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Classification of Fires by Type

The current British/European Standard BS EN 2:1992
Classification of fires defines four categories of fire, according to the type of material burning.

Class A
These are fires on solid materials, usually organic, leaving glowing embers. Class 'A' fires are the most common and the most effective extinguishing agent is generally water in the form of a jet or spray.

Class B
These are fires involving liquids or liquefiable solids. For the purpose of choosing effective extinguishing agents, flammable liquids may be divided into two groups: those that mix (are miscible) with water and those that do not (are immiscible). Extinguishing agents are chosen according to whether the liquid fuel will mix with water or not. Agents which may be used include water spray, foam, light water, vaporising liquids, carbon dioxide and dry chemical powders.

Class C
These are fires involving gases or liquefied gases in the form of a liquid spillage, or a liquid or gas leak, and these include methane, propane, butane, etc. Foam or dry chemical powder can be used to control fires involving shallow liquid spills, though water in the form of spray is generally used to cool the containers.

Class D
These are fires involving metals. Extinguishing agents containing water are ineffective, and even dangerous. Carbon dioxide or dry chemical powders containing bicarbonate will also be hazardous if applied to most metal fires. Powdered graphite, powdered talc, soda ash, limestone and dry sand are normally suitable for Class D fires. Special fusible powders have been developed for fires involving some metals, especially the radioactive ones.

Electrical Fires
Electrical fires are not treated as a class of their own, since any fire involving, or started by, electrical equipment must, in fact, fall into one of the other categories. The normal procedure for dealing with an electrical fire is to cut off the electricity and use an extinguishing method appropriate to what is burning. If this cannot be done with certainty, special extinguishing agents will be required which are non-conducting.

Classification of fires by size
To describe the size of a fire, the Central Fire Brigades Advisory Council has made the following recommendation:

Major fire 20-jets (or more)
Large fire 8-19 jets
Medium fire 3-7 jets
Small fire 1-2 jets, or 3 + hose reels
Minor fire 1-2 hose reels, or hand extinguishers.