The classification system that found in Article 500:
- divides all hazardous (classified) locations into Classes (I, II & III), Divisions (1 & 2) and Groups (A, B, C, D, E, F & G).
- Class I locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitible mixtures.
- Class II locations are those that are hazardous because of the presence of combustible dust.
- Class III locations are those that are hazardous because of the presence of easily ignitible fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitible mixtures.
- Division 1 is a location where an ignitible concentration of a flammable or combustible material is present under normal operating conditions.
- Division 2 is a location where an ignitible concentration of a flammable or combustible material is present only under abnormal operating conditions.
- Class I Group Classifications:
Group A – Acetylene.
Group B – A typical Class I, Group B material is hydrogen.
Group C – A typical Class I, Group C material is ethylene.
Group D – A typical Class I, Group D material is propane.
- Class II Group Classifications:
Group E - Metal dusts.
Group F - Carbonaceous dusts.
Group G - Combustible dusts not included in Groups E or F.
[Note] NEC - National Electrical Code of USA
GCS Safety Team