IEC 62061:2021
(Main)Safety of machinery - Functional safety of safety-related control systems
Safety of machinery - Functional safety of safety-related control systems
IEC 62061:2021 specifies requirements and makes recommendations for the design, integration and validation of safety-related control systems (SCS) for machines. It is applicable to control systems used, either singly or in combination, to carry out safety functions on machines that are not portable by hand while working, including a group of machines working together in a coordinated manner.
This document is a machinery sector specific standard within the framework of IEC 61508 (all parts).
The design of complex programmable electronic subsystems or subsystem elements is not within the scope of this document.
The main body of this sector standard specifies general requirements for the design, and verification of a safety-related control system intended to be used in high/continuous demand mode.
This document:
– is concerned only with functional safety requirements intended to reduce the risk of hazardous situations;
– is restricted to risks arising directly from the hazards of the machine itself or from a group of machines working together in a coordinated manner;
This document does not cover
– electrical hazards arising from the electrical control equipment itself (e.g. electric shock - see IEC 60204-1);
– other safety requirements necessary at the machine level such as safeguarding;
– specific measures for security aspects – see IEC TR 63074.
This document is not intended to limit or inhibit technological advancement.
IEC 62061:2021 cancels and replaces the first edition, published in 2005, Amendment 1:2012 and Amendment 2:2015. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
– structure has been changed and contents have been updated to reflect the design process of the safety function,
– standard extended to non-electrical technologies,
– definitions updated to be aligned with IEC 61508-4,
– functional safety plan introduced and configuration management updated (Clause 4),
– requirements on parametrization expanded (Clause 6),
– reference to requirements on security added (Subclause 6.8),
– requirements on periodic testing added (Subclause 6.9),
– various improvements and clarification on architectures and reliability calculations (Clause 6 and Clause 7),
– shift from "SILCL" to "maximum SIL" of a subsystem (Clause 7),
– use cases for software described including requirements (Clause 8),
– requirements on independence for software verification (Clause 8) and validation activities (Clause 9) added,
– new informative annex with examples (Annex G),
– new informative annexes on typical MTTFD values, diagnostics and calculation methods for the architectures (Annex C, Annex D and Annex H).
Sécurité des machines - Sécurité fonctionnelle des systèmes de commande relatifs à la sécurité
L'IEC 62061:2021 spécifie les exigences et donne des recommandations pour la conception, l'intégration et la validation des systèmes de commande relatifs à la sécurité (SCS) pour les machines. Elle s'applique aux systèmes de commande utilisés, séparément ou en combinaison, pour assurer les fonctions de sécurité de machines qui ne sont pas portables à la main en fonctionnement, y compris un groupe de machines fonctionnant ensemble d'une manière coordonnée.
Le présent document est spécifique au secteur des machines dans le cadre de l'IEC 61508 (toutes les parties).
La conception de sous-systèmes ou d'éléments de sous-système électroniques programmables complexes ne relève pas du domaine d'application du présent document. Ces éléments relèvent du domaine d'application de l'IEC 61508 ou de normes qui lui sont associées.
Le présent document:
– se concerne que les exigences de sécurité fonctionnelle destinées à réduire le risque de situations dangereuses;
– se limite aux risques résultant directement des phénomènes dangereux de la machine elle même ou d'un groupe de machines fonctionnant ensemble d'une manière coordonnée;
Le présent document ne concerne pas
– les phénomènes dangereux électriques provenant du matériel de commande électrique lui même (par exemple choc électrique – voir l'IEC 60204-1);
– les autres exigences relatives à la sécurité nécessaires au niveau de la machine (la protection par protecteur, par exemple);
– les mesures particulières pour les aspects liés à la sécurité – voir l'IEC TR 63074.
Le présent document n'est pas destiné à limiter ou inhiber les progrès technologiques.
L'IEC 62061:2021 annule et remplace la première édition parue en 2005, l’Amendement 1:2012 ainsi que l’Amendement 2:2015. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
– la structure a été modifiée et le contenu a été mis à jour pour refléter le processus de conception de la fonction de sécurité,
– la norme a été étendue aux technologies non électriques,
– définitions mises à jour pour être alignées sur l'IEC 61508-4,
– plan de sécurité fonctionnelle introduit et gestion de configuration mise à jour (Article 4),
– exigences relatives au paramétrage étendues (Article 6),
– référence aux exigences relatives à la sécurité ajoutée (Paragraphe 6.8)
– exigences relatives aux essais périodiques ajoutées (Paragraphe 6.9),
– différentes améliorations et clarifications relatives aux architectures et aux calculs de fiabilité (Article 6 et Article 7),
– décalage entre le "SILCL" et le "SIL maximal" d'un sous-système (Article 7),
– cas d'utilisation pour les logiciels décrits, y compris les exigences (Article 8),
– exigences relatives à l'indépendance des activités de vérification (Article 8) et de validation (Article 9) du logiciel ajoutées,
– nouvelle annexe informative avec des exemples (Annex G),
– nouvelles annexes informatives relatives aux valeurs MTTFD, aux diagnostics et aux méthodes de calcul des architectures (Annex C, Annex D et Annex H).
