ATEX zones 0, 1, 2, 20, 21 and 22 and the equipment each needs
ATEX zones sort hazardous areas by how often an explosive atmosphere occurs. Zones 0, 1, 2 are gas, 20, 21, 22 are dust. Each sets an equipment category.
ATEX zones and equipment requirements for gas and dust
ATEX zones are the six classes that EU workplace law uses to sort hazardous areas by how often and how long an explosive atmosphere is present. Zones 0, 1 and 2 are for flammable gas, vapour or mist, and zones 20, 21 and 22 are for clouds of combustible dust. The same six zones apply under DSEAR in Great Britain and under Suva guidance in Switzerland.
| How often the explosive atmosphere is present | Gas, vapour or mist | Combustible dust cloud | Equipment category allowed |
|---|---|---|---|
| Continuously, for long periods or frequently | Zone 0 | Zone 20 | 1 |
| Likely to occur occasionally in normal operation | Zone 1 | Zone 21 | 1 or 2 |
| Not likely in normal operation, and short if it does occur | Zone 2 | Zone 22 | 1, 2 or 3 |
The zone definitions come from Annex I of Directive 1999/92/EC, and the category rules come from its Annex II Part B. A higher category is allowed in a lower-risk zone. A lower category than the table is allowed only if the explosion protection document, based on the risk assessment, says so.
How ATEX zones are set
The directive defines an explosive atmosphere as a mixture with air, under atmospheric conditions, of flammable gases, vapours, mists or dusts in which, after ignition, "combustion spreads to the entire unburned mixture" (Article 2). The Commission ATEX Guidelines suggest -20 °C to 60 °C and 0.8 to 1.1 bar as a basis for those conditions (p. 61). HSE L138 uses -20 °C to 40 °C for DSEAR. Check which range your regulator uses.
Under Article 7 and Annex I the employer first sorts the workplace into hazardous and non-hazardous places. Hazardous places are then put into zones "on the basis of the frequency and duration of the occurrence of an explosive atmosphere" (Annex I). The zone sets how far the protective measures must go. A few areas, such as patient treatment rooms and most transport, fall outside the directive (Article 1(2)).
Annex I also addresses dust outside a cloud. Layers, deposits and heaps of combustible dust count as sources that can form an explosive atmosphere. "Normal operation" means installations used within their design parameters.
How far a zone extends depends on the release, the ventilation and the site. HSE's zoning guidance walks through those factors.
The employer records all of this in the explosion protection document required by Article 8. It is drawn up before work starts, kept up to date and revised after significant changes. It shows the assessed risks, the measures taken, the places classified into zones and the arrangements for safe use of work equipment. Entry points need the Annex III warning sign: black "EX" letters on a yellow triangle with black edging, yellow at least 50% of the sign.
What ATEX means
ATEX comes from the French "ATmosphères EXplosibles" (European Commission glossary). HSE describes ATEX as "the name commonly given to the 2 European Directives for controlling explosive atmospheres" (HSE):
- Directive 1999/92/EC, the workplace ATEX directive, also called ATEX 137. It covers employers, zones and the explosion protection document. It is still in force. The only later amendment, Directive 2007/30/EC, changed implementation reporting.
- Directive 2014/34/EU, also called ATEX 114 or the Equipment Directive. It covers manufacturers of "equipment and protective systems intended for use in potentially explosive atmospheres" and has applied since 20 April 2016, replacing Directive 94/9/EC (European Commission).
Zones describe places and are the employer's job. Manufacturers classify equipment by category. So equipment sold as "zone 1 certified" is really category 2 (or 1) equipment.
Equipment groups and categories
Directive 2014/34/EU splits equipment into two groups. Group I is for underground mines and their surface installations endangered by firedamp, combustible dust, or both, with categories M1 and M2. Group II is for other places, with three categories:
| Category | Level of protection | Normally used in |
|---|---|---|
| 1 | Very high | Zone 0 or 20 |
| 2 | High | Zone 1 or 21 |
| 3 | Normal | Zone 2 or 22 |
That correspondence is set out in the Commission's ATEX Guidelines, 6th edition (January 2026), page 145. A category 1 item can still go in zone 2, but only if it suits the atmosphere and the operating conditions.
