Page 96 - Electrical Installation in Hazardous Area

72 Electrical installations in hazardous areas

Fig. 3.11 Water sealed gas storage tank. A = 3m, B = 10 m, C = 7m

diaphragm or water seal of the pressure relief valve being considered as
partial. This is not so in the case of abnormal situations where full passage
through the pressure relief valve, or a sigrufrcant part of the water seal, is
considered.

3.4.4 Road and rail tanks for flammable liquids

Liquids are regularly transported by road or rail. In general, the areas
through which they pass in transit are not classified because the time for
which they dwell in those places is limited which, coupled with the fact that
any leakage during transit is abnormal, means that the likelihood of a given
area being contaminated with an explosive atmosphere is so low that area
classification is not relevant. While the above is generally true, care must
be taken in this regard because in areas where transport tanks dwell for
sigruficant times, or where a large number of such tanks are stationary for
a considerable time, area classification may be relevant. In general, the divi-
sion between where area classification is or is not necessary is taken to be
the division between places such as general car parks - where tanks may
reside overnight together with other transporters - and locations specifi-
cally designated for tank parking such as the locality of loading stations on
airports, etc.