8.1.6 Any electrical equipment which has to remain operational during a Major
Accident Event (e.g. rupture of a process vessel or pipe), whether or not installed
in a hazardous zone or location, is to be suitable for use in an explosive gas
atmosphere. Such equipment is to be of a type permitted within Zone 1 locations,
unless it is demonstrated that the equipment is appropriately protected against
potentially coming into contact with a flammable atmosphere by being located in an
enclosed safe area with appropriate mitigating measures. Mitigation methods
acceptable to LR for enclosed safe areas may include, but are not limited to:
installation of suitably sealed barriers and doors, sealing to a suitable level of
smoke and gas tightness; rated gas dampers; suitable gas detection located at
associated air intake ducts, main access doorways, located within the enclosure;
positive pressurisation. Other arrangements may also be submitted for consideration
by LR.
8.1.7 Flame-proof enclosures and intrinsically safe electrical apparatus, and
apparatus incorporating flame-proof or intrinsically safe components or otherwise
tested or certified for particular groups, with reference to the group(s) of gas(es)
that may be present, is to be selected with reference to IEC/TR 60079-20:
Electrical apparatus for explosive gas atmospheres – Part 20: Data for flammable
gases and vapours, relating to the use of electrical apparatus.
8.1.8 The electrical apparatus shall be so selected that its maximum surface
temperature as indicated by its temperature class, or otherwise documented, will not
reach the auto-ignition temperature of any gas or vapour, or mixture of gases or
vapour, which can be present. The ambient temperature range for which the apparatus
is certified is to be taken to be minus 20°C to 40°C, unless otherwise stated, and
account is to be taken of this when assessing the suitability of the equipment for
the auto-ignition temperature of the gases encountered.
8.1.9 Cables are not permitted to pass through locations classified as Zone 0,
and are permitted to enter such locations only where required for the operation of
any electrical equipment located therein.
8.1.10 Cables are to be either:
- Mineral insulated with copper sheath; or
- Armoured or braided, except where:
- The cable is associated with an intrinsically safe
circuit; or
- The cable does not pass into or through any location
classified as Zone 1, and is routed or protected so as to present
only a low risk of mechanical damage; or
- A cable of flexible construction is demanded by
operational requirements, and its construction, routing and means of
support are such as to present only a low risk of mechanical damage;
or
- The cable is installed within a conduit system meeting
the relevant requirements of IEC60079-14.
8.1.11 Metal coverings of cables installed in hazardous zones or spaces are to
be effectively earthed at both ends, at least, except where otherwise permitted by
IEC 60079-14.
8.1.12 Cables associated with intrinsically safe circuits are to be used only
for such circuits. They are to be physically separated from cables associated with
non-intrinsically safe circuits, e.g. neither installed in the same protective
casing nor secured by the same fixing clip, except where alternative arrangements
are permitted by IEC 60079-14.
8.1.13 No more than one intrinsically safe circuit should be run in any
multicore cable unless:
- No circuit is required to be of category ‘ia’, and either:
- The cable is run or protected so as to present little
risk of its suffering mechanical damage; or
- Each intrinsically safe circuit is contained within an
earthed metallic screen; or
- It can be shown that no combination of faults between the
intrinsically safe circuits within the cable can lead to an unsafe
condition.
8.1.14 Cabling, wiring, and connections within enclosures containing more than
one intrinsically safe circuit, or containing both intrinsically safe and other
circuits, are to be arranged in accordance with the relevant requirements of
IEC60079-11 and IEC60079-14 so as to minimise the risk of inadvertent
interconnections between different circuits.