Archives For Categories of risk


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…

For those of you interested in such things, there’s an interesting thread running over on the Safety Critical Mail List at Bielefeld on software failure. Sparked off by Peter Ladkin’s post over on Abnormal Distribution on the same subject. Whether software can be said to fail and whether you can use the term reliability to describe it is one of those strange attractors about which the list tends to orbit. An interesting discussion, although at times I did think we were playing a variant of Wittgenstein’s definition game.

And my opinion? Glad you asked.

Yes of course software fails. That it’s failure is not the same as the pseudo-random failure that we posit to hardware components is neither here nor there. Continue Reading…

Why we should take the safety performance of small samples with a grain of salt

Safety when expressed quantitatively as the probability of a loss over some unit of exposure, is in effect a proportional rate. This is useful as we can compare the performance of different systems or operations when one has of operating hours, and potentially lots of accidents while another has only a few operating hours and therefore fewer accidents. Continue Reading…


Or how do we measure the unknown?

The problem is that as our understanding and control of known risks increases, the remaining risk in any system become increasingly dominated by  the ‘unknown‘. The higher the integrity of our systems the more uncertainty we have over the unknown and unknowable residual risk. What we need is a way to measure, express and reason about such deep uncertainty, and I don’t mean tools like Pascalian calculus or Bayesian prior belief structures, but a way to measure and judge ontological uncertainty.

Even if we can’t measure ontological uncertainty directly perhaps there are indirect measures? Perhaps there’s a way to infer something from the platonic shadow that such uncertainty casts on the wall, so to speak. Nassim Taleb would say no, the unknowability of such events is the central thesis of his Ludic Fallacy after all. But I still think it’s worthwhile exploring, because while he might be right, he may also be wrong.

*With apologies to Nassim Taleb.

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.

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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. 🙂

NASA safety handbook cover

Way, way back in 2011 NASA published the first volume of their planned two volume epic on system safety titled strangely enough “NASA System Safety Handbook Volume 1, System Safety Framework and Concepts for Implementation“, catchy eh?

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