Necessary Conditions for Combustion
There are three necessary conditions for combustion. These are as follows
1. Presence of a Combustible Substance
Presence of substance like petrol, LPG, wood, coal, etc. is necessary for combustion process.
2. Presence of a Supporter of Combustion
A substance which helps in combustion is called a supporter of combustion, e.g. oxygen (or air).
For example, when the clothes of a person catch fire, the person is covered with a blanket to extinguish the fire. The blanket cuts off the supply of air which is needed for the burning of clothes. This shows that air is necessary for combustion.
3. Ignition Temperature
The lowest temperature at which a substance catches fire and starts burning is called its ignition temperature.
Before a substance catches fire and starts burn, it must be heated to a certain minimum temperature by supplying heat. A combustible substance cannot catch fire if its temperature is lower than its ignition temperature.
For example, a matchstick does not catch fire on its own at room temperature. When matchstick rubbed on the rough side of matchbox the heat produced increases its temperature to ignition temperature and its start burning.