ATEX Categories 1, 2, 3 for Surface Use | Atexshop
For surface industries—everything from petrochemical plants to grain silos—the ATEX Equipment Directive uses Equipment Group II with three categories: 1, 2, and 3. Each category provides a different level of protection matched to the probability and duration of explosive atmospheres in different zone classifications.
The Category Hierarchy
Categories are defined by the level of protection they provide against ignition, with Category 1 being the highest and Category 3 the lowest. This hierarchy directly maps to zone classification: more hazardous zones require higher category equipment. The essential health and safety requirements in Annex I of the directive spell out what each category must achieve.
Category 1: Very High Protection (Zone 0/20)
Category 1 equipment is required for Zone 0 (continuous gas hazard) and Zone 20 (continuous dust hazard). The directive specifies that Category 1 equipment must ensure the requisite level of protection even in the event of rare malfunctions relating to equipment.
To achieve this, manufacturers must provide:
- Two independent means of protection, OR
- Safety even when two faults occur independently of each other
Examples include intrinsically safe instruments (Ex ia) where circuit energy is limited to prevent ignition under all fault conditions, or equipment combining multiple protection techniques.
Category 2: High Protection (Zone 1/21)
Category 2 equipment suits Zone 1 (occasional gas hazard during normal operation) and Zone 21 (occasional dust hazard). The directive requires a high level of protection during normal operation and also during frequently occurring disturbances or equipment faults which normally have to be taken into account.
This means the equipment must remain safe not just under ideal conditions but when typical operational issues occur. A single fault should not lead to ignition. Flameproof (Ex d) and increased safety (Ex e) equipment typically falls into Category 2, as does intrinsically safe equipment at the Ex ib level.
Category 3: Normal Protection (Zone 2/22)
Category 3 equipment is intended for Zone 2 (gas hazard only under abnormal conditions) and Zone 22 (dust hazard only under abnormal conditions). The essential requirements specify that Category 3 must ensure the requisite level of protection during normal operation.
Since explosive atmospheres in these zones are unlikely and short-lived, the protection requirements are less stringent. Equipment must prevent ignition during intended use but need not account for equipment malfunctions. Type n (Ex n) protection and equipment certified to Ex ic level are typical Category 3 solutions.
Dust vs Gas Subdivisions
Equipment may be certified for gas atmospheres only (marked "G"), dust atmospheres only (marked "D"), or both. A Category 2 motor might be marked as "II 2 G" (gases only) or "II 2 D" (dusts only) or "II 2 GD" (both). When selecting equipment, verify the marking matches your actual hazardous atmosphere.
Matching Categories to Zones
The ATEX Workplace Directive specifies minimum equipment requirements:
- Zone 0/20: Category 1 equipment mandatory
- Zone 1/21: Category 1 or 2 equipment
- Zone 2/22: Category 1, 2, or 3 equipment
Higher category equipment can always be used in less hazardous zones, but never the reverse. Using Category 3 equipment in Zone 1 violates ATEX requirements regardless of how briefly the hazard exists.
Conformity Assessment
Categories 1 and 2 require Notified Body involvement. Only Category 3 equipment permits manufacturer self-certification through internal production control (Module A), though many manufacturers still choose third-party assessment for commercial credibility.