Zone Equipment Category Group Hazardous Area Characteristics Area Classification Gas Dust NEC 505 NEC 500 0 20 1 II Present continuously or for long periods of time Zone 0 Division 1 1 21 2* Likely to occur in normal operation occasionally Zone 1 2 22 3   Not likely to occur during normal operation Zone 2 Division 2         *Electrical equipment and internal combustion engines only     Material Classification: I = Gas II = Dust III = Fibre :: Ex Protection :: Protection Concepts :: Temperature Class :: Equipment Groups