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IEC 62061 ®
Edition 2.1 2024-03
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Safety of machinery – Functional safety of safety-related control systems
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IEC 62061 ®
Edition 2.1 2024-03
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
colour
inside
Safety of machinery – Functional safety of safety-related control systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.110; 25.040.99; 29.020 ISBN 978-2-8322-8675-3
REDLINE VERSION – 2 – IEC 62061:2021+AMD1:2024 CSV
IEC 2024
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 11
2 Normative references . 12
3 Terms, definitions and abbreviations . 13
3.1 Alphabetical list of definitions . 13
3.2 Terms and definitions . 15
3.3 Abbreviations . 28
4 Design process of an SCS and management of functional safety . 28
4.1 Objective . 28
4.2 Design process . 29
4.3 Management of functional safety using a functional safety plan . 31
4.4 Configuration management . 33
4.5 Modification . 33
5 Specification of a safety function . 34
5.1 Objective . 34
5.2 Safety requirements specification (SRS) . 34
5.2.1 General . 34
5.2.2 Information to be available . 34
5.2.3 Functional requirements specification . 35
5.2.4 Estimation of demand mode of operation . 35
5.2.5 Safety integrity requirements specification . 36
6 Design of an SCS . 37
6.1 General . 37
6.2 Subsystem architecture based on top down decomposition . 37
6.3 Basic methodology – Use of subsystem . 37
6.3.1 General . 37
6.3.2 SCS decomposition . 38
6.3.3 Sub-function allocation . 39
6.3.4 Use of a pre-designed subsystem . 39
6.4 Determination of safety integrity of the SCS . 40
6.4.1 General . 40
6.4.2 PFH . 40
6.5 Requirements for systematic safety integrity of the SCS . 41
6.5.1 Requirements for the avoidance of systematic hardware failures . 41
6.5.2 Requirements for the control of systematic faults . 42
6.6 Electromagnetic immunity . 43
6.7 Software based manual parameterization . 43
6.7.1 General . 43
6.7.2 Influences on safety-related parameters . 43
6.7.3 Requirements for software based manual parameterization . 44
6.7.4 Verification of the parameterization tool . 45
6.7.5 Performance of software based manual parameterization . 45
6.8 Security aspects . 45
6.9 Aspects of periodic testing . 46
7 Design and development of a subsystem . 46
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7.1 General . 46
7.2 Subsystem architecture design . 47
7.3 Requirements for the selection and design of subsystem and subsystem
elements . 48
7.3.1 General . 48
7.3.2 Systematic integrity . 48
7.3.3 Fault consideration and fault exclusion . 51
7.3.4 Failure rate of subsystem element . 52
7.4 Architectural constraints of a subsystem . 55
7.4.1 General . 55
7.4.2 Estimation of safe failure fraction (SFF) . 56
7.4.3 Behaviour (of the SCS) on detection of a fault in a subsystem . 58
7.4.4 Realization of diagnostic functions . 59
7.5 Subsystem design architectures . 60
7.5.1 General . 60
7.5.2 Basic subsystem architectures . 60
7.5.3 Basic requirements . 61
7.6 PFH of subsystems . 62
7.6.1 General . 62
7.6.2 Methods to estimate the PFH of a subsystem . 62
7.6.3 Simplified approach to estimation of contribution of common cause
failure (CCF) . 63
8 Software . 63
8.1 General . 63
8.2 Definition of software levels . 63
8.3 Software – Level 1 . 64
8.3.1 Software safety lifecycle – SW level 1 . 64
8.3.2 Software design – SW level 1 . 65
8.3.3 Module design – SW level 1 . 67
8.3.4 Coding – SW level 1 . 68
8.3.5 Module test – SW level 1 . 68
8.3.6 Software testing – SW level 1 . 68
8.3.7 Documentation – SW level 1 . 69
8.3.8 Configuration and modification management process – SW level 1 . 69
8.4 Software level 2 . 70
8.4.1 Software safety lifecycle – SW level 2 . 70
8.4.2 Software design – SW level 2 . 72
8.4.3 Software system design – SW level 2 . 73
8.4.4 Module design – SW level 2 . 74
8.4.5 Coding – SW level 2 . 75
8.4.6 Module test – SW level 2 . 75
8.4.7 Software integration testing SW level 2 . 76
8.4.8 Software testing SW level 2 . 76
8.4.9 Documentation – SW level 2 . 77
8.4.10 Configuration and modification management process – SW level 2 . 77
9 Validation . 78
9.1 Validation principles . 78
9.1.1 Validation plan . 81
9.1.2 Use of generic fault lists . 81
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IEC 2024
9.1.3 Specific fault lists . 81
9.1.4 Information for validation . 82
9.1.5 Validation record . 82
9.2 Analysis as part of validation . 83
9.2.1 General . 83
9.2.2 Analysis techniques . 83
9.2.3 Verification of safety requirements specification (SRS) . 83
