EN 61508-3:2010

SLOVENSKI STANDARD
01-maj-2011
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Functional safety of electrical/electronic/programmable electronic safety-related systems
- Part 3: Software requirements (IEC 61508-3:2010)
Funktionale Sicherheit sicherheitsbezogener
elektrischer/elektronischer/programmierbarer elektronischer Systeme - Teil 3:
Anforderungen an Software (IEC 61508-3:2010)
Sécurité fonctionnelle des systèmes électriques/électroniques/électroniques
programmables relatifs à la sécurité - Partie 3: Prescriptions concernant les logiciels CEI
61508-3:2010)
Ta slovenski standard je istoveten z: EN 61508-3:2010
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 61508-3
NORME EUROPÉENNE
May 2010
EUROPÄISCHE NORM
ICS 25.040.40 Supersedes EN 61508-3:2001

English version
Functional safety of electrical/electronic/programmable electronic
safety-related systems -
Part 3: Software requirements
(IEC 61508-3:2010)
Sécurité fonctionnelle des systèmes Funktionale Sicherheit sicherheitsbezogener
électriques/électroniques/électroniques elektrischer/elektronischer/programmierbarer
programmables relatifs à la sécurité - elektronischer Systeme -
Partie 3: Exigences concernant Teil 3: Anforderungen an Software
les logiciels (IEC 61508-3:2010)
(CEI 61508-3:2010)
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 61508-3:2010 E
Foreword
The text of document 65A/550/FDIS, future edition 2 of IEC 61508-3, 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 61508-3 on 2010-05-01.
This European Standard supersedes EN 61508-3:2001.
It has the status of a basic safety publication according to IEC Guide 104.
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 61508-3:2010 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 61508-5:2010 NOTE  Harmonized as EN 61508-5:2010 (not modified).
[5] IEC 61508-6:2010 NOTE  Harmonized as EN 61508-6:2010 (not modified).
[6] IEC 61508-7:2010 NOTE  Harmonized as EN 61508-7:2010 (not modified).
[7] IEC 60601 series NOTE  Harmonized in 60601 series (partially modified).
[8] IEC 61131-3 NOTE  Harmonized as EN 61131-3.
__________
- 3 - EN 61508-3:2010
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 61508-1 2010 Functional safety of EN 61508-1 2010
electrical/electronic/programmable electronic
safety-related systems -
Part 1: General requirements
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 61508-4 2010 Functional safety of EN 61508-4 2010
electrical/electronic/programmable electronic
safety-related systems -
Part 4: Definitions and abbreviations

IEC Guide 104 1997 The preparation of safety publications and the - -
use of basic safety publications and group
safety publications
ISO/IEC Guide 51 1999 Safety aspects - Guidelines for their inclusion - -
in standards
IEC 61508-3 ®
Edition 2.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Functional safety of electrical/electronic/programmable electronic safety-related
systems –
Part 3: Software requirements
Sécurité fonctionnelle des systèmes électriques/électroniques/électroniques
programmables relatifs à la sécurité –
Partie 3: Exigences concernant les logiciels

