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. (Group classifications are not applied to this class.)|
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.|
The group defines the hazardous material in the surrounding atmosphere.
|Group||Hazardous Material in Surrounding Atmosphere|
|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||Ethyl and ethylene or gases of equivalent hazard.|
|Group D||Gasoline, acetone, ammonia, benzene, butane, cyclopropane, ethanol, hexane, methanol, methane, 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, 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.|
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