| CLASS I: Areas in which flammable gases or vapors
may be present in the air in sufficient quantities to be explosive
Group A: Atmospheres containing acetylene
Group B: Atmospheres such as butadiene, ethylene oxide, propylene
oxide, acrolein, or hydrogen (or gases or vapors equivalent
in hazard to hydrogen, such as manufactured gas)
Group C: Atmospheres such as cyclopropane, ethyl ether, ethylene,
or gas or vapors of equivalent hazard
Group D: Atmospheres such as acetone, alcohol, ammonia, benzene,
benzol, butane, gasoline, hexane, lacquer solvent vapors, naphtha,
natural gas, propane, or gas or vapors of equivalent hazard
CLASS II: Areas made hazardous by the presence of combustible
dust
Group E: Atmospheres containing combustible
metal dusts, regardless of resistivity
dust of similarly hazardous characteristics having a resistivity
less than 100 kO-cm
electrically conductive dusts
Group F: Atmospheres containing combustible
carbon black, charcoal, or coke dusts having more than 8% total
volatile material
dusts so sensitized that they present an explosion hazard, and
dusts having a resistivity greater than 100 O-cm but less than
or equal to 1 x 108 O-cm
Group G: Atmospheres containing combustible
dust having resistivity equal to or greater than 100 kO-cm
electrically nonconductive dusts
CLASS III: Areas made hazardous by the presence of easily ignitable
fibers or dust, but which are not likely to be in suspension
in the air in quantities that are sufficient to ignite
Division 1: Atmospheres where hazardous concentrations exist
continuously, intermittently, or periodically under normal operating
conditions
Division 2: Atmospheres where hazardous concentrations exist
only in case of accidental rupture or breakdown of equipment
Explosion-proof: Enclosures or housings are designed to withstand
internal explosions and prevent the spread of fire to the outside.
Intrinsically-safe: Systems designed in which electrical energy
in the circuits is not present at levels that would ignite a
flammable mixture of a gas and air.
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