Fire is the result of a chemical reaction called combustion, which requires a combination of fuel and oxygen as well as a source of ignition. Different methods can be used to extinguish fires. The methods often involve the removal of heat by cooling the burning material, the cutting of fuel or air source or the adding of chemical substances.
Cooling the Burning Material
Cooling the burning material is the most common method used to extinguish fire. Water is widely available and the best cooling agent to use specially in fires involving solid materials. By evaporating in contact with fire, water also blankets the fire, cutting off the oxygen supply. However, you should never apply water to fires involving hot cooking oil or fat; water can cause the fire to spread.
Excluding Oxygen from the Fire
Smothering agents are substances used to extinguish a fire by cutting off the oxygen supply. Foam, which is the content of some fire extinguishers, can help to cool down and isolate the fuel surface from the air, eliminating combustion and being able to resist wind and draught disruption. However, never use foam on energised electrical equipment, because it is an electrical conductor. Other smothering agents include carbon dioxide, which is found in some fire extinguishers and is ideally used in electric equipment and sand, which is effective only on small burning areas.
Removing Fuel from the Fire
Another method of extinguishing a fire is to remove the fuel supply by switching off the electrical power, isolating the flow of flammable liquids or removing the solid fuel, such as wood or textiles. In woodland fires, a firebreak cut around the fire helps to isolated further fuel. In the case of gas fire, closing the main valve and cutting off the gas supply is the best way of extinguishing the fire.
Using a Flame Inhibitor
Flame inhibitors are substances that chemically react with the burning material, thus extinguishing the flames. Dry-chemical fire extinguishers work in this way, and can contain monoammonium phosphate, sodium and potassium bicarbonate and potassium chloride. Vaporising liquids, such as Halon, also have a flame inhibiting action. However, most of these substances have been phased out due to high levels of toxicity.