Dust explosions occur when combustible dusts build up in the air and combust rapidly, causing a strong pressure wave to form. They are a deadly hazard in a variety of workplaces, from grain silos to plastics factories. A dust explosion requires several factors to be present at once. These include:
- A combustible dust at the right concentration level
- An enclosed space
- An ignition source
Sometimes these factors are combined into a graphic known as the “Dust Explosion Pentagon.” The component in this graphic called “dispersion” is also known as concentration. If a concentration of dust is too low, there is not enough of it present to fuel an explosion. If the concentration is too high, there is not enough oxygen to support combustion.
While some combustible dusts are easy to guess—wood and paper dust, for example—others aren’t, such as aluminum dust. Combustible dusts become more dangerous as particulates become finer. These dusts feature a high ratio of surface area to volume, adding to their combustibility. When these dusts combine with oxygen within a range of concentrations, a dust explosion is possible.
In these conditions, all that is needed for an explosion is an ignition source. This source can be anything from a cigarette to a spark to an overheated wheel bearing. Under the right conditions, some combustible dusts can self-ignite as a result of static that builds up as particulates rub against one another. The ignition causes the dust to combust quickly—a process called deflagration that creates a wave of high air pressure. Sometimes this explosion can stir dust that has settled in the space, creating a cloud of new dust—a fuel source for an enormous secondary explosion. A dust explosion can blow out walls in a facility and kill or injure workers within the space or nearby.