Fire class is a term used to denote the type of fire, in relation to the combustion materials which have ignited. Different fuels create different fires and require different types of fire extinguishing agents. And it is important to know about class of fire to use right fire extinguisher. There are several different classifications of fires based primarily on the fuel source.
Class A Fire- It is the fire of wood, paper, linen and similar dry materials. They are extinguished by cooling and quenching effect of water. The water reduces the temperature of burning substances below their combustion temperature. These are the most frequent and easiest to extinguish when there is an ample water supply and when water can be directed on the combustible material .Keeping the other combustible material wet will limit the spreading of fire.
Class B Fire- These includes fires of oil, gasoline, grease and other petroleum product. These fires are extinguished by blanketing the source of burning substances and eliminating the supply of Petroleum products is lighter than water and will float on water and continue to burn and spread by means of flowing water to other section of the building, hence water is never used for this category.
Class C Fire- These is the fires of pressurized gases like L.P.G., most of the gases are lighter than air but L.P.G. is heavier than air. Water is not to be used for this class of fire.
Class D Fire- These is fire of metals having low burning temperature like Na, Mg etc. Once a metal ignites do not use water in an attempt to extinguish it. Only use a Dry Powder extinguishing agent. Dry powder agents work by smothering and heat absorption.
Class E Fire- These is electrical fire. The fire extinguishing agent must not conduct electrical energy which could spread the fire. Electrical fires are usually blanketed and cooled down. Water is a good cooling agent but it also conducts electricity, so it is not used to control or extinguish this class of fire. Electrical fire is usually caused by a part of circuit overheating or by short circuit. Controlling the sizes of electrical fuses and circuit breaker will often minimize this class of fire.