Electrical Equipment in Hazardous Areas

22-Mar-2010

Electrical equipment in hazardous areas

In Electrical engineering, a hazardous location is defined as a place where concentrations of flammable gases, vapors, or dusts may occur. Electrical equipment that must be installed in such locations is especially designed and tested to ensure it does not start an explosion, due to arcing contacts or high surface temperature of equipment.

For example a household light switch may emit a small, harmless visible spark when switching; in an ordinary atmosphere this arc is of no concern, but if a flammable vapor was present, the arc might start an explosion. Electrical equipment intended for use in a chemical factory or refinery is designed either not to produce any sparks, or else to safely contain the arc and make sure it cannot ignite any explosive gases, vapors or dusts that might be present around the equipment.

Many strategies exist for safety in electrical installations. The simplest strategy is to minimize the amount of electrical equipment installed in a hazardous area, either by keeping the equipment out of the area altogether or by making the area less hazardous by process improvements or ventilation with clean air. Intrinsic safety is a practice where apparatus is designed with low power levels and low stored energy, so that a fault is unlikely to set off an explosion. Equipment enclosures can be pressurized with clean air, and interlocked so that the equipment is disconnected if the air supply fails. Or, arc-producing elements of the equipment can be isolated from the surrounding atmosphere by encapsulation, immersion in oil, sand, or by sturdy enclosures that prevent propagation of an internal explosion to the surrounding atmosphere.

As in most fields of electrotechnology, different countries have approached the standardization and testing of equipment for hazardous areas in different ways. As world trade becomes more important in distribution of electrical products, international standards are slowly converging so that a wider range of acceptable techniques can be approved by national regulatory agencies.

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