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Gas Groups  -  Grouped by Risk

Gases and vapours are divided into Groups of similar risk. Group I is for gases found below ground e.g. in mines. Group II gases are those found in chemical and process plants and are further subdivided into IIA, IIB and IIC in ascending order of danger. The factors used in grouping gases include the ability of a gas to spread into the atmosphere and its ease in achieving its lowest explosive concentration. When equipment is suitable for IIC gases, it is automatically suitable for IIB and IIA gases also. Hydrogen is regarded as one of the most dangerous gases and is an example of a Group IIC gas.

Classification of Common Gases

    Temperature Classes
    T1 T2 T3 T4 T5 T6
Gas Groups I Methane Ethyl Alcohol Petrol Acetaldehyde    
Acetone I-Amyl Acetate Diesel Ethyl-Ether    
Ethane N-Hexane Aviation Fuel      
Ethyl Acetate N-Butyl Alcohol Heating Oil      
Ammonia          
Benzol          
Acetic Acid          
Carbon Monoxide          
Methanol          
Propane          
Toluene          
IIB Town Gas          
IIC Hydrogen         Hydrogen Disulphide