Class I, Class II and Class III hazardous locations can be either Division 1 or Division 2. Good examples of Class I, Division 1 locations would be the areas near open dome loading facilities or adjacent to relief valves in a petroleum refinery, because the hazardous material would be present during normal plant operations. Closed storage drums containing flammable liquids in an inside storage room would not normally allow the hazardous vapors to escape into the atmosphere. Now let's move on to a discussion of the nature of hazardous substances. The only substance in Group A is acetylene.
Acetylene makes up only a very small percentage of hazardous locations.
Consequently, little equipment is available for this type of location. Acetylene is a gas with extremely high explosion pressures. Group B is another relatively small segment of classified areas. This group includes hydrogen and other materials with similar characteristics. If you follow certain specific restrictions in the Code, some of these Group B locations, other than hydrogen, can actually be satisfied with Group C and Group D equipment.