ER Series motors are rated for Class I, Div 1, Groups B, C and D. The classification of "Class I" means that flammable gases or vapors may be present in the air in quantities sufficient to produce explosive or ignitable mixtures. "Division 1" means that hazardous concentrations in the air may exist continuously, intermittently, or periodically under normal operating conditions. "Group B" allows for atmospheres containing hydrogen, or gases (or vapors) of equivalent hazard, such as manufactured gas. "Group C" allows for atmospheres containing etyhyl-ether vapors, ethylene or cyclo propane. "Group D" allows for atmospheres containing gasoline, hexane, naptha, benzene, butane, alcohol, acetone, benzol, lacquer solvent vapors, or natural gas. ER Series motors are not rated for operation in atmospheres containing acetylene.