The principle of working of any fire extinguisher is based on either of the following three
• cooling the combustible material below its ignition temperature, or
• cutting off the supply of air, or
• cooling the combustible material and at the same time cutting the supply of air.
Soda acid type extinguisher acts by cutting off supply of air. It acts on all types of fire except due to electrical and inflammable liquids
The carbon dioxide is liberated by the action of acid on baking soda. It increases the percentage of carbon dioxide in air (CO2 is non supporter of combustion).
This type of fire extinguisher contains a bottle of sulphuric acid supported by a metallic container
filled with a baking soda solution.When the cylinder is inverted and knob struck, against the
ground, the acid bottle breaks and the acid comes into contact with the backing soda.
2NaHCO3 + H2SO4-> Na2SO4 + 2H2O + 2CO2
Baking sulphuric sodium water carbon
soda acid sulphate dioxide
As a result carbon dioxide is liberated. This increases the percentage of carbon dioxide in air. Due to this the supply of air is cut off and there, fire is extinguished. These types of extinguishers are used in cinema halls, multistorey buildings, etc.