Definitions cont'd - hdbk10920285

DOE-HDBK-1092-98

b. (Over 600 volts, nominal.)--A switching device capable of making, carrying, and breaking

currents under normal circuit conditions, and also making, carrying for a specified time, and

breaking currents under specified abnormal circuit conditions, such as those of short circuit.

Class I locations--Class I locations are those in which flammable gases or vapors are or may be

present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class I locations

include the following:

a. Class I, Division 1--A Class I, Division 1 location is a location:

1. in which ignitable concentrations of flammable gases or vapors may exist under normal

operating conditions; or

2. in which ignitable concentrations of such gases or vapors may exist frequently because of

repair or maintenance operations or because of leakage; or

3. in which breakdown or faulty operation of equipment or processes might release ignitable

concentrations of flammable gases or vapors, and might also cause simultaneous failure of

electric equipment.

NOTE: This classification usually includes 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; inadequately ventilated pump rooms

for flammable gas or for volatile flammable liquids; and all other locations where ignitable

concentrations of flammable vapors or gases are likely to occur in the course of normal

operations.

b. Class I, Division 2--A Class I, Division 2 location is a location:

1. in which volatile flammable liquids or flammable gases are handled, processed, or used, but

in which the hazardous liquids, vapors, or gases will normally be confined within closed

containers or closed systems from which they can escape only in case of accidental rupture

or breakdown of such containers or systems, or in case of abnormal operation of equipment;

2. in which ignitable concentrations of gases or vapors are normally prevented by positive

mechanical ventilation, and which might become hazardous through failure or abnormal

operations of the ventilating equipment; or

3. that is adjacent to a Class I, Division 1 location, and to which ignitable concentrations of

gases or vapors might occasionally be communicated unless such communication is

prevented by adequate positive-pressure ventilation from a source of clean air, and effective

safeguards against ventilation failure are provided.

NOTE: This classification usually includes locations where volatile flammable liquids or flammable

gases or vapors are used, but which would become hazardous only in case of an accident or of

some unusual operating condition. The quantity of flammable material that might escape in case

of accident, the adequacy of ventilating equipment, the total area involved, and the record of the

industry or business with respect to explosions or fires are all factors that merit consideration in

determining the classification and extent of each location. Piping without valves, checks,

B-25