National Electric Code (NEC) Ratings
Hazardous Classifications:
CLASS I: Areas in which flammable gases of 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 k˝-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 ˝-cm but less
than or equal to 1 x 108 ˝-cm
Group G: Atmospheres containing combustible
- dust having resistivity equal to or greater than 100
k˝-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. |