EN 61508-6:2001
(Main)Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3
Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3
Contains information and guidelines on EN 61508-2 and EN 61508-3.
Funktionale Sicherheit sicherheitsbezogener elektrischer/elektronischer/programmierbarer elektronischer Systeme - Teil 6: Anwendungsrichtlinie für IEC 61508-2 und IEC 61508-3
Sécurité fonctionnelle des systèmes électriques/électroniques/électroniques programmables relatifs à la sécurité - Partie 6: Lignes directrices pour l'application de la CEI 61508-2 et de la CEI 61508-3
Contient des informations et lignes directrices sur la EN 61508-2 et la EN 61508-3.
Funkcijska varnost električnih/elektronskih/programirljivih elektronskih varnostnih sistemov - 6. del: Smernice za uporabo IEC 61508-2 in IEC 61508-3 (IEC 61508-6:2000)
General Information
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EUROPEAN STANDARD EN 61508-6
NORME EUROPÉENNE
EUROPÄISCHE NORM December 2001
ICS 25.040.40
English version
Functional safety of electrical/electronic/programmable electronic
safety-related systems
Part 6: Guidelines on the application
of IEC 61508-2 and IEC 61508-3
(IEC 61508-6:2000)
Sécurité fonctionnelle des systèmes Funktionale Sicherheit
électriques/électroniques/électroniques sicherheitsbezogener elektrischer/
programmables relatifs à la sécurité elektronischer/programmierbarer
Partie 6: Lignes directrices pour elektronischer Systeme
l'application de la CEI 61508-2 et Teil 6: Anwendungsrichtlinie für
de la CEI 61508-3 IEC 61508-2 und IEC 61508-3
(CEI 61508-6:2000) (IEC 61508-6:2000)
This 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.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central 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 61508-6:2001 E
Foreword
The text of the International Standard IEC 61508-6:2000, 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 61508-6 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 identical
national standard or by endorsement (dop) 2002-08-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2004-08-01
Annexes 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 annexes A to E are 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.
__________
- 3 - EN 61508-6:2001
Endorsement notice
The text of the International Standard IEC 61508-6:2000 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 61078 NOTE Harmonized as EN 61078:1993 (not modified).
IEC 61131-3 NOTE Harmonized as EN 61131-3:1993 (not modified).
__________
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 61508-1 1998 Functional safety of EN 61508-1 2001
+ corr. May 1999 electrical/electronic/programmable
electronic safety-related systems
Part 1: General requirements
IEC 61508-2 2000 Part 2: Requirements for EN 61508-2 2001
electrical/electronic/programmable
electronic safety-related systems
IEC 61508-3 1998 Part 3: Software requirements EN 61508-3 2001
+ corr. April 1999
IEC 61508-4 1998 Part 4: Definitions and abbreviations EN 61508-4 2001
+ corr. April 1999
IEC 61508-5 1998 Part 5: Examples of methods for the EN 61508-5 2001
+ corr. April 1999 determination of safety integrity levels
IEC 61508-7 2000 Part 7: Overview of techniques and EN 61508-7 2001
measures
IEC Guide 104 1997 The preparation of safety publications--
and the use of basic safety publications
and group safety publications
ISO/IEC Guide 51 1990 Guidelines for the inclusion of safety--
aspects in standards
INTERNATIONAL IEC
STANDARD
61508-6
First edition
2000-04
Functional safety of electrical/electronic/
programmable electronic safety-related systems –
Part 6:
Guidelines on the application of
IEC 61508-2 and IEC 61508-3
IEC 2000 Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical,
including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
XB
Commission Electrotechnique Internationale
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue
61508-6 © IEC:2000 – 3 –
CONTENTS
Page
FOREWORD .11
INTRODUCTION . 15
Clause
1 Scope . 19
2 Normative references. 23
3 Definitions and abbreviations . 23
Annex A (informative) Application of IEC 61508-2 and of IEC 61508-3 . 25
A.1 General. 25
A.2 Functional steps in the application of IEC 61508-2. 29
A.3 Functional steps in the application of IEC 61508-3. 37
Annex B (informative) Example technique for evaluating probabilities of hardware failure . 41
B.1 General. 41
B.2 Average probability of failure on demand (for low demand mode of operation) . 49
B.3 Probability of failure per hour (for high demand or continuous mode
of operation) . 75
B.4 References . 91
Annex C (informative) Calculation of diagnostic coverage and safe failure fraction:
worked example . 93
Annex D (informative) A methodology for quantifying the effect of hardware-related
common cause failures in E/E/PE systems . 101
D.1 General. 101
D.2 Brief overview . 101
D.3 Scope of the methodology. 109
D.4 Points taken into account in the methodology . 109
D.5 Using the β-factor to calculate the probability of failure in an E/E/PE
safety-related system due to common cause failures . 111
D.6 Using the tables to estimate β. 113
D.7 Examples of the use of the methodology. 121
D.8 References . 123
Annex E (informative) Example applications of software safety integrity tables
of IEC 61508-3 . 125
E.1 General. 125
E.2 Example for safety integrity level 2 . 125
E.3 Example for safety integrity level 3 . 135
Bibliography . 145
61508-6 © IEC:2000 – 5 –
Page
Figure 1 – Overall framework of IEC 61508 . 21
Figure A.1 – Application of IEC 61508-2. 33
Figure A.2 – Application of IEC 61508-2 (continued) . 35
Figure A.3 – Application of IEC 61508-3. 39
Figure B.1 – Example configuration for two sensor channels . 45
Figure B.2 – Subsystem structure. 49
Figure B.3 – 1oo1 physical block diagram . 51
Figure B.4 – 1oo1 reliability block diagram . 51
Figure B.5 – 1oo2 physical block diagram . 53
Figure B.6 – 1oo2 reliability block diagram . 55
Figure B.7 – 2oo2 physical block diagram . 55
Figure B.8 – 2oo2 reliability block diagram . 55
Figure B.9 – 1oo2D physical block diagram . 57
Figure B.10 – 1oo2D reliability block diagram. 57
Figure B.11 – 2oo3 physical block diagram . 59
Figure B.12 – 2oo3 reliability block diagram . 59
Figure B.13 – Architecture of an example for low demand mode of operation . 69
Figure B.14 – Architecture of an example for high demand or continuous mode of
operation. 87
Figure D.1 – Relationship of common cause failures to the failures of individual channels. 105
Table B.1 – Terms and their ranges used in this annex (applies
...
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