49 C.F.R. § 173.2a
(a) Classification of a material having more than one hazard. Except as provided in paragraph (c) of this section, a material not specifically listed in the § 172.101 Table or assigned to an entry of articles containing hazardous materials (UN3537 to UN3548) that meets the definition of more than one hazard class or division as defined in this part, shall be classed according to the highest applicable hazard class of the following hazard classes, which are listed in descending order of hazard:
(b) Precedence of hazard table for Classes 3 and 8 and Divisions 4.1, 4.2, 4.3, 5.1 and 6.1. The following table ranks those materials that meet the definition of Classes 3 and 8 and Divisions 4.1, 4.2, 4.3, 5.1 and 6.1:
| 4.2 | 4.3 | 5.1 I 1 | 5.1 II 1 | 5.1 III 1 | 6.1, I dermal | 6.1, I oral | 6.1 II | 6.1 III | 8, I liquid | 8, I solid | 8, II liquid | 8, II solid | 8, III liquid | 8, III solid | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 3 I2 | 4.3 | 3 | 3 | 3 | 3 | 3 | (3) | 3 | (3) | 3 | (3) | ||||
| 3 II2 | 4.3 | 3 | 3 | 3 | 3 | 8 | (3) | 3 | (3) | 3 | (3) | ||||
| 3 III2 | 4.3 | 6.1 | 6.1 | 6.1 | 34 | 8 | (3) | 8 | (3) | 3 | (3) | ||||
| 4.1 II 2 | 4.2 | 4.3 | 5.1 | 4.1 | 4.1 | 6.1 | 6.1 | 4.1 | 4.1 | (3) | 8 | (3) | 4.1 | (3) | 4.1 |
| 4.1 III 2 | 4.2 | 4.3 | 5.1 | 4.1 | 4.1 | 6.1 | 6.1 | 6.1 | 4.1 | (3) | 8 | (3) | 8 | (3) | 4.1 |
| 4.2 II | 4.3 | 5.1 | 4.2 | 4.2 | 6.1 | 6.1 | 4.2 | 4.2 | 8 | 8 | 4.2 | 4.2 | 4.2 | 4.2 | |
| 4.2 III | 4.3 | 5.1 | 5.1 | 4.2 | 6.1 | 6.1 | 6.1 | 4.2 | 8 | 8 | 8 | 8 | 4.2 | 4.2 | |
| 4.3 I | 5.1 | 4.3 | 4.3 | 6.1 | 4.3 | 4.3 | 4.3 | 4.3 | 4.3 | 4.3 | 4.3 | 4.3 | 4.3 | ||
| 4.3 II | 5.1 | 4.3 | 4.3 | 6.1 | 4.3 | 4.3 | 4.3 | 8 | 8 | 4.3 | 4.3 | 4.3 | 4.3 | ||
| 4.3 III | 5.1 | 5.1 | 4.3 | 6.1 | 6.1 | 6.1 | 4.3 | 8 | 8 | 8 | 8 | 4.3 | 4.3 | ||
| 5.1 I 1 | 5.1 | 5.1 | 5.1 | 5.1 | 5.1 | 5.1 | 5.1 | 5.1 | 5.1 | 5.1 | |||||
| 5.1 II 1 | 6.1 | 5.1 | 5.1 | 5.1 | 8 | 8 | 5.1 | 5.1 | 5.1 | 5.1 | |||||
| 5.1 III 1 | 6.1 | 6.1 | 6.1 | 5.1 | 8 | 8 | 8 | 8 | 5.1 | 5.1 | |||||
| 6.1 I, Dermal | 8 | 6.1 | 6.1 | 6.1 | 6.1 | 6.1 | |||||||||
| 6.1 I, Oral | 8 | 6.1 | 6.1 | 6.1 | 6.1 | 6.1 | |||||||||
| 6.1 II, Inhalation | 8 | 6.1 | 6.1 | 6.1 | 6.1 | 6.1 | |||||||||
| 6.1 II, Dermal | 8 | 6.1 | 8 | 6.1 | 6.1 | 6.1 | |||||||||
| 6.1 II, Oral | 8 | 8 | 8 | 6.1 | 6.1 | 6.1 | |||||||||
| 6.1 III | 8 | 8 | 8 | 8 | 8 | 8 | |||||||||
| 1 See § 173.127. | |||||||||||||||
| 2 Materials of Division 4.1 other than self-reactive substances and solid desensitized explosives, and materials of Class 3 other than liquid desensitized explosives. | |||||||||||||||
| 3 Denotes an impossible combination. | |||||||||||||||
| 4 For pesticides only, where a material has the hazards of Class 3, Packing Group III, and Division 6.1, Packing Group III, the primary hazard is Division 6.1, Packing Group III. |
(c) The following materials are not subject to the provisions of paragraph (a) of this section because of their unique properties:
Note 1: The most stringent packing group assigned to a hazard of the material takes precedence over other packing groups; for example, a material meeting Class 3 PG II and Division 6.1 PG I (oral toxicity) is classified as Class 3 PG I.
Note 2: A material which meets the definition of Class 8 and has an inhalation toxicity by dusts and mists which meets criteria for Packing Group I specified in § 173.133(a)(1) must be classed as Division 6.1 if the oral or dermal toxicity meets criteria for Packing Group I or II. If the oral or dermal toxicity meets criteria for Packing Group III or less, the material must be classed as Class 8.
[Amdt. 173-224, 55 FR 52606, Dec. 21, 1990, as amended at 56 FR 66264, Dec. 20, 1991; Amdt. 173-241, 59 FR 67490, Dec. 29, 1994; Amdt. 173-247, 60 FR 48787, Sept. 20, 1995; Amdt. 173-244, 60 FR 50307, Sept. 28, 1995; 64 FR 10776, Mar. 5, 1999; 66 FR 33426, June 21, 2001; 66 FR 45182, 45379, Aug. 28, 2001; 68 FR 45032, July 31, 2003; 80 FR 1151, Jan. 8, 2015; 85 FR 27878, May 11, 2020]