| 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. |
| 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. |
| 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 dust, carbon black, coal black, charcoal, coal or coke dust that have more than 8% total entrapped volatiles or dusts that have been sensitized by other material so they present an explosion hazard. |
| Group G | Flour dust, grain dust, flour, starch, sugar, wood, plastic and chemicals. |