What Are EX Zones? The Engineer’s Map of Explosion Risk (2025)

EX zones are labels (0/1/2 for gas; 20/21/22 for dust) that indicate how often an explosive atmosphere is present at a location, guiding equipment selection and inspection frequency under ATEX/IECEx.

TL;DR

EX zones are the shorthand labels that tell you how often an explosive gas or dust cloud can exist in a location.
Zone 0/20 = continuous hazard, Zone 1/21 = likely in normal operation, Zone 2/22 = rare/brief.
The zone dictates the minimum ATEX/IECEx equipment category (1G–3G / 1D–3D) and the inspection interval—making zoning the first line of defence against ignition.

1. Why zoning exists

ATEX 153 (1999/92/EC) and IEC 60079-10-1/-2 require employers to classify hazardous areas so that everyone—from design engineers to permit-to-work coordinators—knows which ignition-protected equipment is compulsory. A correct zone map equals:

Right equipment → no ignition source
Right maintenance frequency → integrity preserved
Right documentation → insurance & legal compliance

2. Gas & Vapour Zones

Table 1: Gas/Vapour zones and matching ATEX equipment categories
Zone	Presence of Explosive Gas Atmosphere	Typical Examples	ATEX Category*
0	Continuous or > 1 000 h / yr	Inside fuel tanks, digester head-space	1G
1	Likely in normal operation (10–1 000 h / yr)	Pump seals, vent outlets	2G
2	Not likely / brief if it occurs (< 10 h / yr)	Well-ventilated pipe flanges	3G

*IECEx uses EPL (a, b, c) but the technical protection level is identical.

3. Dust Zones

Table 2: Dust zones and matching ATEX equipment categories
Zone	Presence of Explosive Dust Cloud / Layers	Typical Examples	ATEX Category
20	Continuous or > 1 000 h / yr	Interior of grain silos, dust collectors	1D
21	Likely in normal operation	Around bag filters, mill hoppers	2D
22	Not likely / brief	Packing lines, housekeeping sweepings	3D

4. How zoning decisions are made

Identify release sources – vents, seals, filling points, dust collectors.
Grade each release – continuous, primary, secondary (per IEC 60079-10-1/-2).
Evaluate ventilation – “good” ventilation can downgrade a zone.
Draw boundaries – 3-D envelopes on P&IDs and site plans.
Issue a Hazardous-Area Classification Drawing and Explosion Protection Document (EPD).

5. Why zones matter after commissioning

Equipment selection – Zone drives EPL (Ex d, e, i etc.) and gas group.
Inspection interval – EN 60079-17 visual, close or detailed frequency.
Permits to work – hot-work vs cold-work rules differ by Zone.
Legal / insurance exposure – mis-zoning invalidates cover; ATEX 153 fines.

6. Updating zones: triggers & best practice

Change the classification if any of the following occur:

Process chemistry or temperature/pressure changes
New vents or relief valves installed
Ventilation altered (ductwork, louvers, fans)
Dust housekeeping regime downgraded

Modern sites keep the zone map inside a cloud register. EXREG auto-links each equipment record to its zone and flags work orders when zoning changes.

7. Further reading & tools

8. Frequently asked questions (FAQ)

What is the difference between Zone 1 and Zone 2?

Zone 1 expects an explosive gas atmosphere in normal operation (10–1,000 h/yr), while Zone 2 is unlikely and brief (<10 h/yr). Equipment categories are typically 2G (Zone 1) and 3G (Zone 2).

Who decides the EX zone classification?

The employer/site operator is responsible, usually via a competent engineer following EN IEC 60079-10-1/-2. The outcome is documented in the hazardous-area classification and the Explosion Protection Document (EPD).

Do EX zones set inspection frequency?

Yes. EN IEC 60079-17 uses risk/zone to assign visual/close/detailed inspection intervals and sampling rates.

How do gas and dust zones differ?

Gas/vapour zones are numbered 0/1/2; dust zones are 20/21/22. The probability scale is identical, but equipment marking uses G (gas) vs D (dust).

Which standard should I cite on drawings?

Use EN IEC 60079-10-1 for gas/vapours and EN IEC 60079-10-2 for dust. Reference both where relevant.

9. Conclusion

EX zones turn abstract explosion probability into concrete design, inspection, and permit rules. Know your zone → pick the right equipment → schedule the right inspection → avoid ignition. Simple—but only if the zone map stays live.

For inspection intervals and sampling by risk, see our EX inspections guide.Ready to digitise your EX register? Start a 7-day EXREG trial and see your EX register zone counts.