ISO 13824:2020

INTERNATIONAL ISO
STANDARD 13824
Second edition
2020-03
Bases for design of structures —
General principles on risk assessment
of systems involving structures
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Fundamentals of risk assessment of systems involving structures.4
5 Establishment of structural engineering context . 5
5.1 Structural engineering context . 5
5.2 Establishment of design basis . 5
5.3 Assessment of existing structures . 5
5.4 Assessment of exceptional structures or extraordinary events . 5
5.5 Providing support for decisions for other contexts . 5
6 Definition of the system . 6
6.1 General . 6
6.2 Functions of the system . 6
6.3 Identification of the subsystems . 6
7 Identification of hazards and undesirable consequences . 6
7.1 Identification of possible hazards . 6
7.2 Identification of scenarios . 6
7.3 Identification of undesirable consequences . 6
7.4 Hazard screening . 7
7.4.1 General. 7
7.4.2 Hazard screening criteria . 7
8 Risk estimation . 7
8.1 Types of risk estimation . 7
8.1.1 General. 7
8.1.2 Qualitative estimation . 7
8.1.3 Semi-quantitative estimation. 8
8.1.4 Quantitative estimation . 8
8.2 Data for risk estimation . 8
8.2.1 Data collection . 8
8.2.2 Treatment and modelling of uncertainty . 8
8.3 Risk representation . 8
8.4 Estimation of probability . 9
8.4.1 General. 9
8.4.2 Probability of occurrence of hazard . 9
8.4.3 Probability of failure of structures . 9
8.5 Estimation of undesirable consequence . 9
8.6 Sensitivity and bounding analysis . 9
9 Risk evaluation .10
9.1 Risk criteria .10
9.2 Risk acceptance .11
10 Evaluation of options for risk treatment .11
10.1 General .11
10.2 Determination of options .12
10.2.1 General.12
10.2.2 Risk avoidance .12
10.2.3 Risk reduction .12
10.2.4 Risk sharing .12
10.2.5 Risk retention .12
10.2.6 Emergency preparedness .12
10.3 Assessment of options for risk treatment .12
10.4 Risk treatment .13
11 Documentation .13
Annex A (informative) General framework of risk management process for systems
involving structures .14
Annex B (informative) Principles in the implementation of risk assessment .19
Annex C (informative) Examples of extraordinary events and exceptional structures for
risk assessment .26
Annex D (informative) Techniques for treatment of expert opinions .28
Annex E (informative) Examples of quantitative risk representation .31
Annex F (informative) Formulae for risk estimation .35
Annex G (informative) Procedure for the estimation of consequences .39
Annex H (informative) Examples of measures for risk treatment .41
Annex I (informative) Examples of application of risk acceptance and optimization .44
Annex J (informative) Examples of risk estimation .50
Annex K (informative) Terrorism and malevolent events .55
Bibliography .60
iv © ISO 2020 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of may be the subject of patent rights.
ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights
identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www .iso .org/ patents).
Any trade name used in is information given for the convenience of users and does not constitute an
endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 98, Bases for design of structures,
Subcommittee SC 2, Reliability of structures.
This second edition cancels and replaces the first edition (ISO 13824:2009), which has been technically
revised. The main changes compared to the previous edition are as follows:
— risk-informed approach has been newly introduced to risk assessment in order to comply with the
latest edition of ISO 2394 (ISO 2394:2015);
— requirements for treatment of uncertainty in risk estimation have been updated by introducing
requirements related to sensitivity analysis;
— requirements for risk treatment have been updated by emphasizing the importance of optimization
of prevention and mitigation measures including emergency preparedness;
— new informative annexes on examples of risk estimation of undesirable consequences caused by
human-induced or natural events have been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
Introduction
Systems involving structures in public and private sectors depend on civil engineering technologies
and structures. Structures support missions and business functions of whole systems.
Structures are subject to multiple natural, technological and malevolent human-induced hazards.
Hazards can have adverse impacts on performance of systems involving structures, quality of life,
stakeholders’ assets inside or near structures, operations and operability, functions and reputation,
structural safety and sustainability of environment.
