We are all aware of the damage and disaster a fire can cause in certain situations. Now let us see how to control a fire and prevent it from spreading.
A fire is basically a chemical reaction during which heat and light are produced. Three factors are necessary for a fire to start – fuel, oxygen or air, and heat to raise the temperature of the fuel to its ignition temperature.
A fire can be extinguished when one or more of these agents is removed, i.e. fuel, supply of air and lowering the temperature of the combustible substance. All fire extinguishing methods make use of these principles.
The original fire extinguisher, a bucket of water, is still useful in controlling many types of fires. The principal effect of water on a fire is to cool the burning material, thus removing the heat – one of the factors without which combustion cannot continue. It can be applied in a variety of ways such as by flooding the fire with water. Jets of water are used to knock down the flames of fire, and sprays are used to absorb heat and drive back smoke and gases.
Another common extinguisher is the soda-acid type. It sprays a mixture of water and carbon dioxide on the fire. This is based upon the principle of cooling the burning material and cutting the supply of air by non-combustible carbon-dioxide.
In this extinguisher a solution of sodium bicarbonate is placed in a cylindrical vessel of steel. Sulphuric acid is kept in a bottle in a small compartment made within the cylinder, near the top. When required, the knob is hit against the floor. This brings the sodium bicarbonate and sulphuric acid in contact with each other. Immediately carbon dioxide is formed and it comes out of the fire nozzle which is directed towards the fire. These extinguishers are useful only for small and localized fires. They are not effective against gasoline, oil and electrical fires.
Foam extinguishers are based upon the principle of cutting off the supply of air by forming a fire-proof coating of foam around the burning material. In this, a mixture of sodium bicarbonate and aluminium sulphate containing licorice extract is sprayed. It produces foam and extinguishes the fire.
The other types of extinguishers that are used on oil and electrical fires are: Carbon dioxide extinguishers, dry-chemical extinguishers and vaporizing liquid extinguishers.
Water should never be used for extinguishing electrical or oil fires. In case of electrical fires, it can cause electrocution. If water is used on burning oil, the oil simply floats on top of water and continues to burn. As the water flows away, it can carry the oil with it and so spread the fire.
Fire extinguishers are provided by law in all public buildings, factories and schools. Most of the big cities have fire brigades for fire prevention and control.