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BSI PD IEC/TR 63039:2016

BSI PD IEC/TR 63039:2016

$215.11

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

Published By Publication Date Number of Pages
BSI 2016 84
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This document 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.

The relationship between the events covered by this document and associated risks are described in Table 1. Risk is defined as the effect of uncertainty on objectives (see 3.1.1). The uncertainty is here assumed to be composed of two elements: the epistemic and aleatory. The epistemic is categorised into the known and unknown, and the effect of the aleatory is classified into the controlled and the uncontrolled, respectively. Therefore, the risk associated with the known event of which impact is controlled is the controlled risk, and the risk associated with the known event of which impact is not controlled is the uncontrolled risk. Favourable meta-risk is of an unknown event of which impact can be casually controlled even if this unknown event appears, and unfavourable meta-risk is of an unknown event of which impact cannot be controlled.

For example, the risks resulting from random hardware failures of electrotechnical items will be categorised into the controlled or uncontrolled risks, while the risks owing to software bugs could be classified into the favourable or unfavourable meta-risks. This document covers the controlled and uncontrolled risks resulting from the events that can be assumed to occur randomly and independently of time (see Clause 6, 9.1, 9.2, 9.5 and Clause B.3).

Table 1 ā€“ Events and associated risks

PDF Catalog

PDF Pages PDF Title
4 CONTENTS
7 FOREWORD
9 INTRODUCTION
11 1 Scope
Tables
Table 1 ā€“ Events and associated risks
12 2 Normative references
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
19 3.2 Abbreviated terms
4 Difference between frequency and rate of final event
20 Figures
FigureĀ 1 ā€“ Antecedent state, final event, final state and renewal event
21 5 Final event frequency and final event rate at a given initial state
5.1 General
5.2 Classification of final events
Figure 2 ā€“ Time to final event (TTFE) and time to renewal event (TTRE)
22 5.3 Final event frequency in a steady state
23 FigureĀ 3 ā€“ State transition models with various final states
24 5.4 Final event rate at a given initial state and at a recognised state
5.5 Relationship between final event rate and frequency at a given initial state
25 6 Procedure for probabilistic risk analysis and flow to reach risk profile
26 7 Techniques for quantitative analysis of the occurrence of a final event
7.1 Graphical symbols for three types of final events
7.1.1 General
7.1.2 Repeatable final eventTable 3
Figure 4 ā€“ Procedure for analysis of repeatable/unrepeatable final events
27 Table 2 ā€“ Symbols newly introduced for event tree and fault tree analyses
28 Table 3 ā€“ Symbols and graphical representation for a repeatable (final) event
29 Table 4 ā€“ Symbols and graphical representation for a renewable final state
31 Table 5 ā€“ Symbols and graphical representation for an unrenewable final state
32 7.1.3 Unrepeatable final event resulting in a renewable final state
7.1.4 Unrepeatable final event resulting in an unrenewable final state
33 7.2 Analytical example of an unrepeatable final event
7.2.1 General
Figure 5 ā€“ FT for an unrepeatable final event resulting in an unrenewable final state
34 7.2.2 Average final event frequency
Figure 6 ā€“ State transition model resulting in an unrenewable final state
36 7.2.3 Final event rate at a given initial state
37 Figure 7 ā€“ FT for an unrepeatable final event resulting in a renewable final state
FigureĀ 8 ā€“ State transitions resulting in a renewable final state
40 Figure 9 ā€“ FT for unintended inflation of an airbag due to failure of control
41 Figure 10 ā€“ State transition model of unintended inflation of an airbag
42 8 Final event rate at a recognised state and recognised group state
8.1 General
8.2 Example of recognised (group) states
43 TableĀ 6 ā€“ Symbols and graphical representation for the FER at recognised state 3
44 Table 7 ā€“ Symbols and graphical representation for FER at recognised group state G
45 9 Analysis of multiple protection layers
9.1 General
46 FigureĀ 11 ā€“ Event tree of a demand source, int. PL and FPL for a risk
47 9.2 Frequency and rate for repeatable events
9.2.1 General
9.2.2 Independent of event sequence
48 Figure 12 ā€“ Failure of int. PL independent of event sequence
49 9.2.3 Depending on event sequence
51 FigureĀ 13 ā€“ FT for failure of int. PL through sequential failure logic
53 9.3 Final protection layer arranged in a 1-out-of-1 architecture system
9.3.1 General
9.3.2 Final event rate at initial state (0, 0) for unrepeatable final event
55 9.3.3 Final event rate at recognised state (x, y)
Figure 14 ā€“ FT for an unrepeatable final event at initial state (0,0)
FigureĀ 15 ā€“ State transition model for an unrepeatable final event at initial state (0,0)
56 9.3.4 Final event rate at a recognised group state
FigureĀ 16 ā€“ FT for an unrepeatable final event for recognised state (0,1)
Figure 17 ā€“ State transition model for recognised state (0,1)
57 Figure 18 ā€“ FT for an unrepeatable final event for recognised group state G1
58 9.4 Final protection layer arranged in a 1-out-of-2 architecture system
9.4.1 General
FigureĀ 19 ā€“ State transition model for recognised group state G1
59 9.4.2 Independent failure parts of the 1-out-of-2 architecture system
Figure 20 ā€“ RBD of FPL arranged in a 1-out-of-2 architecture system
Figure 21 ā€“ RBD of the independent parts of Ch 1 and Ch 2
60 9.4.3 Fault tree for independent undetected and detected failures
9.4.4 Final event rate at a given initial state owing to independent failures
Figure 22 ā€“ RBD equivalent to that in Figure 21
FigureĀ 23 ā€“ FT for UD failure of Ch 1, D failure of Ch 2 and demand
61 9.4.5 Recognised states at each part
Figure 24 ā€“ State transitions due to UD failure of Ch 1, D failure of Ch 2 and demand
62 9.4.6 Recognised (group) states and final states for the overall system
63 9.5 Common cause failures between protection layers and complexity of a system
9.6 Summary and remarks
64 Annex A (informative) Risk owing to fault recognised only by demand
A.1 Demand, detection and failure logic
Figure A.1 ā€“ Reliability bock diagram with independent and common cause failures
65 Figure A.2 ā€“ Fault tree of unrepeatable final event due to DU failures
66 A.2 Final event rate at a given initial state
Figure A.3 ā€“ State transition model for unrepeatable final event caused by DU failures
67 A.3 Comparison between new and conventional analyses
69 A.4 Further development
Figure A.4 ā€“ Comparison between analyses of r(Ī»M) and Ļ–
70 A.5 Summary and remarks
71 Annex B (informative) Application to functional safety
B.1 Risk-based target failure measures in functional safety
72 B.2 Safe/dangerous system states and failures
74 B.3 Complexity of safety-related systems
Table B.1 ā€“ Relationship between failure modes, hazards, and safe/dangerous failures
75 B.4 Comparison between conventional and new analyses
76 B.5 Splitting up mode of operation
Figure B.1 ā€“ Comparison between conventional and new analyses
77 B.6 Tolerable hazardous/harmful event rate and residual risk
B.7 Procedure for determining the safety integrity level (SIL) of an item
78 B.8 Summary and remarks
TableĀ B.2 ā€“ Safety integrity levels (SILs) in IECĀ 61508 (all parts)
79 Bibliography

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BSI PD IEC/TR 63039:2016
$215.11