Group II markings use G for gas, vapour and mist and/or D for dust. Zone 21 needs dust-suitable equipment: normally category 2D or 1D. A G-only marking doesn't show suitability for zone 21.
The directive also covers non-electrical equipment such as pumps, fans, gears, compressors, mixers and brakes when they have their own potential ignition sources. It also covers safety and control devices outside the hazardous area that are needed for safe operation, marked with the category in brackets, for example "II (2) G" (Guidelines, pp. 41-49).
ATEX certification and marking
"ATEX certified" does not always mean a notified body issued a certificate. If a supplier says ATEX approved or ATEX rated, check the category and the G or D mark, not a voluntary certificate. The conformity route depends on the category (Article 13; Guidelines pp. 89-94):
| Equipment | Route | Notified body |
|---|---|---|
| Category 1 or M1, and protective systems | EU-type examination (B) plus production quality assurance (D) or product verification (F) | Yes |
| Category 2 or M2, electrical equipment and internal combustion engines | EU-type examination (B) plus supervised product testing (C1) or product quality assurance (E) | Yes |
| Category 2 or M2, other equipment | Internal production control (A), technical file sent to a notified body to keep | Receives the file, no certificate |
| Category 3 | Internal production control (A) | No |
Unit verification (module G) is an alternative for any category. The Commission says only notified bodies may certify, and "voluntary or other additional certificates are not a recognised means to prove compliance". NANDO lists the ATEX notified bodies (European Commission).
ATEX equipment carries the CE marking, plus the notified body number where that body is involved in production control. Then comes the Ex mark (epsilon-x in a hexagon), the group, the category and G or D. The plate also gives the manufacturer's name and address, type or series, batch or serial number and year of construction. A typical gas marking reads "II 2 G" followed by the temperature class (HSE L138, para 376).
DSEAR zones in Great Britain
In Great Britain the workplace directive takes effect through the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). Regulation 7 requires every employer to classify places "into hazardous or non-hazardous places" and to classify the hazardous ones into zones. Schedule 2 reproduces the Annex I zones, with "dangerous substances" in place of "flammable substances". Schedule 3 has the same zone-to-category table, again "unless the risk assessment finds otherwise".
HSE's L138 guidance adds some practical points:
- Record the classification as drawings, in plan and elevation, with supporting text (para 354).
- "Marking is not required for individual zones" (para 386). Regulation 7 puts the EX sign at entry points where necessary.
- Equipment in use before 30 June 2003 is exempt from Schedule 3 but must still meet regulation 6 (paras 373, 404).
GB equipment rules sit in SI 2016/1107, with the UKCA mark plus the Ex marking. CE marking is recognised in GB indefinitely under SI 2024/696, and GOV.UK's UKCA guidance confirms CE is accepted "alongside or in place of the UKCA marking", and that Group II category 3 equipment can be self-declared. "UKEX" is industry shorthand, not an alternative legal marking. Northern Ireland still applies 2014/34/EU, so products there must stay CE marked, with the UKNI mark as well where a UK body did the mandatory assessment.
ATEX zones in Switzerland
Switzerland uses the same six zones. Suva leaflet 2153, "Explosionsschutz: Grundsätze, Mindestvorschriften, Zonen" (edition 1 July 2024) follows Directive 1999/92/EC and uses the same category mapping. The EKAS guidance confirms zones 0/20, 1/21 and 2/22.
Swiss equipment falls under the VGSEB (SR 734.6), which applies to products as defined in Directive 2014/34/EU and copies its conformity routes in Article 12. Suva 2153 says zone 0 should be used only where its conditions are actually met, and that surface temperatures there must stay 20% below the ignition temperature. In zones 1 and 2 they must not exceed it.
RegAffairs AI's answer on ATEX zones cites the Irish regulations and Suva 2153.