ATEX zone classification: a practical guide
What zones 0, 1, 2 (and 20, 21, 22) actually mean, what the EU directives say, what an Explosion Protection Document is, and who must have one — explained without the technical-manual jargon.
ATEX zone classification is the process of identifying and mapping, within a plant, the areas where the presence of flammable gases, vapours, mists or combustible dust can generate a potentially explosive atmosphere. Two concrete obligations follow from this classification: a written document (the Explosion Protection Document) and the selection of equipment suitable for the risk level of each zone.
What is an explosive atmosphere
An explosive atmosphere forms when a flammable substance — gas, vapour, mist or combustible dust — mixes with air in proportions such that, in the presence of an ignition source (a spark, a hot surface, an electric arc), the entire mixture can ignite almost instantly. "ATEX" is the informal name, derived from the French ATmosphères EXplosibles, given to the two EU directives that regulate this risk.
Two directives, two different audiences
This is the point that causes the most confusion across the EU, so it's worth separating clearly:
- Directive 2014/34/EU (often called "ATEX 114") addresses manufacturers of equipment and protective systems intended for use in potentially explosive atmospheres. It sets the requirements for Ex marking.
- Directive 1999/92/EC, transposed into the national law of every EU member state (in the UK, the equivalent framework is DSEAR — the Dangerous Substances and Explosive Atmospheres Regulations), addresses employers. It requires an explosion risk assessment and, where relevant, classification of workplace zones.
If you manufacture or sell equipment for hazardous environments, the first directive applies to you. If you run a factory where these substances are present — even in just one department — the second applies to you, regardless of what you produce.
ATEX zones: gas/vapour and dust
Classification distinguishes two families of zones, depending on whether the risk comes from gas/vapour/mist or from clouds of combustible dust. The criterion is the same in both cases: how often and for how long the explosive atmosphere is present.
| Zone | Type | Presence of the explosive atmosphere |
|---|---|---|
| Zone 0 | Gas / vapour / mist | Continuous, for long periods or frequently |
| Zone 1 | Gas / vapour / mist | Likely to occur in normal operation |
| Zone 2 | Gas / vapour / mist | Not likely, and if it occurs, only briefly |
| Zone 20 | Combustible dust | Continuous, for long periods or frequently |
| Zone 21 | Combustible dust | Likely to occur in normal operation |
| Zone 22 | Combustible dust | Not likely, and if it occurs, only briefly |
The Explosion Protection Document
This is the formal document, required under national legislation transposing Directive 1999/92/EC, through which the employer demonstrates that the explosion risk has been assessed. A complete document typically includes:
- identification of the substances and release sources present;
- zone classification, with drawings showing their extent;
- the technical and organisational measures adopted to reduce the risk;
- the criteria used to select equipment installed in classified zones;
- coordination arrangements with contractors operating in the same areas.
It is not a document to be written once and filed away — it must be updated whenever the plant, the process or the substances used change.
How classification is actually carried out
In practice, the process follows recurring steps: identifying release sources (a tank, a valve, a transfer point), estimating how much substance can be released and for how long, assessing ventilation in the area, and finally translating this data into a floor plan with clearly defined zones and extents. This requires specific technical competence — it is not a form to fill in from memory, which is exactly why the regulation explicitly assigns it to competent personnel.
Ex marking: the practical consequence
Once zones are classified, every electrical or mechanical device installed within them must carry an Ex category appropriate to the risk level: category 1 for zones 0/20, category 2 for zones 1/21, category 3 for zones 2/22. The marking also indicates the group (I for mining, II for surface industries) and the type of protection by which the equipment prevents ignition.
Common mistakes
- Buying "Ex-rated equipment" before classifying the zones. Without knowing which zone is being protected, the correct category cannot be chosen.
- An Explosion Protection Document written once and never updated, even as the plant itself has changed several times since.
- Confusing an ATEX-classified zone with a generic fire-risk area: these are different assessments, governed by different legislation.
Frequently asked questions
Who is legally required to carry out ATEX zone classification?
Any employer whose activities can generate explosive atmospheres: spray painting, storage or handling of combustible dust, use of flammable gases or solvents, silos, drying plants. There is no company-size threshold — what matters is the actual risk present, not the headcount.
Is an Explosion Protection Document required even for a small company?
Yes. Under EU Directive 1999/92/EC (transposed into national law in every EU member state), the obligation applies whenever a potentially explosive atmosphere can form in the workplace, regardless of company size.
What happens if a company doesn't have an Explosion Protection Document?
National law in each EU member state provides for penalties, alongside the real and concrete risk to worker safety — which is the actual reason the rule exists in the first place.
How often does ATEX zone classification need to be reviewed?
It should be reviewed whenever the plant, the process, the substances used, or the layout of the premises change — and periodically reassessed even without changes, as part of normal safety management.