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

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

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Date： 2025-05-16

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

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

Group	Hazard Level	Typical Gases / Vapors	Common Applications
IIA	Lower	Propane, gasoline, methane, ethanol, acetone, natural gas	Gas stations, LPG storage, general solvents
IIB	Medium	Ethylene, diethyl ether, butadiene, hydrogen sulfide	Ethylene plants, solvent areas, pharmaceuticals
IIC	Highest	Hydrogen, acetylene, carbon disulfide	Hydrogen stations, acetylene generators, battery rooms

Key Tip: Hydrogen or acetylene = IIC (highest requirement). IIC equipment works for all gas groups.

Group	Type	Typical Dusts	Common Applications
IIIA	Combustible flyings	Cotton lint, wood fibers, plastic flyings	Textile & woodworking
IIIB	Non-conductive dusts	Flour, grain, wood dust, plastic dust, sugar	Food processing, plastics
IIIC	Conductive dusts	Aluminum, magnesium, metal powders, carbon black, coal dust	Metal powder plants, mining

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: e.g., Ex db IIC T4 Gb = Flameproof, IIC gas, T4 temperature, suitable for Zone 1.
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).