IEC TR 63039:2016

Probabilistic risk analysis of technological systems - Estimation of final event rate at a given initial state

IEC TR 63039:2016(E) provides guidance on probabilistic risk analysis (hereafter referred to as risk analysis) for the systems composed of electrotechnical items and is applicable (but not limited) to all electrotechnical industries where risk analyses are performed. This document deals with the following topics from the perspective of risk analysis:
- defining the essential terms and concepts;
- specifying the types of events;
- classifying the occurrences of events;
- describing the usage of modified symbols and methods of graphical representation for ETA, FTA and Markov techniques for applying those modified techniques complementarily to the complex systems;
- suggesting ways to handle the event frequency/rate of complex systems;
- suggesting ways to estimate the event frequency/rate based on risk monitoring;
- providing illustrative and practical examples. Please refer to the Introduction and Scope of the document for addition information regarding the events covered by and associated risks. This document defines the basic properties of events from the perspective of probabilistic risk analysis and use of dependability-related techniques for the analysis of occurrence of the final event that results in a final state in which the final consequences of a risk may appear. Keywords: probabilistic risk analysis, effects of uncertainty, events and associated risks

General Information

• Status: Published
• Publication Date: 04-Jul-2016
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 03.120.01 - Quality in general
• ICS: 03.120.30 - Application of statistical methods
• Technical Committee: TC 56 - Dependability
• Current Stage: PPUB - Publication issued
• Start Date: 30-Sep-2016
• Completion Date: 05-Jul-2016

Standards Content (Sample)

IEC TR 63039 ®
Edition 1.0 2016-07
TECHNICAL
REPORT
colour
inside
Probabilistic risk analysis of technological systems – Estimation of final event
rate at a given initial state
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IEC TR 63039 ®
Edition 1.0 2016-07
TECHNICAL
REPORT
colour
inside
Probabilistic risk analysis of technological systems – Estimation of final event

rate at a given initial state
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 03.120.01; 03.120.30 ISBN 978-2-8322-3511-9

– 2 – IEC TR 63039:2016 © IEC 2016
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references. 10
3 Terms, definitions and abbreviated terms . 10
3.1 Terms and definitions . 10
3.2 Abbreviated terms . 17
4 Difference between frequency and rate of final event . 17
5 Final event frequency and final event rate at a given initial state . 19
5.1 General . 19
5.2 Classification of final events . 19
5.3 Final event frequency in a steady state . 20
5.4 Final event rate at a given initial state and at a recognised state . 22
5.5 Relationship between final event rate and frequency at a given initial state . 22
6 Procedure for probabilistic risk analysis and flow to reach risk profile . 23
7 Techniques for quantitative analysis of the occurrence of a final event . 24
7.1 Graphical symbols for three types of final events . 24
7.1.1 General . 24
7.1.2 Repeatable final event . 24
7.1.3 Unrepeatable final event resulting in a renewable final state . 30
7.1.4 Unrepeatable final event resulting in an unrenewable final state . 30
7.2 Analytical example of an unrepeatable final event . 31
7.2.1 General . 31
7.2.2 Average final event frequency . 32
7.2.3 Final event rate at a given initial state . 34
8 Final event rate at a recognised state and recognised group state . 40
8.1 General . 40
8.2 Example of recognised (group) states . 40
9 Analysis of multiple protection layers . 43
9.1 General . 43
9.2 Frequency and rate for repeatable events . 45
9.2.1 General . 45
9.2.2 Independent of event sequence . 45
9.2.3 Depending on event sequence . 47
9.3 Final protection layer arranged in a 1-out-of-1 architecture system . 51
9.3.1 General . 51
9.3.2 Final event rate at initial state (0, 0) for unrepeatable final event . 51
9.3.3 Final event rate at recognised state (x, y) . 53
9.3.4 Final event rate at a recognised group state . 54
9.4 Final protection layer arranged in a 1-out-of-2 architecture system . 56
9.4.1 General . 56
9.4.2 Independent failure parts of the 1-out-of-2 architecture system . 57
9.4.3 Fault tree for independent undetected and detected failures . 58
9.4.4 Final event rate at a given initial state owing to independent failures . 58
9.4.5 Recognised states at each part . 59

