IEC 61508-6:2010
(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 (see Functional Safety and IEC 61508)
Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3 (see Functional Safety and IEC 61508)
IEC 61508-6:2010 contains information and guidelines on IEC 61508-2 and IEC 61508 3. Annex A gives a brief overview of the requirements of IEC 61508-2 and IEC 61508-3 and sets out the functional steps in their application. Annex B gives an example technique for calculating the probabilities of hardware failure and should be read in conjunction with 7.4.3 and Annex C of IEC 61508-2 and Annex D. Annex C gives a worked example of calculating diagnostic coverage and should be read in conjunction with Annex C of IEC 61508-2. Annex D gives a methodology for quantifying the effect of hardware-related common cause failures on the probability of failure. Annex E gives worked examples of the application of the software safety integrity tables specified in Annex A of IEC 61508-3 for safety integrity levels 2 and 3. This second edition cancels and replaces the first edition published in 1998. This edition constitutes a technical revision. It has been subject to a thorough review and incorporates many comments received at the various revision stages.
NEW! Also available: IEC Standards+ 61508:2010, containing all parts, together with a commented Redline version. Changes made in this 2nd edition are highlighted and commented by a leading world expert.
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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
La CEI 61508-6:2010 contient des informations et lignes directrices sur la CEI 61508-2 et la CEI 61508-3. L'Annexe A présente un bref aperçu des exigences de la CEI 61508-2 et de la CEI 61508-3 et établit les étapes fonctionnelles de leur application. L'Annexe B donne une technique servant d'exemple pour le calcul des probabilités de défaillance du matériel; il convient de la lire conjointement au 7.4.3 et à l'Annexe C de la CEI 61508-2, et à l'Annexe D. L'Annexe C donne un exemple élaboré de calcul de la couverture de diagnostic; il convient de la lire conjointement avec l'Annexe C de la CEI 61508-2. L'Annexe D donne une méthodologie de quantification de l'effet des défaillances de cause commune relatives au matériel sur la probabilité de défaillance. L'Annexe E donne des exemples d'application des tableaux d'intégrité de sécurité du logiciel spécifiés dans l'Annexe A de la CEI 61508-3 pour les niveaux 2 et 3 d'intégrité de sécurité. Cette deuxième édition annule et remplace la première édition publiée en 1998 dont elle constitue une révision technique. Elle a fait l'objet d'une révision approfondie et intègre de nombreux commentaires reçus lors des différentes phases de révision.
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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
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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 .71
Figure B.37 – Example of functional and dysfunctional modelling with a formal
language.72
Figure B.38 – Uncertainty propagation principle.73
Figure D.1 – Relationship of common cause failures to the failures of individual
channels .82
Figure D.2 – Implementing shock model with fault trees.93
Table B.1 – Terms and their ranges used in this annex (applies to 1oo1, 1oo2, 2oo2,
1oo2D, 1oo3 and 2oo3) .27
Table B.2 – Average probability of failure on demand for a proof test interval of six
months and a mean time to restoration of 8 h .36
Table B.3 – Average probability of failure on demand for a proof test interval of one
year and mean time to restoration of 8 h.37
Table B.4 – Average probability of failure on demand for a proof test interval of two
years and a mean time to restoration of 8 h .38
Table B.5 – Average probability of failure on demand for a proof test interval of
ten years and a mean time to restoration of 8 h .39
Table B.6 – Average probability of failure on demand for the sensor subsystem in the
example for low demand mode of operation (one year proof test interval and
8 h MTTR) .40
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