9.3 Testing as part of validation . 84
9.3.1 General . 84
9.3.2 Measurement accuracy . 84
9.3.3 More stringent requirements . 85
9.3.4 Test samples . 85
9.4 Validation of the safety function . 85
9.4.1 General . 85
9.4.2 Analysis and testing . 86
9.5 Validation of the safety integrity of the SCS . 86
9.5.1 General . 86
9.5.2 Validation of subsystem(s) . 86
9.5.3 Validation of measures against systematic failures . 87
9.5.4 Validation of safety-related software . 87
9.5.5 Validation of combination of subsystems . 88
10 Documentation . 88
10.1 General . 88
10.2 Technical documentation . 88
10.3 Information for use of the SCS . 90
10.3.1 General . 90
10.3.2 Information for use given by the manufacturer of subsystems . 90
10.3.3 Information for use given by the SCS integrator . 91
Annex A (informative) Determination of required safety integrity . 93
A.1 General . 93
A.2 Matrix assignment for the required SIL . 93
A.2.1 Hazard identification/indication . 93
A.2.2 Risk estimation . 93
A.2.3 Severity (Se) . 94
A.2.4 Probability of occurrence of harm . 94
A.2.5 Class of probability of harm (Cl). 97
A.2.6 SIL assignment . 97
A.3 Overlapping hazards . 99
Annex B (informative) Example of SCS design methodology . 100
B.1 General . 100
B.2 Safety requirements specification . 100
B.3 Decomposition of the safety function . 100
B.4 Design of the SCS by using subsystems . 101
B.4.1 General . 101
B.4.2 Subsystem 1 design – “guard door monitoring” . 101
B.4.3 Subsystem 2 design – “evaluation logic” . 103
B.4.4 Subsystem 3 design – “motor control” . 104
B.4.5 Evaluation of the SCS . 104
B.4.6 PFH . 105
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B.5 Verification. 105
B.5.1 General . 105
B.5.2 Analysis . 105
B.5.3 Tests . 106
Annex C (informative) Examples of MTTFD values for single components . 107
C.1 General . 107
C.2 Good engineering practices method . 107
C.3 Hydraulic components . 107
C.4 MTTF of pneumatic, mechanical and electromechanical components . 108
D
Annex D (informative) Examples for diagnostic coverage (DC) . 110
Annex E (informative) Methodology for the estimation of susceptibility to common
cause failures (CCF) . 112
E.1 General . 112
E.2 Methodology . 112
E.2.1 Requirements for CCF . 112
E.2.2 Estimation of effect of CCF . 112
Annex F (informative) Guideline for software level 1 . 115
F.1 Software safety requirements . 115
F.2 Coding guidelines . 116
F.3 Specification of safety functions . 117
F.4 Specification of hardware design . 118
F.5 Software system design specification . 120
F.6 Protocols . 122
Annex G (informative) Examples of safety functions. 125
Annex H (informative) Simplified approaches to evaluate the PFH value of a
subsystem . 126
H.1 Table allocation approach . 126
H.2 Simplified formulas for the estimation of PFH . 128
H.2.1 General . 128
H.2.2 Basic subsystem architecture A: single channel without a diagnostic
function . 128
H.2.3 Basic subsystem architecture B: dual channel without a diagnostic
function . 129
H.2.4 Basic subsystem architecture C: single channel with a diagnostic
function . 129
H.2.5 Basic subsystem architecture D: dual channel with a diagnostic
function(s) . 135
H.3 Parts count method . 136
Annex I (informative) The functional safety plan and design activities . 137
I.1 General . 137
I.2 Example of a machine design plan including a safety plan . 137
I.3 Example of activities, documents and roles . 137
Annex J (informative) Independence for reviews and testing/verification/validation
activities . 141
J.1 Software design . 141
J.2 Validation . 141
Bibliography . 143
Figure 1 – Scope of this document . 12
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Figure 2 – Integration within the risk reduction process of ISO 12100 (extract) . 29
Figure 3 – Iterative process for design of the safety-related control system . 30
Figure 4 – Example of a combination of subsystems as one SCS . 31
Figure 5 – By activating a low demand safety function at least once per year it can be
assumed to be high demand . 36
Figure 6 – Examples of typical decomposition of a safety function into sub-functions
and its allocation to subsystems . 39
Figure 7 – Example of safety integrity of a safety function based on allocated
subsystems as one SCS . 40
Figure 8 – Basic subsystem architecture A logical representation . 60
Figure 9 – Basic subsystem architecture B logical representation . 60
Figure 10 – Basic subsystem architecture C logical representation . 61
Figure 11 – Basic subsystem architecture D logical representation . 61
Figure 12 – V-model for SW level 1 . 65
Figure 13 – V-model for software modules customized by the designer for SW level 1 . 65
