Publication 52 - Hazardous, Restricted, and Perishable Mail > Appendix C > USPS Packaging Instruction 1B
Safety fuses consist of a core of black powder overspun with yarns, waterproofing compounds, and/or tapes. A safety fuse assigned identification number UN0105 and classed as a Division 1.4S explosive may be mailed only as permitted in 341.22b and when properly packaged as follows.
Prior written permission must be obtained from:
DIRECTOR, Product Classification USPS Headquarters 475 L’Enfant Plaza SW, Room 4446Washington, DC 20260
Note: Full responsibility rests with the mailer to comply with Bureau of Alcohol, Tobacco, Firearms, and Explosives (BATFE) regulations before mailing. At the time of mailing, the mailer must present to the Postal Service acceptance clerk a legible photocopy of the Product Classification director’s approval letter.