Fires start when a flammable and/or a combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat to sustain a chain reaction. This is commonly called the fire tetrahedron. Fire cannot exist without all of these elements being in place.

Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of an oxidizer and fuel. Fire can be extinguished by removing any one of the elements of the fire tetrahedron.