How Do Fire Extinguishers Work

Fire extinguishers all function in much the same way - you hold their contents under pressure and release them through a nozzle or horn when the operating lever is squeezed.

The fire extinguishing agent or extinguishant inside works by removing one or more of the three things a fire needs to burn – oxygen, heat and fuel.
By removing the supply of oxygen, reducing the heat or reducing the heat around the fuel, a single fire extinguisher can extinguish a small fire in a matter of seconds.

What Happens Inside a Fire Extinguisher?

When you squeeze the lever on the top of a non-gaseous fire extinguisher, you both open a valve to the nozzle and also release a highly pressurised supply of gas stored at the top of the extinguisher.  This gas escapes and pushes out the extinguishing agent from the cylinder through the nozzle.
In CO2 fire extinguishers, the gas is held under tremendous pressure so it liquifies. When you squeeze the lever and release the pressure, the CO2 rapidly expands into a gas again.

Water and Water-additive Fire Extinguishers

Water and water additive extinguishers are filled with water and pressurised with nitrogen. They work by both cooling the fire and soaking the fuel so it will not burn further. Read more

Powder Fire Extinguishers

Regular dry powder extinguishers work by smothering the fire in a layer of power, thereby eliminating the source of oxygen.
Specialist Class D rated fire extinguishers for metal fires work in a similar way, but use agents that do not react with the metals and are delivered at a low pressure. Read more

Foam (AFFF) Fire Extinguishers

Foam fire extinguishers work in the same way as powder extinguishers, by smothering the fire.
The foam also forms a skin that helps to cool the fire, and can soak into absorbent fuel to prevent re-ignition. Read more

Carbon Dioxide Fire Extinguishers

CO2 fire extinguishers hold CO2 gas under great pressure, so it is stored as a liquid. When the pressure is lowered by squeezing the operating lever, the liquid rapidly expands into a gas, which is extremely cold. The cold gas cools the fire and also displaces the oxygen around it, because CO2 is heavier than air. Read more

Wet Chemical Fire Extinguishers

Wet chemical fire extinguishers are specifically for use on Class F fires involving cooking oils and fats. These extinguishers use a chemical additive to turn the surface of burning oil into a non-combustible soft soap – a process called saponification.
The process of converting the oil into this soapy foam draws heat from the oil, and the resulting layer seals the oil away from the oxygen in the air. Read more
Information supplied courtesy of
To see the range fire extinguishers available for leisure and commercial vessels, click here or for further technical advice, contact the Safety Marine technical team on or call +44 (0)2380 226300


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