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Hazardous (Classified) Locations

Learn about hazardous locations classified under NEC, including examples and classification guidelines for Class I, II, and III locations. Explore hazardous groups and zone definitions for safer workplace operations. The material provides essential information for engineers and professionals working in potentially dangerous environments.

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Hazardous (Classified) Locations

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  1. Hazardous (Classified) Locations

  2. Introduction This material was produced under grant number SH-16615-07-60-F-12 from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. This material was produced by the Workplace Safety Awareness Council, a 501(c)(3) not-for-profit organization dedicated to safety in the workplace. For further information about the council or upcoming safety related training, please visit our website at www.wpsac.orgor call us at (863) 537-4053.

  3. In the News February 8, 2008 4 dead in Georgia sugar refinery blast PORT WENTWORTH, Ga. – Volatile dust caused an explosion Friday at a sugar refinery that resulted in the death of four employees and injured dozens more. The refinery was severely damaged and firefighters continued to battle the blaze on Friday.

  4. Hazardous Location Definition The National Electrical Code (NEC) defines hazardous locations as those areas "where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings.“ NOTE: Hazardous Locations are also described as “Classified Locations”

  5. Typical Examples 1910.307(a)(1) Could Include the Following: • Aircraft hangers • Service stations • Storage plants for volatile flammable liquids • Paint booths • Health care facilities • Marinas • Petroleum processing plants • Chemical processing plants

  6. How Hazardous Locations Are Classified

  7. Class I Locations 1910.399 definitions Flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures Class I Locations are divided into two Divisions

  8. Class I - Division I1910.399 definitions • Where gases or vapors exist under normal conditions • May exist frequently because of repair or maintenance • Might exist due to faulty equipment or processes

  9. Class I - Division II1910.399 definitions • Gases or liquids in closed containers or systems and would escape only with accidental rupture or equipment breakdown • Ignitable gases or vapors are prevented by positive mechanical ventilation and would become hazardous through failure or abnormal operations of the ventilating equipment • Area adjacent to Class I Division I and to which ignitable concentrations of gases or vapors might occasionally be communicated

  10. Class II Locations 1910.399 definitions Areas that are hazardous because of the presence of combustible dust. Class II Locations are divided into two Divisions

  11. Class II – Division 11910.399 definitions • Combustible dust in air under normal conditions in quantities sufficient to produce explosive or ignitable mixtures; or • Mechanical failure or abnormal operation of equipment releases dust and might provide a source of ignition; or • Combustible dust of a electrically conductive nature (i.e. magnesium and aluminum dust)

  12. Class II - Division 21910.399 definitions • Combustible dust not normally in high enough quantities to produce explosive or ignitable mixtures • Dust accumulations will normally be insufficient to interfere with the normal operation of electric equipment or other apparatus • Accumulation on, in, or near electrical equipment may cause heat build-up and be ignitable by equipment failure

  13. Class III Locations 1910.399 definitions Areas that are hazardous because of the presence of easily ignitable fibers or flyings. Class III Locations are divided into two Divisions

  14. Class III – Division 1 Location in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used.

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

  16. Hazardous Locations:Groups A: Acetylene B: Hydrogen, etc. C: Ester, etc. D: Hydrocarbons. fuels E: Metal dusts (conductive & explosive) F: Carbon dusts (some are conductive, all are explosive) G: Flour, starch, grain, combustible plastic or chemical dust (explosive) No specific groups

  17. Hazardous Location Summary

  18. Professional Engineer1910.307(g)(4)(i) Classification of areas and selection of equipment and wiring methods shall be under the supervision of a qualified registered professional engineer

  19. “Zone Classification System" (Alternative Method) NOTE: The alternative Zone Classification System only covers Class I installations.

  20. Zone Definitions1910.399 definitions • Zone 0 location is: • Ignitable flammable gases or vapors are present continuously; • Ignitable flammable gases or vapors are present for long periods of time. • Zone 1 location is: • Ignitable flammable gases or vapors are likely under normal conditions; or • Ignitable conditions may exist because of repair, maintenance or leakage; or • Equipment breakdown may cause electric equipment to be a source of ignition; • A location adjacent to a Class I, Zone 0 location where ignitable concentrations of vapors could be communicated • Zone 2 location is: • Ignitable flammable gas or vapor not likely or for short period only; or • Confined in closed systems or containers but could escape due to accident; or • Ignitable accumulation prevented by positive ventilation; or • Area adjacent to Class I Zone I from which ignitable concentrations could be communicated

  21. Groups (Zone) The zone system (0, 1, 2) has three “groups”, designated IIA, IIB, and IIC, with group IIC containing the most volatile gases, and groups IIA and II B containing gases or vapors that are progressively less volatile. Substances classified under groups A and B in the division system generally fall under group IIC of the zone system.

  22. Zone or Division? • The major differences: • International versus U.S. • Allowable protection scheme • Surface temperature of equipment used • Both classifications are acceptable to OSHA • Often dependant on the preference of the Professional Engineer who certifies the location. • Equipment used in the hazardous location will be specified by the Professional Engineer

  23. Design Features1910.307(c)(2)(i) Equipment shall be approved not only for the class of location, but also for the ignitable or combustible properties of the specific gas, vapor, dust, or fiber that will be present. Check Designation: For Haz. Loc. CL I, GR. B, C, D CL II, GR. E, F, G CL III

  24. Design Features

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