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DSEAR challenges
hazardous places. Any hazardous workplace should be further classified into hazardous zones; however firstly, alternative solutions should be sought through reviewing storage and process arrangements, and evaluating if appropriate levels of ventilation will remove or reduce the overall hazardous area classification. Such classification should be undertaken as
part of the risk assessment process and the information recorded. The purpose is to ascertain the extent to which an explosive atmosphere occurs and the frequency of occurrence, which will determine the level of protection required. Hazardous places are classified in terms of zones on the basis of the frequency and duration of the occurrence of an explosive atmosphere. In the information below is an outline of the
zone classifications for gas atmospheres, taken from BS EN 60079-10-1: 2015 Explosive atmospheres. Classification of areas. Explosive gas atmospheres: • Zone 0 – an area in which an explosive gas atmosphere is present continuously or for long periods or frequently
exist in the area concerned. Generally speaking, such gases and vapours are contained within process equipment, which may or may not be totally enclosed. Firstly, it is necessary to establish whether a
flammable atmosphere can exist inside the piece of equipment or machinery, and then to identify possible locations for release into the atmosphere outside the equipment, such as mechanical openings, valves, gaskets and joints. Explosive dust atmospheres are formed from
sources of dust release, a point or location from which dust can be released or raised such that an explosive dust atmosphere can be formed. This definition includes layers of dust capable of being dispersed to form a dust cloud, with the following grades of release: • continuous grade of release, which is continuous or is expected to occur frequently or for long periods
• primary grade of release, which can be expected to occur periodically or occasionally during normal operation
• secondary grade of release, which is not expected to occur in normal operation and, if it does occur, is likely to do so only infrequently and for short periods
Explosive atmospheres Zone 21
Areas where explosive atmospheres may occur need to be classified into hazardous and non
44 MARCH 2020
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A place in which an explosive dust atmosphere, in the form of a cloud of dust
• Zone 1 – an area in which an explosive gas atmosphere is likely to occur in normal operation occasionally
• Zone 2 – an area in which an explosive gas atmosphere is not likely to occur in normal operation, but which if it does occur, will persist for a short period only
The zone’s extent depends on the estimated or calculated distance over which an explosive atmosphere exists before it disperses to a concentration in air below its lower explosive limit with an appropriate safety factor. When assessing the area of spread of gas or vapour before dilution to below its lower explosive limit, expert advice should be sought. Meanwhile, the following information
provides an outline of the zone classifications for dust atmospheres, taken from BS EN 60079-10-2: 2015: Explosive atmospheres. Classification of areas. Explosive dust atmospheres:
Zone 20 A place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is present continuously, for long periods or frequently, and the extent includes the inside of ducts, producing and handling equipment in which explosive dust atmospheres are present. If such an atmosphere outside dust containment is continuously present, a Zone 20 classification is required.
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