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Relevance and advantage of the classification in zones
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| The practice has been established of dividing hazardous areas into zones. This classification takes the different dangers from potentially dangerous atmospheres into account and allows explosion protection measures to be taken which reflect the situation both from the point of view of safety engineering and of economics. For the European community, the zone definitions are uniformly provided in directive 1999/92/EC. It must be applied with technical unterstanding of the concrete situation.
IEC 60079-10 assumes an approximately similar classification for gases and vapours which will also apply to future facilities constructed conforming to the USA standard NEC 505. IEC 61241-3 provides support for the zone classification with dust.
Explosion hazard zones are classified depending on the frequency and duration of the potentially explosive atmosphere.
This classification provides the scope of the measures to be taken according to annex II section A in the directive 1999/92/EC in conjunction with annex I of the directive 94/9/EC.
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Classification of hazardous places |
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| Zone 0 |
A place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently. |
| Zone 1 |
A place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally. |
| Zone 2 |
A place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only. |
| Zone 20 |
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently. |
| Zone 21 |
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasinoally. |
| Zone 22 |
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only. |
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Notes:
1. Layers, deposits and heaps of combustible must be considered as any other source which can form an explosive atmosphere.
2. 'Normal operation' means the situation when installations are used within their design parameters.
In places of work the explosion hazard areas are normally classified at most as zone 1 and 2 and/or 21 and 22. Zones 0 and 20 are restricted to very small inaccessible areas in workplaces or are usually estricted to the inside of technical equipment.
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