Spontaneous Heating

Spontaneous Heating and Pyrophoricity

DOE-HDBK-1081-94

PRINCIPLES OF COMBUSTION

Spontaneous Heating

Pyrophoricity

Hypergolic reactions.

Spontaneous Heating

Spontaneous heating is the slow oxidation of an element or compound which causes

the bulk temperature of the element or compound to rise without the addition of an

external heat source. Spontaneous heating may be the result of direct oxidation of

hydrocarbons (for example, oils, coal, and solvents) or it may occur because of the

action of microorganisms in organic materials. A more detailed discussion on

spontaneous heating is included in the next section.

Pyrophoricity

Pyrophoric substances ignite instantly upon exposure to air (atmospheric oxygen). A

pyrophoric substance may be a solid, liquid, or gas. Most materials are not

pyrophoric unless they are in a very finely divided state. Although there are some

pyrophoric liquids and gases, most pyrophoric materials are metals. Information

concerning specific pyrophoric liquids, gases, nonmetals, and metals are provided in

later sections. It should be noted that pyrophoricity is a special case of a hypergolic

reaction because the oxidizing agent is restricted to atmospheric oxygen. Hypergolic

reactions are described in the following paragraph.

Hypergolic Reactions

Where pyrophoricity is concerned only with the spontaneous combustion of a

material when exposed to air (atmospheric oxygen), a hypergolic reaction describes a

material's ability to spontaneously ignite or explode upon contact with any oxidizing

agent. The remainder of this document will be concerned only with spontaneous

heating and pyrophoricity.

Note: Many of the fuels identified in this handbook react violently or explosively

with the oxidizing agents identified in Appendix B and NFPA 43A because

of hypergolic reactions.

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Pyrophoricity