hei Flashcards
A risk assessment team concludes that the knowledge-based probability of a
specific event A is equal to 0.05 given the knowledge K. Provide an interpretation
of this statement. Give also an interpretation of an imprecise probability of
maximum 0.05.
Interpretation of P(A|K): The team has the same uncertainty and degree of belief
for the event A to occur as randomly drawing a red ball out of an urn that comprise
100 balls and where 5 are red.
Imprecise probability P(A|K) ≤ 0.05: The team has the same uncertainty and
degree of belief for the event A to occur as randomly drawing a red ball out of an
urn that comprise 100 balls and where 5 or less are red. The assessor is not willing
to be more precise. Alternatively the team expresses that the probability is less
than or equal to 0.05, where 0.05 is interpreted as above. The team is not willing
to be more precise.
Does a frequentist probability for the following event B exist? Why/why not?
B: Risk science will be a distinct subject in school in Norway before 2050.
Define a frequentist probability p for an event C.
No, it does not exist as a population of similar type of situations to the one
considered cannot be meaningfully defined.
p= the fraction of time the event C occurs if we could repeat the situation
considered over and over again infinitely under the same conditions
A risk assessment is conducted with the aim of describing the risk related to
severe events which could lead to a high number of fatalities. The following risk
description is used:
P(an event occurring with at least 10 fatalities) = 0.05
Is this a good risk characterization? Why/why not?
The event ‘an event occurring with at least 10 fatalities’ is a severe event with a
high number of fatalities so this is fine, but may be also other numbers should be
covered, for example more than 100 fatalities etc. In addition, the characterization
should include the knowledge that the probability is based on and in particular a
judgment of the strength of this knowledge.
How does Taleb define a Black swan? How is a Black swan defined by Aven
in his books? Explain the three different types of black swans referred to in the
curriculum.
See book.
The following barrier block diagram represents a technical system with six
components:Draw the corresponding fault tree diagram, linking the top event ‘system failure’
to failures of the components 1-6. Assume independence and unreliability qi =
0.1 for each of the components. Calculate the unreliability of the system exactly
and approximately using the minimal cut set approach.
In what sense does the independence assumption represent risk in this case?
Exact:
P(System failure) = (1-p1p2) x (1- (1-q3q4)(1-q5q6)) = (1-0.92) * (1-(1-0.12)2) = 3.781 * 10-3
Approximately:
P(System failure) ≈ q1q3q4 + q1q5q6 + q2q3q4 + q2q5q6 = 4 * 10-3
The assumption can be wrong, and thus the calculated probabilities misleading.
A risk analyst argues that the main objective of the risk assessment is to
accurately estimate the risk. Do you agree? Why/why not?
A risk assessment could have this purpose in some cases (when frequentist based
probabilities can be meaningfully defined and there exist considerable relevant
data) but more generally the purpose of a risk assessment is
to help understand the risk and express risk:
identify risk sources, threats, hazards and opportunities; understanding how these can
materialize/occur, trigger events/event sequences, and what their consequences can be; representing
and expressing uncertainties and risk; and determining the significance of the risk using relevant
criteria.
This again provide decision support, on choices of measures and arrangements,
the need for such measures and arrangements, etc.
Explain the ALARP principle. Discuss to which extent the principle supports
Protection or Development.
The ALARP principle says that risk should be reduced to a level that is As Low As
Reasonably Practicable (ALARP). A risk reducing measure should be implemented unless
it can be demonstrated that the costs are grossly disproportionate relative to the gains
obtained (the burden of proof is reversed).
Thus if there is a safety measure that can improve safety, it shall be implemented as a rule,
unless you can demonstrate that the cost are in gross disproportion to the benefits gained.
This means that Protection is highlighted. On the other hand, if cost benefit analysis is
used to verify ALARP which is often seen in practice, Development is supported as this
analysis is based on expected values.
Argue how a cost-effectiveness analysis based on ICAF calculations can
contribute to identifying suitable safety measures. Discuss the
limitations/weaknesses of this method.
