IEC 61511-2:2016

IEC 61511-2 ®
Edition 2.0 2016-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Functional safety – Safety instrumented systems for the process industry
sector –
Part 2: Guidelines for the application of IEC 61511-1: 2016

Sécurité fonctionnelle – Systèmes instrumentés de sécurité pour le secteur
des industries de transformation –
Partie 2: Lignes directrices pour l'application de l'IEC 61511-1:2016

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IEC 61511-2 ®
Edition 2.0 2016-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Functional safety – Safety instrumented systems for the process industry

sector –
Part 2: Guidelines for the application of IEC 61511-1: 2016

Sécurité fonctionnelle – Systèmes instrumentés de sécurité pour le secteur

des industries de transformation –

Partie 2: Lignes directrices pour l'application de l'IEC 61511-1:2016

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.110; 25.040.01 ISBN 978-2-8322-3227-9

– 2 – IEC 61511-2:2016 © IEC 2016
CONTENTS
FOREWORD. 9
INTRODUCTION . 11
1 Scope . 13
2 Normative references . 13
3 Terms, definitions, and abbreviations . 13
Annex A (informative) Guidance for IEC 61511-1 . 14
A.1 Scope . 14
A.2 Normative references . 14
A.3 Terms, definitions and abbreviations . 14
A.4 Conformance to the IEC 61511-1:– . 14
A.5 Management of functional safety . 14
A.5.1 Objective . 14
A.5.2 Guidance to "Requirements" . 14
A.6 Safety life-cycle requirements . 23
A.6.1 Objectives . 23
A.6.2 Guidance to "Requirements" . 23
A.6.3 Guidance to "Application program SIS safety life-cycle requirements" . 24
A.7 Verification . 25
A.7.1 Objective . 25
A.7.2 Guidance to "Requirements" . 25
A.8 Process hazard and risk assessment (H&RA) . 27
A.8.1 Objectives . 27
A.8.2 Guidance to “Requirements" . 27
A.9 Allocation of safety functions to protection layers . 30
A.9.1 Objective . 30
A.9.2 Guidance to "Requirements of the allocation process". 30
A.9.3 Guidance to "Requirements on the basic process control system as a
protection layer" . 32
A.9.4 Guidance to "Requirements for preventing common cause, common
mode and dependent failures" . 35
A.10 SIS safety requirements specification . 36
A.10.1 Objective . 36
A.10.2 Guidance to "General requirements" . 36
A.10.3 Guidance to "SIS safety requirements" . 36
A.11 SIS design and engineering . 40
A.11.1 Objective . 40
A.11.2 Guidance to "General requirements" . 40
A.11.3 Guidance to "Requirements for system behaviour on detection of a
fault" . 47
A.11.4 Guidance to “Hardware fault tolerance" . 47
A.11.5 Guidance to "Requirements for selection of devices" . 50
A.11.6 Field devices . 53
A.11.7 Interfaces . 53
A.11.8 Guidance to "Maintenance or testing design requirements" . 55
A.11.9 Guidance to "Quantification of random failure" . 56
A.12 SIS application program development . 62

