oSIST prEN IEC 61508-6:2025

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)

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

Funkcijska varnost električnih/elektronskih/elektronsko programirljivih varnostnih sistemov - 6. del: Smernice za uporabo IEC 61508-2 in IEC 61508-3 (glej Funkcijska varnost in IEC 61508)

General Information

• Status: Not Published
• Public Enquiry End Date: 30-May-2025
• ICS: 25.040.40 - Industrial process measurement and control
• Technical Committee: MOV - Measuring equipment for electromagnetic quantities
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 18-Mar-2025
• Due Date: 05-Aug-2025
• Ref Project: prEN IEC 61508-6:2025 - 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)

Relations

• Revises: SIST EN 61508-6:2011 - 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)
• Effective Date: 23-Jan-2023
• Revised: SIST EN 61508-6:2011 - 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)
• Effective Date: 11-Oct-2022

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2025
Funkcijska varnost električnih/elektronskih/elektronsko programirljivih varnostnih
sistemov - 6. del: Smernice za uporabo IEC 61508-2 in IEC 61508-3 (glej Funkcijska
varnost in 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)
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
Ta slovenski standard je istoveten z: prEN IEC 61508-6:2025
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.

65A/1171/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 61508-6 ED3
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2025-03-14 2025-06-06
SUPERSEDES DOCUMENTS:
65A/1061A/CD, 65A/1080B/CC
IEC SC 65A : SYSTEM ASPECTS
SECRETARIAT: SECRETARY:
United Kingdom Ms Stephanie Lavy
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):
TC 8,TC 9,TC 22,TC 31,TC 44,TC 45,TC 56,TC 61,TC
62,TC 65,SC 65B,SC 65C,SC 65E,TC 66,TC 72, TC
77,TC 80,TC 108,SyC AAL,SyC SM,SC 41
ASPECTS CONCERNED:
Safety
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft
for Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they
are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some Countries”
clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for
submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
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)

PROPOSED STABILITY DATE: 2027
NOTE FROM TC/SC OFFICERS:
“Due to committee meetings planned at the end of May in Pisa, Italy, it is appreciated to voluntarily submit
comments on this Part of the IEC 61508 series by 2025-05-12 already. Of course, there will be all comments
accepted for consideration be the committee arriving within the official circulation period, but it will help the
committee for starting their work on the project phase.”

file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions. You may not copy or
"mirror" the file or printed version of the document, or any part of it, for any other purpose without permission in writing from IEC.

– 2 – IEC CDV 61508-6  IEC 2025
1 CONTENTS
3 FOREWORD . 5
4 INTRODUCTION . 7
5 1 Scope . 9
6 2 Normative references . 11
7 3 Definitions and abbreviations . 11
8 Annex A (informative) Application of IEC 61508-2 and of IEC 61508-3 . 12
9 A.1 General . 12
10 A.2 Functional steps in the application of IEC 61508-2 . 14
11 A.3 Functional steps in the application of IEC 61508-3 . 17
12 A.4 Architecture considerations . 19
13 A.4.1 Architecture Description Identification and Overview . 20
14 A.4.2 Stakeholders and Concerns . 20
15 Annex B (informative) Example of technique for evaluating probabilities of hardware
16 failure . 22
17 B.1 General . 22
18 B.2 Considerations about basic probabilistic calculations . 23
19 B.2.1 Introduction . 23
20 B.2.2 Low demand E/E/PE safety-related system . 23
21 B.2.3 Continuous or high demand mode E/E/PE safety-related system . 24
22 B.3 Methods of calculating PFD or PFH of a system . 25
23 B.3.1 Other available guidance . 25
24 B.3.2 Reliability block diagram approach, assuming constant failure rate . 26
25 B.3.3 Average frequency of dangerous failure (for high demand or continuous
26 mode of operation) . 45
27 B.4 Determination of SILs for E/E/PE Safety-Related Systems with (a) Common
28 Functional Element(s) . 56
29 B.4.1 Necessity of multiple protection layers (Multi-PLs) . 56
30 B.4.2 Redundant channels (CHs) and multi-PLs . 57
31 B.4.3 Classification of independency between (E/E/PE) safety-related
32 systems . 59
33 B.4.4 Illustrative example of multi-PLs with common FEs classified into Case
34 2-2 . 59
35 B.5 Safety integrity and modes of operation of the systems with analytical
36 complexity . 63
37 B.6 Handling uncertainties . 63
38 B.7 References . 64
39 Annex C (informative) Calculation of diagnostic coverage and safe failure fraction –
40 worked example . 65
41 Annex D (informative) A methodology for quantifying the effect of hardware-related
42 common cause failures in E/E/PE systems . 69
43 D.1 General . 69
44 D.1.1 Introduction . 69
45 D.1.2 Brief overview . 69
46 D.1.3 Defence against common cause failures . 70
47 D.1.4 Approach adopted in the IEC 61508 series . 71
48 D.2 Scope of the methodology . 73

