The carriage of U.S. Mail by the Postal Service is regulated by Title 39 Code of Federal Regulations (39 CFR) and is not subject to the federal regulations in 49 CFR that apply to commercial carriers. Unlike commercial carriers, the Postal Service is subject to the restrictions in Title 18 United States
Code 1716 (18 U.S.C. 1716), which prohibits from mailing all matter that is outwardly or of its own force dangerous to life, health, or property (see 211). As a result, most hazardous materials are nonmailable.
Accordingly, for legal and safety reasons, although mailing standards for hazardous materials in this publication closely adhere to 49 CFR, the standards also include many additional limitations and prohibitions and often are more restrictive than the requirements of other commercial carriers. For example, 49 CFR allows commercial shippers to send flammable materials by air, but the Postal Service prohibits the mailing of all flammable materials via air transportation.
Postal Service standards generally limit the mailing of hazardous materials to Limited Quantity surface materials or Limited Quantity air materials as defined in 332 through 336, that meet USPS quantity limitations and packaging requirements. This allowance is limited to the following:
- Toy propellant devices and safety fuses in Division 1.4S, as permitted in 341.22.
- Toxic substances in Division 6.1 that have an LD50 for oral toxicity of greater than 5 mg/kg but less than 50 mg/kg, as permitted in 346.231.
- Infectious substances (etiologic agents) and medical wastes in
Division 6.2, as permitted in 346.23.
- Radioactive materials in Class 7 that fall within the specific activity limits permitted in 347 and Exhibit 347.22.
- Lithium batteries, dry ice, and magnetized materials, as permitted in 349.