In our fire safety training guide last month, we mentioned the fire triangle and promised to write a dedicated blog post explaining what it was. With various complicated fire safety procedures to learn (and remember), it is a nice change of pace to focus on basic combustion theory. The fire triangle (AKA combustion triangle or fire diamond) is a model used to explain the relationship between fuel, heat, and oxygen that starts and maintains a fire. This diagram is used in fire safety training to help people understand combustion theory. The more we understand about fire and how it works, the better we are at preventing and fighting it.
Image of the fire triangle
This diagram illustrates the relationship between oxygen, heat, and fuel required to create fire. The chemical reaction in the middle of the triangle is the fire and it is wholly dependent on the right combination of oxygen, fuel, and heat. If you only have oxygen and heat, or just fuel and heat, there will be no combustion reaction. If you understand the interdependence between these three fire components, then you’ll understand how to remove one and put out a fire.
Fire requires fuel in order to burn. There needs to be some kind of combustible material present, otherwise heat and oxygen alone will not cause a fire. There are many different combustible materials that could count as fuel in the fire triangle, such as: wood, paper, textiles, plastics, oil, many kinds of liquids, rubber, etc. The density, moisture content, size, and make-up of the fuel will affect how hot and fast the fire burns.
If a fire runs out of new fuel, then it will gradually burn out the fuel it has left. So, if you remove surrounding fuel or stop fire in its tracks, then it cannot spread any further. This is partly why our fire curtains and fire shutters work so effectively. They keep the fire at bay, blocking it from spreading on to new fuel sources. This buys you time to escape the premises and fight the fire before it spreads any further.
For a fire to be ignited in the first place, it needs heat. Any flammable material gives off flammable vapours which will be ignited if enough heat is introduced. Once the fire has started, a lot of heat is produced; this heat helps it grow as it heats up surrounding fuel, making it dry enough to ignite. As more and more heat is produced, the harder it is to fight the fire.
If you can keep the surrounding area cool and moist, then the fire’s heat will diminish and perhaps even smoulder out altogether. Water will also prevent the fire spreading further by making nearby fuel too moist to ignite.
Oxygen is an oxidising agent in the combustion chemical reaction, without it, the fire will extinguish. Combustion is the reaction between the fuel and the oxygen, which produces the heat, light and gases we associate with fire. The standard oxygen content of ambient air is around 21% and fire only needs 16% oxygen in the air in order to burn.
If you can remove oxygen from the environment, combustion will no longer be able to take place and the fire will go out. This is the principle behind fire blankets.
Removing one of the three ingredients (fuel, heat, oxygen) is at the heart of firefighting and fire prevention. Taking the time to understand the fire triangle could help you do the right thing in an emergency.