Figure 14 – V-model of software safety lifecycle for SW level 2 . 71
Figure 15 – Overview of the validation process . 80
Figure A.1 – Parameters used in risk estimation . 93
Figure A.2 – Example proforma for SIL assignment process . 99
Figure B.1 – Decomposition of the safety function. 101
Figure B.2 – Overview of design of the subsystems of the SCS . 101
Figure F.1 – Plant sketch . 117
Figure F.2 – Principal module architecture design . 120
Figure F.3 – Principal design approach of logical evaluation . 121
Figure F.4 – Example of logical representation (program sketch) . 122
Figure H.1 – Basic subsystem architecture A logical representation . 128
Figure H.2 – Basic subsystem architecture B logical representation . 129
Figure H.3 – Basic subsystem architecture C logical representation . 129
Figure H.4 – Correlation of basic subsystem architecture C and the pertinent fault
handling function . 130
Figure H.5 – Basic subsystem architecture C with external fault handling function . 131
Figure H.6 – Basic subsystem architecture C with external fault diagnostics . 132
Figure H.7 – Basic subsystem architecture C with external fault reaction . 132
Figure H.8 – Basic subsystem architecture C with internal fault diagnostics and internal
fault reaction . 133
Figure H.9 – Basic subsystem architecture D logical representation . 135
Figure I.1 – Example of a machine design plan including a safety plan . 137
Figure I.2 – Example of activities, documents and roles (1 of 2) . 139
Table 1 – Terms used in IEC 62061 . 13
Table 2 – Abbreviations used in IEC 62061 . 28
Table 3 – SIL and limits of PFH values . 36
Table 4 – Required SIL and PFH of pre-designed subsystem . 40
Table 5 – Relevant information for each subsystem . 47
IEC 2024
Table 6 – Architectural constraints on a subsystem: maximum SIL that can be claimed
for an SCS using the subsystem . 56
Table 7 – Overview of basic requirements and interrelation to basic subsystem
architectures . 62
Table 8 – Different levels of application software . 63
Table 9 – Documentation of an SCS . 89
Table A.1 – Severity (Se) classification . 94
Table A.2 – Frequency and duration of exposure (Fr) classification . 95
Table A.3 – Probability (Pr) classification . 96
Table A.4 – Probability of avoiding or limiting harm (Av) classification . 97
Table A.5 – Parameters used to determine class of probability of harm (Cl) . 97
Table A.6 – Matrix assignment for determining the required SIL (or PL ) for a safety
r
function . 98
Table B.1 – Safety requirements specification – example of overview . 100
Table B.2 – Systematic integrity – example of overview . 105
Table B.3 – Verification by tests. 106
Table C.1 – Standards references and MTTF or B values for components . 108
D 10D
Table D.1 – Estimates for diagnostic coverage (DC) (1 of 2) . 110
Table E.1 – Criteria for estimation of CCF Estimation of CCF factor (β) . 113
Table E.2 – Criteria for estimation of CCF . 114
Table F.1 – Example of relevant documents related to the simplified V-model . 115
Table F.2 – Examples of coding guidelines . 116
Table F.3 – Specified safety functions. 118
Table F.4 – Relevant list of input and output signals . 119
Table F.5 – Example of simplified cause and effect matrix . 122
Table F.6 – Verification of software system design specification . 123
Table F.7 – Software code review . 123
Table F.8 – Software validation . 124
Table G.1 – Examples of typical safety functions . 125
Table H.1 – Allocation of PFH value of a subsystem . 127
Table H.2 – Relationship between B , operations and MTTF . 128
10D D
Table H.3 – Minimum value of 1/λ for the applicability of PFH equation (H.43) . 133
D FH
Table J.1 – Minimum levels of independence for review, testing and verification
activities . 141
Table J.2 – Minimum levels of independence for validation activities . 141
REDLINE VERSION – 8 – IEC 62061:2021+AMD1:2024 CSV
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF MACHINERY –
FUNCTIONAL SAFETY OF SAFETY-RELATED CONTROL SYSTEMS
FOREWORD
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This consolidated version of the official IEC Standard and its amendment has been
prepared for user convenience.
IEC 62061 edition 2.1 contains the second edition (2021-03) [documents 44/885/FDIS and
44/888/RVD] and its amendment 1 (2024-03) [documents 44/1020/FDIS and 44/1024/RVD].
In this Redline version, a vertical line in the margin shows where the technical content is
modified by amendment 1. Additions are in green text, deletions are in strikethrough red
text. A separate Final version with all changes accepted is available in this publication.
