IEC 62508:2010

IEC 62508 ®
Edition 1.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Guidance on human aspects of dependability

Lignes directrices relatives aux facteurs humains dans la sûreté de
fonctionnement
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IEC 62508 ®
Edition 1.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Guidance on human aspects of dependability

Lignes directrices relatives aux facteurs humains dans la sûreté de
fonctionnement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 03.120.01 ISBN 978-2-88912-023-9
– 2 – 62508 © IEC:2010
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms, definitions and abbreviations .7
3.1 Terms and definitions .7
3.2 Abbreviations .10
4 Human aspects.10
4.1 Overview .10
4.2 Components of the system and their interactions.11
4.2.1 Introductory remark .11
4.2.2 Goals.11
4.2.3 Humans.12
4.2.4 Machine (interactive system) .12
4.2.5 Social and physical environment.13
4.2.6 Output .13
4.2.7 Feedback from the machine to the person .13
4.3 Human characteristics .14
4.3.1 Introductory remark .14
4.3.2 Human limitations.14
4.3.3 Comparison of humans and machines .14
4.4 Human performance shaping factors .15
4.4.1 External performance shaping factors.16
4.4.2 Internal performance shaping factors.16
4.5 Human reliability analysis (HRA) .16
4.5.1 Overview .16
4.5.2 Identifying the potential for human error .17
4.5.3 Analysing human failures to define countermeasures .17
4.5.4 Quantification of human reliability.18
4.6 Critical systems.18
4.7 Human-centred design guidelines.19
4.8 Human-centred design process .20
4.8.1 Human-centred design principles within the design process .20
4.8.2 Human-centred design activities .21
5 Human-oriented design in the system lifecycle .21
5.1 Overview .21
5.2 The system life cycle .22
5.3 Integrating human-oriented design in systems engineering.23
6 Human-oriented design at each life cycle stage .24
6.1 Overview .24
6.2 Concept/definition stage.24
6.2.1 Concept.24
6.2.2 Human-centred design planning .24
6.2.3 Understanding needs.25
6.2.4 System requirements.25
6.2.5 Human-centred design requirements .25

62508 © IEC:2010 – 3 –
6.3 Design/development.26
6.4 Realization/implementation.26
6.5 Operation/maintenance .27
6.6 Enhancement .27
6.7 Retirement/decommission .28
6.8 Outsourcing projects and related human-centred design issues.28
7 Human-centred design methods .29
7.1 Classification of human-centred design activities.29
7.2 Applications of human-centred design methods.30
Annex A (informative) Examples of HRA methods.31
Annex B (informative) Summary of human-oriented design activities and their impact
on system dependability .37
Annex C (informative) Best practices for human-centred design.41
Bibliography.47

Figure 1 – Components of the system and their interactions .11
Figure 2 – Human performance shaping factors .16
Figure 3 – Simple model of human information processing.17
Figure 4 – Human-centred design activities .21
Figure 5 – Human aspects of the system life cycle.23

Table 1 – People who influence dependability.12
Table A.1 – HRA methods and their application .31
Table B.1 – Automation .37
Table B.2 – Design for maintainability.37
Table B.3 – Computer-human interface.38
Table B.4 – Incorporation of displays, controls and alarm functions .39
Table B.5 – Incorporation of input devices .39
Table B.6 – Environment.40
Table B.7 – Safety .40
Table B.8 – Security .40
Table C.1 – Examples of methods and techniques that contribute to best practices .41

– 4 – 62508 © IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GUIDANCE ON HUMAN ASPECTS OF DEPENDABILITY

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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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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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 62508 has been prepared by IEC technical committee 56:
Dependability.
This first edition cancels and replaces IEC/PAS 62508 published in 2007.
The text of this standard is based on the following documents:
FDIS Report on voting
56/1365/FDIS 56/1373/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.

