Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 2: Requirements for electrical/electronic/programmable electronic safety-related systems (see <a href="http://www.iec.ch/functionalsafety">Functional Safety and IEC 61508</a>)

IEC 61508-2:2010 applies to any safety-related system, as defined by IEC 61508-1, that contains at least:
- one electrical, electronic or programmable electronic element;
- applies to all elements within an E/E/PE safety-related system;
- specifies how to refine the E/E/PE system safety requirements specification, developed in accordance with IEC 61508-1, into the E/E/PE system design requirements specification;
- specifies the requirements for activities that are to be applied during the design and manufacture of the E/E/PE safety-related systems except software, which is dealt with in IEC 61508-3. These requirements include the application of techniques and measures that:
- are graded against the safety integrity level, for the avoidance of, and control of, faults and failures;
- specifies the information necessary for carrying out the installation, commissioning and final safety validation of the E/E/PE safety-related system;
- provides requirements for the preparation of information and procedures needed by the user for the operation and maintenance of the E/E/PE safety-related systems;
- specifies requirements to be met by the organisation carrying out any modification of the E/E/PE safety-related systems.
This second edition cancels and replaces the first edition published in 1998. This edition constitutes a technical revision. It has been subject to a thorough review and incorporates many comments received at the various revision stages. It has the status of a basic safety publication according to IEC Guide 104.
NEW! Also available:  IEC Standards+ 61508:2010, containing all parts, together with a commented Redline version. Changes made in this 2nd edition are highlighted and commented by a leading world expert.
This publication is of high relevance for Smart Grid.

Sécurité fonctionnelle des systèmes électriques/électroniques/électroniques programmables relatifs à la sécurité - Partie 2: Exigences pour les systèmes électriques/électroniques/électroniques programmables relatifs à la sécurité

La CEI 61508-2:2010 s'applique à tout système relatif à la sécurité tel que défini dans la CEI 61508-1, qui contient au moins:
- un composant à base électrique, électronique ou électronique programmable;
- s'applique à tous les éléments d'un système E/E/PE relatif à la sécurité;
- spécifie la manière d'affiner la spécification des exigences de sécurité des systèmes E/E/PE, développée conformément à la CEI 61508-1, dans le cadre de la spécification des exigences de conception des systèmes E/E/PE;
- spécifie les exigences pour des activités qui doivent être appliquées pendant la conception et la fabrication des systèmes E/E/PE relatifs à la sécurité, à l'exception du logiciel qui est traité dans la CEI 61508-3.
Ces exigences comprennent l'application de techniques et de mesures qui sont classées en fonction du:
- niveau d'intégrité de sécurité pour éviter et maîtriser les anomalies et défaillances;
- spécifie les informations nécessaires à l'installation, à la mise en service et à la validation finale de la sécurité des systèmes E/E/PE relatifs à la sécurité;
- fournit des exigences relatives à la préparation des informations et procédures nécessaires à l'utilisateur pour l'exploitation et la maintenance des systèmes E/E/PE relatifs à la sécurité;
- spécifie les exigences auxquelles doit satisfaire l'entité qui effectue une modification des systèmes E/E/PE relatifs à la sécurité.
Cette deuxième édition annule et remplace la première édition publiée en 1998 dont elle constitue une révision technique. Elle a fait l'objet d'une révision approfondie et intègre de nombreux commentaires reçus lors des différentes phases de révision. Elle a le statut d'une publication fondamentale de sécurité conformément au Guide CEI 104.

General Information

Status
Published
Publication Date
29-Apr-2010
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
30-Apr-2010
Completion Date
30-Apr-2010
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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 (see <a href="http://www.iec.ch/functionalsafety">Functional Safety and IEC 61508</a>)
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IEC 61508-2
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 2: Requirements for electrical/electronic/programmable electronic safety-
related systems
Sécurité fonctionnelle des systèmes électriques/électroniques/électroniques
programmables relatifs à la sécurité –
Partie 2: Exigences pour les systèmes électriques/électroniques/électroniques
programmables relatifs à la sécurité
IEC 61508-2:2010
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61508-2
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 2: Requirements for electrical/electronic/programmable electronic safety-
related systems
Sécurité fonctionnelle des systèmes électriques/électroniques/électroniques
programmables relatifs à la sécurité –
Partie 2: Exigences pour les systèmes électriques/électroniques/électroniques
programmables relatifs à la sécurité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 25.040.40 ISBN 978-2-88910-525-0
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 61508-2 © IEC:2010
CONTENTS

