Engineering & Technology
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In order for a fire to burn there are three things that need to be present: oxygen, fuel and heat. The diagram shows what is called a fire triangle which shows these three requirements.
If any of these are missing it is not possible for the fire to burn. Therefore, to extinguish a fire any one side of the fire triangle needs to be eliminated.
How fire extinguishers work
Carbon dioxide is heavier than air and also non-flammable. A carbon dioxide fire extinguisher works by displacing the oxygen thus removing one of the elements of the fire triangle.
A water fire extinguisher can put out a fire because it causes it to cool down, therefore removing the heat element of the fire triangle.
It is important to select the correct fire extinguisher for different types of fire. Chosing the incorrect extinguisher may not put the fire out and could even make it worse. For example putting water on burning oil will cause the oil to disperse into a mist which will burn very quickly indeed. The table below shows the extinguishers you may come across and the types of fire that they are used for,
There are five classes of fire as shown in the table below, along with the extinguishers that may and may not be used for each classs.
