Tolerability and acceptability criteria require updating as changes in the world, risk perception and demographic change. This paper explores how a acceptability curve can be built from a G8 perspective, by analyzing recent events (last decade) such as Fukushima, 9/11 Twin Towers, quakes in Italy, traffic accidents etc.

1. Oboni Riskope Associates Inc.
www.riskope.com
500-1045 Howe Street
Vancouver, B.C., V6Z 2A9
What Fukushima (2010) nuclear accident, the Twin Towers (9/11) terror
attack, deadly traffic accidents and Aquila earthquake (Italy) have in
common?
An update of Whitman's and ANCOLD tolerability/acceptability curves (casualties
from man-made or natural catastrophes, large dams failures) shows evidence for a
G8-wide societal acceptability threshold.
By Franco & Cesar Oboni, Oboni Riskope Associates Inc. Vancouver, www.riskope.com
As already repeatedly stressed, balanced, sensible decisions related to mitigation and various
aspects of planning can be taken only if risks are compared with a tolerability/acceptability
criterion. The term tolerability generally refers to physical losses, business interruption losses etc.,
whereas acceptability refers to life losses, casualties.
Whitman and ANCOLD tolerability/acceptability thresholds
Acceptability criteria were first explicitly established in the mid-eighties by researchers such as
Whitman and Morgan. Their original curves (which used a “double scale”, as they simultaneously
displayed physical losses and casualties -a concept that is quite impopular and therefore rarely used
today) are reproduced in Figure 1, together with another set established by the Australian National
Committee on Large Dams Incorporated (ANCOLD Inc). In general, authors present a "low" curve,
i.e. a conservative one, and a “high”curve, or an aggressive one.
Operational risks tolerability curves can be established, generally for physical losses, business
interruption, etc. Figure 2 shows a real example (names have been replaced with achronims to
protect client's confidentiality, where major risk scenarios are compared to client's tolerability.
Why to update?
For a recent study, it became necessary to check if an update of Whitman curves was due,
specifically in terms of human losses (casualties). The “feeling” was indeed that since our world has
changed, demographics have changed, airplanes are larger, media coverage has changed and, above
all, our social sensitivity has changed, the curves have to be updated.
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2. It also seems that if on one hand we are very sensitive to the single loss, or personal tragedy, on the
other, we are becoming numbed to large numbers.
Fig. 1 TolerabilityAcceptability thresholds defined by Whitman (1984) and Ancold (for each one the
"conservative" and the "aggressive" thresholds are displayed). The bubbles display common events
for various industries. In the original papers the horizontal axis showed casualties as well as
monetary losses -a concept that is considered quite unpopular nowadays.
Fig. 2 Real life Risk Assessment results, with an operational tolerability curve superimposed to the
"risk landscape" of a major operation (fourteen risk scenarios are displayed).
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3. Defining an updated societal, large scale, G8 acceptability threshold
Instead of using Riskope's (www.riskope.com) proprietary algorithm to define the
tolerability/acceptability threshold, for the sake of this exercise, we proceeded empirically, using
facts emerging from the G8 countries, including Japan, United States, Italy as follows:
• Several dozens casualties per week-end, several times per year, lead the Italian government
to invest a large capital in a continuous real time speed checking and enforcing system
(Traffic Tutor), as the situation was intolerable.
• A quake causing 308 casualties (Aquila), thirty years after another catastrophic one (Irpinia)
lead to the conviction of a large number of public officers for mass man-slaughter and
various other charges (no such reaction for the Irpinia one, thirty years before).
• A terrorist act (9/11, New York) caused approx. 3,000 casualties and the USA “declared war
on terrorism”.
• A quake and a tsunami (Fukushima) with a wave considered to be larger than the Maximum
Credible Event (MCE) have caused an evacuation zone of 20km, then 30km radius, with
very large number of afflicted people (which may become ill in the future); Germany and
other countries have decided to stop their nuclear energy programs, showing that the event
was considered intolerable.
