EN 61025:2007

SLOVENSKI STANDARD
01-januar-2008
1DGRPHãþD
SIST HD 617 S1:2004
Analiza drevesa okvar (FTA) (IEC 61025:2006)
Fault tree analysis (FTA)
Fehlzustandsbaumanalyse
Analyse par arbre de panne (AAP)
Ta slovenski standard je istoveten z: EN 61025:2007
ICS:
03.120.01 Kakovost na splošno Quality in general
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61025
NORME EUROPÉENNE
April 2007
EUROPÄISCHE NORM
ICS 03.120.01; 03.120.99 Supersedes HD 617 S1:1992

English version
Fault tree analysis (FTA)
(IEC 61025:2006)
Analyse par arbre de panne (AAP) Fehlzustandsbaumanalyse
(CEI 61025:2006) (IEC 61025:2006)

This European Standard was approved by CENELEC on 2007-03-01. 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, 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

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61025:2007 E
Foreword
The text of document 56/1142/FDIS, future edition 2 of IEC 61025, prepared by IEC TC 56,
Dependability, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61025 on 2007-03-01.
This European Standard supersedes HD 617 S1:1992.
The main changes with respect to HD 617 S1:1992 are as follows:
– added detailed explanations of fault tree methodologies;
– added quantitative and reliability aspects of Fault Tree Analysis (FTA);
– expanded relationship with other dependability techniques;
– added examples of analyses and methods explained in this standard;
– updated symbols currently in use.
Clause 7, dealing with analysis, has been revised to address traditional logic fault tree analysis separately
from the quantitative analysis that has been used for many years already, for reliability improvement of
products in their development stage.
Some material included previously in the body of this standard has been transferred to Annexes A and B.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-12-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-03-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61025:2006 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:
IEC 60300-3-1 NOTE  Harmonized as EN 60300-3-1:2004 (not modified).
IEC 60812 NOTE  Harmonized as EN 60812:2006 (not modified).
IEC 61078 NOTE  Harmonized as EN 61078:2006 (not modified).
__________
- 3 - EN 61025:2007
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

1)
IEC 60050-191 - International Electrotechnical Vocabulary - -
(IEV) -
Chapter 191: Dependability and quality of
service
1) 2)
IEC 61165 - Application of Markov techniques EN 61165 2006

1)
Undated reference.
2)
Valid edition at date of issue.

IEC 61025
Edition 2.0 2006-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Fault tree analysis (FTA)
Analyse par arbre de panne (AAP)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 03.120.01; 03.120.99 ISBN 2-8318-8918-9

61025 © IEC:2006 –– 2 – 3 – 61025 © IEC:2006
CONTENTS
FOREWORD.4
INTRODUCTION.6

1 Scope.7
2 Normative references .7
3 Terms and definitions .7
4 Symbols .10
5 General .11
5.1 Fault tree description and structure .11
5.2 Objectives .12
5.3 Applications.12
5.4 Combinations with other reliability analysis techniques.13
6 Development and evaluation .15
6.1 General considerations.15
6.2 Required system information .18
6.3 Fault tree graphical description and structure .19
7 Fault tree development and evaluation .20
7.1 General .20
7.2 Scope of analysis .20
7.3 System familiarization .20
7.4 Fault tree development.20
7.5 Fault tree construction.21
7.6 Failure rates in fault tree analysis.38
8 Identification and labelling in a fault tree .38
9 Report .39

Annex A (informative) Symbols .41
Annex B (informative) Detailed procedure for disjointing .48

Bibliography.52

Figure 1 – Explanation of terms used in fault tree analyses.10
Figure 2 – Fault tree representation of a series structure .23
Figure 3 – Fault tree representation of parallel, active redundancy .24
Figure 4 – En example of fault tree showing different gate types.26
Figure 5 – Rectangular gate and events representation .27
Figure 6 – An example fault tree containing a repeated and a transfer event .28
Figure 7 – Example showing common cause considerations in rectangular gate
representation.28
Figure 8 – Bridge circuit example to be analysed by a fault tree.32
Figure 9 – Fault tree representation of the bridge circuit .33
Figure 10 – Bridge system FTA, Esary-Proschan, no disjointing.35

61025 © IEC:2006 61025 © IEC:2006 –– 3 – 5 –
Figure 11 – Bridge system probability of failure calculated with rare-event
approximation .36
Figure 12 – Probability of occurrence of the top event with disjointing.37
Figure A.1 – Example of a PAND gate .47

Table A.1 – Frequently used symbols for a fault tree.41
Table A.2 – Common symbols for events and event description .44
Table A.3 – Static gates.45
Table A.4 – Dynamic gates .46

61025 © IEC:2006 –– 4 – 7 – 61025 © IEC:2006
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FAULT TREE ANALYSIS (FTA)
FOREWORD
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