Selection of Equipment

The selection of electrical apparatus for explosive gas atmosphere is based on the general principle that the likelihood of the simultaneous present of a hazardous atmosphere and a source of ignition is reduced to an acceptable low level.

When the electrical apparatus does not have an internal release of flammable material, the classification of the hazardous area surrounding the electrical equipment decide the selection of an adequate type protection.

When the electrical apparatus has an internal release of flammable material, the actual hazard is a combination of the external and internal hazards and both must be taken into account when selecting an adequate type of protection.

The selected electrical apparatus shall be adequately protected against corrosive and solvent agents, and against water ingress and thermal and mechanical stresses as determined by the environmental conditions. These construction requirements should ensure that the protection against explosion is not reduced when the apparatus is used in the specified conditions of service.

Particular consideration shall be given to the location of apparatus which incorporates aluminium or light alloys in construction of its enclosure. These have been outlined in IS: 5571-1979* reference to which should be made (see also B of IS:2148-1981)

As electrical apparatus for flammable gas atmospheres require special safety maintenance after they are installed, the selection of electrical apparatus shall be made with full considerations to the facility and frequency of inspection and maintenance, preparation for spares and repairing materials and the extent of allowable interruption of power supply during maintenance work.

It is advisable that the selection of electrical apparatus be made after full considerations have been given not only to the initial cost of installation but also to the expected life and expenses for operation and maintenance of the apparatus.

Unless otherwise specified for a particular equipment, the guidance provided in Table 2 shall be followed in the selection of equipment for hazardous areas. However, any equipment which in the opinion of the authorised inspector affords a degree of safety not less than that afforded by the equipment specified may be accepted as an alternative.

The necessity for equipment with flameproof enclosures any sometimes be eliminated by the adoption of special design, such as pressurised equipment.