|Hazardous atmosphere is
the atmosphere where any flammable gas or vapour in a concentration capable
of ignition occurs. Any area, where during normal operations a hazardous
atmosphere is likely to occur in sufficient quantity to constitute a hazard
had to be treated in a special manner from the point of the design of electrical
|Many liquids, gases and
vapours which in industry are generated, processed, handled and stored
are combustible. When ignited these may burn readily and with considerable
explosive force when mixed with air in the appropriate proportions. With
regard to electrical installations, essential ignition sources include
arcs, sparks or hot surfaces produced either in normal operation or under
specified fault conditions.
|This Part of the Code is
intended to provide guidelines for electrical installations and equipment
in locations where a hazardous atmosphere is likely to be present with
a view to maximising electrical safely. The scope of this Part therefore
includes installations in hazardous areas such as petroleum refineries
and petrochemical and chemical industries. The requirements laid down herein
are in addition to those-specified in part 4 of the Code. Some examples
of industrial locations which require application of the guidelines in
this Part are given on Page No.8.
|It is recognised that when
electrical equipment is to be installed in or near a hazardous area, it
is frequently possible, by taking care in the layout of the installation,
to locate much of the equipment in less hazardous or non-hazardous areas
and thus reduce the amount of special equipment required.
NOTE:- Hazardous areas can be limited in extent by construction measures, that is, walls or dams. Ventilation or application of protective gas will reduce the probability of the present of explosive gas atmosphere so that areas of greater hazard can be transformed to areas of lesser hazard or to non-hazardous areas.
|This Part includes generalised
statements and recommendations on matters on which there are diverse opinions.
It is, therefore, important that sound engineering judgement should be
exercised while applying these guidelines.
|While preparing this Part,
several standards for electrical equipment for explosive atmosphere have
been referred to. These standards are listed in Appendix A. Some of these
standards deal with particular construction techniques, others with aspects
of standardisation which are relevant to more than one technique.
|As distinct from the hazardous areas in buildings on the surface, environmental conditions in mines demand special consideration. This part of the Code does not include provisions for installations in underground mines.|