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The fire triangle

The Fire Triangle and The Three Elements of Fire

Fire safety is a vast topic with seemingly endless areas for an employer to consider, from fire risk assessments to appointing fire marshals, organising fire trainings and ensuring all the fire safety equipment is in working order. Yet, how fire works and how to extinguish a fire are things you’ve probably learnt a long time ago when you were preparing for your GCSEs – it all comes down to the principle of the fire triangle. Knowing what the three elements of the fire triangle are and how they interact with each other lies at the foundation of your fire safety training. Therefore, we thought we’d revisit the fire triangle in a bit more detail below. 

What is a Fire Triangle?

The fire triangle, also known as the combustion triangle, is a model designed to provide a simple, visual way to remember the main factors needed for the chemical reaction we call fire (yes, fire is a chemical reaction, not a thing) to take place. Each side of the fire triangle represents one of the three elements that must all be present for a fire to occur: fuel, heat and oxygen. 

The principle of the fire triangle teaches us that if you remove any one of the three elements, the fire will stop burning. Therefore, this method is the key to finding various ways to extinguish a fire. Alternatively, you can also implement your knowledge of the fire triangle if you need to start and sustain a fire (useful skill when camping, that’s for sure!). 

As any training starts from the basics, a fire safety training will often refer to the fire triangle and its principles to explain the dynamics of fire and what we can do to contain it shall it occur. From how fire extinguishers work to why we need fire blankets – it can all be traced back to the fire triangle.  

The three elements of the fire triangle 

As we said, the three sides of the triangle or the three essential components of fire are fuel, heat and oxygen. Now, let’s look at each one of them and why it is important. 

Fuel 

For a fire to exist, something needs to burn. This “something” can be any combustible material and it is referred to as fuel. Different materials, such as grease, paper, wood, plastic, rubber, gases and liquids have different moisture content and they burn at a different speed. The type of fuel, combined with the size or quantity of the material that’s burning can affect how quickly the fire spreads.

Interestingly, the classification of fire in the UK is entirely based on the source of fuel for the fire. The various types of fire extinguishers available contain different active materials that work best with specific fire classes. 

Going back to the fire triangle theory, fuel relates to heat in the way that different materials burn at different temperature, so some will require more and others less heat to ignite. 

Heat

Any fuel source will be flammable and will release flammable vapours. Those, combined with oxyge and when exposed to enough heat, lead to combustion. That’s not the only reason why heat is such an important element of the fire triangle though. Once the fire has started, the heat helps it spread by eliminating the moisture from the fuel that surrounds it. It preheats the fuel nearby, opening a clear and easy path for the fire to spread.

When firefighters are trying to put a wildfire under control, for example, they tend to apply water, foam or dirt directly on the burning fuel, in order to reduce the heat sufficiently to prevent the fire from spreading any further. 

Oxygen

OK, with heat and fuel covered, all that’s left to complete the fire triangle is oxygen. For heat to cause fuel to burn, the fuel has to be mixed with a sufficient amount of oxidising agent. In most cases, this is simply air, as the air that we breathe contains about 21% oxygen and fire needs approximately 16% to burn. Therefore, we can say that oxygen is the binding agent between the three elements of the fire triangle. 

Oxygen atoms combine with hydrogen and carbon to produce CO2 (carbon dioxide) and water. This process is called oxidation. When oxidation produces heat faster than it can be released, the combustion which starts the chemical reaction of fire occurs. Once the fire is ignited, the process of oxidation continues and it happens so fast that it produces enough energy (heat) to sustain and spread the fire until all sources of fuel have been consumed by the flames. 

Breaking the fire triangle  

The fire triangle is extremely important in firefighting. Remove one of the three elements of the fire triangle and you will be able to stop a fire:

  • Not enough oxygen and the fire will suffocate
  • No fuel means there’s nothing to burn anymore
  • Not enough heat prevents the fire from sustaining itself, so it goes out

Breaking the fire triangle is at the root of extinguishing any fire. Fire extinguishers, for example, whether they are dry, foam or water-based, are designed to cool down the fire to the point where there isn’t enough heat to sustain it. Whereas fire blankets, target the oxygen part of the equation and are used to suffocate the flames. 

The fire triangle theory informs fire prevention, as well. Fire safety best practices dictate that flammable materials are a fire hazard and must be stored safely. Also, easily-flammable materials, such as paper, plastic or textile should be kept away from heat sources to avoid combustion. In other words, the basis of preventing a fire is found in keeping sources of fuel as far away from ignition materials and heat sources as possible. 


We hope that brushing up on your school knowledge of the fire triangle and the three elements of fire has helped you understand fires, fire prevention and fire extinguishing better. If you have any more fire safety questions, feel free to get in touch with the FMC Fire team.

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