The ratio of the ignition current of gas and vapor explosive mixtures to the ignition current of methane explosive mixtures under specified test conditions. China stipulates that gas and vapor hazardous substances are classified as Class IIA, Class IIB, and Class IIC according to the ignition current ratio. The ignition current ratio of ≤ 1.0 and>0.8 is classified as Class IIA; ≤ 0.8,>0.45 is classified as IIB level; ≤ 0.45 is classified as Grade IIC. For example, ethane, ethylene, and acetylene are classified as Class IIA, Class IIB, and Class IIC hazardous substances, respectively.