The zoning of explosive atmospheres is based on the frequency and duration of the occurrence of explosive gas mixtures.
"Code for Design of Electrical Installations in Explosion and Fire Hazardous Environments" (GB 50058) divides explosive gas atmospheres into three-level hazardous areas.
1. Zone 0. An environment in which explosive gas mixtures are continuously or permanently present.
2. Zone 1. Environments where explosive gas mixtures may occur during normal operation.
3. Zone 2. An environment in which an explosive gas mixture is unlikely to occur during normal operation, or an environment in which an explosive mixture exists only for a short period of time if it occurs.
