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Lightning protection of hazardous areas
TSC-0912 - 09.10.12
Lightning protection of hazardous
areas in line with ATEX/IECEx
With hazardous areas at risk from the consequences
of direct and indirect lightning, a comprehensive
approach to lightning protection in line with
BS EN/IEC 62305 should be considered.
This should cover structural lightning protection,
earthing & equipotential bonding, and transient
overvoltage protection.
The zonal approach to lightning protection, as
established in BS EN/IEC 62305 (see page 272,
Lightning Protection Zones), is applicable for designing
an LPS suitable for hazardous areas, considering the
following points.
Structural lightning protection
For locations with potentially explosive atmospheres,
as defined by BS EN/IEC 62305:2011 the appropriate
Class of LPS required shall be dictated by the risk
assessment process in BS EN/IEC 62305-2.
An isolated LPS is required since the structure includes
combustible materials and/or presents a risk of
explosion, with minimum separation distances adhered
to between the LPS and structural metallic parts to
remove any risk of sparking.
Additionally, catenary conductors raised high above
the structure should be considered, where these are to
protect locations where combustibles are present, such
as gas/oil storage tanks.
Earthing & equipotential bonding
The earth termination system should meet the
requirements set out in BS EN/IEC 62305-3 - a single,
integrated earth termination system combining
lightning protection, power and telecommunications
systems. It should provide low electrical resistance (less
than 10 Ohms) and be appropriately bonded to ensure
no metallic part is at a different potential with respect
to another.
Where incoming or outgoing services cannot be
bonded directly to earth, these should be protected by
a suitable SPD.
Following the zonal approach in BS EN/IEC 62305,
services passing from LPZ 0 to LPZ 1 should be
protected against partial lightning currents using a
lightning current/equipotential bonding SPD (tested to
10/350 µs waveform), as well as transient overvoltages
(SPD tested to 8/20 µs waveform).
Electronic systems protection
Electrical and electronic equipment/systems need to be
protected against transient overvoltages, since damage
to components could lead to risk of sparks or fire.
Equipment/systems sited in a safe area which do not
contribute to safety in a potentially explosive
atmosphere can be protected against transient
overvoltages using appropriate standard SPDs, as
defined by BS EN/IEC 62305.
However, equipment/systems sited in potentially
explosive atmospheres (Zone 1, 2) or contributing to
safety within these atmospheres require an SPD
suitably tested and approved by ATEX.
All SPDs installed on site should form a coordinated
set to ensure protection levels are maintained and
effective throughout.
Protection of intrinsically safe (IS) circuits
Intrinsic Safety (IS) is a concept for protecting
hazardous areas from dangerous sparking, whereby
sparks from electrical equipment and circuitry are
prevented through the use of IS barriers.
These barriers limit the available electrical energy that
could cause an explosion to below ignition threshold.
IS Barriers however are not surge protectors but are
field instruments which are themselves at risk from
transient overvoltages. IS circuits therefore need to be
protected from transient overvoltages by a suitable
(ATEX approved) SPD.
Protection should be applied at the boundary between
the hazardous and non-hazardous area (see Figure 23),
with an isolated screen SPD installed within the
hazardous area (Zone 1, 2).
For more information on protecting hazardous area
installations from lightning, please contact us.
Instrumentation
Instrument
Earth
ESP SL30X/I ESP SL30X
Control cabinet
IP54
enclosure
Instrument
Earth
System
Earth
Field
earth
Open end cable screen
ZONE 0
Hazardous Area Zones 1, 2 Non-Hazardous Area
Isolated
coupling
IS
Barrier
ZONE 1
ZONE 2
Figure 23: The installed SPD
(here the ESP SL30X Series)
provides protection for the
instrumentation as well as
providing protection for
the IS Barrier.
The isolated screen version
(ESP SL30X/I) should be
used in Zone 1, 2.