EN 62740:2015

Root cause analysis (RCA)

IEC 62740:2015 describes the basic principles of root cause analysis (RCA) and specifies the steps that a process for RCA should include. This standard identifies a number of attributes for RCA techniques which assist with the selection of an appropriate technique. It describes each RCA technique and its relative strengths and weaknesses. RCA is used to analyse the root causes of focus events with both positive and negative outcomes, but it is most commonly used for the analysis of failures and incidents. Causes for such events can be varied in nature, including design processes and techniques, organizational characteristics, human aspects and external events. RCA can be used for investigating the causes of non-conformances in quality (and other) management systems as well as for failure analysis, for example in maintenance or equipment testing. RCA is used to analyse focus events that have occurred, therefore this standard only covers a posteriori analyses. It is recognized that some of the RCA techniques with adaptation can be used proactively in the design and development of items and for causal analysis during risk assessment; however, this standard focuses on the analysis of events which have occurred. The intent of this standard is to describe a process for performing RCA and to explain the techniques for identifying root causes. These techniques are not designed to assign responsibility or liability, which is outside the scope of this standard. Keywords: root cause analysis (RCA), RCA techniques

Grundursachenanalyse

Analyse de cause initiale (RCA)

L'IEC 62740:2015 décrit les principes basiques de l'analyse de cause initiale (RCA) et spécifie les étapes qu'il convient qu'un processus de RCA inclue. La présente norme identifie plusieurs attributs de techniques de RCA, qui aident à sélectionner la technique appropriée. Elle décrit chaque technique de RCA, ainsi que ses points forts et limites. La RCA est utilisée pour analyser les causes initiales des événements d'accent, que leurs conséquences soient positives ou négatives, mais est plus couramment utilisée pour l'analyse des défaillances et des accidents. Les causes de tels événements peuvent être de nature multiple, notamment en fonction de la conception, des processus et des techniques, des caractéristiques organisationnelles, des aspects humains et des événements externes. La RCA peut être utilisée pour étudier les causes de non-conformité en termes de qualité (ou autres) des systèmes de gestion ainsi que pour l'analyse des défaillances, par exemple lors de la maintenance ou de l'essai des équipements. La RCA est utilisée pour analyser des événements d'accent qui se sont produits, cette norme ne couvre donc que les analyses a posteriori. Il est reconnu que certaines des techniques de RCA avec adaptations peuvent être utilisées de manière proactive lors de la conception et du développement d'entités et pour l'analyse causale au cours de l'évaluation des risques; cependant, la présente norme met l'accent sur l'analyse des événements qui se sont produits. L'objectif de la présente norme est de décrire un processus en vue de réaliser une RCA et d'expliquer les techniques permettant d'identifier les causes initiales. Lesdites techniques n'ont pas été conçues pour identifier la responsabilité ou la fiabilité, car ceci ne fait pas partie du domaine d'application de la présente norme. Mots clés: analyse de cause initiale (RCA), de techniques de RCA

Analiza izvornih razlogov (RCA) (IEC 62740:2015)

Ta mednarodni standard opisuje osnovne principe analize izvornih razlogov (RCA) in določa korake, ki jih mora proces analize izvornih razlogov vključevati. Ta standard opredeljuje več lastnosti tehnik RCA, ki so v pomoč pri izbiri primerne tehnike. Vsebuje opis vseh RCA tehnik ter njihovih prednosti in slabosti. RCA se uporablja za analizo izvornih razlogov ključnih dogodkov s pozitivnimi in negativnimi rezultati, vendar se najpogosteje uporablja za analizo okvar in incidentov. Razlogi za take dogodke se lahko razlikujejo, mednje pa spadajo procesi in tehnike načrtovanja, organizacijske lastnosti, človeški dejavniki in zunanji dogodki. RCA se lahko uporablja za iskanje vzrokov za neskladnosti pri sistemih vodenja kakovosti (in drugih sistemih vodenja), kot tudi za analizo okvar, na primer pri vzdrževanju in preskušanju opreme. RCA se uporablja za analizo ključnih dogodkov, ki so se zgodili, torej ta standard zajema samo
posteriorne analize. Priznava se, da se nekatere prilagojene RCA tehnike lahko uporablja proaktivno pri načrtovanju in razvoju izdelkov in za vzročno analizo med ocenjevanjem tveganja, vendar se ta standard osredotoča na analizo dogodkov, ki so se že zgodili. Namen tega standarda je opis postopka izvedbe RCA on razlaga tehnik za prepoznavanje izvornih razlogov. Te tehnike niso zasnovane za dodeljevanje odgovornosti ali določanje krivde, kar je zunaj področja uporabe tega standarda.

