Section 173.125 - Class 4-Assignment of packing group(a) The packing group of a Class 4 material is assigned in column (5) of the § 172.101 Table. When the § 172.101 Table provides more than one packing group for a hazardous material, the packing group shall be determined on the basis of test results following test methods given in the UN Manual of Tests and Criteria (IBR, see § 171.7 of this subchapter) and by applying the appropriate criteria given in this section.(b) Packing group criteria for readily combustible materials of Division 4.1 are as follows:(1) Powdered, granular or pasty materials must be classified in Division 4.1 when the time of burning of one or more of the test runs, in accordance with the UN Manual of Tests and Criteria, is less than 45 seconds or the rate of burning is more than 2.2 mm/s. Powders of metals or metal alloys must be classified in Division 4.1 when they can be ignited and the reaction spreads over the whole length of the sample in 10 minutes or less.(2) Packing group criteria for readily combustible materials of Division 4.1 are assigned as follows:(i) For readily combustible solids (other than metal powders), Packing Group II if the burning time is less than 45 seconds and the flame passes the wetted zone. Packing Group II must be assigned to powders of metal or metal alloys if the zone of reaction spreads over the whole length of the sample in 5 minutes or less.(ii) For readily combustible solids (other than metal powders), Packing Group III must be assigned if the burning rate time is less than 45 seconds and the wetted zone stops the flame propagation for at least 4 minutes. Packing Group III must be assigned to metal powders if the reaction spreads over the whole length of the sample in more than 5 minutes but not more than 10 minutes.(c) Packing group criteria for Division 4.2 materials is as follows:(1) Pyrophoric liquids and solids of Division 4.2 are assigned to Packing Group I.(2) A self-heating material is assigned to- (i) Packing Group II, if the material gives a positive test result when tested with a 25 mm cube size sample at 140 °C; or(ii) Packing Group III, if- (A) A positive test result is obtained in a test using a 100 mm sample cube at 140 °C and a negative test result is obtained in a test using a 25 mm sample cube at 140 °C and the substance is transported in packagings with a volume of more than 3 cubic meters; or(B) A positive test result is obtained in a test using a 100 mm sample cube at 120 °C and a negative result is obtained in a test using a 25 mm sample cube at 140 °C and the substance is transported in packagings with a volume of more than 450 L; or(C) A positive result is obtained in a test using a 100 mm sample cube at 100 °C and a negative result is obtained in a test using a 25 mm sample cube at 140 °C and the substance is transported in packagings with a volume of less than 450 L.(d) A Division 4.3 dangerous when wet material is assigned to- (1) Packing Group I, if the material reacts vigorously with water at ambient temperatures and demonstrates a tendency for the gas produced to ignite spontaneously, or which reacts readily with water at ambient temperatures such that the rate of evolution of flammable gases is equal or greater than 10 L per kilogram of material over any one minute;(2) Packing Group II, if the material reacts readily with water at ambient temperatures such that the maximum rate of evolution of flammable gases is equal to or greater than 20 L per kilogram of material per hour, and which does not meet the criteria for Packing Group I; or(3) Packing Group III, if the material reacts slowly with water at ambient temperatures such that the maximum rate of evolution of flammable gases is greater than 1 L per kilogram of material per hour, and which does not meet the criteria for Packing Group I or II.Amdt. 173-224, 55 FR 52634 Dec. 21, 1990, as amended by Amdt. 173-255, 61 FR 50625, Sept. 26, 1996; Amdt. 173-261, 62 FR 24731, May 6, 1997; 62 FR 51560, Oct. 1, 1997; 66 FR 45380 , Aug. 28, 2001; 68 FR 75744 , Dec. 31, 2003