A.12.1 Objective . 62
A.12.2 Guidance to "General requirements" . 62
A.12.3 Guidance to "Application program design" . 64
A.12.4 Guidance to "Application program implementation" . 66
A.12.5 Guidance to "Requirements for application program verification (review
and testing)" . 67
A.12.6 Guidance to "Requirements for application program methodology and
tools" . 70
A.13 Factory acceptance testing (FAT) . 73
A.13.1 Objectives . 73
A.13.2 Guidance to "Recommendations" . 73
A.14 SIS installation and commissioning . 73
A.14.1 Objectives . 73
A.14.2 Guidance to "Requirements" . 73
A.15 SIS safety validation . 74
A.15.1 Objective . 74
A.15.2 Guidance to "Requirements" . 74
A.16 SIS operation and maintenance . 74
A.16.1 Objectives . 74
A.16.2 Guidance to "Requirements" . 75
A.16.3 Proof testing and inspection . 76
A.17 SIS modification . 78
A.17.1 Objective . 78
A.17.2 Guidance to "Requirements" . 79
A.18 SIS decommissioning . 79
A.18.1 Objectives . 79
A.18.2 Guidance to "Requirements" . 79
A.19 Information and documentation requirements . 80
A.19.1 Objectives . 80
A.19.2 Guidance to "Requirements" . 80
Annex B (informative) Example of SIS logic solver application program development
using function block diagram . 81
B.1 General . 81
B.2 Application program development and validation philosophy . 81
B.3 Application description . 82
B.3.1 General . 82
B.3.2 Process description . 82
B.3.3 Safety instrumented functions . 83
B.3.4 Risk reduction and domino effects . 84
B.4 Application program safety life-cycle execution . 84
B.4.1 General . 84
B.4.2 Inputs to application program SRS development . 84
B.4.3 Application program design and development . 87
B.4.4 Application program production . 101
B.4.5 Application program verification and testing . 101
B.4.6 Validation . 101
Annex C (informative) Considerations when converting from NP technologies to PE
technologies . 102

– 4 – IEC 61511-2:2016 © IEC 2016
Annex D (informative) Example of how to get from a piping and instrumentation
diagram (P&ID) to application program . 104
Annex E (informative) Methods and tools for application programming . 107
E.1 Typical toolset for application programming . 107
E.2 Rules and constraints for application program design . 108
E.3 Rules and constraints for application programming . 108
Annex F (informative) Example SIS project illustrating each phase of the safety life
cycle with application program development using relay ladder language . 110
F.1 Overview . 110
F.2 Project definition . 110
F.2.1 General . 110
F.2.2 Conceptual planning . 111
F.2.3 Process hazards analysis . 111
F.3 Simplified process description . 111
F.4 Preliminary design . 113
F.5 IEC 61511 application . 113
F.5.1 General . 113
F.5.2 Step F.1: Hazard & risk assessment . 117
F.5.3 Hazard identification . 117
F.5.4 Preliminary hazard evaluation . 117
F.5.5 Accident history . 117
F.6 Preliminary process design safety considerations . 120
F.7 Recognized process hazards . 120
F.8 Process design definitions strategy . 121
F.9 Preliminary hazard assessment . 124
F.9.1 General . 124
F.9.2 Step F.2: Allocation of safety functions . 128
F.10 SIF safety integrity level determination . 129
F.11 Layer of protection analysis (LOPA) applied to example . 129
F.12 Tolerable risk criteria . 130
F.13 Step F.3: SIS safety requirements specifications . 133
F.13.1 Overview . 133
F.13.2 Input requirements . 133
F.13.3 Safety functional requirements . 134
F.13.4 Safety integrity requirements . 135
F.14 Functional description and conceptual design . 136
F.14.1 Narrative for example reactor system logic . 136
F.15 SIL verification calculations . 137
F.16 Application program requirements . 144
F.17 Step F.4: SIS safety life-cycle . 151
F.18 Technology and device selection . 151
F.18.1 General . 151
F.18.2 Logic solver . 151
F.18.3 Sensors . 152
F.18.4 Final elements . 152
F.18.5 Solenoid valves . 152
F.18.6 Emergency vent valves . 153
F.18.7 Modulating valves . 153
F.18.8 Bypass valves . 153

