Ingeniero Lectrico

EXPLOSIVE ATMOSPHERES - CLASSIFICATION OF HAZARDOUS AREAS (ZONING) AND SELECTION OF EQUIPMENT OVERVIEW ASSESSING THE RISK RELATIONSHIP BETWEEN FIRES AND EXPLOSIONS CLASSIFYING HAZARDOUS AREAS INTO ZONES MAINTENANCE EQUIPMENT IN HAZARDOUS AREAS MARKING OF EQUIPMENT SELECTION OF EQUIPMENT HAZARDOUS AREA ZONES AND EQUIPMENT CATEGORIES Overview Gases, vapours, mists and dusts can all form explosiveatmospheres with air. Hazardous area classification is used to identify places where, because of the potential for an explosive atmosphere, special precautions over sources of ignition are needed to prevent fires and explosions. Hazardous area classification should be carried out as an integral part of the risk assessment to identify places (or areas) where controls over ignition sources are needed(hazardous places) and also those places where they are not (non hazardous places). Hazardous places are further classified in Zones which distinguish between places that have a high chance of an explosive atmosphere occurring and those places where an explosive atmosphere may only occur occasionally or in abnormal circumstances. The definitions of the Zones (which are included in DSEAR) alsorecognise that the chance of a fire or explosion depends on the likelihood of an explosive atmosphere occurring at the same time as an ignition source becomes active. DSEAR defines a place where an explosive atmosphere may occur in quantities that require special precautions to protect the health and safety of workers as hazardous. A place where an explosive atmosphere is not expected to occur inquantities that require such special precautions is deemed to be non-hazardous. For these purposes “special precautions” means precautions to control potential ignition sources within a hazardous area, particularly in relation to the construction, installation and use of equipment. The term “not expected to occur in such quantities” means that employers should consider the likelihood of releases ofexplosive atmospheres as well as the potential quantity of such releases when considering area classification. So if a release is extremely unlikely to occur and/or if the quantities released are small, it may not be necessary to classify the area as hazardous. For example, if a dangerous substance is being carried through a seamless pipe, and that pipe has been properly installed and maintained,it is extremely 1

unlikely that the substance will be released. An explosive atmosphere would not be expected to occur from this source and the area surrounding the pipe would be non-hazardous. A spillage from a small bottle of solvent would release so little flammable material that no special precautions are needed other than the general control of ignition sources (for example, no smoking)and cleaning and disposing of the spillage. It would not be classified as a hazardous area. When considering whether hazardous area classification is necessary for “small” quantities of dangerous substances the actual circumstances of use and any specific industry guidance should also be taken into account. Dangerous substances in small pre-packaged containers for sale, display, etc. in retailpremises would not normally ("normal" is intended to ensure that atypical situations such as a poorly ventilated basement in a Shop etc. where aerosols or other flammables are present remains subject to a hazardous area classification study) require the area to be classified as hazardous. However we would expect a hazardous area classification to be carried out for prepackaged containers held in largequantities e.g. in warehouses. Procedures to clean up and dispose of any spillage/release and to control ignition sources in the event of such a release would be needed. Assessing the risk Identifying hazardous or non-hazardous areas should be carried out in a systematic way. Risk assessment should be used to determine if hazardous areas exist and to then assign zones to those areas. The...