Current through Register Vol. 55, No. 1, January 4, 2025
(a)Normal venting. The normal venting requirements for construction and use of tanks shall conform to the following:(1) Atmospheric tanks shall be adequately vented to prevent, as a result of filling or emptying and atmospheric temperature changes, development of pressure or vacuum sufficient to distort the roof of a cone roof tank or pressure exceeding the design pressure in the case of other atmospheric tanks.(2) Low pressure tanks shall be adequately vented to prevent development of pressure or vacuum, as a result of filling or emptying and atmospheric temperature changes, from exceeding the design pressure of the tank. Protection shall also be provided to prevent overpressure from any pump discharging into the tank where the pump discharge pressure may exceed the design pressure of the tank.(3) If a tank has more than one fill or withdrawal connection and simultaneous filling or withdrawal can be made, the vent size shall be based on the maximum anticipated simultaneous flow.(4) Unless the vent is designed to limit the internal pressure to 2 1/2 psig or less, the outlet of vents and vent drains shall be arranged to discharge in such a manner as to prevent localized overheating of any part of the tank in the event vapors from such vents are ignited.(5) Tanks storing class IA liquids shall be equipped with venting devices which shall be normally closed except when venting under pressure or vacuum conditions. Tanks storing class IB and class IC liquids shall be equipped with venting devices which shall be normally closed except when venting under pressure or vacuum conditions, or with approved flame arresters. This paragraph shall not apply to tanks with capacities of 3,000 barrels or less containing crude petroleum in crude producing areas and outside aboveground atmospheric tanks with capacities under 1,000 gallons containing other than class IA liquids which may have open vents.(6) Flame arresters or venting devices required in paragraph (5) may be omitted for class IB and class IC liquids if conditions are such that their use may, in case of obstruction, result in tank damage. Liquid properties justifying the omission of such devices include, but are not limited to, condensation, corrosiveness, crystallization, polymerization, freezing, or plugging. When any of these conditions exist, consideration may be given to heating, use of devices employing special materials of construction, the use of liquid seals, or inerting; for further information, see Standard No. 69-1978, Explosion Prevention Systems.(7) Normal vents shall be sized in accordance with either the American Petroleum Institute, Standard No. 2000-1982, Venting Atmospheric and Low-Pressure Storage Tanks, or other accepted standard, or shall be at least as large as the filling or withdrawal connection, whichever is larger, but shall not in any case be less than the requirements set forth in the following table: | Capacity of Tank (in gallons) | Diameter of Vent Fitting Iron Pipe Size (in inches) |
| 500 or less | 11/4 |
| 501 to 3,000 | 11/2 |
| 3,001 to 10,000 | 2 |
| 10,001 to 20,000 | 21/2 |
| 20,001 to 35,000 | 3 |
(8) Skid tanks and similar portable equipment shall be provided with a free opening vent of the following nominal pipe size, to relieve vacuum or pressure which may develop in normal operation or from fire exposure: | Tank Size | Vent Size (in inches) |
| 0- 275 | 11/2 |
| 276- 660 | 2 |
| 661- 900 | 21/2 |
| 901-1,000 | 3 |
(i) Vents shall be arranged to discharge in such a way as to prevent localized or overheating of, or flame impingement on, any part of the tank in the event vapors from such vents are ignited.(ii) Drums equipped with dispensing devices must be provided with pressure and vacuum relief vents with flame arresters. These vents are to be in addition to any vent which may be an integral part of the dispensing device being used in connection with the drum.(9) For tanks in excess of 1,100 gallons capacity, emergency relief venting for fire exposure shall be as provided under subsection (b).(b)Emergency relief venting for fire exposure. Every aboveground storage tank shall have some form of construction or device that will relieve excessive internal pressure caused by exposure fires, and such construction or device shall conform to the following: (1) In a vertical tank, the construction may take the form of a floating roof, lifter roof, a weak roof-to-shell seam, or other approved pressure relieving construction. The weak roof-to-shell seam shall be constructed to fail preferential to any other seam. Where entire dependence for such additional relief is placed upon some device other than a weak roof seam or joint, the total venting capacity of both normal and emergency vents shall be enough to prevent rupture of the shell or bottom of the tank if vertical, or of the shell or heads if horizontal. Such device may be a self-closing manhole cover, or one using long bolts that permit the cover to lift under internal pressure.(2) If emergency venting is not provided in accordance with paragraph (1), the total capacity of both normal and emergency venting devices shall be not less than that derived from the following table, except as provided in paragraphs (4) and (5): Wetted Area Versus Cubic Feet Free Air per Hourat 14.7 p.s.i.a. and 60°F.
