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Lightning protection of hazardous areas
TSC-0912 - 09.10.12
Lightning protection of
hazardous areas to ATEX/IECEx
IECEx
Many industries, such as petrochemical, oil & gas
and pharmaceutical, face the ongoing challenge
of protecting people and property from the risk
presented by potentially explosive atmospheres.
These atmospheres create hazardous areas, where
flammable gases, powders, or dusts have the potential
to mix with air at a ratio which would result in an
explosion if ignited by a spark or other source of
ignition (static charge, chemical reaction etc).
Clearly, lightning presents a significant threat to
potentially explosive atmospheres, both through a
direct strike and the risk of partial lightning currents
entering the hazardous area via incoming/outgoing
metallic services.
The employer or plant operator has responsibility for
ensuring safety against potentially explosive
atmospheres, and should therefore reference the
relevant standards and directives - BS EN/IEC 62305 for
lightning protection and ATEX (IECEx outside the EU)
for protecting potentially explosive atmospheres -
when establishing the requirement for lightning
protection on site.
ATEX directives
Two ATEX directives have been published with the aim
to protect employees, the public and the environment
from accidents owing to explosive atmospheres.
They require employers to eliminate or control risks
from hazardous areas, to classify areas where explosive
atmospheres may occur, and to ensure products
suitable for use in those areas are applied.
From July 2006, all existing and new sites where
hazardous areas are present must be ATEX compliant.
ATEX 137, Directive 1999/92/EC
This directive covers health & safety of employees at
risk from explosive atmospheres.
It requires employers to take necessary steps to prevent
formation of explosive atmospheres, to avoid ignition
in explosive atmospheres where they cannot be fully
prevented, and to limit the effects of a explosion
should such an event occur.
It further classifies the places where explosive
atmospheres may occur into a number of zones
(see Table 12).
ATEX Article 100A, Directive 94/9/EC
This directive covers equipment and protective systems
for potentially explosive atmospheres and the health &
safety requirements to which they must conform.
It applies both to equipment and systems used in
potentially explosive atmospheres, and those sited
outside these atmospheres which contribute to the
level of safety in the hazardous area.
Equipment is categorised in line with the protection
level offered against the risk of producing a spark or
source of ignition in a potentially explosive
atmosphere. Categories include:
Applicable zone and equipment group for
gases/vapours (II) or dusts (III)
Protection level, per zone, according to risk from
gases/vapours (Ga; Gb; Gc) or dusts (Da; Db; Dc)
Form of protection (flameproof enclosure - Exd;
Increased Safety - Exe; Intrinsically Safe - Exi etc)
Level of protection to gas/vapour group or dust
group (IIA; IIB; IIC)
Restrictions in product usage (equipment without
restriction; equipment with special condition - X;
component - U)
Temperature Class (T1-T6, spanning temperatures
from 450 ºC down to 85 ºC)
Products classified as intrinsically safe (IS) are further
categorised according to their applicable zone (see
Table 13 below).
Products are tested to ensure compliance with the
requirements of ATEX, with approved products marked
accordingly based on the classification system, and
including their ATEX certification number.
Expectation of potentially explosive Zone Reference
atmosphere/hazard arising Gas Dust
Hazard is continuously present, for long periods or
frequently (> 1000 hours per year)
Zone 0 Zone 20
Hazard is likely to arise occasionally during normal
operation (10-1000 hours per year)
Zone 1 Zone 21
Hazard is not likely to arise during normal operation,
or is of short duration only (< 10 hours per year)
Zone 2 Zone 22
No hazard is present SAFE AREA
Table 12: Zonal classification of hazardous areas
Symbol Suitable for Category Standard
Ex ia Zones 0, 1, 2, 20, 21 & 22 1 EN 50020
Ex ib Zones 1, 2, 21 & 22 2 EN 50039
Table 13: Intrinsically Safe product classification