General Information

• Status: Published
• Publication Date: 02-Apr-2015
• Withdrawal Date: 19-Mar-2018
• ICS: 03.120.01 - Quality in general
• Technical Committee: CLC/SR 56 - Dependability
• Drafting Committee: IEC/TC 56 - IEC_TC_56
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 03-Apr-2015
• Completion Date: 03-Apr-2015
• Ref Project: SIST EN 62740:2015 - Root cause analysis (RCA) (IEC 62740:2015)

Overview

EN 62740:2015 (IEC 62740:2015), published by CLC/CENELEC, defines the basic principles and a structured process for root cause analysis (RCA). The standard describes the steps an a posteriori RCA should include - from initiation and fact‑gathering to analysis, validation and presentation of results - and provides attributes to help select appropriate RCA techniques. While primarily focused on investigating events that have already occurred (failures, incidents, non‑conformances), it notes that some techniques can be adapted for proactive design and risk assessment.

Key topics

• RCA process steps: initiation, establishing facts, analysis, validation, and presentation of results.
• Technique selection: criteria and attributes for choosing suitable RCA techniques based on the event, context and objectives.
• Described techniques and models: the standard summarizes and evaluates commonly used methods and their strengths/limitations, including (but not limited to):
  • Events and Causal Factors (ECF) charting
  • Multilinear Events Sequencing (MES) / STEP
  • The “Why” method and Why‑Because Analysis (WBA)
  • Causes Tree Method (CTM) and Cause Trees
  • Fault Tree and Success Tree analysis
  • Fishbone / Ishikawa diagrams
  • Barrier analysis and Reason’s (Swiss cheese) model
  • AcciMaps, Tripod Beta, MORT, and systems approaches (STAMP/CAST)
• Supporting tools and annexes: guidance on data‑mining/clustering, human performance analysis (TRACEr, HFACS), and practical tools to assist RCA.
• Scope limits: focuses on causal analysis, not on assigning legal responsibility or liability.

Applications

• Investigating root causes of equipment failures, safety incidents and non‑conformances in quality and management systems.
• Supporting maintenance and reliability troubleshooting, safety investigations, and post‑incident learning.
• Informing corrective actions and organizational learning to prevent recurrence.
• Providing structured input to risk assessments if techniques are adapted proactively.

Who should use this standard

• Quality, safety and reliability managers
• Safety investigators and incident analysts
• Maintenance and engineering teams
• Risk assessment and compliance professionals
• Human factors specialists

Related standards

EN 62740:2015 references or aligns with other harmonized standards such as EN 60300‑1, EN 61025, EN 61649, EN 61163‑1, EN 62508:2010, and EN 31010:2010 for risk and reliability methods.

EN 62740:2015 is a practical, technique‑focused reference for organizations wanting a standardized, objective approach to root cause analysis and selection of RCA techniques.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2015
Analiza izvornih razlogov (RCA) (IEC 62740:2015)
Root cause analysis (RCA) (IEC 62740:2015)
Ursachenanalyse (IEC 62740:2015)
Analyse de cause initiale (RCA) (IEC 62740:2015)
Ta slovenski standard je istoveten z: EN 62740:2015
ICS:
03.120.01 Kakovost na splošno Quality in general
29.020 Elektrotehnika na splošno Electrical engineering in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 62740
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2015
ICS 03.120.01
English Version
Root cause analysis (RCA)
(IEC 62740:2015)
Analyse de cause initiale (RCA) Ursachenanalyse
(IEC 62740:2015) (IEC 62740:2015)
This European Standard was approved by CENELEC on 2015-03-20. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 62740:2015 E
Foreword
The text of document 56/1590/FDIS, future edition 1 of IEC 62740, prepared by IEC/TC 56
"Dependability" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be (dop) 2015-12-20
implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2018-03-20
• latest date by which the national
standards conflicting with the
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 62740:2015 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 60300-1 NOTE Harmonized as EN 60300-1.
IEC 61025 NOTE Harmonized as EN 61025.
IEC 61649 NOTE Harmonized as EN 61649.
IEC 61163-1 NOTE Harmonized as EN 61163-1.
IEC 62508:2010 NOTE Harmonized as EN 62508:2010 (not modified).
ISO/IEC 31010:2009 NOTE Harmonized as EN 31010:2010 (not modified).

