미군폭발물전기교범

Chapter 6
Electrical Hazards
Section I
Electrical Service and Equipment
6　1. Overview
The installation and use of electrical equipment within buildings, magazines, operating locations, shelters, and so forth,
containing explosives will comply with the latest edition of the NFPA, Standard 70, unless stated otherwise in this
chapter.
6　2. Hazardous locations
Locations are classified depending on the properties of the flammable vapors, liquids or gases, or combustible dusts or
fibers which may be present and the likelihood that a flammable or combustible concentration or quantity is present.
Where pyrophoric (spontaneously igniting in air) materials are used or handled, these locations will not be classified.
Each room, section, or area will be considered individually in determining its classification. To qualify as a hazardous
location, conditions listed in paragraph 6　2a through c should either exist or be probable in the location. Hazardous
locations are divided into three classes. Each class consists of two division: Division 1 (more hazardous) and division
2. Hazardous locations require either explosives dusts, flammable vapors, or ignitable flyings (or fibers) to be present
in a proper mixture with air. Ammunition storage structures will not normally have the proper mixture and would not
be considered a hazardous location within the context of this definition. Additional information can be found in NFPA
70, article 500.
a. Class I. 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. Rooms or buildings containing vapors from explosives
which may condense will be considered Class I, Division 1 locations. Electrical equipment must have been tested and
listed by a recognized testing agency as suitable for installation and use in Class I hazardous locations for safety of
operation in the presence of flammable mixtures of specific vapors or gases in the air.
(1) Class I, Division 1. Class I, Division 1 locations are those in which　
(a) Hazardous concentrations of flammable gases or vapors exist continuously, intermittently, or periodically under
normal operating conditions.
(b) Hazardous concentrations of flammable gases or vapors may exist frequently because of repair or maintenance
operations or because of leakage.
(c) Breakdown or faulty operation of equipment or processes which might release hazardous concentrations of
flammable gases or vapors might also cause simultaneous failure of electrical equipment.
(d) Explosives may sublime and outgas.
(e) Equipment operating temperatures will not have an external temperature capable of igniting the flammable
mixture of the specific gas or vapor in its location.
(2) Class I, Division 2. Class I, Division 2 locations are those in which　
(a) Volatile flammable liquids or flammable gases are handled, processed, or used. In these areas the hazardous
liquids, vapors, or gases normally are confined within closed containers or systems from which they can escape only in
an accidental rupture or breakdown of such containers or systems or during abnormal operation of equipment.
(b) Positive mechanical ventilation normally prevents hazardous concentrations of gases or vapors from accumulating,
but concentrations might become hazardous if the ventilating equipment fails or malfunctions.
(c) Hazardous concentrations of gases or vapors occasionally might accumulate if they spread from adjacent Class I,
Division 1 locations unless prevented by adequate positive-pressure ventilation from a source of clean air, and effective
safeguards against ventilation failure are provided.

Class II. Class II locations are those locations which are hazardous because of the presence of combustible dust. 불붙기 쉬운 가루의 존재 때문에
wiring defined as explosion-proof is not required in Class II locations, and may not be acceptable unless it meets all the Rooms or buildings that contain explosive dusts or explosives having a chemical composition or physical size such that particles미량of explosives may become disassociated분리 from the whole and disperse흩어지게하다 in the surrounding atmosphere주위공기, will be considered Class II hazardous locations. Equipment installed in Class II locations will be able to function at full rating평가 without developing surface temperatures high enough to cause excessive극단적인 dehydration탈수or gradual carbonization점진적인 탄화of any organic유기적인dust deposits맡기다 that may be present. Dust that is carbonized or excessively dry is highly susceptible가능한 to spontaneous ignition.자연발화 Operating temperatures of electrical equipment will not be high enough to ignite expected예상되는 dusts in its location if equipment, such as motors, power transformers, and so forth기타, becomes overloaded과부하. Equipment and wiring전선 defined한정되다 as explosion-proof폭발을 견디는 is not required in Class II locations, and may not be acceptable unless it meets all the requirements of NFPA 70, Article 500 for Class II locations.
(1) Class II, Division 1. Class II, Division 1 locations are those in which　
(a) Combustible dust is or may be suspended부유하다 in the air continuously,끊임없이 intermittently, or periodically under normal operating conditions in quantities sufficient충분한 to produce an explosion or ignition.
(b) Mechanical failure or malfunctioning machinery or equipment may cause explosive or ignitable mixtures to be produced, or become a source of ignition through simultaneous failure of electrical equipment and protection devices or other causes.
(c) Combustible dusts which are electrically conductive전도성있는 may be present.전기적인 전도성이 있는 가연성먼지가 있을지 모른다.
(d) Explosives or explosive dusts may, during handling, produce dust capable of being dispersed in the atmosphere.
(e) Explosives may outgas.기체를 없애다

(2) Class II, Division 2. Class II, Division 2 locations are those in which　
(a) Combustible dust will not normally be suspended in the air, or thrown into suspension, by the normal operation
of equipment or apparatus in quantities sufficient to produce explosive or ignitable mixtures.
(b) Deposits or accumulations of dust may be sufficient to interfere with the safe dissipation of heat from electrical equipment or apparatus.
(c) Deposits or accumulations of combustible dust on, in, or in the vicinity of, electrical equipment may be ignited
by arcs, sparks, or burning material from electrical equipment.
c. Class III. Class III locations are those that could be hazardous because of the presence of easily ignitable fibers or
flyings, but where these fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce
ignitable mixtures. These locations include combustible fiber manufacturing pressing plants, woodworking plants, and
establishments involving similar hazardous processes or conditions. Easily ignitable fibers and flyings include rayon,
cotton, hemp, oakum, excelsior, and other materials of similar nature.
(1) Class III, Division 1. Class III, Division 1 locations are those in which easily ignitable fibers or materials that
produce combustible flyings are handled, manufactured, or used.
(2) Class III, Division 2. Class III, Division 2 locations are those in which easily ignitable fibers are stored or
handled, excluding locations where ignitable fibers are stored or handled during manufacturing.
d. Change of classification. Operating buildings and magazines are constructed to perform a specific function which
dictates the requirements for electrical equipment installation. If the functions performed in the facility change or are
rearranged, the safety officers must inspect, approve, or reclassify the hazardous locations. Multiple classifications are
discussed in the following paragraph.