What Is Inside A Fire Extinguisher?

We all have seen fire extinguishers around. They are a crucial piece of equipment in every home and workplace.

Fire extinguishers come in a range of different sizes but also for different uses. The type of fire extinguisher you need depends on the kind of fire that you want to put out.

You will need a fire extinguisher with different contents, but what is really inside a fire extinguisher? Is it always the white foam you see in the movies?

Read on to find out!

What Is Inside A Fire Extinguisher?

What’s Inside A Fire Extinguisher?

While the exterior of the traditional red fire extinguisher has changed very little over the years, the chemical inside the canister has become ever more sophisticated.

If you were to open a fire extinguisher, you would find the extinguishing agent. This is either water, liquid foam, or another chemical.

The exact extinguishing agent you need to use depends on the fire you want to extinguish. For this reason, there are different types of fire extinguishers.

Types Of Fire Extinguishers

In order to find out what’s inside your fire extinguisher, it’s worthwhile looking at the different classifications of fire extinguishers.

The main two classifications are by type of fire and the extinguishing agent inside the fire extinguisher.

Classification By Type Of Fire

Fire safety experts have identified different types of fires that can occur in a household, business or anywhere else.

This categorization by fire type is indicated through letters on the fire extinguisher and the can’s color.

Paper, Cloth, Or Wood

Fires that are fed by or started with paper, cloth or wooden materials can be extinguished with a green fire extinguisher which has the letter A.

Flammable Liquids

This is our most popular red fire extinguisher which has the letter B. It can put out combustible liquids such as paint, gasoline, and oil.

Electrical Equipment

This type of extinguisher is not seen very often but the blue class C fire extinguisher is used for any electrical fires.

Flammable Metals

This orange fire extinguisher class D is typically found on construction sites or anywhere else where work with flammable metals may cause a fire.

Cooking Fats And Oils

Typically found in restaurant kitchens, the category K black fire extinguisher is ideal for putting out fires that started with cooking oils and fat.

Classification By Extinguishing Agent

Dry Powder Extinguishers

This classification is commonly used when you are going out to buy a fire extinguisher for your home.

It is also based on the classification of different fire types.

Water Extinguishers

Water extinguishers are the old, traditional fire extinguishers. They contain mainly water which is fired at the fire at high pressure.

Water extinguishers are very basic fire extinguishers. They only block the fire’s access to oxygen by adding water.

However, if you use the water on flammable liquids, then the fire may explode, causing severe damage to property and people.

For this reason, it is essential that you use a water extinguisher only for fires that started on wood, paper, or cloth.

Dry Powder Extinguishers

Just as the name suggests, this fire extinguisher contains a dry powder with compressed nitrogen which is used as a propellant to force the powder out with high pressure.

The dry powder inside this type of fire extinguisher is designed to coat fuels and absorb any heat.

It stops any flammable gases or liquids from spreading, and it also blocks oxygen access for the fire leading it to go out.

The most commonly used powder for these extinguishers is monoammonium phosphate. Other extinguishers of this kind also contain potassium bicarbonate or baking soda.
However, the latter two are less effective when it comes to extinguishing fires than the monoammonium phosphate.

Foam Extinguishers

Foam extinguishers are by far the most popular fire extinguishers across the world. They contain an extinguishing chemical mix of water, foam and nitrogen.

The large foam carpet that is propelled out of the canister smothers a fire quickly and effectively.

It cuts off the air supply to the fire and also absorbs any residual heat.

While this type of fire extinguisher also contains water, the combination with a concentrated foaming solution makes this extinguishing agent much more effective.

Liquid water is difficult to compress into a small canister, so combining it with the foam allows manufacturers to put an extinguishing agent inside which can spread across the fire in a thin carpet.

Just like all other fire extinguishers, foam extinguishers are very easy to use.

When you open the nozzle, the foaming solution and the water combine, and they create a much bigger volume than fits inside the can. 

You can also find foam fire extinguishers under the name AFFF, which stands for aqueous film-forming foam.

This sounds very technical but it simply means that the fire extinguisher contains a solution of water and foam which can spread a film over flammables.

Carbon Dioxide (CO2) Extinguishers

CO2 extinguishers are very similar to foam extinguishers. Instead of a foam-water mix, they contain a combination of gaseous and liquid carbon dioxide.

It’s important to point out here that this carbon dioxide is non-flammable, so it will not aid the fire.

Typically, carbon dioxide is kept in canisters as a gas. In order to liquify carbon dioxide, it needs to be stored at extremely high pressure.

When you use a CO2 fire extinguisher, the carbon dioxide gas and liquid is released at the same time, spreading out over the fire as a thin film.

This extinguishing agent puts out the fire by cutting off the oxygen supply. It also turns the liquid carbon dioxide back into a gas.

This leads to the removal of a lot of residual heat, reducing the temperature of the fire so that it eventually dies down.


The real magic of a fire extinguisher is its extinguishing agent inside. This agent determines how quickly your fire is put out, and how much further damage you can prevent.