Last edit: 03/03/2023
The latest edition of the ATEX standard was published as IEC on December 2020.
The ATEX standard EN 60079-10-1 is concerned with the classification of areas where flammable gas or vapour hazards may arise and may then be used as a basis to support the proper selection and installation of equipment for use in hazardous areas.
This ATEX Directive is intended to be applied where there may be an ignition hazard due to the presence of flammable gas or vapour, mixed with air.
Among the news introduced with the ATEX standard there is a method described in Annex D for the estimation of hazardous areas. The methodology of Annex D is simpler and leads to different results than the method described in the guide CEI 31-35.
Area classification is a method of analysing and classifying the environment where explosive gas atmospheres may occur, so as to facilitate the proper selection, installation and operation of equipment to be used safely in that environment.
The classification also takes into account the ignition characteristics of the gas or vapour such as ignition energy and ignition temperature.
Area classification has two main objectives:
- the determination of the type of any hazardous zone, and
- the extent of the zone.
In determining where a release of flammable gas or vapour may occur, the likelihood and duration of the release should be assessed in accordance with the grades of release. Once the grade of release, the release rate, concentration, velocity, ventilation and other factors are assessed there is then a firm basis on which to assess the likely presence of an explosive gas atmosphere in the surrounding areas and determine the type and/or extent of the hazardous zones.
The ATEX Standard EN 60079-10-1 indicates three emission source:
continuous grade of release [3.4.2]. release which is continuous or is expected to occur frequently or for long periods.
NOTE: Both “frequently” and “long” are the terms which are intended to describe a very high likelihood of a potential release. In that respect, those terms do not necessarily need to be quantified.
primary grade of release [3.4.3]: release which can be expected to occur periodically or occasionally during normal operation.
secondary grade of release [3.4.4]: release which is not expected to occur in normal operation and, if it does occur, is likely to do so only infrequently and for short periods.
The likelihood of the presence of an explosive gas atmosphere depends mainly on the grade of release and the ventilation. This is identified as a ATEX ZONE. Zones are recognized as: ZONE 0, ZONE 1, ZONE 2 and the non-hazardous area.
Where zones created by adjacent sources of release overlap and are of different zonal classification, the more severe classification criteria will apply in the area of overlap. Where overlapping zones are of the same classification, this common classification will normally apply.
The guidance in annex D provides for the estimation of the type of zone and the extent of zone to relate relevant factors including:
- the grade of release;
- the effectiveness of ventilation and degree of dilution;
- the availability of ventilation.
Table D.1 – Zones for grade of release and effectiveness of ventilation can be used for estimating the type of zone for indoor areas and open areas.