percent, while net benefits declined by the same amount annually, from approximately $7,657 million to $7,641 million annually.

In the third example, OSHA doubled the estimated daily amount of housekeeping per worker necessary to comply with the standard, from 10 minutes to 20 minutes. As shown in Table VII-31A, if OSHA's estimates of other input parameters remained unchanged, the total estimated costs of the final rule increased by $12.5 million annually, or by about 1.2 percent, while net benefits declined by the same amount annually, from approximately $7,657 million to $7,645 million annually.

In the fourth example, OSHA examined the effect of increasing its estimate of the frequency with which thorough cleaning of the workplace would be performed in general industry. The Agency examined the effect of increasing the frequency from only one initial thorough cleaning to the initial cleaning plus an annual thorough cleaning, or alternately, a thorough cleaning every 5 years. As shown in Table VII-31A, if thorough cleaning were an annual cost, the total estimated costs of the final rule increased by $17.2 million annually, or by about 1.7 percent, while net benefits declined by the same amount annually, from $7,657 million to $7,640 million annually. In the second variation of this test, for a thorough cleaning every 5 years, as shown in Table VII-31A, the increase in annual costs is only 0.2 percent.

In the fifth example, OSHA increased its estimate of respirator use. In Chapter V of the FEA, OSHA explained that it calculated the costs of respirators for general industry and maritime workers who will still be exposed above the PEL after all feasible controls are in place. In addition, to be conservative, OSHA added costs to provide respirators to 10 percent of the remaining population. For this sensitivity test, OSHA doubled its estimate of the amount of additional respirator use in general industry from 10 percent to 20 percent. As shown in Table VII-31A, the total estimated costs of the final rule increased by $20.0 million annually, or by about 1.9 percent, while net benefits decreased by the same amount annually, from approximately $7,657 million to $7,637 million annually.

In the sixth example, reflecting in part the range of comments the Agency received on the issue (discussed in detail in Chapter V), OSHA explored the effect of increasing, and alternately decreasing, by 50 percent the size of the productivity impact arising from the use of engineering controls in construction. As shown in Table VII-31A, if OSHA's estimates of other input parameters remained unchanged, under the first variation, the total estimated costs of the final rule increased by $99.6 million annually, or by about 9.7 percent, while net benefits declined by the same amount annually, from $7,657 million to $7,558 million annually. Under the second variation, the decrease in costs and increase in net benefits would be of the same magnitude, with final estimated net benefits rising to $7,757 million.

As shown in Table VII-31B, OSHA also performed sensitivity tests on several input parameters used to predict the benefits of the final rule. In the first two tests, in an extension of results previously presented in Table VII-27, the Agency examined the effect on annualized net benefits of employing the high-end estimate of the benefits, as well as the low-end estimate. As discussed previously, the Agency examined the sensitivity of the benefits to both the valuation of individual silica-related disease cases prevented, as well as the number of lung cancer deaths prevented. Table VII-31B presents the effect on annualized net benefits of using the extreme values of these ranges, the high count of cases prevented and the high valuation per case prevented, and the low count and the low valuation per case prevented. As indicated, using the high estimate of cases prevented and their valuation, the benefits rise by 45 percent to $12.6 billion, yielding net benefits of $11.5 billion. For the low estimate of both cases prevented and their valuation, the benefits decline by 45 percent, to $4.8 billion, yielding net benefits of $3.8 billion.

In the third sensitivity test of benefits, OSHA examined the effect of raising the discount rate for benefits to 7 percent. The fourth sensitivity test of benefits examined the effect of removing the adjustment to monetized benefits to reflect increases in real per capita income over time. The results of the first of these sensitivity tests for net benefits was previously shown in Table VII-29 and is repeated in Table VII-31B. Raising the interest rate to 7 percent lowers the estimated benefits by 45 percent, to $4.8 billion, yielding annualized net benefits of $3.8 billion. Removing the two-percent annual increase to monetized benefits to reflect increases in real per capita income over time decreases the benefits by 50 percent, to $4.3 billion, yielding net benefits of $3.3 billion.

b. “Break-Even” Analysis

OSHA also performed sensitivity tests on several other parameters used to estimate the net costs and benefits of the final rule. However, for these, the Agency performed a “break-even” analysis, asking how much the various cost and benefits inputs would have to vary in order for the costs to equal, or break even with, the benefits. The results are shown in Table VII-32.

OSHA also performed sensitivity tests on several other parameters used to estimate the net costs and benefits of the final rule. However, for these, the Agency performed a “break-even” analysis, examining how much the various cost and benefits inputs would have to vary in order for the costs to equal, or break even with, the benefits estimated. The results are shown in Table VII-32.

In the first break-even test on cost estimates, OSHA examined how much costs would have to increase in order for costs to equal estimates benefits. As shown in Table VII-32, this point would be reached if costs increased by $7.7 billion.

In a second test, looking specifically at the estimated engineering control costs, the Agency found that these costs would also need to increase by $7.7 billion for costs to equal estimates benefits.

In a third sensitivity test, on benefits, OSHA examined how much its estimated monetary valuation of an avoided illness or an avoided fatality would need to be reduced in order for the costs to equal the benefits. Since the total valuation of prevented mortality and morbidity are each estimated to exceed at least $2.6 billion, while the estimated costs are $1.0 billion, an independent break-even point for each is impossible. In other words, for example, if no value is attached to an avoided illness associated with the rule, but the estimated value of an avoided fatality is held constant, the rule still has substantial net benefits. Only through a reduction in the estimated net value of both components is a break-even point possible.

OSHA, therefore, examined how large an across-the-board reduction in the monetized value of all avoided illnesses and fatalities would be necessary for the benefits to equal the costs. As shown in Table VII-32, for costs to equal estimated benefits, the estimated value per life saved would have to decline to $1.10 million per life saved, and an equivalent percentage reduction to about $0.3 million per illness prevented.

In a break-even sensitivity test, OSHA estimated how many silica-related fatalities and illnesses would be required for benefits to equal costs. As shown in Table VII-32, a reduction of 88 percent, relative to the morbidity and mortality estimates is required to reach the break-even point—566 fewer fatalities prevented annually, and 809 fewer silica-related illnesses prevented annually.

H. Regulatory Alternatives

This section discusses several major regulatory alternatives to the final OSHA silica standard, pursuant to Executive Orders 13653 and 12866. The presentation of regulatory alternatives in this chapter serves two important functions. The first is to demonstrate that OSHA explored less costly ways (compared to the final rule) to provide workers an adequate level of protection from exposure to respirable crystalline silica. The second is tied to the Agency's statutory requirement, which underlies the final rule, to reduce significant risk to the extent feasible. If OSHA had been unable to support its findings of significant risk and feasibility based on evidence presented during notice and comment, the Agency would then have had to consider regulatory alternatives that do satisfy its statutory obligations.

Each regulatory alternative presented here is described and analyzed relative to the final rule. Where relevant, the Agency notes that some regulatory alternatives are not permissible based on the required legal findings OSHA has made regarding significant risk and feasibility. The regulatory alternatives have been organized into four categories similar to those used in the PEA: (1) Alternative PELs to the new PEL of 50 μg/m³; (2) regulatory alternatives that affect ancillary provisions; (3) a regulatory alternative that would modify the methods of compliance; and (4) regulatory alternatives concerning when different provisions of the final rule would take effect.

Alternative PELs

OSHA selected a new PEL for respirable crystalline silica of 50 μg/m³ for all industries covered by the final rule and developed and included Table 1 for many work activities within the construction sector. The final rule is based on the requirements of the Occupational Safety and Health Act (OSH Act) and court interpretations of the Act. For health standards issued under section 6(b)(5) of the OSH Act (29 U.S.C. 655(b)(5)), OSHA is required to promulgate a standard that reduces the risk of material impairment of health to the extent that it is technologically and economically feasible to do so (see Section II, Pertinent Legal Authority, for a full discussion of the legal requirements for promulgating new health standards under the OSH Act).

OSHA has conducted an extensive review of the literature on adverse health effects associated with exposure to respirable crystalline silica. The Agency has also developed estimates of the risk of silica-related diseases assuming exposure over a working lifetime at the final PEL and action level, as well as at OSHA's preceding PELs. These analyses are presented in a background document entitled “Respirable Crystalline Silica—Health Effects Literature Review and Preliminary Quantitative Risk Assessment” and its final findings are described in this preamble in Section V, Health Effects, and Section VI, Final Quantitative Risk Assessment and Significance of Risk. The available evidence indicates that employees exposed to respirable crystalline silica well below the previous PELs are at increased risk of lung cancer mortality and silicosis mortality and morbidity. Occupational exposures to respirable crystalline silica also can result in the development of kidney and autoimmune diseases and in death from other nonmalignant respiratory diseases. As discussed in Section VI Significance of Risk, in this preamble, OSHA finds that worker exposure to respirable crystalline silica at the previous and new PELs constitutes a significant risk and that the final standard will substantially reduce this risk.

Section 6(b) of the OSH Act (29 U.S.C. 655(b)) requires OSHA to determine that its standards are technologically and economically feasible. OSHA's examination of the technological and economic feasibility of the final rule is presented in the FEA, and is summarized in this section (Section VII) of this preamble. For general industry and maritime, OSHA has concluded that the final PEL of 50 μg/m³ is technologically feasible for all affected industries. In other words, OSHA has found that engineering and work practice controls will be sufficient to reduce and maintain silica exposures to the PEL of 50 μg/m³ or below in most operations most of the time in the affected industries in general industry, and the rule is also feasible in maritime (feasibility for maritime (shipyards) partly depends on it being subject to other standards regulating abrasive blasting). For those few operations where the PEL cannot be achieved even when employers install all feasible engineering and work practice controls, employers in general industry and maritime can supplement controls with respirators to achieve exposure levels at or below the PEL.

For construction, determined that the engineering and work practice controls specified in Table 1 are feasible for all affected activities and in most cases will keep exposures at or below 50 μg/m³ most of the time. For those few activities where the engineering and work practice controls specified in Table 1 are not sufficiently protective of worker health, Table 1 specifies respirator use to supplement those controls. A limited number of activities, such as tunneling and abrasive blasting, are not dealt with under Table 1, but are governed more directly by the PEL of 50 μg/m³, as in general industry and maritime. For construction, while a few tasks like abrasive blasting and those specified on Table 1 as requiring respirators cannot achieve the PEL most of the time with engineering and work practice controls alone, OSHA has concluded that the PEL of 50 μg/m³ is technologically feasible for the construction industry overall because most operations can meet the PEL using the specified controls in Table 1or under the traditional approach.

OSHA developed quantitative estimates of the compliance costs of the final rule for each of the affected industry sectors. The estimated compliance costs were compared with industry revenues and profits to provide a screening analysis of the economic feasibility of complying with the revised standard and an evaluation of the potential economic impacts. Industries with unusually high costs as a percentage of revenues or profits were further analyzed for possible economic feasibility issues. After performing these analyses, OSHA has concluded that compliance with the requirements of the final rule would be economically feasible in every affected industry sector.

OSHA has examined two regulatory alternatives (named Regulatory Alternatives #1 and #2) that would modify the PEL for the final rule. Under Regulatory Alternative #1, the final PEL would be changed from 50 µg/m³ to 100 µg/m³ for all industry sectors covered by the rule, and the action level would be changed from 25 µg/m³ to 50 µg/m³ (thereby keeping the action level at one-half of the PEL). Under Regulatory Alternative #2, the new PEL would be lowered from 50 µg/m³ to 25 µg/m³ for all industry sectors covered by the rule, while the action level would remain at 25 µg/m³ (because of difficulties in accurately measuring exposure levels below 25 µg/m³). For the construction sector under this second alternative, Table 1 requirements would also be modified to include respiratory protection for all workers covered under Table 1 (because none are expected to be mostly under 25 µg/m³ for any of the tasks), and all these covered workers would be subject to the medical surveillance provision.

Tables VII-33 and VII-34 present, for informational purposes, the estimated costs, estimated benefits, and estimated net benefits of the final rule under the new PEL of 50 μg/m³ and for the regulatory alternatives of a PEL of 100 μg/m³ and a PEL of 25 μg/m³ (Regulatory Alternatives #1 and #2), using alternative discount rates of 3 and 7 percent. These two tables also present the incremental costs, the estimated incremental benefits, and the estimated incremental net benefits of going from a PEL of 100 μg/m³ to the new PEL of 50 μg/m³ and then of going from the new PEL of 50 μg/m³ to a PEL of 25 μg/m³. Table VII-33 breaks out costs by provision and benefits by type of disease and by morbidity/mortality, while Table VII-34 breaks out costs and benefits by major industry sector.

As previously noted, Tables VII-33 and VII-34 also show the costs and estimated benefits of a PEL of 25 μg/m³ (Regulatory Alternative #2), as well as the incremental costs and benefits of going from the final PEL of 50 μg/m³ to a PEL of 25 μg/m³. Because OSHA determined that a PEL of 25 μg/m³ would not be feasible (that is, engineering and work practices would not be sufficient to reduce and maintain silica exposures to a PEL of 25 μg/m³ or below in most operations most of the time in the affected industries), the Agency did not attempt to identify engineering controls or their costs for affected industries to meet this PEL. Instead, for purposes of estimating the costs of going from a PEL of 50 μg/m³ to a PEL of 25 μg/m³, OSHA assumed that all workers exposed between 50 μg/m³ and 25 μg/m³ would have to wear respirators to achieve compliance with the 25 μg/m³ PEL. OSHA then estimated the associated additional costs for respirators, exposure assessments, medical surveillance, and regulated areas (the latter three for ancillary requirements specified in the final rule).

As Tables VII-33 and VII-34 show, going from the final rule to Regulatory Alternative #2 (PEL of 25 μg/m³) is estimated to prevent, annually, an additional 295 silica-related fatalities and an additional 122 cases of silicosis. These estimates support OSHA's finding that there is significant risk remaining at the final PEL of 50 μg/m³. However, the Agency has determined that a PEL of 25 μg/m³ is not technologically feasible for most sectors or operations, and for that reason, has not selected it.

Regulatory Alternatives That Affect Ancillary Provisions

Section 6(b)(7) of the OSH Act, 29 U.S.C. 655(b)(7), requires standards to prescribe, where appropriate, the monitoring or measuring of employee exposure for the protections of employees. Section 6(b)(7) also requires the standards to prescribe, where appropriate, the type and frequency of medical exams to be provided by employers “in order to most effectively determine whether the health of [exposed] employees is adversely affected by such exposure.” The final rule contains several ancillary provisions (provisions other than the PEL), including requirements for exposure assessment, medical surveillance, familiarization and training, regulated areas (in general industry and maritime), and a written exposure control plan.

OSHA's reasons for including each of the ancillary provisions are detailed in Section XV of this preamble, Summary and Explanation of the Standards. In particular, OSHA has determined that requirements for exposure assessment (or alternately, using specified exposure control methods for selected construction operations) provide a basis for ensuring that appropriate measures are in place to limit worker exposures. Medical surveillance is particularly important because workers exposed at levels below the new PEL are still at significant risk of death and illness (OSHA's decision not to lower the PEL further was due to limitations on technological feasibility, rather than a determination that significant risk was eliminated at the new PEL). Medical surveillance will allow for identification of respirable crystalline silica-related adverse health effects at an early stage so that appropriate intervention measures can be taken. Regulated areas and a written exposure control plan are important in part because they help limit exposure to respirable crystalline silica to as few employees as possible. Finally, worker training is necessary to inform employees of the hazards to which they are exposed, along with associated protective measures, so that employees understand how they can minimize potential health hazards. Worker training on silica-related work practices is particularly important in controlling silica exposures because engineering controls frequently require action on the part of workers to function effectively.

As shown in Table VII-33, these ancillary provisions represent approximately $340 million (or about 35 percent) of the total annualized costs of the final rule of $962 million (using a 3 percent discount rate). The three most expensive of the ancillary provisions are the requirements for medical surveillance, with annualized costs of $96 million; the requirements for training and familiarization, with annualized costs of $94 million; and exposure assessment, with annualized costs of $71 million.

The requirements for exposure assessment in general industry and maritime are triggered by the action level. The exposures of workers in construction for whom all Table 1 requirements have been met do not have to be assessed, but if Table 1 requirements are not met, the requirements for exposure assessment in construction would also be triggered by the action level. As described in this preamble, OSHA has defined the action level for the standard as an airborne concentration of respirable crystalline silica of 25 μg/m³ calculated as an 8-hour time-weighted average. In this final rule, as in other OSHA health standards, the action level has been set at one-half of the PEL.

As explained in Chapter IV of the FEA, OSHA finds that proper implementation of engineering and work practice controls, particularly those specified in Table 1, will eliminate much of the variability in silica exposure that characterizes baseline conditions in the general industry, maritime, and construction sectors. OSHA recognizes, however, that some variability is unavoidable and uncontrollable even with such controls. Because of this variability of employee exposures to airborne concentrations of respirable crystalline silica, maintaining exposures below the action level should provide reasonable assurance that employees will not be exposed to respirable crystalline silica at levels above the PEL on days when no exposure measurements are made. Even when all measurements on a given day fall between the PEL and the action level, there is some chance that on another day, when exposures are not measured, actual exposure may exceed the PEL. When exposure measurements are below the PEL but above the action level, the employer cannot be certain that employees have not been exposed to respirable crystalline silica concentrations in excess of the PEL during at least some part of the work week. Therefore, requiring periodic exposure measurements when the action level is exceeded provides the employer with a reasonable degree of confidence in the results of the exposure monitoring.

As specified in the final rule, all workers in general industry and maritime exposed to respirable crystalline silica at or above the action level of 25 μg/m³ are subject to the medical surveillance requirements. In the construction sector, medical surveillance is triggered by respirator use for 30 days or more per year (which generally corresponds to a risk of exposure above 50 μg/m³ that prompted the Table 1 respirator requirement), For the final rule, the medical surveillance requirements will apply to an estimated 141,594 workers in general industry and 270,581 workers in construction. OSHA estimates that 989 possible ILO 2/0 silicosis cases will be referred to specialists annually as a result of this medical surveillance.

OSHA's conclusion is that the requirements triggered by the action level will result in a very real and necessary, but non-quantifiable, reduction in risk beyond that provided by the PEL alone. OSHA has determined that these ancillary provisions (periodic exposure assessment, medical surveillance in general industry/maritime) will reduce significant risk in at least three ways: (1) Providing economic incentives to employers to reduce exposures to below 25 μg/m³ to avoid the costs of medical surveillance and exposure monitoring; (2) helping to ensure the PEL is not exceeded; and (3) providing medical exams to workers exposed at the action level, resulting in additional specialist referrals for X-ray findings consistent with silicosis and allowing employees who find out they have a silica-related disease to take action, such as changing jobs or wearing a respirator for additional protection. In sum, the ancillary provisions triggered by the action level in the final rule provide significant benefits to worker health by providing additional layers and types of protection to employees exposed to respirable crystalline silica. Medical surveillance is particularly important for this rule because those exposed at the action level are still at significant risk of illness. OSHA did not estimate, and the benefits analysis does not include, monetary benefits resulting from early discovery of illness. OSHA's choice of using an action level for exposure monitoring of one-half of the PEL is based on the Agency's enforcement experience with other standards, including those for inorganic arsenic (29 CFR 1910.1018), ethylene oxide (29 CFR 1910.1047), benzene (29 CFR 1910.1028), and methylene chloride (29 CFR 1910.1052).

In response to comments on the proposed rule and PEA, among other changes discussed in Chapter V, OSHA added familiarization costs and increased estimated training costs in the FEA, and increased the cost of an industrial hygienist when conducting exposure monitoring. These changes, however, were the result of OSHA revisions to its cost estimates, not changes to the text of the regulation. Medical surveillance and exposure assessments were the ancillary provisions that were the focus of regulatory alternatives in the PEA. For these reasons, the Agency has examined four regulatory alternatives (Regulatory Alternatives #3, #4, #5, and #6) involving changes to one or the other of these two ancillary provisions. These four regulatory alternatives are defined below and the incremental cost impact of each is summarized in Table VII-35. In addition, OSHA has qualitatively considered a regulatory alternative (Regulatory Alternative #7) that would remove all ancillary provisions.

Under Regulatory Alternative #3, the action level would be raised from 25 µg/m³ to 50 µg/m³ in the standard for general industry and maritime, while keeping the PEL at 50 µg/m³. As a result, exposure monitoring and medical surveillance requirements would be triggered only if workers were exposed above 50 µg/m³. No changes would be made to the construction standard because the medical surveillance trigger for that standard is respirator use, not an action level. As shown in Table VII-35, Regulatory Alternative #3 would reduce the annualized cost of the final rule by about $85 million, using a discount rate of 3 percent, and about $86 million using a discount rate of 7 percent.

Under Regulatory Alternative #4, the action level in general industry and maritime would remain at 25 µg/m³ but medical surveillance would now be triggered by the PEL, not the action level. As a result, medical surveillance requirements would be triggered only if workers in general industry and maritime were exposed above the PEL of 50 µg/m³. No changes would be made to the construction standard. This alternative is similar to Alternative #3, but because the action level would remain lower, the amount of exposure monitoring would not decrease in Alternative #4 (applicable to general industry and maritime (and for construction employers following the exposure monitoring method of compliance)), exposure monitoring is required when levels exceed the action level). As shown in Table VII-35, Regulatory Alternative #4 would reduce the annualized cost of the final rule by about $28 million, using a discount rate of 3 percent and about $29 million using a discount rate of 7 percent).

Under Regulatory Alternative #5, the only change to the final rule would be to the medical surveillance frequency requirements. Instead of requiring qualifying workers to be offered a medical check-up every three years, an annual medical check-up would be required to be offered. Assuming all workers will accept this offer, as shown in Table VII-35, Regulatory Option #5 would increase the annualized cost of the final rule by about $110 million, using a discount rate of 3 percent (and by about $108 million, using a discount rate of 7 percent).

Under Regulatory Alternative #6, medical surveillance would be triggered by the PEL (in general industry and maritime), not the action level, and all workers (including in construction) subject to medical surveillance would be required to have a medical check-up annually rather than triennially. As shown in Table VII-35, Regulatory Alternative #6 would cause a net increase of the annualized cost of the final rule by about $42 million, using a discount rate of 3 percent (and by about $40 million, using a discount rate of 7 percent).

While the Agency expects there will be substantial benefits related to its ancillary provisions, it does not have the same quantitative basis for estimating benefits, and therefore does not have quantitative estimates for the benefits of the preceding four regulatory alternatives.

The final regulatory alternative affecting ancillary provisions, Regulatory Alternative #7, would eliminate all of the ancillary provisions of the final rule, including exposure assessment, medical surveillance, training, regulated areas, and the written exposure control plan. This alternative would be difficult to justify legally in light of 29 U.S.C. 655(b)(5) and (b)(7) along with case law requiring OSHA to use ancillary provisions to reduce significant risk remaining at the PEL when these provisions result in more than a de minimis benefit to workers (see Section II, Pertinent Legal Authority). In any event, it should be noted that elimination of the ancillary provisions does not mean that all costs for ancillary provisions would disappear. In order to meet the PEL, employers would still commonly need to conduct exposure monitoring, train workers on the use of controls, and set up some kind of regulated areas (in general industry and maritime) to indicate where respirator use would be required. It is also likely that some employers would follow the many recommendations to provide medical surveillance for employees and establish a written exposure control plan. OSHA has not attempted to estimate the extent to which the costs of these activities would be reduced if they were not formally required.

OSHA finds that the benefits estimated under the final rule will not be fully achieved if employers do not implement the ancillary provisions of the final rule. For example, OSHA believes that the effectiveness of the final rule depends on regulated areas and the written exposure control plan to further limit exposures and on medical surveillance to identify disease cases when they do occur. For construction work, the written exposure control plan is an integral part of the overall scheme to protect workers engaged in activities covered by Table 1. Without this provision, workers would risk exposures from the activities of others and exposure monitoring would need to be significantly increased to ensure protection for those workers.

Both industry and worker groups have recognized that a comprehensive standard, as opposed to a PEL alone, is needed to protect workers exposed to respirable crystalline silica. For example, the industry consensus standards for crystalline silica, ASTM E 1132—06, Standard Practice for Health Requirements Relating to Occupational Exposure to Respirable Crystalline Silica, and ASTM E 2626—09, Standard Practice for Controlling Occupational Exposure to Respirable Crystalline Silica for Construction and Demolition Activities, as well as the draft proposed silica standard for construction developed by the Building and Construction Trades Department, AFL-CIO, have each included comprehensive programs. These recommended standards include provisions for methods of compliance, exposure monitoring, training, and medical surveillance (Document ID 1466; 1504; 1509.

3. A Regulatory Alternative That Modifies the Methods of Compliance

The final standard in general industry and maritime requires employers to implement engineering and work practice controls to reduce employees' exposures to or below the PEL. Where engineering and/or work practice controls are insufficient, employers are still required to implement them to reduce exposure as much as possible, and to supplement them with a respiratory protection program. Under the final construction standard, employers are given two options for compliance. The first option specifies, in Table 1 of the final rule, the exposure control methods and respiratory protection required for compliance when performing the specified task or operating the specified machines. Employers choosing this option must fully and properly implement the control methods and respiratory protection on the table to be considered to be in compliance with Table 1. The second option largely follows the requirements in the general industry and maritime standard: employers must conduct exposure monitoring and provide sufficient controls to ensure that their workers are not exposed above the PEL.

One regulatory alternative (Regulatory Alternative #8) involving methods of compliance would be to eliminate Table 1 as a compliance option in the construction sector. This was suggested by one commenter (Document ID 1950), as a means of promoting innovation.

As discussed in the Summary and Explanation in detail, OSHA fashioned the final rule as a sensible compromise between providing clear direction for employers, in a manner that reduces compliance burdens, and allowing for flexibility and innovation when desired. Table 1 is an option in the final rule that promotes both goals. While OSHA assumes that most establishments will choose to follow Table 1, in part to avoid the cost of monitoring, it is not a requirement. Employers are free to follow the other option (paragraph (d) of the standard) and conduct the required monitoring and devise their own means of complying with the PEL if they choose. To eliminate Table 1, therefore, would actually provide less flexibility and impose additional costs upon employers. OSHA therefore did not quantify costs or benefits for eliminating Table 1. Nonetheless, the Agency seriously doubts that there would be any additional benefits under Alternative #8, and concludes that removing the Table 1 option would significantly increase exposure monitoring costs by taking away a carefully crafted “safe harbor” provision from employers.

Regulatory Alternatives That Affect the Timing of the Standard

The final rule will become effective 90 days following publication of the final rule in the Federal Register. The provisions outlined in the construction standard will become enforceable one year following the effective date, except for those governing sample analysis (two years). The provisions set forth in the general industry and maritime standards will become enforceable two years following the effective date, with the exception that the engineering and work practice control requirements in the hydraulic fracturing industry will become enforceable five years after the effective date.

There are many theoretical options that OSHA could explore with regard to compliance dates. These include: Requiring the fracking industry to follow the same compliance schedule as all other general industry and maritime employers; going back to the dates originally proposed (one year for engineering controls, two years for laboratories, six months for all other provisions); allowing more time for all employers to comply with the final rule; or allowing less time for all employers to come into compliance. These options are explored in detail in the Summary and Explanation for DATES. As indicated in that discussion, there are technical issues, and there may be additional costs, associated with advancing the compliance dates ahead of those laid out in the final rule; in all cases, pushing back the compliance deadlines will also push back the onset of benefits generated by the final rule. OSHA has not quantified the costs or benefits of either advancing or delaying any of the compliance dates because the timing of the effective dates has the same percentage effect on both benefits and costs.

I. Final Regulatory Flexibility Analysis

The Regulatory Flexibility Act, as amended in 1996, requires an agency to prepare a Final Regulatory Flexibility Analysis (FRFA) whenever it promulgates a final rule that is required to conform to the notice-and-comment rulemaking requirements of section 553 of the Administrative Procedure Act (APA) (see 5 U.S.C. 601-612). For OSHA rulemakings, the FRFA analysis must contain:

1. A statement of the need for, and objectives of, the rule;

2. a statement of the significant issues raised by the public comments in response to the initial regulatory flexibility analysis, a statement of the assessment of the agency of such issues, and a statement of any changes made in the proposed rule as a result of such comments;

3. the response of the agency to any comments filed by the Chief Counsel for Advocacy of the Small Business Administration (SBA) in response to the proposed rule, and a detailed statement of any change made to the proposed rule in the final rule as a result of the comments;

4. a description of and an estimate of the number of small entities to which the rule will apply or an explanation of why no such estimate is available;

5. a description of the projected reporting, recordkeeping and other compliance requirements of the rule, including an estimate of the classes of small entities which will be subject to the requirement and the type of professional skills necessary for preparation of the report or record; and

6. a description of the steps the agency has taken to minimize the significant economic impact on small entities consistent with the stated objectives of applicable statutes, including a statement of the factual, policy, and legal reasons for selecting the alternative adopted in the final rule and why each one of the other significant alternatives to the rule considered by the agency which affect the impact on small entities was rejected; and for a covered agency, as defined in section 609(d)(2), a description of the steps the agency has taken to minimize any additional cost of credit for small entities. 5 U.S.C. 604.

The Regulatory Flexibility Act further states that the required elements of the FRFA may be performed in conjunction with or as part of any other agenda or analysis required by any other law if such other analysis satisfies the provisions of the FRFA. 5 U.S.C. 605.

In addition to these elements, OSHA also includes, in this section, the recommendations from the Small Business Advocacy Review (SBAR) Panel and OSHA's responses to those recommendations.

While a full understanding of OSHA's analysis and conclusions with respect to costs and economic impacts on small entities requires a reading of the complete FEA and its supporting materials, this FRFA summarizes the key aspects of OSHA's analysis as they affect small entities.

The Need for and Objectives of the Rule

Exposure to crystalline silica has been shown to increase the risk of several serious diseases. Crystalline silica is the only known cause of silicosis, which is a progressive respiratory disease in which respirable crystalline silica particles cause an inflammatory reaction in the lung, leading to lung damage and scarring, and, in some cases, to complications resulting in disability and death. In addition, many well-conducted investigations of exposed workers have shown that exposure increases the risk of mortality from lung cancer, chronic obstructive pulmonary disease (COPD), and renal disease. OSHA's detailed analyses of the scientific literature and silica-related health risks were presented in OSHA's Review of Health Effects Literature and Preliminary QRA in the NPRM (Document ID 1711, pp. 7-229), and are included in Section VI Significance of Risk in this preamble.

OSHA reviewed numerous studies and found that they all demonstrated positive, statistically significant exposure-response relationships between exposure to crystalline silica and lung cancer mortality (see the Health Risk section in this preamble for more detail). In addition, OSHA noted that in 2009 the International Agency for Research on Cancer (IARC) reaffirmed its finding that respirable crystalline silica is a human carcinogen, identifying in its analysis an overall positive exposure-response relationship between cumulative exposure to crystalline silica and lung cancer mortality (see Section VI, Significance of Risk; Document ID 1711, pp. 269-292). Based on studies, OSHA estimates that the lifetime lung cancer mortality excess risk associated with 45 years of exposure to respirable crystalline silica ranges from 11 to 54 deaths per 1,000 workers at the preceding general industry PEL of 100 µg/m³ respirable crystalline silica, with that risk reduced to 5 to 23 deaths per 1,000 workers at the new PEL of 50 µg/m³ respirable crystalline silica.

OSHA has also quantitatively evaluated the mortality risk from non-malignant respiratory disease, including silicosis and COPD. Risk estimates for silicosis mortality are based on a study by Mannetje et al. (2002b, Document ID 1089), as reanalyzed by ToxaChemica, Inc. (2004, Document ID 0469), which pooled data from six worker cohort studies to derive a quantitative relationship between silica exposure and death rate for silicosis. For non-malignant respiratory disease generally, risk estimates are based on an epidemiologic study of diatomaceous earth workers, which included a quantitative exposure-response analysis (Park et al., 2002, Document ID 0405). For 45 years of exposure to the preceding general industry PEL, OSHA's estimates of excess lifetime risk are 11 silicosis deaths per 1,000 workers for the pooled analysis and 85 non-malignant respiratory disease deaths per 1,000 workers based on Park et al.'s (2002) estimates (Document ID 0405). At the new PEL, OSHA estimates silicosis and non-malignant respiratory disease mortality at 7 and 44 deaths per 1,000, respectively. As noted by Park et al. (2002) (Document ID 0405), it is likely that silicosis as a cause of death is often misclassified as emphysema or chronic bronchitis; thus, Mannetje et al.'s analysis of deaths may tend to underestimate the true risk of silicosis mortality, while Park et al.'s (2002) analysis would more fairly capture the total respiratory mortality risk from all non-malignant causes, including silicosis and COPD.

OSHA also identified five studies that quantitatively described relationships between exposure to respirable crystalline silica and silicosis morbidity, as diagnosed from chest radiography. Based on the results of these studies, OSHA estimates a cumulative risk for silicosis morbidity of 60 to 773 cases per 1,000 workers for a 45-year exposure to the preceding general industry PEL of 100 µg/m³ respirable crystalline silica, and 20 to 170 cases per 1,000 workers exposed at the new PEL of 50 µg/m³ (see Section VI, Significance of Risk, Table VI-1).

OSHA's estimates of crystalline silica-related renal disease mortality risk are derived from an analysis by Steenland et al. (2002, Document ID 0448), in which data from three cohort studies were pooled to derive a quantitative relationship between exposure to silica and the relative risk of end-stage renal disease mortality. The cohorts included workers in the U.S. gold mining, industrial sand, and granite industries. OSHA's analysis for renal disease mortality shows estimated lifetime excess risk of 39 deaths per 1,000 workers at the preceding general industry PEL of 100 µg/m³ respirable crystalline silica, and 32 deaths per 1,000 workers exposed at the new PEL of 50 µg/m³ (see Section VI, Significance of Risk, Table VI-1).

The objective of the final rule is to reduce the numbers of fatalities and illnesses occurring among employees exposed to respirable crystalline silica in general industry, maritime, and construction sectors. This objective will be achieved by requiring employers to install engineering controls where appropriate and to provide employees with the equipment, respirators, training, exposure monitoring, medical surveillance, and other protective measures necessary for them to perform their jobs safely. The legal basis for the rule is the responsibility given to the U.S. Department of Labor through the Occupational Safety and Health Act of 1970 (OSH Act). The OSH Act provides that, in promulgating health standards dealing with toxic materials or harmful physical agents, the Secretary “shall set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life.” 29 U.S.C. 655(b)(5) (see Section II, Pertinent Legal Authority for a more detailed discussion).

Summary of Significant Issues Raised by Comments on the Initial Regulatory Flexibility Analysis (IRFA) and OSHA's Assessment of, and Response to, Those Issues

Small business representatives commented on all aspects of this rule, and their comments and OSHA's responses are covered throughout this preamble and the FEA. This section of the FRFA focuses only on comments that directly concern this FRFA or the screening analysis that precedes it.

One commenter questioned the use of SBA definitions for small businesses, arguing that some definitions include firms with 500 employees or more, which, according to the commenter, are too large to constitute “small” businesses. The commenter commended OSHA for also including an analysis of very small entities with fewer than 20 employees (Document ID 2351, Attachment 1, p. 8). OSHA determined that both the analysis of the impacts on SBA-defined small entities and the analysis of the impacts on very small entities (those with fewer than twenty employees) are useful and important for examining small business impacts.

Two commenters were concerned that their industries had not been covered in the IRFA. The American Railroad Association noted that small railroads had not been covered (Document ID 2366, Attachment 1, p. 4). The commenter is correct that OSHA did not examine small entities in this sector in the IRFA. For the FEA, OSHA has added a discussion of small entities in the railroad industry to Chapter VI, Economic Impacts. The Sorptive Minerals Institute also stated that their industry was not covered in the IRFA (Document ID 4230, Attachment 1, p. 16). As discussed in Chapter IV, the sorptive mineral industry was covered as part of a larger industry. In any case, OSHA has excluded exposures that result from the processing of sorptive clays from the scope of the final rule.

Many commenters were concerned that OSHA had not used economic data that included the effects of the recent “great recession”. This issue was addressed in the Chapter VI Introduction, but some commenters specifically discussed this topic in reference to small entities (Document ID 1822, Attachment 1, p. 1; 2187, Attachment 1, p. 2; 2322, p. 13; 3433, p. 8; 4231, Attachment 1, pp. 15-17). Complete data of the kind that OSHA needs for a thorough analysis of economic impacts were not yet available at the time the PEA was developed. As discussed in Chapter II, Industrial profile, the FEA, including this FRFA, uses 2012, the most recent year with complete data, as a base year and used average profits from years including the recession and surrounding years.

Some commenters were concerned with OSHA's estimates of small business profits. One commenter pointed out that OSHA had relied entirely on C corporation data, even though many affected firms might be S corporations, partnerships or sole proprietorships (Document ID 2296, Attachment 1, p. 23). This is true, but there are no published data on S corporation, partnership, or sole proprietorship profits, and thus C corporation data is the best available data. As another commenter pointed out, reported profits of small business are generally lower than the total returns earned by owners who also act as executives for their firms. The same commenter explained that smaller firms have a great deal of flexibility in deciding what portions of entity gains are reported as profits, what portions are reported as management salaries, and what portions are reported as management bonuses (Document ID 2163, Attachment 1, p. 7). As a result, it is possible that OSHA has underestimated small firm profits and thus overestimated potential impacts on profits.

Stuart Sessions argued that OSHA should have analyzed whether smaller firms have higher or lower profits than larger firms (Document ID 4231, Attachment 1, pp. 11-12). The limited data supplied by Mr. Sessions, however, did not show that small firms either had larger or smaller profits than bigger firms on an across-industry basis (Document ID 4231, Attachment 1, p. 11). Mr. Sessions developed an economic model that used a combination of multiple data sources to determine profit rates of small firms (RMA and BizMiner). In Chapter III Industrial Profile, Revenue and Profit, OSHA discusses why the Agency's analysis does not use these alternate data sources suggested by Mr. Sessions. Mr. Sessions, testifying on behalf of the Construction Industry Safety Coalition, also testified that the use of data aggregated to the four-digit NAICS code level in OSHA's analysis shields small businesses from being captured properly in the analysis, and that “the analysis at the six-digit level would show substantial impacts for masonry contractors who are small business . . ., which the analysis currently doesn't show” (Document ID 3580, Tr. 1402). Mr. Sessions further claimed that, even though OSHA analyzed the costs to employers with 20 or fewer employees, the analysis still “hid” a lot of small businesses (Document ID 3580, Tr. 1402). The use of Internal Revenue Service's Corporation Source Book profit data at a four-digit NAICS code level is explained in Chapter III along with a discussion explaining why alternative data sources suggested by Mr. Sessions are not applied in the FEA.

At least one commenter argued that OSHA might have inaccurately estimated small firm revenues as a result of OSHA's method of projecting revenues for years when Census data are not available (Document ID 4231, Attachment 1, pp. 15-17). This argument is now moot, as OSHA is using data from the 2012 Economic Census, and is not using projected revenues in this analysis.

Some commenters argued that OSHA had not adequately accounted for diseconomies of scale in small firms (Document ID 4231, Attachment 1, pp. 2-5; 2307, Attachment 10, p. 25; 2322, Attachment 1, pp. 15-16). During his testimony, Stuart Sessions testified that it was his “guess . . . that small businesses are substantially more likely to be noncompliant currently than large businesses,” and requested that OSHA conduct additional analysis to “handle the differential compliance rates between small and large business” (Document ID 3580, Tr. 1399). As discussed in Chapter V, OSHA has changed its approach to estimating costs of small firms to account for diseconomies of scale in small firms. However, there is no evidence, other than Mr. Sessions's “guess,” that small firms are less compliant than large firms.

Janet Kaboth, testifying on behalf of a small company in the brick manufacturing industry, stated that small businesses are more impacted by the rule because they have more difficulty accessing capital to upgrade engineering controls:

[Engineering controls] must be purchased and paid for in the first year of compliance. . . . It is extremely unlikely that a small entity such as Whitacre Greer would be able to obtain a bank loan . . . for something that does not reduce costs or increase revenue and additionally adds cost (Document ID 3589, Tr. 3397-3399).

As discussed in Chapter VI, Economic Impacts, small firms will typically be able to pay for the first year costs of engineering controls from a single year's profits. Thus, there is no need to account for possible difficulties in obtaining credit.

A different commenter requested that OSHA provide additional guidance in Table 1 of the construction standard as a way to mitigate the impact on small businesses (Document ID 2322, p. 6). OSHA has done so, and agrees that it will likely ease compliance for small construction businesses because it provides them with task-specific guidance that will allow them to avoid more complicated exposure monitoring processes.

Many companies, associations, and private individuals submitted comments requesting a new SBAR Panel based a number of changes that have occurred since the SBAR Panel for this rule was held in 2003. The first and most common concern was that the economic data and information gathered during the Panel have become outdated and do not represent the dramatic changes in economic conditions that have resulted from the boom and bust economic cycle that occurred in the years following 2003 (Document ID 2224, p. 2; 2004, p. 1; 3580, Tr. 1274-1276; 1779, p. 2; 1767, p. 2; 1783, p. 1; 2140, p. 1; 3495, p. 2; 1798, p. 6; 1811, pp. 1-2; 2023, p. 1; 2222, p. 1; 2224, p. 2; 2230, p. 1; 2248, Attachment 1, p. 5; 2294, p. 2; 2300, p. 2; 2305, p. 13; 2279, p. 11; 2289, p. 9; 2391, p. 2; 3275, pp. 2-3; 2075, p. 4; 2083, p. 1; 2114, Attachment 1, p. 2; 2150, p. 2; 2170, Attachment 1, p. 1; 2210, Attachment 1, pp. 1-2; 4194, p. 5; 4210, Attachment 1, p. 2; 4217, Attachment 1, p. 7). Some commenters claimed that their industries have not recovered from the recession of 2008 and feel that their economic circumstances as small entities have changed as a result (Document ID 1779, p. 2; 1767, p. 2; 1783, p. 1; 2140, p. 1; 3495, p. 2).

OSHA conducted the SBAR Panel early in the rulemaking process in order to address small business concerns during the development of the proposed rule. The Agency used information gathered during the SBAR Panel to make significant changes to the proposed rule itself, as well as to the cost, impact, and other analyses contained in the proposal. OSHA's proposal contained six pages of tables that described every recommendation from the SBAR Panel, along with the Agency's responses.

