Many dusts that are generated, processed, handled and stored are combustible. When ignited they can burn rapidly and with considerable explosive force if mixed with air in the appropriate proportions. When electrical apparatus is used in locations where combustible materials are present, it is important that suitable precautions are taken. In electrical apparatus, potential ignition sources include electrical arcs and sparks, hot surfaces and frictional sparks. To reduce the likelihood of ignition of the external explosive atmosphere, all such electrical apparatus should be adequately protected.
Areas where dust, flyings and fibres in air occur in dangerous quantities are classified as hazardous and are divided into three zones according to the level of risk.
Generally, electrical safety is ensured by the implementation of one of two considerations, i.e. that electrical apparatus be located where reasonably practicable outside hazardous areas, and that electrical apparatus be designed, installed and maintained in accordance with measures recommended for the area in which the apparatus is located.
Combustible dust can be ignited by electrical apparatus in several ways:
By surfaces of the apparatus that are above the minimum ignition temperature of the dust concerned. The temperature at which a type of dust ignites is a function of the properties of the dust, whether the dust is in a cloud or layer, the thickness of the layer and the geometry of the heat source.
By arcing or sparking of electrical parts such as switches, contacts, commutators, brushes, or the like.
By discharge of an accumulated electrostatic charge.
By radiated energy (e.g. electromagnetic radiation).
By mechanical sparking or frictional sparking or heating associated with the apparatus.
Compliance with this standard will only provide the required level of safety if the electrical apparatus is operated wit...
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