Page 73 - Science Class 08

Rapid Combus on HOW TO CONTROL FIRE?
When a substance starts burning as soon as it v There are many different sorts of fire and
is ignited and produces large amount of heat each required careful selec on of fire
and light, this combus on is referred to as ex nguisher. The condi ons necessary for

rapid combus on. burning are (a) combus ble substance (b)
For example, LPG, petrol, paper, kerosene oil, etc. supporter of combus on and (c) heat. A
Slow Combus on device used to ex nguish fire is called a fire

As its name suggests, it is a very slow combus on ex nguisher.
process in which no igni on or external heat is v If someone is on fire, try to roll him/her
required. This process produces very li le heat and wrap in a blanket or carpet or a special
and no light. fireproof blanket if it is available.
For example, oxida on of food in our body, v Highly inflammable substances should
rus ng or iron, etc. never be kept in hot places or near

During the process of respira on, food burns unprotected flames. If they catch fire, try to
and gets oxidised to produce heat energy and cut off their air supply by covering them
carbon dioxide gas. with a cloth or a mat. If you have to use an
Look at the following equa on of combus on ex nguisher, make sure it is a carbon
of food. dioxide one.

C H O + 2O Õ 6CO + 6H O + Heat v Water is used to ex nguish fire by cooling
6 12 6 6 2 2
Food Oxygen Carbon Water the burning substance below its igni on
Energy Dioxide
temperature. But, it cannot be used in case
of fire caused by burning oil or by
electricity.
Aim : To observe the change in igni on
v Water works on the principal of cooling the
temperature. burning substance below its igni on
Materials Required : paper, water, candle, temperature. Though water is the main fire
matchs ck. ex nguishing agent in a soda-acid fire
Process : Make two paper cups by folding a ex nguisher, carbon dioxide is also of some

sheet of paper. Pour about 50 ml of water in use in pu ng out the fire. This is because
one of the cups. Heat both the cups separately carbon dioxide does not burn, it is denser
with a candle. than air and does not support combus on.
Conclusion : If we con nue hea ng the cup, v You know that water is heavier than oil or
we can even boil water in the paper cup.
petrol. Therefore, when water is thrown
Actually, the heat supplied to the cup is
over burning oil, it se les down. The oil
transferred to water by conduc on. So, in the floats on water and con nues to burn. So,
presence of water the temperature of paper
oil fires are ex nguished by using foam
does not reach at igni on temperature.
Hence, it does not burn. type fire ex nguisher. The foam type fire
ex nguisher stops the fire by cu ng off air
Cau on : While doing this experiment, you
supply to the burning substance. Carbon
should be very careful.

Science-8 73