This paper describes the methodology followed in a real-life case study to carry out a comprehensive quantitative As Low As Reasonable Practicable (ALARP) analysis for a Tailings Storage Facility (TSF), and its application in supporting the decision-making process related to closure alternatives.
The methodology is based on a Quantitative Risk Assessment (QRA), which allows the estimation of risk levels for a set of closure alternatives, through the estimation of Probabilities of Failure (PoF) for each mitigation scenario and related consequences. PoFs also allow benchmarking of the estimated hazard levels against the worldwide portfolio of documented failure cases and comparison of harm to people risks with internationally recognized tolerance thresholds.
Later, mitigation CAPEX and annualized risk cost estimations allowed the production of a set of curves for each alternative, which, in turn, were used to determine at which level of mitigation, the residual risk obtained in further reductions of PoF becomes disproportionate with the level of effort required to implement those measures.
Furthermore, the ALARP analysis extended to assess the variability of mitigation efficiency along the expected life of the structure, including factors such as changes in PoF, impact costs and mitigation CAPEX. The real-life case study highlighted the benefits, in economic and risk-reduction terms, of including such variables as part of the selection process of closure alternatives along the lifecycle of the TSF.