F.18.9 Human-machine interfaces (HMIs) . 153
F.18.10 Separation . 154
F.19 Common cause and systematic failures . 155
F.19.1 General . 155
F.19.2 Diversity . 155
F.19.3 Specification errors . 155
F.19.4 Hardware design errors . 155
F.19.5 Software design errors . 156
F.19.6 Environmental overstress . 156
F.19.7 Temperature . 156
F.19.8 Humidity . 156
F.19.9 Contaminants . 157
F.19.10 Vibration . 157
F.19.11 Grounding . 157
F.19.12 Power line conditioning . 157
F.19.13 Electro-magnetic compatibility (EMC) . 157
F.19.14 Utility sources . 158
F.19.15 Sensors . 159
F.19.16 Process corrosion or fouling . 159
F.19.17 Maintenance . 159
F.19.18 Susceptibility to mis-operation . 159
F.19.19 SIS architecture . 159
F.20 SIS application program design features . 160
F.21 Wiring practices . 161
F.22 Security . 161
F.23 Step F.5: SIS installation, commissioning, validation . 162
F.24 Installation . 162
F.25 Commissioning . 163
F.26 Documentation . 164
F.27 Validation . 164
F.28 Testing . 165
F.29 Step F.6: SIS operation and maintenance . 178
F.30 Step F.7: SIS Modification . 181
F.31 Step F.8: SIS decommissioning . 181
F.32 Step F.9: SIS verification . 181
F.33 Step F.10: Management of functional safety and SIS FSA . 182
F.34 Management of functional safety . 183
F.34.1 General . 183
F.34.2 Competence of personnel . 183
F.35 Functional safety assessment . 183
Annex G (informative) Guidance on developing application programming practices . 184
G.1 Purpose of this guidance . 184
G.2 Generic safe application programming attributes . 184
G.3 Reliability . 184
G.3.1 General . 184
G.3.2 Predictability of memory utilisation . 185
G.3.3 Predictability of control flow . 186
G.3.4 Accounting for precision and accuracy . 188
G.3.5 Predictability of timing . 190

– 6 – IEC 61511-2:2016 © IEC 2016
G.4 Predictability of mathematical or logical result . 190
G.5 Robustness . 191
G.5.1 General . 191
G.5.2 Controlling use of diversity . 191
G.5.3 Controlling use of exception handling . 192
G.5.4 Checking input and output . 193
G.6 Traceability . 194
G.6.1 General . 194
G.6.2 Controlling use of built-in functions . 194
G.6.3 Controlling use of compiled libraries . 194
G.7 Maintainability . 194
G.7.1 General . 194
G.7.2 Readability . 195
G.7.3 Data abstraction . 198
G.7.4 Functional cohesiveness . 199
G.7.5 Malleability . 199
G.7.6 Portability . 199
Bibliography . 201

Figure 1 – Overall framework of IEC 61511 series . 12
Figure A.1 – Application program V-Model . 25
Figure A.2 – Independence of a BPCS protection layer and an initiating source in the
BPCS . 34
Figure A.3 – Independence of two protection layers allocated to the BPCS . 35
Figure A.4 – Relationship of system, SIS hardware, and SIS application program . 39
Figure A.5 – Illustration of uncertainties on a reliability parameter . 60
Figure A.6 – Illustration of the 70 % confidence upper bound . 61
Figure A.7 – Typical probabilistic distribution of target results from Monte Carlo
simulation . 62
Figure B.1 – Process flow diagram for SIF 02.01 . 83
Figure B.2 – Process flow diagram for SIF 06.02 . 84
Figure B.3 – Functional specification of SIF02.01 and SIF 06.02 . 85
Figure B.4 – SIF 02.01 hardware functional architecture . 85
Figure B.5 – SIF 06.02 hardware functional architecture . 86
Figure B.6 – Hardware specification for SOV extracted from piping and
instrumentation diagram . 86
Figure B.7 – SIF 02.01 hardware physical architecture . 87
Figure B.8 – SIF 06.02 hardware physical architecture . 87
Figure B.9 – Hierarchical structure of model integration . 91
Figure B.10 – Hierarchical structure of model integration including models of safety
properties and of BPCS logic . 93
Figure B.11 – State transition diagram . 94
Figure B.12 – SOV typical block diagram . 95
Figure B.13 – SOV typical model block diagram . 96
Figure B.14 – Typical model block diagram implementation – BPCS part . 98
Figure B.15 – SOV application program typical model implementation – SIS part . 99

