Functional safety - Safety instrumented systems for the process industry sector - Part 4: Explanation and rationale for changes in IEC 61511-1 from Edition 1 to Edition 2 (IEC/TR 61511-4:2020)

This part of IEC 61511, which is a Technical Report,
•   specifies the rationale behind all clauses and the relationship between them,
•   raises awareness for the most common misconceptions and misinterpretations of the clauses and the changes related to hem,
•   explains the differences between Ed. 1 and Ed. 2 of IEC 61511-1 and the reasons behind the changes,
•   presents high level summaries of how to fulfil the requirements of the clauses, and
•   explains differences in terminology between IEC 61508-4:2010 and IEC 61511-1 Ed. 2.

Funktionale Sicherheit - PLT-Sicherheitseinrichtungen für die Prozessindustrie - Teil 4: Erläuterung und Gründe der Änderungen in der IEC 61511-1 von Edition 1 zu Edition 2 (IEC/TR 61511-4:2020)

Sécurité fonctionnelle - Systèmes instrumentés de sécurité pour le secteur des industries de transformation - Partie 4 : Explication et justifications relatives aux modifications apportées entre l'Edition 1 et l'Edition 2 de l'IEC 61511-1 (IEC/TR 61511-4:2020)

Funkcijska varnost - Sistemi z varnostnimi instrumenti za sektor procesne industrije - 4. del: Pojasnilo in razlogi za spremembe v IEC 61511-1 od 1. do 2. izdaje (IEC/TR 61511-4:2020)

General Information

Status
Published
Publication Date
05-Nov-2020
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
07-Oct-2020
Due Date
12-Dec-2020
Completion Date
06-Nov-2020

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SLOVENSKI STANDARD
SIST-TP CLC IEC/TR 61511-4:2020
01-december-2020
Funkcijska varnost - Sistemi z varnostnimi instrumenti za sektor procesne
industrije - 4. del: Pojasnilo in razlogi za spremembe v IEC 61511-1 od 1. do 2.
izdaje (IEC/TR 61511-4:2020)

Functional safety - Safety instrumented systems for the process industry sector - Part 4:

Explanation and rationale for changes in IEC 61511-1 from Edition 1 to Edition 2 (IEC/TR

61511-4:2020)

Funktionale Sicherheit - PLT-Sicherheitseinrichtungen für die Prozessindustrie - Teil 4:

Erläuterung und Gründe der Änderungen in der IEC 61511-1 von Edition 1 zu Edition 2

(IEC/TR 61511-4:2020)

Sécurité fonctionnelle - Systèmes instrumentés de sécurité pour le secteur des industries

de transformation - Partie 4 : Explication et justifications relatives aux modifications

apportées entre l'Edition 1 et l'Edition 2 de l'IEC 61511-1 (IEC/TR 61511-4:2020)

Ta slovenski standard je istoveten z: CLC IEC/TR 61511-4:2020
ICS:
25.040.01 Sistemi za avtomatizacijo v Industrial automation
industriji na splošno systems in general
SIST-TP CLC IEC/TR 61511-4:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CLC IEC/TR 61511-4:2020
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SIST-TP CLC IEC/TR 61511-4:2020
TECHNICAL REPORT CLC IEC/TR 61511-4
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
September 2020
ICS 13.110; 25.040.01
English Version
Functional safety - Safety instrumented systems for the process
industry sector - Part 4: Explanation and rationale for changes in
IEC 61511-1 from Edition 1 to Edition 2
(IEC/TR 61511-4:2020)

Sécurité fonctionnelle - Systèmes instrumentés de sécurité Funktionale Sicherheit - PLT-Sicherheitseinrichtungen für

pour le secteur des industries de transformation - Partie 4 : die Prozessindustrie - Teil 4: Erläuterung und Gründe der

Explication et justifications relatives aux modifications Änderungen in der IEC 61511-1 von Edition 1 zu Edition 2

apportées entre l'Edition 1 et l'Edition 2 de l'IEC 61511-1 (IEC/TR 61511-4:2020)

(IEC/TR 61511-4:2020)
This Technical Report was approved by CENELEC on 2020-09-14.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. CLC IEC/TR 61511-4:2020 E
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SIST-TP CLC IEC/TR 61511-4:2020
CLC IEC/TR 61511-4:2020 (E)
European foreword

The text of document (65A/911/DTR), future edition 1 of IEC/TR 61511-4, 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 approved by CENELEC as CLC IEC/TR 61511-

4:2020.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice

The text of the International Standard IEC/TR 61511-4:2020 was approved by CENELEC as a

European Standard without any modification.
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SIST-TP CLC IEC/TR 61511-4:2020
CLC IEC/TR 61511-4:2020 (E)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments)

applies.

NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the

relevant EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available

here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-192 - International electrotechnical vocabulary - Part 192: - -
Dependability
IEC 61508-4 2010 Functional safety of EN 61508-4 2010
electrical/electronic/programmable electronic
safety-related systems - Part 4: Definitions and
abbreviations (see href="http://www.iec.ch/functionalsafety">Functional
Safety and IEC 61508)

IEC 61511-1 2016 Functional safety - Safety instrumented systems for EN 61511-1 2017

the process industry sector - Part 1: Framework,
definitions, system, hardware and application
programming requirements
+ A1 2017 + A1 2017
ISO/IEC Guide 51 2014 Safety aspects - Guidelines for their inclusion in - -
standards
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SIST-TP CLC IEC/TR 61511-4:2020
IEC TR 61511-4
Edition 1.0 2020-02
TECHNICAL
REPORT
Functional safety – Safety instrumented systems for the process industry
sector –
Part 4: Explanation and rationale for changes in IEC 61511-1 from Edition 1 to
Edition 2
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.110, ICS 25.040.01 ISBN 978-2-8322-7870-3

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
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SIST-TP CLC IEC/TR 61511-4:2020
– 2 – IEC TR 61511-4:2020 © IEC 2020
CONTENTS

CONTENTS ............................................................................................................................ 2

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

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

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms, definitions and abbreviated terms ........................................................................ 8

3.1 Terms and definitions .............................................................................................. 8

3.2 Abbreviated terms ................................................................................................... 9

4 Background ................................................................................................................... 10

5 Management of functional safety (IEC 61511-1 Ed. 2 Clause 5) ..................................... 10

5.1 Why is this clause important? ............................................................................... 10

5.2 Common misconceptions ...................................................................................... 10

5.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 11

5.3.1 Existing systems ............................................................................................ 11

5.3.2 Change management ..................................................................................... 11

5.3.3 Performance metrics and quality assurance ................................................... 11

5.3.4 Competency .................................................................................................. 12

5.3.5 More requirements for functional safety product and service providers .......... 12

5.4 Summary on how .................................................................................................. 12

6 Safety life cycle (IEC 61511-1 Ed. 2 Clause 6) .............................................................. 12

6.1 Why is this clause important? ............................................................................... 12

6.2 Common misconceptions ...................................................................................... 12

6.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 13

6.4 Summary on how .................................................................................................. 13

7 Verification (IEC 61511-1 Ed. 2 Clause 7)...................................................................... 13

7.1 Why is this clause important? ............................................................................... 13

7.2 Common misconceptions ...................................................................................... 13

7.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 13

7.4 Summary on how .................................................................................................. 13

8 Hazard and risk analysis (IEC 61511-1 Ed. 2 Clause 8) ................................................. 13

8.1 Why is this clause important? ............................................................................... 13

8.2 Common misconceptions ...................................................................................... 14

8.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 14

8.4 Summary on how .................................................................................................. 15

9 Allocation of safety functions to protection layers (IEC 61511-1 Ed. 2 Clause 9) ........... 15

9.1 Why is this clause important? ............................................................................... 15

9.2 Common misconceptions ...................................................................................... 15

9.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 16

9.3.1 Limits on BPCS protection layers ................................................................... 16

9.3.2 Requirements for claiming RRF > 10 000 in total for instrumented

safeguards .................................................................................................... 16

9.4 Summary on how .................................................................................................. 16

10 SIS safety requirements specification (IEC 61511-1 Ed. 2 Clause 10) ............................ 17

10.1 Why is this clause important? ............................................................................... 17

10.2 Common misconceptions ...................................................................................... 17

10.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 18

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10.4 Summary on how .................................................................................................. 18

