The international pictogram for flammable chemicals.
Flammable placard

A flammable liquid is a liquid which can be easily ignited in air at ambient temperatures, i.e. it has a flash point at or below nominal threshold temperatures defined by a number of national and international standards organisations.

The Occupational Safety and Health Administration (OSHA) of the United States Department of Labor defines a liquid as flammable if it has a flash point at or below 93 °C/199.4 °F.[1] Prior to bringing regulations in line with the United Nations Globally Harmonized System of Classification and Labeling of Chemicals (GHS) in 2012, OSHA considered flammable liquids to be those with a flash point below 37.8 °C/100 °F. Those with flash points above 37.8 °C/100 °F and below 93.3 °C/200 °F were classified as combustible liquids.[2][3] Studies show that the actual measure of a liquid's flammability, its flash point, is dependent on the local air pressure, meaning that at higher altitudes where the air pressure is lower, the flash point is also lower.[4]


Both OSHA and GHS further divide flammable liquids into 4 categories:

These categorizations are dependent upon a set altitude and atmospheric pressure, as both boiling point and flash point change with changes in pressure.[4]


Both GHS and OSHA require the labeling of flammable liquids, on containers and safety data sheets, as follows:[3][5]

Category I Category II Category III Category IV
Symbol Flame Flame Flame none
Signal Word Danger Danger Warning Warning
Hazard Statement Extremely flammable liquid and vapour Highly flammable liquid and vapor Flammable liquid and vapour Combustible liquid

See also


  1. ^ a b c d e "1910.106 - Flammable liquids. | Occupational Safety and Health Administration". Retrieved 2019-03-06.
  2. ^ "But It Wasn't Flammable Before! GHS Changed the Meaning of 'Flammable Liquids'". EHS Daily Advisor. 2015-09-23. Retrieved 2019-03-08.
  3. ^ a b "HCS/HazCom 2012 Final Rule & Appendices | Occupational Safety and Health Administration". Retrieved 2019-03-08.
  4. ^ a b Ding, Chao; Yao, Wei; Tang, Yanfei; Rong, Jianzhong; Zhou, Dechuang; Wang, Jian (March 2014). "Experimental study of the flash point of flammable liquids under different altitudes in Tibet plateau". Fire and Materials. 38 (2): 241–246. doi:10.1002/fam.2177. S2CID 137412493.
  5. ^ a b c d e Globally harmonized system of classification and labelling of chemicals (GHS). United Nations. Economic Commission for Europe. Secretariat. (Seventh revised ed.). New York. 2017. ISBN 9789211171310. OCLC 994197992.((cite book)): CS1 maint: location missing publisher (link) CS1 maint: others (link)