Overview of the new EN 60079-10-1 version for ATEX areas classification

In industries that store, produce or use flammable substances in the form of gas or liquid capable of forming an explosive atmosphere, an ATEX Zones classification is the first step outlined by Directive 1999/92/EC as necessary for developing the “integrated safety” process, which is the starting point for all risk assessments.

Both the standard ‘EN-60079: Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres’ and the guide ‘UNE-EN 202007:2006’ of the standard itself are the base documents used when performing this zone classification. The standards are periodically updated based on advances in technology and knowledge, and these updates can range from simple editorial changes to major technical modifications. The latest update to the ATEX zone classification standard (EN-60079-10-1), from October 2016, introduces significant technical changes that need to be addressed.

One of the main updates concerns the concept of “hypothetical explosive atmosphere volume, Vz”, used in the previous version of the standard to determine the degree of ventilation. In this update, this concept is removed, and instead, the concept of dilution is used based on the characteristics of the escape and the air ventilation speed. The “hypothetical volume” concept was linked to theoretical studies, whereas the new concepts are associated with CFD (Computational Fluid Dynamics) or computational analysis of fluid behaviour.

Significant technical changes have been introduced, and while it is not a harmonised standard, it is highly recommended to review any calculations made according to the previous standard, as differences may be found (e.g. in terms of the extent of the zones determined). At this point, it is worth recalling the need for periodic updates of the DPCE (Explosion Protection Document), as indicated in Directive 1999/92/EC, through which this zone classification could be reviewed.

The following is a summary of some of the most relevant updates to the standard:

• Several approaches have been introduced to perform zone classification, for example, by using recognised international standards (such as API RP 505, NFPA 497), or by using industry-specific guides (such as IP15 or IGEM/SR/25). It is also stated that the calculation method and/or a combination of methods can be used.
• The different types of escape (gas, liquefied gas, flammable liquid) and their behaviour in the event of a leak (referred to as buoyancy, i.e., the direction the gas takes when it escapes) have been much better defined. Technical changes have been made in the calculation of the escape rate:
  • A sample table has been updated and expanded to determine the escape orifice more accurately.
  • A discharge coefficient (Cd) has been introduced to account for the viscosity and shape of the escape orifice.
• The initial concept of ventilation has been completely revised, now including parameters such as gas dispersion and its dilution in the atmosphere.
• The concept of “background concentration” has been given much greater importance when dealing with an enclosed space. In fact, it is the primary parameter determining what type of zone will result.
• Information has been added regarding the shape of the escape (jet or diffusive type) and the operation of ventilation in enclosed spaces, along with new formulas for calculating ventilation flow rates (due to wind or temperature differences).

Furthermore, in the new version, the extent of the classified zones is no longer calculated through formulas but through the following graph:

The new calculations generally result in smaller zones, particularly in outdoor areas. In enclosed spaces, although distances are generally smaller, they still depend heavily on the type of ventilation, whether natural or forced, and the arrangement of ventilation grilles, etc. It is now recommended to classify the entire interior of the enclosed space if the resulting distances are significant.

This update also includes new examples of zone classification, as well as specific annexes for flammable mists, hydrogen, and international standards to consider when performing zone classification.