What Is Combustible Dust?

The National Fire Protection Agency (NFPA) defines combustible dust as “any finely divided solid material that is 420 microns or smaller in diameter and presents a fire or explosion hazard when dispersed and ignited in air.” Any combustible material can burn rapidly when in a finely divided form. If such a dust is suspended in air in the right concentration, under certain conditions, it can become explosible. Left uncontrolled, dusts may migrate from the point of production/release, increasing the portion of the facility subjected to combustible dust fire and explosion hazards. Even materials that do not burn in larger pieces, given the proper conditions, can be explosible in dust form. Typical metalworking materials that can form combustible dusts include titanium, aluminum, magnesium and iron. The amount of dust required to produce a dangerous dust cloud can be surprisingly small — a dust layer as little as 1/32 inch thick can be of concern in some situations.