Postal Explorer > Publication 52 - Hazardous, Restricted, and Perishable Mail > 3 Hazardous Materials > 33 Hazard Classes

33 Hazard Classes

331 Nine Classes

Every hazardous material is assigned to one of nine hazard classes as defined in 49 CFR 172.101 and 173. The nine hazard classes are as follows:

a. Class 1: Explosives.

b. Class 2: Gases.

c. Class 3: Flammable and Combustible Liquids.

d. Class 4: Flammable Solids.

e. Class 5: Oxidizing Substances, Organic Peroxides.

f. Class 6: Toxic Substances and Infectious Substances.

g. Class 7: Radioactive Materials.

h. Class 8: Corrosives.

i. Class 9: Miscellaneous Hazardous Materials.

Some of the nine classes are further separated into divisions based on their physical or chemical properties, as shown in Exhibit 331.

Exhibit 331

DOT Hazard Classes and Postal Mailability

332 Limited Quantity

A limited quantity of a hazardous material is the maximum amount of a specific hazardous material exempted from DOT labeling or packaging requirements in 49 CFR. To be eligible to be shipped under DOT's limited quantity provision, a hazardous material must be authorized an exemption in column 8A of the Hazardous Materials Table in 49 CFR 172.101. Not every hazardous material is eligible to be shipped as a limited quantity.

Under Postal Service standards, a material meeting the eligibility criteria for shipment as a limited quantity is mailable only if it can be further reclassed as an ORM-D material (see 333). Not every hazardous material permitted to be shipped as a limited quantity can qualify as an ORM-D material.

Except as specifically permitted in DMM 601.10 and this publication, materials that cannot be reclassed as an ORM-D material are not eligible for mailing.

333 ORM-D Materials

Some of the hazardous materials that qualify under the limited quantity provision are permitted a further exemption in 49 CFR 172.101 (column 8A) to be reclassified as an ORM-D material under 49 CFR 173.144 and renamed with the proper shipping name "Consumer Commodity," which is defined in Appendix D. A mailable ORM-D material is additionally subject to the mailability and quantity limits in DMM 601.10 and this publication, as applicable.

Most mailable hazardous materials fall within the ORM-D category. ORM-D materials present the lowest level of risk during transportation. The ORM-D category is unique to the United States. Its use is prohibited with international shipments of hazardous materials.

It is the responsibility of the mailer to know the correct hazard class of a hazardous material before mailing (see 323).

When assistance is needed to determine eligibility for mailing, the mailer may request a ruling from the PCSC (see 215.2 and DMM 601.10.6).

334 Small Quantity

334.1 Definition

A small quantity is the maximum amount of a specific hazardous material that is not subject to any DOT requirements (e.g., packaging, marking, labeling) other than those in 49 CFR 173.4. Not every hazardous material is eligible to be shipped as a small quantity. Additionally, for Postal Service purposes, Class 7 materials are not permitted to be sent as a small quantity.

The DOT small quantity provision, like the DOT ORM-D category, is unique to the United States. Its use is prohibited with international shipments of hazardous materials and cannot be used in international mail.

334.2 Mailability

Hazardous materials in Class 3, Division 4.1, Division 4.2 (Packing Groups II and III only), Division 4.3 (Packing Groups II and III only), Division 5.1, Division 5.2, Division 6.1 (Packing Groups II and III only), Class 8, and Class 9 are eligible to be sent in the domestic mail under the small quantity provision only when each primary receptacle is limited to the following quantity, as applicable:

a. 30 ml (1 oz) or less for liquids other than Division 6.1 (Packing Group I) materials.

b. 30 g (1 oz) or less for solids other than Division 6.1 (Packing Group I) materials.

c. 1 g (0.04 oz) or less for Division 6.1 (Packing Group I) materials.

334.3 Packaging and Marking

Hazardous materials eligible to be shipped under the small quantity provision permitted in 49 CFR and 334.2 must be prepared following Packaging Instruction 10A in Appendix C. Each mailpiece that qualifies to be sent under the small quantity provision must be clearly marked on the address side with the following words: "This package conforms to 49 CFR 173.4."

335 Packaging Requirements for Hazardous Materials

335.1 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.

335.2 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.

336 Nonmailable Materials Found in the Mailstream

When any mailpiece containing a nonmailable hazardous material is found in the mailstream, the procedures in POM 139.117 must be followed if the materials present an immediate threat to persons or property. When there is not immediate threat to persons or property, follow the procedures in POM 139.118 and Management Instruction (MI) DM-601-05-1, Hazardous Materials Acceptance and Handling.