What are the EX zones?
Ex zones are the shorthand labels engineers use to show how often an explosive gas or dust cloud can exist in a given area. Ex zones are mapped during the hazardous-area classification so that everyone—from designers to maintenance crews—knows which equipment protection level is mandatory. Ex zones are therefore the first line of defence against ignition in refineries, paint shops, grain silos and any other plant where flammable atmospheres may arise.
How hazardous areas are classified under ATEX & IECEx?
When gases, vapours or dusts can form an explosive atmosphere, the site must be zoned so that equipment with the right protection level is installed in the right place. The zoning system tells you how often an explosive mix is expected to be present.
Gas & Vapour Zones
| Zone | Presence of explosive gas atmosphere | Typical examples | ATEX equipment category |
|---|---|---|---|
| Zone 0 | Continuously or for long periods (> 1 000 h / yr) |
Inside a fuel tank | Cat 1G |
| Zone 1 | Likely in normal operation (10 – 1 000 h / yr) |
Pump seals, vent vicinity | Cat 2G |
| Zone 2 | Not likely, brief if it occurs (< 10 h / yr) |
Pipe flanges, well-ventilated areas | Cat 3G |
Dust Zones
| Zone | Presence of explosive dust / flyings | Typical examples | ATEX equipment category |
|---|---|---|---|
| Zone 20 | Continuously or for long periods | Inside grain silos | Cat 1D |
| Zone 21 | Likely in normal operation | Around bag-filters, mill hoppers | Cat 2D |
| Zone 22 | Not likely, brief if it occurs | Packing lines, sweepings near conveyors | Cat 3D |
How zoning decisions are made?
- Identify release sources – vents, seals, dust collectors.
- Grade each source (continuous, primary, secondary).
- Assess ventilation – good air movement can downgrade a zone.
- Draw boundaries on plans and mark them on site.
The result is a hazardous-area classification drawing that insurers, inspectors and equipment suppliers all use.
Why zones matter?
- They dictate the minimum protection level (Ex d, Ex e, Ex i, etc.) an electrical or mechanical item must have.
- They influence maintenance intervals and permit-to-work systems.
- Incorrect zoning can invalidate insurance and expose directors to criminal charges under ATEX 153 (1999/92/EC).
