Primer on spontaneous heating and pyrophoricity

Abstract

The purpose of this Primer is to provide operations and maintenance personnel with the information necessary to identify and prevent potential spontaneous combustion hazards. Throughout the history of industry and the DOE Complex, fires caused by spontaneously heating and pyrophoric materials have occurred, sometimes causing personal injury and significant damage to facilities.

By its very nature, spontaneous heating and pyrophoricity are among the most insidious types of fire hazards. Many times there is no outward evidence of the potential for fires caused by these phenomena. An understanding of the principles of spontaneous heating and pyrophoricity is necessary for instituting fire prevention measures.

Combustion

Combustion (burning, or fire) falls into a class of chemical reactions called oxidation. Oxidation may be defined as the chemical combination of a substance with oxygen or, more generally, the removal of electrons from an atom or molecule. Oxidation reactions are almost always exothermic, or release heat. Many materials react with oxygen to some degree. However, the rates of reactions differ between materials.

The difference between slow and rapid oxidation reactions is that the latter occurs so rapidly that heat is generated faster than it is dissipated, causing the material being oxidized (fuel) to reach its ignition temperature. Once the ignition temperature of a material is reached, it will continue to burn until the fuel or oxygen is consumed.

The heat release during combustion is usually accompanied by a visible flame. However, some materials, such a charcoal, smolder rather than produce a flame.