Components of the Fire Tetrahedron

The fire tetrahedron is a four-sided figure representing the four components needed to sustain combustion. Knowing and understanding this model is crucial to people such as firefighters, who extinguish fires, and outdoorsmen and survivalists, who must be able ignite fires under adverse conditions. For years, the figure was referred to as the "fire triangle," until the fourth element, a chain reaction, was added.

Air

• The first component of the fire tetrahedron is air. The atmosphere is made up of roughly 21 percent oxygen, the combustible component of air that supports fire ignition. Though oxygen itself is not flammable, it is required for combustion to occur.

Fuel

• Fuel is the part of the fire tetrahedron with the broadest variable content -- many natural and manmade substances burn. This variable is important to firefighters, because the type of material burning often dictates the approach that must be taken to extinguish it. Fuel may take the form of a solid, liquid or gas.

Heat

• The heat component of the tetrahedron can be supplied by any type of heat generation. It can be direct flame impingement, mechanically generated heat or heat from an arcing electrical source. Heat may be transferred to fuel by radiation, direct contact or convection. This component is typically attacked by firefighters with the application of cooling water to extinguish the fire.

Chemical Chain Reaction

• The most recently added segment of the tetrahedron is a chemical chain reaction, which represents the exact mixture of the other three components, in the right concentrations, to promote and sustain combustion or ignition. Without the process of chemical reaction, the other three components cannot cause ignition or sustain combustion.