62508 © IEC:2010 – 5 –
The committee has decided that the contents of this amendment and the base 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.
– 6 – 62508 © IEC:2010
INTRODUCTION
This International Standard provides guidelines on human aspects of dependability of
systems. It fills the need for a standard to address the dependability of human/machine
systems.
It gives guidance on how the human aspects of dependability can be considered at all the
system life cycle stages, including ergonomic principles during design and human reliability
understanding for system applications.
This standard provides an overview of the principles with some examples of the types of
methods that can be used.
It is intended that a supporting standard, which describes more detailed methods that include
quantification of human reliability will follow the issue of this standard in due course.
This standard contains recommendations, and does not include any requirements. Attention is
drawn to the possibility of the existence of regulatory requirements for systems covered by
the scope of this standard.
62508 © IEC:2010 – 7 –
GUIDANCE ON HUMAN ASPECTS OF DEPENDABILITY

1 Scope
This International Standard provides guidance on the human aspects of dependability, and
the human-centred design methods and practices that can be used throughout the whole
system life cycle to improve dependability performance. This standard describes qualitative
approaches. Examples of quantitative methods are given in Annex A.
This International Standard is applicable to any area of industry where human/machine
relationships exist, and is intended for use by technical personnel and their managers.
This International standard is not intended to be used for certification, regulatory or
contractual use.
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 60300-1:2003, Dependability management – Part 1: Dependability management
systems
IEC 60300-2, Dependability management – Part 2: Guidelines for dependability management
IEC 60300-3-15, Dependability management – Part 3-15: Application guide – Engineering of
system dependability
3 Terms, definitions and abbreviations
For the purposes of this document, the following terms, definitions and abbreviations apply.
NOTE Certain terms have been taken from the draft text of the second edition of IEC 60050-191, International
Electrotechnical Vocabulary – Part 191: Dependability, currently under consideration.
3.1 Terms and definitions
3.1.1
dependability
ability to perform as and when required
NOTE 1 Dependability characteristics include availability and its inherent or external influencing factors, such as
reliability, fault tolerance, recoverability, integrity, security, maintainability, durability and maintenance support.
NOTE 2 Dependability is also used descriptively as an umbrella term for time-related quality characteristics of a
product or service, and it can also be expressed as a grade, degree, confidence or probability of fulfilling a defined
set of characteristics.
NOTE 3 Specifications for dependability characteristics typically include: the function the product is to perform;
the time for which that performance is to be sustained; and the conditions of storage, use and maintenance.
Requirements for safety, efficiency and economy throughout the life cycle can also be included.
___________
Future IEC 60050-191, definition 191-41-26, second edition, under consideration.

– 8 – 62508 © IEC:2010
3.1.2
ergonomics
human factors
HF
scientific discipline concerned with the understanding of interactions among human and other
elements of a system that applies theory, principles, data and methods to design in order to
optimize human well-being and overall system performance
[ISO 6385:2004, definition 2.3, modified]
3.1.3
error resistance
ability of a system to minimize the probability of human error occurring
3.1.4
error tolerance
ability of a system or component to continue normal operation despite the presence of
erroneous inputs
[ISO/IEC 24765:2009, definition 3.1034]
3.1.5
human aspects
abilities, limitations, and other human characteristics that are relevant to the design, operation
and maintenance of systems and/or their components affecting overall system performance
3.1.6
human-centred design
approach to system design and development that aims to make interactive systems more
usable by focussing on the use of the system, applying human factors, ergonomics and
usability knowledge and techniques
NOTE 1 Usable systems provide a number of benefits including improved productivity, enhanced user well-being,
avoidance of stress, increased accessibility, and reduced risk of harm.
NOTE 2 This standard uses the term "human-oriented design" to refer to the need to take account of humans in
system design, but retains the term "human-centred design" used in ISO standards to refer to the specific
principles and activities.
NOTE 3 The term “human-centred design” is used rather than “user-centred design” in order to emphasize that this
standard addresses a number of stakeholders, not just those typically considered as users. However, in practice,
these terms are often used synonymously.
[ISO 9241-210:–, definition 2.7, modified]
3.1.7
human error
discrepancy between the human action taken or omitted, and the action intended
3.1.8
human error probability
HEP
probability that an operator will fail in an assigned task
NOTE 1 This can be based on the ratio of the average number of errors within a certain task in relation to the
overall number of error possibilities for this type of task.
___________
To be published.
Future IEC 60050-191, definition 191-43-13, second edition, under consideration.

