When we burn coal or wood in a burner or a stove, we see that the coal becomes extreme heat (burning lava) while burning. After some time we see that when the burner cools down, the coal finishes and the ash remains.
Coal gets converted into carbon dioxide and ash on burning. Therefore, on burning, the composition of the burning substance changes, that is, the burning substance changes into another substance. This is called combustion.
Combustion is a chemical change in which heat and light are produced simultaneously and the composition of the burning substance is changed. Burning of paper, petrol, dry leaves and grass are some examples of combustion. Burning substances are called flammable substances, such as petrol.
Those substances which do not burn are called inflammable substances like water. All substances produce heat and light upon burning. When we press the switch of a bulb, it starts illuminating. We get light from it and if we touch that bulb, we find that the illuminated bulb also produces heat. Although, both heat and light are produced when the electric bulb is fluorescent. However, this is not a combustion process, as there is no chemical change. No new substance is formed in it.
Conditions of Combustion
If we lit a matchstick and took it near the petrol, it immediately catches fire and starts burning, but the same burning stick does not bring change to any material like water, stone, glass. These substances do not burn at all, because combustion takes place only in the presence of flammable substances.
We often see that to lit a pressurized stove we take a burning stick near to the kerosene oil filled in a bowl under the burner to burn and the oil catches fire.
We also see that in order to burn coal in the fireplace, first we have to heat a lot by burning paper or cloth soaked with kerosene, so that it attains heat from burning.
If the burning fire is covered, the air and the supply of oxygen is consequently exhausted, which extinguishes the fire. In this way, oxygen is also necessary for burning.
Three conditions are necessary for combustion:
- Presence of flammable substance
- Resumption of combustion heat
- Constant supply of combustion nutrients (usually air)
Fire is highly used in our daily life. But sometimes and especially when it gets out of control, it proves disastrous. Therefore, it is necessary for us to be aware of the measures and means of controlling fire.
The executive principle of fire extinguishers is based on one of the following three conditions:
- Cooling the fire to below its ignition temperature
- Exhausting the supply of combustion nutrients
- Cooling the fire as well as exhausting the air supply