Given the significance of hazards, it is imperative that all stakeholders such as owners, occupants,
designers, operators, regulators at all levels and at all phases of the lifecycle of systems involving
structures understand their responsibilities for achieving adequate structural safety, structural
functionality and managing risk.
This document provides a common basis for assessing risk relevant to planning, design, assessment,
maintenance, decommissioning and removal of structures, in accordance with ISO 31000.
In risk assessment, hazard identification and the estimation of consequence are primary procedures.
For these, it is essential to assess the risk of systems involving structures rather than just the structures,
since structural failure has significant consequences for systems, and a failure of systems such as fire
protection systems can cause serious damages. However, actions for risk treatment are taken within
the scope of structural design. Such considerations are reflected in the title of this document.
This document is intended to serve as a basis, along with other relevant standards on risk management,
for those assessing risk for systems involving structures.
vi © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 13824:2020(E)
Bases for design of structures — General principles on risk
assessment of systems involving structures
1 Scope
This document specifies general principles of risk assessment for systems involving structures. The
focus is on strategic and operational decision-making related to design, assessment, maintenance
and decommissioning of structures. This also includes formulation and calibration of related codes
and standards. Systems involving structures can expose stakeholders at various levels in society to
significant risks. The aim of this document is to facilitate and enhance decision-making with regard to
monitoring, reducing and managing risks, and preparing for emergency in an efficient, cost-effective
and transparent manner. Within the broader context of risk management, risk assessment provides
decision-makers with procedures to determine whether or not, and in what manner, it is appropriate to
treat risks.
This document provides a general framework as well as a procedure for identifying hazards and
estimating, evaluating and treating risks of structures and systems involving structures. This
document also provides a basis for code writers as well as designers to set reasonable target-reliability
levels, such as stated in ISO 2394, based on the result of risk considerations. For existing structures, it is
intended that assessment of the risks associated with the events that were not considered in the original
design or with changes in use be implemented according to the principles stated in this document. This
document can also be used for risk assessment of exceptional structures upon specific adaptation and
detailing, the design of which is not usually within the scope of existing codes.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 2394, General principles on reliability for structures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
acceptable risk
level of risk (3.9) that an individual or society accepts or tolerates to secure certain benefits
3.2
cost/benefit analysis
analysis contributing to decision-making on whether to adopt a project or a plan by quantifying and
comparing its costs and benefits
3.3
extraordinary event
very rare event that causes very severe consequences
3.4
failure
state which does not meet required performance objectives due to structural damage and/or loss of
function
Note 1 to entry: Failure includes insufficient load-bearing capacity or inadequate serviceability of a structure
(3.21) or structural member, or rupture or excessive deformation of the ground, in which the strengths of soil or
rock are significant in providing resistance.
3.5
hazard
potential source of undesirable consequences (3.23)
Note 1 to entry: A hazard can be a risk (3.9) source (see ISO Guide 73). Examples of hazards include a possible
abnormal action or environmental influence, insufficient strength or stiffness, or excessive detrimental deviation
from intended dimensions (see ISO 2394).
3.5.1
hazard identification
process to find, list and characterize hazards (3.5)
3.5.2
hazard curve
exceedance probability of a specified hazard (3.5) intensity for a specified period of time
3.5.3
hazard screening
process of identifying significant hazards (3.5) for consideration during risk assessment (3.11) of systems
(3.22) involving the structures (3.21)
3.6
option
possible measure for managing risk (3.9)
Note 1 to entry: Doing nothing can be one of the feasible options.
3.7
residual risk
risk (3.9) remaining after risk treatment (3.17)
3.8
resilience
ability of a system (3.22) to reduce likelihood of failure (3.4), to absorb effects of such failure if it occurs
and to recover quickly after failure
3.9
risk
effect of uncertainty on objectives
Note 1 to entry: Risk is generally described as a combination of the probability or frequency of occurrence of an
event and the magnitude of its consequence.
Note 2 to entry: From the viewpoint of the decision theory, risk is defined as the expected value of all undesirable
consequences, i.e. the sum of all the products of the consequences of an event and their probabilities. (see
ISO 2394).
[SOURCE: ISO 2394:2015, 2.1.40, modified — Note 1 has been added.]
