Fire Extinguishers work by removing one of the three elements of the Fire Triangle - usually heat or Oxygen.

How can they do this?

• By dousing a fire with water, heat can effectively be removed from a fire. This works by cooling the fuel to below its ignition temperature, and breaks the Fire Triangle.

• By smothering the fuel, you can stop the fuel receiving Oxygen and put out the fire.

• One thing that fire extinguishers cannot do is completely remove fuel from the fire, so extinguishers work by either getting rid of heat or Oxygen.

Inside the Extinguisher

An extinguisher holds a quantity of water or other fire suppressing material (such as dry powder). They work by forcing out their contents at high pressure when the lever is pressed.

How does this happen?

First you must pull out the metal safety pin that stops the handle being pushed accidentally. Next, you push the lever on the top of the extinguisher. This does two things. First, it opens up a valve in the siphon of the extinguisher and secondly it pushes a sharp pin into a cannister of compressed gas.

This gas escapes into the body of the extinguisher and forces the liquid or powder elsewhere. The only place this can go is up the siphon, where it is then propelled out of the hose and nozzle at high speed.

Have a go!

Have a go at using a fire extinguisher with the diagrams below. See what happens inside the case.

Water Extinguisher

Why do you think the gas forces the liquid to move?

CO2 (Carbon Dioxide) Extinguisher

In what ways is this extinguisher different to the water-based extinguisher?

Finally...

The final thing to do is to aim the nozzle at the fuel source, rather than the flames themselves..