Publication 52, Hazardous, Restricted, and Perishable Mail > Appendix C > USPS Packaging Instruction 3C
A cigarette lighter equipped with an ignition element and containing fuel is classified as a Class 3 flammable liquid. A cigarette lighter containing a flammable gas is classed as a Division 2.1 flammable gas. A cigarette lighter that contains either flammable liquid or flammable gas is permitted in domestic mail via surface transportation only with prior written approval, provided all applicable requirements of 343.25 are met.
Note: A legible photocopy of the PCSC manager‘s approval letter must accompany the mailing at the time of deposit.