2023 – Deep ALARP Approach and Justification for Dams with Challenging Multiple Failure Modes

Michel Raymond, Chad Martin, Mark Foster, Christopher Dann, Helena Sutherland

Approaches to demonstrate ALARP for safety risks remain challenging for some dams where risk reduction measures might be considered grossly disproportionate for cost-effectiveness criteria, and the lack of defensive risk controls would remain inadequate to confidently meet good practice criteria.

Justifying ALARP is not a simple process. While some frameworks have been developed to guide ALARP assessments, it is ultimately the rigour in scanning and assessing all plausible options to reduce risk and justification of what is reasonably practicable and what is not reasonably practicable that is needed to arrive at confident conclusions. Complex situations with multiple failure modes can be guided by considering adverse or beneficial compatibility for performance across failure modes. Considering implementation risks and created risks can add strength to justify unreasonableness of measures, and may have more weight than reliance on gross disproportion cost-effectiveness criteria. It requires careful reasoned judgment that would stand the test of future challenge for example about why a particular risk reduction measure was or was not considered. Achieving adequate due diligence for an ALARP conclusion may require multiple iterations and, in many cases, it might not be possible in a one-pass assessment.

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