EN 61508-6:2010

SLOVENSKI STANDARD
01-maj-2011
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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-
6:2010)
Funktionale Sicherheit sicherheitsbezogener
elektrischer/elektronischer/programmierbarer elektronischer Systeme - Teil 6:
Anwendungsrichtlinie für IEC 61508-2 und IEC 61508-3 (IEC 61508-6:2010)
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 (CEI 61508-6:2010)
Ta slovenski standard je istoveten z: EN 61508-6:2010
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61508-6
NORME EUROPÉENNE
May 2010
EUROPÄISCHE NORM
ICS 25.040.40 Supersedes EN 61508-6:2001

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 61508-6:2010)
Sécurité fonctionnelle des systèmes Funktionale Sicherheit sicherheitsbezogener
électriques/électroniques/électroniques elektrischer/elektronischer/programmierbarer
programmables relatifs à la sécurité - elektronischer Systeme -
Partie 6: Lignes directrices Teil 6: Anwendungsrichtlinie für IEC 61508-2
pour l'application de la CEI 61508-2 und IEC 61508-3
et de la CEI 61508-3 (IEC 61508-6:2010)
(CEI 61508-6:2010)
This European Standard was approved by CENELEC on 2010-05-01. 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, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61508-6:2010 E
Foreword
The text of document 65A/553/FDIS, future edition 2 of IEC 61508-6, prepared by SC 65A, System
aspects, of IEC TC 65, Industrial-process measurement, control and automation, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 61508-6 on 2010-05-01.
This European Standard supersedes EN 61508-6:2001.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
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) 2011-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2013-05-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61508-6:2010 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:
[1] IEC 61511 series NOTE  Harmonized in EN 61511 series (not modified).
[2] IEC 62061 NOTE  Harmonized as EN 62061.
[3] IEC 61800-5-2 NOTE  Harmonized as EN 61800-5-2.
[4] IEC 61078:2006 NOTE  Harmonized as EN 61078:2006 (not modified).
[5] IEC 61165:2006 NOTE  Harmonized as EN 61165:2006 (not modified).
[16] IEC 61131-3:2003 NOTE  Harmonized as EN 61131-3:2003 (not modified).
[18] IEC 61025:2006 NOTE  Harmonized as EN 61025:2007 (not modified).
[26] IEC 60601 series NOTE  Harmonized in EN 60601 series (partially modified).
[27] IEC 61508-1:2010 NOTE  Harmonized as EN 61508-1:2010 (not modified).
[28] IEC 61508-5:2010 NOTE  Harmonized as EN 61508-5:2010 (not modified).
[29] IEC 61508-7:2010 NOTE  Harmonized as EN 61508-7:2010 (not modified).
__________
- 3 - EN 61508-6:2010
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

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 61508-2 2010 Functional safety of EN 61508-2 2010
electrical/electronic/programmable electronic
safety-related systems -
Part 2: Requirements for
electrical/electronic/programmable electronic
safety-related systems
IEC 61508-3 2010 Functional safety of EN 61508-3 2010
electrical/electronic/programmable electronic
safety-related systems -
Part 3: Software requirements
IEC 61508-4 2010 Functional safety of EN 61508-4 2010
electrical/electronic/programmable electronic
safety-related systems -
Part 4: Definitions and abbreviations

IEC 61508-6 ®
Edition 2.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Functional safety of electrical/electronic/programmable electronic safety-related
systems –
Part 6: Guidelines on the application of IEC 61508-2 and 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
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XE
CODE PRIX
ICS 25.040.40 ISBN 978-2-88910-529-8
– 2 – 61508-6 © IEC:2010
CONTENTS
FOREWORD.6
INTRODUCTION.8
1 Scope.10
2 Normative references .12
3 Definitions and abbreviations.12
Annex A (informative) Application of IEC 61508-2 and of IEC 61508-3.13
Annex B (informative) Example of technique for evaluating probabilities of hardware
failure .21
Annex C (informative) Calculation of diagnostic coverage and safe failure fraction –
worked example.76
Annex D (informative) A methodology for quantifying the effect of hardware-related
common cause failures in E/E/PE systems.80
Annex E (informative) Example applications of software safety integrity tables of
IEC 61508-3 .95
Bibliography.110

Figure 1 – Overall framework of the IEC 61508 series .11
Figure A.1 – Application of IEC 61508-2 .17
Figure A.2 – Application of IEC 61508-2 (Figure A.1 continued).18
Figure A.3 – Application of IEC 61508-3 .20
Figure B.1 – Reliability Block Diagram of a whole safety loop .22
Figure B.2 – Example configuration for two sensor channels.26
Figure B.3 – Subsystem structure .29
Figure B.4 – 1oo1 physical block diagram .30
Figure B.5 – 1oo1 reliability block diagram.31
Figure B.6 – 1oo2 physical block diagram .32
Figure B.7 – 1oo2 reliability block diagram.32
Figure B.8 – 2oo2 physical block diagram .33
Figure B.9 – 2oo2 reliability block diagram.33
Figure B.10 – 1oo2D physical block diagram.33
Figure B.11 – 1oo2D reliability block diagram .34
Figure B.12 – 2oo3 physical block diagram .34
Figure B.13 – 2oo3 reliability block diagram.35
Figure B.14 – Architecture of an example for low demand mode of operation.40
Figure B.15 – Architecture of an example for high demand or continuous mode of
operation .49
Figure B.16 – Reliability block diagram of a simple whole loop with sensors organised
into 2oo3 logic .51
Figure B.17 – Simple fault tree equivalent to the reliability block diagram presented on
Figure B.1.52
Figure B.18 – Equivalence fault tree / reliability block diagram.52
Figure B.19 – Instantaneous unavailability U(t) of single periodically tested
components .54
Figure B.20 – Principle of PFD calculations when using fault trees.55
avg
61508-6 © IEC:2010 – 3 –
Figure B.21 – Effect of staggering the tests .56
Figure B.22 – Example of complex testing pattern .56
Figure B.23 – Markov graph modelling the behaviour of a two component system .58
Figure B.24 – Principle of the multiphase Markovian modelling .59
Figure B.25 – Saw-tooth curve obtained by multiphase Markovian approach.60
Figure B.26 – Approximated Markovian model .60
Figure B.27 – Impact of failures due to the demand itself.61
Figure B.28 – Modelling of the impact of test duration.61
Figure B.29 – Multiphase Markovian model with both DD and DU failures.62
Figure B.30 – Changing logic (2oo3 to 1oo2) instead of repairing first failure.63
Figure B.31 – "Reliability" Markov graphs with an absorbing state .63
Figure B.32 – "Availability" Markov graphs without absorbing states .65
Figure B.33 – Petri net for modelling a single periodically tested component.66
Figure B.34 – Petri net to model common cause failure and repair resources.69
Figure B.35 – Using reliability block diagrams to build Petri net and auxiliary Petri net
for PFD and PFH calculations .70
Figure B.36 – Simple Petri net for a single component with revealed failures and
repairs .
...