To know how to extinguish a fire you need to understand a little about fire and how it works.
What Is Fire? To begin with, fire is a chemical chain reaction in which oxygen is combined with fuel in the presence of heat. Consequently, this rapid oxidation produces heat and light (flames).
Fire can usually take place only when three critical elements are present. These are:
Oxygen is usually readily available as it makes up 21% of the air we breathe.
Fuel can be solid combustibles like paper, furniture, clothing, wood and plastics. It can also be flammable liquids (like petrol, kerosene, paints, solvents and cooking oils or fats), flammable gases (like natural gas, LPG or acetylene) and sometimes it can be metal.
Heat is required to produce ignition and then the heat given off by the oxidation reaction sustains the fire once the process has begun.
Examples of heat sources that can start a fire can include:
1.Firstly, heating and cooking appliances
2.Secondly, faulty electrical equipment
3.Thirdly, cigarettes, lighters and matches
When these three elements combine in a rapid oxidation process a chemical chain reaction ensues. This chemical chain reaction is also a necessary component of fire and becomes the fourth element of fire.
Note that, even if the fuel is a solid (e.g. wood) or a liquid (e.g. petrol) it is the vapours given off when the fuel is heated that burn.
The Theory Of Extinguishing A Fire
Fires are categorised into different classes. The method you use to extinguish a fire will depend on the class of fire.
1. Class A Fires involving carbonaceous solids, such as wood, cloth, paper, rubber and plastics. Class A does not include flammable metals (see Class D).
2. Class B Fires involving flammable and combustible liquids.
3. Class C Fires involving combustible gases.
4. Class D Fires involving certain combustible metals, including potassium, sodium and magnesium. Specialist advice should be sought.
Class E Fires involving energised electrical equipment.
Class F Fires involving cooking oils and fats.
A fire will burn as long as there is oxygen, fuel and heat available. Removal of any one of these elements will extinguish the fire. Interrupting the chemical chain reaction of the fire will also extinguish the fire.
Starving The Fire
Remove the fuel – i.e. the unburnt material. This can include turning off the gas in the event of a Class C fire.
Smothering The Fire
Prevent oxygen from combining with the fuel. This is how a fire blanket works.
Cooling The Fire
Reduce the temperature of the burning material to below its ignition point. This happens when you put water on a Class A fire.
Interrupting The Chemical Chain Reaction
Some fire extinguishers (e.g. a dry chemical powder extinguisher) interrupt the chain reaction and smother the fire at the same time.
Fire Extinguishing Tools
How To Extinguish A Fire