SIST EN 62502:2011
Analysis techniques for dependability - Event tree analysis (ETA) (IEC 62502:2010)
Analysis techniques for dependability - Event tree analysis (ETA) (IEC 62502:2010)
This International Standard specifies the consolidated basic principles of Event Tree Analysis (ETA) and provides guidance on modelling the consequences of an initiating event as well as analysing these consequences qualitatively and quantitatively in the context of dependability and risk related measures. More specifically, this standard deals with the following topics in relation to event trees: a) defining the essential terms and describing the usage of symbols and ways of graphical representation; b) specifying the procedural steps involved in the construction of the event tree; c) elaborating on the assumptions, limitations and benefits of performing the analysis; d) identifying relationships with other dependability and risk-related techniques and elucidating suitable fields of applications; e) giving guidelines for the qualitative and quantitative aspects of the evaluation; f) providing practical examples. This standard is applicable to all industries where the dependability and risk-related measures for the consequences of an initiating event have to be assessed.
Verfahren zur Analyse der Zuverlässigkeit - Ereignisbaumanalyse (ETA) (IEC 62502:2010)
Techniques d'analyse de la sûreté de fonctionnement - Analyse par arbre d'événement (AAE) (CEI 62502:2010)
La CEI 62502:2010 spécifie les principes de base consolidés de l'Analyse par Arbre d'Evénement (AAE) et donne les lignes directrices pour la modélisation des conséquences d'un événement initiateur, ainsi que pour l'analyse de ces conséquences d'un point de vue qualitatif et quantitatif dans le cadre de mesures liées à la sûreté de fonctionnement et aux risques.
Tehnične analize zagotovljivosti - Analiza z drevesom dogodkov (ETA) (IEC 62502:2010)
Ta mednarodni standard določa konsolidirana osnovna načela analize z drevesom dogodkov (ETA) in podaja vodilo o modeliranju posledic začetnega dogodka, kot tudi o kvalitativnem in kvantitativnem analiziranju teh posledic v okviru zagotovljivosti in ukrepov, povezanih s tveganji. Bolj podrobno ta standard obravnava naslednje teme v zvezi z drevesom dogodkov: a) opredeljevanje bistvenih izrazov in opisovanje uporabe simbolov in načinov grafične predstavitve; b) določevanje postopkovnih korakov, potrebnih za zgradbo drevesa dogodkov; c) izpopolnjevanje predpostavk, omejitev in koristi pri izvajanju analize; d) prepoznavanje odnosov z drugimi tehnikami zagotovljivosti in tehnikami, povezanimi s tveganji ter pojasnjevanje primernih področij uporabe; e) podajanje smernic za kvalitativne in kvantitativne vidike ocenjevanja; f) zagotavljanje praktičnih primerov. Ta standard velja za vse industrije, kjer se ocenjujejo ukrepi zagotovljivosti, in ukrepi, povezani s tveganji, za posledice začetnega dogodka.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 62502:2011
01-januar-2011
7HKQLþQHDQDOL]H]DJRWRYOMLYRVWL$QDOL]D]GUHYHVRPGRJRGNRY (7$ ,(&
Analysis techniques for dependability - Event tree analysis (ETA) (IEC 62502:2010)
Verfahren zur Analyse der Zuverlässigkeit - Ereignisbaumanalyse (ETA) (IEC
62502:2010)
Techniques d'analyse de la sûreté de fonctionnement - Analyse par arbre d'événement
(AAE) (CEI 62502:2010)
Ta slovenski standard je istoveten z: EN 62502:2010
ICS:
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
SIST EN 62502:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 62502:2011
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SIST EN 62502:2011
EUROPEAN STANDARD
EN 62502
NORME EUROPÉENNE
November 2010
EUROPÄISCHE NORM
ICS 21.020
English version
Analysis techniques for dependability -
Event tree analysis (ETA)
(IEC 62502:2010)
Techniques d'analyse de la sûreté de Verfahren zur Analyse
fonctionnement - der Zuverlässigkeit -
Analyse par arbre d'événement (AAE) Ereignisbaumanalyse (ETA)
(CEI 62502:2010) (IEC 62502:2010)
This European Standard was approved by CENELEC on 2010-11-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.
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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 62502:2010 E
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SIST EN 62502:2011
EN 62502:2010 - 2 -
Foreword
The text of document 56/1380/FDIS, future edition 1 of IEC 62502, prepared by IEC TC 56,
Dependability, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 62502 on 2010-11-01.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
(dop) 2011-08-01
national standard or by endorsement
– latest date by which the national standards conflicting
(dow) 2013-11-01
with the EN have to be withdrawn
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 62502:2010 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
[12] ISO/IEC 31010 NOTE Harmonized as EN 31010.
