What is a Hazardous Location?
Hazardous locations are areas where a potential for explosion and/or fires exists due to flammable gases, vapors or finely pulverized dusts in the atmosphere. Easily ignitable fibers or flyings in the atmosphere can also cause a location to become hazardous. The normal processing of certain volatile chemicals, gases, grains, etc. oraccidental failure of storage systems for these materials may produce a hazardous location. It is also possible that a hazardous location can result from volatile solvents or fluids, used in a normal maintenance routine, that vaporize to form an explosive atmosphere. Whatever the cause of a hazardous location, it is necessary to take precautions to guard against ignition of the atmosphere.
HazardousLocations and the National Electric Code
The National Electric 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
Class I locations are those in which inflammable gases or vapors are or may be present in sufficientquantities 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 failureof 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
Class II locations are those thatare 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 equipmentmight 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 insuspension, 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
Class III locations are those considered hazardous due to the presence of easily ignitable fibers or flyings, which are in quantities sufficient to produce ignitable mixtures.
Class III, Division 1
Locationsin 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.
Equipment for Hazardous Locations
Equipment for Class I Locations
Devices for Class I locations should be housed in enclosures strong enough to contain an explosion if hazardous vapors
enteringthe enclosure are ignited: These enclosures then cool and vent the combustion, ensuring that the surrounding atmosphere is not ignited. Heat producing equipment in hazardous locations, such as lighting fixtures, must contain the explosion and vent the cooled products of combustion. They must also operate with surface temperatures below ignition temperatures of the hazardous atmosphere. Since the...