Area classification for explosive atmospheres: comparison between European and North American approaches

The object of this paper is to review various methods of determining the extent of hazardous areas in industrial facilities where explosive gas or vapor atmospheres may be present. Three different approaches are analyzed and compared. The first one is recommended in North American Standards, such as APl500 [1], APl505 [2] and NFPA 497 [3]. The second is one of the proposals for the second edition of the International Standard IEC 60079-10-1 [4] (adopted as European standard EN 60079-10-1). The third approach had been previously worked out with the authors' contribution and had been adopted by the Italian Guide CEI 31-35 since 2001 [5]. The last two approaches are analytical, meanwhile the first one is prescriptive. In the second part of the paper both analytical approaches are applied to the releases which are analyzed in NFPA 497 [3] as practical examples. Resulting hazardous area extents are compared and the differences among the three methods are discussed.