[13] IEC 60300-3-1:2003 NOTE Harmonized as EN 60300-3-1:2004 (not modified).
[15] IEC 60812:2006 NOTE Harmonized as EN 60812:2006 (not modified)
[16] IEC 61078:2006 NOTE Harmonized as EN 61078:2006 (not modified)
[17] IEC 61165:2006 NOTE Harmonized as EN 61165:2006 (not modified)
[18] IEC 61508 series NOTE Harmonized in EN 61508 series (not modified)
[19] IEC 61511-3:2003 NOTE Harmonized as EN 61511-3:2004 (not modified)
[20] IEC 61703:2001 NOTE Harmonized as EN 61703:2002 (not modified)
[22] IEC 62429:2007 NOTE Harmonized as EN 62429:2008 (not modified)
[23] IEC 62508:2010 NOTE Harmonized as EN 62508:2010 (not modified)
1) 2)
[24] IEC 62551 NOTE Harmonized as EN 62551 (not modified)
__________
1)
To be published.
2)
At draft stage.
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SIST EN 62502:2011
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Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application 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 When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year
IEC 60050-191 1990 International Electrotechnical Vocabulary - -
(IEV) -
Chapter 191: Dependability and quality of
service
IEC 61025 2006 Fault Tree Analysis (FTA) EN 61025 2007
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SIST EN 62502:2011
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SIST EN 62502:2011
IEC 62502
®
Edition 1.0 2010-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Analysis techniques for dependability – Event tree analysis (ETA)
Techniques d’analyse de la sûreté de fonctionnement – Analyse par arbre
d’événement (AAE)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 21.020 ISBN 978-2-88912-212-7
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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SIST EN 62502:2011
– 2 – 62502 © IEC:2010
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms, definitions, abbreviations and symbols.7
3.1 Terms and definitions .7
3.2 Abbreviations and symbols.8
3.2.1 Abbreviations .8
3.2.2 Symbols .9
4 General description .9
5 Benefits and limitations of ETA.11
5.1 Benefits.11
5.2 Limitations.11
6 Relationship with other analysis techniques.12
6.1 Combination of ETA and FTA .12
6.2 Layer of protection analysis (LOPA) .13
6.3 Combination with other techniques .13
7 Development of event trees .14
7.1 General .14
7.2 Steps in ETA .14
7.2.1 Procedure.14
7.2.2 Step 1: Definition of the system or activity of interest.15
7.2.3 Step 2: Identification of the initiating events of interest .15
7.2.4 Step 3: Identification of mitigating factors and physical phenomena.16
7.2.5 Step 4: Definition of sequences and outcomes, and their
quantification.16
7.2.6 Step 5: Analysis of the outcomes.17
7.2.7 Step 6: Uses of ETA results.17
8 Evaluation .18
8.1 Preliminary remarks .18
8.2 Qualitative analysis – Managing dependencies.18
8.2.1 General .18
8.2.2 Functional dependencies .19
8.2.3 Structural or physical dependencies .20
8.3 Quantitative analysis .22
8.3.1 Independent sequence of events .22
8.3.2 Fault tree linking and boolean reduction .23
9 Documentation .24
Annex A (informative) Graphical representation .26
Annex B (informative) Examples .27
Bibliography.41
10
Figure 1 – Process for development of event trees .
Figure 2 – Simple graphical representation of an event tree.18
Figure 3 – Functional dependencies in event trees .20
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62502 © IEC:2010 – 3 –
Figure 4 – Modelling of structural or physical dependencies.21
Figure 5 – Sequence of events .22
Figure 6 – Fault tree linking .23
Figure A.1 – Frequently used graphical representation for event trees .26
Figure B.1 – Event tree for a typical fire incident in a diesel generator building.28
Figure B.2 – Simplified event tree for a fire event .29
Figure B.3 – Level-crossing system (LX).31
Figure B.4 – ETA for the level-crossing system.33
Figure B.5 – Simple example .36
Figure B.6 – Fault Tree for the Failure of System 1.36
Figure B.7 – Fault Tree for the Failure of System 2.37
Figure B.8 – Modified event tree .38
Figure B.9 – Event tree with "grouped faults" .39
Table A.1 – Graphical elements .26
Table B.1 – Symbols used in Annex B .29
Table B.2 – System overview.31
Table B.3 – Risk reduction parameters for accidents from Figure B.4 .34
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ANALYSIS TECHNIQUES FOR DEPENDABILITY –
EVENT TREE ANALYSIS (ETA)
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.