- 3 - EN 62740:2015
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050 Series - International Electrotechnical Vocabulary - -
(IEV)
IEC 62740 ®
Edition 1.0 2015-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Root cause analysis (RCA)
Analyse de cause initiale (RCA)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 03.120.01 ISBN 978-2-8322-2246-1

– 2 – IEC 62740:2015 © IEC 2015
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 9
3 Terms, definitions and abbreviations . 9
3.1 Terms and definitions . 9
3.2 Abbreviations . 12
4 RCA – Overview . 12
5 The RCA process . 13
5.1 Overview. 13
5.2 Initiation . 14
5.3 Establishing facts . 15
5.4 Analysis . 17
5.4.1 Description . 17
5.4.2 The analysis team . 18
5.5 Validation . 19
5.6 Presentation of results . 19
6 Selection of techniques for analysing causes . 20
6.1 General . 20
6.2 Selection of analysis techniques . 20
6.3 Useful tools to assist RCA. 21
Annex A (informative) Summary and criteria of commonly used RCA techniques . 22
A.1 General . 22
A.2 RCA techniques . 22
A.3 Criteria . 23
Annex B (informative) RCA models . 26
B.1 General . 26
B.2 Barrier analysis . 26
B.2.1 Overview . 26
B.2.2 Strengths and limitations . 27
B.3 Reason’s model (Swiss cheese model) . 27
B.3.1 Overview . 27
B.3.2 Strengths and limitations . 28
B.4 Systems models . 28
B.5 Systems theoretic accident model and processes (STAMP) . 29
B.5.1 Overview . 29
B.5.2 Strengths and limitations . 29
Annex C (informative) Detailed description of RCA techniques . 30
C.1 General . 30
C.2 Events and causal factors (ECF) charting . 30
C.2.1 Overview . 30
C.2.2 Process . 31
C.2.3 Strengths and limitations . 31
C.3 Multilinear events sequencing (MES) and sequentially timed events plotting
(STEP) . 32

IEC 62740:2015 © IEC 2015 – 3 –
C.3.1 Overview . 32
C.3.2 Process . 32
C.3.3 Strengths and limitations . 33
C.4 The ‘why’ method . 35
C.4.1 Overview . 35
C.4.2 Process . 36
C.4.3 Strengths and limitations . 36
C.5 Causes tree method (CTM) . 36
C.5.1 Overview . 36
C.5.2 Process . 39
C.5.3 Strengths and limitations . 39
C.6 Why-because analysis (WBA) . 39
C.6.1 Overview . 39
C.6.2 Process . 42
C.6.3 Strengths and limitations . 42
C.7 Fault tree and success tree method . 42
C.7.1 Overview . 42
C.7.2 Process . 43
C.7.3 Strengths and limitations . 44
C.8 Fishbone or Ishikawa diagram . 44
C.8.1 Overview . 44
C.8.2 Process . 45
C.8.3 Strengths and limitations . 46
C.9 Safety through organizational learning (SOL) . 46
C.9.1 Overview . 46
C.9.2 Process . 46
C.9.3 Strengths and limitations . 47
C.10 Management oversight and risk tree (MORT) . 48
C.10.1 Overview . 48
C.10.2 Process . 48
C.10.3 Strengths and limitations . 48
C.11 AcciMaps . 49
C.11.1 Overview . 49
C.11.2 Process . 49
C.11.3 Strengths and limitations . 51
C.12 Tripod Beta . 51
C.12.1 Overview . 51
C.12.2 Process . 52
C.12.3 Strengths and limitations . 52
C.13 Causal analysis using STAMP (CAST) . 53
C.13.1 Overview . 53
C.13.2 Process . 56
C.13.3 Strengths and limitations . 57
Annex D (informative) Useful tools to assist root cause analysis (RCA) . 58
D.1 General . 58
D.2 Data mining and clustering techniques . 58
D.2.1 Overview . 58
D.2.2 Example 1 . 58
D.2.3 Example 2 . 58