IEC 2024
IEC 62061 has been prepared by IEC technical committee 44: Safety of machinery –
Electrotechnical aspects. It is an International Standard.
This second constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– structure has been changed and contents have been updated to reflect the design process
of the safety function,
– standard extended to non-electrical technologies,
– definitions updated to be aligned with IEC 61508-4,
– functional safety plan introduced and configuration management updated (Clause 4),
– requirements on parametrization expanded (Clause 6),
– reference to requirements on security added (Subclause 6.8),
– requirements on periodic testing added (Subclause 6.9),
– various improvements and clarification on architectures and reliability calculations (Clause 6
and Clause 7),
– shift from "SILCL" to "maximum SIL" of a subsystem (Clause 7),
– use cases for software described including requirements (Clause 8),
– requirements on independence for software verification (Clause 8) and validation activities
(Clause 9) added,
– new informative annex with examples (Annex G),
– new informative annexes on typical MTTF values, diagnostics and calculation methods for
D
the architectures (Annex C, Annex D and Annex H).
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
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unchanged until the stability date indicated on the IEC website under webstore.iec.ch in the
data related to the specific document. At this date, the document will be
• reconfirmed,
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• revised.
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REDLINE VERSION – 10 – IEC 62061:2021+AMD1:2024 CSV
IEC 2024
INTRODUCTION
As a result of automation, demand for increased production and reduced operator physical
effort, Safety-related Control Systems (referred to as SCS) of machines play an increasing role
in the achievement of overall machine safety. Furthermore, the SCS themselves increasingly
employ complex electronic technology.
IEC 62061 specifies requirements for the design and implementation of safety-related control
systems of machinery. This document is machine sector specific within the framework of
IEC 61508.
NOTE While IEC 62061 and ISO 13849-1 are using different methodologies for the design of safety related control
systems, they intend to achieve the same risk reduction.
This International Standard is intended for use by machinery designers, control system
manufacturers and integrators, and others involved in the specification, design and validation
of an SCS. It sets out an approach and provides requirements to achieve the necessary
performance and facilitates the specification of the safety functions intended to achieve the risk
reduction.
This document provides a machine sector specific framework for functional safety of an SCS of
machines. It only covers those aspects of the safety lifecycle that are related to safety
requirements allocation through to safety validation. Requirements are provided for information
for safe use of SCS of machines that can also be relevant to later phases of the lifecycle of an
SCS.
There are many situations on machines where SCS are employed as part of safety measures
that have been provided to achieve risk reduction. A typical case is the use of an interlocking
guard that, when it is opened to allow access to the danger zone, signals the safety related
parts of the machine control system to stop hazardous machine operation. In automation, the
machine control system that is used to achieve correct operation of the machine process often
contributes to safety by mitigating risks associated with hazards arising directly from control
system failures. This document gives a methodology and requirements to:
• assign the required safety integrity for each safety function to be implemented by SCS;
• enable the design of the SCS appropriate to the assigned safety (control) function(s);
• integrate safety-related subsystems designed in accordance with other applicable functional
safety-related standards (see 6.3.4);
• validate the SCS.
This document is intended to be used within the framework of systematic risk reduction, in
conjunction with risk assessment described in ISO 12100. Suggested methodologies for a
safety integrity assignment are given in informative Annex A.
IEC 2024
SAFETY OF MACHINERY –
FUNCTIONAL SAFETY OF SAFETY-RELATED CONTROL SYSTEMS
1 Scope
This International Standard specifies requirements and makes recommendations for the design,
integration and validation of safety-related cont
...