International Standard IEC 62502 has been prepared by IEC technical committee 56:
Dependability.
The text of this standard is based on the following documents:
FDIS Report on voting
56/1380/FDIS 56/1389/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.
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SIST EN 62502:2011
62502 © IEC:2010 – 5 –
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
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INTRODUCTION
This International Standard defines the basic principles and procedures for the dependability
technique known as Event Tree Analysis (ETA).
IEC 60300-3-1 explicitly lists ETA as an applicable method for general dependability
assessment. It is also used in risk and safety analysis studies. ETA is also briefly described in
the IEC 60300-3-9.
The basic principles of this methodology have not changed since the conception of the
technique in the 1960's. ETA was first successfully used in the nuclear industry in a study by
the U.S. Nuclear Regulatory Commission, the so-called WASH 1400 report in the year 1975
1
[31] .
Over the following years, ETA has gained widespread acceptance as a mature methodology
for dependability and risk analysis and is applied in diverse industry branches ranging from
the aviation industry, nuclear installations, the automotive industry, chemical processing,
offshore oil and gas production, to defence industry and transportation systems.
In contrast to some other dependability techniques such as Markov modelling, ETA is based
on relatively elementary mathematical principles. However, as mentioned in IEC 60300-3-1,
the implementation of ETA requires a high degree of expertise in the application of the
technique. This is due in part to the fact that particular care has to be taken when dealing with
dependent events. Furthermore, one can utilize the close relationship between Fault Tree
Analysis (FTA) and the qualitative and quantitative analysis of event trees.
This standard aims at defining the consolidated basic principles of the ETA and the current
usage of the technique as a means for assessing the dependability and risk related measures
of a system.
___________
1
Figures in square brackets refer to the bibliography.
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62502 © IEC:2010 – 7 –
ANALYSIS TECHNIQUES FOR DEPENDABILITY –
EVENT TREE ANALYSIS (ETA)
1 Scope
This International Standard specifies the consolidated basic principles of Event Tree Analysis
(ETA) and provides guidance on modelling the consequences of an initiating event as well as
analysing these consequences qualitatively and quantitatively in the context of dependability
and risk related measures.
More specifically, this standard deals with the following topics in relation to event trees:
a) defining the essential terms and describing the usage of symbols and ways of graphical
representation;
b) specifying the procedural steps involved in the construction of the event tree;
c) elaborating on the assumptions, limitations and benefits of performing the analysis;
d) identifying relationships with other dependability and risk-related techniques and
elucidating suitable fields of applications;
e) giving guidelines for the qualitative and quantitative aspects of the evaluation;
f) providing practical examples.
This standard is applicable to all industries where the dependability and risk-related measures
for the consequences of an initiating event have to be assessed.
2 Normative references
The following referenced documents are indispensable for the application 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 60050-191:1990, International Electrotechnical Vocabulary – Chapter 191: Dependability
and quality of service
IEC 61025:2006, Fault tree analysis (FTA)
3 Terms, definitions, abbreviations and symbols
For the purposes of this document, the following terms and definitions, as well as those given
in IEC 60050-191, apply.
3.1 Terms and definitions
3.1.1
node
point in the graphical representation of the event tree depicting two or more possible
outcomes for the mitigating factor
NOTE The top event of the corresponding fault tree can directly be linked to a node.
3.1.2
common cause
cause of occurrence of multiple events
[IEC 61025:2006, 3.15]
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NOTE Under particular circumstances the timeframe should be specified in which the multiple events occur, such
as “occurrence of multiple events occurring simultaneously or within a very short time of each other”.
EXAMPLES Particular natural dangers (e.g. fire, flood), failures of an engineered system, biological infections or
human acts.
3.1.3
event
occurrence of a condition or an action
[IEC 61025:2006, 3.8]
3.1.4
headings
listed mitigating factors in a line above the depiction of the event tree
3.1.5
initiating event
event which is the starting point of the event tree and the sequence of events that may lead to
different possible outcomes
3.1.6
mitigating factor
system, function or other circumstantial factor mitigating the consequences of the initiating
event
NOTE Many industries have specific equivalent terms, e.g. lines of defense, protection lines, protection systems,
safety barriers, lines of assurance, risk reduction factor, etc.
3.1.7
outcome
possible result of the sequence of events after all reactions of relevant mitigating factors have
been considered and no further development of the event tree is required
3.1.8
sequence
chain of events, from the initiating event, through subsequent events, leading to a specific
outcome
3.1.9
top event
predefined undesired event which is the starting point of the fault tree analysis, and is of
primary interest in the analysis. It has the top position in the hierarchy of events in the fault
tree
NOTE It is the outcome of combinations of all input events.