– 4 – IEC 62740:2015 © IEC 2015
D.2.4 Example 3 . 59
Annex E (informative) Analysis of human performance . 60
E.1 General . 60
E.2 Analysis of human failure . 60
E.3 Technique for retrospective and predictive analysis of cognitive errors
(TRACEr) . 61
E.3.1 Overview . 61
E.3.2 Process . 62
E.4 Human factors analysis and classification scheme (HFACS) . 63
E.4.1 Overview . 63
E.4.2 Process . 63
Bibliography . 66

Figure 1 – RCA process . 14
Figure B.1 – Broken, ineffective and missing barriers causing the focus event . 26
Figure C.1 – Example of an ECF chart . 31
Figure C.2 – Data in an event building block . 32
Figure C.3 – Example of a time-actor matrix . 34
Figure C.4 – Example of a why tree . 35
Figure C.5 – Symbols and links used in CTM . 37
Figure C.6 – Example of a cause tree . 38
Figure C.7 – Example of a WBG . 41
Figure C.8 – Example of a fault tree during the analysis . 43
Figure C.9 – Example of a Fishbone diagram . 45
Figure C.10 – Example of a MORT diagram . 48
Figure C.11 – Example of an AcciMap . 50
Figure C.12 – Example of a Tripod Beta tree diagram . 52
Figure C.13 – Control structure for the water supply in a small town in Canada . 55
Figure C.14 – Example CAST causal analysis for the local Department of health . 56
Figure C.15 – Example CAST causal analysis for the local public utility operations
management . 56
Figure E.1 – Example of an TRACEr model [25] . 61
Figure E.2 – Generation of internal error modes . 62
Figure E.3 – Level 1: Unsafe acts . 64
Figure E.4 – Level 2: Preconditions . 64
Figure E.5 – Level 3: Supervision Issues . 65
Figure E.6 – Level 4: Organizational Issues . 65

Table 1 – Steps to RCA . 13
Table A.1 – Brief description of RCA techniques . 22
Table A.2 – Summary of RCA technique criteria . 23
Table A.3 – Attributes of the generic RCA techniques . 25
Table B.1 – Examples of barriers . 27
Table B.2 – Example of the barrier analysis worksheet . 27
Table C.1 – Direct and indirect causal factors . 47

IEC 62740:2015 © IEC 2015 – 5 –
Table E.1 – External error modes. 63
Table E.2 – Psychological error mechanisms . 63

– 6 – IEC 62740:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROOT CAUSE ANALYSIS (RCA)
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,
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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.
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services carried out by independent certification bodies.
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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 62740 has been prepared by IEC technical committee 56:
Dependability.
The text of this standard is based on the following documents:
FDIS Report on voting
56/1590/FDIS 56/1608/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.

IEC 62740:2015 © IEC 2015 – 7 –
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.
– 8 – IEC 62740:2015 © IEC 2015
INTRODUCTION
Root cause analysis (RCA) refers to any systematic process that identifies factors that
contributed to a particular event of interest (focus event). RCA is performed with the
understanding that events are addressed by understanding the root causes, rather than the
immediately obvious symptoms. RCA aims to reveal root causes so that either the likelihood
of them occurring, or their impact if they do occur, can be changed.
An important distinction to make is that RCA is used to analyse a focus event that has
occurred and therefore analyses the past (a posteriori). However, knowledge of the root
causes of past events can lead to actions that generate improvements in the future.
This International Standard is intended to reflect current good practices in the conduct of
RCA. This standard is general in nature, so that it may give guidance across many industries
and situations. There may be industry specific standards in existence that establish preferred
methodologies for particular applications. If these standards are in harmony with this
publication, the industry standards will generally be sufficient.
This standard is a generic standard and does not explicitly address safety or accident
investigation although the methods described in this standard may be used for this purpose.

