I. Introduction

  • North American Standard (US)
    • NEC Articles 500, 501, 502 and 503 provide rules for the installation of electrical equipment in classified locations.
    • API RP 500 and NFPA 497 provide guidelines and recommended practices for Class I locations.
    • NFPA 499 provides recommended practices for Class II locations.
    • NFPA 497 and 499 also provide guidelines for using the zonal classification method.
    • In 1996 the NEC added Article 505 for locations classified as Class I, Zone 0, 1, and 2.
    • API RP 505 was published in 1997and provides guidelines and recommended practices for using the zonal classification method in Class I locations.
  • International Standards (IEC)
    • The IEC60079-10 is the international standard used to define the NATURE of the hazards and the hazardous areas, i.e. the zones, gas groups, temperature classes, etc.
    • Each country uses their national Code to establish the EXTENT of the hazardous areas. ISA 12.24.01 is the ANSI-normalized version of IEC 60079-10.
    • API RP 505 is the USA-normalized version of IEC 60079-10 for petroleum facilities.
    • Institute of Petroleum Code 15 (IP 15) is often used when performing area classifications since it provides more detailed guidelines for boundaries and extents than IEC 60079-10.

II. Zone Definitions

  • Zone 0 – An area in which an explosive gas-air mixture is continuously present or present for long periods.This is comparable to Class I, Division 1 hazardous (classified) locations as defined by the NEC. Generally, most industrial users try to keep all electrical equipment out of Zone 0 areas. The only equipment approved for use in Zone 0 applications is intrinsically safe equipment.
  • Zone 1 – An area where an explosive gas-air mixture is likely to occur in normal operations. Zone 1 also comparable to NEC Class I, Division 1 applications.
  • Zone 2 – An area in which an explosive gas-air mixture is not likely to occur and if it does, it is only for a short period of time and occurs under abnormal operating conditions. This is comparable to a Class I, Division 2 location area as defined by the NEC.
  • Zone 10 – An area in which an explosive atmosphere as a result of dust which is continuously present or present for long periods of time. This is comparable to an NEC Class II, Division 1 application.
  • Zone 11 – An area with a short-lived explosive dust atmosphere from unsettling dust deposit. This is comparable to an NEC Class II, Division 2 location.

    • Note: Class III locations (fibers and flyings) are covered in Zone 10 and Zone 11 areas.

    III. Comparison of Area Classifications

    Area Classification Compared
    Hazardous Material NEC U.S. Standards IEC Standards
    Gas or Vapor Class I, Division 1 Zone 0 and Zone 1
    Class I, Division 2 Zone 2
    Dust Class II, Division 1 Zone 10
    Class II, Division 2 Zone 11
    Fibers or Flyings Class III, Division 1 Zone 10
    Class III, Division 2 Zone 11

    IV. Classification of Gases and Vapors

    The grouping of hazardous gases and vapors is based on the explosive characteristics of the material.

    Simplified NEC and IEC systems designation of gases and vapors.
    Gas NEC Explosive Group IEC Explosive Group
    Acetylene A II C
    Hydrogen B II C
    Ethylene C II B
    Propane D II A

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