How to Identify Gas Groups and Dust Groups in the Zone System (ATEX / IECEx)

The Zone system used in ATEX and IECEx is the most common international standard for explosion-proof equipment.

1.Basic Framework
Gas atmospheres: Group II equipment → Subgroups IIA, IIB, IIC
Dust atmospheres: Group III equipment → Subgroups IIIA, IIIB, IIIC

Hazard level (increasing):
Gases: IIA < IIB < IIC
Dusts: IIIA < IIIB < IIIC

2.Gas Groups and Typical Gases
GroupHazard LevelTypical Gases / VaporsCommon ApplicationsIIALowerPropane, gasoline, methane, ethanol, acetone, natural gasGas stations, LPG storage, general solventsIIBMediumEthylene, diethyl ether, butadiene, hydrogen sulfideEthylene plants, solvent areas, pharmaceuticalsIICHighestHydrogen, acetylene, carbon disulfideHydrogen stations, acetylene generators, battery rooms
Key Tip: Hydrogen or acetylene = IIC (highest requirement).
Compatibility: IIC equipment works for all gas groups.

3.Dust Groups and Typical Dusts
GroupTypeTypical DustsCommon ApplicationsIIIACombustible flyingsCotton lint, wood fibers, plastic flyingsTextile & woodworkingIIIBNon-conductive dustsFlour, grain, wood dust, plastic dust, sugarFood processing, plasticsIIICConductive dustsAluminum, magnesium, metal powders, carbon black, coal dustMetal powder plants, mining
Key Tip: Metal dusts = IIIC (most hazardous).

4.Practical Application & Selection
Determine if the environment is gas (Zone 0/1/2) or dust (Zone 20/21/22).
Identify the exact group using IEC standards or material SDS.
Check equipment marking, for example:
Ex db IIC T4 Gb = Flameproof, IIC gas, T4 temperature, suitable for Zone 1.
Ex tb IIIC T135°C Db = Dust protection, IIIC dust, suitable for Zone 21.

Selection Rules:
Use higher-rated equipment for lower hazards (IIC covers IIA & IIB; IIIC covers IIIB).
Always match Temperature Class (T1–T6) and EPL (Ga/Gb/Gc or Da/Db/Dc).
Quick Memory:
Gases: Propane (IIA) → Ethylene (IIB) → Hydrogen (IIC)
Dusts: Metal (IIIC) → Non-metal (IIIB) → Flyings (IIIA)

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