- 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
|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|
|Gas||NEC Explosive Group||IEC Explosive Group|