3.10
risk acceptance
decision to accept a risk (3.9) to secure certain benefits
2 © ISO 2020 – All rights reserved

3.11
risk assessment
overall process of establishment of structural engineering context (3.19), definition of system (3.22),
identification of hazards (3.5) and consequences, risk estimation (3.15), risk evaluation (3.16) and
evaluation of treatment options (3.6)
3.12
risk communication
exchange or sharing of information about risk (3.9) among the decision-makers and stakeholders (3.20)
Note 1 to entry: The information can relate to the existence, nature, form, probability, severity, acceptability,
treatment or other aspects of risk.
Note 2 to entry: Engineers are the main source for risk information and should encourage decision-makers and
stakeholders to communicate with each other. Some engineers are part of, or support, the decision-makers.
3.13
risk control
actions implementing risk-management decisions
Note 1 to entry: Risk control can involve monitoring, re-evaluation and compliance with decisions.
3.14
risk criteria
criteria against which the significance of the results of the risk (3.9)analysis is evaluated
Note 1 to entry: The criteria are generally based on regulations, standards, experience, and/or theoretical
knowledge used as a basis for risk acceptance.
Note 2 to entry: Risk criteria can depend on associated costs and benefits, legal and statutory requirements,
socio-economic and environmental aspects, the concerns of stakeholders, priorities and other inputs to the
assessment.
3.15
risk estimation
process of assigning values to the probability of occurrence of events and their consequences
3.16
risk evaluation
process of comparing the estimated risk (3.9) with given risk criteria (3.14) to determine the significance
of the risk
Note 1 to entry: Risk evaluation is the process for assisting in the decision to accept or to treat a risk.
3.17
risk treatment
process of selection and implementation of measures to mitigate risk (3.9)
3.18
scenario
description of sequences or combinations of events in time and space and their inter-relationship given
the occurrence of a hazard (3.5)
3.19
structural engineering context
background or reasons why the risk assessment (3.11) is implemented from structural perspectives
3.20
stakeholder
any individual, group, organization or authority that can affect, be affected by, or perceive itself to be
affected by, a risk (3.9)
Note 1 to entry: The decision-maker is sometimes categorized as one of the stakeholders.
3.21
structure
arrangement of materials that is expected to withstand certain actions and to perform some intended
function
3.22
system
delimited group of interrelated, interdependent or interacting objects that is assessed for a risk (3.9)
Note 1 to entry: This definition implies that the system is identifiable and is made up of interacting elements or
subsystems, that all elements are identifiable, and that the boundary of the system can be identified.
Note 2 to entry: A system involving structures includes the structural system defined in ISO 2394 as a subsystem.
3.23
undesirable consequence
direct and indirect harm due to structural damage, functionality loss, etc., stated in terms of personal
injury, death, environmental damage, societal harm and/or monetary loss
Note 1 to entry: There can be more than one undesirable consequence from an event.
Note 2 to entry: Consequences can be expressed qualitatively or quantitatively.
Note 3 to entry: Both immediate and long-term consequences are included.
3.24
undesirable event
event that can have undesirable consequences (3.23)
Note 1 to entry: Undesirable events are sometimes caused by natural, technological and human-induced hazards.
4 Fundamentals of risk assessment of systems involving structures
Risk assessment of system involving structures shall be done within the scope of the prescribed
risk management; see Annexes A and B. Risk assessment shall consist of the following elements: the
establishment of the structural engineering context, the definition of system, the identification of
hazards and consequences, the risk estimation, the risk evaluation and the evaluation of options for
risk treatment.
NOTE 1 A risk management process typically consists of the establishment of risk-management goals, a risk
assessment, a risk treatment, communication and consultation, and a monitoring and review; see Annex A. The
establishment of risk-management goals includes the development of risk criteria; see 9.1.
NOTE 2 A risk management process is not a one-way process but an iterative process; see Annexes A and B.
There shall be thorough communication and appropriate consultation with the stakeholders for each
element of the risk assessment. After the risk assessment is complete, its results shall be conveyed in a
suitable manner so that appropriate decisions can be made and the stakeholders can understand them.
The decision concerning structures shall conform to requirements specified in ISO 2394.
