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NOTE: This is an unformatted excerpt from our online fire protection training library.

Fire Behavior- Introduction to Fire Suppression

Fire Chemistry

Combustion

The "fire triangle" is a familiar means of describing how combustion takes place.

Combustion cannot occur unless three elements are present: oxygen, heat, and fuel. These three elements are often shown as three sides of the fire triangle. Fires start when a flammable and/or combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat to sustain a chain reaction.

Oxygen, heat, and a fuel source must all be present for a fire to exist. These elements become locked together in a chain reaction to create fire. The chain reaction exists as a dynamically changing event. Because a chain reaction is a fourth essential element, these four items are sometimes called the "fire tetrahedron"A tetrahedron is made up of four triangles: three for the "walls" and one for the "base," similar to a pyramid..

Once chain reaction happens and ignition occurs, a fire can then sustain itself by the further release of heat energy in the process of combustion and thus 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.

Combustion takes place on the surface of an object. For an object to burn, it has to be heated to the point that it can release burning vapors. Generally speaking, materials that are organic in nature will release vapors at some point. When exposed to a heat source they "break down," so to speak. This is one of the elements of fire development.

Ignition on the surface of a material can be from a heat source adjacent to the object or as the result of a chemical reaction within the object or material itself. A fire cannot start, however, without an ignition source.

NOTE: This is an unformatted excerpt from our online fire protection training library.

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