How does a fire extinguisher work?« Back to Questions List

A Fire extinguisher is a good tool to put out small fires and help limit them, becoming large engulfing the whole area. When an object is hot enough, has lot of oxygen around and is combustible, it can catch fire easily. To extinguish fire, any of its supports has to be removed. That is why we use water or a blanket to put out minor fire. Water cools the object, blanket cuts the oxygen supply.

There are three common types of fire extinguishers – water, gas and dry chemical extinguishers. In water extinguishers compressed air pushes water to come out of the tank to be sprayed on fire.

Gas extinguishers contain high pressure carbon dioxide (CO₂) in liquid form. When used, it expands by a huge amount thereby cutting off oxygen supply. These can be used to extinguish flammable liquids and flammable gases and will not work well on flammable solids.

The fire extinguishers that are commonly used in hotels, homes and other commercial buildings are the dry chemical extinguishers. This works similar to the principle of putting out fire with sand or salt. The extinguisher contains dry chemical powder which is non combustible. When sprinkled around the fire, the powder forms a layer on the top and cuts off the fuel from fire. Normally a very fine powder of  sodium bicarbonae  (NaHCO3, baking soda), potassium bicarbonate (KHCO3, nearly identical to baking soda), or monoammonium phosphate ((NH4)H2PO4) are used.

Not all types of extinguishers can be used on all types of fire. For example, CO₂ fire extinguisher has an advantage over dry powder extinguishers as they do not leave a residue after discharge. Therefore it is used on electrical fires, garages or workshops where oils, petrol, diesel, waxes, solvents and other flammable liquids are used. One must always learn how to make the home fire extinguisher ready to use, before hand as fire emergencies always occur without warning.