Question 1 Name the most common fire extinguisher?
Question 2 Which fire extinguisher is used for fires involving electrical equipments and inflammable materials?
Question 3 What is fire fighting?
Question 4 Why are fire produced by burning oil and petrol cannot be extinguished by using water?
Question 5 Why fires caused by the electrical short circuit in an electrical appliance or in electric wiring should not be extinguished by throwing water?
Question 6 How is the wire caused by electricity extinguished?
Question 7 How is carbon dioxide stored in fire extinguisher?
Question 8 How does carbon dioxide fire extinguisher works?
Question 9 A drum of kerosene catches fire.What is the simplest way to put off the fire?
How to control fire
Burning produces fire.It is useful as well as harmful.We make small fire in a gas stove to cook our food.This is useful fire.Without fire,we cannot cook food.
When fire breaks out in a house,office,factory,oil tanker,petrol pump,then the fire is harmful.It can cause loss of life or property.
The process of extinguishing a fire is called fire-fighting.
Any fire needs three things to be present:
Fire can be extinguished in 3 ways:
1)By removing the fuel
2)By removing the heat
3)By cutting off the air supply to the burning substance
Remove the fuel
When fire starts in a room,all the combustible substances should be removed at once so that fire may not spread.If possible,cooking gas cylinder should be removed and electricity should be switched off.
Remove the heat
Water is used to remove heat from a burning substance and to male it too cool to burn further.Water extinguishes heat by cooling the burning substance.When water is thrown on a burning substance,it gets cooled below its ignition temperature and also stops burning.
When fire brigade man throws a strong stream of water on a building on fire,the burning material get cooled to below their ignition temperature and fire is extinguished.The water vapour produced by the action of heat of fire on water surround the burning material and help in cutting off the supply of air.Fire-men extinguishes the fire by throwing water under pressure on the burning things.
The fire produced by burning oil and petrol cannot be extinguished by using water.This is because water is heavier than oil and petrol.So,when water is thrown over burning oil,it settles down.The oil floats on water and continues to burn.
The fires caused by the electrical short circuit in an electrical appliance or in electric wiring should not be extinguished by throwing water.Because ordinary water conducts electricity.So when water is thrown over the burning electrical appliance,it can give electric shock to the person involved in the fire fighting.
3)Cut off the air supply
The air supply to a burning substance can be cut off in a number of ways such as covering the burning substance with carbon dioxide,sand,blanket or a damp cloth.
The electrical fires are extinguished by using carbon dioxide gas fire extinguisher.
1)Carbon dioxide is denser than air and forms a layer around the burning substance.It covers the fire like a blanket due to which fresh air cannot reach the burning substance.The burning substance does not get oxygen of air and hence stops burning.
2)Carbon dioxide gas neither burns itself nor supports burning.
3)It does not harm the electrical equipment.
The fires caused by the burning of inflammable materials like oil or petrol are also extinguished by using carbon dioxide fire extinguishers.
Carbon dioxide used for extinguishing fire can be stored as a liquid at high pressure in cylinders.When released from the cylinder,carbon dioxide expands enormously in volume and cools down.Carbon dioxide not only forms a blanket around the burning substance,it also cools down the burning substance.
To obtain carbon dioxide for extinguishing a fire is to release a lot of dry powder of chemicals like sodium bicarbonate or potassium bicarbonate over the fire.The heat of fire decomposes these chemicals to produce carbon dioxide gas.
A small fire can be extinguished by throwing sand or soil over it.When sand is thrown over burning kerosene oil,the sand covers it like blanket.The sand cuts off the air supply to the burning kerosene oil due to which the fire gets extinguished.
If the clothes of a person working in the kitchen catch fire,the person is immediately covered with a blanket.When the burning clothes of a person are covered with a blanket,the supply of air to the burning clothes is cut off and hence the burning stops.