The working principle of any fire extinguisher is based on the following three conditions:
- cooling of the combustible material below its ignition temperature
- cutting off the air supply
- cooling the combustible material simultaneously while cutting off the air supply.
This type of fire extinguishers acts on all fires except the fire caused due to electrical and inflammable liquids. It is the most effective of all house-hold fire extinguisher. Soda acid fire extinguisher contains sodium bicarbonate and sulphuric acid. It comprises of a strong iron vessel with a side discharge nozzle. The iron vessel is loaded with sodium bicarbonate solution. Sulphuric acid is supported in a small glass bottle and is kept inside the iron vessel. On striking the knob fixed just above this bottle, the acid bottle breaks open into the sodium bicarbonate solution. This broke open sulphuric acid reacts with sodium bicarbonate to form sodium sulphate, water and carbon dioxide. This carbon dioxide gas projects the enclosed liquid toward the flames successfully extinguishing it.