The ICAF for a safety measure calculates the expected cost per expected number
of saved lives. A high ICAF means that the measure is not justified, it costs too
much compared to the benefits gained, whereas if the ICAF is low, the costs are
not so high and the measure can be justified. The SVL (Statistical value of a life)
provides a reference point for what is too high.
The problem is that the approach is based on expected values which do not capture
all relevant aspects of benefit and costs. The potential for extreme outcomes are
not reflected, nor the strength of the knowledge supporting the judgments made.
Society for Risk Analysis (SRA) has developed a new Glossary. Is the
development of this Glossary to be seen as a contribution to Applied risk science
or Generic risk science? Explain.
The development of the Glossary is a contribution on Generic risk science B, but
with the intention to serve applied risk science A.
Consider the case where a person is thinking about jumping onto a stone (bolt)
located between two rocks, with a direct drop below of several hundred meters
(think of the Kjeragbolt in Lysefjorden if you like).
Trine has high competence in risk science. Her friend Tone asks her: ‘You as an
expert on risk science Trine, is it a good idea to jump on this bolt?’ How should
Trine respond to this question on the basis of the curriculum of this course?
She should say that the risk science does not provide answers what is the best
decision but it provides support for how to think and generate a basis for making
the decision. It helps us for example characterizing the risk and understanding
the balance that has to be made between different concerns (development and
protection).
What is ‘risk science’, and in particular ‘applied risk science’ and ‘generic risk science’?
Climate change research provides knowledge about risk as a result of climate change. Would
you classify this research as contributing to applied or generic risk science? Explain.
Risk science is the most warranted statements (justified beliefs) produced by the risk field or
discipline
Applied risk science: Risk science based applied risk analysis, which is about
supporting risk knowledge generation in relation to specific activities., and supporting the
tackling of specific risk problems (A)
Generic risk science: Risk science based on generic risk analysis, which is about generic
concepts, principles, approaches and methods on how to understand, assess, characterize,
communicate, manage and govern risk (B)
See also book Section 3.1.
Climate change risk: It is Applied risk science as it supports risk knowledge generation in
relation to specific activities.
Define ‘knowledge’ in a risk science context. Give an example to motivate and explain the
definition, which points to the need for deviating from an understanding of knowledge often
referred to in the literature. What is ‘risk research’?
Justified beliefs. See p. 24, arguing that knowledge cannot be ‘justified true beliefs’.
Risk research can be understood as knowledge generation in relation to risk, for concrete
activities and for how to analyse (in a wide sense) risk.
A risk analyst presents the result of a risk assessment for a process plant, and shows some
probability numbers for loss of life categories, including an imprecise probability of one or
more fatalities for a period of one year equal to [0, 0.005]. The assessor states that the numbers
represent the analyst’s degree of belief for these events to occur - where the assessor is not
willing to assign a precise number. Provide an interpretation of the above imprecise probability
statement [0, 0.005]. Is the probability uncertain? Explain why/why not.
Interpretation: The analyst has the same uncertainty and degree of belief for the event (at least
one fatality in that period) to occur as randomly drawing a red ball out of an urn that comprises
1000 balls and where maximum 5 are red. The assessor is not willing to be more precise.
It is not uncertain, it is the analyst’s judgment of uncertainty, but the knowledge supporting it
could be more or less strong.
In its most general form, risk can be described by (A’,C’,Q,K) and vulnerability by
(C’,Q,K|A’). Explain what these terms express.
Give an example illustrating how vulnerability can be described, which also includes the SoK
aspects.
A’: specified event, for example leakage
C’: specified consequences, for example number of fatalities.
Q: measure or description of the uncertainties about A’ and C’. Typically Q is probability P and
strength of knowledge judgments (SoK)
Vulnerability: (C’,Q,K|A’), as above but given the occurrence of an event, for example a gas
leakage in a process plant.
Probability of a fatality given the occurrence of a fire, with a SoK judgment expressing how
strong the background knowledge for this probability is considered.
How is a Black swan defined? Explain the three different types of black swans introduced.
Give an example for each type.
See book pp 77-81.
