2 TERMINOLOGY
Individual Risk (IR): The risk of death, injury and ill health as experienced by
an individual at a given location, e.g. a crew member or passenger on board the ship, or
belonging to third parties that could be affected by a ship accident. Usually IR is
taken to be the risk of death and is determined for the maximally exposed individual.
Individual Risk is person and location specific.
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IRfor Person Y = Fof undesired Event
∗ Pfor Person Y ∗ Eof Person Y
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F = frequency
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P = resulting casualty probability
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E = fractional exposure to that risk
Societal Risk: Average risk, in terms of fatalities, experienced by a whole group
of people (e.g. crew, port employees or society at large) exposed to an accident
scenario. Usually Societal Risk is taken to be the risk of death and is typically
expressed as FN-diagrams or Potential Loss of Life (PLL) (refer to section 2). Societal
Risk is determined for the all exposed, even if only once a year. Societal Risk is not
person and location specific.
FN-Curve: A continuous graph with the ordinate representing the cumulative
frequency distribution of N or more fatalities and the abscissa representing the
consequence (N fatalities). The FN-curve represents the cumulative distribution of
multiple fatality events and therefore useful in representing societal risk. The
FN-curve is constructed by taking each hazard or accident scenario in turn and
estimating the number of fatalities. With the estimated frequency of occurrence of each
accident scenario the overall frequency with which a given number of fatalities may be
equalled or exceeded can be calculated and plotted in the form of an FN-curve.
ALARP (As Low As Reasonably Practicable): Refers to a level of risk that is
neither negligibly low nor intolerable high. ALARP is actually the attribute of a risk,
for which further investment of resources for risk reduction is not justifiable. The
principle of ALARP is employed for the risk assessment procedure. Risks should be As Low
As Reasonably Practicable. It means that accidental events whose risks fall within this
region have to be reduced unless there is a disproportionate cost to the benefits
obtained.
3 PRINCIPLES OF RISK EVALUATION
Risk can be expressed in several complementary fashions. Concerning life safety, the
most commonly used expressions are Individual Risk and Societal Risk. This is risk of
death, injuries and ill health experienced by an individual and/or a group of people.
The notion of risk combines frequency and an identified level of harm. Commonly, the
level of harm is narrowed down to the loss of life and risk is an expression of
frequency and number of fatalities. In other words, life safety is usually taken to
refer to the risk of loss of life, and usually expressed as fatalities per year. In
order to address not only fatalities, but also disabilities and injuries, the Equivalent
Fatality Concept as specified below is advocated. Risk should at least be judged from
two viewpoints. The first point of view is that of the individual, which is dealt with
by the Individual Risk. The second point of view is that of society, considering whether
a risk is acceptable for (large) group of people. This is dealt with by the Societal
Risk.
3.1 The use of Individual Risk
3.1.1 This risk expression is used when the risk from an accident is to be estimated for
a particular individual at a given location. Individual Risk considers not only the
frequency of the accident and the consequence (here: fatality or injury), but also the
individual's fractional exposure to that risk, i.e. the probability of the individual of
being in the given location at the time of the accident.
3.1.2 Example: The risk for a person to be killed or injured in a harbour area, due to a
tanker explosion, is the higher the closer the person is located to the explosion
location, and the more likely the person will be in that location at the time of the
explosion. Therefore, the Individual Risk for a worker in the vicinity of the explosion
will be higher than for an occupant in the neighbourhood of the harbour terminal.
3.1.3 The purpose of estimating the Individual Risk is to ensure that individuals, who
may be affected by a ship accident, are not exposed to excessive risks.
3.2 The use of Societal Risk
3.2.1 Societal Risk is used to estimate risks of accidents affecting many persons, e.g.
catastrophes, and acknowledging risk averse or neutral attitudes. Societal Risk includes
the risk to every person, even if a person is only exposed on one brief occasion to that
risk. For assessing the risk to a large number of affected people, Societal Risk is
desirable because Individual Risk is insufficient in evaluating risks imposed on large
numbers of people. Societal Risk expressions can be generated for each type of accident
(e.g. collision), or a single overall Societal Risk expression can be obtained, e.g. for
a ship type, by combining all accidents together (e.g. collision, grounding, fire).
Societal Risk may be expressed as:
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.1 FN-diagrams showing explicitly the relationship between the cumulative
frequency of an accident and the number of fatalities in a multidimensional
diagram.