OSHA's extensive rulemaking process included small business feedback not only from the original SBREFA review in 2003, but also from the subsequent written comment period in 2013 and 2014, as well as from the public hearings held in 2014. The rulemaking record shows the major issues that arose with respect to technological feasibility, costs, economic feasibility, and possible alternatives to the proposed rule represented largely the same issues addressed by small entity representatives (SERs) in 2003. To the extent there may be new issues that have arisen since the SBAR Panel made its recommendations, OSHA is confident that commenters, including small entities and the Small Business Administration's Office of Advocacy, were able to raise those issues and express whatever concerns they had about them later in the rulemaking process. OSHA has addressed comments regarding recent and current economic conditions under which small businesses are operating by considering this information in developing the final rule and supporting analyses.

A second concern raised by commenters who were advocating for OSHA to hold a new SBAR Panel, related to the changes in technology and work practices that have taken place over the last ten years. For example, one commenter claimed that the comments of the SERs were not reflective of the greater use of tools with dust collection capability, and other devices currently being used that release water at the point of cutting, to control silica dust (Document ID 2210, Attachment 1, p. 1). However, the commenters who wanted OSHA to account for improved technology and work practices did not generally provide information to supplement or update the information OSHA received from the SERs, despite opportunities to do so.

While there has been progress in the development and adoption of technologies that reduce silica exposures, the record (including comments from the commenters calling for a new Panel) brought out few, if any, fundamentally new technologies for reducing silica exposure. In any event, the advancement of technologies that would improve silica control or reduce the cost impact of the final rule would not necessitate a new SBAR panel.

There were also a number of construction firms that expressed disappointment at not being able to comment on Table 1, as presented in the proposed rule, prior to the proposed rule being issued (Document ID 2187, p. 22; 4217, Attachment 1, p. 7; 3580, Tr. 1274-1276). It is typical for OSHA to modify a rule as a result of the SBREFA process. The SBREFA process is a one-time requirement, not a requirement to conduct a new Panel every time a rule is altered in response to SBAR Panel recommendations. The commenters, who did have the opportunity to comment on Table 1 once it was proposed, did not present any compelling argument regarding how the timing of their opportunity to comment impacted their ability to communicate their recommendations about Table 1 to OSHA. The Agency notes that it has made a number of significant changes to Table 1 since the proposal, most in response to post-proposal comments, so it is clear that commenters had ample opportunities to recommend improvements to Table 1.

No SERs from the hydraulic fracturing industry were included in the 2003 SBAR panel. OSHA did not determine that this industry would be affected by this rule until the preparation of the NPRM and the PEA. As a result, OSHA has received comments from associations and businesses requesting a new SBAR Panel that would allow a more detailed analysis of the potential impacts on small entities in this industry. Commenters pointed out that the unique economic circumstances of the hydraulic fracturing industry were not presented for public comment or analysis on regulatory alternatives and small business impacts during the Agency's 2003 SBAR Panel (Document ID 2301, Attachment 1, p. 63; 3589, pp. 15-16; 2288, p. 5).

OSHA is not required to assure that every industry affected by a rule is represented on the Panel by a SER. The hydraulic fracturing industry had extensive opportunities to comment throughout this rulemaking process. In fact, a number of commenters, including several trade associations, submitted comments and testified at the hearing, providing analysis of the hydraulic fracturing industry for the record. OSHA sees no indication that the record would be better developed by convening a different SBAR panel with a SER from the hydraulic fracturing industry. OSHA has, however, extended the compliance deadline for these firms to install the required engineering controls required by this final rule to five years; three more years than for establishments in general industry and four more years than for construction firms.

Response to Comments by the Chief Counsel for Advocacy of the Small Business Administration and OSHA's Response to Those Comments

The Chief Counsel for Advocacy of the Small Business Administration (“Advocacy”) provided OSHA with comments on this rule on February 11, 2014 (Document ID 2349). Advocacy provided comment on OSHA's risk assessment and benefits analysis; technological feasibility analysis; cost analysis; current economic conditions; preferred alternatives; and procedural issues.

Risk Assessment and Benefits Issues

With respect to the risk assessment, Advocacy was concerned that OSHA was attributing benefits to reducing the PEL to 50 μg/m³ that perhaps would better be attributed to eliminating exposures above the existing PEL of 100 μg/m³ (Document ID 2349, pp. 3-4). OSHA does not think this is the case. As discussed in the section on significant risk, OSHA did not assess the risk of silica exposure by attributing existing known cases of silicosis or any other disease to various PELs. Rather, OSHA examined risk assessment studies that assessed the long term consequences of various levels of exposure to silica. Such studies focus on estimating the morbidity and mortality that result from changing lifetime exposure levels from the preceding PELs of 100 μg/m³ in general industry and 250 μg/m³ in construction to the new PEL of 50 μg/m³.

Advocacy also expressed concerns about the accuracy of older exposure data (Document ID 2349, p. 4). OSHA's exposure profile, used for examining feasibility and benefits, now shows only exposures measured after 1990 and includes data from OSHA's OIS system for 2011 to 2014.

Advocacy was also concerned that OSHA might not have adequately accounted for varying risk levels associated with different types of silica (Document ID 2349, p. 4). OSHA carefully considered this issue in the risk assessment section and found there were insufficient data to demonstrate significant risk for silica exposures that result from processing sorptive clays. As a result, OSHA excluded this processing activity from the scope of the final standard. OSHA found that, while the risk from other forms of silica may vary, there is evidence of significant risk for all of the other forms of respirable crystalline silica.

Advocacy also reported that small business representatives were concerned that “OSHA's assumption that silica exposure occurs over a working life of eight hours per day for 45 years does not reflect modern working conditions” (Document ID 2349, p. 4). OSHA is required by the OSH Act to consider the risk of a hazard over a worker's entire working life (see 29 U.S.C. 655(b)(5)). In Chapter VII of the FEA, OSHA also examined other possible average tenure assumptions.

Advocacy also reported that small business representatives “noted the uncertainty of assessing silica-related risk because of confounding factors, such as smoking or exposure to other chemicals, and the long latency period for silica-related illness to appear” (Document ID 2349, p. 4). OSHA notes in Section VI, Significance of Risk, in this preamble that study after study finds that incidence of the diseases caused by exposure to silica rises with increasing exposures to silica. In order to see this type of result, and for those results to be driven by smoking as a confounding factor, it would be necessary not just that the silica-using population smoke more than the comparable non-silica using population, but also that smoking rates rise as silica exposures increase. This seems very unlikely and there is no evidence in the record that this is the case.

Technological Feasibility Issues

Advocacy noted that small business representatives had raised many concerns about whether the controls OSHA indicated as appropriate to achieve the PEL were feasible in all circumstances and could, in fact, allow an employer to fully achieve the PEL (Document ID 2349, p. 4). OSHA has thoroughly examined all comments on this kind of issue across all affected industries in Chapter IV of the FEA, and OSHA notes that employers may raise infeasibility as a defense in enforcement actions. Advocacy also noted that small business representatives were concerned about whether available methods of measuring exposure were sufficiently accurate to correctly measure the action level and PEL (Document ID 2349, p. 4). OSHA has explained in Chapter IV of the FEA why existing equipment is sufficiently accurate to correctly measure airborne respirable silica at the levels established by the new PEL and action level.

Advocacy said that one small business representative “noted that increasing the volume of air needed for additional ventilation could result in a violation of a facility's air permit” (Document ID 2349, p. 5). While the Agency does not believe that most small employers exhaust large enough volumes of air that the additional ventilation required by this final standard will result in needing to alter air permits, OSHA does acknowledge that this may be an issue for some employers. In order to reduce the burden, should this be the case, OSHA has given general industry employers an additional year to meet the PEL, and has added costs for firms subject to air permitting requirements to alter their permits to more fully assess the economic feasibility of this rule.

Advocacy also said that one small business representative “noted that creating regulated areas is not feasible in many open-design facilities” (Document ID 2349, p. 5). Regulated area requirements have been a part of OSHA health standards for many years and employers have consistently found ways to make them work. The Agency does not expect that establishing a regulated area for silica would be any more difficult than establishing such an area for any of the other substances for which OSHA has regulated area requirements. In addition, OSHA does not have a regulated area requirement in construction where workplaces (such as in road building or repair) are more mobile.

Cost Issues

Advocacy stated that small business representatives generally felt that OSHA underestimated costs, and were particularly concerned about OSHA's “cost per exposed worker” approach and OSHA's estimates of the number of workers whose exposures are controlled per engineering control (Document ID 2349, p. 5). The specific methodological issues that Advocacy mentions are issues for OSHA's general industry and maritime cost estimates, but not for construction cost estimates because the cost estimation methodologies for the construction sector are quite different and do not use the “cost per exposed worker” approach. OSHA has provided detailed responses to comments on costs in Chapter V. In general industry and maritime, OSHA continues to use the cost per exposed worker approach and defends this approach in Chapter V. OSHA has lowered its estimate of the number of workers whose exposures are reduced per engineering control in response to comments from small business representatives and others.

Advocacy also noted that small business representatives objected to OSHA focusing on the incremental cost of moving from the preceding PELs to the new PEL. Advocacy reported that small business representatives believed OSHA should have included the costs of reaching the preceding PEL in its analysis (Document ID 2349, p. 5). Contrary to Advocacy's suggestion, OSHA did not conduct the analysis this way because it would require an assumption that employers are not complying with OSHA's existing requirements to meet the preceding PEL, but would now choose to comply with a more stringent requirement. OSHA's exposure profiles do indicate that many employers are failing to meet the preceding PELs, but the question that the Agency has to address with this analysis for this rulemaking is whether OSHA should require employers to meet a lower PEL than the preceding PEL. The costs of meeting the preceding PEL are not relevant to that decision.

Issues Concerning Current Economic Conditions

Advocacy reported that “small business representatives stated that OSHA was using older economic data that does not reflect current economic conditions, and [thus] that OSHA's cost pass-through assumptions are unrealistic” (Document ID 2349, p. 5). For the FEA, OSHA is using 2012 as the base year for economic data and includes data from the recent recession in analyzing average industry profits and historical changes in profits and prices. OSHA has updated its findings on the ability of firms to pass costs on to buyers in light of the updated data, resolving Advocacy's concern on this issue.

Regulatory Alternatives

Advocacy commended OSHA for following the advice of small business representatives and adopting the Table 1 approach for the construction sector, but urged OSHA to make the table clearer, more workable, and more specific, and to relieve employers of any remaining duty to conduct exposure monitoring when engaged in Table 1 tasks (Document ID 2349, p. 6). OSHA has revised Table 1, as Advocacy and small business representatives suggested, to provide employers with a clear alternative to exposure monitoring and to provide greater clarity and specificity in the descriptions of controls.

Advocacy also urged OSHA to consider the option of leaving the PEL unchanged and instead improving enforcement, noting that this was the option most favored by small business representatives (Document ID 2349, p. 3). However, the OSH Act commands OSHA to protect workers from harmful substances by setting

. . . the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life.” 29 U.S.C. 655(b)(5).

The record does not indicate that workers are currently protected in accordance with the Act. There are currently two entirely different PELs, 100 μg/m³ in general industry and 250 μg/m³ in construction. The record does not suggest either that employers in construction cannot feasibly reach a lower PEL or that there is no significant risk below 250 μg/m³. The record shows that most employers in construction currently reach a PEL of 50 μg/m³ most of the time (see Chapter IV) and that it is economically feasible to do so (see Chapter VI).

OSHA did consider the option of lowering the construction PEL to 100 μg/m³ and leaving the general industry PEL unchanged. However, this action would not be in accordance with the OSH Act given that there is still significant risk at a PEL of 100 μg/m³ and that a lower PEL is both technologically and economically feasible. As shown in OSHA's risk assessment, there is still significant risk of material impairment of health at levels all the way down to a lower PEL of 25 μg/m³, but OSHA found compliance with the lower PEL of 25 μg/m³ to be technologically infeasible for all industries.

Finally, Advocacy urged OSHA to consider the option of abandoning the hierarchy of controls, which is OSHA's longstanding policy of preferring engineering controls and administrative controls over personal protective equipment such as respirators (Document ID 2349, pp. 4-5). This issue is addressed in the summary and explanation section discussion of the methods of compliance provision. It should also be noted that OSHA defines technological feasibility in terms of what can be accomplished with engineering controls, not in terms of what can be accomplished with respirators.

Issues With Respect to Small Business Participation

Advocacy also expressed concern that small businesses did not have adequate opportunity for participation in the rulemaking process and that the SBAR panel was held over ten years before the proposed rule was issued (Document ID 2349, p. 7). OSHA responded to these concerns in section two of this FRFA.

A Description and Estimate of the Number of Small Entities To Which the Rule Will Apply

OSHA has analyzed the impacts associated with this final rule, including the type and number of small entities to which the standard will apply. In order to determine the number of small entities potentially affected by this rulemaking, OSHA used the definitions of small entities developed by the Small Business Administration (SBA) for each industry.

OSHA estimates that approximately 646,000 small business or government entities would be affected by the silica standard. Within these small entities, roughly 1.4 million workers are exposed to crystalline silica and would be protected by this final standard. A breakdown, by industry, of the number of affected small entities is provided in Table III-6 in Chapter III of the FEA.

OSHA estimates that approximately 579,000 very small entities would be affected by the silica standard. Within these very small entities, roughly 785,000 workers are exposed to crystalline silica and would be protected by the standard. A breakdown, by industry, of the number of affected very small entities is provided in Table III-7 in Chapter III of the FEA.

A Description of the Projected Reporting, Recordkeeping, and Other Compliance Requirements of the Rule

Tables VII-36 and VII-37 show the average costs of the silica standard and the costs of compliance as a percentage of profits and revenues by NAICS code for, respectively, small entities (classified as small by SBA) and very small entities (those with fewer than 20 employees). The costs for SBA defined small entities ranges from a low of $295 per entity for entities in NAICS 238200 Building Equipment Contractors, to a high of about $161,651 for NAICS 213112 Support Activities for Oil and Gas Operations.

The cost for very small entities ranges from a low of $223 for entities in NAICS 238200 Building Equipment Contractors, to a high of about $119,072 for entities in NAICS 213112 Support Activities for Oil and Gas Operations.

Tables VII-38a and VII-38b show the unit costs which form the basis for OSHA's cost estimates for the average small entity and very small entity.

Description of the Steps OSHA Has Taken To Minimize the Significant Economic Impact on Small Entities Consistent With the Stated Objectives of Applicable Statutes and Statement of the Reasons for Selecting the Alternative Adopted in the Final Rule

OSHA has made a number of changes in the final silica rule that will serve to minimize significant impacts on small entities consistent with the objectives of the OSH Act.

First, OSHA has made two changes to the scope of the rule that will minimize impacts for small business. OSHA has eliminated from the scope of the rule exposures that result from the processing of sorptive clays. OSHA's analysis did not determine whether any or all of the processers of sorptive minerals are small businesses, but to the extent they are, this change will reduce impacts on such entities. OSHA has also rewritten the scope of the rule with respect to the coverage of employers whose employees are exposed to silica at levels below the action level. The final rule does not apply to employers in general industry and maritime where the employer has objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 μg/m³ as an 8-hour time-weighted average under any foreseeable conditions, and does not apply in construction where employee exposure will remain below 25 μg/m³ as an 8-hour time-weighted average under any foreseeable conditions (see Scope in Section XV, Summary and Explanation of the Standards). OSHA expects that these changes may remove all compliance duties for some small businesses, possibly including carpenters, plumbers, and electricians, whose employees' only exposures to respirable crystalline silica is in small amounts for short-duration tasks that are performed infrequently.

OSHA also revised Table 1 for the construction industry in ways that will minimize impacts on small businesses. OSHA requested comment on the approach for construction in the NPRM. After carefully reviewing the comments received on this issue, the Agency significantly revised the structure of the construction rule to focus on the tasks known to generate high exposures to respirable crystalline silica and to expand Table 1 to cover almost all of them (tunnel boring and abrasive blasting are the exceptions). Under this final rule, where employers fully and properly implement the specified engineering controls, work practices, and respiratory protection for each employee engaged in a task identified on Table 1, the employer is not also required to conduct exposure assessments to determine compliance with the PEL. Specifying the kinds of dust controls for construction tasks that are expected to reduce exposures to the 50 µg/m³ target, as an option in lieu of a performance-oriented approach involving a PEL and regular exposure assessment, will make compliance easier for construction employers. Some commenters indicated that this specific guidance is particularly beneficial to small businesses that may not have as many resources to develop their own compliance plans (e.g., Document ID 2322-A1, p. 16). The Agency also revised the notes and specifications on Table 1 to clarify what is required for employers to fully and properly implement the specified engineering controls, work practices, and respiratory protection for tasks on Table 1 (see Specified Exposure Control Methods in Section XV, Summary and Explanation of the Standards).

After carefully reviewing the comments received on respiratory protection requirements for the construction standard and the exposure data in the record (described in Chapter IV of the FEA), OSHA identified those situations where respiratory protection is necessary and made significant revisions to the respiratory protection requirements specified on Table 1 based on those findings. The result is that respiratory protection is not required for most of the tasks covered by Table 1 (see Specified Exposure Control Methods in Section XV, Summary and Explanation of the Standards).

For this final rule, the Agency has significantly revised the requirements for initial exposure assessment and periodic exposure assessment in order to provide employers with greater flexibility. The standard allows the employer to use either the performance option or the scheduled monitoring option for initial and periodic exposure assessments. OSHA also clarified that the performance option provides employers with flexibility in the methods used to assess employee exposures, and provided examples of how employers can accurately characterize employee exposures using the performance option (see Exposure Assessment discussion in Section XV, Summary and Explanation of the Standards).

At the suggestion of many commenters, OSHA has eliminated regulated area/access control plan requirements in construction. Employers in construction now have more flexibility in determining the best way to control exposures through a written exposure control plan.

In the final rule, OSHA has agreed with many commenters to eliminate the requirements for protective clothing, and thus has reduced costs to small businesses.

OSHA requested comment on the use of wet methods as a substitute for dry sweeping in the NPRM. After carefully reviewing the comments received on this issue, the Agency revised the provision to prohibit dry sweeping only where such activity could contribute to employee exposure to respirable crystalline silica. Moreover, the standard contains an exception to the prohibition on dry sweeping in such circumstances if wet sweeping, HEPA-filtered vacuuming, or other methods that minimize the likelihood of exposure are not feasible (see Housekeeping in Section XV, Summary and Explanation of the Standards).

In the NPRM, OSHA requested comment on the prohibition of employee rotation to achieve compliance when exposure levels exceed the PEL. After carefully reviewing the comments received on this issue, OSHA removed the prohibition on employee rotation from the rule (see Methods of Compliance in Section XV, Summary and Explanation of the Standards).

OSHA examined the issue of a 30-day exemption in the NPRM. After carefully reviewing the comments received on this issue, the Agency decided not to include a 30-day exemption from the requirement to implement engineering and work practice controls. However, OSHA clarified that where engineering controls are not feasible, such as for certain maintenance and repair activities, the use of respirators is permitted (see Methods of Compliance and Respiratory Protection in Section XV, Summary and Explanation of the Standards).

OSHA adopted these alternatives to reduce costs and regulatory burdens consistent with the requirements of the OSH Act and court interpretations of the Act. For health standards issued under section 6(b)(5) of the OSH Act, OSHA is required to promulgate a standard that reduces significant risk to the extent that it is technologically and economically feasible to do so (see Section II, Pertinent Legal Authority, for a full discussion of OSHA legal requirements).

OSHA has conducted an extensive review of the literature on adverse health effects associated with exposure to respirable crystalline silica. The Agency has also developed estimates of the risk of silica-related diseases assuming exposure over a working lifetime at the proposed PEL and action level, as well as at OSHA's preceding PELs. These analyses are summarized in this preamble in Section V, Health Effects and Quantitative Risk Analysis. The available evidence indicates that employees exposed to respirable crystalline silica well below the preceding PELs are still at increased risk of lung cancer mortality and silicosis mortality and morbidity. Occupational exposures to respirable crystalline silica also may result in the development of kidney and autoimmune diseases and in death from other nonmalignant respiratory diseases, including chronic obstructive pulmonary disease (COPD).

As discussed in Section VI, Significance of Risk, in this preamble, OSHA determined that worker exposure to respirable crystalline silica constitutes a significant risk and that the final standard will substantially reduce this risk. Further, there is significant risk well below the new PEL of 50 μg/m³, but OSHA has determined that achieving a PEL of 25 μg/m³ is not technologically feasible.

Section 6(b) of the OSH Act requires OSHA to determine that its standards are technologically and economically feasible. OSHA's examination of the technological and economic feasibility of the final rule is presented in the FEA and FRFA. OSHA has concluded that the new PEL of 50 μg/m³ is technologically feasible for all affected sectors in general industry and maritime and that Table 1 is technologically feasible for construction.

For those few operations where the new PEL is not technologically feasible, even when workers use recommended engineering and work practice controls, employers can supplement controls with respirators to achieve exposure levels at or below the new PEL.

OSHA developed quantitative estimates of the compliance costs of the final rule for each of the affected industry sectors in Chapter V of the FEA. The estimated compliance costs were compared with industry revenues and profits to provide a screening analysis of the economic feasibility of complying with the revised standard and an evaluation of the potential economic impacts in Chapter VI of the FEA. Industries with unusually high costs as a percentage of revenues or profits were further analyzed for possible economic feasibility issues. After performing these analyses, OSHA has concluded that compliance with the requirements of the final rule will be economically feasible in every affected industry sector.

OSHA has also provided analyses of the costs and benefits of alternative PELs, though it should be pointed out these are for informational purposes only. Benefit cost analysis cannot be used as a decision criteria for OSHA health standards under the OSH Act. OSHA has examined two regulatory alternatives (named Regulatory Alternatives #1 and #2) that would have modified the PEL for the final rule. Under Regulatory Alternative #1, the PEL would have been 100 μg/m³ for all affected industry sectors, and the action level would have been 50 μg/m³ (thereby keeping the action level at one-half of the PEL). For the construction sector under Regulatory Alternative #1, Table 1 requirements for respirator use would have been eliminated for all workers performing Table 1 tasks. Under this alternative, only abrasive blasters and underground construction workers would have been required to wear respiratory protection, and only workers wearing respirators in these operations would have been subject to the medical surveillance provision. Under Regulatory Alternative #2, the PEL would have been 25 μg/m³ for all affected industry sectors, while the action level would have remained at 25 μg/m³ (because of difficulties in accurately measuring exposure levels below 25 μg/m³). For the construction sector under Regulatory Alternative #2, Table 1 requirements would have been modified to include respiratory protection for all workers covered under Table 1, and all these covered workers would have been subject to the medical surveillance provision.

Table VII-39 presents, for informational purposes, the estimated costs, benefits, and net benefits of the final rule under Regulatory Alternatives #1 and #2, using alternative discount rates of 3 and 7 percent. The tables also present the incremental costs, the incremental benefits, and the incremental net benefits of going from a PEL of 100 μg/m³ to the new PEL of 50 μg/m³ and then of going from the new PEL of 50 μg/m³ to a PEL of 25 μg/m³ for general industry and maritime, as well as the effects in construction of the corresponding changes to Table 1 under Regulatory Alternatives #1 and #2. Table VII-39 breaks out costs by provision and benefits by type of disease and by morbidity/mortality.

Because OSHA determined that a PEL of 25 μg/m³ would not be feasible (that is, engineering and work practices would not be sufficient to reduce and maintain silica exposures to a PEL of 25 μg/m³ or below in most operations most of the time in the affected industry sectors in general industry and maritime), the Agency did not attempt to identify engineering controls or their costs for this alternative PEL. Instead, for purposes of estimating the costs of going from a PEL of 50 μg/m³ to a PEL of 25 μg/m³, OSHA assumed that all workers exposed between 50 μg/m³ and 25 μg/m³ would have to wear respirators to achieve compliance with a PEL of 25 μg/m³. OSHA then estimated the associated additional costs for respirators, exposure assessments, medical surveillance, and regulated areas (the latter three for ancillary requirements specified in the final rule). For the construction sector under Regulatory Alternative #2, as previously indicated, Table 1 requirements would be modified to include respiratory protection for all covered workers, and all covered workers would be subject to the medical surveillance provision.

As shown in Table VII-39, going from the final rule to Regulatory Alternative #2 would prevent, annually, an additional 295 silica-related fatalities and an additional 122 cases of silicosis. These estimates support OSHA's finding that there is significant risk remaining at the new PEL of 50 μg/m³. However, the Agency has determined that it cannot select Regulatory Alternative #2 because a PEL of 25 μg/m³ is not technologically feasible and this alternative would require extensive use of respirators for those using Table 1 under the construction standard (see the Technological Feasibility Summary in this preamble for a further discussion of the feasibility of a PEL of 25 μg/m³).

Recommendations From the SBAR Panel and OSHA's Responses

Table VII-40 lists all of the SBAR Panel recommendations and OSHA's responses to these recommendations.

VIII. Paperwork Reduction Act

The final general industry/maritime (“the general industry standard”) and construction standards (“the standards”) for respirable crystalline silica contain collections of information (also referred to as “paperwork” requirements) that are subject to review by the Office of Management and Budget (OMB). In accordance with the Paperwork Reduction Act (PRA) (44 U.S.C. 3506(c)(2)), OSHA solicited public comments on the Respirable Crystalline Silica Standards for General Industry, Shipyard Employment and Maritime Terminals (29 CFR 1910.1053) and Construction (29 CFR 1926.1053) Information Collection Request (ICR) (paperwork burden hour and cost analysis) for the proposed rule. The Department also submitted this ICR to OMB for review in accordance with 44 U.S.C. 3507(d) on September 12, 2013. On January 23, 2014, OMB authorized the Department to use OMB Control Number 1218-0266 in future paperwork submissions involving this rulemaking. OMB commented, “This OMB action is not an approval to conduct or sponsor an information collection under the Paperwork Reduction Act of 1995” (see http://www.reginfo.gov/public/do/PRAViewICR?ref_nbr=201111-1218-004 ).

The proposed rule invited the public to submit comments to OMB, in addition to OSHA, on the proposed collections of information with regard to the following:

• Whether the proposed collections of information are necessary for the proper performance of the Agency's functions, including whether the information is useful;
• The accuracy of OSHA's estimate of the burden (time and cost) of the collections of information, including the validity of the methodology and assumptions used;
• The quality, utility, and clarity of the information collected; and
• Ways to minimize the compliance burden on employers, for example, by using automated or other technological techniques for collecting and transmitting information (78 FR 56438).

No public comments were received specifically in response to the proposed ICR and supporting documentation submitted to OMB for review. However, public comments submitted in response to the Notice of Proposed Rulemaking (NPRM), described earlier in this preamble, substantively addressed collections of information and contained information relevant to the burden hour and costs analysis. OSHA considered these comments when it developed the revised ICR associated with these final rules.

The Department of Labor submitted the final ICR on the date of publication, containing a full analysis and description of the burden hours and costs associated with the collections of information of the final rule, to OMB for approval. A copy of the ICR is available to the public at http://www.reginfo.gov/public/do/PRAViewICR?ref_nbr=201509-1218-004 (this link will only become active the day following publication of this notice). OSHA will publish a separate notice in the Federal Register that will announce the results of that review. That notice will also include a summary of the collections of information and burdens imposed by the new standard. A Federal agency cannot conduct or sponsor a collection of information unless it is approved by OMB under the PRA, and the collection of information notice displays a currently valid OMB control number (44 U.S.C. 3507(a)(3)). Also, notwithstanding any other provision of law, no employer shall be subject to penalty for failing to comply with a collection of information if the collection of information does not display a currently valid OMB control number (44 U.S.C. 3512).

The major collections of information found in the standards are listed below.

The collections of information in the rule are needed to assist employers in identifying and controlling exposures to respirable crystalline silica in the workplace, and to address respirable crystalline silica-related adverse health effects. OSHA will also use records developed in response to these standards to determine compliance.

The final rule imposes new collections of information for purposes of the PRA. In response to comments on the proposed rule, OSHA has revised provisions of the final rule that affect the collections of information. These revisions include:

—An exception in paragraph (a)(2) of the general industry standard for those circumstances where the employer has objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 micrograms per cubic meter of air (25 μg/m³) as an 8-hour time-weighted average (TWA) under any foreseeable conditions. The construction standard also provides an exception where employee exposure will remain below 25 μg/m³ as an 8-hour TWA under any foreseeable conditions (paragraph (a)). However, the exception in the construction standard does not require the employer to have objective data to support the exception.

—An additional exemption in the general industry standard for occupational exposures that result from the processing of sorptive clays (paragraph (a)(1)(iii)).

—Revisions to paragraph (d) of the general industry standard (paragraph (d)(2) for construction), which sets forth requirements for assessing employee exposures to respirable crystalline silica, including revisions to:

○ General requirements for exposure assessment. Paragraph (d)(1) of the general industry standard (paragraph (d)(2)(i) in construction) was revised and restructured to allow employers to use either the performance option or the scheduled monitoring option to meet their initial and periodic exposure assessment obligations. More specifically, these revisions include replacing the proposed (d)(1)(ii) and (d)(1)(iii), all of (d)(2), and (d)(3) with a simplified general requirement to assess exposures when exposures are expected to be at or above the action level using either the performance option or the scheduled monitoring option. Thus, the final rule does not contain an initial assessment requirement like the proposed rule. Initial monitoring is only required under the scheduled monitoring option and has to be performed as soon as work begins. The proposed standard included a requirement to assess the exposure of employees expected to be exposed to respirable crystalline silica at or above the action level, which consisted of an initial monitoring of employees, unless monitoring had been performed in the previous 12 months, or the employer had objective data to demonstrate that exposures would be below the action level under any expected conditions, as well as periodic exposure assessments, depending on the results of initial monitoring, following either a scheduled monitoring option or a performance option. These revisions from the proposed rule emphasize the performance option in order to provide additional flexibility for employers who are able to characterize employee exposures through alternative methods. However, the content of the performance option requirement remains the same as the content of the proposed requirement.

○ OSHA has also not established time limitations for air monitoring results used to characterize employee exposures under the performance option. Although the proposed rule limited employers using air monitoring data for initial exposure assessment purposes to data obtained no more than twelve months prior to the rule's effective date, there were no such time restrictions on monitoring data used to conduct periodic exposure assessments under the performance option. Nevertheless, many commenters found the 12-month limit on the use of monitoring results for initial exposure assessments using existing data to be too restrictive. OSHA has been persuaded by these commenters not to establish time limitations for monitoring results used to assess exposures under the performance option, as long as the employer can demonstrate the data accurately characterize current employee exposures to respirable crystalline silica.

○ Scheduled monitoring option. Paragraph (d)(3) of the general industry standard (paragraph (d)(2)(iii) for construction) describes the scheduled monitoring option, which provides employers with a clearly defined, structured approach to assessing employee exposures. OSHA made a number of minor changes to the requirements for periodic monitoring under the scheduled monitoring option (paragraphs (d)(3)(iii)-(d)(3)(v) of the general industry standard, paragraphs (d)(2)(iii)(C)-(d)(2)(iii)(E) in construction) to clarify that the “most recent” exposure monitoring sample determines how often an employer must monitor.

○ Revisions to requirements to reassess exposures. Paragraph (d)(4) of the general industry standard (paragraph (d)(2)(iv) in construction) requires employers assessing exposures using either the performance option or the scheduled monitoring option to reassess employee exposures whenever there has been a change in the production, process, control equipment, personnel, or work practices that may reasonably be expected to result in new or additional exposures to respirable crystalline silica at or above the action level, or when the employer has any reason to believe that new or additional exposures at or above the action level have occurred. OSHA added the phrase “or when the employer has any reason to believe that new or additional exposures at or above the action level have occurred” to the proposed language to make clear that reassessment of exposures is required whenever there is reason to believe that a change in circumstances could result in new or additional exposures at or above the action level.

—The addition of paragraph (f)(2)(i) of the general industry standard (paragraph (g)(1) of the construction standard), which requires employers to establish and implement a written exposure control plan for all employees covered by the rule. Under paragraph (f)(2)(i)(A)-(C) (paragraphs (g)(1)(i)-(iii) of the construction standard), the written exposure control plan must contain a description of: The tasks in the workplace that involve exposure to respirable crystalline silica; the engineering controls, work practices, and respiratory protection used to limit employee exposure to respirable crystalline silica for each task; and a description of the housekeeping measures used to limit employee exposure to respirable crystalline silica. Paragraph (g)(1)(iv) of the construction standard requires the written exposure control plan to contain a description of the procedures used to restrict access to work areas, when necessary, to minimize the number of employees exposed to respirable crystalline silica and their level of exposure, including exposures generated by other employers or sole proprietors. OSHA did not propose a requirement for a written exposure control plan, but requested comment on whether to include one in the final rule. The final rule does not include the proposed written access control plan that the employer could prepare in lieu of establishing regulated areas that would only apply to areas with PEL exceedances.

—Alterations to paragraph (i)(1)(i) of the general industry standard, which requires employers to make medical surveillance available at no cost to the employee, and at a reasonable time and place, for each employee who will be occupationally exposed to respirable crystalline silica at or above the action level for 30 or more days per year. Paragraph (h)(1)(i) of the construction standard requires employers to make medical surveillance available to employees who will be required by the standard to use a respirator for 30 or more days per year. In the proposed standards, OSHA specified that employers must make medical surveillance available to those employees who would be occupationally exposed to respirable crystalline silica above the PEL for 30 or more days a year.

—Revisions to the medical surveillance exam requirements in paragraph (i)(2)(iii) of the standard (paragraph (h)(2)(iii) of the standard for construction), which allow digital X-rays, in addition to film X-rays, and no longer allow for an equivalent diagnostic study. The paragraph requires a chest X-ray (a single posteroanterior radiographic projection or radiograph of the chest at full inspiration recorded on film (no less than 14 x 17 inches and no more than 16 x 17 inches) or digital radiography systems) interpreted and classified according to International Labour Office (ILO) International Classification of Radiographs of Pneumoconiosis by a NIOSH-certified B Reader. The only substantive changes from the proposed provision are to (1) specifically allow for the use of digital systems because OSHA concluded that they are an equivalent diagnostic studies as film X-rays and (2) to no longer allow for the use of an equivalent diagnostic study because OSHA concluded there are currently no studies that are equivalent to film and digital X-rays.

—Minor edits to paragraphs (i)(4)(i)-(iv) of the general industry standard (paragraphs (h)(4)(i)-(iv) of the standard for construction), which is entitled: “Information provided to the PLHCP.” For example, in paragraphs (i)(4)(i) and (iv) (paragraphs (h)(4)(i) and (iv) in the standard for construction), “affected employee” was changed to “employee”. The word “affected” was removed because it is clear that the paragraphs refer to employees who will be undergoing medical examinations. In paragraph (i)(4)(iii) (paragraph (h)(4)(iii) in the standard for construction), “has used the equipment” was changed to “has used or will use the equipment” to make it consistent with the earlier part of the paragraph that states “personal protective equipment used or to be used”. Changes to these paragraphs are made to clarify OSHA's intent, which has not changed from the proposed rule.

—Revisions to the information required to be provided by the PLCHP to the employer and the employee. In response to public comments about employee privacy and potential discrimination or retaliation concerning medical findings, the final rule requires a detailed written medical report for the employee and a less detailed written medical opinion for the employer. This is a change from the proposed rule, which required the PLHCP to give the employer a written medical opinion that did not include findings unrelated to respirable crystalline silica exposure, and required the employer to give the employee a copy of the opinion.

○ The contents of the written medical report for the employee are set forth in paragraphs (i)(5)(i)-(iv) of the general industry standard (paragraphs (h)(5)(i)-(iv) of the construction standard). They include: A statement indicating the results of the medical examination, including any medical condition(s) that would place the employee at increased risk of material impairment of health from exposure to respirable crystalline silica and any medical conditions that require further evaluation or treatment; any recommended limitations on the employee's use of respirators; any recommended limitations on respirable crystalline silica exposure; and a statement that the employee should be examined by a specialist if the chest X-ray provided in accordance with this section is classified as 1/0 or higher by the B reader, or if referral to a specialist is deemed appropriate by the PLHCP. The health-related contents of the PLHCP's report to the employee are fairly consistent with the proposed PLHCP's opinion to the employer, but two major exceptions are noted. Because only the employee will be receiving the written medical report, (1) the written medical report should include diagnoses and specific information on health conditions, including those not related to respirable crystalline silica and (2) medical conditions that require further evaluation or follow-up are not limited to those related to respirable crystalline silica exposure. Although the employer will not be responsible for further evaluation of conditions not related to respirable crystalline silica exposure, the PLHCP has an ethical obligation to inform the employee about those conditions. In addition, a minor difference from the proposed opinion is that the report specifies limitations of respirator use rather than personal protective equipment (PPE), because a respirator is the only type of PPE required under this rule.

○ The contents of the PLHCP's written medical opinion for the employer are presented in paragraphs (i)(6)(i)(A)-(C) and (i)(6)(ii)(A)-(B) of the general industry standard (paragraphs (h)(6)(i)(A)-(C) and (h)(6)(ii)(A)-(B) of the construction standard). The contents of the written opinion are to include only the following: The date of the examination, a statement that the examination has met the requirements of the standard, and any recommended limitations on the employee's use of respirators. Paragraphs (i)(6)(ii)(A)-(B) of the general industry standard (paragraphs (h)(6)(ii)(A)-(B) of the construction standard) state that if the employee provides written authorization, the written opinion provided to the employer must also contain: Any recommended limitations on exposure to respirable crystalline silica and a statement that the employee should be examined by a specialist if the chest X-ray provided in accordance with the standard is classified as 1/0 or higher by the B reader, or if referral to a specialist is otherwise deemed appropriate by the PLHCP. As noted above, OSHA proposed that the employer obtain a more detailed written medical opinion from the PLHCP. In the final rule, the only medically related information that is to be reported to the employer without authorization from the employee is limitations on respirator use.

○ Under paragraph (i)(5) of the general industry standard (paragraph (h)(5) of the construction standard), the employer must ensure that the PLHCP explains the results of the examination to the employee and gives the employee a written report within 30 days of each medical examination performed. Under paragraphs (i)(6)(i) and (i)(6)(iii) of the general industry standard (paragraphs (h)(6)(i) and (h)(6)(iii) of the construction standard), employers must ensure that the PLHCP gives them and that the employee receives a copy of the employer's written medical opinion within 30 days of each medical examination. OSHA had proposed that the employer obtain the PLHCP's medical opinion within 30 days of the medical examination and then provide a copy to the employee within 2 weeks after receiving it.

○ The proposed opinion for the employer called for a statement that the PLHCP had explained to the employee the results of the medical examination, including findings of any medical conditions related to respirable crystalline silica exposure that require further evaluation or treatment, and any recommendations related to use of protective clothing or equipment. As noted above, OSHA has retained the requirement that the employer ensure that the PLHCP explains the results to the employee in paragraph (i)(5) of the standard (paragraph (h)(5) of the standard for construction), but no longer requires the PLCHP to include a statement of this fact in the opinion for the employer. OSHA is not mandating how the employer ensures that the employee gets the required information because there are various ways this could be done, such as in a contractual agreement between the employer and PLHCP. PLHCPs could still include the verification in the PLHCP's opinion for the employer if that is a convenient method for them to do so.

—Changes to the provisions regarding referral to a specialist. Paragraphs (i)(5)(iv) and (i)(6)(ii)(B) of the general industry standard (paragraphs (h)(5)(iv) and (h)(6)(ii)(B) of the construction standard) specifies that the PHLCP include a statement that the employee should be examined by a specialist if the X-ray is classified as 1/0 or higher by the B reader, or if referral to a specialist is deemed appropriate by the PLHCP. Those paragraphs now indicate referral to a “specialist.” OSHA has added “specialist” to the definitions in paragraph (b) of the standards, to allow referrals to specialists who are American Board Certified in Pulmonary Disease or Occupational Medicine. OSHA proposed examination by an American Board Certified Specialist in Pulmonary Disease and concludes that expansion of the specialist definition to include board certified occupational medicine physicians will mean that more physicians will be available for referrals, making appointments easier to get.

—Changes to the requirements regarding information given by the specialist to the employer and employee. Under paragraph (i)(7)(iii) of the general industry standard (paragraph (h)(7)(iii) of the standard for construction), the employer must ensure that the specialist explains medical findings to the employee and gives the employee a written medical report (i.e., a report containing results of the examination, including conditions that might increase the employee's risk from exposure to respirable crystalline silica, conditions requiring further follow-up, recommended limitations on respirator use, and recommended limitations on respirable crystalline silica exposure, as required by paragraph (i)(5) except (i)(5)(iv) of the general industry standard ((h)(5) except (h)(5)(iv) of the construction standard). The reasons why the specialist is to give the employee this information and the changes from the proposed rule are discussed above, under the requirements for the PLHCP's report. Likewise, for the same reasons as addressed above, paragraph (i)(7)(iv) of the standard (paragraph (h)(7)(iv) of the standard for construction) requires the specialist to provide the employer with a medical opinion (i.e.,—an opinion indicating the date of the examination, any recommended limitations on the employee's use of respirators, and with the written authorization of the employee, any recommended limitations on the employee's exposure to respirable crystalline silica, as required by paragraph (i)(6) (except (i)(6)(i)(B) and (i)(6)(ii)(B)) of the general industry standard (paragraph (h)(6) (except (h)(6)(i)(B) and (h)(6)(ii)(B)) of the construction standard)).

—Changes to the requirements regarding maintenance of monitoring data records by employers. Paragraph (k)(1)(i) of the general industry standard (paragraph (j)(1)(i) of the construction standard), the substance of which remains unchanged from the proposed standards, requires the employer to make and maintain accurate air monitoring data records of all exposure measurements taken to assess employee exposure to respirable crystalline silica, as prescribed in paragraph (d) of the general industry standard (paragraph (d)(2) of the construction standard). OSHA has added the words “make and” prior to “maintain” in order to clarify that the employer's obligation is to create and preserve such records. The language in this provision is consistent with OSHA's standard on access to employee exposure and medical records, which refers to employee exposure and medical records that are made or maintained (29 CFR 1910.1020(b)(3)). This clarification has also been made for other records required by the silica rule (29 CFR 1910.1053(k)(2)(i), 29 CFR 1910.1053(k)(3)(i), 29 CFR 1926.1153(j)(2)(i), and 29 CFR 1926.1153(j)(3)(i)). In addition, OSHA now refers to “measurements taken to assess employee exposure” rather than “measurement results used or relied on to characterize employee exposure” in paragraph (k)(1)(i) of the general industry standard (paragraph (j)(1)(i) of the construction standard). This change is non-substantive, and is intended to clarify OSHA's intent that all measurements of employee exposure to respirable crystalline silica be maintained.

