According to CENELEC and IEC, hazardous locations in Europe are divided into six different danger zones. The higher the probability that a potentially explosive atmosphere occurs, the more rigorous the requirements on operating equipment to prevent, for example, origination of sparks or hot surfaces.
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Which resources are permitted for use in a zone can be derived from the specific operating equipment and in dependence on the zone allocation. In order to specify for which zone specific operating equipment may be used, the device group and category are relevant. The explosion protection zone in which the operating equipment may be operated is defined based on temperature classes and explosion groups.
In North America, a different classification system based on the standards NEC 500 and NEC 505 is applied. Here, flammable substances are divided into three classes (Classes I to III). Explosive gases, vapors and mists of Class I are subdivided into the gas groups A, B, C and D; flammable dusts of Class II into the groups E, F and G.
Depending on the frequency or duration of occurrence of these materials, the hazardous locations are divided into so-called divisions. Division 1 corresponds to Zones 0 and 1 and Division 2 to Zone 2. In addition to the division of the explosive areas, the construction of the operating equipment and installation of the electrical systems are also differentiated.
| Gas group (group) | Material examples |
| A | Acetylene |
| B | Hydrogen |
| C | Ethylene |
| D | Propane |
| E | Metal dust |
| F | Coal dust |
| G | Grain dust |
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