Professional Articles

Fire & Explosion Protection

How to avoid the "Big Bang" of Bulk Handling

While flammable gases and vapours represent a clear explosion hazard, it is less well appreciated that dusts and powders of combustible solids can also give rise to explosions. Dust explosions are characterised by rapid burning, more properly termed a deflagration, which will lead to a dramatic pressure rise in confined spaces with potentially devastating results. Dust explosions can occur at many stages during the production, storage and handling of combustible materials such as wood, paper, plastics, metals, coal and corn, as well as foodstuffs like sugar and flour. Accordingly, plant at risk includes silos, hoppers, bins, elevators, conveyors, mixers, grinders, mills, driers, ovens, filters, cyclones and dust collectors. Essentially, there are two approaches to dealing with a potential dust explosion hazard: prevention or protection.

1) Explosion Prevention
In simple terms, the three essential ingredients necessary for an explosion are a dust cloud of combustible material, oxygen, and a source of ignition. Accordingly, to remove the risk of explosion, one of these elements must be eliminated. Possible preventative measures include maintaining the concentration of a combustible dust below its lower flammability limit; for example, by adding moisture to prevent dust clouds forming. This method is often not practical and can be unreliable. Alternatively, through purging with an inert gas, the amount of oxygen in an enclosed volume can be reduced to below the level required to support combustion. Purging systems may also be used together with spark detectors to instantly extinguish sources of ignition.
Although dependent on the actual processes and materials involved, the use of inert gas purging can often be judged impractical for reasons of cost, particularly for large-scale plant.
Explosion Protection
As well as aiming to prevent an explosion, protective measures can also be taken to guard against the effects of an explosion. One way is to design the container, plus any connections, to be strong enough to resist the maximum pressure that an explosion may generate, with explosion isolation valves used to. . .