When combustible dust ignites, there are often two explosions known as primary and secondary explosions. The primary dust explosion is the first explosion. It occurs when there is a dust suspension in a confined space (such as a container, room, or piece of equipment) that is ignited and explodes.
The primary explosion will shake other dust that has accumulated (for example, from dusty ledges or sills, or from damaged dust containment systems such as LEV). When this dust becomes airborne, because of the pressure wave or air turbulence created by the primary explosion, it can also ignite - with the ignition source often the primary explosion products of combustion. This is a secondary dust explosion. This secondary dust explosion is often more destructive than the primary one. Industries at risk include those dealing with pharmaceuticals, chemicals, foodstuffs, agricultural, polymeric materials, coal, and wood.
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