The appropriateness of all elements of the risk assessment shall be reviewed in order to ensure continuous
improvement of the risk management process, including risk assessment; see Annexes A and B.
The results of risk assessment shall be documented for future reference to guarantee that decisions are
understood and to assist in the continuous improvement of the process; see Clause 11.
4 © ISO 2020 – All rights reserved

5 Establishment of structural engineering context
5.1 Structural engineering context
Structural engineering context shall be established as the first step of risk assessment. Typical
structural engineering contexts or typical applications of risk assessment of systems, including
structures, are the following:
a) establishment of design basis;
b) assessment of existing structures;
c) assessment of exceptional structures and/or extraordinary events; see Annexes C and K;
d) providing support for decisions in other contexts.
Stakeholders shall be identified based on the established structural-engineering context.
NOTE 1 Examples of decisions in other contexts include situations related to operation such as inspection and
maintenance planning as well as performance and functional level during emergency situation.
NOTE 2 This document considers only structural engineering contexts; however, there are other relevant
contexts; see Annexes A and B and ISO 31000.
5.2 Establishment of design basis
For establishment of the design basis, a series of criteria for the design of structural members shall be
developed. The criteria should be determined based on the target reliability levels.
5.3 Assessment of existing structures
In the event that an existing structure, including a heritage structure, is damaged or has a change of
usage, then a risk assessment shall be undertaken. If the assessed risk is excessive, then actions shall be
undertaken to mitigate the risk and notify the relevant stakeholders.
The risk due to extraordinary events, or beyond the events considered in the original design, should be
assessed to verify that it is within the acceptable level (see 9.1).
NOTE For risk assessment of existing structures, ISO 13822 can be used.
5.4 Assessment of exceptional structures or extraordinary events
Risk assessment of exceptional structures shall be carried out if their failures can have serious
consequences. Risk assessment shall be conducted for unfavourable events, such as fires and other
extraordinary event scenarios including progressive collapse (see Annex C).
5.5 Providing support for decisions for other contexts
When several options, strategies, or concepts are available, an optimal selection shall be based on the
following objectives, considering the result of risk assessment:
a) to minimize risk given constraints such as limited economic resources;
b) to determine the optimal level of investment in risk reduction.
NOTE Prioritization of risk treatment actions to be taken is one of the optimization approaches to reduce
the risk of group of exposures over certain period of time.
In both situations, the optional use of economic resources shall be considered to examine whether it
results in optimal risk reduction.
Options should be compared according to net utility, cost/benefit or cost-effectiveness; see Annex I.
If the aim of decision-making is to minimize risk within economic constraints, the results of the
comparison may be used provided that all technical solutions are consistent with best practice.
6 Definition of the system
6.1 General
The system definition shall support decision-making and thus, the extent of the system that is
considered in risk assessment shall be clearly identified based on the structural engineering context
described in Clause 5.
6.2 Functions of the system
The definition of the system involving structures shall include a clear identification of the functions
focusing on critical functions provided by the elements of the system and how these functions are
supported by the structural components.
6.3 Identification of the subsystems
The characteristics of each subsystem, such as type of structure(s), codes and standards used in
the design of the structure(s), use, importance, location and design/remaining service life, shall be
identified. The limit states of the system shall also be specified.
7 Identification of hazards and undesirable consequences
7.1 Identification of possible hazards
The hazards that can cause undesirable events during their service lives of structures shall be identified.
Temporal and spatial characteristics of hazards such as simultaneous occurrence of multiple hazards
(and more) shall be taken into consideration. Possible simultaneous occurrence of multiple hazards
should be considered.
NOTE For the detailed procedure on scenario analysis for fire, see ISO 16732 (all parts) and
ISO 16733 (all parts).
7.2 Identification of scenarios
Scenarios shall be identified as the sequences or combinations of events or processes necessary for
system failure and resulting undesirable consequences for the system involving structures. The
scenarios should include collapse or damage of the structure(s), loss of functionality, loss of lives or
injury and other economic and/or societal impacts caused by or to the stakeholders.
