Better the devil you know…

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.

A case in point, when we deal with safety critical signal switching the use of ‘ye olde’ electromechanical switches is often favoured over solid state circuits. On the face of it this doesn’t make sense because we can get much better reliability out of solid state switches. But if we look at the decision from the perspective of failure the picture changes somewhat. Solid state switches may be more reliable, but when they do fail their failure mode is more uncertain and more opaque. On the other hand electro-mechanical switches have been around for a long while so their failure modes are that much more visible, simple and well understood.

What we’re doing in this example is making a decision to accept the well understod, aleatory, risk of old school tech thereby eliminating the less well understood, epistemic, risks associated with the use of newer technology. A type of trade-off that I doubt you’ll find recognised (actually I know you won’t) in standards such as IEC 61508 or ISO 31000 for that matter.