Figure B.16 – Complete model for final implementation model checking . 101
Figure D.1 – Example of P&ID for an oil and gas separator . 104
Figure D.2 – Example of (part of) an ESD cause & effect diagram (C&E) . 105
Figure D.3 – Example of (part of) an application program in a safety PLC function
block programming . 106
Figure F.1 – Simplified flow diagram: the PVC process . 112
Figure F.2 – SIS safety life-cycle phases and FSA stages . 114
Figure F.3 – Example of the preliminary P&ID for PVC reactor unit . 123
Figure F.4 – SIF S-1 Bubble diagram showing the PFD of each SIS device . 139
avg
Figure F.5 – S-1 Fault tree . 140
Figure F.6 – SIF S-2 Bubble diagram showing the PFD of each SIS device . 141
avg
Figure F.7 – SIF S-2 fault tree . 142
Figure F.8 – SIF S-3 Bubble diagram showing the PFD of each SIS device . 143
avg
Figure F.9 – SIF S-3 fault tree . 144
Figure F.10 – P&ID for PVC reactor unit SIF . 145
Figure F.11 – Legend (1 of 5) . 146
Figure F.12 – SIS for the VCM reactor . 160

Table B.1 – Modes of operation specification . 88
Table B.2 – State transition table . 93
Table F.1 – SIS safety life-cycle overview . 115
Table F.2 – SIS safety life-cycle – Box 1 . 117
Table F.3 – Some physical properties of vinyl chloride . 119
Table F.4 – What-If/Checklist . 125
Table F.5 – HAZOP . 126
Table F.6 – Partial summary of hazard assessment for SIF strategy development . 127
Table F.7 – SIS safety life-cycle – Box 2 . 129
Table F.8 – Tolerable risk ranking . 131
Table F.9 – VCM reactor example: LOPA based integrity level . 132
Table F.10 – SIS safety life-cycle – Box 3 . 133
Table F.11 – Safety instrumented functions and SILs . 133
Table F.12 – Functional relationship of I/O for the SIF(s) . 134
Table F.13 – SIS sensors, normal operating range & trip points . 134
Table F.14 – Cause and effect diagram . 137
Table F.15 – MTTFd figures of SIS F.1 devices . 138
Table F.16 – SIS safety life-cycle – Box 4 . 151
Table F.17 – SIS safety life-cycle – Box 5 . 162
Table F.18 – List of instrument types and testing procedures used . 166
Table F.19 – Interlock check procedure bypass/simulation check sheet . 178
Table F.20 – SIS safety life-cycle – Box 6 . 178
Table F.21 – SIS trip log . 179
Table F.22 – SIS device failure log . 179
Table F.23 – SIS safety life-cycle – Box 7 . 181

– 8 – IEC 61511-2:2016 © IEC 2016
Table F.24 – SIS safety life-cycle – Box 8 . 181
Table F.25 – SIS safety life-cycle – Box 9 . 182
Table F.26 – SIS safety life-cycle – Box 10 . 182

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
FUNCTIONAL SAFETY –
SAFETY INSTRUMENTED SYSTEMS
FOR THE PROCESS INDUSTRY SECTOR –

Part 2: Guidelines for the application of IEC 61511-1:2016

FOREWORD
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International Standard IEC 61511-2 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 2003. This edition
constitutes a technical revision. This edition includes the following significant technical
changes with respect to the previous edition:
• guidance examples based on all phases of the safety life cycle provided based on usage
st
experience with IEC61511 1 edition;
• annexes replaced to address transition from software to application programming.

– 10 – IEC 61511-2:2016 © IEC 2016
The text of this standard is based on the following documents:
FDIS Report on voting
65A/783/FDIS 65A/787/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.
This International Standard is to be read in conjunction with IEC 61511-1. It is based on the
second edition of that standard.
A list of all parts in the IEC 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 publication will remain unchanged until
the stability date indicated on the IEC websit
...