FOREWORD...........................................................................................................................5

INTRODUCTION.....................................................................................................................7

1 Scope...............................................................................................................................9

2 Normative references .....................................................................................................12

3 Definitions and abbreviations..........................................................................................12

4 Conformance to this standard.........................................................................................12

5 Documentation ...............................................................................................................13

6 Management of functional safety ....................................................................................13

7 E/E/PE system safety lifecycle requirements ..................................................................13

7.1 General .................................................................................................................13

7.1.1 Objectives and requirements – general......................................................13

7.1.2 Objectives .................................................................................................13

7.1.3 Requirements ............................................................................................13

7.2 E/E/PE system design requirements specification .................................................17

7.2.1 Objective ...................................................................................................17

7.2.2 General .....................................................................................................17

7.2.3 E/E/PE system design requirements specification......................................18

7.3 E/E/PE system safety validation planning ..............................................................19

7.3.1 Objective ...................................................................................................19

7.3.2 Requirements ............................................................................................19

7.4 E/E/PE system design and development................................................................19

7.4.1 Objective ...................................................................................................20

7.4.2 General requirements ................................................................................20

7.4.3 Synthesis of elements to achieve the required systematic capability..........22

7.4.4 Hardware safety integrity architectural constraints.....................................23

7.4.5 Requirements for quantifying the effect of random hardware failures .........32

7.4.6 Requirements for the avoidance of systematic faults .................................34

7.4.7 Requirements for the control of systematic faults.......................................35

7.4.8 Requirements for system behaviour on detection of a fault ........................35

7.4.9 Requirements for E/E/PE system implementation ......................................36

7.4.10 Requirements for proven in use elements ..................................................38

7.4.11 Additional requirements for data communications ......................................39

7.5 E/E/PE system integration.....................................................................................40

7.5.1 Objective ...................................................................................................40

7.5.2 Requirements ............................................................................................40

7.6 E/E/PE system operation and maintenance procedures .........................................41

7.6.1 Objective ...................................................................................................41

7.6.2 Requirements ............................................................................................41

7.7 E/E/PE system safety validation ............................................................................42

7.7.1 Objective ...................................................................................................42

7.7.2 Requirements ............................................................................................42

7.8 E/E/PE system modification...................................................................................43

7.8.1 Objective ...................................................................................................43

7.8.2 Requirements ............................................................................................43

7.9 E/E/PE system verification ....................................................................................44

7.9.1 Objective ...................................................................................................44

---------------------- Page: 4 ----------------------
61508-2 © IEC:2010 – 3 –

7.9.2 Requirements ............................................................................................44

8 Functional safety assessment.........................................................................................46

Annex A (normative) Techniques and measures for E/E/PE safety-related systems –

control of failures during operation........................................................................................47

Annex B (normative) Techniques and measures for E/E/PE safety-related systems –

avoidance of systematic failures during the different phases of the lifecycle .........................62

Annex C (normative) Diagnostic coverage and safe failure fraction......................................71

Annex D (normative) Safety manual for compliant items ......................................................74

Annex E (normative) Special architecture requirements for integrated circuits (ICs)

with on-chip redundancy .......................................................................................................76

Annex F (informative) Techniques and measures for ASICs – avoidance of systematic

failures .................................................................................................................................81

Bibliography..........................................................................................................................89

Figure 1 – Overall framework of the IEC 61508 series ..........................................................11

Figure 2 – E/E/PE system safety lifecycle (in realisation phase)............................................14

Figure 3 – ASIC development lifecycle (the V-Model)............................................................15

Figure 4 – Relationship between and scope of IEC 61508-2 and IEC 61508-3 ......................15

Figure 5 – Determination of the maximum SIL for specified architecture (E/E/PE safety-

related subsystem comprising a number of series elements, see 7.4.4.2.3) ..........................28

