Understanding Fire Extinguisher Classes: A Comprehensive Guide

According to OSHA, fire extinguishers are labeled with a letter that represents the fire class on which the unit may be used. Do not use the wrong class on a fire. A water extinguisher meant for Class A fires, for example, will cause a Class K fire to spread. (See Reference 2.)

Class A

• Class A extinguishers are for fires involving cloth, wood, paper, rubber and certain plastics. These materials are known as ordinary combustibles. (See Reference 1.) According to OSHA, the extinguisher should be labeled with a triangle around an A. (See Reference 3.)

Class B

• Class B extinguishers are for fires that involve combustible and flammable liquids. This includes gasoline, oil and certain gases. (See Reference 1.) The extinguisher should be labeled with a B inside of a square. (See Reference 3.)

Class C

• Class C extinguishers are used on fires caused by energized electrical equipment. Fires can start because of wiring, circuit breakers or fuse boxes. (See Reference 1.) The extinguisher should have the symbol of a circle surrounding a C. (See Reference 3.)

Class D

• According to the FDNY, Class D extinguishers are used for fire caused by combustible metals such as sodium, magnesium and titanium. (See Reference 1.) The extinguisher should be labeled with a star surrounding a D. (See Reference 3.)

Class K

• Class K extinguishers are specialty extinguishers found in restaurants and kitchens. (See Reference 1.) These units put out combustible cooking fires caused by grease, fat or vegetable oil. (See Reference 3.)