What is ALARP and How Can it Improve Dam Safety Decisions?

A key principle in achieving tolerable risk is “reducing risks as low as reasonably practicable” (ALARP). The following factors are commonly taken into account in making a judgment on whether risks are ALARP: the level of risk in relation to the tolerable risk limits; the disproportion between the cost (money, time, trouble and effort) of implementing the risk-reduction measures and the subsequent risk reduction achieved; the cost-effectiveness of the risk-reduction measures; compliance with good established practice; and societal concerns as revealed by consultation with the community and other stakeholders. Thus, the ALARP evaluation and demonstration is both qualitative and quantitative in nature. Consideration of the cost effectiveness of achieving life-safety risk reduction relative to life-safety benefit achieved is a quantitative aspect; but it introduces the consideration of cost only to justify further risk reduction below tolerable risk limit(s), and not to justify achieving the limits in the first place.
Following a background overview of the definition tolerable risk, the tolerability of risk framework and examples of tolerable risk guidelines, the paper discusses various considerations in evaluating and demonstrating ALARP for a dam. Reference is made to experience from ALARP evaluations conducted for actual dams.