1、 TECHNICAL REPORT ISA-TR12.24.01-1998 (IEC 60079-10 Mod) Recommended Practice for Classification of Locations for Electrical Installations Classified as Class I, Zone 0, Zone 1, or Zone 2 Approved 31 May 2000 ISA-TR12.24.01-1998 (IEC 79-10 Mod), Recommended Practice for Classification of Locations f
2、or Electrical Installations Classified as Class I, Zone 0, Zone 1, or Zone 2ISBN: 978-1-55617-649-4Copyright 1998 by IEC and ISA. All rights reserved. Printed in the United Statesof America. No part of this publication may be reproduced, stored in a retrieval system,or transmitted, in any form or by
3、 any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher.ISA67 Alexander DriveP. O. Box 12277Research Triangle Park, North Carolina 27709ISA-TR12.24.01-1998 (IEC 79-10 Mod) 3PrefaceThis ISA recommended practice is based on IEC
4、Publication 79-10. It is the intention of the ISA SP12 Committee to develop an ISA Recommended Practice that is harmonized with IEC 79-10 to the fullest extent possible.This preface, as well as all footnotes and annexes, is included for informational purposes and is not part of ISA-TR12.24.01-1998 (
5、IEC 79-10 Mod).This recommended practice has been prepared as part of the service of ISA, the international society for measurement and control, toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static, but should be subject to periodic rev
6、iew. Toward this end, the Society welcomes all comments and criticisms, and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standards.infoisa
7、.org.The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards, recommended practices, and technical reports. The Department
8、 is further aware of the benefits to U.S. users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new
9、and revised standards to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing b) the processing and manufacture of explosives;c) areas where a risk may arise due to the presence of ignitable
10、dusts or fibers;d) catastrophic failures which are beyond the concept of abnormality dealt with in this standard recommended practice (see Note 3);e) rooms used for medical purposes;f) areas where the presence of flammable mist may give rise to an unpredictable risk and which require special conside
11、ration (see Note 5).This standard recommended practice does not take into account the effects of consequential damage.Definitions and explanations of terms are given together with the main principles and procedures relating to hazardous area classification.For detailed recommendations regarding the
12、extent of the hazardous areas in specific industries or applications, reference may be made to the codes, standards, or recommended practices relating to those industries or applications.NOTE 1 For the purpose of this standard recommended practice, an area is a three-dimensional region or space.NOTE
13、 2 Atmospheric conditions include variations above and below reference levels of 101.3 kPa (1.013 mbar) and 20 C (293 K), provided that the variations have a negligible effect on the explosion properties of the flammable materials.NOTE 3 Catastrophic failure in this context is applied, for example,
14、to the rupture of a process vessel or pipeline, and such other events that are not predictable.NOTE 4 In any process plant facility , irrespective of size, there may be numerous sources of ignition apart from those associated with electrical apparatus. Appropriate precautions will be necessary to en
15、sure safety in this context. This standard recommended practice may be used with judgment for other ignition sources.10 ISA-TR12.24.01-1998 (IEC 79-10 Mod)NOTE 5 Mists may form or be present at the same time as flammable vapors. This may affect the way flammable material disperses and the extent of
16、any hazardous areas. The strict application of area classification for gases and vapors may not be appropriate because the flammability characteristics of mists are not always predictable. Whilst it can be difficult to decide upon the type and extent of zones, the criteria applicable to gases and va
17、pors will, in most cases, give a safe result. However, special consideration should always be given to the danger of ignition of flammable mists.1.2 Normative ReferencesThe following normative documents contain provisions which, through reference in this text, constitute provisions of this part of I
18、EC 79 recommended practice. At the time of publication, the editions indicated were valid. All normative documents are subject to revision, and parties to agreements based on this part of IEC 79 recommended practice are encouraged to investigate the possibility of applying the most recent editions o
