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A combustible material is a solid or liquid than can be easily ignited and burned. OSHA, DOT, and other federal regulations, apply specific technical definitions to this term.
Prior to 2012, the U.S. Occupational Safety and Health Administration (OSHA) Standard 29 CFR 1910.106 (then titled "Flammable and Combustible Liquids" but now titled simply "Flammable Liquids" ) defined a combustible liquid as "any liquid having a flash point at or above 100 deg. F (37.8 deg. C), but below 200 deg. F (93.3 deg. C), except any mixture having components with flashpoints of 200 deg. F (93.3 deg. C), or higher, the total volume of which make up 99 percent or more of the total volume of the mixture." This definition has been dropped from the current version of 29 CFR 1910.106 which now addresses such materials as flammable in order to bring the standard into compliance with the Globally Harmonized System.
The previous version of 29 CFR 1910.106 is available for historical reference courtesy of the Internet Wayback Machine.
The National Fire Protection Association maintains NFPA 30 - Flammable and Combustible Liquids Code which defines a combustible liquid as "Any liquid that has a closed-cup flash point at or above 100 deg. F (37.8 deg. C), as determined by the test procedures and apparatus set forth in Section 4.4. Combustible liquids are classified according to Section 4.3." You can view (but not copy, save, or distribute) NFPA 30 on the NFPA web site if you want more details on the classes of combustible liquids.
Combustible solids are those capable of igniting and burning. Wood and paper are examples of such materials. See Additional Info below for more information.
Spontaneously combustible materials can undergo combustion and burn without the addition of heat or flame; arguably, the term "spontaneously flammable" is more appropriate. See the flammable solids entry for more info.
The US Department of Transportation defines the term readily combustible solids at 49 CFR 173.125 (Subpart D) as materials that:
These are closely related to the third broad class of materials listed under flammable solids.
Proper storage and use of combustible materials is absolutely critical in maintaining a safe work place. Avoid placing or using combustible materials near sources of heat or flame (direct sunlight, furnaces, pilot lights etc.). Use caution when disposing of combustible materials such as linseed oil-soaked rags (which can spontaneously combust). When dispensing combustible or flammable liquids, keep in mind that static electricity poses a very real threat; obey all standard bonding and grounding practices.
Two other tools that can be part of your flammable and combustible liquids safety plan are the use of safety cans and flammable storage cabinets. Safety cans have flash arrestors and gasketed lids to prevent solvent vapors from flashing back to the liquid if ignited. Flammable storage cabinets have insulating double walls and automatically closing doors so that stored solvents will not readily ignite in the event of a fire.
Also note that many common dusts such as flours, and grains can readily combust or even explode. See our dust entry for additional information.
See also: decomposition, flammable, flammable solid, flash point, temperature units.
Additional definitions from Google and OneLook.
Entry last updated: Tuesday, February 26, 2019. This page is copyright 2000-2019 by ILPI. Unauthorized duplication or posting on other web sites is expressly prohibited. Send suggestions, comments, and new entry desires (include the URL if applicable) to us by email.
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