WHAT IS FIRE?
Session 3 - P 1 of 6



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THE FIRE TRIANGLE

Combustion is a chemical reaction that happens very quickly and results in the production of heat, light & sound. We can explain this simply using the fire triangle.
 

[PICTURE TO GO HERE WHEN AVAILABLE]

For combustion to occur, three factors must be present; ‘HEAT’, ‘OXYGEN’ & ‘FUEL’. Remove any one of the three and the triangle will collapse, therefore stopping combustion. This means the fire will go out. A simple example of the triangle in action:
 

Here is what you would have you didn’t set a light to the candle with the match in the first place:
 

WHAT HAPPENS WHEN A FIRE BURNS?

   ... FLAMING

This is where moisture is driven out of a fuel by applying heat. As the temperature continues to rise, the fuel gives off a vapour and it is this vapour (when combined with the correct amount of oxygen) that can be ignited, usually by a flame or spark.

   ... SMOULDERING OR CHARRING
 
When a solid fuel such as wood is subject to ‘FLAMING’, all the moisture and vapour is driven off leaving behind a solid residue. When these remains are still hot, they are described as ‘SMOULDERING’ and once they are cool, they are described as ‘CHARRED’.



   ... LIQUID FUELS

Most liquid fuels give off a flammable vapour naturally with out been heated and as a result little heat needs be applied in order for it to combust. A good example of this is petrol. It is still a liquid and vaporises well below the freezing point of water, therefore even if you apply a spark to a spillage of petrol on a cold day it will ignite. For this reason is described as ‘Highly Flammable’.

Gases need no initial heating to produce a vapour as they are already in this state. Simply applying heat e.g. a spark is usually enough for combustion to begin. A typical example of this is a gas cooker in the home.