A note on the layered approach for implementing ALARP and the grossly disproportionate criterion

In this note, we discuss the as low as reasonably practicable (ALARP) principle and the implications for safety management of using the 'layered approach' to implement this principle. It is an approach following a decision logic diagram consisting of three steps to guide the implementation, i.e., a crude analysis, a more detailed analysis and an assessment of other issues, including uncertainties. We show that the weight given to risk reduction and uncertainties largely depends on how this layered approach is interpreted. There are different ways to interpret it. For example, the approach may be interpreted in a way where the ALARP principle gives strong weight to the uncertainties for all decision-making contexts. A very different interpretation, which leads to a more dynamic approach is that the ALARP principle may range from one extreme, where decisions are made with reference to an expected value with limited or no weight on the cautionary principle for some decision contexts, to another, in which the cautionary principle is adopted without any reference to cost-benefit (cost-effectiveness) analyses for others.