—Changes to the requirement for maintaining air monitoring data records by employers. OSHA has made one modification in the rule to describe the information required in the records that differs from the proposed rule in paragraph (k)(1)(ii)(B) (paragraph (j)(1)(ii)(B) of the construction standard) and that is to change “the operation monitored” to “the task monitored.” Both “task” and “operation” are commonly used in describing work. However, OSHA uses the term “task” throughout the rule, and the Agency is using “task” in the recordkeeping provision for consistency and to avoid any potential misunderstanding that could result from using a different term. This change neither increases nor decreases an employer's obligations as set forth in the proposed standards.

—Changes to the requirements regarding maintenance of objective data records by employers. Paragraph (k)(2)(i) of the general industry standard (paragraph (j)(2)(i) for construction), the substance of which remains unchanged from the proposed rule, requires employers who rely on objective data to keep accurate records of the objective data. Paragraph (k)(2)(ii) of the general industry standard (paragraph (j)(2)(ii) of the construction standard) requires the record to include: The crystalline silica-containing material in question; the source of the objective data; the testing protocol and results of testing; a description of the process, task, or activity on which the objective data were based; and other data relevant to the process, task, activity, material, or exposures on which the objective data were based. Paragraphs (k)(2)(ii)(D) and (E) of the general industry standard (paragraphs (j)(2)(ii)(D) and (E) of the construction standard) have been modified from the proposed rule to substitute the word “task” for “operation”, and to clarify the requirements for records of objective data. These changes do not affect the employer's obligations as set forth in the proposed standards.

—Changes to the requirements regarding the maintenance of medical surveillance records by employers. In paragraph (k)(3)(ii)(B) and (C) of the general industry standard (paragraph (j)(3)(ii)(B) and (C) of the construction standard), which requires employers to make and maintain medical surveillance records, OSHA has changed the “PLHCP's and pulmonary specialist's written opinions” to the “PLHCPs' and specialists' written medical opinions.” The change, consistent with paragraph (i) of the general industry standard (paragraph (h) of the construction standard), is made to reflect the revised definition for the term “specialist” included in the rule.

IX. Federalism

The Agency reviewed the respirable crystalline silica rule according to the most recent Executive Order on Federalism, Executive Order 13132, which requires that Federal agencies, to the extent possible, refrain from limiting State policy options, consult with States before taking actions that would restrict States' policy options, and take such actions only when clear constitutional authority exists and the problem is of national scope (64 FR 43255 (8/10/1999)). The Executive Order allows Federal agencies to preempt State law only with the express consent of Congress. In such cases, Federal agencies must limit preemption of State law to the extent possible.

Under Section 18 of the Occupational Safety and Health Act (29 U.S.C. 667), Congress expressly provided that States may adopt, with Federal approval, a plan for the development and enforcement of occupational safety and health standards. OSHA refers to States that obtain Federal approval for such plans as “State-Plan States.” Occupational safety and health standards developed by State-Plan States must be at least as effective in providing safe and healthful employment and places of employment as the Federal standards. Subject to these requirements, State-Plan States are free to develop and enforce their own occupational safety and health standards.

This rule complies with Executive Order 13132. The problems addressed by this new respirable crystalline silica rule are national in scope. As explained in Chapter VI, Final Quantitative Risk Assessment and Significance of Risk, employees face a significant risk of material health impairments from exposure to crystalline silica in the workplace. These employees are exposed to respirable crystalline silica in general industry, construction, and shipyard workplaces across the country. Accordingly, the rule establishes requirements for employers in every State to protect their employees from the risks of exposure to respirable crystalline silica. In States without OSHA-approved State plans, Congress expressly provides for OSHA standards to preempt State occupational safety and health standards in areas addressed by the Federal standards. In these States, this rule limits State policy options in the same manner as every standard promulgated by the Agency. In States with OSHA-approved State plans, this rule does not significantly limit State policy options. Any special workplace problems or conditions in a State with an OSHA-approved State plan may be dealt with by its State standard, provided the standard is at least as effective as this rule.

X. State-Plan States

When Federal OSHA promulgates a new standard or a more stringent amendment to an existing standard, the 28 States and U.S. territories with their own OSHA-approved occupational safety and health plans (“State-Plan States”) must revise their standards to reflect the new standard or amendment. The State standard must be at least as effective as the Federal standard or amendment, and must be promulgated within six months of the publication date of the final Federal rule (29 U.S.C. 667(c)(2); 29 CFR 1953.5(a)).

A State-Plan State may demonstrate that a standard change is unnecessary because the State standard is already the same as or at least as effective as the new or amended Federal standard. In order to avoid delays in worker protection, the effective date of the State standard and any of its delayed provisions must be the date of State promulgation or the Federal effective date, whichever is later. The Assistant Secretary may permit a longer time period if the State timely demonstrates that good cause exists for extending the time limitation (29 CFR 1953.5(a)). Of the 28 States and territories with OSHA-approved State plans, 22 cover public and private-sector employees: Alaska, Arizona, California, Hawaii, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Nevada, New Mexico, North Carolina, Oregon, Puerto Rico, South Carolina, Tennessee, Utah, Vermont, Virginia, Washington, and Wyoming. Six States and territories cover only public-sector employees: Connecticut, Illinois, Maine, New Jersey, New York, and the Virgin Islands.

This respirable crystalline silica rule applies to general industry, construction, and maritime, and imposes additional or more stringent requirements as compared to the existing permissible exposure limits for respirable crystalline silica. This rule requires that all State-Plan States revise their general industry and construction standards appropriately within six months of the date of this notice. In addition, State plans that cover private sector maritime employment or have public employees working in the maritime industry covered by this standard would be required to adopt comparable provisions to their maritime standards within six months of publication of the final rule.

XI. Unfunded Mandates

OSHA reviewed this rule according to the Unfunded Mandates Reform Act of 1995 (UMRA) (2 U.S.C. 1501 et seq.) and Executive Order 13132 (64 FR 43255 (8/10/1999)). Under Section 202 of the UMRA (2 U.S.C. 1532), an agency must prepare a written “qualitative and quantitative assessment” of any regulation creating a mandate that “may result in the expenditure by the State, local, and tribal governments, in the aggregate, or by the private sector, of $100,000,000 or more” in any one year before promulgating a final rule. OSHA's rule does not place a mandate on State or local governments, for purposes of the UMRA, because OSHA cannot enforce its regulations or standards on State or local governments (29 U.S.C. 652(5)). Under voluntary agreements with OSHA, some States require public sector entities to comply with State standards, and these agreements specify that these State standards must be at least as protective as OSHA standards. The Occupational Safety and Health Act (29 U.S.C. 651 et seq.) does not cover tribal governments in the performance of traditional governmental functions, though it does cover tribal governments when they engage in commercial activity. However, the rule would not require tribal governments to expend, in the aggregate, $100,000,000 or more in any one year for their commercial activities. As noted below, OSHA also reviewed this rule in accordance with Executive Order 13175 on Consultation and Coordination with Indian Tribal Governments (65 FR 67249 (11/9/2000)), and determined that it does not have “tribal implications” as defined in that Executive Order.

OSHA concludes that the final rule would impose a Federal mandate on the private sector in excess of $100,000,000 in expenditures in any one year, as documented in the Final Economic Analysis (FEA) (see Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis). However, the final rule does not trigger the requirements of UMRA based on its impact on State, local, or tribal governments. The FEA constitutes the written statement containing a qualitative and quantitative assessment of these anticipated costs and benefits required under Section 202(a) of the UMRA (2 U.S.C. 1532(a)).

XII. Protecting Children From Environmental Health and Safety Risks

Executive Order 13045 requires that Federal agencies submitting covered regulatory actions to the Office of Management and Budget's Office of Information and Regulatory Affairs (OIRA) for review pursuant to Executive Order 12866 must provide OIRA with (1) an evaluation of the environmental health or safety effects that the planned regulation may have on children, and (2) an explanation of why the planned regulation is preferable to other potentially effective and reasonably feasible alternatives considered by the agency (62 FR 19885 (4/23/1997)). Executive Order 13045 defines “covered regulatory actions” as rules that may (1) be economically significant under Executive Order 12866 (i.e., a rulemaking that has an annual effect on the economy of $100 million or more, or would adversely effect in a material way the economy, a sector of the economy, productivity, competition, jobs, the environment, public health or safety, or State, local, or tribal governments or communities), and (2) concern an environmental health risk or safety risk that an agency has reason to believe may disproportionately affect children. In this context, the term “environmental health risks and safety risks” means risks to health or safety that are attributable to products or substances that children are likely to come in contact with or ingest (e.g., through air, food, water, soil, product use).

The respirable crystalline silica rule is economically significant under Executive Order 12866 (see Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis). However, after reviewing the rule, OSHA has determined that the rule would not impose environmental health or safety risks to children as set forth in Executive Order 13045. The rule would require employers to limit employee exposure to respirable crystalline silica and take other precautions to protect employees from adverse health effects associated with exposure to respirable crystalline silica. OSHA is not aware of any studies showing that exposure to respirable crystalline silica disproportionately affects children, that there are a significant number of employees under 18 years of age who may be exposed to respirable crystalline silica, or that employees of that age are disproportionately affected by such exposure.

A few commenters expressed concerns about exposure of children to respirable crystalline silica through their parents' contaminated work clothing (e.g., Document ID 4204, pp. 73-74). The American Federation of Labor and Congress of Industrial Organizations concluded that maintaining OSHA's longstanding hierarchy of controls in the final rule would prevent silica dust from being carried home on work clothing better than would a rule that relies solely on respirators to protect workers (Document ID 4204, pp. 64-65, 72-74). OSHA agrees, and finds that the final rule's primary reliance on engineering and work practice controls to protect workers will result in greater protection to children than either the prior permissible exposure limit for respirable crystalline silica or a rule that places primary reliance on respiratory protection.

Because OSHA does not believe that the health risks of respirable crystalline silica have a disproportionate impact on children, OSHA concludes the respirable crystalline silica rule does not constitute a covered regulatory action as defined by Executive Order 13045. To the extent children are exposed to respirable crystalline silica either as employees or at home as a result of family members' workplace exposures, the final rule offers greater protection than did the previous permissible exposure limits.

XIII. Consultation and Coordination With Indian Tribal Governments

OSHA reviewed this final rule in accordance with Executive Order 13175 on Consultation and Coordination with Indian Tribal Governments (65 FR 67249 (11/9/2000)), and determined that it does not have “tribal implications” as defined in that Executive Order. The Occupational Safety and Health Act (29 U.S.C. 651 et seq.) does not cover tribal governments in the performance of traditional governmental functions, so the rule will not have substantial direct effects on one or more Indian tribes in their sovereign capacity, on the relationship between the Federal government and Indian tribes, or on the distribution of power and responsibilities between the Federal government and Indian tribes. On the other hand, employees in commercial businesses owned by tribes or tribal members will receive the same protections and benefits of the standard as all other covered employees.

XIV. Environmental Impacts

Introduction

OSHA has reviewed the final rule according to the National Environmental Policy Act (NEPA) of 1969 (42 U.S.C. 4321 et seq.), the regulations of the Council on Environmental Quality (40 CFR part 1500 et seq.), and the Department of Labor's NEPA procedures (29 CFR part 11). The Agency has determined that the final rule will have no significant impact on air, water, or soil quality; plant or animal life; the use of land; or other aspects of the external environment. Therefore, OSHA concludes that the final standard will have no significant environmental impacts. This conclusion reaffirms the conclusions set forth in the Preliminary Economic Analysis (PEA).

To reach this conclusion, OSHA examined comments received about the potential environmental impacts posed by the final rule. Comments addressed two main issues: (1) Potential water runoff from construction tasks; and (2) costs associated with federal, state, and local environmental permits employers could be required to obtain as a result of the final rule. There were no specific comments regarding soil quality, plant or animal life, or land use. This section first lays out OSHA's preliminary conclusions regarding environmental impacts and then shows why the best available evidence in the rulemaking record reaffirms those conclusions. SBREFA and Conclusions Contained in the PEA

Pursuant to the recommendations from the Small Business Advocacy Review Panel, the Agency investigated potential environmental impacts and articulated its findings in the PEA. As noted in the SBREFA report (Document ID 0937, p. 77), the Panel requested that OSHA clarify how its silica rulemaking was related to designating silica-containing materials as hazardous wastes. In the PEA, OSHA explained that it did not believe silica wastes are classified as hazardous wastes for purposes of the Environmental Protection Agency (EPA) (Document ID 1720, p. IX-68). And the contents of OSHA's final rule on silica have no direct bearing on whether silica waste is classified as hazardous for EPA purposes.

In addition, some Small Entity Representatives (SERs) raised the possibility that the use of wet methods to limit silica exposures in some areas could violate EPA rules with respect to suspended solids in runoff unless provisions are made for recycling or settling the suspended solids out of the water. The SBAR Panel recommended that OSHA investigate this issue, add appropriate costs if necessary, and solicit comment. In response, the Agency identified six construction tasks where wet methods were utilized and found negligible costs related to controlling excess water because the amount of water used to control silica dust was minimal and typically did not produce runoff. OSHA's estimate of the potential environmental impact of each of these six equipment types was summarized in the PEA as follows:

• Stationary masonry saws: Most stationary saws come equipped with a water basin that typically holds several gallons of water and a pump for recycling water for wet cutting. The water is recirculated and, thus, not continually discharged. When emptied, the amount of water is not sufficient to produce a runoff.
• Hand-held masonry saws: Large quantities of water typically are not required in order to control dust. With these saws, water is supplied from a small capacity water tank. Any slurry residue after cutting could be dealt with by sweeping or vacuuming.
• Walk-behind and other large concrete saws: Larger concrete saws are equipped with a tank to supply water to the blade while cutting. These saws leave a slurry residue, but do not require so much water as to create a runoff.
• Walk-behind concrete grinders and millers: Some tools are equipped with a water-feed system. In these, a water line from a tank, a garden hose, or other water supply leads to the grinding head and delivers water to spray or flood the cutting tool and/or the work surface. When an automatic water feed is not available, a helper can apply water directly to the cutting surface. While such wet methods might generate enough water to create a runoff, these grinding and milling activities are typically done during the finishing stages of structure construction (e.g., parking garages) and are often performed inside the structure. Thus, direct discharges to storm drains or surface waters are unlikely.
• Asphalt millers for pavement resurfacing: A typical asphalt milling machine has a built-in reservoir from which water is applied to the cutting drum. The amount of water used, however, is insufficient to produce a runoff.
• Impact drillers/pavement breakers: Water for dust suppression can be applied manually or by using a semi-automated water-feed device. In the simplest method for suppressing dust, a dedicated helper directs a constant spray of mist at the impact point while another worker operates the jackhammer. The helper can use a hose with a garden-style spray nozzle to maintain a steady and carefully directed mist at the impact point where material is broken and crushed. Jackhammers retrofitted with a focused water mist aimed at the tip of the blade offer a dramatic decrease in silica exposure. Although water-fed jackhammers are not commercially available, it is neither expensive nor difficult to retrofit equipment. Studies suggest that a water flow rate of 1/8 to 1/4 gallon per minute is best for silica dust control. At this rate, about 7.5 to 15 gallons of water per hour would be applied to (i.e., sprayed on) the work area. It is unclear whether this quantity of water applied to a moveable work area at a constant rate would produce a runoff. If the work were in sufficient proximity to a storm drain or surface water, the contractor might need to use a simple barrier to prevent the water from entering the drain, or otherwise filter it. Because the volume of water is relatively small, the costs for such barriers are likely insubstantial and would typically overlap with the contractor's existing obligations for a site-control plan to prevent unwanted runoff from other causes.

In the PEA, OSHA found that employers typically have pre-existing obligations to limit runoff of solid waste, such as from rainfall, into storm drains. The Agency preliminarily concluded that: (1) The use of wet methods for certain construction tasks would not cause significant environmental problems from water runoff; and (2) employers should be able to comply with non-OSHA environmental regulations because runoff from wet methods can be easily controlled. As explained below, in light of the best available evidence contained in the record, OSHA reaffirms its preliminary conclusions.

Potential Water Runoff From Construction Tasks

While the Agency did not receive any comments directly addressing the PEA's discussion of environmental impacts, it did receive several comments on the water runoff issue. Most of the concerns expressed related to construction work, although a few comments came from entities in general industry. The construction and general industry commenters that addressed the issue of water runoff from the use of wet methods to comply with the final PEL included James Hardie Building Products, Inc.; the Unified Abrasives Manufacturers' Association; American Road & Transportation Builders Association; the General Contractors Association of New York; the Masonry & Concrete Saw Manufacturers Institute; and the Fertilizer Institute. None of the commenters to raise this issue provided any evidence to establish that runoff created by wet methods would actually create a problem (Document ID 2322, Attachment G, p. 14; 2243, p. 2; 2245, p. 4; 2314, p. 2; 2316, Attachment 1, pp. 2-3; 2101, pp. 6-7, 11-12). For example, one commenter, the Construction Industry Safety Coalition, advanced a theoretical argument that wet methods would either: (a) Require “tremendous” amounts of water; or (b) fail to effectively control silica. It stated:

For employers using wet methods, even attempting to meet this “no visible dust” standard will require a tremendous amount of water—many studies discussed in the technological feasibility analysis certainly support this notion. Such large amounts of water run counter to OSHA's contractor's assessment that “minimal” water should be used to avoid environmental contamination issues. The Agency contends that construction employers can mitigate any environmental concerns by utilizing as little water as possible to prevent accumulations from occurring or potentially damaging residential or commercial buildings. Even if utilizing only a little water will effectively reduce exposures to below the proposed PEL, the CISC has significant concerns that it will prevent all visible dust from being emitted (Document ID 2320, Attachment 1, pp. 9-10).

In light of the discussion set forth in Chapter VI of the FEA, Technological Feasibility, and evidence in the record, OSHA's preliminary findings regarding water runoff are affirmed. The Agency concludes that the comments it received expressing concerns about the runoff issue are unsubstantiated and theoretical and do not provide a sufficient justification for OSHA to alter its preliminary conclusions. As discussed in the Technological Feasibility section, OSHA finds that appropriate wet methods will typically require only limited application of water, possibly as little as a mist. In such conditions, the water will evaporate before collecting into a body of water. Where a greater water flow is necessary to suppress airborne silica, the runoff, rather than forming a free-flowing stream, will typically consolidate into slurry. In addition, because employers want to keep nearby structures and materials dry, they will typically use as little water as necessary.

OSHA finds support for these findings in the hearing testimony compilation assembled by the Building and Construction Trades Department. That evidence demonstrates the practical reality that water runoff from construction tasks is insignificant (Document ID 4223, pp. 28-30). Indeed, Deven Johnson, of the Operative Plasterers' and Cement Masons' International Association, stated that in her years of experience in using wet methods to control relatively dusty situations involving demolition, she had never had a problem with runoff-related issues. She indicated that runoff tends to create a slurry, which is easily vacuumed up (Document ID 3581, pp. 1695-1696). Gary Fore, a consultant and former Vice President for the American National Asphalt Pavement Association, likewise said that runoff was never a problem. He confirmed the PEA's preliminary conclusion for asphalt milling operations. While there may be a substantial amount of water used in the course of a day, it is applied as an aerosol. Further, although the pavement surface may be temporarily moist, it does not produce runoff from the construction site (Document ID 3583, p. 2209). Finally, Donald Hulk, Safety Director for Manafort, a construction contractor, testified that contrary to hypothetical assertions about potential runoff issues, his company did not find managing potential runoff from wet methods to be a problem. His reasoning confirmed the PEA's finding that the amount of water required for typical silica-containing dust suppression will not create substantial runoff. Moreover, he testified that in the case of demolition related to roadway construction, excess water is typically absorbed into demolition debris or evaporates—which is aided by the fact that most construction activity occurs during the warmer parts of the year (Document ID 3583, Tr. 2384-2385).

Certain industries voiced water runoff concerns specific to their workplaces. For example, the fertilizer industry stated its apprehension about OSHA's “preference” for wet methods to control silica exposure and indicated that such methods would be potentially problematic from an environmental standpoint at its facilities (Document ID 2101, pp. 6-7, 11-12). OSHA finds the fertilizer industry's concern misplaced because the final standard does not require the use of wet methods in general industry. Additionally, as discussed in Chapter III, the Agency estimates that exposures to respirable crystalline silica in the fertilizer industry are sufficiently low that most fertilizer-related manufacturing industries will not be affected by the final standard; the mixing-only fertilizer industry, NAICS 325314, was the only one judged to be affected.

The coal-fired electric industry also raised the issue of water runoff in its industry. The Edison Electric Institute and Alabama Power Company indicated a potential for conflict between an EPA rulemaking regarding ash ponds at the site of coal-fired electric utilities and this rulemaking (Document ID 2357, pp. 28-29; 2185, Attachment 1, p. 11). OSHA considered this concern, but has concluded that this will not be a problem in practice. The commenters never explained how the wet methods that might be required in Table 1 for construction activities (e.g., cutting concrete for transmission and distribution) would result in water flowing into fly ash ponds. In any event, the Agency has found that the proper use of wet methods will not result in significant runoff issues for any of the industries covered by the standard.

Air Quality/Permit Concerns

Regulations that will reduce the atmospheric concentration of respirable crystalline silica in the air within industrial and other facilities and workplaces have the potential to affect, either positively or negatively, the amount of respirable crystalline silica emitted by these sources into the ambient (external) environment. In most cases, the change will be small. As discussed in Chapter V of the FEA, Costs of Compliance, most ventilation is needed to reach the preceding PEL rather than the new PEL. The extent to which the reduction in the PEL—and, hence, occupational exposures—under the OSHA standard will impact air quality depends on how employers handle the increased volume of respirable crystalline silica captured by the relevant control technologies. Taking into account the measures employers are already using to comply with the existing silica PEL, and the fact that the baghouses employers are already using capture at least 99 percent of silica emissions (Document ID 3641, p. VII-19), OSHA concludes that the final rule will not have a significant impact on air quality

A number of commenters raised concerns that the final rule would create an onerous and cost-increasing administrative burden because it would necessitate obtaining EPA environmental permits, notably with regard to air quality regulations and related permits and process approvals at the state and local level. The concern was not an adverse environmental impact, per se, but rather the burden of complying with existing environmental rules in the context of the new OSHA standard (e.g., Document ID 2291, Attachment 1, p. 12; 2379, Appendix 1, p. 14; 2380, Attachment 2, p. 19; 2317, pp. 2-3). OSHA's response to these cost concerns is addressed in Chapter V of the FEA in the section on general industry engineering control costs.

A prime concern voiced by the commenters was having to comply with OSHA compliance deadlines while simultaneously meeting deadlines under applicable air quality permitting regulations.

For example, the Asphalt Roofing Manufacturers Association (ARMA) raised the issue of EPA permits related to changes in ventilation systems.

. . . the proposal appears to completely disregard environmental permitting requirements, which will present a significant time demand in almost every case because the standard will require increased dust collection, and releases to outside air will trigger air pollution limitations and permitting requirements for both State and or Federal agencies. Recent experience of ARMA members relating to implementation of the new National Ambient Air Quality Standards (NAAQS) for particulate matter (PM_2.5) reveals that, even in the case of minor facility modifications which emit particulate matter, authorization to construct or modify a control device can take more than a year to obtain. Even longer permitting times will be experienced in cases requiring complex modeling of nearby sources, or State or Federal approval of modeling methods and protocol inputs. These factors could further delay the issuance of permits by an additional twelve months, assuming the facility is able to develop a passing model. If the model does not pass, further modeling and review by permitting agencies, or additional emissions abatement, may be required to obtain the permits, extending still further this step in the process (Document ID 2291, Attachment 1, p. 12).

As the Agency explains in the Summary & Explanation section of the preamble dealing with paragraph (j), dates, the final rule's effective and enforcement dates have been tailored to allow a sufficient period of time for employers to meet requirements for approval by other regulatory agencies. (A discussion of various state permitting times can be found in “Examples of State Environmental Agency Permit Turnaround Times,” ERG, 2015.) The Agency believes providing longer compliance deadlines should address the primary concerns expressed by commenters regarding the time necessary to obtain any required environmental permit approvals. Ultimately, as discussed in the Summary and Explanation, cases that are unusually problematic can be addressed through OSHA's enforcement discretion if the employer can show that it has made good faith efforts to implement engineering controls, but has been unable to implement such controls due to the time needed for environmental permitting.

Some industries raised permit concerns unique to their operations. The Association of American Railroads and American Short Line and Regional Railroad Association stated that it foresaw a need for a permit under the Clean Water Act if a ballast was sprayed with a chemical, which, through run off or by another means, reached a body of water (Document ID 2366, p. 7).

OSHA considers the railroad industry's concern about the threat of significant water contamination from chemical dust suppressant speculative because of the limited amount of water potentially used. Consequently, the Agency does not foresee a significant environmental impact. Additionally, no current OSHA standard governs the use of chemical dust suppressants. While some state or local governments may require a permit, it is not clear this would pose a new issue for the railroads, as OSHA believes it is likely that they already have to deal with such issues in the context of runoff from deicing chemicals, as well as oil and metal particles from normal operations. OSHA notes, however, that the analysis in the railroad section of Chapter IV of the FEA, Technological Feasibility, discusses chemical suppressants merely as a possibility for reducing exposures, but it is not ultimately identified as necessary to enable employers in the industry to meet the PEL of 50 μg/m³. Accordingly, the FEA's cost analysis for the railroad industry does not include chemical suppressants, but assumes the industry will use wet methods to reduce exposures, and estimates the costs accordingly. To the extent chemical dust suppressants are more cost-effective than water, the FEA has overestimated the cost to the industry. And to the extent suppressants pose an environmental air quality permitting issue, OSHA notes that suppressants are not required under the final rule and is not including relevant permitting costs in its analysis.

The Shipbuilders Council of America (SCA) stated that if the final silica rule altered blasting technologies and/or facility equipment, the data currently used for shipyard permits in certain states (e.g., state air and water permits) would be invalid, necessitating permit and plan updates and creating additional costs for the industry (Document ID 2255, p. 2). The final rule does not specify engineering control changes in this area; nor does the Agency believe the lower PEL will require a change in engineering controls for abrasive blasting, relative to current standards. As laid out in Chapter V in the FEA, employers complying with the hierarchy of controls under the existing silica PEL and ventilation standards will already be using engineering controls to limit exposures. OSHA has found that the only additional feasible engineering controls employers in shipyards can implement to reduce exposures is the use of HEPA vacuums (in lieu of dry sweeping). Implementation of this control will reduce potential environmental problems because the use of HEPA vacuums raises less dust than dry sweeping.

Positive Environmental Effects

Based on its review of the record, OSHA concludes that the final rule will potentially have a positive environmental impact. At least one industry commenter, in the context of the hydraulic fracturing industry, suggested that its technology, the adoption of which would presumably be hastened by the promulgation and enforcement of the final rule, would reduce potential environmental impacts (Document ID 3589, Tr. 4140). In a similar vein, as discussed in both Chapters IV and V of the FEA, the final standard actually helps construction employers' reduce fugitive and co-generated dust, aiding in their compliance with environmental standards related to the dust. (The issue of controlling fugitive dust overlaps with the issue of existing employer obligations to minimize the runoff of solid waste into public water, discussed previously in this chapter, as well as the general expectation that employers clean up their work sites after their work is completed, as discussed in Chapter V).

Conclusion

As a result of this review, OSHA has reaffirmed its conclusions in the PEA, that the silica final rule will have no significant impact on air, water, or soil quality; plant or animal life; the use of land; or aspects of the external environment. It finds that the final standard is in compliance with NEPA and will have no significant environmental impact.

XV. Summary and Explanation of the Standards

OSHA proposed two standards for occupational exposure to respirable crystalline silica—one for general industry and maritime and a second for construction. Both proposed standards were structured according to OSHA's traditional approach, including separate provisions for a permissible exposure limit (PEL), exposure assessments, and methods of compliance, which includes a requirement to follow the hierarchy of controls. The methods of compliance provision in the proposed construction standard included Table 1, which specified engineering controls, work practices, and respiratory protection for common construction operations (now referred to as tasks). Construction employers who would have chosen to fully implement engineering controls, work practices, and respirators for a task in proposed Table 1 would have been exempted from conducting exposure assessments for employees conducting that task, but would have been required to comply with the PEL.

The structure of the final standard for general industry and maritime remains generally consistent with other OSHA health standards. The most significant structural change from the proposed general industry and maritime standard is that “cleaning methods,” which was under the Methods of Compliance paragraph, is now a separate paragraph called Housekeeping. The same change regarding Housekeeping was made to the standard for construction. In addition both standards include a requirement for a written exposure control plan, which is included under the Methods of Compliance paragraph in the standard for general industry and maritime but as a separate paragraph in the standard for construction. Most importantly, the structure for the construction standard is significantly different from OSHA's traditional approach to address stakeholder concerns about compliance in the construction industry.

Many stakeholders thought that construction employers who fully and properly implement the engineering controls, work practices, and respiratory protection specified in Table 1 should be considered to be in compliance with the PEL. As reflected in paragraph (c) of the standard for construction (which includes Table 1), and as discussed in more detail in the summary and explanation, OSHA agrees that construction employers who fully and properly implement the engineering controls, work practices, and respiratory protection for a task on Table 1 do not have to demonstrate compliance with the PEL for that task, because these controls provide a level of protection equivalent to that provided by the alternative approach that includes the 50 µg/m³ PEL.

OSHA also received many comments about the challenges of conducting exposure assessments in the construction industry. OSHA expects that because of these challenges most construction employers will follow Table 1. Therefore, OSHA made major structural changes to the standard for construction to emphasize Table 1 in paragraph (c) for employers who choose to follow that approach. Paragraph (d) of the standard for construction provides alternative exposure control methods for construction employers who choose not to follow Table 1 or who perform tasks that are not included in Table 1 (e.g., abrasive blasting and underground construction (tunnel boring)). Paragraph (d) of the standard for construction contains requirements, including the PEL, exposure assessments, and methods of compliance, that follow OSHA's traditional approach.

Construction employers who choose to follow Table 1 of paragraph (c) are exempt from following paragraph (d) but must comply with provisions in all other paragraphs of the standard for construction. On the other hand, construction employers who follow the alternate exposure control methods in paragraph (d) are exempt from following the provisions in paragraph (c) but must comply with the provisions in all other paragraphs of the standard for construction.

Although the structure of the standard for general industry and maritime differs from the structure of the standard for construction, many of the requirements are the same or similar in both standards. Therefore the summary and explanation is organized according to the main requirements of the standards. It includes paragraph references to the standard for general industry and maritime, followed by paragraph references for the standard for construction. The summary and explanation uses the term “rule” when referring to both standards. Generally, when the summary and explanation refers to the term “rule,” it is referring to the final rule. To avoid confusion, the term “final rule” is sometimes used when making a comparison to or clarifying a change from the proposed rule.

Scope and Application

Separate standards for general industry/maritime and construction. OSHA proposed two separate standards addressing occupational exposure to respirable crystalline silica: one for exposures in general industry and maritime, and another for exposures in the construction industry. The proposed standards were intended to provide equivalent protection for workers while accounting for the different work activities, anticipated exposures, and other conditions in these sectors.

Commenters representing construction employers, labor unions, and governmental entities noted the intrinsic differences between construction and other industries and were generally supportive of OSHA's decision to propose one standard for general industry and maritime and another for construction (e.g., Document ID 1955, p. 2; 2116, p. 40; 2166, p. 3; 2181, p. 4; 2262, p. 14; 2318, p. 13; 2371, p. 5; 3403, p. 3). However, some stakeholders expressed concerns about differentiation among industries.

The Association of Occupational and Environmental Clinics opposed applying occupational health protection measures differently (Document ID 3399, p. 4). Edison Electric Institute (EEI) argued that differences in the standards may create confusion, administrative burden, and ambiguity, and could ultimately frustrate good-faith compliance efforts. EEI suggested that the easiest solution would be for OSHA to have “a single regulation applicable to the electric utility industry, rather than separate General Industry and Construction requirements” (Document ID 2357, p. 17).

Commenters representing utility providers, surface mineral mining, rock crushing, railroad operations, and truck distribution expressed concerns about separate standards creating uncertainty about which requirements would apply to various activities (Document ID 2101, p. 3; 2185, pp. 4-5; 2318, p. 13; 2357, p. 4; 2366, p. 3; 3492, p. 2). Southern Company cited the installation of new power delivery lines versus the repair or maintenance of existing power delivery lines as an example, indicating that once a concrete pole is in the ground the process of mounting hardware is exactly the same, but the applicable standard may be different (Document ID 2185, p. 4).

The International Brotherhood of Teamsters (IBT) also expressed concerns about work activities where it may not be clear whether the general industry or construction standard applies. IBT noted that ready-mix concrete truck drivers frequently travel to more than one work location and may work at many different construction sites on any given day. These workers are typically covered by the general industry standard; however, they may work at construction sites and perform certain tasks that could be considered construction work (Document ID 2318, p. 13).

Several commenters requested that OSHA develop a table listing specified exposure control methods for general industry, comparable to proposed Table 1 for construction, or that OSHA add general industry tasks to Table 1 (Document ID 2116, Attachment 1, p. 3; 2212, p. 2; 2244, p. 4; 2339, p. 8; 2357, p. 1). The American Society of Safety Engineers requested that Table 1 “be considered for the general industry/maritime standard for commonly performed tasks involving high levels of silica exposure” (Document ID 2339, p. 8).

After considering the concerns raised by commenters, OSHA is issuing one standard that addresses occupational exposure to respirable crystalline silica in general industry and maritime work and another for construction work. As reflected primarily in paragraph (c) and Table 1 of the standard for construction, the Agency finds that certain conditions inherent to the construction industry, such as the transient nature of the work, warrant alternatives to protect employees that are somewhat different than those that apply to general industry and maritime work. OSHA has long recognized a distinction between the construction and general industry sectors, and has issued standards specifically applicable to construction work under 29 CFR part 1926. The Agency has provided a definition of the term “construction work” at 29 CFR 1910.12(b), has explained the terms used in that definition at 29 CFR 1926.13, and has issued numerous interpretations over the years explaining the classification of activities as either general industry or construction work.

In issuing separate standards for general industry/maritime and construction, OSHA's intent is to ensure that employees exposed to respirable crystalline silica in construction are, to the extent feasible, provided equivalent protection to that afforded employees in general industry and maritime. Specifically, OSHA intends that Table 1 in paragraph (c) of the construction standard, while providing employers with an alternative, flexible approach to addressing exposure to respirable crystalline silica in construction, will provide the same level of protection against exposures to silica for construction employees as is provided to general industry and maritime employees; the same is true for construction employees whose employers are following the traditional exposure assessment and hierarchy of controls approach under paragraph (d) of the construction standard.

OSHA recognizes that in some circumstances, general industry activities and conditions in workplaces where general industry tasks are performed may be indistinguishable from those found in construction work. In some cases, employers whose primary business is classified as general industry may have some employees who perform construction work, and employers whose primary business is classified as construction may have some employees who perform general industry work. Given the wide variety of tasks performed in the workplace, it is inevitable that questions will arise regarding the classification of certain activities, and these questions have been and will continue to be addressed in letters of interpretation and other guidance issued by OSHA. However, the distinction between sectors is generally well understood by both OSHA enforcement personnel and the regulated community, and OSHA concludes that any attempt to create exceptions or to provide different criteria in this final rule would not improve upon the current criteria but would, rather, cause confusion.

In certain circumstances, tasks performed in a general industry setting may be indistinguishable from the tasks listed on Table 1, and, under these circumstances, OSHA intends to treat full compliance with the construction standard as full compliance with the general industry/maritime standard. Accordingly, OSHA has revised the scope provision (i.e., paragraph (a)) in the general industry and maritime standard by adding paragraph (a)(3) to permit employers to follow the construction standard rather than the general industry and maritime standard when the general industry/maritime task performed is indistinguishable from a construction task listed on Table 1 in paragraph (c) of the construction standard, and the task will not be performed regularly in the same environment and conditions.

These indistinguishable tasks should not be merely parallel or complementary to or occurring at the same time and place as the construction tasks listed on Table 1, but rather should be of the same nature and type as those construction tasks. OSHA anticipates that the option in paragraph (a)(3) will apply primarily to maintenance and repair tasks performed in general industry or maritime settings. For example, an employee using a portable masonry saw to cut brick to patch a section of an existing brick wall, which is typically maintenance, would require tools and controls that are the same as those of an employee cutting brick while building a new brick wall, which is construction work. In performing this task, the employer could follow the construction standard, including paragraph (c)(1)(ii) of Table 1, rather than the general industry and maritime standard. Similarly, the installation of new power delivery lines is considered a construction activity, while the repair or maintenance of existing power delivery lines is considered a general industry task, even though a handheld drill may be used to drill a hole in concrete during both activities. In this situation, if the employer complies with the entry on Table 1 for handheld and stand-mounted drills (paragraph (c)(1)(vii) of the construction standard), in addition to all other applicable provisions of the construction standard (e.g., paragraph (g), Written exposure control plan), the employer would not be obligated under the general industry and maritime standard to perform an exposure assessment for the employee(s) engaged in the drilling task, or be subject to citation for failure to meet the permissible exposure limit (PEL); instead, the employer would have the same accommodation that Table 1 in paragraph (c) of the construction standard affords a construction employer doing that task and following paragraph (c). However, in the event that the employer fails to fully comply with the construction standard by, for example, failing to fully and properly implement the controls on Table 1 or to fully establish and implement a written exposure control plan (e.g., by not designating a competent person to implement the plan), the employer would be subject to the general industry and maritime standard and could be cited for not having performed an exposure assessment or not having achieved the PEL with respect to the employee(s) engaged in that task.

Paragraph (a)(3)(ii) of the general industry and maritime standard provides that, in order for the employer to be able to avail itself of the option to follow the construction standard, the task must not be performed regularly in the same environment and conditions. For example, an employer that performs sanding or cutting of concrete blocks in a concrete block manufacturing plant may not follow the construction standard, because the task is performed regularly in the same environment and conditions. Likewise, an employer whose business includes chipping out concrete from inside the drums of ready-mixed concrete trucks using pneumatic chipping tools may not follow the construction standard, because that task will be regularly performed in a relatively stable and predictable environment that would not require the accommodation of Table 1, which is intended in part to accommodate situations where the tasks will be performed in different environments and conditions.

Regarding comments that exposure controls should be specified in the general industry and maritime standard in a manner similar to that of Table 1 for construction tasks, OSHA concludes that, for most general industry operations, it is not possible to develop a specification that would broadly apply to facilities that vary widely in size, process design, and complexity while being specific enough to provide reasonably objective criteria against which to judge compliance with the standard. Unlike for construction tasks, the rulemaking record does not provide sufficient information for OSHA to account for the wide variety of potential tasks across the range of manufacturing and other general industry work. In manufacturing industries such as foundries and pottery production, local exhaust specifications must be custom designed for each establishment considering its manufacturing processes, equipment, and layout. Based on its over forty years of experience in enforcing occupational safety and health standards, OSHA concludes that in general industry and maritime, employee protection is best provided through a performance-oriented standard that permits employers to implement engineering controls and work practices that best fit their situation. In contrast, the task-based operations performed in construction are uniquely suited to a specification approach since the same equipment and dust controls are generally used regardless of the nature of the construction project, making specification of an effective dust control approach possible.

Agriculture. The proposed rule did not cover agricultural employers due to limited data on exposures and control measures in the agriculture sector. OSHA's authority is also restricted in this area; since 1976, an annual rider in the Agency's Congressional appropriations bill has limited OSHA's use of funds with respect to farming operations that employ fewer than ten employees (Consolidated Appropriations Act, 1976, 94, 90 Stat. 1420, 1421 (1976) (and subsequent appropriations acts)). The Agency requested information on agricultural operations that involve respirable crystalline silica exposures in the Notice of Proposed Rulemaking (NPRM), as well as information related to the development of respirable crystalline silica-related adverse health effects and diseases among employees in the agricultural sector (78 FR 56274, 56288 (9/12/13). OSHA did not receive information that would support coverage of agricultural operations. Therefore, agriculture employers and operations are not covered by the rule, as specified in paragraph (a)(1)(ii) of the general industry and maritime standard.

Mine Safety and Health Administration (MSHA) jurisdictional concerns. The Fertilizer Institute (TFI) and Fann Contracting, Inc. requested that OSHA clarify the jurisdictional limits of the silica rule in light of OSHA's memorandum of understanding (MOU) with MSHA (Document ID 2101, p. 3; 2116, p. 31) (citing Interagency Agreement Between the Mine Safety and Health Administration U.S. Department of Labor and the Occupational Safety and Health Administration U.S. Department of Labor). The MOU, which has been in effect since March 29, 1979 (Document ID 2101, p. 3), delineates certain areas of respective authority, sets forth factors regarding determinations relating to convenience of administration, provides a procedure for determining general jurisdictional questions, and provides for coordination between MSHA and OSHA in all areas of mutual interest. The respirable crystalline silica rule in no way modifies the existing jurisdictional boundaries set forth in the Interagency Agreement, and any issues related to the rule that may arise between MSHA and OSHA are governed by this agreement. Therefore, the final rule does not necessitate a clarification of the jurisdictional limits.

Federal Railroad Administration (FRA) jurisdictional concerns. The Association of American Railroads (AAR) and the American Short Line and Regional Railroad Association (ASLRRA) raised jurisdictional issues about railroad operations (Document ID 2366, pp. 3-4). The stated concern is that railroad operations are also regulated by FRA. AAR and ASLRRA questioned OSHA's jurisdiction over railroad activities that OSHA considered and costed in its preliminary economic analysis, notably those of “ballast dumper” and “machine operator.” AAR and ASLRRA disagreed with OSHA's inclusion of these job categories as being “non-operational,” which allowed them to be included within the scope of the OSHA silica rule. AAR and ASLRRA asserted that the FRA has developed a special expertise, making the FRA uniquely qualified to play the primary role in the federal government's efforts to assure safe employment and places of employment for railroad employees engaged in activities related to railroad operations (Document ID 2366, pp. 3-4).

