Page 76 - Electrical Installation in Hazardous Area

52 Electrical installations in hazardous areas

Zone 0

Zone 1

Zone 2

Fig. 3.1 Identification of zones

much more objective than those created by the generalized method and
can offer a sigruficant saving in both time &d money without endangering
security.
The nomenclature used to describe the various grades of hazardous area
are shown in Fig. 3.1.

3.3.2 Releases from pipe joints

There are five principal methods of joining two pipes: namely welding;
gasketting; use of compression (olive) glands; use of '0' rings; and screwing.
Welded joints effectively make the two sections of pipe one continuous
section and if properly carried out and checked, are not considered to consti-
tute a source of release as far as area classification is concerned. This does
not mean that welds never rupture but the frequency of such ruptures is
so low that it can be neglected as far as area classification is concerned.
None of the other types of joint is considered to be sufficiently unreli-
able to release in normal operation (excepting where human intervention is
likely - see special circumstances) if properly chosen and executed and pipe
joints in general are not considered as producing any primary grade sources
of release and generally constitute Zone 2. They are, however, considered
eminently capable of producing secondary grade sources of release and the
mechanism for this is different in each case. A screwed joint is likely to
produce leakage up its threads and relatively small quantities of released
material at relatively low velocities. In this case wind dispersion is the
norm. A typical compression joint will produce a small-line release up its
olive and, like the screwed joint release, velocities are likely to be rela-
tively low due to the construction of the joint. An '0' ring seal will only