In Figure 3 we show the empirical curve derived from these facts in blue colour, and we display in
black colour (for purposes of comparison with Whitman original acceptability) a least-squares
approximation of the blue curve data. For the sake of this exercise we have extended Whitman's
curves to the right, to cover larger casualties events.
Figure 3 displays in green colour the extended Whitman lower bound (lower limit of societal
tolerability1) roughly passing through 10-6/year (1/1,000,000) and 1M death, i.e. a scenario with a
probability at the lower limit of credibility and losses comparable to a city destroyed to the ground
(a scenario one could imagine, for example, in Naples, with a quake and a catastrophic eruption of
Mount Vesuvius, for which Italian Authorities perform Civil Protection drills, but do not enforce
seismic upgrade of buildings, as opposed to the high levels of capital investments allotted in the
same country to flood protection).
The orange couloured threshold (Fig.3) corresponds to a theoretical constant-risk tolerability
(meaning that the product between the number of casulaties and the probability is constant, in this
case equal to one). This threshold is remarkably parallel, although slightly converging for higher
casualties events, to the updated acceptability threshold (in black), showing that G8 societal
perception leads to lower acceptability than constant risk for larger events.
1 The upper limit of Whitman seems today difficult to defend because it is excessively "permissive", or in
other words, shocking to the public.
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4. Fig 3. Comparison of the various curves, i.e.: Whitman (upper and lower), Ancold (upper and lower),
2011 Riskope's update, constant risk.
Once the acceptability threshold is defined, it becomes possible, for each risk scenario, to determine
if the risk is acceptable or not, then calculate how unacceptable it is (surface colored in orange) as
displayed in Figure 4.
Fig. 4. When probability and consequences of a scenario are evaluated, the total risk is equal (p*C)
to the surface of the rectangle (sum of orange and blue areas). The blue area is the tolerable part of
that scenario, the orange part is the intolerable portion. NB: the log-log scale requires some attention
when interpreting the relative size of surfaces, as shown in the bar diagram at the right, in decimal
scale.
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5. Appropriate responses based on a clear plan pave the road to long-term survival and development of
the system and its owner, as we have noted and discussed in detail in our book2.
Conclusions
The following remarks can be made on the updated curve we generated:
• Between 1984 Whitman lower bound and 2011 we note a clock-wise (to the right) “rotation”
of the curve. This indicates that:
• In the G8 countries, when looking at large scale catastrophes (1M casualties and
more, country wide scale), societies are less tolerant than in the '80s
• as opposite to the prior point, when looking at events potentially generating less than
1M casualties, societies are more tolerant than in the '80s
• as a side note we remind that scale effects are very significant: for example, when
shifting from a country wide scale to a “facility scale”, the acceptability (we are not
showing that case today) is significantly lower than in 1984
• The Whitman aggressive (upper bound) curve is nowadays in the intolerable region starting
at 1,000 casualties, as opposite to being in the tolerable region below 1,000 casualties
• When comparing the 2011 curve with a “theoretical constant risk” curve, we note they are
almost parallel, meaning that one-casualty-high-probability event is as acceptable as high-
casualties-low-probabilities events. Instead, Withman lower and upper bound were “flatter”
than the “theoretical constant risk”, characterising societies getting more tolerant as
casualties increase and probabilities decrease.
As we saw in detail in another paper, we have written several times 3 and anyone can understand by
intuition, the part of intolerable risk is the key to the rational prioritization of risks and rational
decision making when planning mitigations.
Sound mitigation decisions will invest funds and resources appropriately, where risks are indeed the
most critical, i.e. the most intolerable, allowing sustainable, reasonable and transparent risk
management. This will become of paramount importance with new challenges coming from climate
changes, shear demographic and population density, larger cities etc.
Once the right approach has been developed and provided appropriate preparedness measures on a
system have been taken, time required for appropriate responses in case of occurrence of hazards
(sources of risk) will definitely shortened.
Lack of proper preparation can lead the system (and its owner, whether a company, government
entity, an NGO) to collapse.
2) http://book.oboni.net/
3 )http://foboni.wordpress.com/2010/06/08/bp-crisis-rational-analysis-what-bp-did-not-perform/
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