In order for a fire to start and proliferate, there has to be four components all available at the same time. This is known as the fire tetrahedron. Fires can be prevented or suppressed by controlling or removing one or more of the sides of the tetrahedron. A combustion reaction can be characterized by the following four components: Fuel, Heat, Oxidizing agent (usually atmospheric oxygen), and an uninhibited chemical chain reaction.

A fuel is any substance that can undergo combustion. It is generally organic and can be a solid, liquid, or gas. However, fuels can only be consumed in the vapor state. Therefore, combustion of liquid fuels and most solid fuels takes place above the fuel surface in a region of vapors created by heating the fuel surface. Gaseous fuels, however, do not require vaporization or pyrolysis before combustion can occur and only proper mixture with an oxidizer and an ignition source are needed.

Heat can come from ambient conditions, from an ignition source, or from exposure to an existing fire. Heat produces fuel vapors, causes ignition, and promotes fire growth and flame spread by maintaining a continuous cycle of fuel production and ignition. The heat energy must be above the minimum level necessary to release fuel vapors and cause ignition.

The oxidizing agent is generally oxygen found in the earth’s atmosphere, but can be a chemical oxidizer as well, such as ammonium nitrate fertilizer. The fuel to air ratio has an optimum ratio at which combustion will be most efficient.

The oxidation reaction, or burning, must produce enough heat to maintain burning. Combustion is a complex set of chemical reactions that results in the rapid oxidation of a fuel, producing heat, light, and a variety of chemical by-products. If this complex chain reaction is uninhibited, a fire will sustain itself and most likely spread.

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