The fire triangle consists of heat, fuel, and an oxidizer. Fuel is the starting point, and without it, there is no substance to burn. To extinguish a fire, at least one element must be removed. Fire extinguishers deprive the fire of oxygen by suffocating it with monoammonium phosphate.
The fire triangle is an illustrative model used to show what elements are needed to start and sustain a fire. The three elements that make up the triangle are heat, fuel, and an oxidizer (usually oxygen). While this model is a bit simplistic at times, it helps explain, in an easy-to-understand way, how most fires are started and sustained.
The starting point of any fire, and one corner of the triangle, is the fuel source. Without fuel, there is no substance to burn. Almost any substance on earth can serve as a fuel source when exposed to sufficient heat, but the most common are Class A and B fuels, such as wood, paper, gasoline, and propane. For a fuel source to catch fire, two things must be present: enough oxygen to ignite and sustain the fire, and a specific ignition source or high enough ambient temperature to ignite the fuel.
Once a fire has started, as long as enough fuel and oxygen are present, the heat generated by the fuel source continues the combustion process in place of the original ignition source. The self-sustaining nature of fire is what makes it so dangerous and difficult to put out. When a fire gets too out of control, it is sometimes no longer possible to put it out and must be left to burn on its own. Due to the sheer scale of bushfires, forest firefighters often have to fell huge tracts of trees and remove large amounts of undergrowth to keep the fire from spreading, depending on whether the fire burns itself out.
To extinguish a blazing fire, at least one of the elements of the fire triangle must be removed. There are different methods used to put out different types of fires, but the most common way is to deprive the fire of oxygen with the use of a fire extinguisher. Most fire extinguishers spray a dry chemical, monoammonium phosphate, which dissolves upon contact with the fuel source and cuts off the oxygen by suffocating it. The usually orange and red flames seen are not the source of a fire’s heat and only a byproduct, often causing confusion when someone is trying to put out a fire. Many people make the mistake of targeting the visible flames and not the actual fuel source when trying to put out a fire.
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