19、f the normative documents indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ANSI maintains registers of currently valid American National Standards.ANSI/ISA-S12.13, Part I, Performance Requirements, Combustible Gas DetectorsANSI/ISA- RP12.13, Part
20、 II, Installation Operation and Maintenance of Combustible Gas Detection InstrumentsIEC 50(426): 1990, International Electrotechnical Vocabulary (IEV) - Chapter 426.- Electrical apparatus for explosive atmospheresIEC 79-1A: Construction and Verification Tests of Flameproof Enclosures of Electrical A
21、pparatusIEC 79-3: Spark-Test Apparatus For Intrinsically Safe CircuitsIEC 79-4: 1975, Electrical apparatus for explosive gas atmospheres - Part 4: Method of test for ignition temperatureIEC 79-4A: 1970, First supplement to IEC 79-4 (1966)IEC 79-12: Classification of Mixtures of Gases or Vapours With
22、 Air According To Their Maximum Experimental Safe Gaps and Minimum Igniting CurrentsANSI/API RP 14F: Recommended Practice for Design and Installation of Electrical Systems for Offshore Production PlatformsAPI RP 505: Recommended Practice for Classification of Locations for Electrical Installations a
23、t Petroleum Facilities Classified as Class I, Zone 0, Zone 1, or Zone 2ASTM E-659: Test for Autoignition Temperature of Liquid ChemicalsIP 15, Institute of Petroleum: Area Classification Code for Petroleum Installations Part 15NFPA 30: Flammable and Combustible Liquids CodeNFPA 70: National Electric
24、al CodeNFPA 325M: Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile SolidsNFPA 497: Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations For Electrical Installations In Chemical Process Areas ISA-TR12.24.01-1998 (IEC 79-10 Mod) 111.3 P
25、urpose The purpose of this recommended practice is to provide guidelines for classifying hazardous (classified) locations for the selection and installation of electrical equipment. Basic definitions given in the 1995 edition of IEC 79-10, Electrical apparatus for explosive gas atmospheres, Classifi
26、cation of hazardous areas, have been followed in developing this recommended practice. This publication is only a guide and requires the application of sound engineering judgment.Electrical installations in areas where flammable liquids or gases are produced, processed, stored or otherwise handled c
27、an be suitably designed if the locations of potential sources of release and accumulation are clearly defined. Once a location has been classified, requirements for electrical equipment and associated wiring should be determined from applicable publications. Applicable publications may include NFPA
28、No. 70 (NEC) or API RP 14F. Reference Section 1.2 for other possible applicable publications.2 Definitions and termsFor the purpose of this recommended practice part of IEC 79, the following definitions and terms apply.2.1 explosive gas atmosphere: a mixture with air, under atmospheric conditions, o
29、f a flammable material in the form of gas or vapor in which, after ignition, combustion spreads throughout the unconsumed mixture. IEV 426-02-03, modifiedNOTE Although a mixture which has a concentration above the upper explosive limit (UEL) is not an explosive gas atmosphere, it can readily become
30、so and in certain cases, for area classification purposes, it is advisable to consider it as an explosive gas atmosphere.2.2 hazardous area: an area in which an explosive gas atmosphere is present, or may be expected to be present, in quantities such as to require special precautions for the constru
31、ction, installation and use of apparatus. IEV 426-03-01, modifiedNOTE The term “hazardous (classified) location” is defined in ANSI/ISA-S12.1.01. TR12.24.01 uses the term “hazardous area.” The two terms should be considered synonymous.2.3 non-hazardous area: an area in which an explosive gas atmosph
32、ere is not expected to be present in quantities such as to require special precautions for the construction, installation and use of apparatus. IEV 426-03-02, modifiedNOTE The term “unclassified location” is defined in ANSI/ISA S12.1.01. S12.24.01 uses the term “non-hazardous area.” The two terms sh
33、ould be considered synonymous.2.4 zone 0, 1, and 2 locations zone: hazardous areas are classified into zones based upon the frequency of the occurrence and duration of an explosive gas atmosphere as follows:2.4.1 class I, zone 0: an area in which an explosive gas atmosphere is present continuously o
34、r for long periods. IEV 426-03-03, modified2.4.2 class I, zone 1: an area in which an explosive gas atmosphere is likely to occur in normal operation. IEV 426-03-042.4.3 class I, zone 2: an area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it does occur, is