IEC 62740:2015 © IEC 2015 – 9 –
ROOT CAUSE ANALYSIS (RCA)
1 Scope
This International Standard describes the basic principles of root cause analysis (RCA) and
specifies the steps that a process for RCA should include.
This standard identifies a number of attributes for RCA techniques which assist with the
selection of an appropriate technique. It describes each RCA technique and its relative
strengths and weaknesses.
RCA is used to analyse the root causes of focus events with both positive and negative
outcomes, but it is most commonly used for the analysis of failures and incidents. Causes for
such events can be varied in nature, including design processes and techniques,
organizational characteristics, human aspects and external events. RCA can be used for
investigating the causes of non-conformances in quality (and other) management systems as
well as for failure analysis, for example in maintenance or equipment testing.
RCA is used to analyse focus events that have occurred, therefore this standard only covers a
posteriori analyses. It is recognized that some of the RCA techniques with adaptation can be
used proactively in the design and development of items and for causal analysis during risk
assessment; however, this standard focuses on the analysis of events which have occurred.
The intent of this standard is to describe a process for performing RCA and to explain the
techniques for identifying root causes. These techniques are not designed to assign
responsibility or liability, which is outside the scope of this standard.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary
3 Terms, definitions and abbreviations
For the purposes of this document, the definitions given in IEC 60050-192, as well as the
following, apply.
3.1 Terms and definitions
3.1.1
cause
circumstance or set of circumstances that leads to failure or success
Note 1 to entry: A cause may originate during specification, design, manufacture, installation, operation or
maintenance.
[SOURCE: IEC 60050-192:2014, 192-03-11 modified – addition of the words “circumstance
or” and "or success" in the term]

– 10 – IEC 62740:2015 © IEC 2015
3.1.2
causal factor
condition, action, event or state that was necessary or contributed to the occurrence of the
focus event
3.1.3
contributory factor
condition, action, event or state regarded as secondary, according to the occurrence of the
focus event
3.1.4
event
occurrence or change of a particular set of circumstances
Note 1 to entry: An event can be one or more occurrences, and can have several causes.
Note 2 to entry: An event can consist of something not happening.
Note 3 to entry: An event can sometimes be referred to as an “incident” or “accident”.
[SOURCE: ISO Guide 73:2009, 3.5.1.3, modified – Deletion of Note 4 [1]]
3.1.5
failure
loss of ability to perform as required
Note 1 to entry: A failure of an item is an event that results in a fault of that item.
Note 2 to entry: Qualifiers, such as catastrophic, critical, major, minor, marginal and insignificant, may be used to
categorize failures according to the severity of consequences, the choice and definitions of severity criteria
depending upon the field of application.
Note 3 to entry: Qualifiers, such as misuse, mishandling and weakness, may be used to categorize failures
according to the cause of failure.
Note 4 to entry: This is failure of an item, not more generally of behaviour.
[SOURCE: IEC 60050-192:2014, 192-03-01, modified – Introduction of new Note 4]
3.1.6
failure mechanism
process that leads to failure
Note 1 to entry: The process may be physical, chemical, logical, psychological or a combination thereof.
[SOURCE: IEC 60050-192:2014, 192-03-12, modified – the word "psychological" has been
added]
3.1.7
focus event
event which is intended to be explained causally
3.1.8
immediate causal factor
condition, action, event or state where there is no other causal factor between this causal
factor and the focus event
_______________
Numbers in square brackets refer to the Bibliography.

