How does a fire extinguisher work?

Fire extinguishers are a portable piece of equipment designed to extinguish small fires. They are hand held and designed for first attack fire fighting. They are often used by the Fire Service to extinguish small fires so as to minimize damage from fire hoses.

There are different types of fire extinguishers based on the extinguishing agent contained within them. There are different sizes are each designed for different size fires. The details of these differences is contained in another blog article called “what fire extinguisher do I need”.

This article will focus on the mechanics of how a fire extinguisher works.

Parts of a Fire Extinguisher

A fire extinguisher is only made up of a limited number of parts, they are:

  • Cylinder – this holds the stuff inside the fire extinguisher that will be sprayed onto the fire. Combined with the other components it forms a pressure cylinder so must be structurally sound.
  • Hose – this is what the stuff inside the extinguisher squirts out through
  • Head – this contains the handle used to carry the fire extinguisher and the top part of the handle is the trigger that when depressed opens a pathway from the dip tube to the hose
  • Syphon tube – this is a length of tube that travels down from the handle into the cylinder.
  • Fire extinguishing agent – the stuff inside the fire extinguishers, could be water, water and foaming agent mixture, dry powder, wet chemical or CO2 gas compressed into a liquid.
  • Propellant – this is what forces the extinguishing agent out of the fire extinguisher. It is often compressed nitrogen gas.

The extinguisher cylinder contains the extinguishing agent. This agent is then pressurised with a propellant such as nitrogen. The trigger is kept in a closed position holding the pressure within the cylinder.

When the trigger is pushed it opens a pathway from the dip tube to the hose. The pressure inside the cylinder on top of the extinguishing agent pushes the extinguishing agent out through the dip tube, through the fire extinguisher head and into the hose. From the hose it is sprayed onto the fire.

Can I Stop a Fire Extinguisher

This is a common questions we get asked, and the answer is yes.

When you release the trigger the pathway from the dip tube to the hose is closed again, this stops the flow of the extinguishing agent.

It should be noted however that this will only hold the pressure for a short time, say an hour. After this time the propellant will start to leak out through the head so that within 24 hours the fire extinguisher is flat – it has no propellant left to push the fire extinguishing agent out of the cylinder.

The following video shows a dry powder fire extinguisher being used on a fire. Once the fire has been extinguished our operator stops the fire extinguisher by releasing the trigger.

Video of fire extinguisher use

Fire Extinguisher Training

Understanding how a fire extinguisher works, how to use one and how to select the correct fire extinguisher for what is burning is some basic training that every person should have.

If you don’t know how to use a fire extinguisher then contact us and arrange some fire extinguisher training in your workplace, it could save your life, your property or the business you work for.

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