In North America, hazardous locations have traditionally been defined by a combination of classes and divisions as follows:
- Class I – A location made hazardous by the presence of flammable gases or vapors that may be present in the air in quantities sufficient to produce an explosive or ignitable mixture
- Class II – A location made hazardous by the presence of combustible or electrically conductive dust
- Class III – A location made hazardous by the presence of easily ignitable fibers or flyings in the air, but not likely to be in suspension in quantities sufficient to produce ignitable mixtures
- Division 1 – A location where a classified hazard exists or is likely to exist under normal conditions
- Division 2 – A location where a classified hazard does not normally exist but is possible to appear under abnormal conditions
North American transition to the zone system
The U.S. and Canada have recently revised installation codes to recognize an international 3-Zone area classification system for equipment used in hazardous locations.
- Zone 0 – An area in which an explosive gas atmosphere is continuously present for a long period of time
- Zone 1 – An area in which an explosive atmosphere is likely to occur in normal operation
- Zone 2 – An area in which an explosive gas atmosphere does not normally exist.
In Canada, all new installations must use the 3-Zone system. Existing installations may continue to use the 2-Division system or opt to re-classify using the 3-Zone system.
In the U.S., all installations (both new and existing) can either continue using the 2-Division system or re-classify their product using the 3-Zone system.