11 Design and engineering (IEC 61511-1 Ed. 2 Clause 11) ................................................ 18

11.1 Why is this clause important? ............................................................................... 18

11.2 Common misconceptions ...................................................................................... 18

11.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 19

11.3.1 Hardware fault tolerance ................................................................................ 19

11.3.2 Security risk requirements ............................................................................. 20

11.3.3 Safety manual ............................................................................................... 20

11.3.4 Requirements for system behaviour on detection of a fault ............................ 20

11.3.5 Limitations on field device communication design .......................................... 21

11.4 Summary on how .................................................................................................. 21

12 Application program development (IEC 61511-1 Ed. 2 Clause 12) ................................. 21

12.1 Why is this clause important? ............................................................................... 21

12.2 Common misconceptions ...................................................................................... 22

12.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 22

12.4 Summary on how .................................................................................................. 22

13 Factory acceptance test (IEC 61511-1 Ed. 2 Clause 13) ................................................ 22

13.1 Why is this clause important? ............................................................................... 22

13.2 Common misconceptions ...................................................................................... 23

13.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 23

13.4 Summary on how .................................................................................................. 23

14 Installation (IEC 61511-1 Ed. 2 Clause 14) .................................................................... 23

14.1 Why is this clause important? ............................................................................... 23

14.2 Common misconceptions ...................................................................................... 24

14.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 24

14.4 Summary on how .................................................................................................. 24

15 Validation (IEC 61511-1 Ed. 2 Clause 15) ...................................................................... 24

15.1 Why is this clause important? ............................................................................... 24

15.2 Common misconceptions ...................................................................................... 24

15.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 24

15.4 Summary on how .................................................................................................. 24

16 Operation and maintenance (IEC 61511-1 Ed. 2 Clause 16) .......................................... 25

16.1 Why is this clause important? ............................................................................... 25

16.2 Common misconceptions ...................................................................................... 25

16.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 26

16.3.1 Fault detection, bypassing, and compensating measures ............................... 26

16.3.2 Proof testing after repair and change ............................................................. 26

16.4 Summary on how .................................................................................................. 26

17 Modification (IEC 61511-1 Ed. 2 Clause 17) .................................................................. 26

17.1 Why is this clause important? ............................................................................... 26

17.2 Common misconceptions ...................................................................................... 26

17.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 27

Planning for and completing change .............................................................................. 27

17.4 Summary on how .................................................................................................. 27

18 Decommissioning (IEC 61511-1 Ed. 2 Clause 18) .......................................................... 27

18.1 Why is this clause important? ............................................................................... 27

18.2 Common misconceptions ...................................................................................... 27

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18.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 28

18.3.1 Planning for and completing change .............................................................. 28

18.4 Summary on how .................................................................................................. 28

19 Documentation (IEC 61511-1 Ed. 2 Clause 19) .............................................................. 28

19.1 Why is this clause important? ............................................................................... 28

19.2 Common misconceptions ...................................................................................... 28

19.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 28

19.4 Summary on how .................................................................................................. 28

20 Definitions (IEC 61511-1 Ed. 2 Clause 3) ....................................................................... 29

20.1 Why is this clause important? ............................................................................... 29

20.2 Common misconceptions ...................................................................................... 29

20.3 What was changed from Ed. 1 to Ed. 2 and why? .................................................. 29

20.4 Summary on how .................................................................................................. 37

Bibliography .......................................................................................................................... 38

Table 1 – Abbreviated terms used in IEC TR 61511-4 ............................................................. 9

Table 2 – Rationale for IEC 61511-1 Ed. 2 terms and definitions ........................................... 29

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IEC TR 61511-4:2020 © IEC 2020 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FUNCTIONAL SAFETY – SAFETY INSTRUMENTED SYSTEMS
FOR THE PROCESS INDUSTRY SECTOR –
Part 4: Explanation and rationale for changes in IEC 61511-1
from Edition 1 to Edition 2
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.

The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a Technical Report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 61511-4, which is a Technical Report, has been prepared by subcommittee 65A:

Systems aspects, of IEC technical committee 65: Industrial-process measurement, control

and automation.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
65A/911/DTR 65A/920A/RVDTR
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– 6 – IEC TR 61511-4:2020 © IEC 2020

Full information on the voting for the approval of this Technical Report can be found in the

report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the 61511 series, published under the general title Functional safety –

Safety instrumented systems for the process industry sector, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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IEC TR 61511-4:2020 © IEC 2020 – 7 –
INTRODUCTION

IEC 61511 (all parts) addresses safety instrumented systems (SIS) for the process industry

sector. It is written to use terminology that is familiar within this sector and to define practical

implementation requirements based on the sector-independent clauses presented in the

IEC 61508 basic safety standard. IEC 61511-1 is recognized as a good engineering practice

in many countries and a regulatory requirement in an increasing number of countries.