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.2 Annual fatality rate: frequency and fatality are combined into a convenient
one-dimensional measure of societal risk. This is also known as Potential Loss of
Life (PLL).
FN diagrams
3.2.2 Society in general has a strong aversion to multiple casualty accidents. There is
a clear perception that a single accident that kills 1,000 people is worse than 1,000
accidents that kill a single person. Societal Risk expressed by an FN-diagram show the
relationship between the frequency of an accident and the number of fatalities (see
figure 1 below).
Figure 1: FN-diagram (from MSC 72/16)
Potential Loss of Life (PLL)
3.2.3 A simple measure of Societal Risk is the PLL which is defined as the expected
value of the number of fatalities per year. PLL is a type of risk integral, being a
summation of risk as expressed by the product of consequence and frequency. The integral
is summed up over all potential undesired events that can occur.
3.2.4 Compared to the FN-diagram, the distinction between high frequency/low consequence
accidents and low frequency/high consequence accidents is lost: all fatalities are
treated as equally important, irrespective of whether they occur in high fatality or low
fatality accidents. PLL is a simpler format of Societal Risk than the FN-diagram. PLL is
typically measured as fatality per ship-year.
3.3 Comparing Societal Risk and Individual Risk
3.3.1 Societal Risk expressed in an FN-diagram allows a more comprehensive picture of
risk than Individual Risk measures. The FN-diagram allows the assessment not only of the
average number of fatalities but also of the risk of catastrophic accidents killing many
people at once.
3.3.2 However, unlike Individual Risk, both FN-diagrams and PLL values give no
indication of the geographical distribution of a particular risk. Societal Risk
represents the risk to a (large) group of people. In this group, the risk to individuals
may be quite different, depending, e.g. on the different locations of the individuals
when the accident occurs. The Societal Risk value therefore represents an average risk.
There is a general agreement in society that it is not sufficient to just achieve a
minimal average risk. It is also necessary to reduce the risk to the most exposed
individual. It is therefore adequate to look at both Societal Risk and Individual Risk
to achieve a full risk picture.
3.3.3 Societal Risk is difficult to apply to the task of risk reduction, specifically
because it is multidimensional.
3.4 Risk equivalence concept
3.4.1 Normally, from a given activity in industry, there tends to be a relationship
between fatalities and injuries of different severities resulting from an accident.
Furthermore, measures that will reduce the occurrence of fatalities also tend to reduce
injuries in proportion. In the literature there exist some studies on the ratio between
accidental outcomes, e.g. from Bird and German (1966). In document MSC 68/INF.6, a
straightforward approach was introduced, suggesting an equivalence ratio between
fatalities, major injuries and minor injuries:
3.4.2 The QALY and DALY concepts (refer to appendix 7) would represent more general
approaches for measuring injuries and health effects, and are used by e.g. the World
Health Organization (WHO).
4 ALARP PRINCIPLE
By using different forms of risk expressions, risk criteria can be created that meet the
requirement of different principles. The commonly accepted principle is known as the
ALARP principle. Risk criteria are used to translate a risk level into value judgement.
4.1 General
4.1.1 The purpose of FSA is to reduce the risk to a level that is tolerable. IMO has a
moral responsibility to limit the risks to people life and health, to the marine
environment and to property. In addition, IMO should also account for maintaining a
healthy industry. Spending resources on regulations whose benefits are grossly
disproportionate to their costs will put the industry in a less than competitive
position.
4.1.2 This is realized in the ALARP principle, which is shown in figure 2.
Figure 2: The ALARP principle
4.1.3 It states that there is a risk level that is intolerable above an upper bound. In
this region, risk cannot be justified and must be reduced, irrespectively of costs. The
principle also states that there is a risk level that is "broadly acceptable" below a
lower bound. In this region risk is negligible and no risk reduction required. If the
risk level is in between the two bounds, the ALARP region, risk should be reduced to
meet economic responsibility: Risk is to be reduced to a level as low as is reasonably
practicable. The term reasonable is interpreted to mean cost-effective. Risk reduction
measures should be technically practicable and the associated costs should not be
disproportionate to the benefits gained. This is examined in a cost-effectiveness
analysis.
