A Class I, Division 1 location is a location
In which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors can exist under normal operating conditions, or
In which ignitable concentrations of such gases, flammable liquid-produced vapors, or combustible liquid-produced vapors may exist frequently because of repair or maintenance operations or because of leakage, or
In which breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors and might also cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition.
(FPN No. 1): This classification usually includes the following locations:
Where volatile flammable liquids or liquefied flammable gases are transferred from one container to another
Interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used
Locations containing open tanks or vats of volatile flammable liquids
Drying rooms or compartments for the evaporation of flammable solvents
Locations containing fat- and oil-extraction equipment using volatile flammable solvents
Portions of cleaning and dyeing plants where flammable liquids are used
Gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape
Inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids
The interiors of refrigerators and freezers in which volatile flammable materials are stored in open, lightly stoppered, or easily ruptured containers
All other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.
(FPN No. 2): In some Division 1 locations, ignitable concentrations of flammable gases or vapors may be present continuously or for long periods of time. Examples include the following:
The inside of inadequately vented enclosures containing instruments normally venting flammable gases or vapors to the interior of the enclosure
The inside of vented tanks containing volatile flammable liquids
The area between the inner and outer roof sections of a floating roof tank containing volatile flammable fluids
Inadequately ventilated areas within spraying or coating operations using volatile flammable fluids
The interior of an exhaust duct that is used to vent ignitable concentrations of gases or vapors
Experience has demonstrated the prudence of avoiding the installation of instrumentation or other electric equipment in these particular areas altogether or where it cannot be avoided because it is essential to the process and other locations are not feasible [see 500.5(A), FPN] using electric equipment or instrumentation approved for the specific application or consisting of intrinsically safe systems as described in Article 504.