The biggest mistake in ATEX zoning is the one nobody corrects
Hazardous area classifications are often copied from old drawings, standard layouts or previous projects. On paper, Zone 22 may look like a low-risk area. In practice, it is often the place where the technical basis is weakest.
Under the European ATEX workplace framework and the UK DSEAR regime, hazardous area classification is not a drafting exercise. It is a technical assessment of where an explosive atmosphere may occur, how often it may occur and how long it may persist. For combustible dust atmospheres, EN IEC 60079-10-2 and its UK equivalent BS EN IEC 60079-10-2 provide the recognised framework for identifying and classifying areas where explosive dust clouds and combustible dust layers may be present.
That assessment cannot be reduced to a coloured area on a drawing.
For dust, the classification must be based on the source of release, the likelihood and duration of dust emission, the properties of the dust, the influence of ventilation or extraction, the possibility of dust layers and the actual operating conditions of the process. A dust cloud is not created by a zone drawing. It is created by product behaviour, mechanical movement, transfer points, filling and emptying operations, filter performance, cleaning practices and process deviations.
This is where many errors start.
A Zone 22 area is sometimes treated as if it is automatically safe because an explosive dust atmosphere is expected only infrequently and for a short period. That interpretation is dangerous. Zone 22 is still a hazardous area. It still requires suitable equipment, control of ignition sources, appropriate inspection, maintenance and a clear technical justification for the classification.
Common weaknesses are easy to recognise.
A zoning drawing is produced without a real source-of-release analysis. Failing ventilation or extraction is not considered. Dust deposits are ignored because no visible cloud is present during normal operation. Classification from a previous project is copied into a new process. Changes in product, particle size, moisture content, capacity, filter condition or cleaning regime are not reassessed. The result is a drawing that looks compliant, while the physical basis behind it is missing.
This matters because hazardous area classification is the starting point for many later decisions. It influences the required Equipment Protection Level, the selection of electrical and non-electrical equipment, the installation requirements under EN IEC 60079-14 or BS EN IEC 60079-14, and the inspection and maintenance approach under EN IEC 60079-17 or BS EN IEC 60079-17. If the zoning is weak, every decision based on it becomes weak as well.
In the European Union, ATEX 1999/92/EC requires employers to assess explosion risks and classify places where explosive atmospheres may occur. ATEX 2014/34/EU then governs the equipment and protective systems placed on the market for use in those atmospheres. In the United Kingdom, the same operational duty is reflected through DSEAR, while equipment placed on the market is governed through the UK Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations.
The principle is the same on both sides.
A zone is not a drawing.
A zone is a physical model of an explosive atmosphere.
If that model is not based on source strength, dust behaviour, ventilation, dilution, dust layers, foreseeable failures and real operating conditions, the result is only paper safety. It may pass a quick visual review, but it will not stand up to a serious technical audit, an insurance review or an incident investigation.
The real question is therefore not:
“Is this area marked as Zone 22?”
The real question is:
“Can we still prove why this area is Zone 22, based on the actual process conditions today?”
That is where explosion safety begins.
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