How do fire extinguishers work?

As a business owner or operator, it’s your responsibility to ensure that there are proper fire safety measures in place to keep your employees, customers and workplace safe in the event of a fire. Fire extinguishers are one of the methods that you should use to combat fire in the workplace. Understanding what they do (and how they do it) is important to ensuring that you properly fulfil your duties as the responsible person.

Understanding Fire is a type of chemical reaction that occurs between oxygen and fuel when heat is introduced. The fuel is heated to its ignition temperature where combustion occurs. This process continues for as long as oxygen, fuel and heat are present in the reaction.

Stopping the combustion process involves removing or isolating one or more of the 3 elements that permit combustion.

This reaction is known as the ‘fire triangle’.

Fire Extinguishers

There are various types of modern extinguishers available and they work in different ways depending on the application that they are intended for - fires involving combustible materials, flammable liquids or involving electrical risk for example. Sometimes they are chosen for other properties, such as avoidance of damage to delicate equipment or valuables.


Ultimately they all work by removing or isolating one or more elements from the fire triangle in order to stop the combustion process.

W9 Water Fire ExtinguisherConventional fire extinguishers, like the Water Extinguisher, are pressurized containers filled with an extinguishing agent and compressed gas. The fire suppression agent, in this case water, is forced out of the extinguisher by the pressurised gas when the valve is opened.  The user then directs this stream of water at the base of the fire to remove heat from the combustion triangle.

However this doesn’t work with flammable liquid fires (Class B fires) because the fuel vaporises at low temperature, unlike the solids involving combustible materials such as wood, paper. (Class A fires)

In this case another type of extinguishing agent such as Carbon Dioxide (CO2) or Foam, displaces the oxygen with a blast of the inert CO2 gas, or a smothering coat of foam and thus prevents combustion from continuing.

In the case of a fire involving electrical equipment, we need to select an extinguisher that cannot conduct an electrical current from the source to the extinguisher operator.

In a contained flammable liquid fire such as a cooking pan, an extinguisher could make matters worse by blowing the burning oil out of the pan as the extinguishing medium is forced under the surface of the oil and rapidly expands. This why Fire Blankets are used for smothering (preventing ingress of oxygen) for an oil based kitchen fire.  A damp (not wet) tea towel is an alternative if no fire blanket is available, although it’s not as effective as it can quickly burn through, whereas a fire blanket can withstand very high temperatures.


Whichever types of risk you have in your building, it’s important to obtain advice from a professional. Choosing the wrong extinguisher could be dangerous, so the British Standard also requires that extinguishers are installed by a competent person in order to ensure the correct type and location of the extinguisher for the risk.

If you need any advice, do not hesitate to contact us.

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