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XE
CODE PRIX
ICS 25.040.40 ISBN 978-2-88910-526-7
– 2 – 61508-3 © IEC:2010
CONTENTS
FOREWORD.5
INTRODUCTION.7
1 Scope.9
2 Normative references .12
3 Definitions and abbreviations.13
4 Conformance to this standard.13
5 Documentation .13
6 Additional requirements for management of safety-related software .13
6.1 Objectives .13
6.2 Requirements.13
7 Software safety lifecycle requirements.14
7.1 General .14
7.1.1 Objective .14
7.1.2 Requirements .14
7.2 Software safety requirements specification.21
7.2.1 Objectives .21
7.2.2 Requirements .21
7.3 Validation plan for software aspects of system safety.24
7.3.1 Objective .24
7.3.2 Requirements .24
7.4 Software design and development.25
7.4.1 Objectives .25
7.4.2 General requirements .26
7.4.3 Requirements for software architecture design .29
7.4.4 Requirements for support tools, including programming languages.30
7.4.5 Requirements for detailed design and development – software
system design .33
7.4.6 Requirements for code implementation.34
7.4.7 Requirements for software module testing .35
7.4.8 Requirements for software integration testing .35
7.5 Programmable electronics integration (hardware and software) .36
7.5.1 Objectives .36
7.5.2 Requirements .36
7.6 Software operation and modification procedures .37
7.6.1 Objective .37
7.6.2 Requirements .37
7.7 Software aspects of system safety validation.37
7.7.1 Objective .37
7.7.2 Requirements .38
7.8 Software modification .39
7.8.1 Objective .39
7.8.2 Requirements .39
7.9 Software verification.41
7.9.1 Objective .41
7.9.2 Requirements .41
8 Functional safety assessment.44

61508-3 © IEC:2010 – 3 –
Annex A (normative) Guide to the selection of techniques and measures.46
Annex B (informative) Detailed tables .55
Annex C (informative) Properties for software systematic capability.60
Annex D (normative) Safety manual for compliant items – additional requirements for
software elements.97
Annex E (informative) Relationships between IEC 61508-2 and IEC 61508-3.100
Annex F (informative) Techniques for achieving non-interference between software
elements on a single computer .102
Annex G (informative) Guidance for tailoring lifecycles associated with data driven
systems .107
Bibliography.111

Figure 1 – Overall framework of the IEC 61508 series .11
Figure 2 – Overall safety lifecycle .12
Figure 3 – E/E/PE system safety lifecycle (in realisation phase).16
Figure 4 – Software safety lifecycle (in realisation phase).16
Figure 5 – Relationship and scope for IEC 61508-2 and IEC 61508-3 .17
Figure 6 – Software systematic capability and the development lifecycle (the V-model) .17
Figure G.1 – Variability in complexity of data driven systems .108

Table 1 – Software safety lifecycle – overview .18
Table A.1 – Software safety requirements specification .47
Table A.2 – Software design and development – software architecture design .48
Table A.3 – Software design and development – support tools and programming
language.49
Table A.4 – Software design and development – detailed design .50
Table A.5 – Software design and development – software module testing and
integration .51
Table A.6 – Programmable electronics integration (hardware and software).51
Table A.7 – Software aspects of system safety validation .52
Table A.8 – Modification .52
Table A.9 – Software verification .53
Table A.10 – Functional safety assessment .54
Table B.1 – Design and coding standards .55
Table B.2 – Dynamic analysis and testing.56
Table B.3 – Functional and black-box testing .56
Table B.4 – Failure analysis.57
Table B.5 – Modelling .57
Table B.6 – Performance testing.58
Table B.7 – Semi-formal methods .58
Table B.8 – Static analysis.59
Table B.9 – Modular approach .59
Table C.1 – Properties for systematic safety integrity – Software safety requirements
specification .64

– 4 – 61508-3 © IEC:2010
Table C.2 – Properties for systematic safety integrity – Software design and
development – software Architecture Design .67
Table C.3 – Properties for systematic safety integrity – Software design and
development – support tools and programming language.76
Table C.4 – Properties for systematic safety integrity – Software design and
development – detailed design (includes software system design, software module
design and coding) .77
Table C.5 – Properties for systematic safety integrity – Software design and
development – software module testing and integration .79
Table C.6 – Properties for systematic safety integrity – Programmable electronics
integration (hardware and software).81
Table C.7 – Properties for systematic safety integrity – Software aspects of system
safety validation.82
Table C.8 – Properties for systematic safety integrity – Software modification .83
Table C.9 – Properties for systematic safety integrity – Software verification .85
Table C.10 – Properties for systematic safety integrity – Functional safety assessment .86
Table C.11 – Detailed properties – Design and coding standards.87
Table C.12 – Detailed properties – Dynamic analysis and testing .89
Table C.13 – Detailed properties – Functional and black-box testing.90
Table C.14 – Detailed properties – Failure analysis .91
Table C.15 – Detailed properties – Modelling.92
Table C.16 – Detailed properties – Performance testing .93
Table C.17 – Detailed properties – Semi-formal methods.94
Table C.18 – Properties for systematic safety integrity – Static analysis .95
Table C.19 – Detailed properties – Modular approach.96
Table E.1 – Categories of IEC 61508-2 requirements.100
Table E.2 – Requirements of IEC 61508-2 for software and their typical relevance to
certain types of software.100
Table F.1 – Module coupling – definition of terms .104
Table F.2 – Types of module coupling.105