Section 4(b)(1) of the OSH Act limits OSHA's authority; the Act does not apply to working conditions of employees with respect to which other Federal agencies exercise statutory authority to prescribe or enforce standards or regulations affecting occupational safety or health. Many of the regulatory boundaries between FRA and OSHA are documented in an FRA policy statement that outlines the respective areas of jurisdiction between FRA and OSHA with regard to the railroad industry, but the FRA has also defined some boundaries through rulemaking (Document ID 0692 (43 FR 10583-10590 (3/14/78))). In 2003, FRA amended the Railroad Workplace Safety regulations, 49 CFR part 214, to require that new and employer-designated existing on-track roadway maintenance machines be equipped with, among other things, positive pressurized ventilation systems, and be capable of protecting employees in the cabs of the machines from exposure to air contaminants, including silica, in accordance with OSHA's air contaminants standard, 29 CFR 1910.1000 (49 CFR 214.505). In that rulemaking, the FRA articulated the overlap of its authority with OSHA's concerning protection from air contaminants: “when working inside the cab, workers receive protection from FRA; when working outside the cab, workers receive protection from OSHA” (68 FR 44388, 44393-44394 (7/28/03)). Consequently, this OSHA rule applies only to those railroad activities outside the cab (e.g., ballast dumping outside cabs) over which the FRA has not exercised jurisdiction, and only those activities are included in the final economic analysis. Additional discussion of this jurisdictional issue is included in the section on the technological feasibility of railroads (see Chapter IV of the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA)).

Forms of silica covered. OSHA received comments about which forms, or polymorphs, of silica (e.g., quartz, cristobalite, tridymite) to include within the scope of the rule. The Industrial Minerals Association—North America and Ameren Corporation supported including all forms within the scope of the rule (Document ID 1760, p. 2; 2200, p. 2; 2315, p. 2). Other commenters made recommendations regarding specific forms of silica. For example, the National Industrial Sand Association (NISA) suggested including tridymite; however, the National Institute for Occupational Safety and Health (NIOSH) and the North American Insulation Manufacturers Association (NAIMA) did not support inclusion of tridymite due largely to its rarity in the workplace (Document ID 2195, p. 30; 2177, Attachment 2, p. 10; 4213, p. 4). Similarly, Southern Company recommended that neither tridymite nor cristobalite be included within the scope of the rule, due to their rarity in the workplace (Document ID 2185, p. 2, 6). The American Composites Manufacturers Association and Southern Company suggested that OSHA focus exclusively on quartz (Document ID 1732, p. 6; 2185, p. 6). NAIMA suggested OSHA focus on both quartz and cristobalite (Document 4213, p. 4).

As discussed in Section V of this preamble, Health Effects, OSHA has concluded, based on the available scientific evidence, that quartz, cristobalite, and tridymite have similar toxicity and carcinogenic potency. Including all three forms of crystalline silica in the scope of the rule is therefore protective of the health of employees. Coverage of quartz, cristobalite, and tridymite in the scope of the rule maintains the coverage from OSHA's previous PELs for respirable crystalline silica; to eliminate one or more forms from the scope of the rule would lessen protections, contrary to what the OSH Act contemplates (see 29 U.S.C. 655(b)(8)). Therefore, the respirable crystalline silica rule applies to occupational exposure to respirable crystalline silica, as defined in paragraph (b) of each standard to include quartz, cristobalite, and tridymite.

Some commenters contended that OSHA should differentiate between crystalline silica and amorphous silica in the scope of the rule. The Society for Protective Coatings stated that this differentiation would avoid confusion and unnecessary burden, especially for small businesses (Document ID 2120, p. 1; 3544, p. 16). NAIMA stated that NIOSH, IARC (the International Agency for Research on Cancer), EPA (the Environmental Protection Agency), and the California Office of Environmental Health Hazard Assessment all recognize the distinction in potential hazards to workers between amorphous and crystalline silica (Document ID 3544, p. 16). However, OSHA never intended to, and did not, include amorphous silica in the proposed rule. Nor do the final standards apply to amorphous silica. In fact, each standard bears the title, “Respirable crystalline silica”; only the respirable fraction of crystalline silica, where it exists as quartz, cristobalite, and/or tridymite, is covered.

Requests for exemptions. Commenters requested exemptions from the rule for specific operations or industries, such as auto body operations, cement distribution terminals, floor covering dealers, rural electric distribution cooperatives, and painting operations, arguing that these operations involve low levels of exposure to respirable crystalline silica (e.g., Document ID 2300, p. 4; 2358, p. 15; 2359, pp. 3-7; 2365, p. 2; 3751, p. 2; 2239, pp. 4-5). For example, the National Automobile Dealers Association (NADA) said that the likelihood of worker exposure to significant respirable crystalline silica in dealership auto body operations is de minimis, largely due to product substitution, state-of-the-art work practices, and the use of respiratory protection. NADA requested that OSHA confirm this conclusion through a clear statement in the preamble of its final rule (Document ID 2358, p. 3). Similarly, the World Floor Covering Association requested that OSHA revise the rule to exempt retail flooring dealers and installers from all requirements in the standard based on the intermittent and de minimis exposure of its employees to crystalline silica (Document ID 2359, p. 11). The Portland Cement Association also requested an exemption from the silica rule, arguing that its contemporary inhalation survey and historical data show that there is no probability that respirable crystalline silica exposures can be generated above the proposed action level among employees at cement terminals.

OSHA addresses the concerns of commenters regarding situations where they believe exposures are minimal and represent very little threat to the health of workers by including in the standards' scope and application sections an exception based on the level of exposure to respirable crystalline silica. Therefore, paragraph (a)(2) of the standard for general industry and maritime provides an exception for circumstances where the employer has objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 micrograms per cubic meter of air (25 μg/m³) as an 8-hour time-weighted average (TWA) under any foreseeable conditions.

OSHA concludes this approach is sensible policy because providing an exception for situations where airborne exposures are less likely to present significant risk allows employers to focus resources on the exposures of greatest occupational health concern. The Agency has included a definition for “objective data” in the rule (discussed with regard to Definitions) to clarify what information and data can be used to satisfy the obligation to demonstrate that respirable crystalline silica exposures will be below 25 μg/m³ as an 8-hour TWA under any foreseeable conditions.

When using the phrase “any foreseeable conditions” OSHA is referring to situations that can reasonably be anticipated. The Agency considers failure of engineering controls to be a situation that is generally foreseeable. Although engineering controls are usually a reliable means for controlling employee exposures, equipment does occasionally fail. Moreover, OSHA intends the requirements for training on control measures, housekeeping, and other ancillary provisions of the rule to apply where engineering controls are used to limit exposures. Without effective training on use of engineering controls, for example, it is unreasonable to expect that such controls will be used properly and consistently. Thus, the exception does not apply where exposures below 25 μg/m³ as an 8-hour TWA are expected or achieved, but only because engineering or other controls are being used to limit exposures; in that circumstance, but for the controls, exposures above 25 μg/m³ as an 8-hour TWA would be foreseeable, and are foreseeable in the event of control failure or misuse.

OSHA considers the exclusion from the application of the rule for exposures below the 25 μg/m³ action level to be a reasonable point of demarcation. For workplaces or tasks for which exposures are consistently below that threshold, it should be possible for employers to develop or obtain objective data demonstrating that employee exposure will remain below that level under any foreseeable conditions. Other standards have included similar exceptions (e.g., acrylonitrile, 29 CFR 1019.1045; ethylene oxide, 29 CFR 1910.1047; 1,3-butadiene, 29 CFR 1910.1051; chromium (VI), 29 CFR 1910.1026). In order for an employer to take advantage of this exclusion, the employer must have objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 μg/m³ as an 8-hour TWA) under any foreseeable conditions, and must provide this data to the Assistant Secretary upon request.

NADA's submission provides an example of data that can be used to meet the requirements of the standard (Document ID 4197; 4198). NADA conducted air monitoring for employees performing a variety of tasks in automobile body shops. NADA selected body shops from a random sample of members, and worked to ensure that those selected were not the most technologically advanced or cleanest in order to ensure that the results of the study were representative of typical operations. The sampling was conducted in accordance with procedures described in OSHA's Technical Manual, and techniques for controlling dust generated during sanding operations were recorded and monitored. NADA retained a consultant to review testing methodology and final results and worked with Maine's OSHA Consultation Program to gather samples. In the body shops sampled, all but one of the samples taken for respirable crystalline silica indicated that exposures were below the limit of detection. For the one sample where the level of exposure was above the limit of detection, the result was below 25μg/m³ as an 8-hour TWA. A body shop performing tasks in a manner consistent with that described in the NADA submission would be able to rely on these objective data to demonstrate that exposures do not exceed 25 μg/m³ as an 8-hour TWA under any foreseeable conditions.

The construction standard, paragraph (a), also provides an exception where employee exposure will remain below 25 μg/m³ as an 8-hour TWA under any foreseeable conditions, but it does not require the employer to have objective data to support the exception. The data presented in Chapter IV of the FEA indicate that construction tasks can and often do involve exposures that exceed 25 μg/m³ as an 8-hour TWA. However, some construction tasks may involve only minimal exposure to respirable crystalline silica. Some commenters indicated that they believed these tasks were covered under the scope of the proposed construction standard. For example, the Construction Industry Safety Coalition (CISC) and the National Association of Home Builders indicated that they believed that mixing mortar, pouring concrete footers, slab foundation, and foundation walls, and the removal of concrete formwork would be covered by the standard (Document ID 2319, pp. 19-21; 2296, pp. 8-9). OSHA finds that these tasks, when performed in isolation from activities that do generate significant exposures to respirable crystalline silica (e.g., tasks listed on Table 1, abrasive blasting), do not create respirable crystalline silica exposures that exceed 25 μg/m³ as an 8-hour TWA. OSHA's analysis of the rulemaking record also indicates that a substantial number of employees in the construction sector perform tasks involving occasional, brief exposures to respirable crystalline silica that are incidental to their primary work. These employees include carpenters, plumbers, and electricians who occasionally drill holes in concrete or masonry or perform other tasks that involve exposure to respirable crystalline silica. CISC estimated that 1.5 million employees in the construction industry perform such tasks (Document ID 2319, pp. 72-73). Where employees perform tasks that involve exposure to respirable crystalline silica for a very short period of time, OSHA finds that exposures for many tasks will be below 25 μg/m³ as an 8-hour TWA. Short-term respirable crystalline silica exposures must be very high in order for those exposures to exceed 25 μg/m³ as an 8-hour TWA; for example, if an employee is exposed for only 15 minutes, his or her exposure would have to exceed 800 µg/m³ for that 15 minute period before the 8-hour TWA exposure would exceed 25 μg/m³.

When performed without adequate controls, some tasks can generate such high exposures. However, for some construction tasks that may be performed occasionally, for brief periods of time, exposures would not generally be expected to exceed 25 μg/m³ as an 8-hour TWA. For example, for hole drillers using hand-held drills, the highest result identified in OSHA's exposure profile was for a worker performing dry drilling on a wall on the lower level of a concrete parking garage where air circulation was poor (see Chapter IV of the FEA). This result showed an exposure of 300 µg/m³ during the sampling period (Document ID 1423, p. 833). If the duration of exposure was 15 minutes, the 8-hour TWA exposure would be 19 μg/m³, and therefore under the 25 μg/m³ threshold (assuming no exposure for the remainder of the shift).

Rather than require construction employers to develop objective data to support an exception from the construction standard for employees who are exposed to minimal levels of respirable crystalline silica, or who are occasionally exposed to respirable crystalline silica for brief periods, OSHA is structuring the scope paragraph (i.e., paragraph (a)) for the construction standard so that the standard applies to all occupational exposures to respirable crystalline silica, except where employee exposure will remain below 25 μg/m³ as an 8-hour TWA under any foreseeable conditions. This approach relieves construction employers of the burden of developing objective data for such situations.

In the NPRM, OSHA asked stakeholders whether the Agency should limit the coverage of the rule to materials that contain a threshold concentration (e.g., 1 percent, 0.1 percent) of crystalline silica (78 FR at 56288). Stakeholders representing industries including cement and concrete, composites manufacturing, fertilizers, and sand and gravel suggested a threshold, commonly presenting concerns regarding requirements for labels and safety data sheets (SDSs) (e.g., Document ID 1785, p. 4; 2116, Attachment 1, p. 45; 2179, pp. 3-4; 2101, pp. 8-9; 2284, p. 10; 2296, p. 44; 2312, p. 3; 2317, p. 3; 2319, p. 120; 2327, Attachment 1, p. 14; 4208, pp. 19-20). For example, TFI supported a percentage-based threshold for crystalline silica containing materials, indicating that such an approach would be consistent with OSHA's past standard-setting experience for asbestos-containing materials. TFI stated that OSHA should not set a threshold at lower than 1 percent, and recommended that OSHA consider a 5 percent threshold, noting challenges in measuring crystalline silica content in bulk materials at concentrations below 1 percent (Document ID 2101, pp. 5-9).

OSHA has not included a threshold concentration exception in these standards. The Agency has concluded that it would not be appropriate to establish a threshold crystalline silica concentration because the evidence in the rulemaking record is not sufficient to lead OSHA to determine that the suggested concentration thresholds would be protective of employee health. The Agency's exposure assessment findings show that exposures to respirable crystalline silica can exceed the action level of 25 mg/m³ or PEL of 50 mg/m³ even at threshold concentrations less than 1 or 0.1 percent, as demonstrated by the abrasive blasting activities investigated in a NIOSH survey report using Staurite XL in containment (Document ID 0212, p. 12). Issues with regard to requirements for labels and SDSs are addressed in the summary and explanation of requirements for Communication of Respirable Crystalline Silica Hazards to Employees in this preamble.

The Brick Industry Association (BIA) argued that its members should be exempt from compliance with the respirable crystalline silica rule, indicating that the low toxicity of crystalline silica in the brick and structural clay industry does not cause a material risk of health impairment. BIA noted that OSHA has established specific requirements for certain industries in the past, such as the pulp, paper and paperboard mill industry in 29 CFR 1910.216, and the textile industry in 29 CFR 1910.262. BIA requested that OSHA take a similar approach for the brick industry because, BIA argued, silicosis is essentially non-existent in the brick industry's workers (Document ID 2300, pp. 2-4). OSHA also received comments and testimony from stakeholders in the brick, tile, and fly ash industries who argued that in their industries, crystalline silica was most commonly shrouded or occluded within matrices of aluminosilicates, and therefore the silica was less bioavailable and exhibited reduced toxicity (e.g., Document ID 2085, p. 2; 2123, p. 1; 2267, p. 8; 2343, Attachment 1, p. 30; 3587, Tr. 3628; 3587, Tr. 3704).

As discussed in Section V of this preamble, Health Effects, OSHA has reviewed the evidence concerning potential effects on silica-related toxicity of a variety of physical factors, including the age of fractured surfaces of the crystal particle and clay occlusion of the particle. OSHA recognizes that the risk to employees exposed to a given level of respirable crystalline silica may not be equivalent in different work environments due to differences in physical factors that affect the potency of crystalline silica. OSHA also recognizes that workers in these industries (e.g., brick manufacturing) may experience lower rates of silicosis and other health effects associated with exposure to respirable crystalline silica. However, OSHA finds that these employees are still at significant risk of developing adverse health effects from exposure to respirable crystalline silica. The Agency is therefore is not excluding brick, tile, or fly ash from the scope of the rule based on physical characteristics of crystalline silica.

OSHA also received multiple studies, along with testimony and comments from the Sorptive Minerals Institute (SMI) (Document ID 2377; 4230). SMI stated that sorptive clays are limited to a specific and discreet subset of deposits in the U.S., including specifically: The Monterey formation (California), the Porters Creek formation (Mississippi Valley), the Twiggs and Meigs fullers earth (southeastern U.S.), the Wyoming or Western-type sodium bentonite deposits, the calcium bentonite deposits (north-central Florida), and the fullers earth deposits of eastern Virginia (Document ID 4230, p. 3). As discussed in Section V, Health Effects, SMI contended that silica in sorptive clays exists as either amorphous silica or as geologically ancient, occluded quartz, and that neither form poses the health risk described in OSHA's risk assessment (Document ID 4230, p. 2). After evaluation of the evidence SMI submitted to the record, OSHA finds that quartz originating from bentonite and similar sorptive clays is considerably less toxic than unoccluded quartz, and evidence does not exist that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to silica in sorptive clay deposits. OSHA is therefore excluding sorptive clays from the scope of the rule, as described in paragraph (a)(1) of the general industry and maritime standard. The PEL in 29 CFR 1910.1000 Table Z-3 (i.e., the formula that is approximately equivalent to 100 μg/m³) will continue to apply to occupational exposure to respirable crystalline silica from sorptive clays. The exemption covers exposures resulting from the processing, packaging, and distribution of sorptive clays originating from the geological deposits described above (and intended for sorptive clay-specific use such as absorbents for oil, grease, and animal waste, as a carrier for pesticides and fertilizers, or in cosmetics, pharmaceuticals, and animal feeds).

Relationship to other OSHA standards. EEI and the American Iron and Steel Institute (AISI) sought clarification from OSHA regarding how the silica rule would affect the existing coke oven emissions standard or the PEL for coal dust. EEI said that OSHA should expressly exempt coal dust from the rule (Document ID 2357, p. 4). AISI similarly stated that the rule potentially conflicts with the coal dust PEL and is duplicative of existing steel industry standards. AISI stated that OSHA's existing coke oven emissions standard protects employees working in the regulated area around metallurgical coke ovens and metallurgical coke oven batteries where exposures to emissions are of greatest concern. AISI believes that workers covered by OSHA's coke oven emissions standard are therefore already protected adequately from the dangers of crystalline silica exposure and such operations should be exempt from the rule (Document ID 3492, p. 2).

The respirable crystalline silica rule has no effect upon OSHA's standard for coke oven emissions, the existing PEL for coal dust, or any other substance-specific standard. None of these requirements provide the full range of protections afforded by the respirable crystalline silica rule. The PEL for coal dust is only a PEL; it does not provide any additional protections, such as medical surveillance. Other requirements therefore do not provide protection equivalent to the respirable crystalline silica rule. Accordingly, the silica rule applies to these situations to the extent there is silica exposure and the conditions for excluding them from the rule's scope are not met.

Definitions

Paragraph (b) of the standard for general industry and maritime (paragraph (b) of the standard for construction) provides definitions of terms used in the standards.

“Action level” means a concentration of airborne respirable crystalline silica of 25 micrograms of respirable crystalline silica per meter cubed of air (μg/m³), calculated as an 8-hour time-weighted average. The action level triggers requirements for exposure assessment and, in the standard for general industry and maritime, medical surveillance. The definition is unchanged from the proposal.

Because of the variable nature of employee exposures to airborne concentrations of respirable crystalline silica, maintaining exposures below the action level provides reasonable assurance that employees will not be exposed to respirable crystalline silica at levels above the permissible exposure limit (PEL) on days when no exposure measurements are made. Even when all measurements on a given day fall below the PEL but are above the action level, there is a reasonable chance that on another day, when exposures are not measured, the employee's actual exposure may exceed the PEL (Document ID 1501). The importance of the action level is explained in greater detail in the summary and explanation of Exposure Assessment and summary and explanation of Medical Surveillance.

The action level in this rule is set at one-half of the PEL. This is the same ratio of action level to PEL that has been used and been effective in other standards, including those for inorganic arsenic (29 CFR 1910.1018), ethylene oxide (29 CFR 1910.1047), benzene (29 CFR 1910.1028), methylene chloride (29 CFR 1910.1052), and chromium (VI) (29 CFR 1910.1026).

Following the publication of the proposed rule, OSHA received a number of comments pertaining to the definition of the action level. Some commenters, such as National Council for Occupational Safety and Health (NCOSH), American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), International Brotherhood of Teamsters, United Steelworkers (USW), Center for Effective Government (CEG), American Public Health Association (APHA), American Thoracic Society (ATS), and Cara Evens, a private citizen, supported OSHA's proposal to include an action level of 25 μg/m³ (e.g., Document ID 1801, p. 2; 2173, pp. 2-3; 2175, p. 5; 2178, Attachment 1, p. 2; 2318, p. 10; 2336, p. 5; 2341, pp. 2-3; 4204, pp. 42-45, 51-52). For example, USW supported the inclusion of an action level that is half the PEL (25 µg/m³) because:

This action level will further reduce exposure to respirable crystalline silica by workers and will incentivize employers to implement best-practice controls keeping exposures at a minimum as well as reducing costs of monitoring and assessments. The USW believes measuring airborne concentrations of silica at 25ug/m³ will prove feasible given current sampling techniques (Document ID 2336, p. 5).

AFL-CIO noted that action levels have long been incorporated into OSHA standards in recognition of the variability of workplace exposures and argued that the inclusion of an action level is particularly important in this rulemaking because exposures at the PEL pose a significant risk to employees (Document ID 2256, Attachment 2, p. 9). NCOSH and CEG echoed AFL-CIO's concerns about significant risk remaining at the PEL, and NCOSH, further noted that significant risk remains at the action level (Document ID 2173, p. 2; 2341, p. 2).

As discussed in more detail in the summary and explanation of Medical Surveillance, some stakeholders, such as APHA, supported an action level trigger for medical surveillance in the standard for general industry because of significant risk of disease remaining at the action level and even below (Document ID 2178, Attachment 1, p. 2).

The National Institute for Occupational Safety and Health (NIOSH) supported an action level that is lower than the PEL because it is consistent with longstanding industrial hygiene practice, and an action level is included in other OSHA standards. NIOSH did not recommend a value for the action level but cited a 1975 study by NIOSH (Leidel et al. 1975, Document ID 1501) as demonstrating that an action level provides a high level of confidence that most daily exposures will be below the PEL (Document ID 2177, Attachment B, p. 23).

Other commenters supported having an action level, but advocated a higher level (e.g., Document ID 1963, pp. 1-2; 2196, Attachment 1, pp. 1-2; 2200, pp. 1-2; 2213, p. 3; 2232, p. 1; 2233, p. 1; 2301, Attachment 1, p. 78; 2311, p. 3). For instance, the National Industrial Sand Association (NISA) recommended an action level of 50 μg/m³, which is one half the value of the PEL they supported (100 μg/m³). NISA recommended a higher PEL because it disagreed with OSHA that significant risk existed at the proposed PEL of 50 μg/m³. NISA also argued that a PEL of 50 μg/m³ would not be technologically or economically feasible. However, NISA's reasons for recommending an action level set at half of its recommended PEL mirrored many of the reasons offered by USW and AFL-CIO, including maintaining consistency with other OSHA standards, accounting for exposure variability, and providing employers with incentives to keep exposures low. In addition, NISA commented that keeping exposures well below the PEL would provide a margin of safety to protect against uncertainties in the toxicology and epidemiology data supporting a PEL (Document ID 2195, pp. 30-35). NISA also recommended that medical surveillance be triggered at the action level (although, as noted above, NISA recommended an action level of 50 μg/m³); that recommendation is discussed in the summary and explanation of Medical Surveillance.

Southern Company asserted that OSHA set the proposed action level too low, because it believed it is difficult to measure based on current laboratory detection limits (Document ID 2185, pp. 5-6). It recommended that OSHA consider setting the action level at an achievable analysis level (though a suggested level for OSHA to consider was not provided) or conduct further cost analyses of additional sampling and ancillary provisions this may trigger. As stated further below, OSHA's conclusion that silica exposures can be measured with reasonable accuracy at the action level is discussed in the Sampling and Analysis discussion of technological feasibility in Chapter IV of the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA).

Other commenters supported an action level but argued that the proposed action level was set too high. For example, the United Automobile, Aerospace and Agricultural Implement Workers of America (UAW) argued that the action level would need to be set at 12.5 μg/m³, one-fourth of a 50 μg/m³ PEL, in order to ensure that fewer than 5 percent of exposures would exceed a PEL of 50 μg/m³ (Document ID 2282, Attachment 3, p. 14). In support of its recommended action level, UAW cited a study by Rappaport et al. (1988), which reported that no more than 12 percent of log-normally distributed exposures are expected to exceed the PEL with an action level set at one half the PEL (Document ID 2282, Attachment 2, pp. 310, 314). Similarly, the BlueGreen Alliance (BGA) supported a lower action level, indicating that the proposed action level was not protective enough. BGA supported an action level of no higher than 25 percent of the PEL “. . . in order to provide reasonable likelihood that 95% of exposures are below the PEL” (Document ID 2176, p. 2).

Finally, some commenters opposed having any action level (Document ID 2085, p. 3; 2296, p. 40; 2305, pp. 4, 10; 2312, p. 2; 2317, p. 2; 2327, Attachment 1, pp. 13, 15-17; 2305, pp. 4, 10; 2296, p. 40; 3577, Tr. 707-708). Mercatus Center of George Mason University (Mercatus Center) asserted that OSHA did not provide adequate justification for the proposed action level, arguing that because OSHA found a PEL of 25 μg/m³ to be infeasible, the Agency has not shown that employers would have sufficient incentives to limit exposures to the action level (Document ID 1819, p. 2). The Fertilizer Institute indicated that the action level will create a de facto 25 μg/m³ standard because the initial and periodic monitoring requirements will be a time-consuming, expensive endeavor (Document ID 2101, pp. 7-8). The National Concrete Masonry Association and Blue Stone Block Supermarket argued that the best approach would be to remove the action level and only “require action when the PEL is exceeded” (Document ID 2279, p. 9; 2384, p. 9). They believed requiring action only when their recommended PEL of 100 µg/m³ is exceeded would be effective in reducing silica-related illnesses and more cost-effective for industries.

OSHA considered these comments and has decided to retain an action level of 25 µg/m³. OSHA agrees with CEG and AFL-CIO that that the inclusion of an action level of 25 µg/m³ is particularly important in this rulemaking because employees exposed at the action level and revised PEL remain at significant risk of developing respirable crystalline silica-related diseases (see Section VI, Final Quantitative Risk Assessment and Significance of Risk). In addition, as explained in Chapter IV of the FEA, OSHA has found that the revised PEL is technologically and economically feasible. OSHA disagrees with Mercatus Center that an action level of 25 µg/m³ is not appropriate because that level is not feasible as a PEL, and the Agency does not agree with the Fertilizer Institute that a 25 μg/m³ action level creates a de facto standard. The action level only triggers certain requirements (i.e., a requirement for exposure assessment in general industry/maritime and construction, and medical surveillance in general industry/maritime only); employers that exceed it but remain at the PEL or below will not be in violation of the rule, so long as they comply with the requirements associated with the action level. The requirements associated with exposures at or above the action level create an incentive—but not a requirement—for employers to reduce exposures below the action level where it is reasonably possible to do so. Although OSHA could not find that engineering controls and work practices are sufficient to reduce and maintain respirable crystalline silica exposures to a level of 25 μg/m³ or below in most operations most of the time in affected industries, it is likely possible for some employers to reduce exposures to below the action level in some circumstances, without the use of respirators. The Agency also concludes that it is feasible to measure respirable crystalline silica levels at an action level of 25 μg/m³ with reasonable accuracy (see Chapter IV of the FEA). Because employers are not required to reduce exposures below 25 μg/m³, feasibility concerns are not relevant. Consequently, OSHA does not agree with NISA and Southern Company that feasibility concerns warrant revising the proposed action level upward.

OSHA agrees, however, that maintaining exposures below an action level that is half the PEL provides reasonable assurance that employees will not be exposed to respirable crystalline silica at levels above the PEL on days when no exposure measurements are made. OSHA's early standards relied, in part, on a statistical basis for using an action level of one-half the PEL (e.g., acrylonitrile, 29 CFR 1910.1045; ethylene oxide, 29 CFR 1910.1047). OSHA previously determined (based in part on research conducted by Leidel et al., 1975) that where exposure measurements are above one-half the PEL, the employer cannot be reasonably confident that the employee is not exposed above the PEL on days when no measurements are taken (Document ID 1501, pp. 5-6, 29-30, 38). Similarly, Rappaport et al. (1988) used monitoring data and applied a statistical method to estimate that no more than 12 percent of lognormally-distributed exposures would be expected to exceed the PEL if mean exposures remain below an action level set at one-half the PEL (Document ID 2282, Attachment 2).

OSHA thus agrees with UAW and BGA that an action level lower than one-half of the PEL would provide a higher degree of confidence that exposures are not likely to exceed the PEL. However, OSHA's policy is to set the action level at a value that effectively encourages employers to reduce exposures below the action level while still providing reasonable assurance that employee exposures are typically below the PEL. The Agency's experience with previous standards also indicates that an action level of one-half the PEL effectively encourages employers, where feasible, to reduce exposures below the action level to avoid the added costs of required compliance with provisions triggered by the action level.

OSHA is convinced, therefore, that an action level is needed and decided to set the action level at one-half of the PEL, based on residual risk at the PEL of 50 μg/m³, the feasibility of measuring exposures at an action level of 25 μg/m³, and the administrative convenience of having the action level set at one-half the PEL, as it is in other OSHA standards. OSHA's risk assessment indicates that significant risk remains at the PEL of 50 μg/m³. OSHA therefore has a duty to impose additional requirements on employers to reduce remaining significant risk when those requirements will afford benefits to employees and are feasible (Building and Construction Trades Department, AFL-CIO v. Brock, 838 F.2d 1258, 1269 (D.C. Cir 1988)). With significant risk remaining at 50 μg/m³, reducing that risk by incorporating an action level is necessary and appropriate. OSHA concludes that the action level will result in a real and necessary further reduction in risk beyond that provided by the PEL alone.

“Competent person” means an individual who is capable of identifying existing and foreseeable respirable crystalline silica hazards in the workplace and who has authorization to take prompt corrective measures to eliminate or minimize them. The competent person must also have the knowledge and ability necessary to fulfill the responsibilities set forth in paragraph (g) of the construction standard. OSHA has not included requirements related to a competent person in the general industry and maritime standard. This definition therefore is included only in the construction standard.

In the proposal, OSHA defined competent person as one who is capable of identifying existing and predictable respirable crystalline silica hazards in the surroundings or working conditions and who has authorization to take prompt corrective measures to eliminate them. OSHA received a number of comments related to this definition. Many of these commenters suggested that the definition should be expanded. For example, Building and Construction Trades Department, AFL-CIO (BCTD) recommended that OSHA revise the proposed definition to require that the competent person be capable of identifying the proper methods to control existing and predictable hazards in the surroundings or working conditions. BCTD also asked that the definition specify that the competent person be “designated by the employer to act on the employer's behalf.” It proposed specific language that incorporated these suggestions (Document ID 4223, p. 112). International Union of Operating Engineers (IUOE) endorsed the BCTD definition and International Union of Bricklayers and Allied Craftworkers (BAC) agreed with BCTD that OSHA's definition needed to be more fully developed (Document ID 2262, p. 40; 2329, p. 5).

The American Society of Safety Engineers (ASSE) advocated for the following definition, which it based on that of the asbestos standard:

Competent person means, in addition to the definition in 29 CFR 1926.32(f), one who is capable of identifying existing respirable crystalline silica hazards in the workplace and selecting the appropriate control strategy for such exposure and for developing and overseeing written access control plans, who has the authority to take prompt corrective measures to eliminate such hazards, as specified in 29 CFR 1926.32(f), and who is trained in a manner consistent with OSHA requirements for training (Document ID 4201, pp. 3-4).

Finally, NIOSH noted the American National Standards Institute (ANSI) AIO.38 definition of competent person:

One who, as a result of specific education, training, and/or experience, is capable of identifying existing and predictable hazards in the surroundings [or] working conditions that are unsanitary, hazardous or dangerous to employees, and who has the authorization and responsibility to take prompt corrective measures to eliminate them [emphasis omitted] (as cited in Document ID 2177, Attachment B, p. 9).

In determining if the proposed definition for competent person needed to be revised, OSHA considered these comments and the definition of competent person in the safety and health regulations for construction (29 CFR 1926.32(f)). Under 29 CFR 1926.32(f), competent person is defined as one capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees and who is authorized to take prompt corrective measures to eliminate them. OSHA concludes that its definition for competent person is consistent with 1926.32(f) but tailored to respirable crystalline silica by specifying “respirable crystalline silica hazards” instead of “unsanitary, hazardous, or dangerous” conditions. OSHA did make a few minor revisions to its proposed definition. The Agency replaced the word “one” with “individual,” which is merely an editorial change. The Agency removed the phrase “in the surroundings or working conditions” and changed it to “in the workplace” to make it specific to the workplace. The Agency removed the phrase “to eliminate them” and changed it to “to eliminate or minimize them” to denote there may be cases where complete elimination would not be feasible. OSHA also changed “predicted” to “foreseeable” to make the wording consistent with the scope of the standard (paragraph (a)).

OSHA agrees with ASSE and the ANSI definition highlighted by NIOSH that the definition for competent person must indicate that the competent person has appropriate training, education, or experience. Therefore, OSHA further revised the proposed definition for competent person to indicate that the competent person must have the knowledge and ability necessary to fulfill the responsibilities set forth in paragraph (g). Comments regarding knowledge or training for a competent person and OSHA's responses to those comments are discussed in the summary and explanation of Written Exposure Control Plan.

The requirement that the competent person have the knowledge and ability to fulfill the responsibilities set forth in paragraph (g) addresses BCTD's and ASSE's requests to amend the definition to specify that the competent person be capable of identifying or selecting the proper methods to control hazards in the surroundings or working conditions. It is clear from paragraph (g) that the competent person must be familiar with and also capable of implementing the controls and other protections specified in the written exposure control plan.

ASSE also requested that the definition indicate that the competent person be capable of developing and overseeing the written access control plan, which OSHA had proposed. However, the final rule does not specify a written access control plan, and instead requires a written exposure control plan. Regardless, OSHA does not agree with ASSE's suggestion that the definition should be revised to indicate capability to develop a written plan. OSHA assigns that responsibility to the employer because under paragraph (g)(4), the competent person is someone on the job site who makes frequent and regular inspections, and thus may not be involved in developing the written exposure control plan in an office environment. OSHA also disagrees with BCTD that the definition should specify that the competent person is designated by the employer to act on behalf of the employer. The employer's obligation to designate a competent person is clearly specified in paragraph (g)(4) and the definition clearly states that the competent person has authority to promptly apply corrective measures.

The competent person concept has been broadly used in OSHA construction standards (e.g., 29 CFR 1926.32(f) and 1926.20(b)(2)), particularly in safety standards. This standard does not affect the competent person provisions in these other standards.

“Employee exposure” means the exposure to airborne respirable crystalline silica that would occur if the employee were not using a respirator. This definition clarifies the requirement that employee exposure must be measured as if no respiratory protection is being worn. The definition, which is consistent with OSHA's previous use of the term in other standards, did not generate any comment and is unchanged from the proposal.

“High-efficiency particulate air (HEPA) filter” means a filter that is at least 99.97 percent efficient in removing mono-dispersed particles of 0.3 micrometers in diameter. The definition is unchanged from the proposal. HEPA filters are more efficient than membrane filters because they are designed to target much smaller particles. In the housekeeping requirements of paragraph (h)(1) of the standard for general industry and maritime (paragraph (f)(1) of the standard for construction), OSHA refers to HEPA-filtered vacuuming as an example of an appropriate cleaning method, and the Table 1 entry for handheld and stand-mounted drills requires use of a HEPA-filtered vacuum (if a commercially available hole-cleaning kit connected to a dust collector is not being used). OSHA had also proposed HEPA-filtered dust collectors as controls for some tasks listed on Table 1 of the proposed standard for construction.

The Agency received one comment related to HEPA filters from the Occupational and Environmental Health Consulting Services (OEHCS). First, OEHCS recommended that the definition be expanded to indicate that HEPA filters are effective at removing particles in the 0.3-micrometer size range, as measured by a laser particle counter. Second, it requested addition of the term “Portable High Efficiency Air Filtration (PHEAF)” device, defined as a portable device equipped with a certified HEPA filter that, when tested as a complete unit, is 99.97 percent effective in removing particles in the 0.3-micrometer size range, as measured by a laser particle counter (Document ID 1953, pp. 4-6). OEHCS advocated for a requirement that portable filtration devices (e.g., HEPA vacuums, dust collectors used on tools, and filter systems for enclosed cabs) meet the definition of PHEAF. It argued that HEPA vacuums or other portable filtration devices might not perform effectively in the field due to inadequate, damaged, or deteriorating sealing surfaces; replacement filters that do not fit correctly; filter cabinets that are damaged; or filters that are punctured. Claiming that damaged filters might not build up enough pressure differential to signal that they should be changed, OEHCS recommended a requirement for field testing the devices using a laser particle counter to ensure that HEPA filters function as intended (Document ID 1953, Attachment 1, pp. 2-4).

OSHA encourages employers to ensure that HEPA filters function in the field according to the specifications of this definition. However, the Agency concludes that it is not appropriate to include requirements for PHEAF devices, as defined by OEHCS, or laser particle counting testing, in the rule due to the lack of documented effectiveness or consistency with the definition and because of the lack of support in the record. As a result, OSHA is retaining its proposed definition for HEPA filter and is not adding PHEAF to the definitions section.

“Objective data” means information, such as air monitoring data from industry-wide surveys or calculations based on the composition of a substance, demonstrating employee exposure to respirable crystalline silica associated with a particular product or material or a specific process, task, or activity. The data must reflect workplace conditions closely resembling or with a higher exposure potential than the processes, types of material, control methods, work practices, and environmental conditions in the employer's current operations.

The proposed definition of “objective data” also included “calculations based on the . . . chemical and physical properties of a substance” as an example of a type of objective data that might demonstrate employee exposure to respirable crystalline silica. BCTD objected to this example's inclusion in the definition (Document ID 2371, Attachment 1, pp. 11-12). Although BCTD agreed that the chemical and physical properties of a substance are among the factors that may be relevant in determining whether data from one set of circumstances can be used to characterize the exposures in other circumstances, BCTD stated that the proposed definition suggested that the chemical and physical properties of the material could be determinative in every instance. It also maintained that on construction sites the work processes themselves are more consistently a significant predictor of ambient silica exposures than percentage of silica in the material itself. Finally, BCTD argued that it is very important to focus not only on the overall operation, but also the specific silica dust-generating task.

In including this item in the definition, OSHA did not intend to imply that it would be relevant in all circumstances. Nonetheless, OSHA has removed the phrase “chemical and physical properties” from the final definition of “objective data” because it has concluded that a substance's chemical and physical properties are not typically relevant for demonstrating exposures to respirable crystalline silica. However, in those instances where a substance's physical and chemical properties demonstrate employee exposure to respirable crystalline silica associated with a particular product or material or a specific process, task, or activity, an employer may use that information as objective data under this rule.

The proposed rule also stated that objective data is information demonstrating employee exposure to respirable crystalline silica associated with a particular product or material or a specific process, operation, or activity. Throughout this rule, OSHA has often replaced the word “operation” with the word “task” (see summary and explanation of Specified Exposure Control Methods for further discussion). OSHA has made the change to “task” (instead of “operation”) in this definition to remain consistent with that change. This is also consistent with NIOSH's recommendation to add specificity to the definition by including the term “task” (Document ID 2177, Attachment B, p. 12).

In addition, the proposal indicated that “objective data” needed to reflect workplace conditions closely resembling the processes, types of material, control methods, work practices, and environmental conditions in the employer's current operations. Dow Chemical Company stated that this requirement is generally appropriate, but argued that when data pertain to a more challenging work environment with higher potential for exposure, those data should be considered objective data (Document ID 2270, p. 2). It explained:

If data from a more challenging environment demonstrate compliance with the Permissible Exposure Limit, then one may infer with confidence that workers in a less challenging environment (i.e., with less potential for exposure) are also not exposed above the PEL. Even if the two work environments are not “closely resembling,” the data are still an objective, valid method of screening workplaces that have a clearly lower risk of exposure (Document ID 2270, p. 2).

OSHA agrees with Dow that data pertaining to an environment with higher exposure potential can be used as objective data for other environments with less potential for exposure. Therefore, OSHA added “or with a higher exposure potential” to the definition.

Edison Electric Institute (EEI) requested that OSHA harmonize the definition of “objective data” throughout its regulations (Document ID 2357, p. 22). OSHA recognizes that the term has evolved over time based on the Agency's experience implementing those standards. “Objective data”, as defined in this standard, is based on the record in this rulemaking and reflects an appropriate definition in the context of exposures to respirable crystalline silica. Additionally, OSHA has established a process, the Standards Improvement Project, to improve and streamline OSHA standards, including the revision of individual requirements within rules that are inconsistent. OSHA will consider reviewing the consistency of this definition in the next iteration of this ongoing effort.

Many commenters suggested that OSHA add specificity with regards to what is considered objective data and establish criteria for objective data in the definition (e.g., Document ID 2177, Attachment B, p. 11; 2181, p. 5; 2253, p. 4; 2256, Attachment 2, p. 10; 2339, p. 7; 2371, Attachment 1, p. 12; 2379, Appendix 1, pp. 54-55; 2380, Attachment 2, p. 26; 4223, p. 70). As discussed in the summary and explanation of Exposure Assessment, OSHA intends for the performance option to give employers flexibility to accurately characterize exposures using whatever processes or data are most appropriate for their circumstances. The Agency concludes it would be inconsistent to include specifications or criteria in the definition of objective data and thus has not done so here.

Commenters also provided examples of alternative exposure measurement and characterization strategies that could generate objective data, such as: area sampling (Document ID 2195, pp. 36-37); area exposure profile mapping (Document ID 2379, Appendix 1, pp. 48-49); real-time monitoring (Document ID 2256, Attachment 3, p. 12; 2357, pp. 37-38; 2379, Appendix 1, pp. 48-49, 55-56; 3578, Tr. 941-942; 3579, Tr. 161-162; 3588, Tr. 3798-3800; 4204, p. 56); and geotechnical profiling with testing for crystalline silica content (Document ID 2262, p. 13). Trolex LTD pointed to emerging methods and technologies, such as new optical methods for particle counting and identification, which might provide enhanced measurements of real-time employee exposure to respirable crystalline silica in the future (Document ID 1969, p. 2).