35、 likely to do so only infrequently and will exist for a short period only. IEV 426-03-05, modified12 ISA-TR12.24.01-1998 (IEC 79-10 Mod)2.4.1 class I, zone 0:a Class I, Zone 0, location is a location (1) in which ignitable concentrations of flammable gases or vapors are present continuously; or (2)
36、in which ignitable concentrations of flammable gases or vapors are present for long periods of time.NOTE 1 As a guide in determining when flammable gases or vapors are present continuously or for long periods of time, refer to Recommended Practice for Classification of Locations for Electrical Insta
37、llations of Petroleum Facilities Classified as Class I, Zone 0, Zone 1, or Zone 2, API RP 505-1996; Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous Areas, IEC 79-10; and Area Classification Code for Petroleum Installations, Model Code, Part 15, Institute of Petroleum
38、; and Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous (Classified) Locations, ISA S12.24.01-1997.NOTE 2 This classification includes locations inside vented tanks or vessels containing volatile flamable liquids; inside inadequately vented spraying or coating enclosur
39、es, where volatile flammable solvents are used; between the inner and outer roof sections of a floating roof tank containing volatile flammable liquids; inside open vessels, tanks and pits containing volatile flammable liquids; the interior of an exhaust duct that is used to vent ignitable concentra
40、tions of gases or vapors; and inside inadequately ventilated enclosures containing normally venting instruments utilizing or analyzing flammable fluids and venting to the inside of the enclosures.NOTE 3 It is not good practice to install electrical equipment in Zone 0 locations except when the equip
41、ment is essential to the process or when other locations are not feasible. (See NEC Section 505-2 FPN No. 2.) If it is necessary to install electrical systems in a Zone 0 location, it is good practice to install intrinsically safe systems as described by NEC Article 504.2.4.2 class I, zone 1: a Clas
42、s I, Zone 1 location is a location (1) in which ignitable concentrations of flammable gases or vapors are likely to exist under normal operating conditions; or (2) in which ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or becau
43、se of leakage; or (3) in which equipment is operated or processes are carried on, of such a nature that equipment breakdown or faulty operations could result in the release of ignitable concentrations of flammable gases or vapors and also cause simultaneous failure of electrical equipment in a mode
44、to cause the electrical equipment to become a source of ignition; or (4) that is adjacent to a Class I, Zone 0 location from which ignitable concentrations of vapors could be communicated, unless communication is prevented by adequate positive pressure ventilation from a source of clean air and effe
45、ctive safeguards against ventilation failure are provided.NOTE 1 Normal operations is considered the situation when facility equipment is operating within its design parameters. Minor releases of flammable material may be part of normal operations. Minor releases include the releases from mechanical
46、 packings on pumps. Failures that involve repair or shutdown (such as the breakdown of pump seats and flange gaskets, and spillage caused by accidents) are not considered normal operation.NOTE 2 This classification usually includes locations where volatile flammable liquids or liquefied flammable ga
47、ses are transferred from one container to another. In areas in the vicinity of spraying and painting operations where flammable solvents are used; adequately ventilated drying rooms or compartments for evaporation of flammable solvents; adequately ventilated locations containing fat and oil extracti
48、on equipment using volatile flammable solvents; portions of cleaning and dyeing plants where volatile flammable liquids are used; adequately ventilated gas generator rooms and other portions of gas manufacturing facilities where flammable gas may escape; inadequately ventilated pump rooms for flamma
49、ble gas or for volatile flammable liquids; the interiors of refrigerators and freezers in which volatile flammable materials are stored in the open, lightly stoppered, or easily ruptured containers; and other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operation, but not classified Zone 0.2.4.3 class I, zone 2: a Class I, Zone 2 location is a location (1) in which ignitable concentrations of flammable gases or vapors are not
