The EU ATEX Directive 1999/92/EC (ATEX 137) regarding the minimum requirements to protect the health and safety of workers
potentially at risk from explosive atmospheres came into European law in January 2000. In the UK, the ATEX 137 Directive has
been implemented as part of the Dangerous Substances and Explosive Atmospheres Regulations (DSEARs), which were issued in
December 2002.
The directive requires that specific risks arising from explosive atmospheres are assessed and that employers classify places
where explosive atmospheres may arise and select appropriate work equipment to use in these areas. The directive applies fully
to workplaces put into operation for the first time or modified after 30 June 2003. Existing workplaces have until 30 June
2006 to fully comply with the directive. For new workplaces in operation after 30 June 2003, explosion safety must be verified
by a person competent in the field of explosion protection with appropriate experience and professional training.
To assess explosion risks, places where explosive atmospheres may arise must first be identified. When such atmospheres occur
in sufficient quantities to require special precautions to protect the health and safety of workers, they must be considered
as hazardous areas and zoned according to the likelihood and frequency of explosive atmospheres occurring.
Table1. ATEX zone definitions.
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When defining hazardous areas it is important to be realistic about zone extents and to avoid unnecessary blanket zoning,
particularly when the zones in question are Zones 0 or 20, or Zones 1 or 21, which indicate that explosive atmospheres are
present either frequently or occasionally in normal operation (Table 1). Such concentrations (e.g., typically >20000 ppm for
gases/vapours or >50 g/m3 for dusts) are several orders of magnitude greater than occupational exposure limits permitted under the Control of Substances
Hazardous to Health (COSHH) regulations. In the majority of cases, zones in the general workplace should be no worse than
Zone 2 or 22.
Categorized equipment
Appropriately categorized equipment should normally be selected for use in areas in accordance with EU ATEX Directive 94/9/EC
(ATEX 100), as implemented in the UK by The Equipment and Protective Systems Intended for Use in Explosive Atmospheres Regulations
(EPS), unless the risk assessment finds otherwise.
The Heath and Safety Executive (HSE) approved code of practice and guidance for DSEARs states that the phrase "unless the
risk assessment finds otherwise" is intended to introduce a degree of flexibility to allow equipment of a higher or lower
category than normally required for the zone in question to be used where:
- equipment is temporarily taken into a zoned area and alternative effective precautions are in place to control the risk
- workers can be excluded from the hazardous area and will not be at risk from ignition of an explosive atmosphere
- equipment of the required category is not available, but a lower category can be used in combination with other protective
measures to achieve the purposes.
One misconception that has arisen in equipment selection is that the zone inside the equipment is relevant when determining
the appropriate ATEX category of the equipment. This is not the case. The fact that a potentially explosive atmosphere may
be present within the equipment is not relevant when selecting equipment, unless devices with an autonomous function are installed
within the equipment (e.g., level probes). Instead, it is the zone in the workplace that is relevant when identifying the
category of equipment that must be installed and, in the majority of cases, this means that Category 3 equipment will suffice.
However, consideration must still be given to internal ignition sources as legislation also requires that equipment is safe
to handle in explosive atmospheres.
Another misconception is that existing equipment in hazardous areas must be replaced by ATEX-categorized equipment. However,
existing equipment does not need to be replaced or upgraded if it complies with legislation in force before 1 July 2003 and
is in fact considered safe. Equipment purchased before 1 July 2003 and held in stores can be installed in hazardous areas
after 1 July 2003 as long as it meets the same criteria. Similarly, second hand equipment put onto the market before 1 July
2003 does not need to comply with EPS if it is safe to use in hazardous areas.
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