ATEX zones classify hazardous work environments based on the frequency and duration of an explosive atmosphere.
Gas hazards use Zones 0, 1, and 2, while dust hazards use Zones 20, 21, and 22.
Direct Zone Comparison
The table below breaks down the classification rules across both atmospheres:
| Presence of Explosive Hazard | Gas, Vapor, or Mist | Combustible Dust |
|---|---|---|
| Continuously or for long periods (>1,000 hours/year) | Zone 0 | Zone 20 |
| Likely to occur during normal operation (10–1,000 hours/year) | Zone 1 | Zone 21 |
| Unlikely to occur, or lasts for a short time (<10 hours/year) | Zone 2 | Zone 22 |
Gas, Vapor, and Mist Atmosphere (Zones 0, 1, 2)
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- Zone 0: High-risk areas where explosive mixtures are constantly present. Examples include the inside of fuel storage tanks or chemical processing vessels.
- Zone 1: Medium-risk areas where explosive mixtures happen during regular work. Examples include sampling points or areas near relief valves during normal venting.
- Zone 2: Low-risk areas where explosive mixtures only appear due to an accident or equipment failure. Examples include the general room housing sealed storage pipelines.
Combustible Dust Atmosphere (Zones 20, 21, 22)
- Zone 20: High-risk areas where dangerous dust clouds are constantly present. Examples include the inside of dust containment silos, hoppers, or cyclones.
- Zone 21: Medium-risk areas where dust clouds are likely to form during regular work. Examples include the immediate area around a bag-emptying station or a powder mixer.
- Zone 22: Low-risk areas where dust layers might collect and blow into a cloud during a mishap. Examples include warehouse floors near milling machinery where dust builds up on surfaces.
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