Pyrophoricity

A substance is pyrophoric (from Ancient Greek: πυροφόρος, pyrophoros, 'fire-bearing') if it ignites spontaneously in air at or below 54 °C (129 °F) (for gases) or within five minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylborane, as well as actinides. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air. They can be handled safely in atmospheres of argon or (with a few exceptions) nitrogen. Class D fire extinguishers are designated for use in fires involving metals but not pyrophoric materials in general. A related concept is hypergolicity, in which two compounds spontaneously ignite when mixed.