Classes of Fire and Extinguishers

Flammable and combustible materials can be divided into classes, which can be used to determine the appropriate extinguishing material and technique.

Class	Material	Extinguishing Material
A	wood, cloth, paper, rubber, many plastics, and other ordinary combustible materials	water or solutions with high percentage of water; halogenated agent; dry chemical; wet chemical
B	petroleum greases, tars, oil-based paints, solvents, lacquers, alcohols, flammable liquids, combustible liquids, flammable gases	film-forming foam, carbon dioxide, dry chemical, halogenated agent (smothering or exclusion of air, interrupting the chemical chain reaction )
C	energized electrical equipment	dry chemical; carbon dioxide (see below); halogenated agent (nonconducting agent)
D	magnesium, titanium, zirconium, sodium, lithium, potassium and combustible metals	graphite, sodium chloride, special extinguishing agents
K	cooking appliances using cooking oils or fats	dry chemical; wet chemical

where:

• Class A and/or B extinguishers may be appropriate in Class C fires after the electrical equipment has been de-energized.

• Halogenated agents may be associated with ozone depletion if released into the atmosphere.

• Wet chemical extinguishers include aqueous solutions of potassium carbonate, potassium citrate, and/or potassium acetate.

• Fires involving computers and delicate electrical equipment should be extinguished with carbon dioxide or halogenated agent type extinguishers.

• Carbon dioxide extinguishers using a metal horn are not suitable for Class C fires.

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