IEC 62061 ®
Edition 2.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Safety of machinery – Functional safety of safety-related control systems
Sécurité des machines – Sécurité fonctionnelle des systèmes de commande
relatifs à la sécurité
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IEC 62061 ®
Edition 2.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Safety of machinery – Functional safety of safety-related control systems
Sécurité des machines – Sécurité fonctionnelle des systèmes de commande
relatifs à la sécurité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.110; 25.040.99; 29.020 ISBN 978-2-8322-9333-1
– 2 – IEC 62061:2021 IEC 2021
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 11
2 Normative references . 12
3 Terms, definitions and abbreviations . 13
3.1 Alphabetical list of definitions . 13
3.2 Terms and definitions . 15
3.3 Abbreviations . 28
4 Design process of an SCS and management of functional safety . 28
4.1 Objective . 28
4.2 Design process . 29
4.3 Management of functional safety using a functional safety plan . 31
4.4 Configuration management . 33
4.5 Modification . 33
5 Specification of a safety function . 34
5.1 Objective . 34
5.2 Safety requirements specification (SRS) . 34
5.2.1 General . 34
5.2.2 Information to be available . 34
5.2.3 Functional requirements specification . 35
5.2.4 Estimation of demand mode of operation . 35
5.2.5 Safety integrity requirements specification . 36
6 Design of an SCS . 37
6.1 General . 37
6.2 Subsystem architecture based on top down decomposition . 37
6.3 Basic methodology – Use of subsystem . 37
6.3.1 General . 37
6.3.2 SCS decomposition . 38
6.3.3 Sub-function allocation . 39
6.3.4 Use of a pre-designed subsystem . 39
6.4 Determination of safety integrity of the SCS . 40
6.4.1 General . 40
6.4.2 PFH . 40
6.5 Requirements for systematic safety integrity of the SCS . 41
6.5.1 Requirements for the avoidance of systematic hardware failures . 41
6.5.2 Requirements for the control of systematic faults . 42
6.6 Electromagnetic immunity . 43
6.7 Software based manual parameterization . 43
6.7.1 General . 43
6.7.2 Influences on safety-related parameters . 43
6.7.3 Requirements for software based manual parameterization . 44
6.7.4 Verification of the parameterization tool . 45
6.7.5 Performance of software based manual parameterization . 45
6.8 Security aspects . 45
6.9 Aspects of periodic testing . 46
7 Design and development of a subsystem . 46
7.1 General . 46
7.2 Subsystem architecture design . 47
7.3 Requirements for the selection and design of subsystem and subsystem
elements . 48
7.3.1 General . 48
7.3.2 Systematic integrity . 48
7.3.3 Fault consideration and fault exclusion . 51
7.3.4 Failure rate of subsystem element . 52
7.4 Architectural constraints of a subsystem . 55
7.4.1 General . 55
7.4.2 Estimation of safe failure fraction (SFF) . 56
7.4.3 Behaviour (of the SCS) on detection of a fault in a subsystem . 57
7.4.4 Realization of diagnostic functions . 58
7.5 Subsystem design architectures . 59
7.5.1 General . 59
7.5.2 Basic subsystem architectures . 59
7.5.3 Basic requirements . 61
7.6 PFH of subsystems . 62
7.6.1 General . 62
7.6.2 Methods to estimate the PFH of a subsystem . 62
7.6.3 Simplified approach to estimation of contribution of common cause
failure (CCF) . 62
8 Software . 62
8.1 General . 62
8.2 Definition of software levels . 63
8.3 Software – Level 1 . 64
8.3.1 Software safety lifecycle – SW level 1 . 64
8.3.2 Software design – SW level 1 . 65
8.3.3 Module design – SW level 1 . 67
8.3.4 Coding – SW level 1 . 67
8.3.5 Module test – SW level 1 . 68
8.3.6 Software testing – SW level 1 . 68
8.3.7 Documentation – SW level 1 . 69
8.3.8 Configuration and modification management process – SW level 1 . 69
8.4 Software level 2 . 70
8.4.1 Software safety lifecycle – SW level 2 . 70
8.4.2 Software design – SW level 2 . 71
8.4.3 Software system design – SW level 2 . 73
8.4.4 Module design – SW level 2 . 73
8.4.5 Coding – SW level 2 . 74
8.4.6 Module test – SW level 2 . 75
8.4.7 Software integration testing SW level 2 . 75
8.4.8 Software testing SW level 2 . 75
8.4.9 Documentation – SW level 2 . 76
8.4.10 Configuration and modification management process – SW level 2 . 77
9 Validation . 77
9.1 Validation principles . 77
9.1.1 Validation plan . 80
9.1.2 Use of generic fault lists . 80
– 4 – IEC 62061:2021 IEC 2021
9.1.3 Specific fault lists . 80
9.1.4 Information for validation . 81
9.1.5 Validation record . 81
9.2 Analysis as part of validation . 82
9.2.1 General . 82
9.2.2 Analysis techniques . 82
9.2.3 Verification of safety requirements specification (SRS) . 82
9.3 Testing as part of validation . 83
9.3.1 General . 83
9.3.2 Measurement accuracy . 83
9.3.3 More stringent requirements . 84
9.3.4 Test samples . 84
9.4 Validation of the safety function . 84
9.4.1 General . 84
9.4.2 Analysis and testing . 85
9.5 Validation of the safety integrity of the SCS . 85
9.5.1 General . 85
9.5.2 Validation of subsystem(s) . 85
9.5.3 Validation of measures against systematic failures . 86
9.5.4 Validation of safety-related software . 86
9.5.5 Validation of combination of subsystems . 87
10 Documentation . 87
10.1 General . 87
10.2 Technical documentation . 87
10.3 Information for use of the SCS . 89
