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BRITISH STANDARD BS EN61508-4:2002Incorporating Corrigendum No.1 to BS IEC 61508-4:1998 and Amendment No.1 to BS IEC61508-4:1998Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIFunctional safety ofelectrical/electronic/ programmable electronicsafety-related systems Part 4: Definitions and abbreviationsThe European Standard EN 61508-4:2001 has the status of aBritish StandardICS 01.040.25; 01.040.29; 25.040.40; 29.020 (renumbers theBS IEC asBS EN 61508-4:2002)BS EN 61508-4:2002National forewordThis British Standard is the official English language version ofEN 61508-4:2001. It is identical with IEC 61508-4:1998 including corrigendumApril 1999.The UK participation in its preparation was entrusted to Technical Committee GEL/65, Measurement and control, to Subcommittee GEL/65/1, System considerations, which has the responsibility to:aid enquirers to understand the text;present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;monitor related international and European developments and promulgate them in the UK.A list of organizations represented on this committee can be obtained on request to its secretary.Cross-referencesThe British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue.A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.Compliance with a British Standard does not of itself confer immunity from legal obligations.Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIThis British Standard, having been prepared under the direction of the Electrotechnical Sector Committee, was published under the authority of the Standards Committee and comes into effecton 15 June 1999 BSI 15 March 2002ISBN 0 580 32721 3Summary of pagesThis document comprises a front cover, an inside front cover, the EN title page, pages 2 to 28, an inside back cover and a back cover.The BSI copyright date displayed in this document indicates when the document was last issued.Amd. No.DateComments10632Corrigendum No.1August 1999Incorporation of IEC CorrigendumApril 19991378215 March 2002Implementation of the European StandardAmendments issued since publicationEUROPEAN STANDARDEN 61508-4NORME EUROPENNEEUROPISCHE NORMDecember 2001ICS 25.040.40;29.020English versionFunctional safety of electrical/electronic/programmable electronic safety-related systemsPart 4: Definitions and abbreviations(IEC 61508-4:1998 + corrigendum 1999)Scurit fonctionnelle des systmes lectriques/lectroniques/lectroniques programmables relatifs la scurit Partie 4: Dfinitions et abrviations(CEI 61508-4:1998 + corrigendum 1999)Funktionale Sicherheit sicherheitsbezogener elektrischer/ elektronischer/programmierbarer elektronischer SystemeTeil 4: Begriffe und Abkrzungen(IEC 61508-4:1998 + Corrigendum 1999)Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIThis European Standard was approved by CENELEC on 2001-07-03. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.CENELECEuropean Committee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische NormungCentral Secretariat: rue de Stassart 35, B - 1050 Brussels 2001 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.Ref. No. EN 61508-4:2001 EPage 27EN 615084:2001Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIForewordThe text of the International Standard IEC 61508-4:1998 including its corrigendum April 1999, prepared by SC 65A, System aspects, of IEC TC 65, Industrial-process measurement and control, was submitted to the Unique Acceptance Procedure and was approved by CENELEC as EN 61508-4 on 2001-07-03 without any modification.The following dates were fixed: latest date by which the EN has to be implemented at national level by publication of an identicalnational standard or by endorsement(dop) 2002-08-01 latest date by which the national standards conflictingwith the EN have to be withdrawn(dow) 2004-08-01Annexes designated normative are part of the body of the standard. Annexes designated informative are given for information only.In this standard, annex ZA is normative and annex A is informative.Annex ZA has been added by CENELEC.IEC 61508 is a basic safety publication covering the functional safety of electrical, electronic and programmable electronic safety-related systems. The scope states:This International Standard covers those aspects to be considered when electrical/electronic/ programmable electronic systems (E/E/PESs) are used to carry out safety functions. A major objective of this standard is to facilitate the development of application sector international standards by the technical committees responsible for the application sector. This will allow all the relevant factors associated with the application, to be fully taken into account and thereby meet the specific needs of the application sector. A dual objective of this standard is to enable the development of electrical/electronic/ programmable electronic (E/E/PE) safety-related systems where application sector international standards may not exist.The CENELEC Report R0BT-004, ratified by 103 BT (March 2000) accepts that some IEC standards, which today are either published or under development, are sector implementations of IEC 61508. For example: IEC 61511, Functional safety - Safety instrumented systems for the process industry sector; IEC 62061, Safety of machinery Functional safety of electrical, electronic and programmable electronic control systems; IEC 61513, Nuclear power plants Instrumentation and control for systems important to safety General requirements for systems.The railways sector has also developed a set of European Standards (EN 50126; EN 50128 and prEN 50129).NOTE EN 50126 and EN 50128 were based on earlier drafts of IEC 61508. prEN 50129 is based on the principles of the latest version of IEC 61508.This list does not preclude other sector implementations of IEC 61508 which could be currently under development or published within IEC or CENELEC.Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIEndorsement noticeThe text of the International Standard IEC 61508-4:1998 including its corrigendum April 1999 was approved by CENELEC as a European Standard without any modification.In the official version, for Bibliography, the following note has to be added for the standard indicated:IEC 61131-3:1993 NOTE Harmonized as EN 61131-3:1993 (not modified). ISO 9000-3:1991NOTE Harmonized as EN 29000-3:1993 (not modified).Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSICONTENTSPageINTRODUCTION .5Clause1Scope .72Normative references .93Definitions and abbreviations .103.1Safety terms .103.2Equipment and devices .113.3Systems: general aspects .133.4Systems: safety-related aspects .153.5Safety functions and safety integrity .163.6Fault, failure and error .193.7Lifecycle activities .213.8Confirmation of safety measures .22Annex A (informative) Bibliography .25Annex ZA (normative) Normative references to international publications with theircorresponding European publications . 