61508-3 © IEC:2010 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/
PROGRAMMABLE ELECTRONIC SAFETY-RELATED SYSTEMS –

Part 3: Software requirements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
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.
International Standard IEC 61508-3 has been prepared by subcommittee 65A: System
aspects, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This second edition cancels and replaces the first edition published in 1998. This edition
constitutes a technical revision.
This edition has been subject to a thorough review and incorporates many comments received
at the various revision stages.
It has the status of a basic safety publication according to IEC Guide 104.

– 6 – 61508-3 © IEC:2010
The text of this standard is based on the following documents:
FDIS Report on voting
65A/550/FDIS 65A/574/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61508 series, published under the general title Functional safety
of electrical / electronic / programmable electronic safety-related systems, can be found on
the IEC website.
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.
61508-3 © IEC:2010 – 7 –
INTRODUCTION
Systems comprised of electrical and/or electronic elements have been used for many years to
perform safety functions in most application sectors. Computer-based systems (generically
referred to as programmable electronic systems) are being used in all application sectors to
perform non-safety functions and, increasingly, to perform safety functions. If computer
system technology is to be effectively and safely exploited, it is essential that those
responsible for making decisions have sufficient guidance on the safety aspects on which to
make these decisions.
This International Standard sets out a generic approach for all safety lifecycle activities for
systems comprised of electrical and/or electronic and/or programmable electronic (E/E/PE)
elements that are used to perform safety functions. This unified approach has been adopted
in order that a rational and consistent technical policy be developed for all electrically-based
safety-related systems. A major objective is to facilitate the development of product and
application sector international standards based on the IEC 61508 series.
NOTE 1 Examples of product and application sector international standards based on the IEC 61508 series are
given in the bibliography (see references [1], [2] and [3]).
In most situations, safety is achieved by a number of systems which rely on many
technologies (for example mechanical, hydraulic, pneumatic, electrical, electronic, programmable
electronic). Any safety strategy must therefore consider not only all the elements within an
individual system (for example sensors, controlling devices and actuators) but also all the
safety-related systems making up the total combination of safety-related systems. Therefore,
while this International Standard is concerned with E/E/PE safety-related systems, it may also
provide a framework within which safety-related systems based on other technologies may be
considered.
It is recognized that there is a great variety of applications using E/E/PE safety-related
systems in a variety of application sectors and covering a wide range of complexity, hazard
and risk potentials. In any particular application, the required safety measures will be
dependent on many factors specific to the application. This International Standard, by being
generic, will enable such measures to be formulated in future product and application sector
international standards and in revisions of those that already exist.
This International Standard
– considers all relevant overall, E/E/PE system and software safety lifecycle phases (for
example, from initial concept, through design, implementation, operation and maintenance
to decommissioning) when E/E/PE systems are used to perform safety functions;
– has been conceived with a rapidly developing technology in mind; the framework is
sufficiently robust and comprehensive to cater for future developments;
– enables product and application sector international standards, dealing with E/E/PE
safety-related systems, to be developed; the development of product and application
sector international standards, within the framework of this standard, should lead to a high
level of consistency (for example, of underlying principles, terminology etc.) both within
application sectors and across application sectors; this will have both safety and economic
benefits;
– provides a method for the development of the safety requirements specification necessary
to achieve the required functional safety for E/E/PE safety-related systems;
– adopts a risk-based approach by which the safety integrity requirements can be
determined;
– introduces safety integrity levels for specifying the target level of safety integrity for the
safety functions to be implemented by the E/E/PE safety-related systems;
NOTE 2 The standard does not specify the safety integrity level requirements for any safety function, nor does it
mandate how the safety integrity level is determined. Instead it provides a risk-based conceptual framework and
example techniques.
– 8 – 61508-3 © IEC:2010
– sets target failure measures for safety functions carried out by E/E/PE safety-related
systems, which are linked to the safety integrity levels;
– sets a lower limit on the target failure measures for a safety function carried out by a
single E/E/PE safety-related system. For E/E/PE safety-related systems operating in
– a low demand mode of operation, the lower limit is set at an average probability of a
–5
dangerous failure on demand of 10 ;
– a high demand or a continuous mode of operation, the lower limit is set at an average

