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Publication 52 - Hazardous, Restricted, and Perishable Mail >
Appendix C > USPS Packaging Instruction 3B
A combustible liquid having a flashpoint of 141° F (60.5° C) but no more than 200° F (93° C) is mailable if it can qualify as a consumer commodity or ORM-D material and meet all applicable requirements in 343. A flammable liquid having a flashpoint of at least 100° F (38° C) but not more than 141° F (60.5° C) may be reclassed as a combustible liquid within the limits of 49 CFR 173.120(b).
Separate packaging requirements apply, depending on the flashpoint of the combustible liquid.