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Hazardous (Classified) Locations


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This material was produced under grant number SH-16615-07-60-F-12 from theOccupational Safety and Health Administration, U.S. Department of Labor. It doesnot necessarily reflect the views or policies of the U.S. Department of Labor, nordoes mention of trade names, commercial products, or organizationsimply endorsement by the U.S. Government.

This material was produced by the Workplace Safety Awareness Council, a501(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.org or call us at (863) 537-4053.

Introduction


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In the News

4 dead in Georgia sugar refinery blastPORT WENTWORTH, Ga.

Volatile dust caused an

explosion Friday at a sugar refinery that resulted in thedeath of four employees and injured dozens more. Therefinery was severely damaged and firefighterscontinued to battle the blaze on Friday.

February 8, 2008


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Hazardous Location Definition

The National Electrical Code (NEC) defines hazardouslocations as those areas

"where fire or explosion hazards may exist due toflammable gases or vapors, flammable liquids,combustible dust, or ignitable fibers or flyings.

NOTE: Hazardous Locations are also described as

Classified Locations


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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

Typical Examples1910.307(a)(1)


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How Hazardous LocationsAre Classified


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Class I Locations1910.399 definitions

Flammable gases or vapors are or may bepresent in the air in quantities sufficient toproduce explosive or ignitable mixtures

Class I Locations are divided into two Divisions


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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


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Class I - Division II1910.399 definitions

Gases or liquids in closed containers or systems and would escapeonly with accidental rupture or equipment breakdown

Ignitable gases or vapors are prevented by positive mechanicalventilation and would become hazardous through failure orabnormal operations of the ventilating equipment

Area adjacent to Class I Division I and to which ignitableconcentrations of gases or vapors might occasionally becommunicated


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Areas that are hazardous because of the presence ofcombustible dust.

Class II Locations are divided into two Divisions

Class II Locations1910.399 definitions


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Class II Division 11910.399 definitions

Combustible dust in air under normal conditions in quantitiessufficient to produce explosive or ignitable mixtures; or

Mechanical failure or abnormal operation of equipment releases dustand might provide a source of ignition; or

Combustible dust of a electrically conductive nature (i.e. magnesiumand aluminum dust)


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Class II - Division 21910.399 definitions

Combustible dust not normally in high enough quantities to produceexplosive or ignitable mixtures

Dust accumulations will normally be insufficient to interfere with thenormal operation of electric equipment or other apparatus

Accumulation on, in, or near electrical equipment may cause heatbuild-up and be ignitable by equipment failure


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Class III Locations1910.399 definitions

Areas that are hazardous because of the presence ofeasily ignitable fibers or flyings.

Class III Locations are divided into two Divisions


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Class III Division 1

Location in which easily ignitable fibers or materials producing

combustible flyings are handled, manufactured, or used.


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Class III Division 2

Location in which easily ignitable fibers are stored orhandled, other than in the process of manufacture.

d


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Hazardous Locations:Groups

A: Acetylene

B: Hydrogen, etc.C: Ester, etc.D: Hydrocarbons.

fuels

E: Metal dusts (conductive &explosive)

F: Carbon dusts (some areconductive, all are explosive)

G: Flour, starch, grain, combustibleplastic or chemical dust(explosive)

No specific groups


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Hazardous Location Summary

Summary of Class I, II, III Hazardous Locations

Classes Groups Divisions 1 2

Class IGases, Vapors & Liquids

A: AcetyleneB: Hydrogen, etc.C: Ester, etc.D: Hydrocarbons. fuels

Normally explosiveand hazardous

Not normally presentin an explosiveconcentrationbut mayaccidentallyexist.

Class IIDusts

E: Metal dusts(conductive and explosive)F: Carbon dusts(some are conductive, all are

explosive)G: Flour, starch, grain,

combustible plastic orchemical dust (explosive)

Ignitable quantitiesof dust are ormay be insuspension, orconductive dustmay be present

Dust not normallysuspended in anignitableconcentration(but mayaccidentallyexist). Dust layersare present.

Class IIIFibers & Flyings

Textiles, woodworking etc. (easilyignitable but not usuallyexplosive)

Handled or used inmanufacturing

Stored or handled instorage(exclusive ofmanufacturing)


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Professional Engineer1910.307(g)(4)(i)

Classification of areas and selection of equipmentand wiring methods shall be under the supervision

of a qualified registered professional engineer

Z Cl ifi i S "


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Zone Classification System"(Alternative Method)

NOTE: The alternative Zone Classification System only covers Class I installations.


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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 ofvapors 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 becommunicated


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Groups (Zone)

The zone system (0, 1, 2) has three groups, designatedIIA, IIB, and IIC, with group IIC containing the mostvolatile gases, and groups IIA and II B containing gasesor vapors that are progressively less volatile.

Substances classified under groups A and B in the divisionsystem generally fall under group IIC of the zone system.


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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 ProfessionalEngineer who certifies the location.

Equipment used in the hazardous location will bespecified by the Professional Engineer


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Design Features1910.307(c)(2)(i)

Equipment shall be approved not only for theclass of location, but also for the ignitable orcombustible properties of the specific gas, vapor,

dust, or fiber that will be present.

Check Designation:For Haz. Loc.CL I, GR. B, C, DCL II, GR. E, F, GCL III


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Design Features

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