–9 -1
frequency of a dangerous failure of 10 [h ];
NOTE 3 A single E/E/PE safety-related system does not necessarily mean a single-channel architecture.
NOTE 4 It may be possible to achieve designs of safety-related systems with lower values for the target safety
integrity for non-complex systems, but these limits are considered to represent what can be achieved for relatively
complex systems (for example programmable electronic safety-related systems) at the present time.
– sets requirements for the avoidance and control of systematic faults, which are based on
experience and judgement from practical experience gained in industry. Even though the
probability of occurrence of systematic failures cannot in general be quantified the
standard does, however, allow a claim to be made, for a specified safety function, that the
target failure measure associated with the safety function can be considered to be
achieved if all the requirements in the standard have been met;
– introduces systematic capability which applies to an element with respect to its confidence
that the systematic safety integrity meets the requirements of the specified safety integrity
level;
– adopts a broad range of principles, techniques and measures to achieve functional safety
for E/E/PE safety-related systems, but does not explicitly use the concept of fail safe.
However, the concepts of “fail safe” and “inherently safe” principles may be applicable and
adoption of such concepts is acceptable providing the requirements of the relevant
clauses in the standard are met.

61508-3 © IEC:2010 – 9 –
FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/
PROGRAMMABLE ELECTRONIC SAFETY-RELATED SYSTEMS –

Part 3: Software requirements
1 Scope
1.1 This part of the IEC 61508 series
a) is intended to be utilized only after a thorough understanding of IEC 61508-1 and
IEC 61508-2;
b) applies to any software forming part of a safety-related system or used to develop a
safety-related system within the scope of IEC 61508-1 and IEC 61508-2. Such software is
termed safety-related software (including operating systems, system software, software in
communication networks, human-computer interface functions, and firmware as well as
application software);
c) provides specific requirements applicable to support tools used to develop and configure a
safety-related system within the scope of IEC 61508-1 and IEC 61508-2;
d) requires that the software safety functions and software systematic capability are
specified;
NOTE 1 If this has already been done as part of the specification of the E/E/PE safety-related systems (see 7.2 of
IEC 61508-2), then it does not have to be repeated in this part.
NOTE 2 Specifying the software safety functions and software systematic capability is an iterative procedure; see
Figures 3 and 6.
NOTE 3 See Clause 5 and Annex A of IEC 61508-1 for documentation structure. The documentation structure
may take account of company procedures, and of the working practices of specific application sectors.
NOTE 4 Note: See 3.5.9 of IEC 61508-4 for definition of the term "systematic capability".
e) establishes requirements for safety lifecycle phases and activities which shall be applied
during the design and development of the safety-related software (the software safety
lifecycle model). These requirements include the application of measures and techniques,
which are graded against the required systematic capability, for the avoidance of and
control of faults and failures in the software;
f) provides requirements for information relating to the software aspects of system safety
validation to be passed to the organisation carrying out the E/E/PE system integration;
g) provides requirements for the preparation of information and procedures concerning
software needed by the user for the operation and maintenance of the E/E/PE safety-
related system;
h) provides requirements to be met by the organisation carrying out modifications to safety-
related software;
i) provides, in conjunction with IEC 61508-1 and IEC 61508-2, requirements for support
tools such as development and design tools, language translators, testing and debugging
tools, configuration management tools;
NOTE 4 Figure 5 shows the relationship between IEC 61508-2 and IEC 61508-3.
j) Does not apply for medical equipment in compliance with the IEC 60601 series.
1.2 IEC 61508-1, IEC 61598-2, IEC 61508-3 and IEC 61508-4 are basic safety publications,
although this status does not apply in the context of low complexity E/E/PE safety-related
systems (see 3.4.3 of IEC 61508-4). As basic safety publications, they are intended for use by
technical committees in the preparation of standards in accordance with the principles
contained in IEC Guide 104 and ISO/IEC Guide 51. IEC 61508-1, IEC 61508-2, IEC 61508-3
and IEC 61508-4 are also intended for use as stand-alone publications. The horizontal safety