62508 © IEC:2010 – 9 –
NOTE 2 Human error probability is expressed in a distribution where the distribution needs to be determined in
accordance with the human variations and situational variations under which the task needs to be conducted.
3.1.9
human failure
deviation from the human action required to achieve the objective, regardless of the cause of
that deviation
NOTE For any particular system or situation the range of human failures is the combination of human errors and
violations that lead to system failures and/or hazardous outcomes.
3.1.10
human-oriented design
takes a user-centric approach to design by adapting technologies to meet human performance
requirements, account for human limitations, achieve mental comfort and enhance overall
system performance
3.1.11
human reliability
capability of human beings to complete a task under a given condition within a defined period
of time and within the acceptance limits
3.1.12
human reliability analysis
HRA
systematic process to evaluate human reliability
NOTE Evaluation methods can be just qualitative but can be expanded to provide quantitative results.
3.1.13
mistake
deficiency or failure in the judgemental or inferential process involved in selection of an
objective or in specification of the means to achieve it irrespective of whether or not the
actions run according to plan
3.1.14
performance shaping factors
characteristics of the external environment, of the task and of humans that shape individual
performance
3.1.15
requirement
need or expectation that is stated, generally implied or obligatory
[ISO 9000:2005, definition 3.1.2]
NOTE In the context of this standard, this is a need or expectation which should be met or possessed by a
system, system component, product, or service.
3.1.16
situational awareness
human perception of the elements in the environment within a volume of time and space, the
comprehension of their meaning and the projection of their status in the near future
3.1.17
system
set of interrelated or interacting elements
[ISO 9000:2005, definition 3.2.1]

– 10 – 62508 © IEC:2010
NOTE 1 In the context of dependability, a system will have:
 a defined purpose expressed in terms of intended functions;
 stated conditions of operation/use; and
 defined boundaries.
NOTE 2 The structure of a system may be hierarchical.
[IEC 60300-1:2003, definition 3.6]
NOTE 3 For some systems, such as information technology products, data is an important part of the system
elements.
NOTE 4 Humans can form part of a system.
3.1.18
violation
deliberate but not necessarily reprehensible deviation from practices deemed necessary
3.2 Abbreviations
ASEP Accident Sequence Evaluation Program
ATHEANA A Technique for Human Error ANAlysis
CAD Computer Aided Design
CAHR Connectionism Assessment of Human Reliability
CARA Controller Action Reliability Assessment
COTS Commercial Off The Shelf
CPC Common Performance Condition
CREAM Cognitive Reliability and Error Analysis Method
EFC Error Forcing Context
ESAT ExpertenSystem zur Aufgaben-Taxonomie (expert system for task taxonomy)
FMEA Failure Modes and Effects Analysis
FMECA Failure Modes Effects and Criticality Analysis
HCD Human-Centred Design
HCR Human Cognitive Reliability
HEART Human Error Assessment and Reduction Technique
HEP Human Error Probability
HF Human Factors
HRA Human Reliability Analysis
HR Human Resources
HS Human System
HSI Human System Interaction
ILS Integrated Logistics Support
MERMOS Méthode d’Evaluation de la Réalisation des Missions Opérateur pour la Sûreté
(method for the evaluation of the relisation of an operator’s mission regarding
safety)
ORE Operator Reliability Experiments
PSF Performance Shaping Factor
RR Reliability Rating
SHERPA Systematic Human Error Reduction and Prediction Approach
SLI Success Likelihood Index
SLIM Success Likelihood Index Methodology
SPAR-H Standardized Plant Analysis Risk
THERP Technique for Human Error Rate
UI User Interface
4 Human aspects
4.1 Overview
Human actions can have a strong influence on the dependability of the whole system and the
quality of the output. Therefore important benefits accrue from consideration of human
aspects, among which are preventing failures, improving system performance, ensuring
safety, increasing reliability and enhancing cost effectiveness. A system that requires human

