Customer Support Ruling

Mailing Flammable and Combustible Liquids That Do Not Sustain Combustion

UPDATED July 2014

PS-331 (601.8)

This Customer Support Ruling (CSR) describes the conditions under which certain flammable and combustible liquids that do not sustain combustion are mailable when sent to domestic, non-APO/FPO/DPO, addresses.

The Domestic Mail Manual (DMM) and Publication 52, Hazardous, Restricted and Perishable Mail, define flammable or combustible liquids based solely on their flash point.  Department of Transportation (DOT) and International Air Transport Association (IATA) regulations allow shipping of these materials when they do not sustain combustion as described below.

DOT regulations are found in Title 49 of the Code of Federal Regulations (CFR).  49 CFR §173.120(a) defines a flammable liquid as “a liquid having a flash point of not more than 60°C (140°F).  DOT lists several exceptions, among them “(3) Any liquid with a flash point greater than 35°C (95°F) that does not sustain combustion according to ASTM D 4206…or the procedure in Appendix H of this part” and “(5) Any liquid with a flash point greater than 35°F (95°C) which is in a water-miscible solution with a water content of more than 90 percent by mass.” 49 CFR §173.120(b)(1) defines a combustible liquid as “any liquid that does not meet the definition of any other hazard class specified in this subchapter and has a flash point above 60°C (140°F) and below 93°C (200°F).” §173.120(b)(3) further states that a “combustible liquid that does not sustain combustion is not subject to the requirements of this subchapter as a combustible liquid.”

IATA Dangerous Goods Regulations § provides that liquids “with a flash point exceeding 35°C (95°F) which do not sustain combustion need not be considered as flammable liquids for the purposes of these Regulations, if…they have passed a suitable test for combustibility…or they are miscible solutions with a water content of more than 90% by weight.”

Liquids that do not sustain combustion may be mailed when the mailer presents a Material Safety Data Sheet (MSDS) that indicates its composition as a water-miscible solution of more than 90% water and the solution is unable to sustain combustion as indicated by standardized test ASTM D 4206.  These factors preclude the liquid’s classification as a flammable liquid under both DOT and IATA rules and define it as not subject to DOT requirements as a combustible liquid.  After consideration of all the factors, the liquid is properly classified as a non-regulated material by DOT standards and is not subject to the restrictions for flammable or combustible liquids when it is mailed to domestic, non-APO/FPO/DPO, addresses.  The material is still subject to the general packaging requirements for liquids in DMM 601.1 through 601.8 and in Publication 52.

Sharon Daniel


Mailing Standards

Headquarters, US Postal Service

Washington DC  20260-3436