Basic Forest Fire Suppression Course - Online Lessons


2.3 The Fire Triangle

Fire is the simultaneous release of heat, light and flame, generated by the combustion of flammable material. Three elements must be present in order for combustion to take place, by removing one of the elements the process will not occur.

The three elements are:

Air or Oxygen: Fire requires Oxygen as a “breathing source” and as long as this element is present, fire will continue to burn. The movement of Air (wind) will affect fire in the following ways: determine rate of spread, direction and intensity levels

Heat: Heat is required by fuels in order for the combustion process to develop. Not all fuels will react the same to a distinct heat source; therefore, the amount of heat applied and duration of time will then determine combustion (small dry fuels require a low amount of heat for shorter periods of time).

Fuels: Fire requires fuel as a “food source”and cannot burn if this element is not present. Once ignition has occurred, certain fuel characteristics will determine how that fuel will behave.

Breaking the Fire Triangle

There are various methods to remove one of the elements from the fire triangle such as: applying water to remove heat; smothering with mineral soil to remove oxygen; or constructing a fuel break ahead of the fire to remove fuels. Frequently firefighters will use natural fuel breaks such as roads, creeks, swamps, lakes or other areas that will not burn.

Breaking the Fire Triangle cycle has limitations and crews must be made aware:

If not enough water is applied to the heat source, the fire may rekindle itself after evaporation.

Applying mineral soil may not remove all the oxygen supply; small amounts of oxygen can be sufficient to support combustion allowing the fire to spread underneath the mineral soil.

Fuel breaks (hose line) will not likely work on high intensity surface fires or during spotting conditions (burning embers carried away from the fire).