Every year lives and properties are lost in fires. The common causes of fire are faulty electrical wiring, leaking LPG tanks, and neglected electrical appliances such as a forgotten electrical flat iron. During brownout lit candles and gasera also often cause fire.

        One of the concerns of chemists is controlling fires. Burning is rapid oxidation of a combustible material. The heat, which is released by the burning material, keeps the reaction going. The fuel is a combustible material, which burns in the presence of heat and oxygen. Once heated, the combustible material is converted into very reactive species called combustion intermediates. For burning to occur, fuel, source of heat and oxygen should be present. The fuel has to be heated up to its ignition point. This is the temperature at which a material starts to burn. Without oxygen, burning is not possible. Therefore, to extinguish fire, three ways can be done:

1. Cool the fuel.
2. Cut off the oxygen supply.
3. Trap the combustion intermediates so they cannot react with oxygen.

        These three are considered in firefighting.

        Fireman are summoned whenever there is fire - usually a burning house or a big building. The fire caused by a burning solid fuel such as the wooden frame of a house, is a class A fire. This kind of fire is extinguished using water. Water cools the fuel below its ignition point. The heat of the fire converts water to steam, which dilutes the oxygen in the air around the fire.

        Fire caused by oil or gas is class B fire. It cannot be extinguished by water. Since oil and combustible gases are not soluble in water, they will spread if splashed with water and the fire will occupy an even bigger area. For class B fire, a carbon dioxide fire extinguisher is used. Because carbon dioxide is more dense than air, it serves as a blanket which covers the burning material to cut off its supply of oxygen from the air. Class C fire is caused by an energized electrical circuit. Since water is an electrical conductor, it cannot be used to put fires caused by electricity. A carbon dioxide fire extinguisher is used for class C fires.

        A burning metal is labeled as a class D fire. Water cannot be used to put out this class of fire since it will be a source of oxygen. Neither can carbon dioxide fire extinguisher be used in this class of fire because carbon dioxide may react with the hot metal. Thus. for burning metals, a dry chemical powder fire extinguisher can be used. The simplest of these chemicals is sodium bicarbonate. This chemical, when exposed to heat, produces carbon dioxide, which shuts off the oxygen supply from the air.