Hazardous zone classification electrical

Following the historical development of electrical engineering and explosion protection, zone classification was the objective of national standards and installation rules. Most of the leading industrial countries established an installation practice for chemical plants and the oil and gas industry with two or three zones for areas hazardous due to gas- or vapour-air mixtures and two zones for areas with hazardous dust-air mixtures. Apart from this philosophy, the coal mining industry in most countries tends to avoid an area classification and defines only one category of explosion protection ( firedamp-proof ). More recent standards or directives present a three-zone concept for areas endangered by combustible gas- (vapour-, mist-) air mixtures and dust-air mixtures in industrial plants (other than coal mines). 

At the present time, IEC 61241-3 combined with IEC 61241-1-1 and with IEC 61241-1-2 as international standards describe construction and testing of electrical apparatus for areas hazardous due to combustible dusts on the basis of a three-zone classification (zones 20,21 and 22). 

Human error Control system reliability Task/HRA or procedural study Power supply, common mode failure Fir explosion Electrical zone classification/ hazardous study/ equipment compliance... 

For zone classification process flow diagram (PFD), P IDs, cause and effect diagrams, area classification of plants for electrical apparatus (ref. Chapter X) and plot plans are required documents for zone classification. In process plants, different areas have different leakage or release hazards, for example, hydrocarbon storage area will have flammable gas release whereas sulfur recovery units pose a H2S toxic gas hazard. So, it is imperative to define and segregate the zones from each other. 

Employers in control of hazardous areas need to determine the locations and extents of these zones in each of the hazardous areas, an exercise known as hazardous area classification. At present, in 2001, there is no specific legal duty to carry out hazardous area classification, apart from the general duties to carry out risk assessments and, in the context of mines, in Regulation 19 of the Electricity at Work Regulations. However, the Protection of Workers Potentially at Risk from Explosive Atmospheres Regulations expected to be enacted soon, will contain specific provisions relating to area classification and the need to record the area classification information in an explosion protection document. 

Where there are flammable materials that constitute an explosion risk, the locations in which the explosion risk exists are called hazardous areas. These areas are classified into zones according to the extent of the risk, using guidance published in BS EN 60079-10 1996 Electrical apparatus for explosive gas atmospheres. Part 10 Classification of hazardous areas. The zones are also defined in the European Directive on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres. The zones are ... 

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