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In this blogpost we attempt an update of Whitman’s and ANCOLD tolerance/acceptability curves.
These link casualties from man-made or natural catastrophes, large dams failures to a “tolerable” annual probability.
The attempt shows evidence for a G8-wide societal acceptability which has only slightly changed since the original studies by Whitman..
We have already discussed many times how well-balanced and sustainable decisions can only be taken if risks are compared to properly defined risk tolerance /acceptability criteria.
The first explicit examples of Risk Tolerance/Acceptability criteria were published in the mid-eighties by Whitman and Morgan. In more recent times the Australian National Committee on Large Dams (ANCOLD Inc) also came out with its own criteria.
In general those authors defined two criteria. A prudent or risk averse one, thus a low bound curve, and a risk prone aggressive, high bound curve.
The curve we built is not necessarily the “true” large scale acceptability. Indeed, we used a few examples of events that:
a) caused significant casualties,
b) by the generated reactions, clearly showed the events were not tolerable in G8 countries.
Furthermore, by the very nature of the events, our curve is not the lower bound one. It is instead most likely near of just higher than the new upper bound 2011 tolerance/acceptability threshold.
As mentioned above we used 2000-2011 events from G8 countries, Japan, USA, Italy as follows:
Several dozens traffic accidents casualties per week-end, several times per year. Those accidents lead the Italian government to invest a large capital in a continuous real-time speed checking and enforcing system (Traffic Tutor), road safety, as the situation was intolerable.
A quake causing 308 casualties (Aquila), thirty years after another catastrophic one (Irpinia). The second event 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. As a result 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). That event 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. Thus they showed they considered the event was intolerable.
We can make the following remarks on the 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, Whitman lower and upper bound were “flatter” than the “theoretical constant risk”, characterising societies getting more tolerant as casualties increase and probabilities decrease.