Flammable liquid explained

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]

Categorization

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

• Category I flammable liquids are those with boiling points ≤ 35 °C/95 °F and flash points < 23 °C/73 °F^{[5] [6]}
• Category II flammable liquids are those with boiling points > 35 °C/95 °F and flash points < 23 °C/73 °F
• Category III flammable liquids are those with flash points > 23 °C/73 °F and ≤ 60 °C/140 °F
• Category IV flammable liquids are those with flash points > 60 °C/140 °F and ≤ 93 °C/199.4 °F

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

Labeling

Both GHS and OSHA require the labeling of flammable liquids, on containers and safety data sheets, as follows:^[7]

	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

• Fire prevention
• Fire protection
• Flammability
• List of R-phrases

Notes and References

1. Web site: 1910.106 - Flammable liquids. Occupational Safety and Health Administration. www.osha.gov. 2019-03-06.
2. Web site: But It Wasn't Flammable Before! GHS Changed the Meaning of 'Flammable Liquids'. 2015-09-23. EHS Daily Advisor. en-US. 2019-03-08.
3. Web site: HCS/HazCom 2012 Final Rule & Appendices Occupational Safety and Health Administration. www.osha.gov. 2019-03-08.
4. Ding . Chao . Yao . Wei . Tang . Yanfei . Rong . Jianzhong . Zhou . Dechuang . Wang . Jian . Experimental study of the flash point of flammable liquids under different altitudes in Tibet plateau . Fire and Materials . March 2014 . 38 . 2 . 241–246 . 10.1002/fam.2177 . 137412493 .
5. Web site: 1910.106 - Flammable liquids. Occupational Safety and Health Administration. www.osha.gov. 2019-03-06.
6. Book: Globally harmonized system of classification and labelling of chemicals (GHS). United Nations. Economic Commission for Europe. Secretariat.. 2017 . 9789211171310. Seventh revised . New York. 994197992.
7. Book: Globally harmonized system of classification and labelling of chemicals (GHS). United Nations. Economic Commission for Europe. Secretariat.. 2017 . 9789211171310. Seventh revised . New York. 994197992.