Archives For Epistemic Risk

When you look at the safety performance of industries which have a consistent focus on safety as part of the social permit, nuclear or aviation are the canonical examples, you see that over time increases in safety tend to plateau out. This looks like some form of a learning curve, but what’s the mechanism, or mechanisms that actually drives this process?

There are actually two factors at play here, firstly the increasing marginal cost of improvement and secondly the problem of learning from rare events. In the first case increasing marginal cost is simply an economist’s way of stating that it will cost more to achieve that next increment in performance. For example, airbags are more expensive than seat-belts by roughly an order of magnitude (based on replacement costs) however airbags only deliver 8% reduced mortality when used in conjunction with seat belts, see Crandall (2001). As a result the next increment in safety takes longer and costs more (1).

The second case is a more subtle version of the first. As we reduce accident rates accidents become rarer. Now one of the traditional ways in which safety improvements occur is through studying accidents when they occur and then to eliminate or mitigate identified causal factors. Obviously as the accident rate decreases this likewise the opportunity for improvement also decreases. When accidents do occur we have a further problem because (definitionally) the cause of the accident will comprise a highly unlikely combination of factors that are needed to defeat the existing safety measures. Corrective actions for such rare combination of events therefore are highly specific to that events context and conversely will have far less universal applicability.  For example the lessons of metal fatigue learned from the Comet airliner disaster has had universal applicability to all aircraft designs ever since. But the QF-72 automation upset off Learmouth? Well those lessons, relating to the specific fault tolerance architecture of the A330, are much harder to generalise and therefore have less epistemic strength.

In summary not only does it cost more with each increasing increment of safety but our opportunity to learn through accidents is steadily reduced as their arrival rate and individual epistemic value (2) reduce.

Notes

1. In some circumstances we may also introduce other risks, see for example the death and severe injury caused to small children from air bag deployments.

2. In a Popperian sense.

References

1. Crandall, C.S., Olson, L.M.,  P. Sklar, D.P., Mortality Reduction with Air Bag and Seat Belt Use in Head-on Passenger Car Collisions, American Journal of Epidemiology, Volume 153, Issue 3, 1 February 2001, Pages 219–224, https://doi.org/10.1093/aje/153.3.219.

Crowely (Image source: Warner Bro's TV)

The psychological basis of uncertainty

There’s a famous psychological experiment conducted by Ellsberg, called eponymously the Ellsberg paradox, in which he showed that people overwhelmingly prefer a betting scenario in which the probabilities are known, rather than one in which the odds are actually ambiguous, even if the potential for winning might be greater.  Continue Reading…

4blackswans

One of the problems that we face in estimating risk driven is that as our uncertainty increases our ability to express it in a precise fashion (e.g. numerically) weakens to the point where for deep uncertainty (1) we definitionally cannot make a direct estimate of risk in the classical sense. Continue Reading…

I’ve rewritten my post on epistemic, aleatory and ontological risk pretty much completely, enjoy.

SFAIRP

The current Workplace Health and Safety (WHS) legislation of Australia formalises the common law principle of reasonable practicability in regard to the elimination or minimisation of risks associated with industrial hazards. Having had the advantage of going through this with a couple of clients the above flowchart is my interpretation of what reasonable practicability looks like as a process, annotated with cross references to the legislation and guidance material. What’s most interesting is that the process is determinedly not about tolerance of risk but instead firmly focused on what can reasonably and practicably be done. Continue Reading…

Well it was either Crowley or Kylie Minogue given the title of the post, so think yourselves lucky (Image source: Warner Brothers TV)

Sometimes it’s just a choice between bad and worse

If we accept that different types of uncertainty create different types of risk then it follows that we may in fact be able to trade one type of risk for another, and in certain circumstances this may be a preferable option.

Continue Reading…

Interesting article on old school rail safety and lessons for the modern nuclear industry. As a somewhat ironic addendum the early nuclear industry safety studies also overlooked the risks posed by large inventories of fuel rods on site, the then assumption being that they’d be shipped off to a reprocessing facility as soon as possible, it’s hard to predict the future. 🙂