Class 1
Flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Class 2
Combustible or conductive dusts are present.
Class 3
Ignitable fibers or flyings are present, but not likely to be in suspension in sufficient quantities to produce ignitable mixtures. (Group classifications are not applied to this class)
DIVISIONS

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.