IEC 62740:2015 © IEC 2015 – 11 –
Note 1 to entry: There may be more than one immediate causal factor.
3.1.9
necessary causal factor
condition, action, event or state, that resulted in the given event or state, without which the
given event or state would not have occurred
3.1.10
human error
discrepancy between the human action taken or omitted, and that intended or required
Note 1 to entry: The first edition of IEC 60050-191:1990 identified “mistake” as a synonym for "human error", but
a mistake is a type of human error.
Note 2 to entry: The term human error applies to any situation where the outcome is not as intended whether the
intent of the person was correct or not.
[SOURCE: IEC 60050-192: 2014 192-03-14, modified – Omission of the example, addition of
Note 1 and 2]
3.1.11
item
subject being considered
Note 1 to entry: The item may be an individual part, component, device, functional unit, equipment, subsystem, or
system.
Note 2 to entry: The item may consist of hardware, software, people or any combination thereof.
Note 3 to entry: The item is often comprised of elements that may each be individually considered.
[SOURCE: IEC 60050-192: 2014, 192-01-01, modified – omission of internal references and
Notes 4 and 5]
3.1.12
root cause
causal factor with no predecessor that is relevant for the purpose of the analysis
Note 1 to entry: A focus event normally has more than one root cause.
Note 2 to entry: In some languages, the term root cause refers to the combination of causal factors which have no
causal predecessor (a cut set of causal factors).
3.1.13
root cause analysis
RCA
systematic process to identify the causes of a focus event
Note 1 to entry: IEC 60050-192:2014, definition 192-12-05 provides the following more restrictive definition
“systematic process to identify the cause of a fault, failure or undesired event, so that it can be removed by design,
process or procedure changes”. This standard uses an extended definition to allow a wider applicability of the
process.
Note 2 to entry: This note applies to the French language only.
3.1.14
stakeholder
person or organization that can affect, be affected by, or perceive themselves to be affected
by a decision or activity
[SOURCE: IEC 60300-1:2014, 3.1.15] [2]

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3.1.15
stopping rule
reasoned and explicit means of determining when a causal factor is defined as being a root
cause
3.2 Abbreviations
BGA Ball grid array
CAST Causal analysis using STAMP
CCT Causal completeness test
CT Counterfactual test
CTM Causes tree method
ECF Events and causal factors
EEM External error mode
FTA Fault tree analysis
GEMS Generic error modelling system
HFACS Human factor analysis and classification scheme
IEM Internal error mode
MES Multilinear events sequencing
MORT Management oversight and risk tree
PEM Psychological error mechanism
PSF Performance shaping factors
RCA Root cause analysis
SOL Safety through organizational learning
STAMP Systems theoretic accident model and processes
STEP Sequentially timed events plotting
TRACEr Technique for restrospective and predictive analysis of
cognitive errors
WBA Why-because analysis
4 RCA – Overview
RCA refers to any systematic process that identifies the cause or causes that contribute to a
focus event. The immediate or obvious cause of a focus event is often a symptom of
underlying causes and may not truly identify the root cause or causes that should be identified
and addressed. RCA provides a greater understanding about why events have occurred. RCA
may identify the following:
a) a single root cause;
b) multiple root causes in which the elimination of any cause will prevent the focus event
from occurring;
c) root causes which are contributory factors where elimination will change the likelihood of
the focus event occurring but may not directly prevent it;
d) root causes of successes.
By addressing the root cause or causes it is possible to make decisions regarding appropriate
actions that will generate better outcomes in the future; implementing appropriate actions
based on RCA are more effective at preventing the same or similar events with negative

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outcomes occurring or increasing the probability of repeating events with positive outcomes,
when compared with just addressing the immediately obvious symptoms.
RCA can be applied to any focus event whether success or failure, for example:
1) investigation for technological, medical and occupational focus events;
2) failure analysis of technological systems, to determine why an item failed to perform as
and when required;
3) analysis of quality control and business processes;
4) analysis of successful outcomes.
RCA can be carried out at various levels of decomposition, for example, from system to
component level or by selecting different events or outcomes as a starting point. The level
appropriate to conduct the analysis will be dependent on the focus event.
RCA is used to analyse focus events which have actually occurred and is therefore applicable
during the testing and operational phases of a project or product life cycle. RCA can identify
problems of process including design, quality control, dependability management and project
management.
The benefits of performing RCA include:
• obtaining a greater understanding into what has happened;
• finding the source of problems so corrective action can prevent future events;
• identifying the causes of events with beneficial outcomes so they can be repeated;
• identifying more effective actions to address the causes of focus events;
• achieving the objectives of focus event investigations more effectively;
• supporting traceability between focus event investigation evidence and conclusions;
• increasing consistency between investigations of similar focus events;
• increasing objectivity of focus event analysis.
5 The RCA process
5.1 Overview
To be effective, RCA should be performed systematically as an investigation, with the root
causes and conclusions backed up by documented evidence. To achieve this, RCA should
include the five steps shown in Table 1 and illustrated in Figure 1.
Table 1 – Steps to RCA
Step Concepts and tasks to be performed
Initiation Based on the knowledge available on the focus event, determine the need to carry
out RCA and define the purpose and scope
Establishing facts Collect data and establish the facts of what happened, where, when and by whom
Analysis Use RCA tools and techniques to ascertain how and why the focus event occurred
Validation Distinguish and resolve the different possibilities as to how and why the focus event
was caused
Presentation of results Present the results of the focus event analysis

