Inflammable gases or vapors must be present in sufficient amounts to create explosive or flammable combinations in Class I settings.
Division 1 of Class I
Locations in Class I, Division 1 may have hazardous air during regular operations. It might exist continually, sporadically, irregularly, during routine maintenance or repair work, or in locations where a breakdown in processing equipment emits dangerous gases at the same time that electrical equipment fails.
Division 2 of Class I
Locations that fall under Class I, Division 2 are those that handle, process, or use volatile, flammable substances or gases. They are often contained within closed containers or in closed systems, and the only way they may escape is if the containers or systems rupture or start to degrade.
Class II Places
Locations in class II are dangerous because they contain flammable dust.
CLASS II, DIVISION 1 Class II, Division 1 locations include those where combustible dust may be suspended in the air under normal circumstances in sufficient amounts to produce explosive or ignitable mixtures (Dust may be emitted into the air continuously, intermittently, or periodically), or where failure or malfunction of equipment might cause a hazardous location to exist and provide an ignition source at the same time as electrical equipment failure, such as
CLASS II, DIVISION 2 Class II, Division 2 locations are those where combustible dust will not typically be in suspension and where normal operations will not put dust in suspension, but where an accumulation of dust may obstruct the heat dissipation from electrical equipment or where an accumulation may ignite close to electrical equipment.
