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In general hazardous locations in North America are separated by
classes, divisions, and groups to define the level of safety required
for equipment installed in these locations.
Classes


The classes defines the general nature of hazardous material in the surrounding atmosphere.
Class Hazardous Material in Surrounding Atmosphere
Class I Hazardous because flammable gases or vapors are present in the
air in quantities sufficient to produce explosive or ignitable mixtures.
Class II Hazardous because combustible or conductive dusts are present.
Class III Hazardous because ignitable fibers or flying's are present,
but not likely to be in suspension in sufficient quantities to produce
ignitable mixtures. Typical wood chips, cotton, flax and nylon. Group
classifications are not applied to this class.


Divisions


The division defines the probability of hazardous material being present
in an ignitable concentration in the surrounding atmosphere.
Division Presence of Hazardous Material
Division 1 The substance referred to by class is present during normal conditions.
Division 2 The substance referred to by class is present only in
abnormal conditions, such as a container failure or system breakdown.


Groups


The group defines the hazardous material in the surrounding atmosphere.
Group Hazardous Material in Surrounding Atmosphere
Group A Acetylene
Group B Hydrogen, fuel and combustible process gases containing more
than 30% hydrogen by volume or gases of equivalent hazard such as
butadiene, ethylene, oxide, propylene oxide and acrolein.
Group C Carbon monoxide, ether, hydrogen sulfide, morphline, cyclopropane, ethyl and ethylene or gases of equivalent hazard.
Group D Gasoline, acetone, ammonia, benzene, butane, cyclopropane,
ethanol, hexane, methanol, methane, vinyl chloride, natural gas,
naphtha, propane or gases of equivalent hazard.
Group E Combustible metal dusts, including aluminum, magnesium and their
commercial alloys or other combustible dusts whose particle size,
abrasiveness and conductivity present similar hazards in connection with
electrical equipment.
Group F Carbonaceous dusts, carbon black, coal black, charcoal, coal or
coke dusts that have more than 8% total entrapped volatiles or dusts
that have been sesitized by other material so they present an explosion
hazard.
Group G Flour dust, grain dust, flour, starch, sugar, wood, plastic and chemicals.