In addition, commenters provided specific examples of types of information and information sources that they felt should be considered objective data. For example, the American Foundry Society (AFS) commented that objective data should include data that permits reliable estimation of exposure, such as: data from real-time monitors and area exposure mapping; data from less than full-shift samples where professional judgment can be used to determine exposure levels; and exposure data where the percent of silica is calculated using a historical average for the area or operation involved (Document ID 2379, Appendix 1, pp. 54-55). The National Association of Manufacturers suggested the following as reliable sources of objective data: published scientific reports in the open scientific literature; NIOSH Health Hazard Evaluations; insurance carriers' loss prevention reports; and information that the silica in a process cannot be released because it is bound in a matrix preventing formation of respirable particles (Document ID 2380, Attachment 2, p. 26). ASSE identified industry-wide data, safety data sheets from product manufacturers, prior historical sampling data under comparable conditions, and aggregated company-wide sampling information as reliable sources of objective data (Document ID 3578, Tr. 1036). Commenters also pointed to data collected by a trade association from its members (e.g., Document ID 2181, pp. 5-6, 7; 2371, Attachment 1, Appendix A; 3544, pp. 12-13; 3583, Tr. 2394; 3585, Tr. 2905-2906; 3588, Tr. 3936-3938; 4197, pp. 1-6; 4198, pp. 1-181; 4223, pp. 68-70).

The Agency, while including specific examples in the definition (i.e., air monitoring data from industry-wide surveys and calculations based on the composition of a substance), does not intend to limit the information that can be considered objective data to the information from those sources. OSHA agrees that data developed with alternative exposure measurement and characterization strategies, both those currently available and those that become available in the future, and the types of information and information sources suggested by commenters can be used as objective data where the conditions of the definition are satisfied. Monitoring data obtained prior to the effective date of the rule can also be considered objective data if it demonstrates employee exposure to respirable crystalline silica associated with a particular product or material or a specific process, task, or activity and reflects workplace conditions closely resembling or with a higher exposure potential than the processes, types of material, control methods, work practices, and environmental conditions in the employer's current operation.

Objective data is further discussed in the summary and explanation of Scope and Application (paragraph (a)(2) for general industry and maritime) and Exposure Assessment (paragraph (d) for general industry and maritime standard and paragraph (d)(2) for the construction standard).

“Physician or other licensed health care professional [PLHCP]” means an individual whose legally permitted scope of practice (i.e., license, registration, or certification) allows him or her to independently provide or be delegated the responsibility to provide some or all of the particular health care services required by paragraph (i) of this section (paragraph (h) of the standard for construction). This definition is unchanged from the proposal, and is included because the standard requires that all medical examinations and procedures be performed by or under the supervision of a PLHCP.

OSHA received two comments on the definition of PHLCP, both of which addressed the scope of the PHLCP's qualifications, from APHA and ATS (Document ID 2175, p. 5; 2178, Attachment 1, p. 5). ATS agreed with OSHA's determination of who is qualified to be a PLHCP (Document ID 2175, p. 5). APHA advocated that the PLHCP:

. . . should be licensed for independent practice . . . and have training and experience in clinical and in population/preventive health, in managing and interpreting group surveillance information, and in the care and management of respiratory illness (Document ID 2178, Attachment 1, p. 5).

APHA commented that:

. . . different members of the health team may provide different required services through referral or other arrangements, but the designated PLHCP should have responsibility for program oversight and coordination (Document ID 2178, Attachment 1, p. 5).

As discussed further in the summary and explanation of Medical Surveillance, OSHA agrees that different tasks may be performed by various PLHCPs, according to their licenses, but has determined that requiring a license for independent practice and the extra training and responsibilities advocated by APHA are neither necessary nor appropriate for the PLHCP in OSHA standards. Any PLHCP may perform the medical examinations and procedures required under the standard when he or she is licensed, registered, or certified by state law to do so. Who qualifies to be a PLHCP is determined on a state-by-state basis by state licensing bodies. OSHA's broad definition for PLHCP gives the employer the flexibility to retain the services of a variety of qualified licensed health care professionals. Moreover, since the term PHLCP includes more than just physicians, it addresses concerns about the limited availability of medical providers in rural areas (e.g., Document ID 2116, Attachment 1, p. 43; 2365, p. 10).

OSHA has included the same definition for PLHCP in other standards and continues to find that it is appropriate to allow any individual to perform medical examinations and procedures that must be made available under the standard when he or she is appropriately licensed by state law to do so and is therefore operating under his or her legal scope of practice. PLHCP, as defined and used in this standard, is consistent with other recent OSHA standards, such as chromium (VI) (29 CFR 1910.1026), methylene chloride (29 CFR 1910.1052), and respiratory protection (29 CFR 1910.134). OSHA's experience with PLHCPs in these other standards supports the Agency's determination.

“Regulated Area” means an area, demarcated by the employer, where an employee's exposure to airborne concentrations of respirable crystalline silica exceeds, or can reasonably be expected to exceed, the PEL. The definition is unchanged from the proposed standard. This definition is consistent with the use of the term in other OSHA standards, including those for chromium (VI) (29 CFR 1910.1026), 1,3-butadiene (29 CFR 1910.1051), and methylene chloride (29 CFR 1910.1052).

OSHA proposed the inclusion of regulated areas in the standards for both construction and general industry/maritime, but has not included this provision, or the associated definition, in the final standard for construction. Construction industry stakeholders should instead refer to paragraph (g)(1)(iv) for written exposure control plan requirements to describe procedures for restricting access.

Several stakeholders, including the Construction Industry Safety Coalition (CISC) and National Association of Home Builders, requested that OSHA clarify what “reasonably expected” means (e.g., Document ID 2296, p. 25; 2319, p. 89). CISC argued that “[s]uch subjective language is not enforceable and . . . will be fraught with compliance problems . . .” (Document ID 2296, p. 25; 2319, p. 89).

As noted above, the language in the regulated areas definition has been included in a number of previous OSHA standards. Based on OSHA's experience with these standards, OSHA expects that employers will have little difficulty understanding the meaning of the phrase “reasonably be expected to exceed.” One reason OSHA chooses to utilize language that has been used in previous standards, where possible, is to avoid the sort of confusion CISC describes. In addition, the basis for establishing regulated areas in general industry and maritime and the reason for omitting this requirement in the construction standard are discussed in further detail in the summary and explanation of Regulated Areas.

“Respirable crystalline silica” means quartz, cristobalite, and/or tridymite contained in airborne particles that are determined to be respirable by a sampling device designed to meet the characteristics for respirable-particle-size-selective samplers specified in the International Organization for Standardization (ISO) 7708:1995: Air Quality—Particle Size Fraction Definitions for Health-Related Sampling. The definition in the rule is very similar to the proposed definition with one modification. OSHA changed the wording from “means airborne particles that contain quartz, cristobalite, and/or tridymite and whose measurement is determined by a sampling device . . .” to “means quartz, cristobalite, and/or tridymite contained in airborne particles that are determined to be respirable by a sampling device . . .” to make it clear that only that portion of the particles that is composed of quartz, cristobalite, and/or tridymite is considered to be respirable crystalline silica.

The definition for respirable crystalline silica encompasses the forms of silica (i.e., quartz, cristobalite, and tridymite) covered under current OSHA standards and harmonizes the Agency's practice with current aerosol science and the international consensus that the ISO convention represents. The American Conference of Governmental Industrial Hygienists (ACGIH) and the European Committee for Standardization (CEN) have adopted the ISO criteria for respirable particulate collection efficiency, and the criteria are sometimes referred to as the ISO/CEN definition. NIOSH has also adopted the ISO definition in its Manual of Sampling and Analytical Methods (Document ID 0903, p. 2). Adoption of this definition by OSHA allows for workplace sampling for respirable crystalline silica exposures to be conducted using any particulate sampling device that conforms to the ISO criteria (i.e., a device that collects dust according to the particle collection efficiency curve specified in the ISO standard). The relationship between the ISO criteria for respirable particulate collection efficiency and the ACGIH criteria is discussed in greater detail in the Sampling and Analysis discussion in Chapter IV of the FEA.

The U.S. Chamber of Commerce (the Chamber), Halliburton, and the National Rural Electric Cooperative Association (NRECA) asserted that OSHA's proposed definition of respirable crystalline silica would encompass non-respirable particles (Document ID 2288, p. 15; 2302, p. 7; 2365, p. 12). NRECA stated:

. . . the proposed definition would include anything that gets collected onto the sampling media from respirable-particle size-selective samplers. Unfortunately, these samplers are not fool-proof and often much larger sized particles do make their way into the sampling media; that is, they collect total crystalline silica dusts rather than just the respirable portions. This definition will include all total dusts that make their way through the cyclone and into the sampling media, thus suggesting a much larger exposure than is otherwise the case . . . (Document ID 2365, p. 12).

As indicated in the discussion of the feasibility of measuring respirable crystalline silica exposures in Chapter IV of the FEA, there is currently no sampling device that precisely matches the ISO criteria in capturing respirable dust. However, available research indicates that many existing devices can achieve good agreement with the ISO criteria. When operated correctly, the sampling devices do not collect total dusts; they collect only the respirable fraction.

The Chamber and NRECA also argued that OSHA's proposed definition of respirable crystalline silica would include substances other than crystalline silica (Document ID 2288, p. 15; 2365, p. 12; 3578, Tr. 1138). NRECA stated:

An additional concern with the definition is that it states “any particles that contain quartz, cristobalite, and/or tridymite . . .” It is possible to interpret this portion of the definition to mean that any other mineral/impurities that were able to be collected into the sampling media will be counted/weighed as opposed to just the silica portions . . . (Document ID 2365, p. 12).

In addition, American Industrial Hygiene Association (AIHA) indicated that the proposed definition would include the entirety of a sample of dust containing any miniscule but detectable quantity of quartz, cristobalite or tridymite, and recommended revising the definition (Document ID 2169, pp. 2-3).

OSHA recognizes that the proposed definition could have been misunderstood to encompass components of respirable dust particles other than quartz, cristobalite, and tridymite. This was not the Agency's intent, and, in response to these comments, OSHA has revised the definition to clarify that only the portion of the particles composed of quartz, cristobalite, or tridymite is considered to be included in the definition of respirable crystalline silica.

Ameren Corporation supported OSHA's inclusion of quartz and cristobalite and allowing the use of a sampling device designed to meet the characteristics for respirable particle size-selective samplers specified in ISO 7708:1995 in the definition, but indicated that the definition should be limited to a “percentage of 1% or greater” (Document ID 2315, p. 3). However, it did not provide a rationale for why OSHA should include this in the definition. Including such a limitation in the definition of respirable crystalline silica would have the effect of limiting coverage of the rule to situations where crystalline silica concentrations in a mixture exceed the 1 percent threshold. As discussed in the summary and explanation of Scope and Application, OSHA concludes that it is not appropriate to limit coverage of the rule to situations where concentrations of crystalline silica in a mixture exceed a 1 percent threshold.

The Society for Protective Coatings (SSPC) and the National Automobile Dealers Association recommended that OSHA distinguish between amorphous silica and crystalline silica in the definition (Document ID 2120, p. 2; 2358, p. 5). SSPC also provided a link to a Web page ( http://www.crystallinesilica.eu/content/what-respirable-crystalline-silica-rcs ) to guide the Agency on revising the definition. OSHA finds that the term “crystalline” is sufficiently descriptive and does not merit further explanation in the definition. However, the Agency affirms here that fused quartz and other forms of amorphous silica are not considered crystalline silica under the rule.

The SEFA Group (formerly the Southeastern Fly Ash Company) suggested adding a definition for “free respirable crystalline silica” to describe crystalline silica as an independent structure with varying surface chemistry, as distinguished from crystalline silica that is incorporated into a larger matrix of the parent mineral (Document ID 2123, p. 2). OSHA has revised the definition to clarify that respirable crystalline silica includes only the crystalline silica contained in airborne particles, i.e., the component in dust that is crystalline silica and not some other mineral. The Agency does not agree that defining the term “free respirable crystalline silica” will alter the meaning or enhance the clarity of the rule, and has not added this term.

“Specialist” means an American Board Certified Specialist in Pulmonary Disease or an American Board Certified Specialist in Occupational Medicine. The term is used in paragraph (i) of the standard for general industry and maritime, (paragraph (h) of the standard for construction), which sets forth requirements for medical surveillance. For example, paragraph (i)(7)(i) of the standard for general industry and maritime, (paragraph (h)(7)(i) of the standard for construction) requires that the employer make available a medical examination when specialist referral is indicated in the PLHCP's written medical opinion for the employer.

The proposed rule did not include this term in the Definitions paragraph because it only allowed referral to an American Board Certified Specialist in Pulmonary disease, which was clearly addressed in the Medical Surveillance paragraph of the rule. However, several commenters recommended that OSHA expand the types of specialists to whom employees could be referred. For example, Dow Chemical requested that OSHA not require the pulmonary specialist to be board certified to expand availability of specialists and noted that several OSHA standards, such as benzene and 1,3-butadiene, do not require the specialist to be board certified (Document ID 2270, pp. 5-8). The Glass Association of America, Asphalt Roofing Manufacturers Association, North American Insulation Manufacturers Association, ATS, and BCTD requested that OSHA also allow referral to an occupational medicine specialist, with many of them specifying a board certified occupational medicine specialist (Document ID 2215, p. 9; 2291, p. 26; 2348, Attachment 1, p. 40; 3577, Tr. 778; 4223, p. 129).

OSHA is retaining the requirement for board certification to ensure a high level of competency. However, OSHA is persuaded by comments and testimony that individuals who are either American Board Certified in Occupational Medicine or American Board Certified in Pulmonary Disease are recognized specialists qualified to examine patients referred for possible respirable crystalline silica-related diseases. OSHA concludes that both pulmonary disease and occupational medicine specialists are qualified to counsel employees regarding work practices and personal habits that could affect their respiratory health, consistent with recommendations in Section 4.7.2 in ASTM standards E 1132-06, Standard Practice for Health Requirements Relating to Occupational Exposure to Respirable Crystalline Silica and E 2626-09, Standard Practice for Health Requirements Relating to Occupational Exposure to Respirable Crystalline Silica for Construction and Demolition Activities (Document ID 1466, p. 5; 1504, p. 5). OSHA therefore added the definition to allow referrals to providers who are American Board certified in pulmonary disease or occupational medicine. The addition of the term to definitions also allows OSHA to simply refer to “specialist” when referring to American Board certified pulmonary disease and occupational medicine specialists in the medical surveillance paragraph of the rule.

“Assistant Secretary,” “Director,” and “This section” are also defined terms. The definitions are consistent with OSHA's previous use of these terms in other health standards and have not changed since the proposal, which elicited no comments.

Finally, stakeholders suggested that OSHA define a number of new terms, including: “affected employee” (American Iron and Steel Institute (AISI) (Document ID 2261, p. 4)), “aged silica” (the Sorptive Minerals Institute (Document ID 3587, Tr. 3698-3699)), “asphalt milling” (IUOE (Document ID 2262, pp. 23-24)), “chest radiograph” (NIOSH (Document ID 2177, Comment B, pp. 40-41)), “controlling employer” (BAC and BCTD (Document ID 2329, p. 7; 2371, pp. 38-40)), “each employee” or “each affected employee” (AISI (Document ID 3492, p. 3)), “earth moving” (IUOE (Document ID 2262, pp. 6-9, 15)), “earth moving equipment” (IUOE (Document ID 3583, Tr. 2356-2360; 2262, pp. 6-9, 15)), “estimating respirable dust, excessive” (Industrial Hygiene Specialty Resources (Document ID 2285, p. 7)), “gross contamination” or “grossly contaminated” (ORCHSE, AFS, and NAHB (Document ID 2277, p. 4; 3584, Tr. 2669-2671; 3487, pp. 21-22; 2296, p. 29; 2379, Attachment B, p. 32)), “grossly” (Tile Council of North America (Document ID 2363, p. 6)), “intermittent work” (EEI (Document ID 2357, p. 14)), “respirable dust” (AFS (Document ID 2379, Attachment B, pp. 16, 28)), “safety and health professional technician” (Dr. Bird of the Chamber (Document ID 3578, Tr. 1176-1177)), “short duration” (EEI (Document ID 2357, p. 14)), and “silica exposure” (AIHA (Document ID 2169, p. 5)).

OSHA has concluded that these terms do not need to be defined in the rule. Many of the terms were part of the proposal or were included in stakeholder's comments on the proposal, but do not appear in the rule. For example, the proposed rule contained a provision related to protective work clothing in regulated areas that would have been triggered where there is potential for employees' work clothing to become grossly contaminated with finely divided material containing crystalline silica. As discussed in summary and explanation of Regulated Areas, OSHA has not included a requirement for employers to provide protective work clothing or other means of removing silica dust from clothing in the rule, and the rule does not otherwise use the terms “grossly,” “gross contamination,” or “grossly contaminated.” Therefore, there is no reason to define these terms.

OSHA concludes that many of the other terms that stakeholders asked the Agency to define are sufficiently explained in the preamble or their meanings are clear. For example, OSHA explains the term “affected employee” in the summary and explanation of Exposure Assessment. Because the term only appears in paragraphs (d)(6) and (7) of the standard for general industry and maritime (paragraphs (d)(2)(vi) and (vii) for construction) and is thoroughly explained in the summary and explanation, OSHA concludes that it need not be defined in this section.

Specified Exposure Control Methods. OSHA's standard requires employers engaged in construction to control their employees' exposure to respirable crystalline silica. Paragraph (c) of the standard for construction describes the specified exposure control methods approach. This approach includes “Table 1: Specified Exposure Control Methods When Working With Materials Containing Crystalline Silica,” a table identifying common construction tasks known to generate high exposures to respirable crystalline silica and specifying appropriate and effective engineering controls, work practices, and respiratory protection for each identified task. For each employee engaged in a task identified on Table 1, the employer is required to fully and properly implement the engineering controls, work practices, and respiratory protection specified for the task on Table 1, unless the employer assesses and limits the exposure of the employee to respirable crystalline silica in accordance with paragraph (d) of the standard for construction. If the employer fully and properly implements the engineering controls, work practices, and respiratory protection specified for each employee engaged in a task identified on Table 1, the employer is not required to conduct exposure assessments or otherwise comply with a PEL for those employees. If the employer does not follow Table 1 for employees engaged in identified tasks or if the respirable crystalline silica-generating task is not identified on Table 1, the employer must assess and limit the exposure of employees in accordance with paragraph (d) of the standard for construction. Paragraph (d) of the standard for construction imposes requirements similar to OSHA's traditional approach of requiring employers to demonstrate compliance with a PEL through required exposure assessments and controlling employee exposures through the use of feasible engineering controls and work practices (i.e., the hierarchy of controls) (see the summary and explanation of Alternative Exposure Control Methods for further discussion of this approach).

The concept for the specified exposure control methods approach was included in the proposed rule. OSHA also included a version of Table 1 in the proposed rule for construction employers, identifying specific engineering controls, work practices, and respiratory protection for common construction tasks that employers could use to meet the requirement to implement engineering and work practice controls. Employers fully implementing the engineering controls, work practices, and respiratory protection on Table 1 would not have been required to conduct exposure assessments for employees performing a listed task, but would have been required to comply with the 50 µg/m³ PEL for those employees. For tasks where respirator use was to be required, employees were presumed to be exposed above the PEL, and thus the proposed standard would have required the employer to comply with all provisions that would be triggered by exposure above the PEL (e.g., regulated areas, medical surveillance), except for exposure monitoring.

Prior to the NPRM, OSHA included this alternative compliance approach in the Preliminary Initial Regulatory Flexibility Analysis (PIRFA) provided to small business representatives during the Small Business Regulatory Enforcement Fairness Act (SBREFA) process (Document ID 0938, pp. 16-17). Participants in the SBREFA process generally supported the approach and their comments further informed the Agency in developing the proposed rule (Document ID 0937, pp. 37-39). An alternative compliance approach similar to that developed by OSHA for the SBREFA process was also included in ASTM E 2625-09, Standard Practice for Controlling Occupational Exposure to Respirable Crystalline Silica for Construction and Demolition Activities, a consensus standard issued in May 2009 developed by a committee consisting of both labor and industry representatives for crystalline silica exposures in construction (Document ID 1504). Following this, on December 10, 2009, the Advisory Committee on Construction Safety and Health (ACCSH) recommended that OSHA include the specified exposure control methods approach in its proposed rule (Document ID 1500, p. 13).

The approach of specifying a list of tasks with a corresponding list of controls to simplify compliance in the construction industry received wide support from representatives in government, including the National Institute for Occupational Safety and Health (NIOSH); professional organizations, including the American Industrial Hygiene Association (AIHA) and the American Society of Safety Engineers (ASSE); labor, including the International Union of Operating Engineers (IUOE), the Building and Construction Trades Department of the AFL-CIO (BCTD), the Laborers' Health and Safety Fund of North America (LHSFNA), and the International Union of Bricklayers and Allied Craftworkers (BAC); and industry groups, including the Associated General Contractors of New York State, the Edison Electric Institute (EEI), and the National Asphalt Pavement Association (NAPA) (e.g., Document ID 2177, Attachment B, p. 23; 3578, Tr. 1028; 2339, p. 8; 3583, Tr. 2337-2338; 2371, Attachment 1, p. 22-23; 3589, Tr. 4192-4193; 2329, pp. 5-6; 2145, pp. 4-5; 3583, Tr. 2171; 2357, p. 26). Walter Jones, an industrial hygienist representing LHSFNA, testified that the approach “not only makes compliance . . . easier to determine, enforce, and teach, it also assures acceptable levels of healthfulness” (Document ID 3589, Tr. 4193).

Industry trade associations, such as the Construction Industry Safety Coalition (CISC), Leading Builders of America (LBA), the Mechanical Contractors Association of America, and individual construction employers, including Atlantic Concrete Cutting, Inc. and Holes Incorporated, generally supported the overall approach while being critical of the specifics of Table 1 (e.g., Document ID 4217, p. 20; 2367, p. 2; 2338, p. 3; 2269, pp. 21-22; 2143, pp. 2-3). CISC stated that its group of employers “continues to be appreciative of OSHA's efforts to try to make a simple compliance option . . . for construction employers” (Document ID 4217, p. 20).

One commenter, Francisco Trujillo, safety director for Miller and Long, Inc., suggested that the specified exposure control methods approach to compliance in the construction industry is not a substitute for safety professionals and industrial hygienists conducting exposure assessments and selecting the appropriate engineering controls, work practices, and respiratory protection for each task based on the results. He commented that “[t]he implication that if Table 1 is followed everything will be fine is unrealistic . . .” and recommended that Table 1 be at most non-mandatory guidance (Document ID 2345, p. 4).

OSHA agrees that safety professionals and industrial hygienists play a key role in ensuring the safety of employees exposed to silica during certain activities, including those not listed on Table 1, and can also help ensure that the engineering controls, work practices, and respiratory protection specified on Table 1 are fully and properly implemented. However, as discussed below, the Agency is not persuaded that construction employees will always be better protected by the traditional performance approach of establishing a PEL and requiring periodic exposure assessments, particularly when the tasks and tools that cause high exposures to respirable crystalline silica, and the dust control technologies available to address such exposures, can be readily identified.

Although there was general agreement among commenters that an alternative approach was needed to simplify compliance for the construction industry, commenters provided various opinions on how such an alternative compliance approach should be structured to ensure that it was workable in practice. Several commenters, including BCTD, LHSFNA, EEI, LBA, Fann Contracting, Inc., CISC, ASSE, the National Association of Home Builders (NAHB), the Associated Builders and Contractors (ABC), and Holes Incorporated, urged OSHA to exempt employers complying with Table 1 from also complying with the PEL (e.g., Document ID 2371, Attachment 1, p. 26; 4223, p. 92-94; 4207, p. 3; 2357, p. 26; 2269, pp. 21-22; 2116, Attachment 1, p. 29; 2319, pp. 123-124; 2339, pp. 8-9; 2296, p. 41; 2289, p. 7; 3580, Tr. 1364). Holes Incorporated and ABC suggested that employers would not use an approach that required compliance with both the PEL and specified engineering controls (Document ID 3580, Tr. 1364; 2289, p. 7). The National Utility Contractors Association (NUCA) argued that not linking the actions on Table 1 directly to compliance with the regulation was confusing and would make it difficult for contactors to be certain they are in compliance (Document ID 2171, p. 2). ASSE suggested that Table 1 should constitute compliance with the PEL because the listed controls “can be viewed as akin to implementing all technologically feasible controls” (Document ID 2339, pp. 8-9). BCTD commented that the focus of OSHA's enforcement efforts should be on ensuring that employers have fully and properly implemented the controls listed on Table 1 (Document ID 2371, Attachment 1, p. 26).

Similarly, commenters from both industry and labor, including the American Federation of State, County, and Municipal Employees, Mechanical Contractors Association of America, the American Federation of Labor and Congress of Industrial Organizations, BAC, BCTD, and LHSFNA, also argued that exposure assessments should not be required where employers implement control measures specified on Table 1 for construction tasks (e.g., Document ID 2106, p. 3; 2143, pp. 2-3; 2256, Attachment 2, p. 10; 2329, pp. 5-6; 2371, Attachment 1, pp. 6-7; 4207, p. 2). LHSFNA stated that:

. . . air monitoring is less practical in construction, where the jobsite and work is constantly changing, than in general industry where work exposures are more stable. In construction, air monitoring results often come back from the lab after the task has ended and thus are of little value . . . (Document ID 2253, p. 2).

On the other hand, other commenters, including NIOSH, argued that fully implementing the controls described on Table 1 would not automatically provide a sufficient level of confidence that exposures are adequately controlled; employers would also need to ensure that the exposures of employees performing Table 1 tasks would not exceed the revised PEL (e.g., Document ID 2177, Attachment B, p. 17). Mr. Trujillo's comment emphasizing the role of safety professionals and recommending that Table 1 be at most non-mandatory guidance was to the same effect (Document ID 2345, p. 4).

Several commenters, including Fann Contracting, IUOE, LBA, CISC, Charles Gordon, a retired occupational safety and health attorney, Arch Masonry, Inc., and NUCA argued that as proposed, the alternative compliance option would not necessarily simplify compliance for some employers, as they would still need to do exposure assessments for a variety of reasons, such as monitoring employees working in the vicinity of Table 1 tasks, complying with the PEL, providing monitoring data to controlling employers on multi-employer worksites, and complying with the rule for tasks that are not listed on Table 1 (Document ID 2116, Attachment 1, p. 3; 2262, pp. 44-45; 2269, pp. 21-22; 2319, p. 6; 3538, p. 16; 3580, Tr. 1473-1474; 3587, Tr. 3677-3679; 3583, Tr. 2243).

Other commenters supported the inclusion of exposure assessment requirements for employees performing tasks on Table 1 even where employers implement the specified engineering controls, work practices, and respiratory protection to best protect employees in the construction industry. The Center for Progressive Reform commented that:

[t]he same principles that weigh in favor of a requirement to monitor silica exposure in other industries holds for the construction industry—monitoring gives workers, employers, OSHA, and researchers valuable information that can be used to reduce workplace hazards (Document ID 2351, p. 11).

The International Safety Equipment Association (ISEA) opined that the most protective approach for employees is for employers to take air samples of respirable crystalline silica (Document ID 2212, p. 1). AIHA argued that there remained a need for exposure monitoring to verify that the controls in place for Table 1 tasks actually reduce exposures (Document ID 2169, p. 3). NIOSH recommended periodic exposure monitoring requirements for these tasks to provide a sufficient level of confidence that exposures are adequately controlled and that the employers' selection of equipment, maintenance practices, and employee training were effective (Document ID 2177, Attachment B, pp. 17, 26). Charles Gordon proposed that when performing a Table 1 task, employers should be required to semi-annually monitor each task and keep records of that monitoring to ensure that workers are not exposed to high levels of respirable crystalline silica (Document ID 3539; 3588, Tr. 3801).

After reviewing the comments on this issue, OSHA concludes that the best approach for protecting employees exposed to respirable crystalline silica in the construction industry is to provide a set of effective, easy to understand, and readily implemented controls for the common equipment and tasks that are the predominant sources of exposure to respirable crystalline silica. OSHA is persuaded by comments and data in the record that requiring specific engineering controls, work practices, and respiratory protection for construction tasks, in lieu of a performance-oriented approach involving a PEL and exposure assessment, is justified for several reasons so long as employers fully and properly implement the engineering controls, work practices, and respiratory protection specified on Table 1.

First, the controls listed on Table 1 represent the feasible controls identified in the record for each listed task, and there is substantial evidence that demonstrates that, for most of the Table 1 tasks, exposure to respirable crystalline silica can be consistently controlled below 50 µg/m³ using those controls (see Chapter IV of the Final Economic and Regulatory Flexibility Analysis (FEA)). As such, Table 1 provides a less burdensome means of achieving protection at least equivalent to that provided by the alternative exposure control methods that include the 50 µg/m³ PEL, which OSHA has determined to be the lowest feasible exposure level that could be achieved most of the time for most of the tasks listed on Table 1. For example, as discussed in Section 5.7 of Chapter IV of the FEA, exposure data demonstrates that the engineering controls and work practices specified on Table 1 for stationary masonry saws (wet cutting) significantly reduce employees' exposures to respirable crystalline silica from a mean of 329 µg/m³, when cutting masonry dry, to a mean of 41 µg/m³. Additionally, the record developed during the rulemaking process has contributed greatly to the Agency's understanding of the effectiveness of the prescribed controls. Based on the record, OSHA is confident that exposures will be adequately controlled using the specified methods supplemented with appropriate respiratory protection for those few tasks that are very difficult to control using engineering controls and work practices alone.

Second, this approach recognizes and avoids the challenges of characterizing employee exposures to crystalline silica accurately in many construction tasks while also ensuring that employees are protected. In manufacturing settings and other more stable environments subject to the general industry standard, exposure assessment can provide an accurate depiction of the silica exposure that could be typically expected for employees in normal operating conditions. In general, such assessments need not be repeated frequently, costs are therefore minimized, and the results will be timely even if there is a delay for lab processing. In contrast, the frequent changes in workplace conditions that are common in construction work (e.g., environment, location), along with potential time-lags in the exposure assessment process, provide a compelling argument for the specified exposure control methods approach that emphasizes clear and timely guidance capable of protecting the employees during their shifts instead of relying on a minimum exposure assessment requirement to characterize employee exposures.

Third, requiring employers to implement specified dust controls absent an additional PEL requirement simplifies compliance for employers who fully and properly implement the engineering controls, work practices, and respiratory protection listed on Table 1. Simplifying compliance will also encourage employers performing tasks listed on Table 1 to use this approach, rather than the alternative of performing exposure assessments and implementing dust controls, as required by paragraph (d) of the standard for construction, and thus, will also reduce regulatory burden on construction employers of all sizes. For this reason, OSHA expects that the vast majority of construction employers will choose to follow Table 1 for all Table 1 tasks.

Fourth, this approach will also create greater awareness of appropriate controls, which may in turn facilitate better implementation and compliance, by making it far easier for employees to understand what controls are effective for a given task and what controls the employer must provide. Employees can locate the task they are performing on Table 1 and immediately see what controls are required, along with any specifications for those controls. It will, further, be clear if an employer is not providing the correct controls or ensuring that they are being used appropriately.

“Fully and properly” implementing the specified exposure control methods. In order for employers to comply with paragraph (c) of the standard for construction, they must “fully and properly” implement the engineering controls, work practices, and respiratory protection for each employee engaged in a task identified on Table 1. While several commenters, including BAC and BCTD, supported this requirement (e.g., Document ID 2329, p. 6; 2371, Attachment 1, p. 24), BCTD also urged OSHA to clarify the meaning of “fully and properly” implementing the specified engineering controls and work practices on Table 1 to ensure that employers know what is required of them and how the standard will be enforced (Document ID 4223, p. 92; 2371, Attachment 1, p. 27-29).

Other commenters provided suggestions for what they believed should be considered “fully and properly implementing” the controls specified on Table 1. NIOSH recommended that OSHA provide checklists and require a daily evaluation of engineering controls to determine if the controls are performing as designed and to ensure that employees using the controls are trained and have the appropriate materials to operate the controls properly (Document ID 2177, Attachment B, pp. 21-22). IUOE recommended that regular inspections of engineering controls in enclosed cabs should be required (Document ID 2262, p. 29). Anthony Bodway, Special Projects Manager at Payne & Dolan, Inc., representing NAPA, testified that his paving company uses a daily maintenance checklist to ensure that the controls are functioning properly and meeting the standards set by the equipment manufacturers (Document ID 3583, Tr. 2194-2197). AIHA suggested that OSHA require employers to follow the manufacturer's user instructions for installation, use, and maintenance of engineering controls, unless there is a written variance from the manufacturer (Document ID 2169, p. 5). Charles Gordon argued that OSHA should require a competent person to evaluate the use of the controls specified on Table 1 initially and periodically in order to ensure that they are fully and properly implemented (Document ID 4236, p. 4). In general disagreement with these comments, the National Stone, Sand, and Gravel Association (NSSGA) argued that, while employers should conduct routine maintenance of the controls, OSHA should not require an employer to complete an evaluation or inspection checklist of controls or work practices at a certain frequency (Document ID 2327, Attachment 1, p. 21).

Although the specified exposure control methods approach affords compliance flexibility for the employer, OSHA sees value in reminding employers and employees that this option will only be protective if they take steps to ensure that the engineering controls, work practices, and respiratory protection are as effective as possible. Thus, the Agency is requiring employers to fully and properly implement the specified engineering controls, work practices, and respiratory protection for each employee performing a task described on Table 1 in order to be in compliance with paragraph (c)(1) of the standard for construction. To do otherwise would undermine the entire basis for this compliance approach.

Merely having the specified controls present is not sufficient to constitute “fully and properly” implementing those controls. Employees will not be protected from exposure to respirable crystalline silica if the specified engineering controls, work practices, and respiratory protection are not also implemented effectively. In order to be in compliance with paragraph (c)(1) of the standard for construction, employers are required to ensure that the controls are present and maintained and that employees understand the proper use of those controls and use them accordingly.

While OSHA has decided not to further define “fully and properly” by providing specific checklists for employers or requiring employers to conduct inspections at set intervals, there are several readily identifiable indicators that dust controls are or are not being fully and properly implemented, many of which are discussed with regard to specific equipment and tasks in Chapter IV of the FEA and in the discussions of specific controls that appear further below in the section. For example, for dust collection systems, the shroud or cowling must be intact and installed in accordance with the manufacturer's instructions; the hose connecting the tool to the vacuum must be intact and without kinks or tight bends that would prevent the vacuum from providing the air flow recommended by the tool manufacturer; the filter(s) on the vacuum must be cleaned or changed as frequently as necessary in order to ensure they remain effective (it may be necessary to activate a back-pulse filter cleaning mechanism several times during the course of a shift); and dust collection bags must be emptied as frequently as necessary to avoid overfilling, which would inhibit the vacuum system from operating effectively. For water-based dust suppression systems, an adequate supply of water for dust suppression must be available on site. For worksites without access to a water main, a portable water tank or water truck having enough water for the task must be provided. The spray nozzles must be working properly to produce a spray pattern that applies water at the point of dust generation and inspected at regular intervals to ensure they are not clogged or damaged. All hoses and connections must be inspected as necessary for leaks that could signal that an inadequate flow rate is being delivered.

Manufacturer's instructions can also provide information about how to fully and properly implement and maintain controls. For example, the operator's instruction manual for EDCO concrete/asphalt saws provides a pre-start checklist that includes information about the proper functioning of wet-cutting equipment (Document ID 1676, p. 5). In some cases, industry associations and employers, in collaboration with equipment manufacturers, have also developed best practices with regard to the full and proper implementation of engineering controls, work practices, and respiratory protection for their particular industry or operation. For example, NAPA and the Association of Equipment Manufacturers (AEM) provided operational guidance for water systems during milling operations that includes pre-operation inspection activities, preparations for safe operation, and other operation considerations (Document ID 2181, p. 52).

In addition, paragraph (g) of the standard for construction requires employers to establish and implement a written exposure control plan, which includes provisions for a competent person to make frequent and regular inspection of job sites, materials, and equipment in order to implement the plan (see the summary and explanation of Written Exposure Control Plan for discussion about this requirement). Thus, the requirement for a written exposure control plan and the competent person, which was added to the final standard for construction, provides additional safeguards for ensuring that employers fully and properly implement Table 1.

OSHA expects that in most instances it will be straightforward for a designated competent person to identify whether the controls have been fully and properly implemented. For example, a significant amount of visible dust being frequently or continuously emitted from the material being worked on can serve as an indication that controls are not fully and properly implemented. A small amount of dust can be expected even with new equipment that is operating as intended by the manufacturer. The amount of visible dust associated with the new dust controls should be noted when equipment is put into service and checked periodically. A noticeable increase in dust emissions would indicate that the dust control system is not operating as intended.

Employees engaged in Table 1 tasks. Commenters expressed concerns about the lack of requirements in the proposed rule to protect employees assisting with Table 1 tasks or working in the vicinity of others engaged in Table 1 tasks (e.g., Document ID 2116, Attachment 1, pp. 2-3). In response, OSHA has clarified the language in paragraph (c)(1) of the standard for construction to encompass all employees “engaged in a task identified on Table 1.” This phrasing is intended to include not only the equipment operator, but also laborers and other employees who are assisting with the task or have some responsibility for the completion of the task, even if they are not directly operating the equipment. For example, where an employee is assisting another employee operating a walk-behind saw indoors by guiding the saw and making sure that the cutting is precise, that employee would be considered to be engaged in the task and would need to wear a respirator. Similarly, employees assisting a jackhammer task would be considered to be engaged in the task and would also be required to wear a respirator if they engaged in the task outdoors for more than four hours in a work shift.

It is not OSHA's intent, however, for all employees who are in the vicinity of a listed task to be considered “engaged in the task.” To protect the other employees in the vicinity of a listed task, the employer must account for the potential exposures of these employees to respirable crystalline silica as part of its written exposure control plan. As discussed in the summary and explanation of Written Exposure Control Plan, paragraph (g)(1)(iv) of the standard for construction requires a description of the procedures used to restrict access to work areas, when necessary, to limit the number of employees exposed and their exposure levels. Employers must develop procedures to restrict or limit access when employees in the vicinity of silica-generating tasks are exposed to excessive respirable crystalline silica levels. Such a situation might occur in a variety of circumstances, including when an employee who is not engaged in the task, but is working in the vicinity of another employee performing a Table 1 task requiring respiratory protection, is exposed to clearly visible dust emissions (e.g., an employee directing traffic around another employee jackhammering for more than four hours in a shift). In that case, the competent person, as required under paragraph (g)(4) of the standard for construction, would assess the situation in accordance with the employer's procedures to determine if it presents a recognized hazard, and if it does, take immediate and effective steps to protect employees by implementing the procedures described in the written exposure control plan. For the above example, this could include positioning the employee directing traffic at a safe distance upwind from the dust-generating activity.

Table 1. As discussed above, paragraph (c)(1) of the standard for construction includes “Table 1: Specified Exposure Control Methods When Working With Materials Containing Crystalline Silica,” which identifies 18 common construction equipment/tasks known to generate high exposures to respirable crystalline silica. For each equipment/task identified, Table 1 specifies appropriate and effective engineering and work practice control methods. Some entries contain multiple engineering controls and work practices. In those instances, OSHA has determined that the specified combination of engineering controls and work practices is necessary for reducing exposures and requires employers to implement all of the listed engineering controls and work practices in order to be in compliance. Some entries contain multiple compliance options denoted with an “OR” (e.g., (c)(1)(ix), (c)(1)(x), (c)(1)(xii), (c)(1)(xiii), (c)(1)(xv), and (c)(1)(xviii) of the standard for construction). For those entries, OSHA has determined that more than one control strategy could effectively reduce exposures and permits the employer to decide which option could be best implemented on the worksite. Table 1 also specifies respiratory protection for those entries where OSHA has determined from its analysis of technological feasibility it is needed to ensure employees are protected from exposures to respirable crystalline silica. These respirator requirements are divided by task duration (i.e., “less than or equal to four-hours-per-shift” and “greater than four-hours-per-shift”).

Table 1 in the final standard differs from Table 1 in the proposed standard in a number of respects. As proposed, “Table 1—Exposure Control Methods for Selected Construction Operations,” listed 13 construction operations that expose employees to respirable crystalline silica, as well as control strategies and respiratory protection that reduce those exposures. In developing Table 1 for the proposed standard, OSHA reviewed the industrial hygiene literature across the full range of construction activities and focused on tasks where silica-containing materials were most likely to be fractured or abraded and where control measures existed to offer protection against a variety of working conditions. OSHA also included additional specifications on proposed Table 1 to ensure that the strategies listed were properly implemented and remained effective.

Table 1 was the subject of many comments in the rulemaking record. Commenters, such as BCTD, urged OSHA to reconsider its use of the proposed term “operation” to describe the activities listed on Table 1 (Document ID 2371, Attachment 1, p. 23). Kellie Vazquez, on behalf of Holes Incorporated and CISC, suggested that it would be helpful to include more specifically-defined tasks, rather than broader operations (Document ID 2320, pp. 8-9). In the same vein, BCTD suggested that OSHA “revise [Table 1] to make clear that its focus is on particular silica dust-generating tasks, not more broadly-defined operations” as “there is an important distinction between specific tasks that may generate silica dust and the employer's overall operation, which may include different silica dust-generating tasks, requiring different controls” (Document ID 2371, Attachment 1, p. 23). BCTD also recommended that, to avoid confusion, Table 1 should specify that each task is being performed on or with a material that contains silica (Document ID 2371, Attachment 1, p. 24). Responding to both suggestions, OSHA has changed the terminology used in Table 1 from “Operation” to “Equipment/Task” to clarify that the controls apply to silica-generating activities done by employees and silica exposure generated by equipment, and has revised the title of Table 1 accordingly to “Specified Exposure Control Methods When Working with Materials Containing Crystalline Silica.”