Nevertheless, standards evolve with the application experience in the affected sector. The

second edition of IEC 61511-1 was edited based on a decade of international process sector

experience in applying the requirements of the first edition of IEC 61511-1:2003. The changes

from Edition 1 to Edition 2 were initiated by comments from National Committees representing

a broad spectrum of users of the standard worldwide.

In Edition 1:2003 (Ed. 1) , the requirements addressing the avoidance and control of

systematic errors that occur during design, engineering, operation, maintenance and

modification were adapted primarily to support independent safety functions up to a SIL 3

performance target. In contrast, Edition 2:2016 (Ed. 2) needed to address a prevailing trend of

sharing automation systems across multiple safety functions.

Ed. 2 also needed to address the common misinterpretations of the Ed. 1 requirements that

became evident to the IEC 61511 maintenance team (MT 61511) over the intervening years.

For example, Ed. 2 reinforced the necessity to design for functional safety management rather

than a narrow focus on a calculation and to manage the actual performance of the SIS over

time.

IEC TR 61511-4 was created to provide a brief introduction of the above issues to a general

audience, with the more detailed content remaining in the main parts of the IEC 61511 series.

IEC TR 61511-4 describes the underlying rationale of the primary clauses in IEC 61511-1,

clarifies some common application misconceptions, provides a listing of the main differences

between the first and second editions of IEC 61511-1, and gives a brief explanation of the

typical process sector approaches to the application of each primary clause.
____________
For ease of reading, "Ed. 1" and "Ed. 2" will be used in this document.
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– 8 – IEC TR 61511-4:2020 © IEC 2020
FUNCTIONAL SAFETY – SAFETY INSTRUMENTED SYSTEMS
FOR THE PROCESS INDUSTRY SECTOR –
Part 4: Explanation and rationale for changes in IEC 61511-1
from Edition 1 to Edition 2
1 Scope
This part of IEC 61511, which is a Technical Report,
• specifies the rationale behind all clauses and the relationship between them,

• raises awareness for the most common misconceptions and misinterpretations of the

clauses and the changes related to them,

• explains the differences between Ed. 1 and Ed. 2 of IEC 61511-1 and the reasons behind

the changes,

• presents high level summaries of how to fulfil the requirements of the clauses, and

• explains differences in terminology between IEC 61508-4:2010 and IEC 61511-1 Ed. 2.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.

IEC 60050-192, International Electrotechnical Vocabulary (IEV) – Part 192: Dependability

(available at http://www.electropedia.org)

IEC 61508-4:2010, Functional safety of electrical/electronic/programmable electronic safety-

related systems – Part 4: Definitions and abbreviations

IEC 61511-1:2016, Functional safety – Safety instrumented systems for the process industry

sector – Part 1: Framework, definitions, system, hardware and application programming

requirements
IEC 61511-1:2016/AMD1:2017

ISO/IEC Guide 51:2014, Safety aspects – Guidelines for their inclusion in standards

3 Terms, definitions and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/IEC Guide 51,

IEC 60050-192, IEC 61508-4 and IEC 61511-1 apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
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3.2 Abbreviated terms

Abbreviated terms used throughout this document are given in Table 1. Also included are

some common abbreviated terms related to process sector functional safety.
Table 1 – Abbreviated terms used in IEC TR 61511-4
Abbreviated term Full expression
AIChE American Institute of Chemical Engineers
ANSI American National Standards Institute
BPCS Basic process control system
CCPS Centre for Chemical Process Safety (AIChE)
Ed. edition
FAT Factory acceptance test
FMEA Failure mode and effects analysis
FMEDA Failure modes, effects, and diagnostic analysis
FPL Fixed program language
FSA Functional safety assessment
FVL Full variability language
HFT Hardware fault tolerance
H&RA Hazard and Risk Assessment
HAZOP Hazard and Operability Study
HMI Human machine interface
IEC International Electrotechnical Commission
...

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