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.