RCA is iterative in nature, especially for data collection and analysis, in that data is collected
on ‘what’ happened, which is then analysed in order to determine what other data needs to be
collected. Once gathered, further analysis is conducted and any gaps identified, for which

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further data is collected. This process is repeated until the purpose of the analysis is fulfilled
and the root causes identified. The outputs of the RCA will be dependent on its purpose and
scope.
Establish What, How and why Potential
the need, Where, (identify causes
purpose & When & By potential distinguished
scope Whom causes) and resolved
Outputs
Current Data Application of Further data
Knowledge Collection specific tools and testing
Step 5: Presentation
Step 1: Initiation Step 2: Establishing Facts Step 3: Analysis Step 4: Validation
of Results
IEC
Figure 1 – RCA process
5.2 Initiation
The first step initiates the RCA process by evaluating the need to carry out RCA. It defines
the purpose and scope of the analysis, in response to the focus event, and establishes a team
and resources to carry out the RCA.
There is usually some criterion which is used to determine when an RCA is required, which
may include:
• any single event with a large effect;
• multiple similar undesirable events;
• a parameter moving out of a defined tolerance level;
• failures or successes (whatever the level of effect) that involve critical items of equipment
or activities.
When defining the type of events that require the conduct of RCA, it is important to consider
that an event with a large effect may have common root causes to events with minor effects.
Analysing and addressing root causes for events with minor effects may prevent a large effect
event occurring. Examples of events where RCA may be required include: completion of a
project (successes and failures), failures that result in unaccepfigure costs, injury or fatality,
unacceptable performance or delays, large contractual consequences and equipment
breakdown.
If a RCA is required, the focus event(s) to be analysed is/are described and an appropriate
team appointed for the analysis. The description should include the background and context in
which the focus event(s) occurred. A good description of a focus event is short, simple and
easy to understand and should not be biased towards a specific solution. This description is
used to identify appropriate members of the analysis team and ascertain where to start
collecting data.
The purpose and scope of the RCA should be determined, taking into account knowledge of
system, functions, interfaces etc. In some cases, the purpose of the analysis is to identify the
causes of the focus event. In others, the purpose may be broader, for example, to also
identify matters of concern outside those that led to the focus event.

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There are in general two different types of RCA that have different objectives and should not
be mixed up. These two types can be described as follows:
1) analysing a focus event using only verifiable factual information;
2) analysing a focus event to obtain hypotheses of sequences of events and cause.
The first version focuses on observed facts only. It may be an analysis "per se" according to
the purpose of the study and no hypothesis about event occurrence is acceptable for this
analysis. The second can be implemented when sufficient factual information is not available
and hypotheses of potential causes are acceptable for the purpose of the analysis.
The outputs required of the RCA should also be identified. Examples are as follows:
• provide a description of each root cause along with sufficient background information to
allow the identification of suitable actions;
• recommend actions that, taken together, prevent further occurrences of similar events with
adverse consequences and improve the likelihood of successes;
• identify, implement and review actions to address root causes.
RCA can include the analysis of systems in which the boundaries continually evolve and
interact with their environment; this interaction can take the form of information, energy, or
material transfer. Therefore, the scope should specify the boundary of the analysis (what is
included and what is excluded).
The scope of the analysis should where possible include a definition of the ‘stopping rule’,
which is the point at which action can be defined or additional proof of cause is no longer
necessary for the purpose of the analysis. For example, the last point where corrective ac
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