In fire classes, a Class B fire is a fire in flammable liquids or flammable gases, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, or alcohols.[1] For example, propane, natural gas, gasoline and kerosene fires are types of Class B fires.[2][3] The use of lighter fluid on a charcoal grill, for example, creates a Class B fire.[4] Some plastics are also Class B fire materials.[3]
Class B fires are distinguished from the other fire classes: Class A fires ("ordinary combustibles" such as wood, paper, or rubber); Class C fires (in which the burning material is energized electrical equipment) and Class D fires (in which the burning material is combustible metals).[3] The less-commonly-used Class F (known in the United States as Class K) refers to fires involving cooking oil or fat; these materials are technically part of Class B.[5]
Fires are classified by the proper extinguishing agent. While water is used on Class A fires, using water on a Class B fire (e.g., a grease fire) is extremely dangerous.[3][5] This is because Class B fires typically have a fuel with a lower density than water (causing it to rise) and the burning fluid is hotter than the boiling point of water (212 °F or 100 °C). The resulting sudden rising of a column of flames together with droplets of boiling fuel and water is generally known as a slopover.[6][7] For example, when water is placed on grease, it creates steam which expands rapidly and splatters burning droplets in a phenomenon causing burns and spreading the fire.[3] Because of this, Class A fire extinguishers use water, while Class B fire extinguishers use dry chemicals (foam or powder),[5] such as aqueous film-forming foam, multi-purpose dry chemicals such as ammonium phosphate, and halogenated agents (such as Halon 1301 and Halon 1211)[8] or highly pressurized carbon dioxide.[5] Some fire extinguishers contain chemicals designed to fight both Class A and Class B fires.[8]
Grease and cooking oil fires pose a greater safety risk. One ten-year study, examining the years 1976 to 1985, found that 4.7% of hospitalized burn patients suffered burns from hot grease or oil, with 78% of such injuries occurring in the home.[9] According to the National Fire Protection Association, between 2010 and 2014, nearly half (46%) of home structure fires reported to fire departments in the United States involved cooking; over the same time period, cooking equipment was implicated in 19% of home fire deaths, 44% of home fire injuries, and 17% of total direct property damage.[10] Grease fires are an object of study in food science.[11]
Class B fire icon
Combustible materials fire symbol
Other combustible materials fire symbol
See also
- Grease duct – a duct designed to vent grease-laden flammable vapors to prevent them from building up near the flame of cooking apparatuses
- Exhaust hood – a device containing a mechanical fan that for use above the stove or cooktop in the kitchen to remove airborne elements produced by cooking
- Ignitable Liquid Drainage Floor Assembly – an active fire protection system designed to respond to Class B fires inside infrastructure by removing flammable liquids into secondary containment
References
External links
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