10.3.1 General . 89
10.3.2 Information for use given by the manufacturer of subsystems . 89
10.3.3 Information for use given by the SCS integrator . 90
Annex A (informative) Determination of required safety integrity . 92
A.1 General . 92
A.2 Matrix assignment for the required SIL . 92
A.2.1 Hazard identification/indication . 92
A.2.2 Risk estimation . 92
A.2.3 Severity (Se) . 93
A.2.4 Probability of occurrence of harm . 93
A.2.5 Class of probability of harm (Cl). 96
A.2.6 SIL assignment . 96
A.3 Overlapping hazards . 98
Annex B (informative) Example of SCS design methodology . 99
B.1 General . 99
B.2 Safety requirements specification . 99
B.3 Decomposition of the safety function . 99
B.4 Design of the SCS by using subsystems . 100
B.4.1 General . 100
B.4.2 Subsystem 1 design – “guard door monitoring” . 100
B.4.3 Subsystem 2 design – “evaluation logic” . 102
B.4.4 Subsystem 3 design – “motor control” . 103
B.4.5 Evaluation of the SCS . 103
B.4.6 PFH . 104
B.5 Verification. 104
B.5.1 General . 104
B.5.2 Analysis . 104
B.5.3 Tests . 105
Annex C (informative) Examples of MTTFD values for single components . 106
C.1 General . 106
C.2 Good engineering practices method . 106
C.3 Hydraulic components . 106
C.4 MTTF of pneumatic, mechanical and electromechanical components . 107
D
Annex D (informative) Examples for diagnostic coverage (DC) . 109
Annex E (informative) Methodology for the estimation of susceptibility to common
cause failures (CCF) . 111
E.1 General . 111
E.2 Methodology . 111
E.2.1 Requirements for CCF . 111
E.2.2 Estimation of effect of CCF . 111
Annex F (informative) Guideline for software level 1 . 114
F.1 Software safety requirements . 114
F.2 Coding guidelines . 115
F.3 Specification of safety functions . 116
F.4 Specification of hardware design . 117
F.5 Software system design specification . 119
F.6 Protocols . 121
Annex G (informative) Examples of safety functions. 124
Annex H (informative) Simplified approaches to evaluate the PFH value of a
subsystem . 125
H.1 Table allocation approach . 125
H.2 Simplified formulas for the estimation of PFH . 127
H.2.1 General . 127
H.2.2 Basic subsystem architecture A: single channel without a diagnostic
function . 127
H.2.3 Basic subsystem architecture B: dual channel without a diagnostic
function . 128
H.2.4 Basic subsystem architecture C: single channel with a diagnostic
function . 128
H.2.5 Basic subsystem architecture D: dual channel with a diagnostic
function(s) . 133
H.3 Parts count method . 134
Annex I (informative) The functional safety plan and design activities . 135
I.1 General . 135
I.2 Example of a machine design plan including a safety plan . 135
I.3 Example of activities, documents and roles . 135
Annex J (informative) Independence for reviews and testing/verification/validation
activities . 138
J.1 Software design . 138
J.2 Validation . 138
Bibliography . 140
Figure 1 – Scope of this document . 12
– 6 – IEC 62061:2021 IEC 2021
Figure 2 – Integration within the risk reduction process of ISO 12100 (extract) . 29
Figure 3 – Iterative process for design of the safety-related control system . 30
Figure 4 – Example of a combination of subsystems as one SCS . 31
Figure 5 – By activating a low demand safety function at least once per year it can be
assumed to be high demand . 36
Figure 6 – Examples of typical decomposition of a safety function into sub-functions
and its allocation to subsystems . 39
Figure 7 – Example of safety integrity of a safety function based on allocated
subsystems as one SCS . 40
Figure 8 – Subsystem A logical representation . 60
Figure 9 – Subsystem B logical representation . 60
Figure 10 – Subsystem C logical representation . 60
Figure 11 – Subsystem D logical representation . 61
Figure 12 – V-model for SW level 1 . 64
Figure 13 – V-model for software modules customized by the designer for SW level 1 . 64
Figure 14 – V-model of software safety lifecycle for SW level 2 . 70
Figure 15 – Overview of the validation process . 79
Figure A.1 – Parameters used in risk estimation . 92
Figure A.2 – Example proforma for SIL assignment process . 98
Figure B.1 – Decomposition of the safety function. 100
Figure B.2 – Overview of design of the subsystems of the SCS . 100
Figure F.1 – Plant sketch . 116
Figure F.2 – Principal module architecture design . 119
Figure F.3 – Principal design approach of logical evaluation . 120
Figure F.4 – Example of logical representation (program sketch) . 121
Figure H.1 – Subsystem A logical representation . 127
Figure H.2 – Subsystem B logical representation . 128
Figure H.3 – Subsystem C logical representation . 128
Figure H.4 – Correlation of subsystem C and the pertinent fault handling function . 129
Figure H.5 – Subsystem C with external fault handling function . 129
Figure H.6 – Subsystem C with external fault diagnostics . 131
Figure H.7 – Subsystem C with external fault reaction . 131
Figure H.8 – Subsystem C with internal fault diagnostics and internal fault reaction . 131
Figure H.9 – Subsystem D logical representation . 133
Figure I.1 – Example of a machine design plan including a safety plan . 135
Figure I.2 – Example of activities, documents and roles . 136
Table 1 – Terms used in IEC 62061 . 13
Table 2 – Abbreviations used in IEC 62061 . 28
