Page 130 - Pipeline Rules of Thumb Handbook

Electrical Design 117

in which ignitible concentrations of such gases or vapors may (FPN No. 1): This classification usually includes locations
exist frequently because of repair or maintenance operations where volatile flammable liquids or flammable gases or vapors
or because of leakage; or (3) in which breakdown or faulty are used, but which, in the judgment of the authority having
operation of equipment or processes might release ignitible jurisdiction, would become hazardous only in case of an acci-
concentrations of flammable gases or vapors, and might also dent or of some unusual operating condition. The quantity of
cause simultaneous failure of electric equipment. flammable material that might escape in case of accident, the
adequacy of ventilating equipment, the total area involved,
(FPN): This classification usually includes locations where
and the record of the industry or business with respect to
volatile flammable liquids or liquefied flammable gases are
explosions or fires are all factors that merit consideration in
transferred from one container to another; interiors of spray
determining the classification and extent of each location.
booths and areas in the vicinity of spraying and painting oper-
ations where volatile flammable solvents are used; locations (FPN No. 2): Piping without valves, checks, meters, and
containing open tanks or vats of volatile flammable liquids; similar devices would not ordinarily introduce a hazardous
drying rooms or compartments for the evaporation of flam- condition even though used for flammable liquids or gases.
mable solvents; locations containing fat and oil extraction Locations used for the storage of flammable liquid or of
equipment using volatile flammable solvents; portions of liquefied or compressed gases in sealed containers would
cleaning and dyeing plants where flammable liquids are used; not normally be considered hazardous unless subject to other
gas generator rooms and other portions of gas manufacturing hazardous conditions also.
plants where flammable gas may escape; inadequately venti- Group A: Atmospheres containing acetylene.
lated pump rooms for flammable gas or for volatile flamma-
ble liquids; the interiors of refrigerators and freezers in which Group B: Atmospheres containing hydrogen, fuel and
volatile flammable materials are stored in open, lightly stop- combustible process gases containing more than 30 percent
pered, or easily ruptured containers; and all other locations hydrogen by volume, or gases or vapors of equivalent hazard
where ignitible concentrations of flammable vapors or gases such as butadiene,* ethylene oxide,** propylene oxide,** and
are likely to occur in the course of normal operations. acrolein.**
Group C: Atmospheres such as cyclopropane, ethyl ether,
(b) Class I, Division 2. A Class I, Division 2 location is a loca- ethylene, or gases or vapors of equivalent hazard.
tion: (1) in which volatile flammable liquids or flammable
gases are handled, processed, or used, but in which the Group D: Atmospheres such as acetone, ammonia,***
liquids, vapors, or gases will normally be confined within benzene, butane, ethanol, gasoline, hexane, methanol,
closed containers or closed systems from which they can methane, natural gas, naptha, propane or gases of vapors of
escape only in case of accidental rupture or breakdown of equivalent hazard.
such containers or systems, or in the case of abnormal oper-
ation of equipment; or (2) in which ignitible concentrations
of gases or vapors are normally prevented by positive mechan-
ical ventilation, and which might become hazardous through * Group D equipment may be used for this atmosphere if such equipment
is isolated in accordance with Section 501-5(a) by sealing all conduit 1/2-inch
failure or abnormal operation of the ventilating equipment; or larger.
or (3) that is adjacent to a Class I, Division 1 location, and to ** Group C equipment may be used for this atmosphere if such equipment
which ignitible concentrations of gases or vapors might occa- is isolated in accordance with Section 501-5(a) by sealing all conduit 1/2-inch
sionally be communicated unless such communication is or larger.
prevented by adequate positive-pressure ventilation from a *** For classification of areas involving ammonia atmosphere, see Safety
Code for Mechanical Refrigeration, ANSI/ASHRAE 15-1978, and Safety
source of clean air, and effective safeguards against ventila- Requirements for the Storage and Handling of Anhydrous Ammonia,
tion failure are provided. ANSI/CGA G2.1-1981.

NEMA Enclosure Types 1

Nonhazardous Locations

Type Intended Use and Description 2 Enclosures are intended for indoor use primarily
to provide a degree of protection against limited
1 Enclosures are intended for indoor use primarily amounts of falling water and dirt.
to provide a degree of protection against limited 3 Enclosures are intended for outdoor use primarily to
amounts of falling dirt. provide a degree of protection against rain, sleet,