How to Comply with OSHA Hazardous (Classified) Location Requirements

Date First Published on SafetySmart Compliance: March 12th, 2012
Topics: Electricity |

Shock and the risk of arc flash make electrical installations and equipment inherently dangerous. But putting those electrical properties in the vicinity of flammable or combustible substances, is like danger on steroids. That’s why the OSHA electrical safety requirements (Subpart S of the General Industry Standard) includes a standard (Sec. 1910.307) specifically addressing the safety precautions needed when electrical installations and equipment are contained in hazardous or “classified” locations. Here are the requirements and how to comply.

Step 1: Classify Locations

The first thing you need to do is determine if there are any classified locations in your workplace and, if so, what classification they fall into. In determining classification, you must consider each room, section or area individually. Section 1910.307(a) establishes the different tiers of “classified” locations you need to use:

Class Locations

Class I Locations contain or potentially contain ample quantities of flammable gases or vapors in the air to produce explosive or ignitable mixtures. Class I locations are broken down into 3 subdivisions:

Class I, Division 1 locations are those in which:

  • Ignitable concentrations of flammable gases or vapors may exist under normal operating conditions; or
  • Ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
  • Breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.

Class I, Division 1 locations typically include:

  • Locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another;
  • Interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used;
  • Locations containing open tanks or vats of volatile flammable liquids;
  • Drying rooms or compartments for the evaporation of flammable solvents;
  • Locations containing fat and oil extraction equipment using volatile flammable solvents; portions of cleaning and dyeing plants where flammable liquids are used;
  • Gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape;
  • Inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids;
  • Interiors of refrigerators and freezers in which volatile flammable materials are stored in open, lightly stoppered or easily ruptured containers; and All other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.

Class I, Division 2 locations include those:

  • In which volatile flammable liquids or flammable gases are handled, processed or used, but in which the hazardous liquids, vapors or gases are normally confined within closed containers or closed systems from which they can escape only in the event of accidental rupture or breakdown of such containers or systems, or as a result of abnormal operation of equipment; or
  • In which ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operations of the ventilating equipment; or
  • That are adjacent to a Class I, Division 1 location, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.

Class I, Division 2 locations typically include locations where volatile flammable liquids or flammable gases or vapors are used, but which would become hazardous only in case of an accident or some unusual operating condition. Factors influencing the classification of such location include: the quantity of flammable material that might escape; the adequacy of ventilating equipment, the total area involved; and the record of the industry or business regarding explosions or fires are all factors that merit consideration in determining the classification and extent of each location.

Class I, Zone 0 locations are those i.e., a location in which one of the following conditions exists:

  • Ignitable concentrations of flammable gases or vapors are present continuously; or
  • Ignitable concentrations of flammable gases or vapors are present for long periods of time.

Class I, Zone 1 locations are those in which one of the following conditions exists:

  • Ignitable concentrations of flammable gases or vapors are likely to exist under normal operating conditions; or
  • Ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
  • Equipment is operated or processes are carried on of such a nature that equipment breakdown or faulty operations could result in the release of ignitable concentrations of flammable gases or vapors and also cause simultaneous failure of electric equipment in a manner that would cause the electric equipment to become a source of ignition; or
  • The location is adjacent to a Class I, Zone 0 location from which ignitable concentrations of vapors could be communicated, unless communication is prevented by adequate positive pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.

Class I, Zone 2 locations are those in which one of the following conditions exists:

  • Ignitable concentrations of flammable gases or vapors aren’t likely to occur in normal operation and if they do occur will exist only for a short period; or
  • Volatile flammable liquids, flammable gases, or flammable vapors are handled, processed or used, but in which the liquids, gases or vapors are normally confined within closed containers or closed systems from which they can escape only as a result of accidental rupture or breakdown of the containers or system or as the result of the abnormal operation of the equipment with which the liquids or gases are handled, processed or used; or
  • Ignitable concentrations of flammable gases or vapors normally are prevented by positive mechanical ventilation, but which may become hazardous as the result of failure or abnormal operation of the ventilation equipment; or
  • Locations that are adjacent to a Class I, Zone 1 location, from which ignitable concentrations of flammable gases or vapors could be communicated, unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.

Click here to find out how to use the Zone rather than the Division classification system for Class I locations.

Class II Locations

Class II locations are hazardous because of the presence of combustible dust. Class II locations include:

Class II, Division 1 locations are those:

  • In which combustible dust is or may be in suspension in the air under normal operating conditions in quantities sufficient to produce explosive or ignitable mixtures; or
  • Where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitable mixtures to be produced, and might also provide a source of ignition through simultaneous failure of electric equipment, through operation of protection devices, or from other causes; or
  • In which combustible dusts of an electrically conductive nature may be present.

Class II, Division 1 locations  may include areas of grain handling and processing plants, starch plants, sugar-pulverizing plants, malting plants, hay-grinding plants, coal pulverizing plants, areas where metal dusts and powders are produced or processed, and other similar locations that contain dust producing machinery and equipment (except where the equipment is dust-tight or vented to the outside).

Class II, Division 2 locations are those where:

  • Combustible dust isn’t normally suspended in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations are normally insufficient to interfere with the normal operation of electric equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment; and
  • Resulting combustible dust accumulations on, in, or in the vicinity of the electric equipment may be sufficient to interfere with the safe dissipation of heat from electric equipment or may be ignitable by abnormal operation or failure of electric equipment.
  • Class II, Division 2 includes locations where dangerous concentrations of suspended dust wouldn’t be likely, but where dust accumulations might form on or in the vicinity of electric equipment. These areas may contain equipment from which appreciable quantities of dust would escape under abnormal operating conditions or be adjacent to a Class II Division 1 location, as described above, into which an explosive or ignitable concentration of dust may be put into suspension under abnormal operating conditions.

