What is a fire triangle?

The fire triangle's three sides illustrate the three elements of fire: heat, fuel and oxidization

A simplified cousin to the fire tetrahedron, the fire triangle is a model for conveying the components of a fire. The fire triangle’s three sides illustrate the three elements of fire: heat, fuel and oxidization.

The three elements must be combined in the right proportions for a fire to occur. If any of the three elements are removed, the fire is extinguished.

The first element in the fire triangle is heat, which is perhaps the most essential of fire elements. A fire cannot ignite unless it has a certain amount of heat, and it cannot grow without heat.

The fire triangle’s three sides represent heat, fuel and oxidization.
The fire triangle’s three sides represent heat, fuel and oxidization.

One of the first things firefighters do to extinguish a fire is to apply a cooling agent – usually water. Another cooling agent is a chemical fire retardant, such as the ones used in fire extinguishers.

Another method of diffusing heat from a fire is to scrape the embers from the fire source, such as wood embers on a burning building. Firefighters will also turn off the electricity in a burning building to remove a source of heat.

The second element in the fire triangle is fuel. A fire needs a fuel source in order to burn. The fuel source can be anything that is flammable, such as wood, paper, fabric, or chemicals. Once the fuel element of the fire triangle is removed, the fire will go out.

If a fire is allowed to burn without any attempt to extinguish it, as in the case of a controlled burn conducted by the Forest Service, it will extinguish on its own when it is consumed all of the fuel.

The final element of the fire triangle is oxygen, which is also an essential component of fire. A fire needs oxygen to start and continue. That is why one recommendation for extinguishing a small fire is to smother it with a non-flammable blanket, sand or dirt

A decrease in the concentration of oxygen retards the combustion process. In large fires where firefighters are called in, decreasing the amount of oxygen is not usually an option because there is no effective way to make that happen in an extended area. 

An alternative to the fire triangle model is the fire tetrahedron. The fire tetrahedron adds another element to the fire, which is chemical reaction. Fires involving metals such as titanium, lithium and magnesium have a chemical reaction that requires a different approach for firefighters.

This is called a Class D fire and the application of water will exacerbate the combustion. Because of the chain reaction caused by the metals in Class D fires, firefighters must use a different approach involving the introduction of inert agents like sand to smother it.

Learning about the fire triangle is a good way to understand the elements of fire and is an essential component of firefighting education.

This article, originally published on December 21, 2011, has been updated

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