Hazardous areas according to ATEX and IECEx Zones
Zones - define the type of explosive atmosphere as well as the likelihood of an explosive atmosphere being present
0 - Explosive gas atmosphere present continuously or for long periods
1 - Explosive gas atmosphere likely to occur in normal operation
2 - Explosive gas atmosphere not likely to occur in normal operation but may be present for short periods
20 - Explosive dust atmosphere present continuously or for long periods
21 - Explosive dust atmosphere likely to occur in normal operation
22 - Explosive dust atmosphere not likely to occur in normal operation but may be present for short periods
Hazardous areas according to North American classes and divisions
Classes - define the type of explosive atmosphere
I - A location made hazardous by the presence of flammable gas or vapour that may be present in the air in quantities sufficient to produce an explosive or ignitable mixture
II - A location made hazardous by the presence of combustible or electrically conductive dust
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
Divisions - define the likelihood of an explosive atmosphere being present
1 - A location where a classified hazard exists or is likely to exist under normal conditions
2 - A location where a classified hazard does not normally but is possible to appear under abnormal conditions
In the USA, all installations can use either the Class / Division or the Class / Zone system.
In Canada new installation must now use the Class / Zone system of Zones instead of Divisions. Existing installations may use either system.
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