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Table 12:
Zonal classification of hazardous areas
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
Technical reference
Lightning protection of hazardous areas to ATEX/IECEx
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, flash
over 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
- IEC/BS EN 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 and 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 and 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 categorized 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)
–– lLevel 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
categorized according to their applicable zone (see Table 13).
Products are tested to ensure compliance with the
requirements of ATEX, with approved products marked
accordingly based on the classification system, including their
ATEX certification number.
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.
Table 13:
Intrinsically Safe product classification
Symbol
Suitable for zones
Category
Standard
Ex ia
0, 1, 2, 20, 21 & 22
1
IEC 60079-11
Ex ib
1, 2, 21 & 22
2
IEC 60079-11