– 10 – 61508-3 © IEC:2010
function of this international standard does not apply to medical equipment in compliance with
the IEC 60601 series.
1.3 One of the responsibilities of a technical committee is, wherever applicable, to make
use of basic safety publications in the preparation of its publications. In this context, the
requirements, test methods or test conditions of this basic safety publication will not apply
unless specifically referred to or included in the publications prepared by those technical
committees.
1.4 Figure 1 shows the overall framework of the IEC 61508 series and indicates the role that
IEC 61508-3 plays in the achievement of functional safety for E/E/PE safety-related systems.

61508-3 © IEC:2010 – 11 –
Technical Requirements Other Requirements
Part 4
Part 1
Definitions &
Development of the overall
abbreviations
safety requirements
(concept, scope, definition,
hazard and risk analysis)
7.1 to 7.5
Part 5
Example of methods
for the determination Part 1
of safety integrity Documentation
levels Clause 5 &
Part 1
Annex A
Allocation of the safety requirements
to the E/E/PE safety-related systems
7.6
Part 1
Management of
functional safety
Clause 6
Part 1
Specification of the system safety
requirements for the E/E/PE
safety-related systems
Part 1
Functional safety
7.10 assessm ent
Clause 8
Part 6
Guidelines for the
application of
Parts 2 & 3
Part 2 Part 3
Realisation phase Realisation phase
for E/E/PE for safety-related
safety-related software
systems
Part 7
Overview of
techniques and
measures
Part 1
Installation, commissioning
& safety validation of E/E/PE
safety-related systems
7.13 - 7.14
Part 1
Operation, maintenance,repair,
modification and retrofit,
decommissioning or disposal of
E/E/PE safety-related systems
7.15 - 7.17
Figure 1 – Overall framework of the IEC 61508 series

– 12 – 61508-3 © IEC:2010
Concept
Overall scope definition
Hazard and risk
analysis
Overall safety
requirements
Overall safety
requirements allocation
E/E/PE system safety
requirements specification
Overall planning
Other risk
Overall Overall Overall
reduction measures
6 7 8
operation and safety installation and
maintenance validation commissioning
E/E/PE Specification and
planning planning planning
safety-related systems Realisation
Realisation
(see E/E/PE system
safety lifecycle)
Overall installation and
commissioning
Overall safety
Back to appropriate
validation
overall safety lifecycle
phase
Overall operation, Overall modification
maintenance and repair and retrofit
Decommissioning or
disposal
Figure 2 – Overall safety lifecycle
2 Normative references
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.
IEC 61508-1: 2010, Functional safety of electrical/electronic/programmable electronic safety-
related systems – Part 1: General requirements

