Figure 1. Fire triangle.

PRINCIPLES OF COMBUSTION

DOE-HDBK-1081-94

Spontaneous Heating and Pyrophoricity

Combustion

Heat Source

Figure 1. Fire triangle.

relative hazards and classifications of oxidizing agents may be found in Appendix B

and in NFPA 43A, Code for the Storage of Liquid and Solid Oxidizing Materials.

Fuel

A fuel is the substance that reacts with the oxidizing agent during combustion. Fuels

can be solids, liquids, gases, and even metals. Familiar fuels are coal, firewood, and

gasoline. For the purpose of this document, the discussion of fuels will be limited to

those that are known to combust spontaneously.

Heat Source

Normally, a heat source such as a flame of spark is required to ignite a mixture of a

fuel and oxidizing agent. That is, heat must be added or the fuel and oxidizing agent

will not react. The reactions that are the subject of this document are special

instances where no heat source is required to ignite the fuel. These fuels react so

readily with oxygen that a heat source is not required for ignition. Ignition for these

fuels occurs as a result of spontaneous heating or pyrophoricity.

Spontaneous Combustion

Spontaneous combustion is the ignition of a combustible material caused by the accumulation

of heat from oxidation reactions. Fires started by spontaneous combustion are caused by the

following mechanisms:

Pyrophoricity

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