Class and Division classification
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Class I Locations
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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 are
further subdivided into two Divisions and three Zones.
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Class I, Division 1:
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There are three different
situations that could exist to classify an area as a Class I, Division 1
location
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Ignitable concentrations of
flammable gases or vapors may exist under normal operating conditions.
·
Ignitable concentrations of
such gases or vapors may exist frequently because of repair or maintenance
operations or because of leakage.
·
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.
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Class I, Division 2
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One of the following three situations
must exist in order for an area to be considered a Class I, Division 2
location
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·
Volatile flammable liquids or
flammable gases are handled, processed or used, but 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.
·
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.
·
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.
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Class I, Zone 0
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One of the following two situations must
exist in order for an area to be considered a Class I, Zone 0 location
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Ignitable concentrations of
flammable gases or vapors are present continuously.
·
Ignitable concentrations of
flammable gases or vapors are present for long periods of time
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Class I, Zone 1
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One of the following four situations must
exist in order for an area to be considered a Class I, Zone 1 location
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·
Ignitable concentrations of
flammable gases or vapors are likely to exist under normal operating
conditions.
·
Ignitable concentrations of
flammable gases or vapors may exist frequently because of repair or
maintenance operations or because of leakage
·
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
·
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.
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Class I, Zone 2
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One of the following four situations must
exist in order for an area to be considered a Class I, Zone 2 location
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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.
·
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.
·
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.
·
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.
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Class II Locations
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Class II hazardous locations are areas
where combustible dust, rather than gases or liquids, may be present in
varying hazardous concentrations. Class II locations are further subdivided
into two divisions.
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Class II, Division 1
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One of the following three situations
must exist in order for an area to be considered a Class II, Division 1
location
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Where combustible dust is
present in the air under normal operating conditions in such a quantity as to
produce explosive or ignitable mixtures. This could be on a continuous,
intermittent or periodic basis.
·
Where an ignitable and/or
explosive mixture could be produced if a mechanical failure or abnormal
machinery operation occurs.
·
Where electrically conductive
dusts in hazardous concentrations are present.
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Class II, Division 2
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One of following two situations must
exist in order for an area to be considered a Class II, Division 2 location
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·
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.
·
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.
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Class III Locations
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Class III hazardous locations contain easily ignitable fibers or
flyings, but the concentration of these fibers or flyings are not suspended
in the air in such quantities that would produce ignitable mixtures.
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Class III, Division 1
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Easily ignitable fibers or materials
producing combustible flyings are handled, manufactured or used.
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Class III, Division 2
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Easily ignitable fibers are stored or
handled, other than in the process of manufacture.
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Class
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Hazardous
Material
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Division
System
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Zone
System
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1
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Gases
or Vapors
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Division
1
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Zone
0 and Zone 1
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Division
2
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Zone
2
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2
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Combustible dust
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Division
1
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Division
2
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3
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Easily ignitable fibers or flying's
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Division
1
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Division
2
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Hazardous Groupings
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Group A
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Acetylene
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Group B
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Hydrogen
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Group C
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Ethylene
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Group D
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Propane
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Group E
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Metal dusts
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Group F
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Coal, carbon black, charcoal and coke
dusts
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