What dusts are explosible?
The dust of many combustible materials in everyday use, such as coal, wood, grain, sugar, certain metals and synthetic organic chemicals, when dispersed in air to form a cloud, can explode if an ignition source is present. When a mass of solid combustible material i.e a log of wood is heated it burns away slowly, layer by layer, owing to the limited surface area exposed to the oxygen of the air. The result is quite different if the same mass of material is ground to a fine powder and suspended in air as a dust cloud. The surface area of material exposed is much greater, if ignition occurs the whole of the material may burn very rapidly. If the dust cloud is contained i.e. within an extraction unit, the rapid release of heat causes the pressure to rise to levels which most industrial plant cannot withstand. In addition, explosion may be caused in the dust of combustible and non-combustible materials due to the build-up of static electricity in the particles. Such explosions have occurre