28Index .26Figures1Overall framework of this standard .82Programmable electronic system (PES): structure and terminology .143Electrical/electronic/programmable electronic system (E/E/PES):structure and terminology .144Failure model .20Table1Abbreviations used in this standard .10Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIINTRODUCTIONSystems comprised of electrical and/or electronic components have been used for many years to perform safety functions in most application sectors. Computer-based systems (generically referred to as programmable electronic systems (PESs) are being used in all application sectors to perform non-safety functions and, increasingly, to perform safety functions. If computer system technology is to be effectively and safely exploited, it is essential that those responsible for making decisions have sufficient guidance on the safety aspects on which to make those decisions.This International Standard sets out a generic approach for all safety lifecycle activities for systems comprised of electrical and/or electronic and/or programmable electronic components (electrical/electronic/ programmable electronic systems (E/E/PESs) that are used to perform safety functions. This unified approach has been adopted in order that a rational and consistent technical policy be developed for all electrically based safety-related systems. A major objective is to facilitate the development of application sector standards.In most situations, safety is achieved by a number of protective systems which rely on many technologies(forexamplemechanical,hydraulic,pneumatic,electrical,electronic, programmable electronic). Any safety strategy must therefore consider not only all the elements within an individual system (for example sensors, controlling devices and actuators) but also all the safety-related systems making up the total combination of safety-related systems. Therefore, while this International Standard is concerned with electrical/elec- tronic/programmable electronic (E/E/PE) safety-related systems, it may also provide a framework within which safety-related systems based on other technologies may be considered.It is recognised that there is a great variety of E/E/PES applications in a variety of application sectors and covering a wide range of complexity, hazard and risk potentials. In any particular application, the required safety measures will be dependent on many factors specific to the application. This International Standard, by being generic, will enable such measures to be formulated in future application sector international standards.This International Standardconsiders all relevant overall, E/E/PES and software safety lifecycle phases (for example, from initial concept, through design, implementation, operation and maintenance to decommissioning) when E/E/PESs are used to perform safety functions;has been conceived with a rapidly developing technology in mind; the framework is sufficiently robust and comprehensive to cater for future developments;enables application sector international standards, dealing with safety-related E/E/PESs, to be developed; the development of application sector international standards, within the framework of this International Standard, should lead to a high level of consistency (for example, of underlying principles, terminology, etc.) both within application sectors and across application sectors; this will have both safety and economic benefits;provides a method for the development of the safety requirements specification necessary to achieve the required functional safety for E/E/PE safety-related systems;Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIuses safety integrity levels for specifying the target level of safety integrity for the safety functions to be implemented by the E/E/PE safety-related systems;adopts a risk-based approach for the determination of the safety integrity level requirements;sets numerical target failure measures for E/E/PE safety-related systems which are linked to the safety integrity levels;sets a lower limit on the target failure measures, in a dangerous mode of failure, that can be claimed for a single E/E/PE safety-related system; for E/E/PE safety-related systems operating ina low demand mode of operation, the lower limit is set at an average probability of failure of 10-5 to perform its design function on demand,a high demand or continuous mode of operation, the lower limit is set at a probability of a dangerous failure of 109 per hour;NOTE A single E/E/PE safety-related system does not necessarily mean a single-channel architecture.adopts a broad range of principles, techniques and measures to achieve functional safety for E/E/PE safety-related systems, but does not use the concept of fail safe which may be of value when the failure modes are well defined and the level of complexity is relatively low; the concept of fail safe was considered inappropriate because of the full range of complexity of E/E/PE safety-related systems that are within the scope of the standard.Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSIFUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/PROGRAMMABLE ELECTRONIC SAFETY-RELATED SYSTEMS Part 4: Definitions and abbreviations1Scope1.1This part of IEC 61508 contains the definitions and explanation of terms that are used in parts 1 to 7 of this standard.1.2The definitions are grouped under general headings so that related terms can be understood within the context of each other. But it should be noted that these headings are not intended to add meaning to the definitions, and in this sense the headings should be disregarded.1.3Parts 1, 2, 3 and 4 of this standard are basic safety publications, although this status does not apply in the context of low complexity E/E/PE safety-related systems (see 3.4.4 of part 4). As basic safety publications, they are intended for use by technical committees in the preparation of standards in accordance with the principles contained in IEC Guide 104 and ISO/IEC Guide 51. Parts 1, 2, 3, and 4 are also intended for use as stand-alone publications.One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. In this context, the requirements, test methods or test conditions of this basic safety publication will not apply unless specifically referred to or included in the publications prepared by those technical committees.1.4Figure 1 shows the overall framework for parts 1 to 7 of IEC 61508 and indicates the role that IEC 61508-4 plays in the achievement of functional safety for E/E/PE safety-related systems.NOTE In the USA and Canada, until the proposed process sector implementation of IEC 61508 (i.e. IEC 61511) is published as an international standard in the USA and Canada, existing national process safety standards based on IEC 61508 (i.e. ANSI/ISA S84.01-1996) can be applied to the process sector instead of IEC 61508.PART 1Development of the overall safety requirements (concept, scope definition, hazard and risk analysis) (E/E/PE safety-related systems, other technology safety-related systems and external risk reduction facilities)7.1 to 7.5Technical requirementsPART 5Risk based approaches to the development of the safety integrity requirementsPART 1Allocation of the safety requirements to the E/E/PE safety-related systemsOther requirementsRealisation phase for E/E/PE safety- related systemsPART 27.6Realisation phase for safety-related softwarePART 3PART 7Overview of techniques and measuresPART 6Guidelines for the application of IEC 61508-2 and IEC 61508-3Definitions and abbreviationsPART 4DocumentationClause 5 and annex APART 1PART 1Installation and commissioning and safety validation o
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