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Text version of the page
| 5. Classification of Dust Explosion Hazardous Areas into Zones | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The classification into zones has proved its effectiveness in gas atmospheres for years. The definition of zones agreed on throughout Europe in accordance with Directive 99/92/EC applies only to swirled-up dust. Accumulations and deposits of combustible dust must be taken into consideration as well, like all other factors that could lead to the creation of an explosive atmosphere. Dust deposits are seen merely as a "source of release" for an explosive atmosphere. Among other sources, EN 50281-3 (Classification of areas where combustible dusts are or may be present) can provide help with the classification. In Table 6 and Table 7, zone classification and zone definitions are once again given, as well as the connection between the zones and the equipment categories of Directive 94/9/EC. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Table 6: Zone Definitions | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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. NOTE: In general these conditions, when they occur, arise inside containers, pipes and vessels etc. 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 occasionally. NOTE: This zone can include, among others, areas in the immediate vincinity of e.g. powder filling and emptying points and areas where dust layers occur and are likely in normal operation to give rise to an explosive concentration of combustible dust in a mixture with air. Zone 22 A place in which 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, will persist for a short period only. NOTE: This zone can include, among others, areas in the vincinity of equipment, protective systems, and components containing dust, from which dust can escape from leaks and from dust deposits (e.g. milling rooms, in which dust escapes from the mills and then settles). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Table7: Zone Concept and Impacts of Directives 94/9/EC and 1999/92/EC | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| R.STAHL Explosion protection | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||