2 The combustion triangle

Combustion (burning) is a chemical reaction between a substance and oxygen that releases heat, light, or both, and forms new substances that depend on what is burned.

For combustion to occur, three things must be present together. They form the combustion triangle (fire triangle):

1. Fuel: a flammable material.
2. Oxygen (from the air).
3. Heat energy: an ignition source that brings the fuel to its ignition point.

• Remove any one of the three and the fire stops.
• This is the principle of fire extinguishing: water removes heat (by absorbing it), a lid or fire blanket removes oxygen, and clearing away trees or switching off a gas supply removes fuel.