Question

Which type of fire extinguisher is used to extinguish fire caused by burning oil and petrol?
(a) foam type
(b) water type
(c) soda acid type
(d) ${ CCl }_{ 4 }$ type

Answer 1

Hint: There are different classes of fire that are classified in terms of the type of fuel that burns for the fire to take place. Only certain kinds of fire extinguishers can be used for a particular Class of fire.

Complete step by step answer:
To answer this question, we first need to understand the different classes of fire. They are classified in terms of the type of fuel that is burning.
Class A: They are caused by the burning of solid combustible materials (excluding metals). For example wood, cloth, paper etc.
Class B: They are caused by the burning of a non-metal in a liquid state that is flammable. It also includes flammable gases. For example gasoline, grease, acetone, oil etc.
Class C: It is caused by electrical current or energized electrical equipment.
Class D: It is caused by the burning of metals such as potassium, aluminium, magnesium, sodium etc.

For a fire to take place there are certain conditions that need to be met:
-Oxygen is required to maintain the combustion.
-The material needs to be supplied the required heat in order to raise its temperature to its ignition temperature.
-The material should be combustible.
-The chemical reaction that takes place when the material is ignited needs to be exothermic.
The fire extinguishers target any one or more of these conditions in order to put out the fire.

-Air-pressurized water extinguisher: They are filled with ordinary water and pressured with normal gas. Water extinguishers can only be used for Class A fires. This type of fire usually leaves an ash. They target the “heat” element that is necessary for a fire to take place.

-Soda acid extinguisher: The first soda acid extinguisher produced carbon dioxide by the reaction between a solution of sodium bicarbonate and tartaric acid. A different kind of soda acid extinguisher used the reaction between sodium bicarbonate solution and sulphuric acid to produce pressurized water onto the fire. Actually the reaction between sodium bicarbonate and sulphuric acid produces propellant carbon dioxide which in turn is used to pressurize the water. Since it is using water to put out the fire it can be used only for Class A fires.

-${ CCl }_{ 4 }$ type: It utilises carbon tetrachloride to extinguish fire. It inhibits the chemical chain reaction of the combustion process by removing oxygen supply. It can be used for extinguishing Class B and Class C fires.

-Foam type extinguisher: It is similar to the soda acid type but with slight differences. It uses an aqueous solution of sodium bicarbonate and a solution of aluminium sulphate. When the two solutions react they produce a frothy foam and carbon dioxide gas. The ${ CO }_{ 2 }$ gas is used to expel the foam onto the fire. It can be used to extinguish Class A fire.
So, the correct answer is “Option D”.

Note: Water and foam fire extinguishers take away the “heat” element that is one of the conditions for the fire to take place. Foam type extinguishers also coat the fuel such that it cuts off the contact between the fuel and oxygen.