Explain the concept of validity of a risk assessment.
See Section 5.1.1
What is the difference between risk perception and professional judgments about risk?
See Section 6.1.1
The risk descriptions and characterization provide ‘pure’ judgements of the consequences of
the activities studied and associated uncertainties as in (A’,C’, Q,K), without adding feelings
and value judgements related to how people like or dislike the consequences and uncertainties.
Risk perception, on the other hand, is a personal judgement or appraisal of risk, also including
such aspects. We know from the literature on risk perception and behavioural decision-making
that aspects like affect, familiarity, control, catastrophic potential, etc., are important for how
people understand and deal with risk
Discuss to what extent successful risk communication depends on high quality risk analysis.
See Section 6.2.1
A risk scientist argues that it is important to stress that the decision-making should not be
purely ‘risk-assessment-based’. What is this scientist thinking about? Explain the concept of
managerial review and judgment.
The key is that the risk results should not prescribe what to do, as the risk assessments have
limitations in capturing all aspects of risks and uncertainties, and there are also different values
(we may all agree on the risks, but disagree on what to do as we have different values, what is
important, how much weight to give to uncertainties, how to balance protection and
development). The decision making should be risk informed.
Managerial review and judgement: process of summarising, interpreting and deliberating
over the results of risk assessments and other assessments, as well as of other relevant issues
(not covered by the assessments), in order to make a decision
The managerial review and judgment is the process between risk assessment and the
decision-making.
Discuss to what extent resilience analysis and management are a part of risk analysis and
management.
See Section 7.4
A risk analyst presents the result of a risk assessment for a process plant, and
shows some probability numbers for loss of life categories, including a probability
of one or more fatalities for a period of one year equal to 0.001 = 1 x 10-3. The
analyst states that the numbers represent the analyst’s degree of belief for these
events to occur. Provide an interpretation of the probability 0.001 in line with
this. What do we call this type of probability? Is it uncertain? Explain why/why
not.
Interpretation: The analyst has the same uncertainty and degree of belief for the
event (at least one fatality in that period) to occur as randomly drawing a red ball
out of an urn that comprises 1000 balls and where 1 is red.
It is referred to as a knowledge-based, or subjective or judgmental probability.
It is not uncertain, it is the analyst’s judgment of uncertainty, but the knowledge
supporting it could be more or less strong.
A person listening to the above risk analyst is not familiar with this type of
probability and thinks the number is a frequentist probability estimate. Suppose
that this was the case. Would the number then be subject to uncertainty?
Why/why not? Provide an interpretation of the underlying frequentist probability
being estimated.
Yes, as the number is an estimate of an underlying frequentist probability p which
has a true value: the fraction of time the event (at least one fatality) would occur
if we could repeat the situation considered (producing similar process plant years)
over and over again infinitely under the same conditions
In its most general form, risk can be described by (A’,C’,Q,K). Explain what
these elements express. A risk analyst establishes a 90% prediction interval for
the number of gas leakages in a process plant, with related strength of knowledge
judgments. Explain how to interpret this interval, and how it relates to
(A’,C’,Q,K). How can vulnerability be expressed using the (A’,C’,Q,K)
terminology?
A’: specified event, for example leakage
C’: specified consequences, for example number of fatalities.
Q: measure or description of the uncertainties about A’ and C’. Typically Q is
probability P and strength of knowledge judgments (SoK)
A 90 % prediction interval [a,b] is such that P(a ≤ number of leakages ≤ b |K) =
0.90. Hence we can interpret the interval as a way of expressing Q in relation to
A’ types of events (or C’ if C’ has a component referring to the number of
leakages).
Vulnerability description: (C’,Q,K|A’)
- How is a Black swan defined by Aven in the curriculum? What is an unknown
known in a risk assessment context? And unknown unknown? What are the
‘problems’ raised by restricting the Black swan metaphor to unknown unknowns?
See book.
Problems: a) unknown unknowns are so rare events, so not so relevant comparted
to other types of surprises (unknown knowns …) b) not in line with the origin of
the metaphor