C4.6 Proportionality

risk-engineering.org [26]

The sixth component requires that treatment of a risk in the tolerable region continue until the next step of reduction is grossly disproportionate to the benefit it would bring, and that the disproportion be argued in writing rather than assumed. The source is the acceptability module of the open engineering course [26], which places a risk in one of three regions, unacceptable, tolerable and broadly acceptable, and in the middle region applies the test known by its initials as ALARP: as low as reasonably practicable, where reasonably practicable has a meaning and gross disproportion must be shown. Chapter 11 adopted “tolerable” in exactly this sense, as a state between accepted and unacceptable that is conditional on the argument being made.

This reconciles two failures that sit at opposite ends of most risk committees. One is the instinct to mitigate everything, which spends the control budget on the risks that are easiest to control rather than the ones that matter and buries the process under administrative measures that decay. The other is the instinct to accept whatever is cheap, which is the undecided decision in another form. The component gives a stopping rule that is neither, and it gives the auditor something to read: not whether the risk was reduced, but whether the organization wrote down why it stopped where it did.