62508 © IEC:2010 – 11 –
interaction involves human(s), machine(s) and the social and physical environment in which
they operate. The dependability of the system and the efficiency and effectiveness with which
the goals of the system are achieved depend on each component of the system individually
and the interactions between them (Figure 1).
Social and physical
environment
Goals Output
Human
Individual
Machine
characteristics, skills
(Interactive
and experience
system)
Individual human
performance
Feedback
IEC  1541/10
Figure 1 – Components of the system and their interactions
The grey arrows represent the performance shaping factors (PSFs) (described in 4. 4) .
The components shown in Figure 1 are as follows.
• Goals: what the work system has to achieve ( 4. 2. 2) .
• Human: person who performs the task ( 4. 2. 3) .
• Machine: interactive system designed to support achievement of the work system goals
( 4. 2. 4) .
• Environment: social and physical factors that can influence the human(s) and machine
( 4. 2. 5) .
• Output: that which should be achieved with the required level of effectiveness and
efficiency ( 4.2 . 6) .
• Feedback: feedback coming from the machine ( 4. 2. 7) .
4.2 Components of the system and their interactions
4.2.1 Introductory remark
This subclause describes each component of Figure 1.
4.2.2 Goals
The objective of the work system is to achieve goals with a desired effectiveness and
efficiency.
– 12 – 62508 © IEC:2010
4.2.3 Humans
The role of humans in the system is to perform a task or interact with a machine in order to
achieve a defined goal. The human operator can either have a monitoring role (such as in a
process control or road traffic control room), or an active role (for example when resolving a
road traffic incident).
Human influence can both be negative (e.g. human errors and violations) or positive (e.g.
preventing system breakdowns or system problems). Humans can influence the system
through action or inaction. Even in an automated system a human is part of the system,
through design, maintenance and monitoring functions.
A range of people (shown in Table 1) may be involved in the different phases in the life cycle
of a system each influences the dependability of the system through their actions and
decisions.
Table 1 – People who influence dependability
Job function Examples of influence
Project manager Awareness of dependability needs in system concepts
Designer
• Takes account of human factors in normal use and
reasonably foreseeable misuse
• Designs for recognition and recovery from fault
conditions including where there are multiple failure
modes
Operational procedure writer Establishes procedures that minimize human failures
Operational manager and supervisor
• Ensures appropriate working conditions resources,
communication, feedback and training
• Motivates operators
• Ensures compliance with procedures

Operator Observes and reports consequences of human error
Trainer Highlights error-prone situations in training
Maintenance personnel Understand, interpret and ensure compliance with
procedures
Human performance including strengths and limitations and the potential for humans to
improve or degrade system operation should be taken into account when considering total
system dependability. Although this appears to be additional work with financial implications,
the cost of failure, if total system dependability is not considered, could be significant. The
possible adverse consequences of human failures (including mistakes, slips, lapses,
violations or malicious human actions) are particularly important when the human is part of a
complex system with safety, security or mission critical applications. Human error can also
have severe consequences in business and e-commerce environments.
For details of human characteristics, see 4.3.
4.2.4 Machine (interactive system)
The machine is designed to achieve functional and performance objectives within the
environments in which it is to function.