Other commenters requested that OSHA include additional activities on Table 1. The Sheet Metal Air Conditioning Contractors National Association (SMACNA) commented that using powder-actuated tools should be added (Document ID 2226, p. 2), and the Interlocking Concrete Pavement Institute (ICPI) suggested that OSHA include compacting pavers, sweeping sand into paver joints, and compacting the aggregate base (Document ID 2246, pp. 2, 11). NAHB noted that Table 1 failed to cover hand-mixing concrete (Document ID 2334, p. 4). OSHA did not receive data showing that employees engaged in many of these additional minor tasks (pulling concrete forms, mixing concrete for post holes, etc.) experience significant routine exposure to respirable crystalline silica above the action level that would require their employers to comply with provisions of this rule. Because OSHA does not currently have data indicating that additional controls for these tasks would be needed on a regular basis or would be effective, it has determined not to include them on Table 1.

OSHA recognizes the possibility that employers may later discover that there are tasks that are not covered by Table 1 where they may have difficulty meeting the PEL. If such cases arise, OSHA can address them in several ways, including: considering technological or economic infeasibility defenses, and applying its variance process—either temporary or permanent, pursuant to which an employer can apply to exclude an industry or process from enforcement of the standard based principally on a showing that it is providing equivalent protection for its workers.

Several commenters requested that OSHA add tasks or activities and equipment to Table 1 that are associated with general industry operations such as asphalt plant operations, shale gas fracturing, and artificial stone and granite countertop work (Document ID 2212, p. 2; 2116, Attachment 1, p. 28; 2244, p. 4). OSHA is not including these in the construction standard for the reasons discussed in the summary and explanation of Scope.

NUCA requested that OSHA add underground construction, specifically excavation, onto Table 1, stating:

The nature of excavation underground construction is continuously mobile. Exposure assessments take time to evaluate by a lab, and in that time, the jobsite conditions will change or crews will move to other sites. Test results simply could not be available in enough time to be relevant to a particular jobsite. This not only makes costly lab assessments irrelevant to particular sites, it also does nothing to protect the workers on those sites (Document ID 2171, p. 2).

OSHA's technological feasibility analysis for underground operations (Section 5.12 of Chapter IV of the FEA) indicates that employees performing activities not specific to tunneling, such as grinding, hole drilling, or chipping, receive similar exposures from their equipment as employees performing those same activities aboveground in enclosed environments (e.g., indoors). As a result, employers can comply with the dust control requirements of the standard by fully and properly implementing the dust controls specified on Table 1 of the final standard for construction for those tasks. However, as explained in the technological feasibility analysis cited above, OSHA determined that it was not possible to develop a clear control specification that would prove effective for most situations where tunnel boring machines, road headers, and similar kinds of equipment are used. Effective dust control for operations that use these kinds of equipment consists of a combination of water sprays at the tunnel face and along the conveyors that remove material from the face, general dilution ventilation through the tunnel, local exhaust ventilation for excavating equipment and conveyor transfer points, and enclosed cabs for the operators. Dust control may also require enclosures for conveyors and belt cleaning mechanisms. Designing effective and efficient dust control systems must take into account specific factors of the tunnel project and equipment being used, and are analogous to dust control strategies used in underground mines, as described in NIOSH's Handbook for Dust Control in Mining (Document ID 0887). Given the degree of complexity and project-specific considerations that should be taken into account, OSHA determined that it was not possible to devise an effective specification applicable to all tunnel projects and thus has not added an entry for tunnel boring in underground construction to Table 1.

Likewise, although abrasive blasting is a common source of silica exposure in construction, OSHA does not include an entry for abrasive blasting on Table 1 for reasons explained more fully below. As described in the Introduction to Chapter IV of the FEA, the tasks included on Table 1 of the final rule are those that have been widely recognized as high-exposure tasks in construction, and for which there has been considerable research performed on the effectiveness of dust control strategies. The record indicates that the tasks reflected in Table 1, with few exceptions such as underground construction and abrasive blasting, are the tasks that employers will most frequently need to address to ensure employee protection from crystalline silica hazards. For tasks not included on Table 1 that foreseeably generate silica exposures above the action level, construction employers will, in accordance with paragraph (d) of the standard for construction, need to conduct an exposure assessment and maintain exposures at or below the PEL through use of the traditional hierarchy of controls.

Commenters also weighed in on OSHA's general approach to selecting the engineering controls and work practices for each task. LBA argued that there was a disconnect between the feasibility evidence and the controls and work practices included on Table 1 (Document ID 2269, p. 17). NAHB urged OSHA to ensure that the protection methods included on Table 1 are based on verifiable studies that show effective solutions (Document ID 2296, p. 28). BCTD also opined that only “control measures supported by good quality evidence should be listed on Table 1” (Document ID 2371, Attachment 1, p. 24).

OSHA agrees that the engineering controls, work practices, and respiratory protection specified on Table 1 need to be consistent with the evidence presented in its technological feasibility analyses (see Chapter IV of the FEA). To that end, OSHA has based the specifications on Table 1 on extensive exposure data collected from a variety of sources including NIOSH reports, data submitted to the record, OSHA's compliance case files, and published literature.

Requirements for water delivery systems and dust collection systems. OSHA is requiring the use of an integrated water delivery system supplied by the equipment manufacturer for several types of equipment listed on Table 1: Stationary masonry saws; handheld power saws (any blade diameter); walk-behind saws; drivable saws; rig-mounted core saws or drills; handheld grinders for uses other than mortar removal; and walk-behind milling machines and floor grinders. OSHA is requiring the use of systems that are developed in conjunction with the tool because they are more likely to control dust emissions effectively by applying water at the appropriate dust emission points based on tool configuration and not interfere with other tool components or safety devices.

CISC commented that the requirement for an integrated water system limited options for employers and may reduce the use of the table, stating “. . . if a construction employer finds a way to effectively deliver water through another mechanism, in the CISC's view that should be encouraged” (Document ID 2319, p. 103; 2320, p. 16). OSHA expects that most employers will use integrated water systems, as provided by manufacturers, and will follow Table 1 but its intent is not to prohibit the use of other dust suppression methods during cutting. Employers may implement other controls or wet method configurations if they determine that the alternative control is more appropriate for their intended use. However, employers who choose to use controls not listed on Table 1 will be required to conduct exposure assessments and comply with the PEL in accordance with paragraph (d) of the standard for construction.

CISC also questioned the appropriateness of requiring an integrated water delivery system when most integrated systems are intended to keep the blade cool and are not designed for dust suppression (Document ID 2319, p. 103; 2320, p. 16). In written testimony, Rashod Johnson of the Mason Contractors Association of America stated that

the vast majority of masonry saws provide water on the blade itself. This is solely for the purpose of keeping the blade cool during cutting. A side effect, just happens to be dust suppression. Now, manufacturers of these saws are starting to explicitly state that the water used is for cooling the blade only and should not be used to suppress dust (Document ID 2286, p. 2).

However, product literature from five major saw manufacturers (Andreas Stihl, Husqvarna, Hilti, Makita USA, and Wacker Group) highlights the use of water application equipment to suppress dust in addition to blade cooling (Document ID 3998, Attachment 12a, pp. 9, 15-16; 3998, Attachment 12e, p. 3; 3998, Attachment 12f; 3998, Attachment 12g, p. 5; 3998, Attachment 12h, p. 8). For example, Stihl's manual for the model 410 and 420 cut-off machines (handheld masonry saws) specifically recommends a water flow rate for dust suppression (Document ID 3998, Attachment 12a, pp. 9, 15-16). Furthermore, Stihl is not the only cut-off saw manufacturer to state that water used with its product is intended to suppress dust emissions. Husqvarna's product literature for the K 3000 Wet describes the product as a power cutter for wet applications that is equipped with a dust extinguisher system (Document ID 3998, Attachment 12f, p. 1). Hilti also recognizes that water suppresses dust and recommends the use of wet cutting to reduce dust in its instruction manual for the Hilti DSH 700/DSH 900 model handheld masonry saws (Document ID 3998, Attachment 12e, p. 3).

CISC asked that OSHA clarify whether there needs to be a separate integrated water delivery system in addition to the system provided by the manufacturer to keep the blade cool (Document ID 2319, p. 104). Beamer et al. (2005) conducted experiments to observe the differences in the various wet cutting methods available and found that the greatest improvement in dust reduction occurred with freely flowing water applied at a rate of 48 gallons per hour (0.8 gallons per minute), resulting in dust reduction of about 93 percent and confirming the benefits of water flowing over the stationary saw cutting blade compared with other misting systems (Document ID 1555, p. 509). That, in addition to the manufacturer information submitted to the record, indicates that the existing water systems for blade cooling are effective at respirable dust capture and will satisfy the requirements under paragraphs (c)(1)(i) through (c)(1)(xviii) of the standard for construction where integrated water systems are required. Therefore, OSHA has determined that, where water-based dust suppression can be used with tools and equipment, those that are equipped with an integrated water delivery system are effective and the best available technology for controlling respirable crystalline silica. A separate integrated water delivery system in addition to the system provided by the manufacturer to keep the blade cool is not required.

OSHA is requiring the use of a commercially available dust collection system (i.e., local exhaust ventilation (LEV)) for several types of equipment listed on Table 1, including: handheld power saws for fiber cement board (with a blade diameter of 8 inches or less), handheld and stand-mounted drills (including impact and rotary hammer drills), jackhammers and handheld power chipping tools (as an alternative to a water delivery system), handheld grinders for mortar removal, and handheld grinders for uses other than mortar removal (as an alternative to a water delivery system). OSHA's intent is to ensure that employers use equipment that is appropriately designed for the tool being used and that will be effective in capturing dust generated from using the tool.

CISC opposed OSHA's requirement for commercially available systems, stating “[t]his specification eliminates specialty manufactured products that may be equally effective” (Document ID 2320, p. 11). However, CISC did not provide examples or describe what is meant by “specialty manufactured products.” It is not OSHA's intent to prevent employers from using products that are custom made by aftermarket manufacturers (i.e., made by someone other than the original tool manufacturer) which are intended to fit the make and model of the tool and designed to meet the particular needs and specifications of the employer purchasing the product. These systems are designed to work effectively with the equipment and not introduce new hazards such as obstructing or interfering with safety mechanisms. The “commercially available” limitation is meant only to eliminate do-it-yourself on-site improvisations by the employer. An employer is free to improvise and use controls that are not commercially available. However, those systems would not meet the requirements of Table 1 and the employer will be required to conduct exposure assessments and comply with the PEL in accordance with paragraph (d) of the standard for construction.

In Table 1 of the proposed rule, OSHA would have required dust collection systems be equipped with High-Efficiency Particulate Air (HEPA) filters, which are 99.97 percent efficient in capturing particles having an aerodynamic diameter of 0.3 μm or larger. In the final standard, OSHA is not requiring the use of HEPA filters and instead is requiring the use of filters with a capture efficiency of 99 percent or greater for respirable particulate. Although OSHA received comments and testimony in support of using HEPA filters to capture silica dust (Document ID 1953, pp. 3-4; 1973, pp. 2-3), extensive comments were submitted to the record expressing concern regarding this requirement.

Occupational and Environmental Health Consulting Services, Inc. (OEHCS) noted the numerous deficiencies found with HEPA filtration from ineffective seals, deterioration of the filter, and inadequate testing prior to use, which often results in employee exposure to potentially-hazardous particles and possible recontamination of the work environment (Document ID 1953, Attachment 1). The Precast/Prestressed Concrete Institute (PCI), NUCA, and LBA noted that HEPA filters do not work well in the construction environment because filters will clog up quickly and must be changed often (Document ID 2276, p. 10; 3729, p. 3; 2269, p. 23). CISC noted that HEPA filters will typically not last an entire shift, stating that they clog up quickly and need to be monitored and changed frequently (Document ID 2320, p. 114). Consequently, CISC asserted, HEPA filters are not effective at filtering respirable dust or at reducing exposures to respirable silica (Document ID 2319, p. 95).

OSHA reached the same conclusion in its technological feasibility finding for mortar and concrete grinding as well (see Section 5.11 of Chapter IV of the FEA). Finding that best practices may counsel toward the use of HEPA-rated filters in the case of grinding, and particularly mortar grinding, OSHA nonetheless determined that under field conditions HEPA filters may rapidly clog, leading to an increase in static pressure drop and loss of the airflow needed for LEV to effectively capture silica dust at the point of generation (Document ID 0731, pp. 375, 384).

OSHA is persuaded that it should not require that dust collection systems be equipped with HEPA filters because HEPA filters in some applications will result in loss of airflow and concomitant degradation of dust-capture efficiency. In examining manufacturers' specifications for many commercially-available dust collectors, OSHA finds that most offer, in addition to HEPA filters, other filters with a 99 percent efficiency or better in the respirable-particle-size range. Many examples of products equipped with filters that do not meet HEPA specifications but nevertheless meet the requirement for 99 percent efficiency in the respirable-particle-size range were submitted to the record and include the EDCO Vortex 2000 (captures 99 percent of 0.5 µm or larger particles) (Document ID 4073, Attachment 4a, Row 55), the iQ 360x stationary saw (99.5 percent, particle size unspecified) (Document ID 4073, Attachment 4a, Row 58), a Porter-Cable vacuum (99.85 percent, particle size unspecified) (Document ID 3998, Attachment 13p), the Bosch 3931A (99.93 percent of 3 µm particles) (Document ID 3998, Attachment 10, p. 29), the CS Unitec (99.93 percent of 0.3 µm particles) (Document ID 4073, Attachment 4a, Row 99), and the Dustless 16-gallon collector (“almost HEPA,” filters to 0.5 µm particles) (Document ID 4073, Attachment 4a, Row 211). A filter efficiency of at least 99 percent allows for longer tool usage, compared to one with a HEPA filter, before significant drops in airflow of the dust collection system. Furthermore, as explained above, requiring that dust collectors be equipped with HEPA filters can cause rapid airflow drop, reducing dust capture efficiency at the shroud or hood and exposing employees to high respirable dust and silica concentrations. Therefore, OSHA has decided not to require HEPA filters on Table 1 for dust collection systems and instead requires that dust collectors have a filter with 99 percent or greater particle capture efficiency. Employers should consult with their suppliers to determine the dust collection equipment that will best suit their needs for a given application.

OSHA also received many specific comments about particular changes to the notes and additional specifications, associated with the entries on Table 1, and on the specified engineering and work practice control methods identified for each entry, which are further discussed later in this section.

Notes and additional specifications on Table 1. Several commenters responded to the appropriateness of including the notes and additional specifications in the individual entries on Table 1. OSHA included these in the proposed rule to ensure that the strategies listed were properly implemented and remained effective.

Some commenters stated that the notes were too detailed, while others argued that the notes were not detailed enough (Document ID 2319, p. 6; 2262, p. 29; 3581, Tr. 1631-1632; 3585, Tr. 2924-2925, 3052-3053; 4223, pp. 95-97). Several commenters expressed concern that certain notes were unrealistic or too confusing for an employer to comply with. CISC stated that the inclusion of the notes left Table 1 “unworkable” for most employers in the construction industry (Document 2319, p. 6). Others questioned whether these additional specifications were a mandatory component of Table 1 or simply suggested guidelines to help determine the efficacy of the control (Document ID 2296, p. 28; 3441, pp. 4-5). On the other hand, some commenters asserted that the additional specifications were needed on Table 1 to ensure that controls are properly operated and effective (Document ID 3589, Tr. 4286-4287; 3581, Tr. 1631-1632; 4223, pp. 95-97).

To balance the need to clarify how the specifications apply to make Table 1 workable with the need to provide more specific information about the controls in order to ensure that they are effective, OSHA has removed most of the notes and additional specifications from the individual entries on Table 1 and has instead included revised specifications for the controls in paragraph (c)(2) of the standard for construction. This approach has the added benefit of making Table 1 more readable because specifications that apply to multiple rows can now be addressed in a single subparagraph.

Paragraph (c)(2)(i) of the standard for construction requires employers to provide a means of exhaust as needed to minimize the accumulation of visible airborne dust for tasks performed indoors or in enclosed areas. When tasks are performed indoors or in enclosed areas, the dispersal of dust can be impeded such that concentrations can build up without the aid of forced ventilation. Flanagan et al. (2006) concluded that the degree to which a work area is enclosed is an important determinant of employee exposure based on data demonstrating increased exposures to respirable crystalline silica for enclosed environments (those with two to four walls, as well as those having walls, a roof, and windows), as compared to outdoor environments (Document ID 0677, pp. 148-149). Increased exposures to respirable crystalline silica were also demonstrated for tasks listed on Table 1 in enclosed areas, such as jackhammering inside a large pool area (Document ID 3958, Rows 1064, 1065, 1066) and handheld sawing in a large garage building open in front and closed on three sides (Document ID 3777, p. 65).

Sufficient air circulation in enclosed or indoor environments is important to ensure the effectiveness of the control strategies included on Table 1 and to prevent the accumulation of airborne dust. The “means of exhaust” necessary to minimize the accumulation of visible airborne dust could include dilution ventilation through the use of portable fans that increase air movement and assist in the removal and dispersion of airborne dust, which would otherwise remain in the enclosure and contribute to elevated exposures. To be effective, the ventilation must be implemented so that movements of employees, or the opening of doors and windows, will not adversely affect the airflow.

Paragraph (c)(2)(ii) of the standard for construction requires employers, for tasks performed using wet methods, to apply water at flow rates sufficient to minimize release of visible dust generated by the task. BCTD and LHSFNA encouraged OSHA to specify minimum flow rates for water where there are data or studies to support such a recommendation (Document ID 3581, Tr. 1632; 3589, Tr. 4286-4287). NIOSH recommended a flow rate of 0.5 L/min for handheld power saws based on experimental data and recommended that OSHA specify a minimum water flow rate of 300 mL/minute for jackhammers based on a field study of control equipment fabricated specifically for the study (Document ID 2177, Attachment B, pp. 19, 33; 0867, p. 6). Water has been proven an efficient engineering control method to reduce exposures to airborne crystalline silica-containing dust. Adequate dust capture is dependent on a variety of factors such as dust particle size, velocity, spray nozzle size and location, use of surfactants or other binders, and environmental factors (water hardness, humidity, weather, etc.) that must be considered when implementing wet methods. Water flow rates suggested by various studies, while perhaps instructive, may not be applicable to all of the different types of equipment that could be used or the conditions that may be encountered by employers following Table 1. Because the appropriate water flow rates for controlling silica dust emissions can vary, OSHA is not establishing a required flow rate for wet suppression systems or specifying a flow rate for individual Table 1 entries.

Paragraphs (c)(2)(iii)(A)-(F) of the standard for construction require employers implementing measures that include an enclosed cab or booth to ensure that the enclosed cab or booth is maintained as free as practicable from settled dust, has door seals and closing mechanisms that work properly, has gaskets and seals that are in good condition and work properly, is under positive pressure maintained through continuous delivery of fresh air, has intake air that is filtered through a pre-filter that is 95 percent efficient in the 0.3-10.0 µm range (e.g., MERV-16 or better), and has heating and cooling capabilities.

Dust can be unintentionally carried into enclosed cabs or booths through a number of routes, including on employees' boots, during the opening of doors when accessing or exiting the cab, through leaks in the system, or when employees roll down windows. IUOE, recommending that OSHA add specificity to the cab requirements (e.g., heating and air conditioning, housekeeping), argued that without greater specificity “there is a grave danger that intended safeguards become counterproductive as dust is re-circulated within the enclosures” (Document ID 2262, pp. 29-33).

Direct-reading instruments show that fine particle (0.3 micron (μm) in size) concentrations inside operator cabs can be reduced by an average of 93 percent when cabs are clean, sealed, and have a functionally adequate filtration and pressurization system (Document ID 1563, p. 1). Cecala et al. (2005) studied modifications designed to lower respirable dust levels in an enclosed cab on a 20-year-old surface drill at a silica sand operation. The study found that effective filtration and cab integrity (e.g., new gaskets, sealed cracks to maintain a positive-pressure environment) are the two key components necessary for dust control in an enclosed cab (Document ID 1563, p. 1).

OSHA determined that the requirements specified in paragraphs (c)(2)(iii)(A)-(F) of the standard for construction reduce the likelihood of respirable crystalline silica exposure in enclosed cabs or booths when employees are present by lowering the potential for dust to be re-suspended inside the enclosure, promoting the ability of the enclosed cab or booth to keep dust from entering through cracks or openings (e.g., seals, gaskets, and closing mechanisms are present, in good condition, and work properly), ensuring that the working conditions in the cab are comfortable so that employees are less likely to open the window of the cab, and ensuring that the fresh air provided to the employee does not contain silica particles.

IUOE also suggested that OSHA require employers to provide boot brushes or mudflingers to minimize the dust brought into the cab, to equip cabs with dust-resistant materials, and to affix warning labels to the interior of the cab (Document ID 2262, p. 30; 4025, p. 17). The Agency has not included these additional requirements since it expects that the specifications in paragraphs (c)(2)(iii)(A)-(F) of the standard for construction combined with frequent inspections by the competent person will be sufficient to protect employees against the potential respirable crystalline silica exposures within the enclosure.

OSHA has not included more specific requirements in paragraphs (c)(2)(i)-(c)(2)(iii) of the standard for construction (e.g., establishing a minimum face velocity, volumetric flow rate for air movement, or a required number of air changes; flow rate for wet suppression systems; or a frequency for the cleaning of cabs or booths). However, as discussed in the summary and explanation of Written Exposure Control Plan, paragraph (g)(1)(ii) of the standard for construction requires the employer to establish and implement a written exposure control plan that describes the engineering controls and work practices used to limit employee exposure to respirable crystalline silica. This description should include details such as the appropriate means of exhaust needed to minimize the accumulation of visible airborne dust for a particular task, the appropriate flow rate and droplet size needed for wet suppression systems to minimize release of visible dust, and the procedures for maintaining and cleaning an enclosed cab or booth. Paragraph (g)(4) of the standard for construction also requires a competent person to make frequent and regular inspections of the jobsite, materials, and equipment (including engineering controls) to implement the written exposure control plan.

OSHA did not include specifications on visible dust and wet slurry, included as notes in individual entries on proposed Table 1, in the standard. The Agency has determined that these issues are best addressed by other provisions of the standard, rather than as a note or additional specification included in each relevant Table 1 entry. Further discussion about these specifications is also included below.

Many commenters expressed concern with the note, contained in proposed Table 1 for all but two entries, requiring employers to operate equipment such that no visible dust is emitted from the process. Industry commenters, including the Power Tool Institute (PTI), Western Construction Group, SMACNA, the Independent Electrical Contractors, the Distribution Contractors Association, CISC, the Utility and Transportation Contractors Association of New Jersey, Atlantic Concrete Cutting, ABC, LBA, Holes Incorporated, and N.S. Giles Foundations objected to this note, stating that it was an unrealistic requirement which made Table 1 unworkable (e.g., Document ID 1973, pp. 2-9; 2183, p. 3; 2226, p. 2; 2250, p. 2; 2309, p. 4; 2319, pp. 97-98; 4217, p. 6; 2356, p. 2; 2367, p. 2; 2289, p. 7; 2269, p. 21; 3441, p. 5; 3598, pp. 1-2).

Some industry commenters asserted that it is impossible to perform tasks, such as sawing, grinding, and drilling, without generating any visible dust (Document ID 2357, pp. 27-28; 3441, p. 6; 4073, Attachment 9e, p. 1). Holes Incorporated noted that when grinding or using other hand-held pieces of equipment, the work cannot be performed with the tool flush against the impacted surface, and at times, there will be a gap and visible dust will be emitted even when local exhaust ventilation or wet methods are utilized (Document ID 3441, p. 6).

Other commenters expressed concern that there is no true dustless system, clarifying that even those tools marketed as “dustless” produce some level of airborne dust (Document ID 2345, p. 4; 3585, Tr. 2960; 4216, pp. 2-3). Francisco Trujillo, safety director for Miller and Long, stated that:

Every “dustless” system I have ever witnessed has produced some level of airborne dust. This fact alone should show that Table 1 sets criteria that are impossible to achieve . . . (Document ID 2345, p. 4).

On the other hand, commenters, including NAPA and BAC, noted that in their experience there is no visible dust generated when certain equipment, such as asphalt machines for milling or stationary masonry saws, is used with available dust controls (Document ID 3583, Tr. 2216; 3585, Tr. 3072). They did not, however, provide any indication that the same results could be achieved with all of the other equipment listed on Table 1.

Several commenters provided a different rationale for their objections to this note. AIHA opined that the requirement to operate equipment such that no visible dust is emitted from the process is a subjective determination and recommended it be removed from Table 1 entries (Document ID 3578, Tr. 1029-1030; 2169, p. 5). The Masonry and Concrete Saw Manufacturers Institute (SMI) noted that “[a]dding requirements for . . . avoiding visible dust have not been researched specific to respirable silica dust and may have no beneficial impact” (Document ID 2316, p. 2). NAHB and Holes Incorporated expressed concern that the requirement was a general dust rule, rather than regulating crystalline silica since Table 1 doesn't specify whether “no visible dust” refers to visible silica dust or just dust in general (Document ID 2296, p. 29; 3580, Tr. 1355-1356).

Not all industry commenters objected to the note on visible dust contained in the proposed Table 1. ICPI supported a version of Table 1 that included the no-visible-dust requirement for nearly all of the operations listed (Document ID 2352, pp. 4-8).

Commenters from both industry and labor suggested revisions to clarify the note and make it workable. LHSFNA believed the note was needed to ensure the effective use of controls and was not too vague, but acknowledged that the language could be clarified to say something like “visible dust should be minimized” (Document ID 4207, p. 2). BCTD also provided significantly revised language for the no-visible-dust requirement. For those operations that involve cutting and grinding on silica-containing substrate, BCTD suggested that, for wet systems, Table 1 of the standard should require that water flow be “sufficient to control the dust generated so that no visible dust . . . is emitted from the process once the blade has entered the substrate being cut” and that the relevant note on Table 1 be revised to read:

A small amount of visible dust may be present when the blade or tool initially enters the substrate and when it is being removed at the end of a task. However, if visible dust is present after the blade or tool has entered the work surface/substrate, this is a sign that the control is not working properly. The operation should be stopped and the equipment and/or workers' cutting technique checked and fixed (Document ID 4223, Appendix 1, p. 14).

PTI's suggested revisions to Table 1 include a note for many of the entries specifying that “during operation, if excessive visible dust is emitted from the process, immediately stop work and verify that the dust control system is functioning properly” (Document ID 1973, pp. 2-9).

While opinions varied widely on the utility of a no-visible-dust requirement, no commenters suggested that excessive visible dust generated from tasks abrading silica-containing materials (sawing, grinding, etc.) does not present a risk of significant employee exposure to silica. As noted above, BCTD confirmed that the presence of visible dust after the blade or tool has entered the work surface/substrate is a sign that the control method is not working properly (Document ID 4223, Appendix 1, p. 14). PTI recommended that, when excessive visible dust was present, work stop immediately until the employer could verify the proper functioning of the control (Document ID 1973, pp. 2-9).

OSHA agrees that excessive visible dust is an indication that a control's effectiveness may be compromised, but, after reviewing the entire record on this point, has decided not to include a no-visible-dust requirement for the Table 1 entries. Instead, it has concluded that the purpose of such a requirement is best achieved by bolstering other requirements in the rule, as it applies to construction. First, OSHA considers the written exposure control plan to be centrally important and expects employers to address signs that controls may not be working effectively (e.g., dust is visible) as part of their written exposure control plans required under paragraph (g) of the standard for construction (see summary and explanation of Written Exposure Control Plan for further discussion). Second, during the designated competent person's frequent and regular inspections of job sites, materials, and equipment to implement the written exposure control plan, as required under paragraph (g)(4) of the standard for construction, OSHA expects that person to make routine observations of dust generated from tasks being conducted. Where increases in visible dust occur, the competent person's assigned role is to take prompt corrective action (e.g., make corrections or adjustments as needed).

OSHA finds that the difference between the small amount of dust generated when control measures are operated effectively and the large amount of dust generated during tasks when control measures are not used or not operated effectively can readily be observed. Several videos presented in the record support this conclusion (e.g., Document ID 4073, Attachment 4b). These videos demonstrate that when a task is uncontrolled or inadequately controlled, a large dust plume can be seen. When controls such as water or vacuum-based ventilation are used, little dust is observable. These significant differences in the observable dust generated during controlled and inadequately-controlled tasks provide an opportunity for employers to readily detect poorly-performing equipment and address these problems quickly. The principle concern, however, is with a lot of visible dust, rather than any visible dust, which is a concern for which the appropriate corrective action is difficult to quantify or state in objective terms. Instead, the presence of significant visible dust lends itself to a more process-oriented control approach, as exemplified by the written exposure control plan and competent person requirements. OSHA thus concludes that the issue of visible dust is best addressed by the requirement to fully and properly implement the controls specified on Table 1, and the written exposure control plan and competent person requirements, rather than as a note or additional specification included in each Table 1 entry.

Commenters also objected to the specification to prevent wet slurry from accumulating and drying when implementing wet methods, as proposed for several Table 1 entries. Both Holes Incorporated and NAHB objected to the ambiguity of the requirement and presented concerns about how employers on a construction site would comply with such a requirement (Document ID 3441, p. 9; 2296, p. 28).

Other commenters expressed concern regarding the disposal of silica slurry (Document ID 2246, pp. 9-10; 3585, Tr. 2886; 2319, p. 94). ICPI noted that employers have to expend extra effort to locate a place to dispose of dust-filled slurry, which is not possible in some conditions or locations (Document ID 2246, pp. 9-10). CISC described how slurry created using wet-cutting methods outside can flow into storm drains, potentially violating environmental regulations (Document ID 2319, p. 94). The Mason Contractors Association of America explained that in California, silica slurry produced from wet cutting is classified as a hazardous material, requiring contractors working in the state to follow hazmat procedures for its disposal (Document ID 3585, Tr. 2886).

However, NIOSH argued that since the vast majority of masonry saws provide water on the blade itself to cool and lubricate the blade and suppress dust, employers already have to deal with slurry when cutting masonry and concrete (Document ID 4233, Attachment 1, p. 6). OSHA agrees that the standard does not pose any new requirements regarding the disposal of slurry on employers who already use wet methods for sawing masonry products.

OSHA concludes that any measures necessary to manage slurry in order limit employee exposure to respirable crystalline silica (i.e., exposure that results from slurry drying and dust particles becoming airborne) are best addressed through the employer's written exposure control plan and competent person requirements, rather than as a note or additional specification included in each Table 1 entry. These requirements are discussed above and in the summary and explanation of Written Exposure Control Plan.

In several Table 1 entries, OSHA has included a requirement to operate and maintain tools in accordance with manufacturer's instructions to minimize dust emissions. This requirement is intended to ensure that the controls are implemented effectively to reduce exposures to respirable crystalline silica. Manufacturer's instructions that influence the effectiveness of the tool and controls with regard to minimizing dust emissions may include, but are not limited to, additional specifications for water flow rates, air flow rates, vacuum equipment, rotation of the blade, maintaining and changing blades, and frequencies for changing water.

Respiratory protection specified on Table 1. Industry associations, including the American Subcontractors Association (ASA), the Institute of Makers of Explosives (IME), the General Contractors Association of New York (GCANY), and CISC, commented on the appropriateness of the respirators that OSHA proposed for Table 1 (e.g., Document ID 2213, p. 2; 2187, p. 3; 2314, p. 2; 2319, p. 102). For example, ASA stated:

OSHA's proposed Table 1 for construction would seem to suggest that the Agency believes a construction employer can achieve the PEL with engineering and work practice controls. Yet the Agency then requires respiratory protection for 60 percent of the operations listed in Table 1. This failure is even more perplexing since OSHA failed to identify, obtain and/or cite sufficient data for its conclusions with respect to the 13 operations addressed in Table 1 (Document ID 2187, p. 3).

GCANY explained in their comments that “[c]urrent respiratory protective equipment is cumbersome to wear and to work in and would expose the worker to other hazards on a job site” (Document ID 2314, p. 2). CISC urged OSHA to “eliminate the heavy use of respiratory protection,” arguing that:

OSHA's reliance on respiratory protection is analytically inconsistent with its position that it is technologically feasible to reach the proposed PEL in most construction operations most of the time, and particularly when the control measures specified in Table 1 are used. Requiring such heavy use of respirators . . . will serve as a significant barrier to effective use of [Table 1] (Document ID 2319, p. 102).

Respirator requirements on Table 1 of the final rule are based on a review of all the evidence pertaining to exposure profiles and available controls in the rulemaking record, including an evaluation of the updated exposure profiles and evidence on available controls submitted to the rulemaking record, as described in Chapter IV of the FEA. A primary purpose of such evaluation was for OSHA to better identify those situations where exposures above the PEL are likely to persist despite full and proper implementation of the specified engineering and work practice controls and supplemental respiratory protection will therefore be necessary to ensure employees are protected from silica-related health risks. As documented in its analyses of technological feasibility for each Table 1 task, OSHA finds that most of the time employees are performing tasks on Table 1, respiratory protection will not be required. For most of the tasks or equipment on Table 1, OSHA expects that work will be performed for four hours or less and/or outdoors (see Chapter IV of the FEA). For certain tasks listed on Table 1, OSHA was able to distinguish indoor environments, where exposures are typically above 50 µg/m³ even with the use of engineering controls and work practices, from outdoor environments, where engineering controls can typically maintain exposures below 50 µg/m³, in order to eliminate requirements for respiratory protection where tasks are performed outdoors (e.g., using handheld grinders for uses other than mortar removal (c)(1)(xii)). Elsewhere, OSHA was able to further refine the equipment or tasks listed on Table 1 (e.g., handheld power saws (c)(1)(ii)-(iii); walk-behind and drivable masonry saws (c)(iv)-(v); milling machines (c)(1)(xiii)-(xv)) in order to eliminate previously proposed requirements for respiratory protection. In other cases, OSHA found engineering controls and work practices specified on Table 1 sufficient to maintain employee exposures at or below 50 µg/m³ when fully and properly implemented (e.g., (c)(1)(i), (c)(1)(ix), (c)(1)(xiv)), and thus determined that a respiratory protection requirement was not necessary. Specific changes to the respiratory protection requirements for each task listed on Table 1 are discussed in more detail below.

Consequently, required respiratory protection under Table 1 is limited to situations in which OSHA has determined that exposures over 50µg/m³ will often occur. For example, OSHA is not requiring the use of respiratory protection when handheld power saws (any blade diameter) are used outdoors, for less than four hours, with water-based dust suppression systems because OSHA's exposure profile indicates that exposures will be below 50 µg/m³ TWA most of the time that saws are used, given typical work patterns (e.g., outdoors for less than four hours per shift) (see Section 5.6 of Chapter IV of the FEA). Data submitted to the record by the Concrete Sawing and Drilling Association (CSDA) (Document ID 3497) also show that wet sawing produces exposures below 50 µg/m³ TWA with typical use patterns during the work shift. In contrast, indoor use of handheld wet power saws generates frequent exposures in excess of 50 µg/m³ TWA with typical use patterns during the work shift; from OSHA's exposure profile, half of the exposure samples associated with using handheld power saws indoors exceed 50 µg/m³ TWA, and two indoor samples included in the data submitted by CSDA were above a TWA of 50 µg/m³ (Document ID 3497, p. 5). As a result, Table 1 requires supplemental respirator use when handheld power saws are used indoors or in an enclosed area with water-based dust suppression systems.

OSHA has also used the terms “indoors or in an enclosed area” rather than “indoors or within a partially sheltered area” in order to clarify that any requirement to use respiratory protection when the task is performed under these conditions is limited to those areas where the dispersal of dust can be impeded such that concentrations can build up without the aid of forced ventilation. For example, a work area with only a roof that does not impede the dispersal of dust would not be considered “enclosed,” while it may have been considered by some to be a “partially sheltered area.”

As a result of these modifications, OSHA expects that many fewer employees will need to use respiratory protection than was the case for the proposed rule, and respiratory protection will not be necessary for the most commonly encountered work situations and environments specified on Table 1.

ISEA suggested that OSHA make the respirator requirements on Table 1 more user-friendly and performance-oriented by listing only an APF and recommending that users consult the APF table found in the respiratory protection standard, rather than listing generic respirator types (Document ID 2212, p. 2). In response to this comment, OSHA has maintained certain requirements for respiratory protection, but has eliminated specific requirements for the type of respirator that must be used (e.g., half-mask respirator, powered air-purifying respirator (PAPR) with loose-fitting helmet or negative pressure full facepiece). Instead, OSHA includes on Table 1 only the minimum Assigned Protection Factor (APF) required. This change from the proposal provides the employer with the option of determining which respirator offers the best protection for its employees in the multitude of construction environments that may be encountered. However, this is only the minimum protection factor required for the respirator, and employers have the flexibility to provide a more protective respirator to those employees who request one or require a more protective respirator based on the employer's evaluation of the worksite. As discussed in the summary and explanation of Respiratory Protection, paragraph (d)(3)(i)(A) of the respiratory protection standard (29 CFR 1910.134), which includes a table that can be used to determine the type or class of respirator that is expected to provide employees with a particular APF, can help employers determine the type of respirator that would meet the required minimum APF specified by Table 1. In order to reflect this change to the respirator requirements, the Agency has modified the heading on Table 1 to “Required Respiratory Protection and Minimum Assigned Protection Factor (APF).”

The respirator requirements on Table 1 are divided by task duration: “less than or equal to four hours/shift” and “greater than four hours/shift.” AIHA recommended that OSHA clarify what time is included when determining less than or greater than four hours (Document ID 2169, p. 6). OSHA has determined that time starts when the operator begins using the tool, and continues to be counted until he or she completes the task. This time includes intermittent breaks in tool usage and clean-up. For example, an employee cuts and places bricks, one at a time, for three hours consecutively. The employee then spends 30 minutes cleaning up the saw and empting slurry or dust collectors. All three hours spent cutting and laying bricks along with the 30 minutes for clean-up count. Tasks that are performed multiple times per day, during distinct time periods, should be counted as separate tasks, and times should be combined. For example, an employee cuts multiple bricks for 15 minutes, lays bricks for two hours and returns to cut more bricks for another 30 minutes. The two hours spent laying bricks do not count towards the total time for compliance with Table 1.

The duration of a task that generates respirable crystalline silica influences the extent of employee exposure and, in some cases, requirements for use of respirators. Some commenters suggested that OSHA modify the time breakdown for activities and respirator usage, such as BCTD's suggestion to divide tasks on Table 1 into two hours, four hours, and eight hours. Other commenters such as CISC, Holes Incorporated, and the Mason Contractors Association of America, suggested that OSHA exclude short duration tasks (e.g., 90 minutes or less) from Table 1, and NUCA suggested that the four hour cutoff is arbitrary and had no data to support it (Document ID 4073, Attachment 14f, p. 2; 2319, pp. 100-102; 3580, Tr. 1453; 3585, Tr. 2882; 3729, p. 3).

After reviewing these comments, OSHA has decided to maintain this division in the standard. OSHA selected four hours as an appropriate division point for respirator usage because it finds that employers and employees can anticipate whether a task will take less than half of a shift or more than half of a shift (as opposed to smaller time intervals), and so can plan accordingly on the need for respirator use on a given job. In addition, OSHA selected only a single durational division for respirator tasks in all of the relevant Table 1 tasks to avoid the confusion that could result from triggering mandatory respirator use at different times for different tasks. OSHA also determined that excluding short duration tasks from Table 1, although included in the ASTM E 2625-09 consensus standard, was inappropriate, given that employees engaged in a task listed on Table 1 are best protected using the available engineering controls, work practices, and respiratory protection specified for the task and are only exempt from complying with the standard where employee exposure will remain below 25 µg/m³ as a time-weighted average under any foreseeable conditions (see summary and explanation of Scope for further discussion of this exclusion).

Table 1 of the proposed rule used the phrase “4 hours per day” to indicate when respirators were required, but Table 1 of the final standard uses “4 hours per shift.” OSHA's exposure data is largely drawn from samples of employee exposure averaged over an 8-hour period, which is a typical time for a shift. The proposed rule referred to a time period of four hours “per day” for the purpose of limiting employee's exposure during the normal 8-hour shift that most employees work during a single day. OSHA recognizes, however, that some common tasks such as jackhammering during nighttime highway construction may occur during an 8-hour period that spans two calendar days (e.g., 8 p.m. until 4 a.m.). OSHA did not intend to allow employees to be exposed to respirable crystalline silica without respiratory protection for longer than four hours in that scenario, so OSHA has specified four hours “per shift” in the final rule.

OSHA also recognizes that the form and length of a shift may vary such that an employee may have a break between work periods (e.g., four hours on, two hours off, four hours on), work shifts may be longer than eight hours, or employees may work double shifts within a single day. The work periods in each of those examples constitutes a “shift” for purposes of determining the maximum amount of time that an employee may spend on one of the applicable Table 1 tasks without respiratory protection. OSHA's exposure data is not sufficient to support the conclusion that a longer duration of exposure without respiratory protection would be safe just because that exposure is spread out over a period that is longer than the normal 8-hour shift. Thus, an employee who works a 12-hour shift from 8 p.m. to 10 a.m. with a 2-hour rest break in the middle would have to wear a respirator if engaged in an applicable Table 1 task such as jackhammering outdoors if the employee will be jackhammering from 8 p.m. to 11 p.m., taking a break from 11 p.m. until 2 a.m., and then jackhammering again from 2 a.m. until 4 a.m. for a total of five hours of jackhammering. However, assuming no other silica exposure, the employee would not require respiratory protection if the jackhammering is limited to 8 p.m. until 11 p.m. and 2 a.m. until 3 a.m. for a total of four hours, even if the employee repeats the same shift and jackhammering times every day of the week. Accordingly, the change from “per day” to “per shift” clarifies OSHA's original intention regarding when respirator use is required for Table 1 tasks.

The requirement to provide respirators for Table 1 tasks is based on the anticipated duration of the task. Some commenters, such as EEI, expressed confusion about how this requirement would apply to non-continuous work (e.g., Document ID 2357, p. 27). EEI opined that:

The nature of non-continuous work can also make it hard to anticipate when a certain task may exceed four hours per day. Suppose, for example, a job task using a stationary masonry saw is not anticipated to last beyond four hours, so all controls listed in Table 1 are followed, and the employee does not wear a respirator. Then, due to unforeseen complications, the job lasts beyond four hours. Simply following the regulations as proposed, it is unclear whether the employee would be allowed to put on a half-mask after four hours, or if OSHA will not allow the employer to use the Table 1 option because the employee was not in a half-mask for the first four hours (Document ID 2357, p. 27).

