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A catastrophic dust explosion occurred at a sugar refinery in 2008, resulting in 14 fatalities and major facility destruction. While dust explosions in the food industry are nothing new, as facilities have increased in size, the consequences of incidents have also grown.
Many foodstuffs and food ingredients, including grain, sugar, artificial sweeteners, starch, flavors and cellulosic additives, will burn slowly or with difficulty as a layer on a surface, but can explode if dispersed as a cloud. In fact the vast majority of powders in the food industry can form explosible dust clouds if the particle size is small and moisture content is low. The concentration of dust in the cloud is important.
The concentration of an explosible dust cloud resembles a dense fog. Although such concentrations are not normally expected to be present within processing buildings, explosible dust clouds are regularly formed inside the material handling/processing equipment, i.e., when bins are being filled, powders are being transferred, or dust is being collected in a dust collector.
When Conditions are Right
The particle size of the dust is a property which influences the explosibility of the dust cloud. Powders include pellets (sizes greater than about 2 mm), granules (approximate sizes between 2 and 0.4 mm), and dust particles (sizes less than about 0.4 mm). The finer the particles the greater the surface area per unit mass and thus the more explosible a given dust is likely to be.
When the cloud is composed of a series of particle sizes ranging from fine to coarse, the fines play a prominent part in the ignition and the explosion propagation. The presence of dusts should therefore be anticipated in the process stream, regardless of the starting particle size of the material. For example, friable materials such as sugar will create dust in transfer operations.
The moisture...