Next Back 1. Thus, a pyrophoric material is any material that ignites spontaneously or emits sparks when rubbed, scratched, or struck. In consideration of the many fire and explosion incidents that have occurred involving the handling, transportation, and shipment of many materials in such diversified physical forms as metal machine turnings, chips, pellets, derbies, massive metal, etc., any definition of pyrophoric material should not be restricted to finely divided powders. Old newspapers tend to turn yellow and brittle with age because of a relatively slow oxidation rate. Since paper is a carbohydrate, the yellowing is a result of the oxidation or slow burning of carbon and hydrogen.
Oil is another carbon compound that oxidizes in contact with air.
When oily rags are left to accumulate around the house, for example, the heat of oxidation may not be able to escape and after enough heat accumulates, the oily rags may be set aflame. This process is known as spontaneous combustion. Ignition is the process of initiating self-sustained combustion. In a chemical context, all elements that are not in their highest oxidation state can undergo oxidation. Some metals oxidize so slowly that the heat generated during oxidation is dissipated so that the ignition temperature is never reached.