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GENERAL: Zone 0, Zone 1 and Zone 2 locations are those in which flammable gases or vapours are or may be present in the air in quantities sufficient to become hazardous.
These are locations in which flammable gases or vapours are continuously present in concentrations within the lower and upper limits of flammability.
NOTE: Such a condition is rarely encountered and is limited mainly to confined spaces (such as the vapour space of closed process vessels, closed tanks and closed containers), although it may also occur in larger rooms, such as rooms in chemical plants. Even in such spaces it is possible that the gas-air or vapour-air mixture is normally outside the flammability range.
These are locations:
a) in which hazardous concentrations of flammable gases or vapours occur intermittently or periodically under normal operating conditions, or
b) in which hazardous concentrations of flammable gases or vapours may occur frequently because of repair or maintenance operations or leakage, or
c) in which breakdown or faulty operation of equipment or processes, which release dangerous concentrations of flammable gases or vapours, might also cause simultaneous failure of electrical equipment.
NOTE: this classification usually includes locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another; interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used; locations containing open tanks or vats of volatile flammable liquids; drying rooms or compartments for the evaporation of flammable solvents; locations containing fat or oil-extraction apparatus using volatile flammable solvents; portions of cleaning and drying plants where flammable liquids are used; gas generator rooms; inadequately ventilated pump rooms for flammable gases or for volatile flammable liquids and all other locations where hazardous concentrations of flammable vapours or gases may occur in the course of normal operations
These are locations in which operations concerned with flammable or explosive substances, gases, or vapours or volatile liquids are so well controlled that an explosive or ignitable concentration is only likely to occur under abnormal conditions.
NOTE 1: The following shall be regarded as the minimum requirements for a location to which this classification is applicable: a) The area is so well ventilated that, if abnormal conditions arise, ignitable concentrations of the gas or vapour are rapidly dispersed and their possible contact with electrical equipment is of minimum duration.
GENERAL: Zone 21 and 22 locations are those which are hazardous because of the presence of combustible dust and fibres.
NOTE: Locations that house only plant and machinery that become non-operative if they lose their dust-tightness or if their internal pressure ceases to be below atmospheric pressure and locations where combustible dust is stored in dust tight containers only, need not be classified. The classification of locations where dust is not normally in suspension in the air, but where mechanical failure or abnormal operation of machinery or equipment might cause suspension of dust and might also provide a simultaneous source of ignition through failure of electrical equipment, operation of protective devices, etc., depends on the specific circumstances.
These are locations:
a) in which, under normal operating conditions, combustible dust or fibre is (or is likely to be) in suspension in the air in quantities sufficient to produce an explosive or ignitable mixture,
b) in which metallic dusts may be present.
NOTE: This classification usually includes, for example, rooms containing machines (such as grinders, pulverisers, cleaners, graders and scrapers that are not provided with suitable dust extraction or exhaust systems, open bins and hoppers, terminal points of open conveyors and spouts in grain processing plants, starch plants, sugar plants, malting plants, hay plants and coal plants); and all working areas where metallic dusts and powders are produced, processed, handled, packed, or stored (except when these are stored in sealed containers).
These are locations in which combustible dust or fibre will not normally be in suspension in the air, or will not be likely to be thrown into suspension by the normal operation of equipment or apparatus, in quantities sufficient to produce an explosive or ignitable mixture, but where
a) Deposits or accumulations of such dust may be enough to interfere with the safe dissipation of heat from electrical apparatus, or
b) Deposits or accumulations of dust in, on, or in the vicinity of electrical apparatus might be ignited by arcs, sparks, or burning materials from such apparatus.