CLASSIFICATION OF FIRES
Although the principles of fire development and spread apply to all fire, fires are classified as types A, B, C or D depending on the actual combustible materials involved. This classification is extremely important when deciding which extinguisher should be used in the event of a fire, not all extinguishers are suitable for all fires.
Class A These are fires involving solid materials, usually of an organic nature, in which combustion normally takes place with the formation of glowing embers, e.g. wood, paper and textile fabrics. Cooling by water is the most effective way of extinguishing this type of fire.
Class B These fires involving liquids or liquefiable solids, such as petrol, oil, greases and fats, where the blanketing or smothering effects of extinguishing agents which exclude oxygen are the most effective.
Class C These are fires involving gases such as hydrogen, propane, butane, etc. Fighting fires of this nature should be left to the experts as extinguishing burning gases without cutting off the supply could lead to an explosion if re-ignition occurs. The most effective method of extinguishing the fire is to cut off the supply, where possible, and subsequently deal with other burning materials (if any) with the appropriate extinguishing agent.
Class D These are fires involving metals such as magnesium, aluminium, sodium, potassium, calcium and zirconium, where special materials and techniques are necessary to secure extinction.
It should be noted that there is no classification in the standard for what are erroneously called ‘electrical fires’ as these are really fires in materials where electricity is present. Such fires will fall into one or more of the four classes defined. Therefore, after the electrical supply has been isolated, the choice of extinguisher will depend upon the materials involved in the fire. However, the most suitable types of extinguisher for use on live electrical equipment are Carbon Dioxide (CO2).
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