| Publication 52 - Hazardous, Restricted, and Perishable Mail > Appendix C > USPS Packaging Instruction 6F Forensic material containing a biological material, such as tissue, body fluid, excreta, or secreta, and sent on behalf of a federal, state, local, or Indian tribal government agency must be packaged under 346.325 when it is not known or suspected to contain a Category A or Category B infectious substance. Forensic material known or suspected to contain a Category A infectious substance is not mailable. Forensic material known or suspected to contain a Category B infectious substance as identified in 346.321 is mailable via air transportation, when triple-packaged in a primary receptacle, secondary packaging, and a rigid outer packaging. Labels and markings must be placed on the address side of the mailpiece unless specified differently in 221.1 and 325.1. Substances identified in IMM 135.11b must be sent only by authorized laboratories to their foreign counterparts in those countries that have indicated a willingness to accept them. Note: Countries distinguish between infectious and noninfectious (nonregulated) biological substances and may prohibit one or the other or both. Refer to “Prohibitions” in the Individual Country Listings. | |