62508 © IEC:2010 – 13 –
During operation the machine receives input from the human through its controls and will
provide output that progresses the system’s task. The output will often be displayed to provide
feedback to the human on the operation of the machine.
For the system as a whole to work effectively the interface and interaction between the
machine and the people who work with it at all stages of the life cycle from design to disposal
needs to take account of the human aspects. These include the fundamental human
characteristics together with specific skills and experience, and the tasks that are to be
performed. In particular, the interaction between the human operator and the machine (i.e.
tasks, displays and controls) should be designed to be easy for the operator to use and to
ensure acceptable levels of mental comfort.
4.2.5 Social and physical environment
4.2.5.1 Social environment
Organizational structure, work flows and the resulting social factors influence the human and
system performance and need to be designed to support efficient and reliable human
performance. An organizational structure is characterized by the transfer of tasks
(delegation), decision competence, information, communication and decision paths as well as
the number of hierarchy levels. The work process is characterized for example by the work
flow method, the shift system, the work time and the work planning and execution.
Other features like leadership behaviour, participation, safety culture and climate can also
influence human motivation and behaviour when using a system.
4.2.5.2 Physical environment
Physical environmental factors that affect people, and hence system reliability, include light,
noise, mechanical vibrations, climate, dirt, humidity, air pressure, toxic gas and radiation.
Environmental factors can directly influence the capabilities of human beings (e.g. noise, toxic
gas, etc.), or they can influence interactions between people and machines (e.g. mechanical
vibration) or they can influence the machine itself (e.g. side winds when driving a car).
However, apart from their negative effects, they can also provide a feedback function that
enhances the ability of the human to interact effectively with the machine (e.g. the engine
noise/vibration when driving a car).
Some factors of the physical environment can require people to use protective equipment
(e.g. breathing apparatus). Some individual human limitations can require the use of assistive
technologies (e.g. reading spectacles or specialized input devices). These technologies can
have an effect on their ability and will need to be taken into account in design.
4.2.6 Output
The task goals should be achieved with the required level of effectiveness and efficiency.
4.2.7 Feedback from the machine to the person
Appropriate feedback from the machine is an important characteristic of dependable design.
Feedback concerning input occurs from the machine to the person through sonic, visual and
tactile signals. Feedback concerning the output of the system as a whole provides information
on the achievement of the goals.
Feedback is important for a number of reasons. It allows a person to correct undesired
behaviour of the machine or the system as a whole in order to improve performance or to
correct undesired actions. In addition, lack of appropriate feedback can produce errors, e.g.
when a computer is slow to provide visual feedback in response to the delete button, the
operator will often repeat the action. Feedback can also contribute to performing a task more
accurately, e.g. feedback from the car brake pedal helps the driver brake smoothly. Feedback

– 14 – 62508 © IEC:2010
from the machine and the system also help provide situational awareness. In some
circumstances, feedback can result in a change to the goals.
4.3 Human characteristics
4.3.1 Introductory remark
Human beings have a set of physical, cognitive and psychological characteristics that vary
from person to person (4.5.2). These characteristics provide fundamental limitations to the
human capabilities that need to be taken into account in systems design. Appropriate training
and experience will enable people to work more effectively, but only within their limitations.
Human reliability and performance will be influenced by the design of the machine and by the
physical and social environment (4.5.1). To ensure a working situation with high
dependability, the system should be designed so that the stress on the human being due to
the work task, work environment and technical design remains within acceptable limits.
4.3.2 Human limitations
The design should take account of human limitations.
a) Physical limitations
• Anthropometric and biomechanical constraints.
• Sensory constraints (e.g. the range of signals that can be perceived and
differentiated).
b) Cognitive limitations
• The time needed between perception of a signal and an action in response. This can
range from a few hundred milliseconds for skill-based actions where response is quasi
automatic (and is not reasoned), to several seconds or minutes where reasoning and
analysis is necessary.
• Limitations of short-term memory. Only 5 to 7 items of information can be held in
short-term memory. For larger amounts of information, mental models or patterns are
constructed.
• Limitations on the amount of information that can be processed at one time (working
memory).
• The inability to focus effectively on more than one task at a time or process
information in parallel.
• Potential for loss of situational awareness resulting in actions based on incorrect
perception of reality.
c) Psychological limitations
• Performance degradation due to physical and mental fatigue or boredom.
• Tendency for decisions and actions to be based on emotional rather than reasoned
responses particularly under situations of stress.
Since these characteristics of humans cannot be designed out of the system, the division of
tasks between people and the rest of a system and the design of technical systems and
interfaces have to be taken into account. The relative strengths of humans and machines
should be considered (4.4.3).
4.3.3 Comparison of humans and machines
The allocation of activities and operational steps between human beings and machines should
take into account the relative strengths of humans and machines.

