The Fire Triangle
The Fire Triangle is a simple way of understanding the factors of fire. Each side of the triangle represents one of the three ingredients needed to have a fire – oxygen, heat, and fuel – demonstrating the interdependence of these ingredients in creating and sustaining fire. When there is not enough heat generated to sustain the process, when the fuel is exhausted, removed, or isolated, or when oxygen supply is limited, then a side of the triangle is broken and the fire will die.
A heat source is responsible for the initial ignition of fire, and heat is also needed to maintain the fire and permit it to spread. Heat allows fire to spread by removing the moisture from nearby fuel, warming surrounding air, and preheating the fuel in its path, enabling it to travel with greater ease.
Fuel is any kind of combustible material, and is characterized by its moisture content (how wet the fuel is), size and shape, quantity, and the arrangement in which it is spread over the landscape. The moisture content determines how easily that fuel will burn.
Air contains about 21% oxygen, and most fires require at least 16% oxygen content to burn. Oxygen supports the chemical processes that occur during a wildland fire. When fuel burns, it reacts with oxygen from the surrounding air releasing heat and generating combustion products (i.e. gases, smoke,embers). This process is known as oxidation.