Page 49 - Gi flipbook May 2018

gas leaks dispersed in housings (HSE
report RR630). The HSL work used FIGURE 3: Example of outdoor 16bar installation with moderate distance between 16bar
the concept contained within PRS section and 2bar metering section allowing an area where NE is possible
BS EN 60079-10-1 that small gas
releases (even continuous) can give
rise to zones of ‘negligible extent’
(designated by the appropriate zone
number followed by NE; e.g., zone 2
NE), which do not result in a need for
any special precautions regarding
allowable equipment. This concept did
not exist in IGE/SR/25 Edition 1. Any
potential release gave rise to a zoned
area, resulting in zones even around
low pressure pipework in the open air.
Thus, in some cases, hazardous area
zones as determined by SR/25 Edition
2 will be less onerous and have a
smaller extent than if determined by
earlier versions. To keep in step with
IGEM/SR/25, Edition 2 of IGEM/
GM/7B now also includes the
modified calculation method which, in
some cases, includes the negligible
extent concept.
So what is NE? It is the special case
where a number of requirements are
met resulting in the distance ‘X’ to be
so small that it effectively zero.

To achieve a classification of NE the
following conditions have to be present:
• MOP (meter operating pressures)
not to exceed 10bar
• Potential leak source not confined electricity meter/electrical apparatus, an additional zone 2 area near the
and not congested (which also and not less than 25mm away from a ceiling, but this is no longer required.
means the installation housing will 240V electricity supply and distribution Also, in some situations (typically low
have a volume greater than 10m3) cables. If this is not possible, a non- pressures and/or moderate distances
• Ventilation “more than adequate” combustible partition made of an between the installation and the
• Maintenance procedures in place to electrically insulating material needs to walls) there is no longer a hazardous
ensure no change in ventilation be placed between them. area at the outlet of ventilation grills
A hazardous area zone classified as A zone of negligible extent is not in the walls. However, hazardous areas
NE requires no action to control the same as a safe area. In particular, it at the outlets can now be slightly
sources of ignition within it. Thus, may be that a zone of negligible more onerous in other circumstances
items of electrical equipment that are extent becomes more onerous if (typically if the interior is not zone 2/
not necessary certificated for use in a ventilation is reduced during non-hazardous).
hazardous area, may be installed in modifications to buildings and In installations that have
areas designated NE. This could be housings. If this occurs and ventilation unconfined and uncongested areas,
particularly useful because it means cannot be improved, the NE status having high levels of ventilation and
that non-certificated, electrically has to be revoked. with gas pressures up to 10bar, it
operated, gas safety shut-off valves Hazardous area zones in and may be possible to assign a zone 2
may be used to isolate the gas supply around meter houses are now NE designation.
in the case of emergency. In addition, treated slightly differently. As with previous editions, lower
uncertificated motors and lighting levels of ventilation are likely to result
may also be installed. SUMMARY in the entire housing being classified
However, in the specific case of gas As with previous editions, well as zone 1, or so low that more
meters the following is still required: ventilated housings that are only ventilation would be required (to
the gas meter, and any equipment slightly larger than the meter avoid zone 0). This is still determined
electrically connected to it, needs to be installation will be zone 2 throughout. by the use of the coloured charts. ■
suitable for use in a zone 2 area or to New to the latest edition is the
be suitable for use in the zone in which situation where the housing is large ■ Buy these standards and more by
it is to be used, whichever is the more enough that a significant distance is visiting shop.igem.org.uk. Want to
onerous requirement. A gas meter and present between the installation’s access our technical standards online?
its associated fittings needs to be fitted zone and the walls or ceiling. The Email technical@igem.org.uk to find
not less than 150mm from a 240V previous edition would have indicated out more about our flexible access.

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