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a) Human strengths
• Ability to perceive patterns of light or sound.
• Ability to improvise and use flexible procedures.
• Ability to store very large amounts of information for long periods and to recall relevant
facts at the appropriate time.
• Ability to reason inductively.
• Ability to exercise judgement.
b) Machine strengths
• Ability to detect small amounts and a wider range of visual and acoustic signals.
• Ability to respond quickly to control signals, and to apply great force smoothly and
precisely.
• Ability to perform repetitive and routine tasks consistently and accurately.
• Ability to store information briefly and then to erase it completely.
• Ability to reason deductively, including computational ability.
• Ability to handle highly complex operations and to do many different things at once.
There are major differences between humans and machines.
• Machines can be modified, redesigned, and retrofitted whereas humans cannot.
Humans are born with innate, genetically determined differences that are shaped by
the environment. Innate aptitudes or abilities are developed through education and
training.
• Machines can be manufactured to provide exact output and duplicate precise
operation. Humans are not identical and vary across all sensory, cognitive, physical
and performance characteristics. Specific aspects of human performance can be made
more equal through selection and training.
4.4 Human performance shaping factors
4.4.1 General
The performance and reliability of people within a system will vary depending on a range of
internal and external conditions that differ from person to person and from one instant to
another. The factors that influence the capability of human beings to reliably accomplish a
task are called performance shaping factors (also known as the context of use).
Figure 1 indicates the types of performance shaping factors with grey arrows.
Figure 2 provides examples distinguishing between external and internal performance shaping
factors.
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Human performance
External performance shaping factors Internal performance shaping factors
Organisational Technical Performance
Willingness
prerequisites prerequisites capacity
Organisational Organisational Task- Situational Physiological Psychological Physiological Psychological
structure dynamics difficulty factors capacity capacity fitness motivation
Hierarchies Working hours Machinery- Work-layout Constitution Talent Circadian Intrinsic
Remuneration Work design Anthropometric Sex Education rhythm motivation
Education - Structure Task-content Environmental Age Experience Sicknesses (including
- Resources Task-design Design Training Emotional interest, social
Instructions Technical- stability integration)
implementation Condition Extrinsic
motivation
(including career
opportunities,
work-climate)
Occupational health and safety
Quality assurance
IEC  1542/10
Figure 2 – Human performance shaping factors
4.4.2 External performance shaping factors
External performance shaping factors are the result of organizational and technical
prerequisites. Organizational prerequisites ( 4.2.5.1) can often only be described qualitatively.
Technical prerequisites including machine design ( 4.2.4) and environmental factors ( 4 . 2. 5. 2) ,
on the other hand, can most often be described quantitatively.
Taking account of the external performance shaping factors in design will have a positive
impact on the performance.
4.4.3 Internal performance shaping factors
Internal performance shaping factors can be separated into performance capacity and
willingness. They represent factors caused by physiological and psychological variations in
people and are shown as “individual characteristics, skills and experience” in Figure 1.
These include human limitations ( 4.3.2), and differences in size and strength, differences in
talent, skill, experience and knowledge, psychological variations and motivational factors.
4.5 Human reliability analysis (HRA)
4.5.1 Overview
The analysis of human reliability is part of the overall analysis of the reliability of a technical
system. Human reliability analysis involves the following activities.
• Identification of potential for human failure.
• Analysis of sources of error and causes of violations so as to be able to define appropriate
counter-measures.
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• Where appropriate, quantificatio
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