| Square Feet | CFH | Square Feet | CFH | Square Feet | CFH |
| 20 | 21,100 | 160 | 168,000 | 900 | 493,000 |
| 30 | 31,600 | 180 | 190,000 | 1,000 | 524,000 |
| 40 | 42,100 | 200 | 211,000 | 1,200 | 557,000 |
| 50 | 52,700 | 250 | 239,000 | 1,400 | 587,000 |
| 60 | 63,200 | 300 | 265,000 | 1,600 | 614,000 |
| 70 | 73,700 | 350 | 288,000 | 1,800 | 639,000 |
| 80 | 84,200 | 400 | 312,000 | 2,000 | 662,000 |
| 90 | 94,800 | 500 | 354,000 | 2,400 | 704,000 |
| 100 | 105,000 | 600 | 392,000 | 2,800 | 742,000 |
| 120 | 126,000 | 700 | 428,000 | and over |
| 140 | 147,000 | 800 | 462,000 |
(3) The wetted area of the tank, when such term is used in paragraph (2), shall be calculated on the basis of 55% of the total exposed area of a sphere or spheroid, 75% of the total exposed area of a horizontal tank, and the first 30 feet abovegrade of the exposed shell area of a vertical tank. Approximate wetted areas for horizontal tanks may be found in the following table: | Tank Diameter (feet) | Approximate Wetted Areas for Horizontal Tanks |
| (Wetted Area Equals 75% Total Area) |
| 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| Tank Length (feet) | Approximate Wetted Area Of Tanks With Flat Heads |
| 3 | 32 |
| 4 | 39 | 55 |
| 5 | 46 | 65 | 88 |
| 6 | 53 | 74 | 100 | 128 |
| 7 | 60 | 84 | 112 | 142 | 173 |
| 8 | 67 | 93 | 124 | 156 | 190 | 226 |
| 9 | 74 | 102 | 136 | 170 | 206 | 245 | 286 |
| 10 | 82 | 112 | 147 | 184 | 223 | 264 | 308 | 353 |
| 11 | 88 | 121 | 159 | 198 | 239 | 283 | 329 | 377 | 428 |
| 12 | 95 | 131 | 171 | 213 | 256 | 301 | 350 | 400 | 454 | 509 |
| 13 | 102 | 140 | 183 | 227 | 272 | 320 | 371 | 424 | 480 | 537 |
| 14 | 109 | 150 | 194 | 241 | 289 | 339 | 393 | 447 | 506 | 565 |
| 15 | 116 | 159 | 206 | 255 | 305 | 358 | 414 | 471 | 532 | 594 |
| 16 | 123 | 169 | 218 | 269 | 322 | 377 | 435 | 495 | 558 | 622 |
| 17 | 130 | 178 | 230 | 283 | 338 | 395 | 456 | 518 | 584 | 650 |
| 18 | 137 | 188 | 242 | 298 | 355 | 414 | 477 | 542 | 610 | 678 |
| 19 | 197 | 253 | 312 | 371 | 433 | 499 | 565 | 636 | 707 |
| 20 | 206 | 265 | 326 | 388 | 452 | 520 | 589 | 662 | 735 |
| 21 | 216 | 277 | 340 | 404 | 471 | 541 | 612 | 688 | 763 |
| 22 | 225 | 289 | 354 | 421 | 490 | 562 | 636 | 714 | 792 |
| 23 | 235 | 300 | 368 | 437 | 508 | 584 | 659 | 740 | 820 |
| 24 | 244 | 312 | 383 | 454 | 527 | 605 | 683 | 765 | 848 |
| 25 | 324 | 397 | 470 | 546 | 626 | 706 | 791 | 876 |
| 26 | 336 | 411 | 487 | 565 | 647 | 730 | 817 | 905 |
| 27 | 347 | 425 | 503 | 584 | 668 | 754 | 843 | 933 |
| 28 | 359 | 440 | 520 | 603 | 690 | 777 | 869 | 961 |
| 29 | 371 | 454 | 536 | 621 | 711 | 801 | 895 | 989 |
| 30 | 383 | 468 | 553 | 640 | 732 | 824 | 921 | 1018 |
| 31 | 395 | 482 | 569 | 659 | 753 | 848 | 947 | 1046 |
| 32 | 496 | 586 | 678 | 775 | 871 | 973 | 1074 |
| 33 | 510 | 602 | 697 | 796 | 895 | 999 | 1103 |
| 34 | 524 | 619 | 715 | 817 | 918 | 1025 | 1131 |
| 35 | 539 | 635 | 734 | 838 | 942 | 1051 | 1159 |
| 36 | 553 | 652 | 753 | 860 | 966 | 1077 | 1187 |
| 37 | 567 | 668 | 772 | 881 | 989 | 1103 | 1216 |
| 38 | 685 | 791 | 902 | 1013 | 1129 | 1244 |
| 39 | 701 | 810 | 923 | 1036 | 1155 | 1272 |
| 40 | 718 | 828 | 944 | 1060 | 1181 | 1301 |
| 41 | 734 | 847 | 966 | 1083 | 1207 | 1329 |
| 42 | 751 | 866 | 987 | 1107 | 1233 | 1357 |
| 43 | 767 | 885 | 1008 | 1130 | 1259 | 1385 |
| 44 | 904 | 1029 | 1154 | 1284 | 1414 |
| 45 | 923 | 1051 | 1178 | 1310 | 1442 |
| 46 | 941 | 1072 | 1201 | 1336 | 1470 |
| 47 | 960 | 1093 | 1225 | 1362 | 1498 |
| 48 | 979 | 1114 | 1248 | 1388 | 1527 |
| 49 | 998 | 1135 | 1272 | 1414 | 1555 |
| 50 | 1157 | 1295 | 1440 | 1583 |
| 51 | 1178 | 1319 | 1466 | 1612 |
| 52 | 1199 | 1342 | 1492 | 1640 |
| 53 | 1220 | 1366 | 1518 | 1668 |
| 54 | 1246 | 1389 | 1544 | 1696 |
| 55 | 1263 | 1413 | 1570 | 1725 |
| 56 | 1437 | 1593 | 1753 |
| 57 | 1460 | 1622 | 1781 |
| 58 | 1484 | 1648 | 1809 |
| 59 | 1507 | 1674 | 1839 |
| 60 | 1531 | 1700 | 1866 |
| 61 | 1726 | 1894 |
| 62 | 1752 | 1923 |
| 63 | 1778 | 1951 |