4.2 Cost-effectiveness Analysis (CEA)
With this approach the amount of risk reduction that can be justified in the ALARP
region is determined. Several researchers have proven that most risks in shipping fall
into this region. As such, most of risk-based decisions will require a CEA. However, it
should be noted that this has not yet been verified for all ship types. There are
several indices which express cost-effectiveness in relation to safety of life such as
GCAF and NCAF, as described in appendix 7.
5 RECOMMENDED RISK EVALUATION CRITERIA
5.1 Individual Risk
5.1.1 Individual Risk criteria for hazardous activities are often set using risk levels
that have already been accepted from other industrial activities.
5.1.2 The level of risk that will be accepted for an individual depends upon two
aspects:
5.1.3 If a person is voluntarily exposing himself to a risk and/or has some control over
it, then the risk level that is accepted is higher as if this person was exposed
involuntarily to that risk or had no control over it.
5.1.4 For example: A passenger on a cruise ship or an occupant living in the vicinity of
a port have little or no control over the risks they are exposed to from the ship and/or
the port activity. They are involuntarily exposed to risks. A crew member on a ship,
instead, has chosen his workplace on a voluntary basis, and due to skills and training
has some control over the risks he/she is exposed to at the workplace.
5.1.5 An appropriate level for the risk acceptance criteria would be substantially below
the total accident risks experienced in daily life, but might be similar to risks that
are accepted from other involuntary sources.
5.1.6 The lower and upper bound risk acceptance criteria as listed in table 1 are
provided for illustrative purposes only. The specific values selected as appropriate
should be explicitly defined in FSA studies.
5.2 Societal Risk/FN-Diagram
5.2.1 When setting upper and lower bounds for societal risk acceptance, both an anchor
point and a slope should be defined. The slope reveals the risk inherent attitude: risk
prone, neutral or averse. It is recommended to use a slope equal of -1 on a log/log
scale to reflect the risk aversion.
5.2.2 In document MSC 72/16 it was pointed out that Societal Risk acceptance criteria
cannot be simply transferred from one industrial activity to another. This could lead to
illogical and unpredictable results. A method was introduced where the Societal Risk
acceptance criteria reflect the importance of the activity to the society (for more
detail, refer to document MSC 72/16, Skjong and Eknes (2001, 2002)).
5.2.3 For a given activity, an average acceptable Potential Loss of Life (PLL) is
developed by considering the economic value of the activity and its relation to the
gross national product. This can be done for crew/workers, passengers and other third
parties. The risk is defined to be intolerable if it exceeds the average acceptable risk
by more than one order of magnitude, and it is negligible (broadly acceptable), if it is
one order of magnitude below the average acceptable risk. These upper and lower bounds
represent the ALARP region, which thus ranges over two orders of magnitude, which is in
agreement with other published Societal Risk acceptance criteria.
5.2.4 It is recommended to apply this method to define Societal Risk acceptance criteria
on different ship types and/or marine activities, as the method can contribute to
transparency in using risk acceptance criteria for Societal Risk. In document MSC 72/16,
Societal Risk criteria developed with this method and expressed in FN-diagrams are
provided for different ship types.
5.3 Examples of risk acceptance criteria
5.3.1 The following criteria are broadly used in other industries and have been also
published in HSE (2001).
| Decision
Parameter
|
Acceptance
Criteria
|
| Lower bound for ALARP region
|
Upper bound for ALARP region
|
| Negligible (broadly acceptable) fatality risk
per year
|
Maximum tolerable fatality risk per
year
|
| Individual Risk
|
to crew members
|
10-6
|
10-3
|
| to passenger
|
10-6
|
10-4
|
| to third parties, member of public
ashore
|
10-6
|
10-4
|
| target values for new shipsfootnote
|
10-6
|
Above values to be
|
| Societal Risk
|
to groups of above persons
|
To be derived by using
economic parameters as per MSC 72/16
|
5.3.2 It is important to understand, that the above risk acceptance criteria always
refer to the total risk to the individual and/or group of persons. Total risk means the
sum of all risks that, e.g. a person on board a ship is exposed to. The total risk
therefore would contain risks from hazards such as fire, collision, etc. There is no
criterion available to determine the acceptability of specific hazards. Therefore, the
above criteria can be used to assess the acceptability of the total risk on being, e.g.
on a passenger ship, but not for assessing the specific risk of dying on a passenger
ship due to a fire.