IEC CDV 61508-6  IEC 2025 – 3 –
49 D.3 Points taken into account in the methodology . 73
50 D.4 Using the β-factor to calculate the probability of failure in an E/E/PE safety-
51 related system due to common cause failures . 74
52 D.5 Redundancy at system level estimate of β . 75
53 D.6 Redundancy at PCB device level estimation of β . 78
54 D.7 Estimation of β suitable for complex semiconductor . 80
55 D.8 casecasecasecasecasecaseCaseCaseBinomial failure rate (Shock model) –
56 CCF approach . 81
57 D.9 References . 83
58 Annex E (informative) Example applications of systematic capability tables of
59 IEC 61508-3 . 84
60 E.1 General . 84
61 E.2 Example for safety integrity level 2 . 84
62 E.3 Example for safety integrity level 3 . 91
63 Annex F Annex F (informative) Examples on how to include failures of the diagnostic
64 function in the PFH / PFD calculation . 101
AVG
65 F.1 Possible approach A . 101
66 F.2 Possible approach B . 102
67 F.3 Possible approach C . 104
68 Annex G (informative) Failure rate estimation from field feedback, with confidence
69 intervals . 107
70 G.1 Introduction . 107
71 G.2 Assumptions for data collection . 107
72 G.3 Assumptions and notations for parameters estimation . 108
73 G.4 Failure rate estimation for detected failures . 108
74 G.5 Failure rate estimation for undetected failures. 109
75 G.6 Examples of failure rates estimation with upper confidence bound . 111
76 Annex H Guidance for robust safety architecture. . 113
77 Bibliography . 116
79 Figure A.1 – Application of IEC 61508-2 . 16
80 Figure A.2 – Application of IEC 61508-2 (Figure A.1 continued) . 17
81 Figure A.3 – Application of IEC 61508-3 . 19
82 Figure B.1 – Reliability Block Diagram of a whole safety loop . 23
83 Figure B.2 – Example configuration for two sensor channels . 28
84 Figure B.3 – Subsystem structure . 29
85 Figure B.4 – 1oo1 physical block diagram . 31
86 Figure B.5 – 1oo1 reliability block diagram . 31
87 Figure B.6 – 1oo2 physical block diagram . 32
88 Figure B.7 – 1oo2 reliability block diagram . 32
89 Figure B.8 – 2oo2 physical block diagram . 33
90 Figure B.9 – 2oo2 reliability block diagram . 33
91 Figure B.10 – 1oo2D physical block diagram. 34
92 Figure B.11 – 1oo2D reliability block diagram . 34
93 Figure B.12 – – 2oo3 physical block diagram . 35
94 Figure B.13 – 2oo3 reliability block diagram . 36
95 Figure B.14 – – Systems block diagram of biped nursing robot . 57

– 4 – IEC CDV 61508-6  IEC 2025
96 Figure B.15 – – Hazardous event described by FT of multi-PLs . 58
97 Figure B.16 – – Hazardous event described by FT of multi-CHs system . 58
98 Figure B.17 – – Reliability block diagrams of typical mul
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