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Gas Group Lookup Tool — IIA IIB IIC Gas Selector

EX Academy Knowledge Base · IEC 60079 · CompEx Preparation · 2025

Use this reference to look up the gas group classification for common flammable gases and vapours. Gas group classification determines the minimum equipment requirements for hazardous area installations — the higher the group number (IIC), the more sensitive the gas and the more stringent the equipment requirements.

Gas Group Reference Table

Gas / VapourGas GroupMESG (mm)Auto-Ignition Temp
HydrogenIIC0.29500°C
AcetyleneIIC0.37305°C
Carbon disulphideIIC0.3490°C
EthyleneIIB0.65425°C
Hydrogen sulphideIIB0.87270°C
CyclopropaneIIB0.75500°C
Methane (natural gas)IIA1.14537°C
PropaneIIA0.92470°C
ButaneIIA1.09365°C
HexaneIIA0.93225°C
AmmoniaIIA3.17651°C
Petrol (gasoline)IIA0.92280°C
Equipment Selection Rule

Equipment must be rated for the gas group present, or a higher group. IIC equipment is suitable for any area. IIB equipment is suitable for IIA and IIB areas but not IIC. IIA equipment is only suitable for IIA areas. When in doubt, specify IIC equipment — it provides the highest level of protection.

How Gas Group Affects Equipment

Gas group affects the flamepath gap limits for Ex d equipment (IIC requires the tightest gaps), the IS circuit design for Ex i equipment (IIC gases have the lowest ignition energy), and the MESG used for equipment certification testing. Always verify the gas group classification for your specific hazardous area from the area classification drawings before selecting equipment.

Practice Gas Group Selection

EX Academy's equipment selection simulator tests your ability to match equipment to the correct gas group. Scenario 02 (Zone 1 IIC) and Scenario 08 (LCS in IIC) specifically test IIC requirements. Try Scenario 01 free — no card required.

Put This Into Practice

Interactive inspection simulations, equipment selection decisions, and 1,185+ practice questions referenced to IEC 60079. Try free — no card required.

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