In contrast, other commenters suggested that, despite the variable nature of the work, employers and employees generally know how long it will take to complete a particular task (e.g., Document ID 3581, Tr. 1684, 1686). OSHA recognizes, based on the comments above and the nature of construction work in general, that application of this requirement warrants some flexibility. For several Table 1 tasks, respiratory protection with the appropriate APF is required if the duration of a task is anticipated to exceed four hours, but is not required if the duration of a task is less than or equal to four hours (e.g., (c)(1)(ii), (c)(1)(x), (c)(1)(xii)). For these tasks, the Agency does not expect employers to know exactly how long it will take to perform a task. Rather, OSHA expects employers to make a good-faith judgment of the task's anticipated duration over the work shift based on previous experience and all other available information. If the employer anticipates that an employee will be engaged in a task for more than four hours, the employer must provide respirators (if required by Table 1) to the employee at the beginning of the shift. For example, in the case of an employee grinding concrete walls indoors, the employer should know, in advance, the area of surface that is to be worked on in the course of a shift. If, based on the employer's experience, the time needed to grind that area is typically less than four hours, the employer would not be required to provide respirators to the employee. If, however, using the same example, the employer experiences unforeseen difficulties that extend the task duration beyond four hours, the employer would be required under Table 1 to provide the listed respiratory protection as soon as it becomes evident that the duration of the grinding task may exceed the 4-hour limit, measured from the beginning of the task rather than the point when the need for extra time becomes evident.

Commenters, including BCTD, Fann Contracting, and IUOE, expressed confusion about whether an employee must wear a respirator for the entire duration of a task when that task is expected to last more than four hours, or rather wear the respirator for only the portion of the task that exceeds four hours (e.g., Document ID 3581, Tr. 1681; 2116, Attachment 1, p. 28; 2262, p. 27). OSHA hereby clarifies that the intent is to require respirator use throughout the duration of the task.

The objective of the silica standard is to limit an employee's average exposure over a work shift. In each of OSHA's health standards, this is accomplished by establishing a PEL expressed as an 8-hour TWA. Because a PEL is a time-weighted average, the Agency has traditionally required employees to use respirators throughout a shift when employees work on a task or in an area where exposure to a hazardous substance contributes significantly to an employee's exposure in excess of the PEL at any point during that shift. This same reasoning applies to wearing a respirator from the beginning of a shift where respirators are required on Table 1. Thus, OSHA is continuing the same approach to respirator use for tasks listed on Table 1 of the standard for construction as it has for other OSHA health standards. Under Table 1 of the final standard for construction, when a respirator is required only when a task is performed for more than four hours per shift and when the employer estimates that the duration of the task will exceed four hours, the employer must provide and ensure that a respirator is used the entire time that task is performed over the shift, not just during the time beyond the first four hours that the task is performed. For example, if an employer anticipates that an employee will operate a jackhammer outdoors for more than four hours, the employer must provide respiratory protection with an APF of 10 and require that it be used for the entire duration of the task. For tasks that are typically intermittent, employers are required to estimate at the outset the total time during the shift that the task itself will be performed and provide respirators required by Table 1 based on that estimate. If an employer knows from experience that an employee will perform a single task listed on Table 1 for four hours or less during a single shift, then the employer must ensure that the employee uses whichever respirator is specified in the “≤ 4 hr/shift” column on Table 1 (or need not provide a respirator if no respirator is required on Table 1 for that duration). As another example, if a contractor needs to cut four concrete walls using a handheld power saw (outdoors), and cutting each wall typically takes 45 minutes to complete, for a total time of 3 hours, the employer would not be required by Table 1 to provide a respirator. But if cutting each wall typically takes in excess of 60 minutes, the employer should expect that the total duration of the task will exceed four hours and provide respirators as required under Table 1. The employer is required to provide respirators as soon as it becomes evident that the duration of the task will exceed four hours. Thus, in most situations an employee will be protected by a respirator for all or the majority of a task that exceeds four hours because the rate of progress on the task will become apparent to the employer early on. An employee cannot be allowed to work more than four hours without a respirator when one is required under Table 1 because the employer will have certainty at that point that the task is exceeding four hours.

The above examples assume that employees are engaged in only one task covered by Table 1 each shift. Paragraph (c)(3) of the standard for construction requires that, where employees perform more than one task on Table 1 during the course of a shift for a combined total of more than four hours, employers must provide, for the entire duration of each task performed, respiratory protection that is consistent with that specified in the “> 4 hr/shift” column of Table 1, even if the individual duration of each task is less than four hours. If no respirator is specified for a task in the “> 4 hr/shift” column of Table 1, then respirator use would not be required for that part of the employee's shift. For example, if an employer plans to have his employee use a handheld grinder outdoors on a concrete wall for three hours and then use a chipping hammer for two additional hours, the employer would not be required to ensure that his employee uses a respirator for the three hours the employee is using the grinder, since respiratory protection is not specified on Table 1 for the use of a grinder outdoors for more than four hours per shift; however, the employer would be required to ensure that his employee uses a respirator with an APF of 10 for the two hours the employee is using the chipping hammer. This is so even though use of the chipping hammer, if performed with no grinding beforehand, would not have required a respirator for the duration that the tool was used. If the employee will be engaged in two activities that both have “None” specified for respiratory protection in both the “≤ 4hr/shift” and the “> 4 hr/shift” columns, such as driving a half-lane milling machine and then operating a walk-behind milling machine equipped with an integrated water delivery system, then respirator use would not be required for any part of an employee's shift even if the employer knows that the cumulative total of that work will exceed four hours.

When an employee performs multiple tasks that do not exceed a combined total of more than four hours, employers must provide the respiratory protection specified in the “≤ 4 hr/shift” column of Table 1 for each task. For example, if an employer plans to have his employee use a handheld grinder for mortar removal for one hour and a stationary masonry saw for an additional two hours, the employer is required to ensure that his employee uses a respirator with an APF of 10 for the one hour the employee is using the grinder. The employer would not be required to ensure that his employee uses a respirator for the two hours the employee is using the stationary masonry saw, since respiratory protection is not specified on Table 1 for the use of a stationary masonry saw.

Thus, whatever permutations may arise, the employer must estimate the duration of the task(s) to determine whether Table 1 will trigger the requirement for respiratory protection. If unforeseen conditions arise that cause the estimated duration to be revised for any of the tasks, the employer is required to provide the required respiratory protection as soon as it becomes evident that the employee will be engaged in the task for more than four hours during the shift.

Updating Table 1. Commenters, including LHSFNA, BAC, BCTD, Charles Gordon, and James Hardie Building Products, Inc., suggested that the utility of Table 1 will diminish over time if OSHA has no mechanism to include new control methods that may be developed (e.g., Document ID 4207, pp. 2-3; 4219, pp. 20-21; 4223, pp. 98-102; 3588, Tr. 3792-3793; 2322, pp. 21-23).

Commenters also provided specific recommendations for the frequency at which OSHA should update Table 1 and the process by which OSHA should do so. James Hardie Building Products, Inc. commented that additional controls demonstrated to maintain or increase employee protection should be incorporated by reference whenever they become available “without the need to undergo a formal rulemaking process” (Document ID 2322, pp. 21-22). The National Consumers League and the American Public Health Association suggested that OSHA consider updating Table 1 periodically (e.g., every five years) and publish a direct final rule to adopt a revised Table 1 when NIOSH deemed new dust control technology effective and feasible (Document ID 2373, p. 3; 2178, p. 3). Similarly, the Center for Effective Government urged OSHA to review Table 1 every five years and make revisions when new control technologies are found to be technologically and economically feasible (Document ID 3586, Tr. 3319).

Other commenters urged OSHA to consider mechanisms to update Table 1 without going through the rulemaking process. NIOSH suggested that the Agency develop a database of control technologies to supplement those on Table 1, rather than initiate rulemaking to update Table 1 (Document ID 2177, Attachment B, pp. 20-21). LHSFNA suggested that OSHA post enforcement decisions based on objective data online and permit employers performing similar tasks to use the controls specified in those decisions to meet their obligations under Table 1 (Document ID 4207, pp. 2-3). Holes Incorporated argued that Table 1 should be amendable by employers when testing proves that using such controls would ensure compliance with the PEL (Document ID 3441, p. 12; 3580, Tr. 1491).

IUOE, BCTD, and BAC argued that Table 1 should be an appendix to the rule so that it can be more easily updated (Document ID 2262, pp. 48-49; 2329, p. 6; 2371, Attachment 1, pp. 30-31). BCTD offered an approach for updating Table 1 that relied on the Agency establishing a mechanism for employers, equipment manufacturers, and others to submit data to the Agency for evaluation and subsequent inclusion in future versions of Table 1. BCTD proposed:

OSHA could publish the criteria in a non-mandatory appendix to the standard, so employers, manufacturers and researchers would have a clear understanding of what they will have to demonstrate to get their proposed controls onto the table.

Interested parties could then request that OSHA evaluate a control option, supporting their request with objective data, peer-reviewed studies, reports by NIOSH or other governmental agencies, or other reputable sources. If OSHA determined, based on the supporting data, that the technology meets its criteria for inclusion on Table 1, OSHA would issue an interpretative letter to that effect and/or issue a compliance directive advising its compliance officers that employers that fully and properly implement the particular control should be treated as if they were in compliance with the requirements of Table 1. This approach would enable OSHA to continually add to the options employers can utilize as new technologies come on-line, while at the same time ensuring that these additional controls meet the Agency's criteria (Document ID 4223, p. 100).

Charles Gordon also provided a detailed suggestion for the addition of regulatory text to address the issue of updating Table 1:

Updating controls. (i) Three years from the effective date of this standard and every 3 years thereafter, OSHA shall request comments on new or improved engineering controls which can achieve the PEL or Action Level without supplementary respirator use for operations specified in Table 1 or other operations not in Table 1 that have crystalline silica exposure over the Action Level.

(ii) If OSHA concludes that a new control will achieve the PEL without supplementary respirator use, it shall publish a notice permitting that control to be used for that Table 1 operation along with the other permitted controls or publish a direct final rule including that other operation in Table I and permitting the use of that control.

(iii) If a commenter submits to OSHA an engineering control for an operation in Table 1, which can achieve the action level without supplementary respirator use based on valid studies and cost data showing it is feasible, then no later than the date specified in paragraph (f)(6)(i), OSHA shall publish a proposal, proposing that that engineering control be the required engineering control for that operation (Document ID 4236, Appendix 1, p. 1).

Based on the comments and perspective reflected in the rulemaking record, OSHA sees the value in periodically updating Table 1 and is concerned that a static Table 1 may discourage innovation in the development of control technologies for reducing silica exposure. However, while OSHA may certainly consider future updates or adjustments to Table 1 if warranted, it will likely need to accomplish substantive changes through additional rulemaking. In any event, it has no intention to bind a future Administration to such rulemaking, whether to update Table 1 in particular or the entire rule in general, according to a schedule built into this rule. Meanwhile, the need to revise Table 1 in the future should be limited since the controls specified—primarily wetting the dust or ventilating and collecting the dust—are stated in general terms that will not be rendered obsolete by, for example, design improvements to water spraying or vacuuming equipment.

Even if the proposed mechanisms are consistent with the law governing rulemaking, OSHA is unwilling to specify a mechanism for updating Table 1 for several reasons. First, the procedures outlined by BCTD and Charles Gordon would commit the Agency to spend future resources to accept a large volume of information from interested parties, evaluate it in a timely manner, and prepare the needed economic and technological feasibility analysis and other rulemaking documents. OSHA may have higher rulemaking priorities and demands on its resources at that time, however. Second, Table 1 cannot both contain enforceable means of compliance and also be contained in a non-mandatory appendix. To ensure that employers who do not conduct exposure monitoring comply fully with the Table 1 provisions, OSHA must include the control specifications of Table 1 in the final standard for construction as requirements rather than as non-mandatory recommendations. Third, the controls specified on Table 1 are flexible and not tied to existing technology. The controls specified on Table 1 provide for the use of wet methods, ventilation, and in some cases, isolation. OSHA did not provide specific criteria for ventilation systems (size, air flow rate, etc.) or water flow rates. Instead, OSHA specifies that employers must operate the tools with integrated dust controls in accordance with the manufacturer's instructions. These instructions provide flexibility to take advantage of advances in technology. For example, as manufacturers develop effective surfactants to be used with water to further reduce silica exposure, there will be no need for OSHA to update Table 1 to specifically allow employers to use them. The requirement to use wet methods would still be satisfied.

Thus, OSHA rejects the suggestions to establish a specific mechanism for updating Table 1 in the future. If significant technological advances occur that require OSHA to initiate rulemaking in order to incorporate emerging technology not already encompassed by this rule, it will do so in the context of its rulemaking priorities at that time. Of course, interested parties may petition the Agency at any time to modify the dust control specifications on Table 1 of the standard for construction, and OSHA will consider such petitions based on the likely benefit that will accrue to workers and the Agency's available resources at the time.

Comparison with consensus standards. The requirements in paragraph (c) of the standard for construction are generally consistent with ASTM E 2625-09, the national consensus standard for controlling occupational exposure to respirable crystalline silica in construction. The ASTM standard provides a task-based control strategy, including five tables that specify control measures and respiratory protection for common construction equipment and tasks. While the ASTM standard provides this task-based control strategy, it also applies the PEL and exposure assessment to these tasks, as OSHA did in its proposal. However, OSHA's final standard for construction, as discussed above, takes a different approach by requiring specific engineering controls, work practices, and respiratory protection for construction tasks on Table 1; where employers fully and properly implement the engineering controls, work practices, and respiratory protection specified on Table 1, compliance with Table 1 is in lieu of the performance-oriented approach involving a PEL and exposure assessment, as provided as an alternative exposure control method in paragraph (d) of the standard for construction. Additionally, there are numerous differences between the tasks listed and the engineering controls, work practices, and respiratory protection specified on OSHA's Table 1 and those included on ASTM's tables. The ASTM standard also does not divide tasks according to duration and does not apply the approach to tasks limited to 90 minutes total time. The differences between OSHA's standard and the consensus standard, including those in the overall approach to compliance and in the format of Table 1, the tasks listed, and the engineering controls, work practices, and respiratory protection specified, best reflect the evidence received into the rulemaking record and the realities of the construction industry. These differences will also enhance compliance with OSHA's standard in the construction industry and, in doing so, better effectuate the purposes of the OSH Act and protect employees in the construction industry from the significant risks posed by exposures to respirable crystalline silica.

Table 1 entries. Table 1 identifies 18 common construction equipment/tasks known to generate high exposures to respirable crystalline silica. For each kind of equipment/task identified, Table 1 specifies appropriate and effective engineering controls, work practices, and, when necessary, respiratory protection. As proposed, Table 1 listed 13 construction operations that expose employees to respirable crystalline silica and identified control strategies and respiratory protection that reduce those exposures. OSHA received many specific comments about particular entries on Table 1 and on the specified engineering controls, work practices, and respiratory protection included for each entry. The additional equipment/tasks included on Table 1 of the final rule for construction are handheld power saws for cutting fiber-cement board (with blade diameter of 8 inches or less) and rig-mounted core saws and drills. Other entries on Table 1 of the final standard for construction were broken out from those proposed and added as separate entries. These include dowel drilling rigs for concrete (included under “Operating Vehicle-Mounted Drilling Rigs for Concrete” on proposed Table 1), walk-behind milling machines and floor grinders (included under “Milling” on proposed Table 1), small drivable milling machines (included under “Milling” on proposed Table 1), large drivable milling machines (included under “Milling” on proposed Table 1), heavy equipment and utility vehicles used to abrade or fracture silica-containing materials or used during demolition activities involving silica-containing materials (included under “Heavy Equipment During Earthmoving” on proposed Table 1), and heavy equipment and utility vehicles for tasks such as grading and excavating, but not demolishing, abrading, or fracturing silica-containing materials (included under “Heavy Equipment During Earthmoving” on proposed Table 1). One entry on Table 1 of the final standard for construction, vehicle-mounted drilling rigs for rock and concrete, is the result of combining two entries from proposed Table 1 (“Operating Vehicle-Mounted Drilling Rigs for Rock” and “Operating Vehicle-Mounted Drilling Rigs for Concrete”). One proposed entry, “Drywall Finishing,” was not included on Table 1 of the final standard for construction. A discussion of each of the 18 Table 1 entries in the construction standard, including the comments received and the changes made from the proposed Table 1 entries, follows below in the order in which they appear on Table 1.

Stationary masonry saws. Stationary masonry saws are used in the construction industry to cut silica-containing masonry materials such as bricks, concrete blocks, stone, and tile (see Section 5.7 of Chapter IV of the FEA). They are mounted either on a table-top or a stand, and include a flat platform where the work piece (e.g., a brick) sits before the worker brings a rotating circular abrasive blade into contact with the work piece by either pressing a swing arm mounted blade onto the piece or by moving the piece on a sliding platform into contact with a fixed blade (Document ID 4073, Attachment 4a, Rows 42-48, 55-63, 179-188, 288-297, 343-351). The cutting surface is about waist-high and at arm's length from the worker's breathing zone. A nozzle for spraying water is usually attached near the blade, and is connected to a water basin of some kind via a hose.

When using stationary masonry saws, paragraph (c)(1)(i) of the standard for construction requires that saws be equipped with an integrated water delivery system that continuously feeds water to the blade and that the tool be operated and maintained in accordance with manufacturer's instructions to minimize dust emissions. Saw designs vary between manufacturers and, as with other operating parameters, manufacturer's recommendations for optimizing wet methods are likely to vary somewhat with the saw size and design. OSHA is not specifying a minimum flow rate; based on the evidence in the record, OSHA anticipates that the water flow rate specified by the manufacturer will optimize dust reduction. OSHA recognizes that the employer's best available information for reducing dust with a specific control comes from the manufacturer's operating instructions. This is why OSHA is requiring the saw be operated and maintained according to the manufacturer's instruction to minimize dust.

The language describing the required control for stationary masonry saws was revised from the proposed rule to clarify that water must be continuously applied to the blade, and language was added to require that manufacturer's instructions be followed. This reflects OSHA's intent that employers use a saw with integrated water delivery system supplied by the saw manufacturer. OSHA finds that systems that are developed in conjunction with the tool are more likely to control dust emission effectively by applying water at the appropriate dust emission points based on tool configuration, and not interfere with other tool components or safety devices. These include free-flowing water systems, with or without a pump and basin, that are designed for blade cooling, as well as manufacturer systems designed for dust suppression alone (Document ID 1555, p. 509; 3998, Attachment 12a, pp. 9, 15-16; 3998, Attachment 12e, p. 3).

The proposed entry for stationary masonry saws also included a note requiring that water be changed frequently to avoid silt build-up in water and that the blade not be excessively worn. CISC commented that terms such as these were too ambiguous and would thus prevent the table from being a realistic compliance option (Document 2319, p. 98). OSHA understands that these notes could be subject to interpretation and in response, has removed the notes from Table 1. However, these practices are often included in manufacturer's instructions, and OSHA considers these type of instructions to be part of fully and properly implementing engineering controls (e.g., Document ID 4073, Attachment 4a, Rows 59-61).

In the FEA, OSHA's exposure profile for stationary masonry saws shows that wet cutting is an effective dust control. The median 8-hour TWA exposure in the profile is 34 μg/m³ for workers using saws with water delivery systems (Table IV-5.7-B in Section 5.7 of Chapter IV of the FEA) and the mean exposure for wet cutting is 41 μg/m³, substantially lower than the mean of 329 μg/m³ for dry cutting operations, a disparity that affirms that use of water on stationary saws significantly reduces exposure to respirable crystalline silica. Additional field data also show the effectiveness of water to control respirable crystalline silica exposures during cutting. Flanagan et al., in their 2006 study and 2009 data set, found that wet cutting methods (details not available) were associated with markedly lower exposure levels than were reported for all workers using table-mounted saws (Document ID 0677; 0677, Attachment 2). The silica concentrations reported by Flanagan et al. over the sampling period (ranging from 12 to 505 minutes) when wet cutting ranged from 6 μg/m³ to 316 μg/m³, with a mean of 73 μg/m³ and median of 46 μg/m³ (Document ID 0677; 0677, Attachment 2). Since most of the sample durations in this dataset were less than 360 minutes, workers' 8-hour TWA exposures were even lower. These data also included indoor work.

In addition to these field results, the record includes experimental studies that examined the effectiveness of wet dust control systems. Meeker et al. (2009) compared intensive masonry cutting done without controls to exposures while using saws with integrated water delivery systems and maximum flow rates of 2.3 and 2.4 liters per minute (0.6 and 0.63 gallons per minute) and found that wet saws were associated with a 91 percent reduction in exposure to respirable quartz (Document ID 803, p. 1; 2177, Reference 11, pp. 104, 107-108). Carlo et al. (2010) found reduction rates of 99 percent in the respirable dust exposure when water was applied at the manufacturer-recommended water flow rate, compared to dry cutting (Document ID 3612, pp. 246-247, 249). While respirable dust reductions do not always translate to exactly the same percent reduction in respirable silica levels, OSHA finds that respirable dust reductions are a reliable indicator of the capability of the control to reduce respirable silica. Therefore, OSHA anticipates that the control discussed in Carlo et al. (2010) would result in significant reductions to silica exposures.

CISC questioned the appropriateness of requiring an integrated water delivery system when most integrated systems are intended to keep the blade cool and are not designed for dust suppression (Document ID 2319, p. 109). However product literature submitted to the docket from five major saw manufacturers (Andreas Stihl, Husqvarna, Hilti, Makita USA, and Wacker Group) highlights the use of water application equipment to suppress dust in addition to blade cooling (Document ID 3620, pp. 6, 10, 24, 30; 3998, Attachment 12a, pp. 9, 15-16; 3998, Attachment 12e, p. 3; 3998, Attachment 12f; 3998, Attachment 12h; 4233, Attachment 1, p. 6). Beamer et al. (2005) conducted experiments to observe the differences in the various wet cutting methods available and found that the greatest improvement in dust reduction occurred with freely flowing water applied at a rate of 48 gallons per hour (0.8 gallons per minute), resulting in dust reduction of about 93 percent and confirming the benefits of water flowing over the stationary saw cutting blade compared with other misting systems (Document ID 1555, p. 509). Therefore, based on the evidence in the record, OSHA has determined that stationary masonry saws equipped with an integrated water delivery system are effective and the best available technology for controlling respirable crystalline silica.

Several commenters suggested that OSHA include an option for dry cutting on Table 1 (i.e., using LEV or other non-wet methods to control dust) because wet methods were not always available and certain materials are required to be cut dry. Commenters explained that freezing temperatures, lack of available water sources on new construction sites, concerns of water damage to surrounding areas during indoor work and problems with discoloration or water staining materials were all reasons why an employer may elect to cut without water (Document ID 0861, p. iv; 1431, pp. 1-6-1-9; 2296, p. 31; 2319, p. 94; 2320, pp. 6-7; 3587, Tr. 3609-3610; 4220, p. 5).

OSHA addresses the issue of freezing temperatures and availability of water in the technological feasibility analysis (Chapter IV of the FEA) and has determined that these barriers can be overcome in most instances, for example by wrapping gutter heat tape around drums of water or adding environmentally-friendly antifreeze additives to water (e.g., Document ID 3589, Tr. 4214, 4230). Moreover, evidence in the record indicates that LEV is not as effective as wet methods for controlling silica dust emissions from stationary saws. In the only study available to OSHA that directly compared wet dust suppression with LEV under the same experimental conditions, Carlo et al. (2010) determined that, even though the use of LEV resulted in substantial respirable dust capture, the water application system reduced the dust to a greater extent, reducing respirable dust levels by a factor of 10 more than the LEV systems tested (Document ID 3612, pp. 247-250). Unlike for wet dust control systems, there is little evidence in the record that LEV systems have proven effective in actual field use; the database compiled by Flanagan et al. contains no sample results from using stationary saws with LEV (Document ID 0677, Attachment 2).

OSHA finds that the study by Carlo et al. indicates that LEV systems on stationary saws are not as effective as water-based dust suppression systems and that respiratory protection will likely be needed. In the PEA, OSHA acknowledged that there was some evidence that exposures could be reduced to or below 50 μg/m³ with LEV when saws were used for typical cutting periods (15 to 30 percent of the shift) but that the effectiveness of LEV systems for stationary saws had not been widely evaluated. However, no evidence came into the record after the PEA that would allow OSHA to have greater confidence in the use of LEV when dry cutting or to consider it to be as effective as wet cutting in reducing silica dust exposure. Therefore, OSHA has not included a control alternative for the use of dry cutting with LEV in Table 1, and is only allowing integrated water systems for compliance with Table 1.

OSHA understands that there may be limited situations where the use of wet systems is not feasible for a given application. For those situations, the employer may use other means of dust control such as LEV systems, but the employer must then follow paragraph (d) rather than paragraph (c) of the standard for construction, i.e., comply with the 50 μg/m³ PEL, perform exposure assessments to determine compliance with the PEL, and supplement the engineering and work practice controls with respiratory protection where the PEL is not being met.

Stationary masonry saws with integrated water systems are readily available from several manufacturers including EDCO, Andreas Stihl, Hilti, Makita USA, Husqvarna, Wacker Group, MK Diamond, and Bosch (for tile cutting) and are effective and the best control option available (Document ID 4073, Attachment 4a, Rows 59-63, 183-188, 292-297, 347-351, 417-419; 4073, Attachment 4b, pp. 10-12, 21; 3998, Attachment 12a; 3998, Attachment 12e; 3998, Attachment 12f; 3998, Attachment 12g; 3998, Attachment 12h). Therefore, OSHA has determined that an integrated water delivery system is the appropriate control for inclusion on Table 1.

In the proposed rule, OSHA required the use of a half-mask respirator for employees who operated stationary masonry saws for more than four hours. OSHA made this determination based on the highest exposure results included in its exposure profile. OSHA has since determined that when fully and properly implementing all of the provisions under paragraph (c), employees can operate stationary masonry saws without the use of respirators. This is supported by the exposure profile contained in Table 5.7-B in Section 5.7 of Chapter IV of the FEA, which shows a mean exposure of 41 μg/m³, a median of 34 μg/m³ and 75 percent of the sample results below 50 μg/m³. Flanagan et al. reported similar exposures with a mean exposure of 48 μg/m³ crystalline silica from four exposure samples taken while workers operated saws indoors or in enclosed areas (Document ID 0677, Attachment 2). While water use was not described in any detail, these data show that exposures can be consistently maintained at a level where respiratory protection is not needed. Therefore, the final rule does not require the use of respiratory protection when employers are using wet stationary saws in accordance with Table 1, even when stationary masonry saws are used indoors or in otherwise enclosed areas (situations which are the most likely to generate high exposures).

Handheld power saws (any blade diameter). In the proposed rule, this entry was listed as “Using Handheld Masonry Saws.” OSHA has changed the title of this entry in the final rule to clarify that the requirements in Table 1 apply to any use of handheld power saws, not just those involving masonry materials. However, the tools included under this entry have not changed and include cut-off, chop, quickie, and handheld masonry saws.

Handheld power saws are used in the construction industry for cutting a variety of materials (see Section 5.6 of Chapter IV of the FEA). They usually consist of a semi-enclosed circular blade, directly adjacent to or in front of two handle grips which are perpendicular to each other. The blade enclosure covers the half (or more) of the blade directly facing the worker. A worker typically will use the blade to cut a work piece (e.g., a brick) placed on the ground by starting the device and slowly lowering the entire handheld saw with both hands to the work piece until the rotating blade makes contact and begins to cut, at which point the worker applies pressure to the work piece and cuts appropriately (Document ID 4073, Attachment 4a, Row 47). A nozzle for spraying water is usually located near the blade, and a water source is usually connected to the saw from a water source via a hose (Document ID 3998, Attachment 12e; 3998, Attachment 12f; 3998, Attachment 12h, pp. 10-11).

When using handheld power saws with any blade diameter (except saws used to cut fiber-cement board), paragraph (c)(1)(ii) of the standard for construction requires that saws be equipped with an integrated water delivery system that continuously feeds water to the blade and that it be operated and maintained in accordance with manufacturer's instructions to minimize dust emissions. Like stationary saws, designs vary between manufacturers and, as with other operating parameters, recommendations for optimizing wet methods are likely to vary somewhat with the saw size and design. In light of these variables, OSHA is not specifying a minimum flow rate. In addition, OSHA is recognizing that the employer's best available information for reducing dust with a specific control comes from the manufacturer's operating instructions, which is why OSHA is requiring the saw be operated and maintained according to the manufacturer's instructions to minimize dust. Water-fed handheld saws are commercially available from a variety of sources (Document ID 0615; 0737; 3998, Attachment 12e; 3998, Attachment 12a; 3998, Attachment 12f; 3998, Attachment 12g; 3998, Attachment 12h).

The data in the record and the studies reviewed by OSHA demonstrate that water spray suppression systems reduce respirable crystalline silica exposures substantially where the system was well designed and properly implemented and maintained (Document ID 0868; 1181; 3497; 3610; 3777; 4073, Attachment 8a). Use of an integrated water delivery system on the cut-off, chop, quickie or masonry saws has been shown to reduce respirable dust exposures by 78-96 percent (Document ID 0868, p. v; 1181, p. 443; 3610, p. 157; 3777, p. 67). Data compiled by the CSDA from member jobsites as well as NIOSH documents showed that all outdoor hand sawing using a saw equipped with a water supply produced exposure levels below a TWA of 50μg/m³ (Document ID 3497, p. 5).

In a laboratory study, Thorpe et al. (1999) evaluated the effectiveness of two types of water supplies commonly used with handheld saws: (1) A pressurized portable water supply and (2) a constant water supply (Document ID 1181, pp. 443, 445-447). During this evaluation, 15-minute PBZ samples were collected during uncontrolled and controlled (i.e., water-fed) cutting of concrete slabs containing 20 percent to 40 percent silica (i.e., worst-case conditions) (Document ID 1181, p. 447). The study protocol involved short sampling durations because handheld saws are typically used intermittently to make short cuts. The uncontrolled mean silica concentration during multiple 15-minute trials of intensive cutting ranged from 1,700 μg/m³ to 4,800 μg/m³ (reported as 1.7 to 4.8 mg/m³) (Document ID 1181, p. 448). Reductions in exposure to respirable silica dust when cutting concrete slabs using wet methods compared with no controls were 75 percent for diamond blades and 94 percent for resin blades when using water supplied by mains, and 75 percent for diamond blades and 77 percent for resin blades when using water supplied by a portable tank. Both sources of water were effective at reducing respirable dust, however, the portable tank needed to be periodically re-pressurized to maintain the necessary flow rate, while the water supplied from the mains provided a more constant flow rate. Both types of systems used to supply water to an integrated water delivery system would be acceptable under the table.

NIOSH also evaluated the performance of a commercially available water backpack and spray attachment, pre-set by the attachment manufacturer to provide 1.4 liters per minute water consumption (0.36 gallons per minute) for handheld saws during concrete block cutting (Document ID 0868, pp. 8, 11). The handheld electric abrasive cutter was used outdoors to make cuts through concrete blocks laid lengthwise on a plank 17 inches above the ground. During the 5- to 10-minute trials with water-fed saws, the water spray attachment reduced quartz exposures by an average of 90 percent from uncontrolled levels (Document ID 0868, p. 10). Middaugh et al. (2012) conducted a workplace field study to evaluate the effectiveness of dust controls on cut-off saws (Document ID 3610, p. 158). Air sampling was conducted for 10 days at 5 job sites on 4 experienced operators using gas-powered cutoff saws with 14 inch (35.6mm) diameter blades to cut concrete curbs (Document ID 3610, p. 159). Air sampling was conducted both with and without wet methods; sampling ranged from 4 to 16 minutes and corresponded to the entire duration of the task (Document ID 3610, pp. 159-161). With wet suppression, the concentration of respirable silica levels was reduced 78 percent to 210 μg/m³ (Document ID 3610, p. 162).

Based on the information in the record, OSHA concludes that most of the time, handheld power saw operators use the saw for two hours or less over the course of a workshift, typically using handheld saws for brief, intermittent periods repeated numerous times over the course of a shift (Document ID 1431, p. 3-63). The Mason Contractors Association of America stated that “90 minutes is actually a really long time to be cutting something. The vast majority of [cutting tasks] are under 15 minutes [total] in any given day” (Document ID 3585, Tr. 2911). The Bay Area Roofers Waterproofers Training Center agreed, clarifying that when cutting is performed as part of its work it is usually half an hour to 45 minutes a day (Document ID 3581, Tr. 1598). Information contained in research supports this as well. Thorpe et al. (1999) used 15-minute sampling durations in the study protocol because handheld saws are typically used intermittently to make short cuts (Document ID 1181, pp. 447-448). Middaugh et al. (2012) explained that concrete cutting in roadway construction is frequently performed with a handheld saw, noting that “although some applications may require cutting for an entire 8-hour workday, typical cutting is performed for less than two hours per day” (Document ID 3610, p. 162). Sample times from the Flanagan et al. database support this; the median time for using handheld portable saws was 101 minutes and the range of cutting times was from 9 to 447 minutes, indicating that saws are typically used for only a portion of the shift, although some workers cut for longer durations (Document ID 0677, Attachment 2).

Estimated TWA exposures (i.e., averaged over eight hours) using task measurements from field studies may exceed 50 μg/m³ when workers cut with water for two or more hours per day (Document ID 3610; 4073, Attachment 8a, p. 1; 0868). Shepherd and Woskie (2013) estimated that if typical cutting conditions (intensive cutting) were performed outdoors with wet methods for two hours and no other exposure occurred for the remainder of the day, 83 percent (88 out of 106) of the saw operators' 8-hour TWA exposures would be 50 μg/m³ or less (Document ID 4073, Attachment 8a, p. 1). In further analysis, the authors considered what would happen if operators used the water-fed saws outdoors at this same level of intensity for a full 6 hours of the shift, in which case 61 percent of operators would have 8-hr TWA exposures of 50 μg/m³ or less (Document ID 4073, Attachment 8a,p. 1).

In the proposal, OSHA based its requirement to use respiratory protection for operating saws more than four hours per shift on the few higher exposure values in its exposure profile, which indicated that exposures would exceed 50 μg/m³ occasionally when wet cutting with portable saws. However, OSHA concludes that the study by Shepherd and Woskie (Document ID 4073, Attachment 8a) as well as other material contained in the record and discussed above provide a better basis on which to determine the need for respiratory protection. Based on these studies, OSHA determined that outdoor wet cutting for more than four hours could result in more frequent exposures over 50 μg/m³ than are experienced with shorter task durations. Therefore, paragraph (c)(1)(ii) of the standard for construction requires use of respiratory protection having an APF of at least 10 for employees using a handheld power saw of any blade diameter equipped with an integrated water delivery system for more than four hours per shift. When cutting for four hours or less outdoors, no respiratory protection is required.

The vast majority of samples reviewed by OSHA involve the use of handheld saws outdoors. However, employees may occasionally use handheld saws indoors. When an employee uses a water-based system indoors or within enclosed areas, elevated exposures can still occur (Document ID 0675; 0177; 0846; 3497; 3777). Data submitted by CSDA shows that almost all indoor hand sawing using wet methods produced exposure levels above 50μg/m³ (Document ID 3497, pp. 1-4, 6, 8). Additionally, a field study of wet sawing found that an enclosed location (in a large garage building open in front and closed on 3 sides) resulted in significantly higher exposures than when the work was done outdoors (Document ID 3777, p. 1); a separate study found levels as high as 240 and 260 μg/m³ during indoor wet sawing (Document ID 0675, p. 1098). OSHA's exposure profile contained in Section 5.6 of Chapter IV of the FEA shows that using wet methods indoors results in higher exposures when compared to outdoor cutting with only 50 percent of the exposures in indoor environments being 50 μg/m³ or less, compared to 80 percent of the outdoor wet sawing samples. Although wet methods substantially reduce operator exposures compared to uncontrolled dry cutting indoors, elevated exposures still occur routinely. To reduce these exposures, OSHA is requiring that work done indoors or in enclosed areas have additional general ventilation such as exhaust trunks, fans, air ducts or other means of forced air ventilation to prevent the accumulation of dust in the work area. Accordingly, for indoor work, paragraph (c)(1)(ii) requires the use respiratory protection with an APF of 10 regardless of task duration.

Representatives from the roofing industry expressed concern regarding the use of wet methods in their industry, citing primarily the potential increase in slips and falls from introducing water to elevated worksites (Document ID 2320, p. 116; 2192, p. 4; 3526, p. 7). The Tile Roofing Institute stated that in California and Arizona, rooftop operations with roofing tiles or pavers are given an exemption from the requirement to use a dust reduction system because there is no way to address both the silica and fall protection hazard (Document ID 3587, Tr. 3595). Conversely, testimony from the public hearings indicates that wet dust control systems can be used to reduce exposures to silica during cutting of roofing tiles and pavers. Dan Smith, director of training for the Bay Area Roofers and Waterproofers Training Center, testified that the roofing industry in California is starting to voluntarily cut roofing tiles and pavers wet (Document ID 3581, Tr. 1600-1601; 1638) and that use of controls may actually increase visibility, thereby reducing a potential fall hazard (Document ID 3581, Tr. 1603-1604). He also explained that dry cutting of roofing tiles is prohibited in the U.K., and that the contractors association (the National Federation of Roofing Contractors), “. . . provides guidance and training. They use wet saws on scaffolding at the roof level . . . they use a [water] mister on the tile saw. They use a system like the hytile . . . which is a tile breaking tool” (Document ID 3581, Tr. 1601).

OSHA understands the concerns expressed by representatives from the roofing industry regarding the use of wet methods and increased risk for falls; however, OSHA concludes that alternate project planning can enable employers to use wet methods by implementing some of the measures described above.

In the proposed rule, OSHA included an option under Table 1 for the use of LEV when using portable masonry saws. While including LEV as an alternative to wet methods in the table was supported by both labor and industry groups (Document ID 2296, p. 32; 4223, p. 140; 4233, Attachment 1, p. 1), OSHA has removed this option from Table 1 based on information contained in the record indicating that LEV cannot consistently maintain exposure at or below a TWA exposure level of 50 μg/m³ (see Section 5.6 of Chapter IV of the FEA). OSHA is not prohibiting use of LEV for dry cutting, as LEV may be effective in reducing exposure to or below 50 μg/m³ in situations where, for example, saw use is intermittent. Employers who choose to do so may still use LEV in lieu of an integrated water system; however, those employers would be required to comply with the PEL and exposure assessment requirements under paragraph (d) of the standard for construction.

Handheld power saws for cutting fiber-cement board (with blade diameter of 8 inches or less). These specialized saw configurations consist of blades (with four to eight teeth) specifically designed for cutting fiber-cement board (see Section 5.6 of Chapter IV of the FEA) (Document ID 2322, p. 9; 2322, Attachment B, p. 8). The blades are fitted to a circular saw (or occasionally to other saws) with dust reduction systems (Document ID 2322, p. 9; 2322, Attachment B, p. 36). These saws have been specifically designed and tested by a member of the fiber-cement siding industry and by NIOSH for controlling the silica exposure of installers who perform cutting in that industry, and the saw is intended specifically for use on fiber-cement board (Document ID 2322, pp. 5, 9; 2322 Attachment B, pp. 33, 36).

When using handheld power saws with a blade diameter of 8 inches or less for cutting fiber-cement board outdoors, paragraph (c)(1)(iii) of the standard for construction requires saws to be equipped with a commercially available dust collection system that provides the air flow recommended by the manufacturer and a filter with a 99 percent or greater efficiency, operated in accordance with the manufacturer's instructions to minimize dust emissions. OSHA is not providing an entry for use of these saws indoors on Table 1 because fiber-cement board, used as siding and fascia applied to the exterior of buildings, is usually cut outdoors and the record lacks information on exposures to silica that would result from cutting fiber-cement board indoors. Therefore, employers who choose to operate saws to cut fiber-cement board indoors must conduct exposure assessments and comply with the PEL in accordance with paragraph (d) of the standard for construction.

This entry was added to Table 1 of the final standard for construction in response to comments NIOSH and the fiber-cement board industry submitted to the rulemaking record. These submissions provided substantial data on control technology (a specially configured saw) for controlling silica exposure when saw operators cut fiber-cement board (Document ID 2177, Attachment B, pp. 17-19; 2322, Attachment B-E and H).

The James Hardie Building company submitted 75 samples for workers using specially configured circular saws (with specialty blades of less than 8 inches) for cutting fiber-cement board with LEV (Document ID 2322, pp. 19-20). These saws were all fitted with cutting blades designed for the fiber-cement board product and some form of dust collector (but not always designed with vacuum suction). Workers using these saws had a mean 8-hour TWA exposure of 11 μg/m³ (median 7 μg/m³), although elevated exposures (maximum exposure of 76 μg/m³) occurred with some saw/control configurations that proved less reliable (for example, saws attached to a dust receptacle, without the benefit of a vacuum dust collection device) (Document ID 2322, pp. 19-20). Although the cutters sawed fiber-cement board products containing 15 to 50 percent silica, the respirable dust collected in the samples was 0 to 12 percent silica and percentages in the lower half of that range were most typical (Document ID 2322, Attachment D, pp. 5-10; 2322, Attachment E, pp.5-9; 2322, Attachment F, pp. 5-10). Most of the sawyers for whom exposures were elevated cut siding for approximately half the shift (four to five hours), a duration representative of typical cutting activities during a normal day of fiber-cement siding installation (Document ID 2322, Attachment D, p. 16; 2322, Attachment E, p. 16; 2322, Attachment F, p. 18). Several NIOSH reports demonstrate that this and other saw configurations are effective in achieving exposures of 50 μg/m³ or below when the saw is used with a vacuum dust collector (Document ID 4138; 4139, p. 11; 3998, Attachment 4a; 3998, Attachment 4b; 3998, Attachment 4c).

