Powdered and thinly sliced Plutonium is a pyrophoric substance .
A pyrophoric substance ( from Greek πυροφόρος , pyrophoros , `` fire-bearing '' ) ignites spontaneously in air at or below 55 °C ( 130 °F ) .SEMI , standard F6-92 , Guide for Secondary Containment of Hazardous Gas Piping Systems , as cited by ChemiCool.com Examples are iron sulfide and many reactive metals including plutonium and uranium , when powdered or thinly sliced .
Pyrophoricity