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ATEX and Explosive Atmospheres


What is an explosive atmosphere?

Explosive atmospheres can be caused by flammable gases, mists or vapours or by combustible dusts. If there is enough of the substance, mixed with air, then all it needs is a source of ignition to cause an explosion. Explosions can cause loss of life, serious injuries as well as significant damage. Preventing the release of such substances as well as preventing sources of ignition are the two main ways of reducing the risk of explosion.

What is DSEAR?

The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) places a duty on employers to eliminate or control the risks from explosive atmospheres in the workplace. Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. These could include, but are not limited to, places of work that produce or use flammable gases and vapours such as paint spraying, or work places that handle fine organic dusts such as flour, grain or sawdust.

DSEAR defines an explosive atmosphere as a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapours, mist or dust, in which, after ignition has occurred, combustion spreads to the entire unburned mixture. Atmospheric conditions are often referred to as ambient temperatures and pressures, that is to say temperatures of –20°C to 40°C and pressures of 0.8 to 1.1 bar.

Employers must provide workers who work in zoned areas with appropriate clothing that does not create the risk of an electrostatic discharge igniting the explosive atmosphere, e.g. anti-static footwear. The clothing provided depends on the level of risk identified in the risk assessment.

What is ATEX?

ATEX is the name commonly given to the two European Directives for controlling explosive atmospheres:

1) Directive 99/92/EC (also known as 'ATEX 137' or the 'ATEX Workplace Directive') on minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres. The text of the Directive and the supporting EU produced guidelines are available on the EU-website. For more information on how the requirements of the Directive have been put into effect in Great Britain see the information in the section Explosive atmospheres in the workplace below.

2) Directive 2014/34/EU (also known as 'ATEX 95' or 'the ATEX Equipment Directive') on the approximation of the laws of Members States concerning equipment and protective systems intended for use in potentially explosive atmospheres. The text of the Directive and EU produced supporting guidelines are available on the EU website. For more information on how the requirements of the Directive have been put into effect in Great Britain see the section on Equipment and protective systems intended for use in explosive atmospheres.

Classification of ATEX Zones

Employers must classify areas where hazardous explosive atmospheres may occur into zones. The classification given to a particular zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring and its persistence if it does. Schedule 2 of DSEAR contains descriptions of the various classifications of zones for gases and vapours and for dusts.

For gases, vapours and mists the zone classifications are:

Zone 0 - A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is present continuously or for long periods or frequently.

Zone 1 - A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally.

Zone 2 - A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

For dusts the zone classifications are:

Zone 20 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently.

Zone 21 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally.

Zone 22 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

Equipment categories and zones

The hazardous area zone classification and corresponding equipment categories are:

Zone 0 or zone 20 - category 1 equipment

Zone 1 or zone 21 - category 2 equipment

Zone 2 or zone 22 - category 3 equipment

PPE for ATEX Environments

Selecting the correct Personal Protective Equipment (PPE) for use in explosive (Ex) environments is problematic as PPE is excluded from the equipment categories of the ATEX Equipment Directive (2014/34/EU). However PPE manufacturers, in conjunction with independent specialist test houses, are able to assess their garments against the relevant standards (IEC TS 60079-32-1:2013, IEC 60079-32-2:2013 and TGRS 727:2016 ) for use in ATEX environments and identify the zones in which they are safe to be used.


More information on ATEX environments can be found on the Health & Safety Executive website: https://www.hse.gov.uk/fireandexplosion/atex.htm#whatatex.

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