Explosion-proof appliances gas group
The explosive capacity of an explosive gas mixture indicates the level of its explosion risk. The greater the explosive capacity of an explosive mixture, the higher the risk. The explosive capacity of an explosive mixture can be represented by the maximum test safety clearance. At the same time, the degree of difficulty in the ignition of explosive gases, liquid vapors, and mists also indicates the degree of explosion risk, which is expressed in terms of the minimum ignition current ratio. Type II flameproof electrical equipment or intrinsically safe electrical equipment is further classified into categories IIA, IIB and IIC according to the maximum test safety clearance or minimum ignition current ratio applicable to explosive gas mixtures.
As shown in table 2. 
Table 2 Relationship between group of explosive gas mixtures and maximum test safety clearance or minimum ignition current ratio