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For potentially explosive atmospheres the term“hazardous (classified) locations” is used in North America.These are defined in Articles 500 and 505 of the National Electrical Code (NEC) in the USA and in Section 18 and Annex J of the Canadian Electrical Code (CEC) in Canada. Hazardous locations are locations, where fire or explosion hazards may exist due to flammable gases, vapours or mists (Class I), combustible dusts (Class II), or ignitable fibres or flyings (Class III).Based on the likelihood or risk that an ignitableconcentration of a flammable substance will be present the hazardous locations are traditionally subdivided into Division 1 and Division 2. In 1996 the IEC classification system was intro-duced as a parallel system to the existing system for ClassI in the USA.This system was imple- mented by the new Article 505.This now gives the end user the possibility to choose the system that best suits his needs.The IEC zone classification for Class I was alsointroduced in Canada (CEC, 1988 edition). All newly built facilities in Canada need to be classified according to this principle.The traditional North American classification system divides Class I flammable gases, vapours, mists and liquids into Gas Groups A, B, C and D, and Class II combustible dusts into Groups E, F and G.Group A is the most hazardous gas group in thetraditional NEC system whereas Group IIC is the most hazardous group in the IEC system in Article 505 of the NEC.In Canada both gas grouping systems may be usedwith the zone classification system.The maximum surface temperature determinationgiven in the new Article 505 maintains a pure IEC approach of having main temperature classes T1 to T6 with further subdivisions of the tempera- ture classes in the Division system. In the 1998 CEC, this structure T1–T6 with intermediate sub- divisions was maintained.Table 19 in appendix 7.3 provides an overview of the classification of hazardous locations in North America.

The basics of explosion protection - 9224 6.explosion protection in north america

6.2 Classification of Hazardous Locations 31 6. Explosion Protection in North America6.1 Introduction The basic principles of explosion protection are the same all over the world. However, tech- nologies have developed in North America in the field of explosion protection for electrical equip- ment and installations which deviate considerably from those of the IEC (International Electrotech- nical Commission).The differences from IEC tech- nologies are among others the classification of hazardous locations, the construction of apparatus and the installation of electrical systems.
R.STAHL explosion protection