How Does a Fire Extinguisher Work?

Whenever there’s a fire at home or at work, the first thing that most people do is look for the fire extinguisher. It’s almost an impulse reaction and everybody knows to look for a fire extinguisher because this is the tool that could save lives. If you have one, Test and tag it. If you don’t have one, purchase one and keep it accessible in your home. You may have seen a fire extinguisher in action, you may have even used one, but do you know how it actually works?

The Fire Triangle

If you can think back to your school days (this is further away for some than for others!), you may remember learning about the fire triangle in science lessons. Essentially, the triangle shows the three things that a fire needs to keep burning:

  • Air
  • Heat
  • Fuel

When all three are available, a fire will keep burning. To put out a fire, we need to remove one of these conditions. We either need to remove the air, the heat, or the fuel. If you think of a candle, this is a type of fire. Therefore, we need to eliminate one element of the fire triangle to extinguish the flame. For those with a candle snuffer, you’re eliminating the air. With no air, the fire cannot survive and the flame dies.

Alternatively, those who blow candles out are pushing the flame away from the fuel source (the wick and wax). If you blow gently, the flame stays and sometimes even grows as we add air to the equation. However, it soon disappears with a forceful blow because we’re pushing the small flame away from the fuel source.

With a pan fire or a fire in the home, it’s a larger scale but the techniques that fire-fighters use are designed to do the same thing. Whether it’s switching off the hob, placing a water-soaked towel onto the flame, or using a fire extinguisher, the reason these techniques are popular is that they attempt to remove either the air, heat, or fuel from a fire.

Types of Fire Extinguisher

With this in mind, you’re in the right position to learn about the different types of fire extinguisher.

Dry Powder

With this type, nitrogen acts as the propellant and the tank contains dry powder. Rather than any old powder, it’s normally a special formula designed to not only absorb the heat but also coat the fuel and take away this source. At the same time, it also blocks oxygen and suffocates the flame – therefore, it acts on more than one side of the fire triangle at once.

Common powders include:

  • Alkali salts sodium bicarbonate
  • Monoammonium phosphate
  • Potassium bicarbonate


With a water fire extinguisher, the propellent is either carbon dioxide or nitrogen. Either way, the goal is to remove the heat source from the fire thus extinguishing the flames. When used correctly, water can also remove the supply of oxygen.

Carbon Dioxide

Normally, these will combine a gaseous carbon dioxide and a liquid form. How does carbon dioxide go from a gas to a liquid? Well, it occurs under high pressure. After pushing down the lever, the gas expands, and we see a white jet escape the tank. Just as we’ve seen before, carbon dioxide extinguishers attack the triangle from two sides: heat and oxygen. With the former, it actually reverts back to a gas and sucks in the heat.


Finally, foam combines with water to smother the flame and cut off the oxygen supply. Thanks to the water in the tank, it should also cool the flame and remove the heat source.

Although different in nature, all four types of fire extinguisher aim to remove at least one side of the fire triangle, and this is how a fire extinguisher works!

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