IEC 60079‑10-1: ATEX STANDARD AND CLASSIFICATION OF HAZARDOUS AREAS WITH GAS PRESENCE

The ATEX standard IEC 60079-10-1 addresses the classification of areas where hazards may arise due to the presence of flammable gases or vapours. It therefore provides the basis for the correct selection and installation of equipment intended for use in hazardous locations.

The classification of ATEX areas is a method used to analyse and categorise environments in which explosive atmospheres may form due to the presence of gases or dusts. The purpose is to facilitate the proper selection, installation, and operation of equipment to ensure safe use within such environments. This classification also considers the ignition characteristics of gases or dusts, such as ignition energy and ignition temperature.

The classification of hazardous areas has two main objectives:

• the determination of the type of each hazardous zone;
• the determination of the extent of each zone.

When identifying where a release of flammable gas or dust may occur, it is necessary to consider both the likelihood and the duration of the release, in relation to the grade of release. For each grade, the relevant factors are evaluated to establish the basis for assessing the presence of an explosive atmosphere and, where applicable, to determine the type and/or extent of hazardous areas.

Previously, due to the lack of a precise methodology in the international standard, the approach described in CEI Guide 31-35 was primarily adopted.

Among the updates introduced by IEC 60079-10-1:2020 Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres, a methodology for estimating hazardous areas is now provided in Annex D. This approach is simpler than that described in CEI 31-35 (now withdrawn); however, it may lead to different results, requiring a more informed and conscious approach by designers.

The main changes compared to the previous edition:

• the exclusion from the scope for low-pressure combustible gases is no longer stated in Clause 1; it is now addressed in Clause 5.3.2. Substantially, no changes have been introduced in this regard;
• the definition of Zone NE (Non-Explosive) has been expanded and now includes: limitations on explosion pressure, limitations on explosion heat release, for gases with pressures above 10 barg, a risk assessment is required, and for gases above 20 barg, Zone NE shall not be classified unless supported by a detailed risk assessment.
• the minimum air speed to be taken for indoor environments (previously set at 0.05 m/s in the II Edition) has been removed;
• the safety factor k is no longer included in the calculation of the release characteristic used in Figure D.1, allowing for a less conservative approach;
• equations from C.2 to C.6 for airflow calculation have been revised;
• it is specified that the minimum classification distance shown in the nomogram (Figure D.1) is 1 m;
• the equation for evaporating pool flow rate has been corrected;
• the determination of hazardous distances using the nomogram is no longer applicable in enclosed environments with low or medium dilution;
• CEI Guides 31-35:2012 and CEI 31-35/A:2012 are no longer referenced in Annex K of EN IEC 60079-10-1:2021 (however, CEI Guide 31-35 is still cited in the bibliography).