Page 49 - Electrical Installation in Hazardous Area

28 Electrical installations in hazardous areas

Zone 2

Zone 2 is a zone in which an explosive gas, vapour, midair mixture (explo-
sive atmosphere) is not likely to occur in normal operation and, if it occurs,
it will only exist for a short time.
These definitions are given in BS 5345 part 22 and similar ones with the
same intended meaning, can be found in many documents. The current
reference to places where explosive atmosphere can occur specifies them as
zones but the term is no different in meaning to more historic references
to areas. Many countries have national area classification systems, either
historic or current, which are related to the now internationally recognized
system described above and as shown in Table 2.1.

Table 2.1 Relationships between national area classification systems

IEC / CENELEC / GB German French USA
(Note 1) (Note 2) (Note 3)

Zone 0 Special area in Ex order Division 1 Division 1
Zone 1 Normal area in Ex order Division 1 Division 1
Zone 2 Hazardous area not Division 2 Division 2
within Ex order
~~ ~ ~ ~
Notes:
1 Although not specifically naming them it is clear that Germany historically operated the
three-level risk system. The IEC/CENELEC/GB system is now used.
2 France historically has merged Zone 0 and 1 to form a single Division 1. It now uses the
IEC/CENELEC/GB system.
3 The USA has historically operated in the same way as France but has recently begun to use
the IEC/CENELEC/GB three-Zone system.

2.5.2 Dusts

In respect of dusts the situation is more fluid. The degree of formality is less
than that for gases and vapours and has only been effectively addressed in
the UK and internationally in the last 15-20 years. Within the UK, hazar-
dous areas caused by dusts are currently defined in a different way to those
caused by gases, vapours and mists.

Zone Z

Zone Z is a zone in which a combustible dust is, or may be, present as a
cloud during normal processing, handling or cleaning operations in suffi-
cient quantity result in an explosible concentration of combustible dust in
mixture with air (explosive atmosphere).