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

0. metal dusts, regardless of resistivity
   
1. dust of similarly hazardous characteristics having a resistivity less than 100 k½-cm
   
2. electrically conductive dusts

Group F: Atmospheres containing combustible

0. carbon black, charcoal, or coke dusts having more than 8% total volatile material
   
1. dusts so sensitized that they present an explosion hazard, and dusts having a resistivity greater than 100 ½-cm but less than or equal to 1 x 108 ½-cm

Group G: Atmospheres containing combustible

0. dust having resistivity equal to or greater than 100 k½-cm
   
1. 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.