ELECTRICAL CODE
The National Electrical Code treats installations in hazardous locations
in articles 500 through 516. Hazardous locations are classified by NEC
definitions. The following are interpretations of these classifications
and applications.
CLASS
I LOCATIONS
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Class I locations
are those in which inflammable gases or vapors are or may be present
in sufficient quantities to produce explosive or flammable mixtures.
CLASS I, DIVISION
1
Class I, Division 1 locations are where hazardous atmosphere may be
present during normal operations. It may be present continuously, intermittently,
periodically or during normal repair or maintenance operations, or those
areas where a breakdown in processing equipment releases hazardous vapors
with the simultaneous failure of electrical equipment.
CLASS I, DIVISION
2
Class I, Division 2 locations are those in which volatile flammable
liquids or gases are handled, processed or used. Normally they will
be confined within closed containers or in closed systems from which
they can escape only in the case of rupture or deterioration of the
containers or systems.
CLASS
II LOCATIONS
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Class II locations are those that are hazardous because of the presence
of combustible dust.
CLASS II, DIVISION
1
Class II, Division 1 locations include areas where combustible dust
may be in suspension in the air under normal conditions in sufficient
quantities to produce explosive or ignitable mixtures (Dust may be emitted
into the air continuously, intermittently or periodically), or where
failure or malfunction of equipment might cause a hazardous location
to exist and provide an ignition source with the simultaneous failure
of electrical equipment, included also are locations in which combustible
dust of an electrically conductive nature may be present.
CLASS II, DIVISION
2
Class II, Division 2 locations are those in which combustible dust will
not normally be in suspension nor will normal operations put dust
in suspension, but where accumulation of dust may interfere with heat
dissipation from electrical equipment or where accumulations near electrical
equipment may be ignited.
CLASS
III LOCATIONS
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Class III locations are those considered hazardous due to the presence
of easily ignitable fibers of flyings, which are in quantities sufficient
to produce ignitable mixtures.
CLASS III, DIVISION
1
Locations in which easily ignitable fibers or materials producing combustible
flyings are handled, manufactured or used.
CLASS III, DIVISION
2
Locations where easily ignitable fibers are stored or handled.
