Back to Basics with the Fire Triangle

Trying to understand the seemingly endless list of fire safety regulations can be a complex and confusing task. Whether you are attempting to identify the different types of fire extinguishers and their appropriate uses or are learning about the benefits of a fire blanket, it is vital to remember that the various rules are there for a reason and this ultimately relates to the fire triangle.

In this article, we’re going to explore why understanding the fire triangle and how its different elements work together is essential in order to ensure effective fire safety policies and practices at your commercial premises.

What is the fire triangle?

The fire triangle (also sometimes referred to as the combustion triangle) is a simple model for understanding the chemical reaction that must take place to start and sustain a fire. It is composed of three elements – fuel, heat and oxygen – all of which must be present for a fire to thrive. 

It also demonstrates the interdependence of these elements in creating and sustaining a fire and shows us how removing any one of these elements would prevent or extinguish the fire.

The fire triangle is often used as a basic form of fire safety training and looks at the dynamics of fire itself. By looking at and understanding this in more detail, it is much easier to grasp the need for, and details of, fundamental fire regulations. 

So let’s get back to basics…

What are the three elements of fire?

• Fuel

In order for a fire to start, there must be a material to burn – and this is referred to as the fuel. Fuel is any kind of combustible material, which can include paper, oils, wood, gases, fabrics, liquids, plastics and rubber. The fuel for a fire is usually characterised by its moisture content, size, shape and quantity and this will determine how easily the fuel will burn and at what temperature.

• Heat

In addition to a fuel source, heat must be present in order for ignition to take place. All flammable materials give off flammable vapours which, when heat is present, combust. Heat is also responsible for the spread and maintenance of fire as it removes the moisture from nearby fuel, warming the surrounding area and pre-heating any fuel in its path, enabling it to travel and develop with greater ease.

• Oxygen

As well as fuel and heat, fires also need oxygen to stay alight. Ambient air is made up of approximately 21% oxygen and, as most fires only require at least 16% oxygen to burn, it acts as the oxidising agent in the chemical reaction. This means that when the fuel burns, it reacts with the oxygen to release heat and generate combustion.

How to extinguish the three elements of fire

To stop a fire, one of the three elements of the fire triangle must be removed. So, if a fire runs out of fuel, it will smoulder out; if you can cool a fire down, it will lose heat and go out; and if the oxygen is removed, it will suffocate. 

Therefore, attempts at both fighting and also preventing a fire are based upon these principles. So which of the common fire extinguishers can be used to remove which of the fire triangle elements?

• Water extinguishers remove the heat by using water to cool down the fire.
• Foam extinguishers remove the heat and the oxygen by using foam to both cool down and smother the fire.
• CO2 extinguishers displace the oxygen the fire needs, because the heavier CO2 gas forces it elsewhere. The CO2 is also extremely cold when emitted, so these extinguishers also remove the heat from the fire.
• Dry powder extinguishers remove the oxygen by smothering the fire with the powder.
• Wet chemical extinguishers remove the oxygen by smothering the fire with a fine spray, which also cools the fire to remove the heat.

What is the fire tetrahedron?

Recent analysis has developed the triangle of fire further to come up with the concept of the ‘fire tetrahedron’.

Unlike a triangle, a tetrahedron – otherwise known as a ‘triangular pyramid’ – is made up of four triangular bases, which all connect to each other. What this means in the context of a fire is that there are now four elements that need to be present in order for a fire to start and continue.

So what is the extra element that has been added to the fire triangle to make it the fire tetrahedron?

What are the different elements in the fire tetrahedron?

The concept of the fire tetrahedron recognises that something else – beyond the mere presence of fuel, heat and oxygen – needs to happen for a fire to start and be sustained. That extra element is the chemical reaction that occurs between the other three elements, thus causing a fire to continue to burn once it has started. 

Without that chemical reaction, no fire would be possible. Removing any of those three elements will still put out a fire, but recognising the role of the reaction between the three is key to our understanding of how a fire works.

As things stand, there are no commonly available extinguishers that can put out a fire solely by interrupting the chemical reaction. Halon fire extinguishers used to be able to do that and were recognised as being an effective universal extinguishing agent on aircraft. However, their use has been identified as causing significant damage to the ozone layer and they have been banned for a number of years. 

Here at Scutum South East, we bring decades’ worth of experience and knowledge to fire safety. We are proud to offer customers across South East England the very latest tools for fast and effective fire prevention, fire detection and fire control, including professional fire risk assessments, state-of-the-art fire alarm systems and a wide range of fire extinguishers. 

Find out more and start the process of improving fire safety at your commercial premises by getting in touch with our experienced team of advisors today.