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The main uses of type i are for instrumentation, telecommunication
devices, and similar equipment. It is well
known, inexpensive and readily available, but special design
and installation rules need to be followed. Two categories
of intrinsic safety are available. Category ia, which provides
the highest degree of explosion protection available,
ensures safety under two faults. Category ib ensures safety
under a single fault.
Design and Assembly Stage Inspections
Inspections of the installation need to be conducted throughout
the stages of its life cycle in accordance with IEC 60079.
Design Stage. Inspections should start at the design stage
by means of design review because mistakes identified at this
stage are almost always easier and less costly to rectify.
Factory Assembly Stage. When factory assembly of skid
mounted equipment is completed and after the factory has
conducted its own inspection, an inspection done by our
team is advantageous. Whilst this does not present a
comprehensive picture of the final installation, it can often
show mistakes, and corrective measures can be planned
during shipping to the construction site.
Final Construction Inspection
A final construction inspection, along with possible rectification
of any mistake, is mandatory before explosive fluid can
be introduced to the plant. The objective of the inspections
is to verify the installation complies with the applicable code
of practice. In the case of IEC 60079, this requires ensuring
that the appropriate components were selected and that
they were installed correctly. Discovery of an installation
mistake at this stage may lead to project time delay.
Verification of Explosion Protection. The first part of
any inspection work is to make sure that the equipment is
explosion protected in conformance with IEC 60079. Whilst
it may be labelled with compliance information, a visual check
of labelling is not enough. It is necessary to obtain a copy
of the original certificate of conformance and use this as
the inspection start-point. The inspector should check
the certificate validity, cross check the certificate against
equipment labels and verify the installation method complies
with the requirements as stated in the certificate.
Use of Check Sheets. It is good practice to record the
outcome of the inspection using check-sheets. The minimum
points to be considered are peculiar to each type of protection,
as summarised in the box below. In addition, the check-sheets
should contain a record of each item’s certificate number.
The methods used are straightforward; however, each item of
plant has its own peculiarities and some of these are often
overlooked. The importance of this matter dictates that an
expert lead the inspection at this stage.
Minimum Check Points for Installation of
Three Common Types of Explosion Protection
Flame proof enclosure installation (type d).
• The EEx d label is correct.
• The cover has been fitted correctly.
• The serial number on the cover and base unit match (if applicable).
• Cable entries are by means of EEx d certified gland (special rule
for enclosure > 2 litre size), EEx d certified plug or stopper, EEx d
certified cable bushing/termination or sealed conduit.
• All conduits are wrench-tight with at least five full threads engaged.
• Any reducer used is certified.
Increased safety installation (type e).
• The EEx e label is correct.
• Any breather is of an approved type (see certificate schedule).
• Any breather is installed in correct face.
• Any unused cable hole is sealed properly.
• All terminal screws are tightened, including spare terminals.
• Insulation is within 1 mm (0.04 inch) of the terminal throat.
• If mineral-insulated copper clad (MICC) cable is used, an EEx e
gland is applied.
• The glanding technique maintains IP54 (washers may be used).
• There is no more than one conductor per clamp, unless a special
joint is used.
• Terminal creepages and clearances are within specifications.
• Terminal temperatures will not exceed the temperature of the
component certificate.
• All terminals and accessories have been installed per the
manufacturer’s recommendations.
• Terminal ratings do not exceed their label.
Intrinsic safety installation (type i).
• The barrier is installed in safe area (may be in zone 1 area if inside
EEx d enclosure).
• The EEx marking is correct on the barrier and device, if applicable.
• Wiring has been segregated.
• Enclosures are protected to at least IP20.
• Earthing has been connected in accordance with the EEx certificate.
• Wiring properties are consistent with EEx certification.
• If a colour code is applied, the colour used is light blue.
Related Web Sites:
Additional information about the use of electrical equipment in
hazardous areas is publicly available at numerous certification body
and specialist manufacturer’s Web sites, including:
• http://www.baseefa.com/ • http://www.mtl-inst.com/
• http://www.ptb.de/index_en.html • http://www.stahl.de/en/start.html
Stewart Gray is a principal engineer with more than 30 years’ project engineering experience, including 10 in a construction-based consulting role. With his detailed knowledge
of the subjects of safety and inspections, he has identified a variety of hazardous area installation errors on behalf of several clients before their plants went into service.
In most cases, these errors were attributable to incorrect material selection or inappropriate installation techniques.
PB Network #68 / August 2008 12