CompEx Ex02 covers the installation of electrical equipment in areas classified for gas group IIC — which includes hydrogen, acetylene, and carbon disulphide. These gases have the smallest flammability gaps and the lowest ignition energies, requiring the most stringent Ex equipment and the most careful installation practices.
The Additional Requirements of IIC
IIC areas require everything that IIA/IIB areas require, plus additional considerations driven by the properties of hydrogen and acetylene:
- Every component must be IIC rated — this cannot be overstated. A single IIB gland in an IIC area is a serious non-compliance.
- Tighter flamepath requirements — Ex d enclosures for IIC have tighter flamepath gap limits per IEC 60079-1 Table 1
- Barrier glands — in IIC Ex d enclosures >2 litres, barrier glands are required; in IIC areas with clearance entries, barrier glands are always required
- IIC stopping plugs — must be IIC certified, not IIB
- IIC certified instruments and luminaires — equipment ratings must match the area classification
Hydrogen has a flammability range of 4% to 75% in air — far wider than most gases. It also has a very low ignition energy (<0.02 mJ) and high flame speed. This is why IIC gas group requirements are the most stringent — the equipment must contain any internal ignition more effectively than for IIA or IIB gases.
Where is IIC Classification Used?
IIC areas are found at hydrogen production and storage facilities, LNG terminals, coke oven plants, battery manufacturing facilities (hydrogen evolved during charging), chemical plants with hydrogen by-products, and acetylene production sites. As hydrogen becomes more prominent in the UK energy transition, demand for Ex02 qualified electricians is increasing rapidly.
Ex02 Installation Checklist
When carrying out an Ex02 installation, the candidate (and the practical assessment) will focus on these specific verification steps:
- Confirm gas group on every component — enclosure, gland, stopping plugs, and any sub-assembly must each carry IIC certification individually; checking only the main enclosure rating is not sufficient
- Verify flamepath gap compliance — for Ex d enclosures, confirm the manufacturer's certificate states gaps compliant with IEC 60079-1 IIC limits for the relevant enclosure volume
- Select barrier glands correctly — apply the same volume and entry-type rules as IIB, but using IIC-rated barrier gland components specifically
- Cross-check stopping plug certification — a stopping plug correctly sized but only IIB rated is a non-compliance in an IIC installation
- Document the certification trail — installation records should clearly show the IIC rating was verified for each component, supporting future inspection and audit
Ex01 vs Ex02 — What Changes in Practice
If you already hold Ex01, the practical skills largely transfer directly to Ex02 — gland selection methodology, stopping plug installation, and earthing practices follow the same underlying principles. What changes is the certification standard you're checking against at every step, and the margin for error shrinks considerably. An IIB component substituted into an IIA installation might be a minor non-compliance in some contexts; the same substitution of an IIB component into an IIC installation is a serious safety failure, since IIC gases like hydrogen can propagate through gaps that IIB equipment isn't designed to contain.
EX Academy's equipment selection simulator includes IIC-specific scenarios that mirror this exact decision process — selecting the correct gland, stopping plug, and accessories for a hydrogen-classified installation, with immediate feedback on any component that doesn't meet the IIC standard.