Table 3 – SIL and limits of PFH values . 36
Table 4 – Required SIL and PFH of pre-designed subsystem . 40
Table 5 – Relevant information for each subsystem . 47
Table 6 – Architectural constraints on a subsystem: maximum SIL that can be claimed
for an SCS using the subsystem . 56
Table 7 – Overview of basic requirements and interrelation to basic subsystem
architectures . 61
Table 8 – Different levels of application software . 63
Table 9 – Documentation of an SCS . 88
Table A.1 – Severity (Se) classification . 93
Table A.2 – Frequency and duration of exposure (Fr) classification . 94
Table A.3 – Probability (Pr) classification . 95
Table A.4 – Probability of avoiding or limiting harm (Av) classification . 96
Table A.5 – Parameters used to determine class of probability of harm (Cl) . 96
Table A.6 – Matrix assignment for determining the required SIL (or PL ) for a safety
r
function . 97
Table B.1 – Safety requirements specification – example of overview . 99
Table B.2 – Systematic integrity – example of overview . 104
Table B.3 – Verification by tests. 105
Table C.1 – Standards references and MTTF or B values for components . 107
D 10D
Table D.1 – Estimates for diagnostic coverage (DC) . 109
Table E.1 – Criteria for estimation of CCF . 112
Table E.2 – Criteria for estimation of CCF . 113
Table F.1 – Example of relevant documents related to the simplified V-model . 114
Table F.2 – Examples of coding guidelines . 115
Table F.3 – Specified safety functions. 117
Table F.4 – Relevant list of input and output signals . 118
Table F.5 – Example of simplified cause and effect matrix . 121
Table F.6 – Verification of software system design specification . 122
Table F.7 – Software code review . 122
Table F.8 – Software validation . 123
Table G.1 – Examples of typical safety functions . 124
Table H.1 – Allocation of PFH value of a subsystem . 126
Table H.2 – Relationship between B , operations and MTTF . 127
10D D
Table H.3 – Minimum value of 1/λ for the applicability of PFH equation (H.4) . 132
D FH
Table J.1 – Minimum levels of independence for review, testing and verification
activities . 138
Table J.2 – Minimum levels of independence for validation activities . 138
– 8 – IEC 62061:2021 IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF MACHINERY –
FUNCTIONAL SAFETY OF SAFETY-RELATED CONTROL SYSTEMS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 62061 has been prepared by IEC technical committee 44: Safety of machinery –
Electrotechnical aspects. It is an International Standard.
This second edition cancels and replaces the first edition, published in 2005,
Amendment 1:2012 and Amendment 2:2015. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– structure has been changed and contents have been updated to reflect the design process
of the safety function,
– standard extended to non-electrical technologies,
– definitions updated to be aligned with IEC 61508-4,
– functional safety plan introduced and configuration management updated (Clause 4),
– requirements on parametrization expanded (Clause 6),
– reference to requirements on security added (Subclause 6.8),
– requirements on periodic testing added (Subclause 6.9),
– various improvements and clarification on architectures and reliability calculations (Clause 6
and Clause 7),
– shift from "SILCL" to "maximum SIL" of a subsystem (Clause 7),
– use cases for software described including requirements (Clause 8),
– requirements on independence for software verification (Clause 8) and validation activities
(Clause 9) added,
– new informative annex with examples (Annex G),
values, diagnostics and calculation methods for
– new informative annexes on typical MTTF
D
the architectures (Annex C, Annex D and Annex H).
The text of this International Standard is based on the following documents:
Draft Report on voting
44/885/FDIS 44/888/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.
– 10 – IEC 62061:2021 IEC 2021
INTRODUCTION
As a result of automation, demand for increased production and reduced operator physical
effort, Safety-related Control Systems (referred to as SCS) of machines play an increasing role
in the achievement of overall machine safety. Furthermore, the SCS themselves increasingly
employ complex electronic technology.
IEC 62061 specifies requirements for the design and implementation of safety-related control
systems of machinery. This document is machine sector specific within the framework of
IEC 61508.
NOTE While IEC 62061 and ISO 13849-1 are using different methodologies for the design of safety related control
systems, they intend to achieve the same risk reduction.
This International Standard is intended for use by machinery designers, control system
manufacturers and integrators, and others involved in the specification, design and validation
of an SCS. It sets out an approach and provides requirements to achieve the necessary
performance and facilitates the specification of the safety functions intended to achieve the risk
reduction.
This document provides a machine sector specific framework for functional safety of an SCS of
machines. It only covers those aspects of the safety lifecycle that are related to safety
requirements allocation throug
...
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