Class III Locations

Class III locations are hazardous because of the presence of easily ignitable fibers or flyings, but in which such fibers or flyings aren’t likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures. Class III locations include:

Class III, Division 1 locations, i.e., those in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used.

Such locations usually include some parts of:

  • Rayon, cotton and other textile mills;
  • Combustible fiber manufacturing and processing plants;
  • Cotton gins and cotton-seed mills; flax-processing plants;
  • Clothing manufacturing plants;
  • Woodworking plants, and establishments; and
  • Industries involving similar hazardous processes or conditions.

Class III, Division 2 locations are those in which easily ignitable fibers are stored or handled, other than in the process of manufacture.

Step 2: Document Classifications

One classification is complete, you must document all areas designated as hazardous (classified) locations under the Class and Zone system and the Class and Division system.

You need to make this documentation available to those authorized to design, install, inspect, maintain or operate electric equipment at the location.

Step 3: Ensure the Safety of Electrical Installations in Classified Locations

You need to ensure that equipment, wiring methods and installations of equipment in hazardous (classified) locations meet a level of safety. There are 3 levels of safety:

Intrinsically safe equipment means equipment and associated wiring that’s officially approved as intrinsically safe. Such equipment is allowed to be in any hazardous (classified) location for which it’s approved.

Equipment approved for the hazardous (classified) location means equipment that’s been approved not only for the class of location, but also for the ignitable or combustible properties of the specific gas, vapor, dust or fiber present in that location. Such equipment must be marked to show the class, group and operating temperature or temperature range, based on operation in a 40-degree C ambient, for which it’s approved.

The temperature marking can’t exceed the ignition temperature of the specific gas or vapor to be encountered. Exceptions:

* Equipment of the nonheat-producing type, such as junction boxes, conduit and fittings, and equipment of the heat-producing type having a maximum temperature not more than 100º C (212º F) need not have a marked operating temperature or temperature range;

* Fixed lighting fixtures marked for use in Class I, Division 2 or Class II, Division 2 locations only need not be marked to indicate the group;

* Fixed general-purpose equipment in Class I locations, other than lighting fixtures, that’s acceptable for use in Class I, Division 2 locations need not be marked with the class, group, division or operating temperature;

* Fixed dust-tight equipment, other than lighting fixtures, that’s acceptable for use in Class II, Division 2 and Class III locations need not be marked with the class, group, division or operating temperature; and

* Electric equipment suitable for ambient temperatures exceeding 40º C (104º F) must be marked with both the maximum ambient temperature and the operating temperature or temperature range at that ambient temperature.

Equipment that’s safe for the hazardous (classified) location means equipment you can demonstrate provide protection from the hazards arising from the combustibility and flammability of vapors, liquids, gases, dusts or fibers involved. The National Electrical Code, NFPA 70, contains guidelines for determining the type and design of equipment and installations that will meet this requirement that address electric wiring, equipment,and systems installed in hazardous (classified) locations and contain specific provisions for the following: wiring methods, wiring connections; conductor insulation, flexible cords, sealing and drainage, transformers, capacitors, switches, circuit breakers, fuses, motor controllers, receptacles, attachment plugs, meters, relays, instruments, resistors, generators, motors, lighting fixtures, storage battery charging equipment, electric cranes, electric hoists and similar equipment, utilization equipment, signaling systems, alarm systems, remote control systems, local loud speaker and communication systems, ventilation piping, live parts, lightning surge protection and grounding.

All conduits in any classified location must be threaded and made wrench-tight. (A bonding jumper can be used if it’s impractical to make a threaded joint tight.)

It’s okay install equipment that has been approved for a Division 1 location in a Division 2 location of the same class and group.

Step 4: Implement Protection Techniques

  • You must implement protection techniques for electric and electronic equipment in hazardous (classified) locations that are permissible for those locations, including:
  • Explosionproof apparatus: Okay for equipment in the Class I, Division 1 and Class I, Division 2 locations for which it’s approved;
  • Dust ignitionproof:  Okay for equipment in the Class II, Division 1 and Class II, Division 2 locations for which it’s approved;
  • Dust-tight: Okay for equipment in the Class II, Division 2 and Class III locations for which it’s approved;
  • Purged and pressurized: Okay for equipment in any hazardous (classified) location for which it’s approved;
  • Nonincendive circuit: Okay for equipment in Class I, Division 2,  Class II, Division 2, Class III, Division 1  or Class III, Division 2 locations;
  • Nonincendive equipment: Okay for equipment in Class I, Division 2, Class II, Division 2, Class III, Division 1  or Class III, Division 2 locations;
  • Nonincendive component: Okay for equipment in Class I, Division 2, Class II, Division 2, Class III, Division 1  or Class III, Division 2 locations;
  • Oil immersion: Okay for certain current-interrupting contacts in Class I, Division 2 locations;
  • Hermetically sealed: Okay for equipment in Class I, Division 2, Class II, Division 2, Class III, Division 1  or Class III, Division 2 locations; and
  • Any other protection technique that meet Sec. 1910.307(c), i.e., which are intrinsically safe, approved for the hazardous (classified) location or safe for the hazardous (classified) location are okay in any hazardous (classified) location.

Conclusion

Proper classification of hazardous locations is a crucial step toward complying with electrical safety requirements. If locations are misclassified, attendant safety protections will be wrong for the hazards. In addition to OSHA citations, such misclassification can result in fatal fires and explosions in your facilities.