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| NFPA 497 |
| Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas |
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NFPA 497 - Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
Scope
This recommended practice applies to those locations where flammable gases or vapors, flammable liquids, or combustible liquids are processed or handled; and where their release into the atmosphere could result in their ignition by electrical systems or equipment.
This recommended practice provides information on specific flammable gases and vapors, flammable liquids, and combustible liquids, whose relevant combustion properties have been sufficiently identified to allow their classification into the groups established by NFPA 70, National Electrical Code® (NEC®), for proper selection of electrical equipment in hazardous (classified) locations. The tables of selected combustible materials contained in this document are not intended to be all-inclusive.
This recommended practice applies to chemical process areas. As used in this document, a chemical process area could be a large, integrated chemical process plant or it could be a part of such a plant. It could be a part of a manufacturing facility where flammable gases or vapors, flammable liquids, or combustible liquids are produced or used in chemical reactions, or are handled or used in certain unit operations such as mixing, filtration, coating, spraying, and distillation.
This recommended practice does not apply to situations that could involve catastrophic failure of or catastrophic discharge from process vessels, pipelines, tanks, or systems.
This recommended practice does not apply to oxygen enriched atmospheres or pyrophoric materials.
Purpose
The Purpose of this recommended practice is to provide the user with a basic understanding of the parameters that determine the degree and the extent of the hazardous (classified) location. This recommended practice also provides the user with examples of the applications of these parameters.
Referenced Publications
The documents or portions thereof listed in this chapter are referenced within this recommended practice and should be considered part of the recommendations of this document.
NFPA Publications. National Fire Protection Association
- NFPA 30, Flammable and Combustible Liquids Code, 2003 edition.
- NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials, 2003 edition.
- NFPA 34, Standard for Dipping and Coating Processes Using Flammable or Combustible Liquids, 2003 edition.
- NFPA 35, Standard for the Manufacture of Organic Coatings, 1999 edition.
- NFPA 36, Standard for Solvent Extraction Plants, 2004 edition.
- NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals, 2000 edition.
- NFPA 50A, Standard for Gaseous Hydrogen Systems at Consumer Sites, 1999 edition.
- NFPA 50B, Standard for Liquefied Hydrogen Systems at Consumer Sites, 1999 edition.
- NFPA 58, Liquefied Petroleum Gas Code, 2004 edition.
- NFPA 59A, Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG), 2001 edition.
- NFPA 70, National Electrical Code®, 2002 edition.
API Publications. American Petroleum Institute
- ANSI/API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2, 1998. (Reaffirmed, November 2002.)
- ANSI/API RP 505, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2, 1998.
ASHRAE Publication. American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc
- ASHRAE 15, Safety Code for Mechanical Refrigeration, 1994.
ASTM Publication. American Society for Testing and Materials
- ASTM D 323, Standard Method of Test for Vapor Pressure of Petroleum Products (Reid Method), 1999.
CGA Publication. Compressed Gas Association
- ANSI/CGA G2.1, American National Standard Safety Requirements for the Storage and Handling of Anhydrous Ammonia, 1999.
IEC Publication. International Electrotechnical Commission.
- IEC/TR3 60079-20, Electrical apparatus for explosive gas atmospheres-Part 20: Data for flammable