61508-3 © IEC:2010 – 13 –
IEC 61508-2: 2010, Functional safety of electrical/electronic/programmable electronic safety-
related systems – Part 2: Requirements for electrical/electronic/programmable electronic
safety-related systems
IEC 61508-4: 2010, Functional safety of electrical/electronic/programmable electronic safety-
related systems – Part 4: Definitions and abbreviations
IEC Guide 104:1997, The preparation of safety publications and the use of basic safety
publications and group safety publications
IEC/ISO Guide 51:1999, Safety aspects – Guidelines for their inclusion in standards
3 Definitions and abbreviations
For the purposes of this document, the definitions and abbreviations given in IEC 61508-4
apply.
4 Conformance to this standard
The requirements for conformance to this standard are given in Clause 4 of IEC 61508-1.
5 Documentation
The objectives and requirements for documentation are given in Clause 5 of IEC 61508-1.
6 Additional requirements for management of safety-related software
6.1 Objectives
The objectives are as detailed in 6.1 of IEC 61508-1.
6.2 Requirements
6.2.1 The requirements are as detailed in 6.2 of IEC 61508-1, with the following additional
requirements.
6.2.2 The functional safety planning shall define the strategy for software procurement,
development, integration, verification, validation and modification to the extent required by the
safety integrity level of the safety functions implemented by the E/E/PE safety-related system.
NOTE The philosophy of this approach is to use the functional safety planning as an opportunity to customize this
standard to take account of the required safety integrity for each safety function implemented by the E/E/PE safety-
related system.
6.2.3 Software configuration management shall:
a) apply administrative and technical controls throughout the software safety lifecycle, in
order to manage software changes and thus ensure that the specified requirements for
safety-related software continue to be satisfied;
b) guarantee that all necessary operations have been carried out to demonstrate that the
required software systematic capability has been achieved;
c) maintain accurately and with unique identification all configuration items which are
necessary to meet the safety integrity requirements of the E/E/PE safety-related system.
Configuration items include at least the following: safety analysis and requirements;
software specification and design documents; software source code modules; test plans

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and results; verification documents; pre-existing software elements and packages which
are to be incorporated into the E/E/PE safety-related system; all tools and development
environments which are used to create or test, or carry out any action on, the software of
the E/E/PE safety-related system;
d) apply change-control procedures:
• to prevent unauthorized modifications; to document modification requests;
• to analyse the impact of a proposed modification, and to approve or reject the request;
• to document the details of, and the authorisation for, all approved modifications;
• to establish configuration baseline at appropriate points in the software development,
and to document the (partial) integration testing of the baseline;
• to guarantee the composition of, and the building of, all software baselines (including
the rebuilding of earlier baselines).
NOTE 1 Management decision and authority is needed to guide and enforce the use of administrative and
technical controls.
NOTE 2 At one extreme, an impact analysis may include an informal assessment. At the other extreme, an
impact analysis may include a rigorous formal analysis of the potential adverse impact of all proposed changes
which may be inadequately understood or implemented. See IEC 61508-7 for guidance on impact analysis.
e) ensure that appropriate methods are implemented to load valid software elements and
data correctly into the run-time system;
NOTE 3 This may include consideration of specific target location systems as well as general systems.
Software other than application might need a safe loading method, e.g. firmware.
f) document the following information to permit a subsequent functional safety audit:
configuration status, release status, the justification (taking account of the impact
analysis) for and approval of all modifications, and the details of the modification;
g) formally document the release of safety-related software. Master copies of the software
and all associated documentation and version of data in service shall be kept to permit
maintenance and modification throughout the operational lifetime of the released software.
NOTE 4 For further information on configuration management, see IEC 61508-7
7 Software safety lifecycle requirements
7.1 General
7.1.1 Objective
The objective of the requirements of this subclause is to structure the development of the
software into defined phases and activities (see Table 1 and Figures 3 to 6).
7.1.2 Requirements
7.1.2.1 A safety lifecycle for the development of software shall be selected and specified
during safety planning in accordance with Clause 6 of IEC 61508-1.
7.1.2.2 Any software lifecycle model may be used provided all the objectives and
requirements of this clause are met.
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