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1、 NFPA 496 Standard for Purged and Pressurized Enclosures for Electrical Equipment 2003 Edition NFPA, 1 Batterymarch Park, PO Box 9101, Quincy, MA 02269-9101 An International Codes and Standards Organization NFPA License Agreement This document is copyrighted by the National Fire Protection Associati
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26、 Protection Association Provided by IHS under license with NFPALicensee=Purdue University/5923082001 Not for Resale, 11/02/2006 02:51:43 MSTNo reproduction or networking permitted without license from IHS -,-,- Copyright 2003, National Fire Protection Association, All Rights Reserved NFPA 496 Standa
27、rd for Purged and Pressurized Enclosures for Electrical Equipment 2003 Edition This edition of NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equip- ment, was prepared by the Technical Committee on Electrical Equipment in Chemical Atmo- spheres and acted on by NFPAat its May
28、AssociationTechnical Meeting held May 1821, 2003, in Dallas,TX. It was issued by the Standards Council on July 18, 2003, with an effective date of August 7, 2003, and supersedes all previous editions. ThiseditionofNFPA496wasapprovedasanAmericanNationalStandardonJuly18,2003. Origin and Development of
29、 NFPA 496 This standard was developed in two parts by the Technical Committee on Electrical Equip- ment in Chemical Atmospheres. The first part, addressing purged enclosures for electrical equipment in Class I hazardous (classified) locations, was adopted as a tentative standard at the 1966 NFPAAnnu
30、al Meeting and as an official standard at the 1967 NFPAAnnual Meeting. The second part, addressing pressurized enclosures for electrical equipment in Class II haz- ardous (classified) locations, was tentatively adopted at the 1970 NFPAAnnual Meeting and officially adopted at the 1971 NFPAAnnual Meet
31、ing. TheTechnical Committee on Electrical Equipment in ChemicalAtmospheres presented a complete revision of the entire standard in 1974. In 1980, the committee began another complete revision. This work culminated in the 1982 edition. In 1983, the Technical Committee on Electrical Equipment in Chemi
32、cal Atmospheres recognized the need for specific requirements applicable to process control analyzers that have internal sources of a flammable or combustible material, such as a direct connection to the process stream. Two chapters were added to address analyzer enclosures and analyzer rooms or bui
33、ldings.Additional changes were also made to certain existing portions of the text specifically to address problems in the interpretation of the existing text. The 1986 edition of NFPA 496 was the result of this effort. In 1987, the Technical Committee on Electrical Equipment in ChemicalAtmospheres r
34、ecog- nized a need for editorial revisions to the figures in Chapter 2 as well as some minor editorial changes in Chapters 2 and 9 andAppendixA. The 1989 edition was the result of this effort. Beginning in 1990, an ad hoc committee consisting of members of the Technical Commit- tee on Electrical Equ
35、ipment in Chemical Atmospheres started a major rewrite of this docu- ment to develop a more comprehensive standard and to reduce redundancy in the text. Definitions were added for further clarity, and references to Class III were deleted, since the standard did not cover this application and could c
36、reate some confusion. References to purging were replaced with pressurizing, and protective gas was introduced as a new term. The requirements based on gross internal volume were deleted and replaced with general and specific requirements for all pressurized enclosures used in Class I and Class II l
37、ocations. The result of this rewrite was the 1993 edition. In 1997, the Technical Committee on Electrical Equipment in Chemical Atmospheres enteredNFPA496intherevisioncycletoupdatetherequirements.Thestandardwasupdated toincludedefinitionsandreferencestoArticle505inNFPA70,NationalElectricalCode,which
38、 deals with Class I, Zone 1, and Zone 2 locations. It also was changed to provide an exception for control rooms where doors and other openings used solely for equipment relocation are permitted to be excluded from the calculation for outward air velocity from the central room. In 2001, the Technica
39、l Committee on Electrical Equipment in Chemical Atmospheres entered NFPA 496 into the May 2003 revision cycle. The 2003 edition has been significantly revised and reorganized for conformance with the 2000 NFPA Manual of Style. These organi- zational and editorial changes enhance the standards usabil
40、ity. Additionally, technical changes include revision of the term alarm to clarify its function with protected enclosures, and a revision that permits the use of a means other than a timing device to ensure that electrical equipment within a protected enclosure is not energized until the specified a
41、mount of protective gas has passed through the enclosure. 4961 Copyright National Fire Protection Association Provided by IHS under license with NFPALicensee=Purdue University/5923082001 Not for Resale, 11/02/2006 02:51:43 MSTNo reproduction or networking permitted without license from IHS -,-,- Tec
42、hnical Committee on Electrical Equipment in Chemical Atmospheres James G. Stallcup, Chair Keller, TX SE A. W. Ballard, Crouse-Hinds, NY M Rep. National Electrical Manufacturers Association Edward M. Briesch, Underwriters Laboratories Inc., ILRT Stephen R. Carlson, Pharmacia Corporation, MI U William
43、 T. Fiske, Intertek Testing Services NA, Inc., NY RT William G. Lawrence, Jr., FM Global, MA I Rep. FM Global/FM Research Robert Malanga, Union Camp Corporation, NJ U Joseph V. Saverino, Air Products and Chemicals, Inc., PA U Richard F. Schwab, Honeywell, Inc., NJ U Sukanta Sengupta, FMC Corporation
44、, NJ U Andreas U. Spintzyk, GE Global Asset Protection Services, OH I David B. Wechsler, The Dow Chemical Company, TX U Rep. American Chemistry Council Jack H. Zewe, Electrical Consultants Inc., LA SE Alternates Kerry L. McManama, Underwriters Laboratories Inc., IL RT (Alt. to E. M. Briesch) Samuel
45、A. Rodgers, Honeywell, Inc., VA U (Alt. to R. F. Schwab) James W. Stallcup Jr., Keller, TX SE (Alt. to J. G. Stallcup) Dann Strube, Intertek Testing Services NA, Inc., IN RT (Alt. to W. T. Fiske) Nonvoting George H. St. Onge, Shelbyville, DE (Member Emeritus) Jeffrey S. Sargent, NFPA Staff Liaison T
46、his list represents the membership at the time the Committee was balloted on the final text of this edition. Since that time, changes in the membership may have occurred. A key to classifications is found at the back of the document. NOTE:Membershiponacommitteeshallnotinandofitselfconstituteanendors
47、ementoftheAssociationor any document developed by the committee on which the member serves. Committee Scope: This Committee shall have primary responsibility for documents on (1) developing data on the properties of chemicals enabling proper selection of electrical equipment for use in atmospheres c
48、ontaining flammable gases, vapors, or dusts; (2) making recommendations for the prevention of fires and explosions through the use of continuously purged, pressurized, explosion-proof, or dust-ignition-proof electrical equipment where installed in such chemical atmospheres. 4962PURGED AND PRESSURIZE
49、D ENCLOSURES FOR ELECTRICAL EQUIPMENT 2003 Edition Copyright National Fire Protection Association Provided by IHS under license with NFPALicensee=Purdue University/5923082001 Not for Resale, 11/02/2006 02:51:43 MSTNo reproduction or networking permitted without license from IHS -,-,- Contents Chapter 1Administration. 496 4 1.1Scope. 496 4 1.2Pu