① Zones
② Equipment categories
③ Cat ↔ Zone compatibility
④ Equipment groups
⑤ Temperature classes T1–T6
⑥ Protection types
① Explosive atmosphere zones IEC 60079-10 / ATEX 1999/92/EC
Environment:
| Zone | Environment | Frequency / Duration | Description | Typical locations |
|---|---|---|---|---|
| Zone 0 | Gas / Vapour | Continuously or long periods (>1 000 h/yr) | Explosive atmosphere present continuously or for long periods | Interior of tanks, vessels, pipelines with flammable liquids |
| Zone 1 | Gas / Vapour | Occasionally during normal operation (10–1 000 h/yr) | Explosive atmosphere likely to occur in normal operation | Areas around Zone 0, pump rooms, flammable liquid handling |
| Zone 2 | Gas / Vapour | Rarely and only briefly (<10 h/yr) | Explosive atmosphere not likely in normal operation; if it occurs, only infrequently and briefly | Areas surrounding Zone 1, storage areas, normal plant areas |
| Zone 20 | Dust | Continuously or long periods | Explosive dust cloud present continuously or frequently | Inside dust collection equipment, silos, hoppers, mills |
| Zone 21 | Dust | Occasionally during normal operation | Explosive dust cloud likely to occur in normal operation | Filling/emptying areas, conveyor transfer points, baghouses |
| Zone 22 | Dust | Rarely and only briefly | Explosive dust cloud unlikely in normal operation; if occurs, only briefly | Areas surrounding Zone 21, dust storage rooms |
② Equipment categories ATEX 2014/34/EU Annex I
| Category | Environment | Zone(s) suitable for | Required protection level | Fault tolerance | Notes |
|---|---|---|---|---|---|
| Category 1G | Gas / Vapour | Z 0 Z 1 Z 2 | Very high — EPL Ga | Safe even with two independent faults | Highest protection; intrinsically safe Ex ia, Ex ma |
| Category 2G | Gas / Vapour | Z 1 Z 2 | High — EPL Gb | Safe even with one expected fault | Ex d, Ex e, Ex ib, Ex p, Ex q, Ex o |
| Category 3G | Gas / Vapour | Z 2 | Normal — EPL Gc | Safe during normal operation | Ex n, Ex ic, Ex pz |
| Category 1D | Dust | Z 20 Z 21 Z 22 | Very high — EPL Da | Safe even with two independent faults | Ex ia (dust), Ex ma (dust) |
| Category 2D | Dust | Z 21 Z 22 | High — EPL Db | Safe even with one expected fault | Ex tb (dust-tight enclosure), Ex ib (dust) |
| Category 3D | Dust | Z 22 | Normal — EPL Dc | Safe during normal operation | Ex tc, Ex ic (dust) |
| Category M1 | Mining (firedamp) | Mines — underground | Very high — EPL Ma | Safe even during explosive atmosphere (stays energised) | Group I, must remain functional in presence of firedamp |
| Category M2 | Mining (firedamp) | Mines — underground | High — EPL Mb | Safe with one expected fault; de-energised in explosive atm. | Group I, equipment can be switched off when hazard arises |
③ Category ↔ Zone compatibility matrix
| Equipment category | Zone 0 | Zone 1 | Zone 2 | Zone 20 | Zone 21 | Zone 22 |
|---|---|---|---|---|---|---|
| 1G | ✓ | ✓ | ✓ | — | — | — |
| 2G | — | ✓ | ✓ | — | — | — |
| 3G | — | — | ✓ | — | — | — |
| 1D | — | — | — | ✓ | ✓ | ✓ |
| 2D | — | — | — | — | ✓ | ✓ |
| 3D | — | — | — | — | — | ✓ |
✓ = permitted | Higher category equipment is always permitted in lower-risk zones (e.g. Cat 1G can replace Cat 2G or 3G).
④ Equipment groups & representative gases IEC 60079-0
| Group | Application | MESG (mm) | MIC ratio | Ignition hazard | Representative substances |
|---|---|---|---|---|---|
| Group I | Mining — underground coal mines (firedamp / methane) | > 0.9 | > 0.8 | Lowest (mine-specific) | Methane (CH₄), firedamp |
| Group IIA | Surface industries — least hazardous gas | > 0.9 | > 0.8 | Low | Propane, butane, methane, acetone, ammonia, benzene, toluene |
| Group IIB | Surface industries — intermediate hazard | 0.5–0.9 | 0.45–0.8 | Medium | Ethylene, cyclopropane, diethyl ether, town gas |
| Group IIC | Surface industries — most hazardous gas | < 0.5 | < 0.45 | Highest | Hydrogen (H₂), acetylene (C₂H₂), carbon disulfide (CS₂) |
MESG = Maximum Experimental Safe Gap | MIC = Minimum Igniting Current ratio (vs. methane) | IIC equipment is also suitable for IIA and IIB locations.
⑤ Temperature classes T1–T6 IEC 60079-0
| Class | Max. surface temp. (°C) | Suitable for gases with auto-ignition temp. (>) | Example gases / substances |
|---|
T6 equipment (max 85 °C) is the most restrictive and can be used anywhere T1–T5 equipment is required. Equipment must be marked with its temperature class (or max. surface temperature in °C).
⑥ Protection types (Ex designations) IEC 60079 series
Environment:
Marking & identification
ATEX marking example
⑥Ex d IIB T4 Gb
- ⑥Ex — ATEX conformity mark
- d — Protection type (flameproof)
- IIB — Equipment group
- T4 — Temperature class (max 135 °C)
- Gb — Equipment Protection Level
EPL — Equipment Protection Level
- Ma / Da — Very high (two independent faults)
- Mb / Db — High (one expected fault)
- Gc / Dc — Enhanced (normal operation)
EPL suffix: a = gas/vapour, b = dust, no suffix = mining.
Directives & standards
- ATEX 2014/34/EU — Equipment & protective systems
- ATEX 1999/92/EC (DSEAR) — Workplace safety / zoning
- IEC 60079-0 — General requirements
- IEC 60079-10 — Classification of hazardous areas (gas)
- IEC 60079-11 — Intrinsic safety Ex i
- IEC 61241-10 — Dust zone classification
Key design rules
- Select equipment category matching or exceeding zone requirement
- Equipment group must match gas group (IIC covers IIA+IIB)
- Temperature class must exceed auto-ignition temp. of present gases
- Zone classification is the responsibility of the plant operator (ATEX 1999/92/EC)
- Equipment certification is by Notified Body for Cat 1 & 2; self-cert for Cat 3