NOTE The essential techniques used for schematic representation of scenarios include fault trees, event
trees, failure modes, effects and criticality analysis (FMECA) and layer of protection analysis (LOPA).
7.3 Identification of undesirable consequences
Undesirable consequences resulting from the hazards and following events shall be identified. They
should be described in terms of human fatalities and injuries, environmental damage and/or monetary
loss. Some consequences can be identified by scenario analyses considering the extent of influences due
to failure of the structures in time and space.
NOTE When conducting scenario analyses, influences of failure of subsystems other than structures are
taken into consideration if such failure can cause damages to structural elements.
6 © ISO 2020 – All rights reserved

7.4 Hazard screening
7.4.1 General
Hazards important to a system shall be screened on the basis of the significance of risk associated with
those hazards and incorporated in the risk assessment. As each hazard has its inherent characteristics
and possible undesirable consequences, it is recommended that the hazards be categorized on the
basis of the original cause, the degree of quantification, and the significance of the consequences. The
screening of hazards in accordance with their importance for risk assessment can then be performed
based on the experience and expertise of the engineer. The results of the hazard screening shall be
documented.
7.4.2 Hazard screening criteria
Preliminary risk estimation (see 8.1) shall be carried out to identify the significant risks. The criteria for
the hazard screening should, in principle, be based on the magnitude of the risk from the preliminary
risk estimation. The frequency of the hazard and/or significance of the relevant consequences can also
be useful criteria. Hazards with obviously negligible risk compared with the acceptable risk level may
be screened out.
The hazard screening criteria shall be clearly described in terms of frequency of the event and
magnitude of its consequence. They may be based on the past experience, human perception and
relevant values specified elsewhere.
8 Risk estimation
8.1 Types of risk estimation
8.1.1 General
Risk estimation shall be undertaken according to the purpose of the estimation, required degrees
of details, information, data and resources available. The types of estimation fall into three broad
categories, qualitative, semi-quantitative, and quantitative, depending on the circumstances.
NOTE In practice, qualitative estimation is often used as a preliminary risk estimation to obtain a general
indication of the level of risk and to reveal the risks that shall be considered. Later, it can be necessary to
undertake more specific or quantitative estimation on the revealed risk.
8.1.2 Qualitative estimation
In qualitative estimation, risk shall be estimated and ranked in a descriptive manner. Qualitative
estimation should be used, in the following cases:
a) as an initial screening activity to identify risks that require more detailed estimation;
b) where the qualitative estimation provides sufficient information for decision-making;
c) where the numerical data or resources are insufficient to allow a quantitative estimation.
NOTE Tools like “what-if” analysis, checklists, event trees, fault trees, influence diagrams, barrier block
(bow-tie) diagrams, hazard and operability (HAZOP) studies and failure mode and effects and criticality analysis
(FMECA) can be used for qualitative estimation of risk.
8.1.3 Semi-quantitative estimation
In semi-quantitative estimation, a ranking scale more expanded than the one usually achieved in
qualitative estimation shall be adopted.
NOTE 1 If the ranking scale chosen cannot properly reflect relativities, this can lead to inconsistent, anomalous
or inappropriate outcomes.
NOTE 2 Tools like risk matrix and criticality, accessibility, recuperability, vulnerability, effect and
recognizability (CARVER) analysis can be used for semi-quantitative estimation of risk.
8.1.4 Quantitative estimation
In quantitative estimation, numerical values shall be used for both undesirable consequences and
probability of occurrence based on data from a variety of sources.
NOTE The quality of the estimation depends on the scenario credibility, accuracy and completeness of the
numerical values and the validity of the models used.
8.2 Data for risk estimation
8.2.1 Data collection
Data for risk estimation shall be taken from appropriate sources of information. The most pertinent
information sources and techniques should be used when estimating probability as well as undesirable
consequences. Information sources can include the following:
a) past records;
b) practice and relevant data (field data collection);
c) relevant published data (incident data);
d) experiments and prototypes;
e) engineering or other models;
f) specialist and expert judgment (expert opinions).
8.2.2 Treatment and modelling of uncertainty
All uncertainties associated with data relevant to estimating probability as well as undesirable
consequences shall be identified and taken into consideration.
