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
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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

– 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

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

– 4 – IEC TR 61511-4:2020 © IEC 2020
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? .
...