USPS Homepage

337 Packaging Requirements for Hazardous Materials

337.1 DOT Packing Groups

Hazardous materials in Classes 1, 3-6, and 8-9 are assigned to a DOT packing group based on the degree of danger presented by the material during transport. The packing group assigned to a hazardous material is listed in column 5 of the Hazardous Material Table in 49 CFR 172.101 and in column (d) of Appendix A. Packing Group I indicates a great danger, Packing Group II a medium danger, and Packing Group III a minor danger.

337.2 Postal Service Packaging Instructions

For mailing purposes, the packaging of a mailable hazardous material must follow the appropriate Packaging Instruction in Appendix C. The correct Packaging Instruction to use for a specific hazardous material can be determined using Appendix A.

Mailers may not package or combine hazardous materials assigned to different hazard classes within a single mailpiece unless permitted by Postal Service standard.