There are industrial processes which involve a risk of fire or explosion . Generally , the risk arises because flammable vapour or dusts are present in the atmosphere . For example , in coal mines there is always the possibility of methane appearing in sufficient concentration to ignite or burn . In such cases any electrical equipment in the area subject to risk must be specially designed to reduce that risk .
The mere flow of electricity will not ignite a vapour unless the temperature becomes to high . The temperature can be kept low by adequate sizing of the cables so that this is not a problem as far as the installation is concerned . The surface temperature of motors , luminaires and other electrical equipment must , however , be considered . Vapour can also be ignited by spark at a terminal or switch or as a result of mechanical damage causing a spark or local hot spot . THere are various ways of designing equipment to reduce the risk in harzardous with European standard if the national standard do not exactly match . If the national standard are identical , then they will be designated as a Euro-Norm EN .
Under the European ATEX directive 1992/92/EC . on the /minimum requirement for Improving the Safety and Health Protection of Workers at Risk from Explosive Atmospheres ' , it is necessary to consider both the type and magnitude of the risk . The magnitude of the risk is the probability of a dangerous concentration of flammable vapour , and hazardous areas are classified into three zones according to the likelihood of such a concentration :
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