How Fire Extinguishers Work

There are two main types of fire extinguisher: those with internal stored pressure, and those where pressure is delivered through a cartridge system.

The most common by far of these two is the former, with cartridge-based systems reserved mainly for industrial use. Both variants of extinguisher work in the same way though, removing one of the three things fire needs to burn: oxygen, heat or fuel.

This is achieved by holding their contents under pressure – either from pressure within the main tank or from the external cartridges -causing a rapid expulsion of extinguishing agent when operated. Basically, when the lever is squeezed on the top of the canister, a valve is forced open allowing the release of the pressurized gas and contained agent through the fire extinguisher’s nozzle.

Despite the delivery method and vehicle split between only two main variants, there are many differing extinguishing agents used in modern-day fire extinguishers. Water and water-additive fire extinguishers work by propelling water by pressurized gas onto afire to cool it and soak its fuel, preventing it burning further.

Foam and powder extinguishers – which propel powder and foam under low pressure – do not put out fires in this manner, achieving a neutral environment by smothering a fire with its agent, cutting off its oxygen supply instead of dowsing its fuel. CO2-based systems work in a similar manner too, expelling the gas – which is extremely cold – onto the blaze, cooling it and displacing any oxygen in the atmosphere.

The modern pressurised fire extinguisher we are familiar with today was created in 1818 and consisted of a three-gallon copper vessel of a potassium carbonate solution contained within compressed air.

Fire extinguishers facts

Remove basic elements – All fire extinguishers work by removing any one of the three basic elements necessary for fire to burn -these being oxygen, heat and fuel.

Type matters – There are eight different types of fire extinguisher available, including: water and foam, dry and wet chemical, clean agent and powder variants.

Class of fire – The five classes of fire are class a, ordinary combustibles; class b, flammable liquids; class c, electrical; class d, combustible metals and finally class k, oil fires.

Fire in the hole – The fire grenade was an early experiment involving a small glass bottle filled with extinguishing agent thrown into fires in an attempt to put them out.

Colour co-ordinated – The colour of a fire extinguisher varies from country to country. UK fire extinguishers are red with coloured bands to denote their type.