| 64 | 1803 | 1979 |
| 65 | 1829 | 2007 |
| 66 | 1855 | 2036 |
| 67 | 2064 |
| 68 | 2092 |
| 69 | 2120 |
| 70 | 2149 |
| 71 | 2177 |
| 72 | 2205 |
(4) The total emergency relief venting capacity for any specific liquid may be determined by the following formula: Cubic feet of free air per hour =
Click to view image
V = cubic feet of free air per hour from the table of paragraph (2).
L = latent heat of vaporization of specific liquid in Btu per pound.
M = molecular weight of specific liquid.
(5) The required air flow rate, as set forth in paragraphs (2) and (3), may be multiplied by the following appropriate factor set forth when protection is provided as indicated; only one factor may be used for any one tank:(i) Factor .5 for drainage in accordance with the drainage provisions of § 14a.6 (relating to dikes, walls and drainage) for tanks over 200 square feet of wetted area.(ii) Factor .3 for approved water spray.(iii) Factor .3 for approved insulation.(iv) Factor .15 for approved water spray with approved insulation.(6) Venting devices shall be certified by the manufacturer as to actual rated flow capacity in cubic feet of free air per hour, specifying the pressure in psig at which the flow capacity was determined. The stamping of such information on the devices by the manufacturer shall be acceptable as certification for this purpose.(7) The outlet of all vents and vent drains on tanks equipped with emergency venting to permit pressures exceeding 21/2 psig shall be arranged to discharge in such a way as to prevent localized overheating of any part of the tank in the event vapors from such vents are ignited.(c)Vent piping for aboveground tanks. Vent piping for aboveground tanks shall conform to the following: (1) Vent piping shall be constructed under §§ 14a.51-14a.58 (relating to piping, valves and fittings). Where vent piping for tanks storing class I liquids is adjacent to buildings or public ways, the vent piping shall be located so that the vapors are released at a safe point away from buildings and not less than 12 feet above the adjacent ground level. In order to aid their dispersion, vapors shall be discharged upward so that flammable vapors will not be trapped by eaves or other obstructions and shall be at least 5 feet from building openings. Vent outlets for all classes of flammable and combustible liquids shall be above normal snow accumulation on top of tanks.(2) When tank vent piping is manifolded, pipe sizes shall be able to discharge, within the pressure limitations of the system, the vapors they may be required to handle when manifolded tanks are subject to the same fire exposure. The manifolding of tank vent piping shall be avoided except if required for special purposes such as vapor recovery, vapor conservation or air pollution control.(3) Vent piping for tanks storing class I liquids shall not be manifolded with vent piping for tanks storing class II or class III liquids unless positive means are provided to prevent the vapors from class I liquids from entering tanks storing class II or class III liquids to prevent contamination and possible change in classification of the less volatile liquid.The provisions of this § 13.8 amended through June 22, 1984, effective 6/18/1984, 14 Pa.B. 2131; transferred from 37 Pa. Code and renumbered as 34 Pa. Code § 14a.8, February 28, 2014, effective 3/1/2014, 44 Pa.B. 1233.The provisions of this § 13.8 issued under act of April 27, 1927 (P. L. 450, No. 291) (35 P. S. §§ 1181-1194); transferred from 37 Pa. Code and renumbered as 34 Pa. Code § 14a.8 under section 4(b) of the Combustible and Flammable Liquids Act (35 P. S. § 1244(b)).
This section cited in 34 Pa. Code § 14a.25 (relating to vents for underground tanks); 34 Pa. Code § 14a.111 (relating to storage and handling); 34 Pa. Code § 14a.141 (relating to scope and application); 34 Pa. Code § 14a.151 (relating to scope and application); and 34 Pa. Code § 14a.161 (relating to general provisions).