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Publication 52 - Hazardous, Restricted, and Perishable Mail >
Appendix C > USPS Packaging Instruction 3A
A flammable liquid having a flashpoint greater than 20° F (–7° C) but less than 100° F (38° C) is mailable in domestic mail via surface transportation, if the liquid can qualify as an ORM–D material and all applicable requirements in 343 are met.
Flammable liquids having a flashpoint of 20° or less are not mailable.
Flammable liquids mailed under DOT-SP 9275 must be prepared and marked as specified in 343.27 or DMM 601.10.13.5.
Separate packaging requirements apply depending on the flashpoint of the flammable liquid.