CLC IEC/TR 63161:2024

Assignment of safety integrity requirements - Basic rationale

This Technical Report is applicable, where a risk assessment according to ISO 12100 has been conducted for a machine or process plant and where a safety related control function has been selected for implementation as a protective measure against specified hazards. For the given case, this Technical Report describes the basic logical rationale, which is followed to assign a safety integrity requirement to the selected function. This Technical Report is applicable to safety related control functions in all modes of application: continuous mode, high demand mode and low demand mode of application

Zuordnung der Sicherheitsintegritäts-Anforderungen - Grundlegende Begründungen

Attribution des exigences en matière d'intégrité de la sécurité - Justification fondamentale

Dodelitev zahtev celovite varnosti - Osnovni princip (IEC/TR 63161:2022)

To tehnično poročilo se uporablja, kadar je bila za stroj ali procesni obrat izvedena ocena tveganja v skladu s standardom ISO 12100 in kot zaščitni ukrep za preprečevanje določenih nevarnosti izbrana nadzorna funkcija, povezana z varnostjo.
Za dani primer je v tem tehničnem poročilu opisan osnovni logični princip, na podlagi katerega se izbrani funkciji dodeli zahteva celovite varnosti.
To tehnično poročilo se uporablja za nadzorne funkcije, povezane z varnostjo, v vseh načinih uporabe:
neprekinjenem načinu ter načinu z visokimi in nizkimi zahtevami.

General Information

• Status: Published
• Publication Date: 01-Feb-2024
• ICS: 13.110 - Safety of machinery
• Technical Committee: CLC/TC 44X - Safety of machinery: electrotchnical aspects
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 02-Feb-2024
• Due Date: 06-Dec-2024
• Completion Date: 02-Feb-2024
• Ref Project: SIST-TP CLC IEC/TR 63161:2024 - Assignment of safety integrity requirements - Basic rationale (IEC/TR 63161:2022)

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2024
Dodelitev zahtev celovite varnosti - Osnovni princip (IEC/TR 63161:2022)
Assignment of safety integrity requirements - Basic rationale (IEC/TR 63161:2022)
Zuordnung der Sicherheitsintegritäts-Anforderungen - Grundlegende Begründungen
(IEC/TR 63161:2022)
Attribution des exigences en matière d'intégrité de la sécurité - Justification
fondamentale (IEC/TR 63161:2022)
Ta slovenski standard je istoveten z: CLC IEC/TR 63161:2024
ICS:
13.110 Varnost strojev Safety of machinery
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT CLC IEC/TR 63161

RAPPORT TECHNIQUE
TECHNISCHER REPORT February 2024
ICS 13.110
English Version
Assignment of safety integrity requirements - Basic rationale
(IEC/TR 63161:2022)
Attribution des exigences en matière d'intégrité de la Zuordnung der Sicherheitsintegritäts-Anforderungen -
sécurité - Justification fondamentale Grundlegende Begründungen
(IEC/TR 63161:2022) (IEC/TR 63161:2022)

This Technical Report was approved by CENELEC on 2024-01-22.

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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. CLC IEC/TR 63161:2024 E

European foreword
This document (CLC IEC/TR 63161:2024) consists of the text of IEC/TR 63161:2022 prepared by
IEC/TC 44 "Safety of machinery - Electrotechnical aspects".
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Technical Report IEC/TR 63161:2022 was approved by CENELEC as a
European Technical Report without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 61508-1 NOTE Approved as EN 61508-1
IEC 61508-4:2010 NOTE Approved as EN 61508-4:2010 (not modified)
IEC 61508-5:2010 NOTE Approved as EN 61508-5:2010 (not modified)
IEC 61511-1:2016 NOTE Approved as EN 61511-1:2017 (not modified)
IEC 62061:2021 NOTE Approved as EN IEC 62061:2021 (not modified)
ISO 13849 (series) NOTE Approved as EN ISO 13849 (series)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 1  Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
ISO 12100 2010 Safety of machinery – General principles for EN ISO 12100 2010
design – Risk assessment and risk reduction