9.4.6 Recognised (group) states and final states for the overall system . 60
9.5 Common cause failures between protection layers and complexity of a
system . 61
9.6 Summary and remarks . 61
Annex A (informative) Risk owing to fault recognised only by demand . 62
A.1 Demand, detection and failure logic . 62
A.2 Final event rate at a given initial state . 64
A.3 Comparison between new and conventional analyses . 65
A.4 Further development . 67
A.5 Summary and remarks . 68
Annex B (informative) Application to functional safety . 69
B.1 Risk-based target failure measures in functional safety . 69
B.2 Safe/dangerous system states and failures . 70
B.3 Complexity of safety-related systems . 72
B.4 Comparison between conventional and new analyses . 73
B.5 Splitting up mode of operation . 74
B.6 Tolerable hazardous/harmful event rate and residual risk . 75
B.7 Procedure for determining the safety integrity level (SIL) of an item . 75
B.8 Summary and remarks . 76
Bibliography . 77

Figure 1 – Antecedent state, final event, final state and renewal event . 18
Figure 2 – Time to final event (TTFE) and time to renewal event (TTRE) . 19
Figure 3 – State transition models with various final states . 21
Figure 4 – Procedure for analysis of repeatable/unrepeatable final events . 24
Figure 5 – FT for an unrepeatable final event resulting in an unrenewable final state . 31
Figure 6 – State transition model resulting in an unrenewable final state . 32
Figure 7 – FT for an unrepeatable final event resulting in a renewable final state . 35
Figure 8 – State transitions resulting in a renewable final state . 35
Figure 9 – FT for unintended inflation of an airbag due to failure of control . 38
Figure 10 – State transition model of unintended inflation of an airbag . 39
Figure 11 – Event tree of a demand source, int. PL and FPL for a risk . 44
Figure 12 – Failure of int. PL independent of event sequence . 46
Figure 13 – FT for failure of int. PL through sequential failure logic . 49
Figure 14 – FT for an unrepeatable final event at initial state (0,0) . 53
Figure 15 – State transition model for an unrepeatable final event at initial state (0,0) . 53
Figure 16 – FT for an unrepeatable final event for recognised state (0,1) . 54
Figure 17 – State transition model for recognised state (0,1) . 54
Figure 18 – FT for an unrepeatable final event for recognised group state G1 . 55
Figure 19 – State transition model for recognised group state G1. 56
Figure 20 – RBD of FPL arranged in a 1-out-of-2 architecture system . 57
Figure 21 – RBD of the independent parts of Ch 1 and Ch 2 . 57
Figure 22 – RBD equivalent to that in Figure 21 . 58
Figure 23 – FT for UD failure of Ch 1, D failure of Ch 2 and demand . 58
Figure 24 – State transitions due to UD failure of Ch 1, D failure of Ch 2 and demand . 59

– 4 – IEC TR 63039:2016 © IEC 2016
Figure A.1 – Reliability bock diagram with independent and common cause failures . 62
Figure A.2 – Fault tree of unrepeatable final event due to DU failures . 63
Figure A.3 – State transition model for unrepeatable final event caused by DU failures . 64
Figure A.4 – Comparison between analyses of r(λ ) and ϖ . 67
M
Figure B.1 – Comparison between conventional and new analyses . 74

Table 1 – Events and associated risks . 9
Table 2 – Symbols newly introduced for event tree and fault tree analyses . 25
Table 3 – Symbols and graphical representation for a repeatable (final) event . 26
Table 4 – Symbols and graphical representation for a renewable final state . 27
Table 5 – Symbols and graphical representation for an unrenewable final state . 29
Table 6 – Symbols and graphical representation for the FER at recognised state 3 .
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