3.1.10
branch
graphical representation of one out of two or more possible outcomes originating from a node
3.2 Abbreviations and symbols
3.2.1 Abbreviations
CCA Cause-Consequence Analysis
ETA Event Tree Analysis
FMEA Failure Mode and Effects Analysis
FTA Fault Tree Analysis
IRF Individual Risk of Fatality
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62502 © IEC:2010 – 9 –
LESF Combination of two dependability techniques: Large Event Trees (LE)
with connected Small Fault Trees (SF)
LOPA Layers Of Protection Analysis
RBD Reliability Block Diagrams
PRA Probabilistic Risk Assessment
PRA/PSA Probabilistic Risk/Safety Analysis
SELF Combination of two dependability techniques: Small Event Trees (SE)
with connected Large Fault Trees (LF)
3.2.2 Symbols
A When used in italics, an upper case letter indicates that the event A has
occurred.
A When used in italics with a bar, an upper case letter indicates that the event
A has not occurred.
I When used in italics, this indicates that the initiating event has occurred.
E
O This denotes the outcome which results, if all of the events in the subscript
I ,A,B
E
(with upper case letters in italics separated by commas) have occurred in
the order of the events stated in the subscript (see an example in Figure 3).
α,K,δ Lower case Greek letters denote particular outcomes of the event tree.
“+” This symbol denotes a logical “OR”.
“.” This symbol denotes a logical “AND”.
P()A Probability of an event A. P(A) is a real number in the closed interval [0,1]
assigned to an event, see [25 ].
P()I . A.B .C
E
Probability that the initiating event I has occurred and event A has occurred
E
and event B has not occurred and event C has not occurred.
P()A | I
E
Conditional probability of event A given that the initiating event I has
E
occurred.
f
Frequency (the number of events per unit of time, see [ 25] ) .
f
Frequency of outcome δ .
δ
4 General description
Event tree analysis (ETA) is an inductive procedure to model the possible outcomes that
could ensue from a given initiating event and the status of the mitigating factors as well as to
identify and assess the frequency or probability of the various possible outcomes of a given
initiating event.
The graphical representation of an event tree requires that symbols, identifiers and labels be
used in a consistent manner. Since the representation of event trees varies with user
preference, a collection of commonly used graphical representations is given in An nex A.
Starting from an initiating event, the ETA deals with the question "What happens if.". Based
on this question, the analyst constructs a tree of the various possible outcomes. It is therefore
crucial that a comprehensive list of initiating events is compiled to ensure that the event trees
properly depict all the important event sequences for the system under consideration. Using
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this logic, the ETA can be described as a method of representing the mitigating factors in
response to the initiating event – taking into account applicable mitigating factors.
From the qualitative point of view, ETA helps to identify all potential accident scenarios
(fanning out like a tree with success- or failure-branches) and potential design or procedural
weaknesses. The success branch models the condition that the mitigating factor is operating
as intended. As with other analysis techniques, particular care has to be taken with the
modelling of dependencies, bearing in mind that the probabilities used for quantifying the
event tree are conditioned on the event sequence that occurred prior to the occurrence of the
event concerned. Clause 8 deals with these qualitative aspects of the analysis as well as the
basic quantitative rules for the calculations required to estimate the (dimensionless)
probabilities or frequencies (1/h) of each of the possible outcomes. Though one could, in
theory, model the effect of failures of the operator or software by an event tree, this standard
does not deal with their quantification since these issues are covered by other IEC
publications, e.g. IEC 62508 [23] and IEC 62429 [22].
The advantages of ETA as a dependability and risk-related technique, as well as the
limitations, are discussed in Clause 5. As an example of the limitations of ETA, the time-
dependent evolution has to be considered cautiously because it can be handled properly only
in particular cases. This limitation has led to the development of strongly related methods
such as the dynamic event tree analysis method, which facilitate the modelling of time-
dependent evolutions. This dynamic event tree analysis method will not be detailed in this
standard; however, references are included in the bibliography for further information.
ETA bears a close relationship with FTA whereby the top events of the FTA yield the
conditional probability for a particular node of the ETA. This is explained more fully in
Clause 6 which also covers the relationships between ETA and other analysis techniques
such as cause-consequence analysis (CCA) and layer of protection analysis (LOPA). CCA
combines cause analysis and consequence analysis hence using deductive and inductive
approaches. LOPA has been developed by the process industry as a special adaptation of the
ETA.
7
Since the first steps and a well constructed approach are crucial for success, Clause
describes the development of the event tree, starting with a precise system definition.
Furthermore, Clause 7 deals with the different aspects of the system (technical, operational,
human and func
...
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