We all understand that many materials are inherently combustible on their own—and there are ways to make them burn better. One could add oxygen or fan the flames. Another way is increase the ratio of surface area to mass. This is why a piece of paper ignites easier than a piece of wood and diesel fuel burns better when atomized.
So, when solid combustible materials are ground into very small particles or dust, they burn even better. Even materials that we don't consider combustible will ignite and burn when ground up.
Combustible dust includes everything from sawdust to powdered iron. Combustible dusts mimic flammable liquids in that they can explode if properly suspended in air and can even float on water while burning and in some cases flow themselves.
Combustible dust has been a concern for the fire-protection community ever since the first recorded explosion of flour dust in Italy in 1785. In the middle of the 20th century, a rash of agricultural dust explosions culminated in the issuance of strict standards for that industry.
Despite this, the public—including most of the fire service—has remained relatively unfamiliar with the hazard.
Several recent combustible-dust explosions in industry that resulted in deaths and serious injuries to workers prompted an in-depth review by the U.S. Chemical Safety and Hazard Board (CSB). As the CSB was preparing to release its report, a severe dust explosion occurred at a sugar refinery in Georgia, killing eight and injuring dozens more, many critically. In light of this event, the CSB evaluation made it clear that they wanted to see more stringent combustible-dust regulations.
OSHA released its National Emphasis Program on Combustible Dust in 2007 and revised it in 2008. This effort, while just short of a formal OSHA dust regulation, has brought combustible-dust awareness to a new level both in industry and in the fire service.
To foster greater awareness of the hazard, OSHA's fire-protection experts drafted a guide for the fire service on dealing with fire emergencies involving combustible dust. The document is organized not as a prescriptive firefighting procedure, but rather as a description of the threat posed by combustible dust and available means to deal with it.
As the first several pages of the document clearly demonstrate, the fire service has sustained several casualties in handling these events over the years; this document will hopefully help prevent more.