Explanation on hazardous area classification

Hazardous area classificatie is related to the prevention of explosion risks on a site, factory or installation. The first step in the systematic approach on reducing explosion hazards is to identify those area’s where such hazards are present: typically those locations where high concentrations of flammable substances (like gases, liquids or dusts) can be present.

Identification of possible leak sources

To identify those locations, the total factory, plant or installation has to be assessed and the assessors needs to identify release sources of flammable substances. These release sources can be present continuously, like in the internals of a storage tank with ethanol, or can only be present very rare, like a spill from a coupler in pipework for the transport of flammable liquids or gases.

All these release sources needs to be identified and assessed on the possible formation of explosive mixtures of gases, liquids or dusts in air. Judgement of release rates of gases, evaporation rates of liquids and cloud formation of dusts particles have to be made.

For these judgements several models or instruments can be used which. Globally there are several standards for that, like IEC 60079-10, API 500/505, EI 15 and many other industry standards.

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These standards are mainly based on an example approach or release point approach. Example approaches are a bit more general and release point approach are a bit more specific. Besides that, there are also possibilities for more advanced approaches like Computational Fluid Dynamics or advanced other software tools.

Atex zone system

All models have the same purpose: making a judgement of the possibility of formation of explosive atmospheres in or around installations in factories or plants. Such locations are classified as ATEX zones.
In North America there is a comparable system based on Divisions and Classes.

Based on the probability of the presence of explosive atmospheres, 3 zones can be divided:

  • zone 0: an area where an explosive atmosphere is present continuously (e.g. more than 10% of the time);
  • zone 1: an area where an explosive atmosphere is present regular (e.g. between 0,1 and 10% of the time);
  • zone 2: an area where an explosive atmosphere is present incidentally (e.g. less than 0,1 % of the time).

For dusts these area are identified as zone 20, 21 and 22 respectively.

Hazcalc can be used for such assessments for flammable gases and liquids, app.hazcalc.com