Zoning of hazardous areas

Within the EU, a hazardous zone is normally determined according to the rules set out in EN60079-10. The key points of area classification are:

  • Safety and area classification
  • Area classification procedure
  • Ventilation
  • Documentation

Zoning is only part of the process for ensuring workplace safety where potentially explosive atmospheres exist. In the UK, the applicable legislative requirement is the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). See later Notes on DSEAR.

Hazardous zones and equipment categories

ATEX recognises three classes of zone for both gas and dust environments.  Table 1 compares the ATEX and US National Electrical Code 500 and 505 classifications.  It is worth noting that all of these classification systems sub-divide the gas groups and temperature classes within the gas classification. The US and ATEX systems differ in that the ATEX system does not have dust groups (defining them instead by temperature classification alone) and the US system defines its hazardous locations into two rather than three types (although there is some equivalence between the types).  See separate page Hazloc certification for USA and Canadian markets.

For each zone classified, the level of protection required for equipment to be used in that zone is defined.  Whereas the US systems directly link equipment to location, the ATEX system divides equipment into three categories 1, 2 and 3 and only permits certain categories of equipment to be used in a given zone.  Each ATEX category is sub-divided into either gas (G) or dust (D) hazard protection e.g. 2G, 1D.

A risk assessment approach for the acceptance of Ex equipment has been introduced by the IECEx within installation standard IEC60079-14.  This is an alternative method to the current prescriptive and relatively inflexible approach, which links equipment directly to zones within IECEx standards.  Hence the most recent IEC60079-0 standard (5th edition, 2007) adopts the concept of Equipment Protection Levels (EPL).  These apply to gases (Ga, Gb and Gc) and dusts (Da, Db and Dc) and are equivalent to the ATEX categories 1, 2 and 3.  IEC60079-0 (5th Ed) will be adopted as EN60079-0 during 2008 and harmonised for ATEX purposes.

Table 1 - ATEX zoning and categories

Area classification /
Surface applications 		EU ATEX US NEC Article
500 505
Gas Dust Permitted equipment Gas Dust Gas
Flammable atmosphere is present continuously or for long period of time (often quantified as >1000hrs/yr) Zone 0 Zone 20 Gas - 1G (Ga)
Dust - 1D (Da)		 See note See note Class I, Zone 0
Flammable atmosphere is likely to occur during normal operation (often quantified as >10 and <1000hrs/yr) Zone 1 Zone 21 Gas – 1G (Ga), 2G (Gb)
Dust - 1D (Da), 2D (Db)		 Class I, Div 1 Class II, Div 1 Class I, Zone 1
Flammable atmosphere is not likely to occur in normal operation (i.e. only rarely) and, if it occurs, will exist for only a short time (often quantified as <10hrs/yr) Zone 2 Zone 22 Gas - 1G (Ga), 2G (Gb), 3G (Gc)
Dust - 1D (Da), 2D (Db), 3D (Dc)		 Class I, Div 2 Class II, Div 2 Class I, Zone 2

Note: There is no direct equivalent of a zone 0 or 20 in the US NEC Article 500 system.

Notes on DSEAR

According to the UK Health and Safety Executive, DSEAR applies to workplaces where dangerous substances are present, used, or produced. These include industrial and commercial premises, land-based and offshore installations, mines and quarries, construction sites, vehicles and vessels, etc. DSEAR places duties on employers to assess and eliminate or reduce risks from dangerous substances. See separate section on Hazardous Area Safety in the UK (DSEAR).