Figure 6 – Determination of the maximum SIL for specified architecture (E/E/PE safety-

related subsystem comprised of two subsystems X & Y, see 7.4.4.2.4).................................30

Figure 7 – Architectures for data communication...................................................................40

Table 1 – Overview – realisation phase of the E/E/PE system safety lifecycle.......................16

Table 2 – Maximum allowable safety integrity level for a safety function carried out by

a type A safety-related element or subsystem.......................................................................26

Table 3 – Maximum allowable safety integrity level for a safety function carried out by

a type B safety-related element or subsystem.......................................................................27

Table A.1 – Faults or failures to be assumed when quantifying the effect of random

hardware failures or to be taken into account in the derivation of safe failure fraction ...........49

Table A.2 – Electrical components ........................................................................................51

Table A.3 – Electronic components.......................................................................................51

Table A.4 – Processing units ................................................................................................52

Table A.5 – Invariable memory ranges..................................................................................52

Table A.6 – Variable memory ranges ....................................................................................53

Table A.7 – I/O units and interface (external communication)................................................53

Table A.8 – Data paths (internal communication) ..................................................................54

Table A.9 – Power supply .....................................................................................................54

Table A.10 – Program sequence (watch-dog)........................................................................55

Table A.11 – Clock ...............................................................................................................55

Table A.12 – Communication and mass-storage ...................................................................55

Table A.13 – Sensors ...........................................................................................................56

Table A.14 – Final elements (actuators)................................................................................56

Table A.15 – Techniques and measures to control systematic failures caused by

hardware design ...................................................................................................................58

---------------------- Page: 5 ----------------------
– 4 – 61508-2 © IEC:2010
Table A.16 – Techniques and measures to control systematic failures caused by

environmental stress or influences........................................................................................59

Table A.17 – Techniques and measures to control systematic operational failures................60

Table A.18 – Effectiveness of techniques and measures to control systematic failures .........61

Table B.1 – Techniques and measures to avoid mistakes during specification of

E/E/PE system design requirements (see 7.2) ......................................................................63

Table B.2 – Techniques and measures to avoid introducing faults during E/E/PE

system design and development (see 7.4) ............................................................................64

Table B.3 – Techniques and measures to avoid faults during E/E/PE system

integration (see 7.5)..............................................................................................................65

Table B.4 – Techniques and measures to avoid faults and failures during E/E/PE

system operation and maintenance procedures (see 7.6)......................................................66

Table B.5 – Techniques and measures to avoid faults during E/E/PE system safety

validation (see 7.7) ...............................................................................................................67

Table B.6 – Effectiveness of techniques and measures to avoid systematic failures..............68

Table E.1 – Techniques and measures that increase β ....................................................79

B-IC

Table E.2 – Techniques and measures that decrease β ..................................................80

B-IC

Table F.1 – Techniques and measures to avoid introducing faults during ASIC’s design

and development – full and semi-custom digital ASICs (see 7.4.6.7).....................................83

Table F.2 – Techniques and measures to avoid introducing faults during ASIC design

and development: User programmable ICs (FPGA/PLD/CPLD) (see 7.4.6.7) ........................86

---------------------- Page: 6 ----------------------
61508-2 © IEC:2010 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/
PROGRAMMABLE ELECTRONIC SAFETY-RELATED SYSTEMS –
Part 2: Requirements for electrical/electronic/programmable
electronic safety-related systems
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

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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

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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

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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

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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 61508-2 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 2000. 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.
---------------------- Page: 7 ----------------------
– 6 – 61508-2 © IEC:2010
The text of this standard is based on the following documents:
FDIS Report on voting
65A/549/FDIS 65A/573/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 maintenance result 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.
---------------------- Page: 8 ----------------------
61508-2 © 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, though 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.
---------------------- Page: 9 ----------------------
– 8 – 61508-2 © 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;

– a low demand mode of operation, the lower limit is set at an average probability of a

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.
---------------------- Page: 10 ----------------------
61508-2 © IEC:2010 – 9 –
FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/
PROGRAMMABLE ELECTRONIC SAFETY-RELATED SYSTEMS –
Part 2: Requirements for electrical/electronic/p
...

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