IEC TR 63161 ®
Edition 1.0 2022-07
TECHNICAL
REPORT
colour
inside
Assignment of safety integrity requirements – Basic rationale

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.110 ISBN 978-2-8322-3944-5

– 2 – IEC TR 63161:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Risk based quantitative approach . 10
4.1 General . 10
4.2 Sequence of steps in functional safety assignment . 10
4.3 Reference information . 12
4.3.1 General . 12
4.3.2 Accident scenario . 13
4.3.3 Hazard zone . 13
4.3.4 Severity of harm . 13
4.3.5 Safety control function . 14
5 Quantified parameters of a functional safety assignment . 14
5.1 General . 14
5.2 Parameter types . 14
5.2.1 General . 14
5.2.2 Probability . 14
5.2.3 Event rate . 14
5.3 Probability of occurrence of harm . 15
5.4 Quantification of risk . 15
5.5 Target failure measure . 15
5.6 Probability of occurrence of a hazardous event – P . 16
r
5.7 Exposure parameter – F . 17
r
5.8 Probability of avoiding or limiting harm – A . 18
v
5.8.1 General . 18
5.8.2 Vulnerability (V) . 18
5.8.3 Avoidability (A) . 19
5.9 Demand types and related event rates . 19
5.9.1 Event classes . 19
5.9.2 Demand and demand rate . 20
5.9.3 Initiating events and rate of initiating events I . 20
R
5.9.4 Safety demands and safety demand rate D . 21
R
5.9.5 Tolerable risk limit – Parameter L . 22
(S)
5.10 Additional parameters . 23
6 General principle of functional safety assignment . 25
6.1 Basics . 25
6.1.1 Applicability to complete functions . 25
6.1.2 Risk relation . 25
6.1.3 Logical independence of parameters . 25
6.2 High demand or continuous mode of operation . 25
6.3 Low demand mode of operation . 26
7 Assignment of the demand mode . 27
7.1 Demand mode – General . 27

IEC TR 63161:2022 © IEC 2022 – 3 –
7.2 Assignment criteria . 30
8 Relation to ISO 12100 . 30
9 Tools for functional safety assignment . 31
9.1 General . 31
9.2 Selection of independent parameters . 32
9.3 Logarithmizing parameters . 32
9.4 Discretization of parameters . 32
9.5 Parameter scores . 33
9.6 Scoring methods in strict sense . 34
Annex A (informative) Examples of SIL assignment tools numerical analysis . 35
A.1 General . 35
A.2 Assignment of score values to parameter entries . 35
A.3 Extraction of tolerable risk limits . 36
A.4 Risk matrix of IEC 62061 . 38
A.5 Risk graph of ISO 13849 . 41
A.6 Risk graphs for low demand mode of operation . 43
Bibliography . 46

Figure 1 – Sequence of steps in functional safety assignment. 12
Figure 2 – Protection layers, event rates and their relation. 22
Figure 3 – Hazard rate according to the Henley / Kumamoto equation . 29
Figure 4 – Elements of risk according to ISO 12100 . 31
Figure 5 – Discretization of parameters . 33
Figure A.1 – Extraction of tolerable risk limits . 37
Figure A.2 – Risk matrix based on IEC 62061 . 38
Figure A.3 – Maximum allowable PFH as function of the score sum for the different
severity levels . 39
Figure A.4 – Representation by a continuous numerical interpolation . 40
Figure A.5 – Risk graph of ISO 13849-1 . 41
Figure A.6 – Interpolation per severity level . 43
Figure A.7 – Risk graph for low demand mode of operation . 44
Figure A.8 – Risk graph for low demand mode of operation – from Figure 7 of VDMA
4315-1 . 45

Table 1 – Parameters overview . 24
Table A.1 – Relation between PLs and ranges in PFH . 42

– 4 – IEC TR 63161:2022 © IEC 2022
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