| Scope: |
This ESSENTIAL describes the regulatory requirements for equipment and protective systems intended for use in potentially explosive atmospheres as defined in
- 29 CFR Part 1910 Occupational Safety and Health Standrads (Hazardous Locations)
- NFPA 70 (NEC), Articles 500 - 506
It does not cover Specific Hazardous (Classified) Locations acc. to NFPA 70 (NEC) Art.511 and following (e.g. Commercial Garages, Aircraft Hangars, Motor Fuel Dispensing Facilities etc.)
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| Legislation in force: |
29 CFR Part 1910 Occupational Safety and Health Standards
§ 1910.307 Hazardous (classified) locations
SCOPE: This section covers the requirements for electric equipment and wiring in locations that are classified depending on the properties of the flammable vapors, liquids or gases, or combustible dusts or fibers that may be present therein and the likelihood that a flammable or combustible concentration or quantity is present. Hazardous (classified) locations may be found in occupancies such as, but not limited to, the following: aircraft hangars, gasoline dispensing and service stations, bulk storage plants for gasoline or other volatile flammable liquids, paint-finishing process plants, health care facilities, agricultural or other facilities where excessive combustible dusts may be present, marinas, boat yards, and petroleum and chemical processing plants. Each room, section or area shall be considered individually in determining its classification.
§ 1910.399 - Definitions applicable to this subpart (defines Classes, Divisions and Zones )
Class I locations.
Class I locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Class I locations include the following:
(1) Class I, Division 1.
A Class I, Division 1 location is a location:
(i) In which ignitable concentrations of flammable gases or vapors may exist under normal operating conditions; or
(ii) In which ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
(iii) In which 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.
(2) Class I, Division 2.
A Class I, Division 2 location is a location:
(i) In which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the hazardous liquids, vapors, or gases will normally be 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
(ii) 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
(iii) That is 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.
(3) Class I, Zone 0.
A Class I, Zone 0 location is a location in which one of the following conditions exists:
(i) Ignitable concentrations of flammable gases or vapors are present continuously; or
(ii) Ignitable concentrations of flammable gases or vapors are present for long periods of time.
(4) Class I, Zone 1.
A Class I, Zone 1 location is a location in which one of the following conditions exists:
(i) Ignitable concentrations of flammable gases or vapors are likely to exist under normal operating conditions; or
(ii) Ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
(iii) 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
(iv) A location that 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.
(5) Class I, Zone 2.
A Class I, Zone 2 location is a location in which one of the following conditions exists:
(i) Ignitable concentrations of flammable gases or vapors are not likely to occur in normal operation and if they do occur will exist only for a short period; or
(ii) 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
(iii) 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
(iv) A location that is 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.
Class II locations.
Class II locations are those that are hazardous because of the presence of combustible dust. Class II locations include the following:
(1) Class II, Division 1.
A Class II, Division 1 location is a location:
(i) 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
(ii) 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
(iii) In which combustible dusts of an electrically conductive nature may be present.
(2) Class II, Division 2.
A Class II, Division 2 location is a location where:
(i) Combustible dust will not normally be in suspension in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations will normally be 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
(ii) 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 III locations.
Class III locations are those that are hazardous because of the presence of easily ignitable fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures. Class III locations include the following:
(1) Class III, Division 1.
A Class III, Division 1 location is a location in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used.
(2) Class III, Division 2.
A Class III, Division 2 location is a location in which easily ignitable fibers are stored or handled, other than in the process of manufacture.
Title 29 - Labor
Subtitle B Regulations Relating to Labor
Chapter XVII Occupational Safety and Health Administration, Department of Labor
Part 1926 - Safety and Health Regulations for Construction
Subpart K - Electrical Installation Safety Requirements
§ 1926.407 Hazardous (classified) locations.
(a) Scope. This section sets forth requirements for electric equipment and wiring in locations which are classified depending on the properties of the flammable vapors, liquids or gases, or combustible dusts or fibers which may be present therein and the likelihood that a flammable or combustible concentration or quantity is present. Each room, section or area shall be considered individually in determining its classification. These hazardous (classified) locations are assigned six designations as follows:
Class I, Division 1
Class I, Division 2
Class II, Division 1
Class II, Division 2
Class III, Division l
Class III, Division 2
For definitions of these locations see § 1926.449. All applicable requirements in this subpart apply to all hazardous (classified) locations, unless modified by provisions of this section.
The official note of §1926.407 refers to: The National Electrical Code, NFPA 70
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| Comment on the comparability to EU legislation: |
Not comparable to the EU ATEX legislation.... |