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Fire Classifications

To extinguish a fire successfully, it is necessary to use the most suitable type of extinguishing agent-one that will accomplish the task in the least amount of time, cause the least amount of damage and result in the least danger to the crew members.

The job of selecting the right agent is made easier by the classification of fires.

There are six classifications of fires A, B, C, D, E and F.

Class A

Involving common (ash-producing) combustible materials, such as wood, paper and fabric. This is best fought using water. Foam, some powders, vaporising liquid and wet chemicals make also be used. CO2 has limited effect.

Class B

Involving flammable and combustible liquids and liquefiable solids (paint and oils).These fire are fought with foam, CO2, and dry chemical. Water must not be used unless in a fine spray from a fire hose with a fog nozzle.

Class C

Involving flammable gases or liquefied gases (LPG, oxygen, acetylene) in the form of a jet or a spray. These fires require a very fast response whereby the supply valve allowing the gas to vent to atmosphere must be turned off. This usually requires a heavy water curtain to reduce the radiated and conducted heat to be reduced sufficiently for the valve to be closed. Dry powders may be used on these fires, CO2 and vaporising liquid have limited effectiveness.

Class D

Involving combustible metal (magnesium, sodium, potassium, titanium, aluminium).These are generally fought with special dry powder extinguishers.

Water is not used on these fires as the molten metal may spatter and cause further outbreaks.

Class E

This designation on a portable extinguisher means that the contents can be used on an energised electrical circuit with safety. It should be noted that there is no such thing as an electrical fire in practice-electricity does not burn!

Dry powder, CO2, vaporising liquid maybe used on these fires.

Class F

Involving cooking oils and fats. Foam and Wet Chemical extinguishers are used on these fires. Some types of dry chemical and CO2 extinguishers have limited effectiveness