A Class B fire is a fire involving 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 They are also Class B fireproof materials.[3]​.

Class B fires are distinguished from the other classes of fires: Class A fires ("ordinary fuels" 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 K (known outside the United States as Class F) refers to fires involving cooking oil or grease; These materials are technically part of Class B.[5]​.

Fires are classified according to the appropriate extinguishing agent. While water is used on Class A fires, using water on Class B fires (such as a grease fire) is extremely dangerous.[3][5]​ This is because the burned fat is hotter than the boiling point of water (100 degrees Celsius); When water is placed on grease, vapor is generated that expands rapidly and splashes, 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)[6]​ or highly pressurized carbon dioxide.[5]​ Some extinguishers contain chemicals designed to combat Class A and Class B fires.[6]​.

Cooking grease and oil fires pose a greater safety risk. A ten-year study, which examined the years 1976 to 1985, found that 4.7% of hospitalized burn patients suffered burns from hot grease or oil, and 78% of such injuries occurred in the home.[7] According to the U.S. National Fire Protection Association, between 2010 and 2014, nearly half (46%) of residential structure fires reported to U.S. fire departments involved cook; During 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.[8]​ Grease fires are an object of study in food science.[9]​.

• - Wikimedia Commons hosts a multimedia category on Class B Fire.

• - Extractor Hood: A device containing a mechanical fan used over the stove or cooktop in the kitchen to remove airborne elements produced by cooking.