Fire extinguishers are used to put off the flames caused by any accidental fire.
Use of a particular kind of fire extinguisher depends upon the type and nature of the fire. For combustion to take place, three things are needed: a) combustible substance b) oxygen, which is supporter of combustion and c) Ignition temperature.
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In the absence of any of these, the fire stops. A fire extinguisher may either disconnect the contact of oxygen from the combustible substance or bring down the temperature of the material on fire below its ignition temperature. Different types of extinguishers are
(a) Water as fire extinguisher:
Water cools the bombing substance below its ignition temperature and does not support combustion. It is not useful in cases where fire is caused by burning oil or by electricity.
(b) Soda-acid extinguisher:
It releases C02 which also cools the burning substances; more over CO, forms a protective layer over the substance displacing air, which is heavier. In absence of 02, fire extinguishers. It is used to extinguish fire caused by oil burning.
(c) Foam extinguisher:
Works on the same principle as that of the water extinguisher, but it can be used in case of burning oils. Foam unlike water, being lighter rests on the oil surface and cuts off the oxygen supply.
(d) Electrical fire extinguisher:
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Water and foam conduct electricity; hence these cannot be used in case of fires caused by electricity. Carbon tetrachloride, being non-combustible, non-supporter of combustion, and heavier than air (even in vapor form) is used as electrical fire extinguisher. It displaces air, thus cutting oxygen supply.