Based on the evidence in the record, commercially available dust collection systems for handheld power saws with a blade diameter of 8 inches or less and a dust collection device providing the air flow recommended by the manufacturer have been demonstrated to be particularly effective in controlling silica during outdoor cutting of fiber-cement board. One type of saw evaluated was a handheld, dust collecting model equipped with dust collection device rated at 200 cfm over a 7.25-inch-diameter blade (27.5 cfm per inch); however, the measured flow rate was reported to be 69 to 106 cfm. Using this configuration, all 21 exposure samples taken for siding cutters on construction sites were 41 μg/m³ TWA or less (20 sample results were less than 25 μg/m³) while cutting a variety of fiber-cement board siding products containing up to 50 percent silica (Document ID 3998, Attachment 4a; 3998, Attachment 4b; 3998, Attachment 4c; 4138; 4139). Accordingly, OSHA is requiring in paragraph (c)(1)(iii) that dust collectors be used with saws when cutting fiber-cement board.

Based on the evidence in the record, OSHA is not requiring the use of respiratory protection when employees are using handheld power saws with a blade diameter of 8 inches or less, for cutting fiber-cement board outdoors in accordance with Table 1 for any task duration. OSHA has determined that in such circumstances, employee exposures will be reduced to 50 μg/m³ or less when the controls specified for this task on Table 1 are fully and properly implemented.

Walk-behind saws. When using walk-behind saws (see Section 5.6 of Chapter IV of the FEA), paragraph (c)(1)(iv) of the standard for construction requires that saws be equipped with an integrated water delivery system that continuously feeds water to the blade and that the tool be operated and maintained in accordance with manufacturer's instructions to minimize dust emissions. OSHA is specifying that the saws be used with an integrated water feed system because the Agency has identified this as the most effective means of reducing exposures to respirable crystalline silica. This requirement is essentially the same as was proposed for the entry “Using Portable Walk-Behind and Drivable Masonry Saws.” As explained below, requirements in the final rule for drivable saws have been separated from those for walk-behind saws.

Saw designs vary among manufacturers, and as with other operating parameters, recommendations for optimizing wet methods are likely to vary somewhat with the saw size and design. As with other saws, OSHA is not specifying a minimum flow rate, but rather anticipates that the water flow rates specified by the manufacturer will optimize dust reduction. OSHA recognizes that the employer's best available information for reducing dust with a specific control comes from the manufacturer's operating instructions, which is why OSHA is requiring the saw be operated and maintained according to the manufacturer's instructions to minimize dust. Water-fed walk-behind saws (manual and self-propelled) are widely available from many manufacturers and construction tool distributors, such as Grainger, EDCO, MK Diamond, and CS Unitec (Document ID 0715; 1676; 1185; 0643; 0615).

CSDA stated that “nearly 100% of CSDA contractors use water on each and every job and this has to do with extending the life of the expensive diamond tools. The use of water has an additional benefit of containing silica particles that could become airborne” (Document ID 3496, p. 3). This was supported by others during the public hearings (Document ID 3580, Tr. 1438; 3585, Tr. 2885) and in written comments (Document ID 2316, p. 3). Disagreeing, both SMI and the Mason Contractors Association of America commented that most water-fed systems are designed to keep the blade cool, and their ability to suppress dust has not been sufficiently researched (Document ID 2316, p. 3; 3585, Tr. 2885). CISC similarly asked whether an additional water feed is needed for these saws or whether the one currently integrated for the purpose of cooling the saw will suffice (Document ID 2319, p. 104).

OSHA finds that considerable evidence in the record shows that water application reduces dust emissions, and several saw manufacturers state that using wet cutting will suppress dust (see discussion about requirements for water delivery systems above). Furthermore, the water delivery system described in Linch (2002) was for the purpose of cooling or protecting the blade, but was effective in suppressing respirable silica levels to below 50μg/m³ (Document ID 0784, p. 216). CSDA submitted exposure data collected during slab sawing with saws “equipped with water supply,” presumably for blade cooling. Those data show that of 26 measurements of silica concentrations taken during outdoor work, 21 (80 percent) were less than 25 μg/m³, and only one sample (65 μg/m³) exceeded 50 μg/m³ (Document ID 3497, pp. 2-4). Therefore, OSHA concludes water provided as coolant can also control silica exposure.

CISC questioned the feasibility of using wet methods in situations where there is no established water main on site (Document ID 2319, p. 112). OSHA finds that water tanks, which were used to provide water to the walk-behind saws in Linch (2002), are already commonly available on many construction sites and could provide water for a walk-behind saw (Document ID 0784, pp. 216-217).

Data contained in the record show that none of the respirable silica results associated with wet cutting outdoors using walk-behind saws exceeds 50μg/m³, with the majority of these results being less than or equal to the limit of detection (Document ID 0784, pp. 216-217). These results were obtained using the saw's normal water feed system intended for cooling the blade. Therefore, OSHA has determined that no respiratory protection is required when working outdoors with a walk-behind saw for any task duration.

Since walk-behind saws are used to cut pavement, they are most commonly used outdoors, though they can also be used indoors (Document ID 1431, pp. 3-63). Although the data are limited, water-fed walk-behind saws used indoors or in enclosed areas may result in higher exposures than those measured outdoors. Studies by both NIOSH and Flanagan et al. (2001) noted the potential for elevated exposure when walk-behind saws with continuous water application are used indoors, with Flanagan et al. reporting four 8-hour TWA sample results between 65 to 350 μg/m³ for four to seven hours of work (Document ID 4233, Attachment 1, p. 10; 0675, pp. 1098-1099). Additionally, the CSDA report submitted to the record shows the only exposure result from indoor slab sawing exceeded 50 μg/m³ despite the use of equipment with water supply (Document ID 3497, pp. 2-4). These results indicate that the source for the elevated exposure is likely due to the build-up of respirable aerosol within the enclosed space, rather than direct exposure to slurry spray (Document ID 0675, p. 1099). While OSHA anticipates that the results for indoor sawing can be reduced by minimizing the build-up of dust with supplemental ventilation as required under paragraph (c)(2)(i) of the rule, OSHA is unable to conclude that exposures can be consistently reduced to 50 μg/m³ or less for this task when performed indoors. Therefore, when used indoors or in an enclosed area, OSHA is requiring the use of respiratory protection with an APF of 10 regardless of task duration.

Drivable saws. Paragraph (c)(1)(v) of the standard for construction requires that, when using drivable saws to cut silica-containing materials, the saw must be equipped with an integrated water delivery system that continuously feeds water to the blade and that the tool be operated and maintained in accordance with the manufacturer's instructions to minimize dust emissions. Drivable saws include those where the operator typically sits in a cab (open or enclosed) away from the pavement cut point, guiding the saw to make long cuts such as are common for utility installation along roadways. These saws are cumbersome to move and are typically only used when making long cuts. The blade housed by the vehicle can be large (e.g., 8 feet in diameter and 2 inches thick) and is usually equipped with a water-fed system to cool the blade (Document ID 1431, pp. 3-63—3-64). The requirement to use integrated water systems on drivable saws is unchanged substantively from the proposal.

In its Technological Feasibility analysis (see Section 5.6 of Chapter IV of the FEA), OSHA analyzes exposures for workers using drivable saws. The exposure profile includes three samples, two using wet methods as required by Table 1 and one operating under other conditions. The two samples taken on workers using wet saws showed TWA silica exposures of 12 μg/m³ (i.e., below the limit of detection (LOD)) and 33μg/m³ over sampling times of 70 and 125 minutes, respectively. OSHA considers these exposure results to reflect typical work patterns in that operators will often operate the saw for one or two hours before moving the saw to another location. CISC questioned OSHA's use of short term samples and the assumption of zero exposure during the unsampled portion of the shift and noted that this could underestimate the exposures for these workers (Document ID 2319, pp. 51-52). While OSHA acknowledges that this situation may occur at times, there is no evidence that this is the case for these drivable saws samples. These samples were collected by OSHA inspectors, who are instructed to sample for the entire duration of silica exposure. Accordingly, OSHA concludes that these samples accurately characterize the sampled workers' exposure.

In the proposed rule, dust control requirements were specified for drivable and walk-behind saws together, and the proposed rule would have required respirator use when operating either saw in indoor or enclosed environments. In the final standard for construction, the requirements for these kinds of saws are separated on Table 1 because, unlike walk-behind saws, drivable saws are rarely, if ever, used in indoor environments. Because the requirements of Table 1 only apply to outdoor use of drivable saws, and the data available to OSHA demonstrate that the wet methods described above can consistently control exposures in that environment, Table 1 does not require the use of respiratory protection when these controls are implemented, regardless of task duration.

SMI and CISC commented that currently drivable saws use water to cool the cutting tool, and the effectiveness of cooling water for respirable crystalline silica dust mitigation has not been comprehensively researched (Document ID 2316, Attachment 1, p. 3; 2319, p. 112). SMI stated specifically that “parameters such as flow rate, volume, flow delivery characteristics, velocity, and delivery location have not been evaluated or compared” (Document ID 2316, p. 3). However, Atlantic Concrete Cutting agreed that all of its cutting services were performed with water (Document ID 2367, p. 2), and that the application of water minimized and most likely eliminated exposure to respirable crystalline silica. Atlantic Concrete Cutting also stated that the use of a “water-fed system that delivers water continuously at the cut point” would be an appropriate silica dust control for drivable saws and that respirators would not be needed to further protect employees (Document ID 2367, pp. 2-4). In light of this testimony, OSHA concludes that it is appropriate to permit employers to fully and properly implement water-based systems on drivable saws in compliance with Table 1, eliminating their need to conduct exposure assessments for employees engaged in a task using drivable saws. Moreover, as reflected in Table 1, OSHA concludes that full and proper implementation of this control will not require the use of respirators for this task even if performed for more than four hours in a shift and so has not included respiratory protection for this task.

Rig-mounted core saws or drills. Paragraph (c)(1)(vi) of the standard for construction, an entry for rig-mounted core saws or drills, was not included in proposed Table 1. Core saws or drills are used to perform core cutting (also called core drilling, boring, or concrete coring) to create round holes for pipes, ducts and conduits to pass through walls, ceilings and floor slabs made of concrete, masonry or other materials that may contain silica (see Section 5.6 of Chapter IV of the FEA). Core cutting machines (also called core drills) use a thin continuous round cutting surface on the round end of a cylindrical coring tool (“bit”) (Document ID 0679, pp. 18-20). The machine is typically attached to the surface being drilled (bolted on via a rig for stability) (Document ID 3998, Attachment 13e, pp. 4, 9). When the rotating diamond core cutting bit is applied to solid material, the bit cuts away a thin circle of material. The cut separates the central “core” of material, within the circumference of the bit, from its surroundings, leaving the core generally intact as it is removed from the hole (Document ID 3501, p. 6). The cylindrical bit can range in size; for example NIOSH described a coring operation used to produce holes 2 to 31 inches in diameter in large sections of concrete conduit (Document ID 0898,p. 6).

For rig-mounted core drills, there is one specified control that consists of using a tool equipped with an integrated water delivery system that supplies water to the cutting surface, operated and maintained in accordance with manufacturer's instructions to minimize dust emissions. Based on evidence in the record, OSHA has determined that baseline conditions for core cutting involve using wet methods and that most core cutting machines are provided with and intended to be used with a water feed system (e.g., Document ID 0675, p. 1097; 0679, pp. 18-21; 0898, p. 6; 3580, Tr. 1415, 1435; 3581, Tr. 1584; 3585, Tr. 2902). Like other saws included in Table 1, these existing systems will fulfill the requirements of Table 1.

Comments submitted by SMI expressed confusion as to whether or not core drilling was included on the table under the entry for drills and the appropriateness of using LEV as required under the proposed table during core cutting (Document ID 2316, p. 2). In the proposed rule, OSHA specifically excluded core cutters from hole drillers using handheld drills (see PEA, p. IV-403). OSHA did not include this information because OSHA lacked specific information on exposures to silica that result from core drilling or from industry's practice of using water during coring operations. Upon OSHA's review of core cutter/driller operator exposures and hearing testimony from industry, OSHA determined that there is the potential for silica exposure when employing core saws and that these saws are different enough from other drills and cutting tools to warrant the inclusion of its own separate entry on Table 1.

Kellie Vasquez of Holes Incorporated testified that the process of core drilling is much different than other types of drilling due to the different drill bits used, resulting in much less silica exposure (Document ID 3580, Tr. 1484). This is supported by OSHA's review of record data on core cutting/drilling, which shows that operators generally experience little or no silica exposure during this low-speed process, which is already performed using water-fed equipment as a standard practice (Document ID 0675, pp. 1097-1098; 0898, p. 15).

Additional exposure data compiled by CSDA from member jobsites (Document ID 3497) and other studies (Document ID 0675; 0679; 0898) show that using a core drill with wet methods results in exposure levels of less than 50 μg/m³ (Document ID 3497). During hearing testimony, BCTD commented that core drills are always used with wet methods (Document ID 3581, Tr. 1584). This was supported by Kellie Vasquez of Holes Incorporated who stated that her concrete cutting operations employ water 100 percent of the time (Document ID 3580, Tr. 1483). Accordingly, OSHA added dust control specifications for core sawing and drilling to Table 1 of the final standard for construction. Because the available evidence described above demonstrates that using wet dust suppression systems for core cutting does not result in silica exposures exceeding 50 μg/m³, the final standard for construction does not require the use of respiratory protection.

Handheld and stand-mounted drills (including impact and rotary hammer drills). Handheld drills are used to, among other tasks, create holes for attachments and small openings in concrete and other silica containing materials (see Section 5.4 of Chapter IV of the FEA). These drills can: (1) Be electric, pneumatic, or gas-powered; (2) use rotary hammers or percussion hammers; and (3) be free-standing or stand-mounted. Handheld drills consist of a handle with a trigger button to begin drilling, a motor compartment above and perpendicular to the handle, and a socket to insert drill bits of varying lengths and styles at the end of the motor compartment. Impact and rotary hammer drills appear the same, but provide the ability to drill with extra motor-generated impacts and/or torque. The drills may have a second handle in front of the main handle for a worker to grasp with the off hand. To control dust, they may contain attachable dust collection systems where the end of the drill bit is surrounded by a vacuuming compartment which connects to the rest of the drill, allowing for dust to be removed while drilling (Document ID 4073, Attachment 4a, Row 68). Handheld drills can also be stand-mounted, in which case a drill is turned on its side and mounted to an adjustable stand, allowing the worker to drill directly into a work product with precision (Document ID 4073, Attachment 4a, Row 72).

Paragraph (c)(1)(vii) of the standard for construction requires that handheld and stand-mounted drills be equipped with a commercially available shroud or cowling with dust collection system that provides at least the minimum air flow recommended by the manufacturer. The dust collection system must include a filter cleaning mechanism and be equipped with a filter with 99 percent or greater efficiency. The dust collection system must be operated in accordance with the manufacturer's instructions to minimize dust emissions. In addition, OSHA is requiring that a HEPA-filtered vacuum be used when cleaning debris from drill holes.

The proposed Table 1 labeled this category of tools “Using rotary hammers or drills (except overhead).” In response to several comments, OSHA has revised this description to make clear that drills mounted on stands are also included and also removed the exclusion for overhead drilling. For example, SMACNA recommended expanding the entry for rotary hammers and drills to include overhead drilling, contending that overhead drilling would be just a safe as other drilling if done as directed on the table (Document ID 2226, p. 2). The Mechanical Contractors Association of America commented that overhead drilling should be included in Table 1 since overhead drilling is a common operation in several trades (Document ID 2143, p. 2). OSHA received testimony that overhead drilling along with a drill stand with a vacuum attachment addresses both ergonomic and silica exposure hazards. After review of the evidence in the record, OSHA has determined that it is appropriate to remove the exclusion for overhead drilling in the Table 1 entry for handheld and stand-mounted drills.

As proposed, Table 1 had separate entries for “Rotary Hammers or Drills” and “Jackhammers and Other Impact Drillers.” OSHA received comments from PTI suggesting that impact drills be covered by the entry for “Rotary Hammers or Drills,” rather than by the “Jackhammers and Other Impact Tools” entry (Document ID 1973, Attachment 1, p. 4). NIOSH also commented on the potential for confusion, noting that a rotary hammer or drill is technically an impact driller (Document ID 2177, Attachment B, pp. 32-33). Therefore, the entry for handheld or stand-mounted drills in final Table 1 covers activities related to the use of impact and rotary hammer drills. Chipping and breaking activities, which are associated with more intense silica exposures, are covered by the entry for jackhammers and handheld power chipping tools.

CISC commented that OSHA did not state in the proposed rule that the dust collection system needs to be “commercially available” (Document ID 2320, p. 112). In the final standard for construction, OSHA has clarified that Table 1 requires that the handheld or stand-mounted drill be equipped with a commercially available shroud or cowling with dust collection system. Several drilling equipment manufacturers sell dust extractors or dust collectors to minimize dust escaping into the work area. These systems include a vacuum with a filter cleaning mechanism and a filter with 99 percent or greater efficiency. Some examples include Bosch, DeWalt, Hilti, and Metabo (Document ID 3998, Attachment 10; 4073, Attachment 4a, Rows 15-18, 64-70, 111-119, 189-195, 289-301, 352-357). OSHA has determined that it is feasible for employers to obtain controls for handheld and stand-mounted drills that meet the specifications in Table 1.

Based on evidence in the record, OSHA finds that, for most tools, a commercial dust control system using an appropriate vacuum will provide the most reliable dust capture. Average respirable quartz levels varied among the different cowling/vacuum combinations. In one study, all commercial cowl/vacuum combinations tested resulted in personal breathing zone exposures of 28 μg/m³ or less during drilling (Document ID 1142, p. 42). Another study reported median silica exposures of 60 μg/m³ and 45 μg/m³, depending on drill bit size, in a room with limited air exchange (Document ID 1391, pp. 11-12, 15-19). These findings indicate that providing a means of exhaust when working indoors or in enclosed areas, as required under paragraph (c)(2)(i) of the standard for construction, in addition to using dust collection systems, will maintain exposures below 50 μg/m³. Based on these findings, OSHA is not requiring the use of respiratory protection when using handheld or stand-mounted drills, including overhead drilling, for any task duration.

The practice of dry sweeping or brushing debris from a hole, or using compressed air to clean holes, contributes to the exposure of employees using drills. Based on the evidence in the record, OSHA is requiring that holes be cleaned with a HEPA-filtered vacuum. Any method for cleaning holes can be used, including the use of compressed air, if a HEPA-filtered vacuum is used to capture the dust. If a HEPA-filtered vacuum is not used when cleaning holes, then the employer must assess and limit the exposure of that employee in accordance with paragraph (d) of the standard for construction.

While the paragraph on housekeeping (paragraph (f) of the standard for construction) also applies when employers are following paragraph (c) of the standard for construction, the employer must ensure that all of the engineering controls and work practices specified on Table 1 are implemented. For example, paragraph (f)(2)(i) of the standard for construction permits the use of compressed air when used in conjunction with a ventilation system that effectively captures the dust cloud. However, to fully and properly implement the controls on Table 1, an employer using compressed air when cleaning holes during tasks using handheld or stand-mounted drills or dowel drilling rigs for concrete must use a HEPA-filtered vacuum to capture the dust, as specified in paragraphs (c)(1)(vii) and (viii) of the standard for construction, not just a ventilation system as specified in paragraph (f)(2)(i) of the standard for construction.

PCI noted that anchor holes must be blown clean to obtain adequate adhesion, and recommended that the use of compressed air and dry sweeping be allowed unless exposures will exceed 50 μg/m³ (Document ID 2276, pp. 10-11). This recommendation assumes exposure assessment, however, the construction standard does not require such assessment where the task is included in Table 1 and the employer is following Table 1. Although OSHA is allowing the use of compressed air if used in conjunction with a HEPA-filtered vacuum to capture the dust, OSHA has determined that there are a number of feasible alternatives to using compressed air. At least one tool manufacturer offers an anchor system with “no hole cleaning requirement whatsoever,” due to the use of a drill with a ventilated drill bit (Document ID 4073, Attachment 4b, Slide 12). Another manufacturer offers a “hole cleaning kit” for large hammer hole drilling, which consists of a doughnut-shaped dust collection head that attaches directly to a vacuum cleaner hose. The head is placed against the surface to be drilled and captures dust generated as the hole is drilled (Document ID 4073, Attachment 4b, Slide 17). This hole cleaning kit also includes two sizes of hole cleaning tubes. Such a control could be used with existing as well as new drills (e.g., Document ID 3998, Attachment 10, p. 42).

Data suggest that decreasing employees' reliance on blowing or dry sweeping drilling debris can reduce exposures by approximately 50 percent (e.g., Document ID 1391, pp. 32-33). This 50 percent reduction would bring exposure levels to 50 μg/m³ or below for all the drill operators who are currently exposed to silica at levels between 50 μg/m³ and 100 μg/m³. Thus, OSHA has determined that a HEPA-filtered vacuum must be used when cleaning holes in order to reduce silica exposure.

Dowel drilling rigs for concrete. Paragraph (c)(1)(viii) of the standard for construction covers dowel drills (i.e., gang drills), which are drills with one or more drill heads used to drill holes in concrete for the placement of steel supports (see Section 5.9 of Chapter IV of the FEA). When operating dowel drills, Table 1 requires that the rig be equipped with a shroud around the drill bit and a dust collection system that has a filter with 99 percent or greater efficiency. In addition, Table 1 requires that dust collection equipment be equipped with a filter cleaning mechanism.

NIOSH found that employees using compressed air to clean the filter after dowel drilling resulted in some of the highest measured exposure to respirable dust during the task, and could cause damage to the filter (Document ID 4154, p. 26). NIOSH also pointed out that the reverse pulse feature on the dust collector should preclude the need to remove filters for cleaning (Document ID 4154, p. 26). OSHA agrees and has included the specification for a filter cleaning mechanism for dowel drills in Table 1. Finally, Table 1 requires that a HEPA-filtered vacuum is used when cleaning holes. OSHA recognizes that it may be necessary at times for employers to use compressed air to clean holes, and thus, as with handheld and stand-mounted drills, Table 1 does not preclude its use when cleaning the debris from holes caused by dowel drilling, so long as a HEPA-filtered vacuum is employed at the same time to effectively capture the dust.

In the proposed rule, OSHA included dowel drills within the entry titled “Operating Vehicle-Mounted Drilling Rigs for Concrete.” However, OSHA has determined that the exposures that result from dowel drilling rigs equipped with LEV systems are substantially higher than is the case for vehicle-mounted concrete drilling rigs. Therefore, respirator requirements are different for the two kinds of equipment (see Sections 5.4 and 5.9 of Chapter IV of the FEA).

Exposure information on concrete dowel drilling in the record is limited but shows that, even with LEV, exposures are likely to exceed 50 μg/m³. Exposure studies by NIOSH on concrete dowel drills, manufactured by both EZ Drill and Minnich Manufacturing, that were equipped with close capture hoods and a dust collection system showed that workers were often still exposed to respirable silica dust levels well above 50 μg/m³, with 8-hour TWA exposures to respirable quartz ranging from 24 to 420 μg/m³ with a geometric mean of 130 μg/m³ (Document ID 4154, p. 25). NIOSH found that using an air lance and compressed air to clean holes and to clean the filter and hoses of the dust collector contributed to these high exposures, and NIOSH recommended the use of a pneumatic vacuum to clean holes and components of the dust collector (Document ID 4154, p. 26). The record contains no information on exposures that result when vacuums are used to clean holes. As stated previously, exposures that result from dowel drilling rigs equipped with LEV systems are substantially higher than is the case for vehicle-mounted concrete drilling rigs. Based on this information, OSHA has modified the respirator requirement for dowel drilling, and is requiring the use of respiratory protection with a minimum APF of 10 regardless of task duration.

Comments on OSHA's proposed requirements for dowel drilling were limited. Holes Incorporated, Atlantic Concrete Cutting and CISC all stated that outdoor concrete dowel drilling should be included on Table 1 (Document ID 2338, p. 3; 2320, p. 14; 2367, p. 4). Atlantic Concrete Cutting further suggested that the appropriate control for dowel drilling is to limit this task to outdoors only and “provide sufficient ventilation” (Document ID 2367, p. 4). As suggested, OSHA has included a separate entry for concrete dowel drilling on Table 1, but with more detailed control requirements than suggested by Atlantic Concrete Cutting based on information contained in the record. OSHA agrees with Atlantic Concrete Cutting that the entry on Table 1 should be limited to outdoor operations since there is no information in the record as to the appropriate level of respiratory protection needed when operating dowel drills in enclosed areas, and has accordingly revised Table 1 of the final rule to so indicate.

PCI commented that anchor holes must be blown clean using compressed air to obtain adequate adhesion (Document ID 2276, p. 10). In its feasibility analysis, OSHA identified this task as a significant source of exposure to respirable crystalline silica. Therefore, for the reasons previously stated, Table 1 also includes a requirement to use a HEPA-filtered vacuum when cleaning holes, with or without the use of compressed air, in connection with this task.

Vehicle-mounted drilling rigs for rock and concrete. Paragraph (c)(1)(ix) of the standard for construction requires that vehicle-mounted rock and concrete drilling rigs be equipped with a dust collection system with a close capture hood or shroud around the drill bit with a low-flow water spray to wet the dust discharged from the dust collector, or be operated from within an enclosed cab in conjunction with water applied at the drill bit for dust suppression (see Section 5.9 of Chapter IV of the FEA). The specifications of paragraph (c)(2)(iii) of the standard for construction apply to the cabs.

The proposed rule had separate entries for vehicle-mounted drilling rigs for rock and vehicle-mounted drilling rigs for concrete, both of which specified a combination of LEV and water use. OSHA has determined that, since the rigs and the approach to dust control are similar for both, they can be combined in Table 1 of the final standard for construction. OSHA has also determined that it is appropriate to allow employers the option of having the drill operator work within an enclosed cab meeting the requirements of paragraph (c)(2)(iii) of the standard for construction and to apply water at the drill bit to ensure that the operator and other employees assisting are protected when working near the drill bit.

Workers using vehicle-mounted drilling rigs position and operate the drill rigs from control panels mounted on the rigs. These workers may also perform intermittent tasks near the drilling point such as fine-tuning the bit position, moving debris away from the drill hole, and working directly or indirectly with compressed air to blow debris from deep within the holes. Workers using drilling rigs can be exposed to dust generated by the action of the drill bit and from dust raised by air movement or a compressed air nozzle. Although rig-based drilling is often a one-person job, some of the associated activities, such as fine-tuning the drill position and clearing debris from in or around the holes, can be performed by a second worker (Document ID 0908, p. 1; 1563, p. 3).

In the proposed rule, OSHA specified requirements for the dust collections systems regarding smooth ducts, transport velocities, clean-out points, pressure gauges, and activation of the LEV. These requirements came from a NIOSH evaluation of control technology for dowel-pin drilling (Document ID 1628). The final rule does not require these specific control parameters for vehicle-mounted drilling rigs for rock and concrete. OSHA has determined that dust controls for dowel drilling rigs are substantially different than vehicle-mounted rock and concrete drilling rigs; they are addressed separately in the previous section. Dust collection systems that use a hood or shroud around the drill bit have been proven effective in reducing exposures to respirable crystalline silica. NIOSH found that, when used properly, modern shroud designs now help achieve dust control objectives more consistently for rock drilling rigs than in the past (Document ID 0967, pp. 5-9). Based on information contained in the record, OSHA finds that dust collectors and shrouds are commercially available (Document ID 0669; 0813).

Although the LEV system will control dust emissions at the drill bit, there are still dust emissions at the dust collector discharge area, which can contribute to either the operator's or other employees' exposures. Organiscak and Page (1995) found that enclosing the dust collector discharge area with a shroud can reduce respirable dust levels by 80 percent (Document ID 3613, p. 11). However, evidence in the record shows that the combination of LEV at the drill bit and water application will be more effective in that water can be used to control dust emission points where drilled material is discharged. Organiscak and Page (1995) illustrated the effectiveness of combined wet methods and dust collectors in their U.S. Bureau of Mines study, which compared rock drilling using LEV with and without the addition of water for dust suppression. The addition of wet methods to the LEV system showed a 92 percent reduction in respirable dust and eliminated nearly all of the visible dust. Quartz results decreased from 143 μg/m³ when the water was off (LEV alone) to 9 μg/m³ when water was added. OSHA obtained sample results of 54 μg/m³ and 35 μg/m³ during an inspection for two workers drilling in granite that contained 30-40 percent crystalline silica (Document ID 0034, pp. 8, 23-26, 35-38). Both drillers were reportedly using water and LEV, although specific details about the configuration of the controls were not discussed (Document ID 0034, pp. 23, 89-93). A third sample that was below the limit of detection for crystalline silica was collected on the same site for a laborer who helped with positioning the drills (Document ID 0034, pp. 39-42).

OSHA received many comments related to the proposed requirements for rock and concrete drillers. CISC noted that it is more common to use wet methods when operating vehicle-mounted drilling rigs for rocks as opposed to using dust collection systems (Document ID 2319, pp. 108-109). A number of other commenters noted the prevalence of wet methods use in the industry (e.g., Document ID 1983, pp. 1-2; 2116, Attachment 1, p. 33; 3496, p. 6). For instance, CSDA commented that nearly 100 percent of CSDA contractors use water on every job in order to prolong the life of the diamond blade (Document ID 3496, p. 6). The National Ground Water Association (NGWA) noted that it is industry practice when drilling water wells to use foam as a wet control method:

Industry practice is to use the engineering control of soap injection where water is mixed with foam. The foam mixtures of water and foam products are effective in mitigating the hazard of dust when properly used as they can carry particles ranging from .03 mm to the size of a quarter. There are multiple manufacturers of the foam products and these products have been approved for use when drilling sanitary water wells. The foam agents are NSF approved and have also been approved for use in many states (Document ID 1983, pp. 1-2).

NGWA also explained that all rotary drilling machines have been equipped with some type of water injection system since the early 1970s (Document ID 1983, p. 2).

Historically, construction and mining investigators have reported dust control efficiencies of 96 to 98 percent through the routine use of wet dust suppression methods, depending on the methods used; however, the water flow necessary for dust control can create problems under certain working conditions (e.g., moisture shortening the life of certain drill bits (such as tricone roller bits), high-pressure water causing spalling of the drill hole wall) (Document ID 0967, p. 6). Advances in recent decades have produced equipment that permits workers to use wet methods in a wider range of circumstances. New “water separator sub” designs extend bit life beyond the previous norm and reduce spalling in a variety of rock types (Document ID 0967, p. 6). Several commenters stated that wet methods are used frequently and are effective in controlling dust (Document ID 1983, pp. 1-2; 3580, Tr. 1435; 3496, p. 6).

OSHA's exposure profile contains five sample results for workers using wet methods with no other controls while drilling. These five samples have a mean of 24 μg/m³ and a median of 17 μg/m³, with a high exposure of 57 μg/m³ and two results below the LOD (Document ID 0034; 0226). A review of studies by NIOSH (2008) evaluated the use of wet methods in different types of drilling, including roof bolting (rock bolting) and surface rock drilling (Document ID 0967). NIOSH found that for roof bolting, silica dust was best controlled at its source through dust collection or wet drilling, similar to the standard practice in metal mines of using pneumatic percussion drills with water in addition to compressed air to flush the drill cuttings from the hole. This drilling method was found to be the best method of dust control, with dust reductions ranging from 86 percent to 97 percent (Document ID 0967, pp. 2, 4). The high dust reductions from wet drilling were confirmed in later studies that evaluated the use of water mists and foams injected through the drill steel and found that those controls reduced dust concentrations by 91 percent and 96 percent, respectively (Document ID 0967, p. 2). NIOSH also found that for surface drilling, wet drilling techniques provided the best dust control. Wet drilling provided dust control efficiencies of up to 97 percent at a water flow rate of 4.5 L/min (1.2 gallons per minute) (Document ID 0967, p. 6). OSHA thus finds that water directed at the material discharge point is an effective dust suppressant in vehicle-mounted rock and concrete drilling and specifies its use on Table 1 for this task.

OSHA also finds that the use of an enclosed cab can effectively reduce exposures for vehicle-mounted drill operators. Enclosed cabs, however, only benefit the operator when the operator remains in the cab, and they do not control employee exposure during positioning or hole-tending activities. Therefore additional controls are necessary to protect employees from exposure to silica dust when performing activities outside of the cab. As described above, OSHA has determined that the use of water for dust suppression on the drill bit will effectively reduce exposures in situations where employees must also perform activities outside the cab.

Based on the information discussed above, Table 1 of this standard provides the option for employees to operate a vehicle-mounted rock or concrete drill from within an enclosed cab in conjunction with water applied at the drill bit for dust suppression; wherever cabs are specified in Table 1, however, the cabs must meet the requirements of paragraph (c)(2)(iii) of the standard for construction, as discussed above. OSHA has determined that the enclosed cab will adequately protect the operator while the addition of water at the drill bit will reduce exposures for employees in the area. The alternative control option included in Table 1, a dust collection system and water sprays at the discharge point (where the system ultimately dumps extracted dust), has also been proven to reduce exposures for both the operator at the drill controls and those employees in the vicinity. When the specified dust control methods are fully and properly implemented, TWA exposure levels are expected to remain below 50 μg/m³, and therefore, Table 1 does not require use of respiratory protection regardless of task duration for either control option. In the proposed rule, OSHA required the use of respiratory protection when the task lasted more than four hours. However, this was due to the inclusion of dowel drilling rigs within the entry for “Operating Vehicle-Mounted Drilling Rigs for Concrete.” As explained above, OSHA has determined that the exposures that result from dowel drilling rigs equipped with LEV systems, for which respirators are required regardless of task duration, are substantially higher than is the case for vehicle-mounted concrete drilling rigs.

IUOE commented that Table 1 would be clearer if it specified that employers who use open cabs during concrete drilling are not exempt from exposure assessment when employers implement the other controls listed for vehicle-mounted drilling rigs for concrete (Document ID 2262, Attachment 1, p. 48). OSHA considers the rule to be clear as written: If an employer chooses to operate vehicle-mounted drilling rigs for rock and concrete from within an enclosed cab, it must follow the requirements in paragraph (c)(2)(iii) of the standard for construction and apply water for dust suppression at the drill bit. Otherwise, the employer must follow the alternative shrouded dust-collection-system compliance method in Table 1 or the requirements in paragraph (d) of the standard for construction, which allow for alternate exposure control methods provided that employee exposures are assessed and exposures are kept at or below the PEL. Additionally, IUOE suggested that OSHA explicitly state on Table 1 that the employer does not have the option of respirator use as a means to control exposures during rock crushing or rock and concrete drilling if the employer chooses not to use enclosed cabs as an engineering control (Document ID 2262, Attachment 1, p. 48). OSHA notes that Table 1 of this final standard does not require that drilling rig operators work from enclosed cabs exclusively. Because employers can choose between the two control methods listed on Table 1, employees that use open cabs during drilling activities would not be required to conduct exposure assessments if they are using a dust collection system with a close capture hood or shroud around the drill bit and are ensuring that the material at the dust collector discharge point is being wetted. If that method is followed, OSHA, having found based on the exposure profile and record evidence that exposures will consistently be at or below the PEL, has not included a respirator requirement on Table 1; where respirators are not required to satisfy compliance obligations (as is the case here if Table 1 is fully and properly implemented), OSHA does not expect employers to require the use of respirators anyway. However employers that do not follow either control strategy specified in Table 1 must comply with paragraph (d) of the standard for construction, which could require respirator use if exposures are measured at or above the PEL when using feasible engineering and work practice controls.

IME stated that the final rule should allow for the use of equivalent, alternative control methods (Document 2213, Attachment 1, p. 2). Table 1 is intended to represent the most reliable control methods available for reducing exposures, based on the evidence contained in the record. Employers who wish to implement an alternative control method can do so, but those employers must comply with paragraph (d) of the standard for construction.

IUOE, among others, urged OSHA to explore additional options for exposure controls to protect operators working outside the cab when drilling. Both IUOE and Fann Contracting asserted that Table 1 does not address protection of operators who perform construction activities outside the cab with or without remote controls (Document ID 2262, Attachment 1, p. 45; 2116, Attachment 1, p. 5). In response, Table 1 of the final standard now includes a requirement to use water for dust suppression at the drill bit when the drill is being operated from an enclosed cab to minimize the exposure to other employees outside the cab.

OSHA's proposed Table 1 entry for rock drilling would have required that employees use respirators when working under the shroud. OSHA proposed this requirement based on a determination that employees' exposures would be high given their proximity to the point of dust generation. IME suggested that respirators should not be required at all times because there are circumstances where the time spent working under the shroud is extremely brief or infrequent and potential exposures will be minimal or negligible (Document ID 2213, p. 2). NUCA commented that this requirement creates hazards for employees working under the shroud (Document ID 2171, p. 10). In response to these comments and after reviewing the record, OSHA has not retained this respirator requirement in the final standard. The Agency finds that the record contains substantial evidence that when the dust controls required by Table 1 are fully and properly implemented, TWA exposures to silica are unlikely to exceed 50 μg/m³ (see Section 5.9 of Chapter IV of the FEA). In reviewing dust controls historically for drilling operations, NIOSH found that, when used properly, modern shroud designs now help achieve dust-control objectives more consistently than in the past (Document ID 0967, pp. 5-9). Furthermore, the record indicates that work under a shroud is periodic or intermittent and contains no evidence suggesting that this work is likely to result in silica exposures exceeding 50 μg/m³ as an 8-hour time-weighted average. Accordingly, Table 1, unlike in the proposed rule, does not include a respiratory protection requirement for rock and concrete drillers on open (or enclosed) vehicle-mounted rigs.

NSSGA recommended that OSHA clarify the requirement for wearing respirators while working under the shroud by replacing the term “shroud” with “engineered fugitive dust control method, e.g., a shroud, water spray, etc.” (Document ID 2327, Attachment 1, p. 21). Since the Agency has eliminated the requirement for using respirators under the shroud, NSSGA's suggestion is moot.

Jackhammers and handheld powered chipping tools. Hand-operated breaking and chipping power tools and equipment, commonly known as jackhammers, pavement breakers, breaker hammers, percussion or chipping hammers, and needle guns, are used in construction for fracturing materials, which often include silica (e.g., rock, concrete, asphalt, or masonry surfaces), by delivering rapid repetitive blows (see Section 5.5 of Chapter IV of the FEA). The hammers typically consist of a large compartment containing a motor, two attached handles to grip the tool, and a large socket out of which the drill or hammer-like metal breaking/chipping implement extends. A worker typically will aim the metal drill/hammer at a target surface while standing one to five feet away either directly overhead or at an angle, and press the point of contact into the surface to break, fracture, or chip away at it (Document ID 4073, Attachment 4a, Row 199).

In the proposed standard, this entry was titled “Using Jackhammers and Other Impact Drillers.” OSHA had a separate entry for “Rotary Hammers or Drills.” NIOSH commented on the potential for confusion with these titles, noting that a rotary hammer or drill is technically an impact driller (Document ID 2177, Attachment B, pp. 32-33). OSHA has revised the headings for the relevant Table 1 entries ((c)(1)(vii) and (x)). The revised heading for paragraph (c)(1)(x) removes the term “other impact drillers” and replaces it with “handheld powered chipping tools.” This change was made to clarify that this entry applies only to handheld tools that use an impact movement to chip or fracture the material being worked on. The heading for (c)(1)(vii) was revised from “Using Rotary Hammers of Drills” to “Handheld and Stand-Mounted Drills (Including Impact and Rotary Hammer Drills)” in order to clarify that all handheld drills, including impact drilling, are covered under that entry.

When using jackhammers and other handheld powered chipping tools at construction sites to fracture silica-containing material, paragraph (c)(1)(x) of the standard for construction requires the employer to operate the tools using either a water delivery system that supplies a continuous stream or spray of water at the point of impact, or a tool equipped with a commercially available shroud and dust collection system operated and maintained in accordance with manufacturer's instructions to minimize dust emissions. If the employer is operating a tool with the shroud and dust collection system, Table 1 requires that the dust collector (i.e., LEV) must provide at least the air flow recommended by the tool manufacturer, and have a filter with 99 percent or greater efficiency and a filter cleaning mechanism. These specified controls are essentially the same as those that were proposed, but the final standard makes clear that if a shroud and dust collector are used, it must be commercially available equipment. Unlike the use of a shrouded dust collection system, a water delivery system is not required to be commercially available but can be assembled and installed by the employer.

OSHA revised the respirator use requirements from the proposed rule by distinguishing between indoor and outdoor environments. Table 1 of the final standard for construction does not require respiratory protection if tools are used outdoors for four hours or less per shift. OSHA based this revision on record evidence showing that exposures can be maintained at or below 50 μg/m³ using either water sprays or LEV, provided work does not exceed the median task duration (231 minutes) reported by Flanagan et al. (Document ID 0677, p. 147; 0677, Attachment 2) (see Section 5.5 of Chapter IV of the FEA). If tools are used outdoors for more than four hours per shift, Table 1 requires the use of respiratory protection having a minimum APF of 10 to ensure that employees are protected from exposures above 50 µg/m³. If the tools are used indoors or in an enclosed area, Table 1 requires the use of respiratory protection having a minimum APF of 10 to ensure that employees are protected from exposures above 50 µg/m³, regardless of the amount of time the tools are operated during the work shift.

NUCA testified during the hearing that jackhammering is one of the construction activities most likely to expose employees to silica (Document ID 3583, Tr. 2255). OSHA's exposure profile for this task confirms this (Table IV.5.5-B in Section 5.5 of Chapter IV of the FEA); 73 of 98 TWA sample results (74 percent) were above 50 µg/m³ for workers using jackhammers and handheld power chipping tools operated without controls. For tools operated with water, 12 of 16 TWA sample results (75 percent) exceeded 50 µg/m³, but information on how the water was applied and whether it was sufficient was lacking. Various studies have demonstrated that properly used wet methods can substantially reduce respirable silica levels by 90 percent and higher (Document ID 0865, p. iv; 0867, p. 3; 0838, p. 1; 0914; 1267, pp. 493-494; 2177, Attachment D, p. 19). NIOSH studies that examined water spray devices designed to optimize dust suppression (directed mist or solid cone nozzle) have found that dust and/or silica exposures are reduced by 72 to 90 percent at a flow rate of approximately 350 milliliters per minute (ml/min) (Document ID 0865; 0867; 1267, pp. 493-494). Although not commercially available at this time, the record shows a number of examples of water suppression systems that have been developed and tested and are ready for commercial introduction or can be easily assembled from readily available hardware materials and instructions from the New Jersey Laborers' Health and Safety Fund (Document ID 0741; 0838; 0914; 2177, Attachment D, pp. 4-7; 3732, Attachment 3, p. 10).