Explosion-proof defined

Explosion-proof enclosures are characterized by strong metal enclosures with special close-fitting access covers and breathers that contain an ignition to the inside of the enclosure. Field wiring in the hazardous environment is enclosed in a metal conduit of the mineral-insulated-cable type. All conduit and cable connections or cable terminations are threaded and explosion-proof. Conduit seals are put into the conduit or cable system at locations defined by the National Electric Code (Article 501) to prevent gas and vapor leakage and to prevent flames from passing from one part of the conduit system to the other. 

Originally the classification of materials was derived from tests of proprietary explosion-proof (flameproof) enclosures. There were no published criteria. Equipment was approved relative to the lowest ignition temperature of any material in the group (Magison 1987). In about 1965 the U.S. Coast Guard asked the National Academy of Sciences (NAS) to form a panel to classify 200 materials of commerce. The Electrical Hazards Panel of the Committee on Hazardous Materials was formed by the NAS. The Panel studied many ways to estimate the hazard classification of materials. The Panel finally reported to die U.S. Coast Guard in 1970 that no workable, predicdve scheme could be defined, and it then proceeded to assign tentative classifications to the 200 materials. 

Define plant areas requiring explosion-proof, drip-proof and open motor and associated electrical components. Refer to National Electrical Code and National Electrical Manufacturer s Association Standards. 

Note Type 7 enclosures are termed explosion proof as defined in NEMA and the National Electrical Code. 

Turnkey plant. Consists of all the hardware, software, technical data, and technical assistance necessary for the installation of a complete operating facility for the production of the commodity, a chemical substance, at defined production rates and to specified product qualities. Hardware consists of all the equipment, components, control valves, instruments, reaction vessels, feed lines, and exposition proof barriers necessary for the conduct of the unit operations of the overall production process, whether the items arc assembled or disassembled for transportation. The plant may be designed for installation at a prepared site that includes locally constructed and installed explosion-proof barricades... 

NFPA 432, 4.5.2 4.5.7 Refrigerators used for storing organic peroxide formulations shall be Class 1, Group D, and Division 1 (i.e., "explosion-proof, as defined in Article 500 of NFPA 70. 

Steel conduits are made to a specification defined by BS 4568 and are either heavy gauge welded or solid drawn. Heavy gauge is made from a sheet of steel welded along the seam to form a tube and is used for most electrical installation work. Solid drawn conduit is a seamless tube which is much more expensive and only used for special gas-tight, explosion-proof or flameproof installations. 

Groups further define the materials for which a motor is designed to be explosion proof. Group D is for common flammable solvents and fuels, such as acetone, ammonia, benzene, butane, gasoline, hexane, methane, methanol, propylene, propane, styrene, and similar compounds. Many explosion-proof motors are rated Division 1, Class I, Group D. Group C motors provide additional protection for... 

It is necessary to consider the environment to choose the proper motor endosuie. Explosion-proof motors usually have a UL label certifying that they are suitable for the defined classified area. The UL label, however, is suitable only for 60 Hz sine-wave power. When an explosion-proof motor is operated on adjustable-frequency control power, the 60 Hz sine-wave UL label is voided. In addition, induction motors are normally rated for 40 C (104°F) ambient temperature. Use in a higher ambient temperature may require additional cooling or overframing. 

Following the historical development of electrical engineering and explosion protection, zone classification was the objective of national standards and installation rules. Most of the leading industrial countries established an installation practice for chemical plants and the oil and gas industry with two or three zones for areas hazardous due to gas- or vapour-air mixtures and two zones for areas with hazardous dust-air mixtures. Apart from this philosophy, the coal mining industry in most countries tends to avoid an area classification and defines only one category of explosion protection ( firedamp-proof ). More recent standards or directives present a three-zone concept for areas endangered by combustible gas- (vapour-, mist-) air mixtures and dust-air mixtures in industrial plants (other than coal mines). 

Quality. JIS standard G2302 shows that the first class material has 88 93% silicon content and it is used for explosives(carlit) or generating hydrogen gas in combination with sodium hydroxide. From the second to the fifth class, the silicon contents are defined as 75 80 , 3 7%, 25 30%, 20 25% respectively, and these classes are used as the deoxidation against in iron manufacture or the silicon supply for manufacturing silicon steel plate etc. The sixth class has 15 19% silicon content and is used for acid-proof iron vessels. For firework use(for the red thermit) the first class is recommended. 

Type 9 enclosures are intended for use indoors in atmospheres defined as Class II and Group E, F or G in the National Electrical Code. The letters E, F or G, which indicate the dust atmospheres in the hazardous location, must appear as a suffix to the designation Type 9, to give the complete NEMA designation. These enclosures prevent the ingress of explosive amounts of hazardous dust. If gaskets are used, they must be mechanically attached and of a non-combustible, non-deteriorating, vermin-proof material. 

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