Hazardous area ratings for electrical controls

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Some industrial process environments carry a risk of fire or explosion due to the presence of flammable gas, vapour or dust; these are known as hazardous areas. There are documented international standards covering the specification of electrical equipment in these areas where the risk of accidental ignition is high, and different hazardous area ratings apply in different applications.

Here are three of the more common types of protection used for hazardous area electrical controls in Australia:

Ex d hazardous area ratings

An Ex d rating indicates the equipment is flameproof and can withstand an internal explosion. The enclosure design is capable of containing and cooling hot gases from an internal explosion before they reach the outside and cause an ignition hazard.

Ex ia/ib hazardous area ratings

An Ex ia or Ex ib rated control system is intrinsically safe, typically used for sensors. This means the power supply to the sensor does not have sufficient energy to generate a spark or ignition source to cause an explosion. This is achieved with the use of intrinsically safe barriers, which greatly reduce and limit the voltage and current supplied to the field instruments located in the hazardous area. The control panel is then mounted outside the hazardous area.

Ex p hazardous area ratings

Ex p is pressurised protection. This means the control panel is fitted with a pressurising system which pumps clean (non-hazardous) air or inert gas into the enclosure to maintain the internal pressure at a higher level than the surrounding atmosphere. The hazardous atmosphere is therefore prevented from coming into contact with potential ignition sources inside the control panel.

Hazardous area control panels tend to be very specialised and very expensive. In some cases, it’s a much simpler, easier and cost-effective option to locate the electrical control panel outside the hazardous area.