Using the Zone Instead of the Division Classification for Class I Locations

Date First Published on SafetySmart Compliance: January 3rd, 2012
Topics: Electricity |

The article, How to Comply with OSHA Hazardous (Classified) Location Requirements explains the OSHA hazardous (classified) location system and the safety precautions it requires be taken when electrical installations are located in environments containing flammable or combustible substances. Class I Locations contain or potentially contain ample quantities of flammable gases or vapors in the air to produce explosive or ignitable mixtures. The OSHA standard (1910.307) gives you the option to use the zone classification system as an alternative to the division classification system for electric and electronic equipment and wiring for all voltages in Class I, Zone 0, Class I, Zone 1, and Class I, Zone 2 hazardous (classified) locations where fire or explosion hazards may exist due to flammable gases, vapors or liquids. Here’s how the rules work.

Classification Requirements

Locations must be classified based on the properties of the flammable vapors, liquids or gases that may be present and the likelihood that a flammable or combustible concentration or quantity is present. Exception: Locations in which pyrophoric materials are the only materials used or handled need not be classified.You must consider each room, section or area individually in determining its classification.

Equipment Requirement

All threaded conduit must be threaded with an NPT (National (American) Standard Pipe Taper) standard conduit cutting die that provides 3/4-in. taper per foot. The conduit must be made wrench tight to prevent sparking when fault current flows through the conduit system and to ensure the explosion-proof or flameproof integrity of the conduit system where applicable. Equipment provided with threaded entries for field wiring connection must be properly installed.

For equipment provided with threaded entries for NPT threaded conduit or fittings, listed conduit, conduit fittings, or cable fittings must be used. For equipment with metric threaded entries, such entries must be identified as being metric, or listed adaptors to permit connection to conduit of NPT-threaded fittings are provided with the equipment. Adapters must be used for connection to conduit or NPT-threaded fittings.

Implement Protection Techniques

You must use one or more of the following protection techniques for electric and electronic equipment in hazardous (classified) locations classified under the zone classification system:

  • Flameproof “d”: Okay for equipment in the Class I, Zone 1 locations for which it’s approved;
  • Purged and pressurized: Okay for equipment in the Class I, Zone 1 or Class I, Zone 2 locations for which it’s approved;
  • Intrinsic safety: Okay for equipment in the Class I, Zone 0 or Class I, Zone 1 locations for which it’s approved;
  • Type of protection “n”: Okay  for equipment in the Class I, Zone 2 locations for which it’s approved (Type of protection “n” is further subdivided into nA, nC and nR);
  • Oil Immersion “o”: Okday for equipment in the Class I, Zone 1 locations for which it’s approved;
  • Increased safety “e”: Okay for equipment in the Class I, Zone 1 locations for which it’s approved;
  • Encapsulation “m”: Okay for equipment in the Class I, Zone 1 locations for which it’s approved; or
  • Powder Filling “q”: Okay for equipment in the Class I, Zone 1 locations for which it’s approved.

Equipment construction and installation must ensure safe performance under conditions of proper use and maintenance. You also need to ensure that classification of areas and selection of equipment and wiring methods is under the supervision of a qualified registered professional engineer.

Overlapping of Classified Areas within the Same Location & Reclassification

Where areas within the same facility are classified separately:

  • Class I, Zone 2 locations may not overlap (but  may abut) Class I, Division 2 locations;  and
  • Class I, Zone 0 and/or Class I, Zone 1 locations may not abut Class I, Division 1 or Class I, Division 2 locations.

Class I, Division 1 or Class I, Division 2 locations may be reclassified as a Class I, Zone 0, Class I, Zone 1 or Class I, Zone 2 location only if all of the space that’s classified because of a single flammable gas or vapor source is reclassified.

Equipment Installation & Markings

Equipment listed for a Zone 0 location may be installed in a Zone 1 or Zone 2 location of the same gas or vapor. Similarly, equipment listed for a Zone 1 location may be installed in a Zone 2 location of the same gas or vapor.

All equipment must be properly marked.Equipment approved for Class I, Division 1 or Class 1, Division 2 must also marked with the following:

  • Class I, Zone 1 or Class I, Zone 2 (as applicable);
  • Applicable gas classification groups; and
  • Temperature classification.

Equipment meeting one or more of the protection techniques used in hazardous (classified) locations classified under the zone classification (which are listed above starting with Flameproof “d”) must be marked with the following in the order shown:

  • Class (except for intrinsically safe apparatus);
  • Zone (except for intrinsically safe apparatus);
  • Symbol “AEx;”
  • Protection techniques;
  • Applicable gas classification groups; and
  • Temperature classification (except for intrinsically safe apparatus).

Exception: Equipment need not be marked if you can demonstrate that it provides protection from the hazards arising from the flammability of the gas or vapor and the zone of location involved and is recognized as providing such protection by employees.

(Note: The National Electrical Code, NFPA 70, contains guidelines for determining the type and design of equipment and installations that meets this provision.)