8.3 Risk representation
The results obtained in risk estimation may be converted to a common scale such as potential fatalities,
expected monetary loss (see Annex I). These may be related to the probability of occurrence of various
hazards and may be compared with other hazardous activities or another risk level.
In qualitative risk representation, risk shall be rated in a descriptive manner. In quantitative
representation, the whole profile of risk shall be presented by a combination of probability and
undesirable consequence. The expectation of the consequence may be used for risk representation; see
Annex E.
NOTE A risk curve is also one of the pictorial representations of risk, where undesirable consequences and
associated probability of occurrence are plotted for different scenarios of system failure (see Annex E).
8 © ISO 2020 – All rights reserved

8.4 Estimation of probability
8.4.1 General
In quantitative estimation, probability estimates may be obtained from any or all of the following three
approaches:
a) direct statistical estimation from data;
b) uncertainty propagation using model analysis tools;
c) expert opinion elicitation (see Annex D).
NOTE For the purposes of risk evaluation as well as risk communication, it is sometimes preferable to
differentiate between aleatory uncertainty (inherent natural variability) and epistemic uncertainty (model
uncertainties and statistical uncertainties). For risk assessment of safety-critical facilities where decision
making has an impact on a variety of stakeholders, aleatory and epistemic uncertainties are sometimes treated
separately. Uncertainty analysis is conducted to quantify the effects of epistemic uncertainty on estimated
probability.
8.4.2 Probability of occurrence of hazard
The probability of occurrence of each hazard identified in Clause 7 shall be estimated based on past
data, if available. If data are not available, expert judgement should be used; see Annex D.
NOTE It is important to reflect the characteristics of the hazard, although a hazard is often represented
simply in terms of a hazard curve; see F.2.2.1, J.3.1 and K.2.
8.4.3 Probability of failure of structures
The probability of failure of structures shall be estimated using all of the following procedures, taking
into account the design/remaining service life (see Annexes F, J and K):
a) modelling of action;
b) modelling of capacity;
c) response analysis of structures to the action.
NOTE Modelling of capacity can include functional capacity of subsystems in addition to structural
resistance.
8.5 Estimation of undesirable consequence
Undesirable consequences shall be determined by modelling the outcomes of an event or a set of events,
or by judging from experimental studies or past data. A scenario analysis shall be performed from the
occurrence of an initiating event with regard to the extent of the consequences, as specified in 7.2.
A quantitative estimation of undesirable consequence should be expressed numerically to define the
extent of human fatality and injuries, economic loss and environmental damage caused by structural
damage and functional loss. In addition to direct consequences, indirect consequences should be
included when estimating undesirable consequence of failure of structures. Uncertainty associated
with estimation of undesirable consequences should also be considered.
NOTE Indirect consequences are caused by subsequent effects of failure and are related to robustness as
well as resilience (see ISO 2394).
8.6 Sensitivity and bounding analysis
When some risk estimation results are not sufficiently robust for decision-making, a sensitivity analysis
shall be carried out to investigate the effect of uncertainty in assumptions, models and data. A higher
sensitivity should suggest that more care and/or effort can be required in obtaining data or estimates
for the variables concerned. Sensitivity analysis may also be used to examine the appropriateness and
effectiveness of possible risk controls and risk treatment options.
Bounding analysis, the analysis to assess range of critical parameters can be used for a simplified
estimation of the effects of uncertainties. It can also be used to supplement sensitivity analysis.
9 Risk evaluation
9.1 Risk criteria
Risk criteria shall be developed prior to the risk estimation as a part of establishing the risk-management
goals. They can be determined based on regulations, standards, the as low as reasonably practicable
(ALARP) principle, marginal life-saving costs principle, cost/benefit considerations or net utility.
NOTE Risk criteria can be modified after risk estimation based on the cost/benefit analysis and
optimization; see Annexes B and I. Although risk criteria are initially developed as a part of the risk management,
they can be further developed and refined subsequently as particular risks are identified and as procedures for
risk estimation are chosen.
Risk criteria shall be consistent with the risk-management goals and shall reflect the values of society
and/or the decision-maker. The acceptable risk level of the parties who do not directly benefit from
the series of activities shall be consi
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