Interpretation of the Safety Risk Tolerance Criteria for Integrated Asset Management of Pipelines

Abstract Safety risk tolerance criteria are commonly established using the risk measures for individual risk and societal risk. Several studies on the review of international standards for safety risk acceptance criteria have identified that in most international standards, the societal risk criterion is expressed in terms an F-N curve where N is the expected number of fatalities due to hazardous conditions posed by an infrastructure element and F is the estimated frequency of N or more fatalities. The Netherlands and the UK have pioneered establishing the risk tolerance criteria for both individual and societal risk. The development of the safety risk tolerance criteria was primarily in the context of regulatory decision-making for the permitting process of the facilities, which was later expanded to include hazardous materials transport and pipelines. For the existing facilities and pipelines, the risk tolerance criteria are used extensively for land-use planning and development. Recently, Canadian standard, CSA Z662:2023 “Oil and Gas Pipeline Systems” has included quantitative risk criteria for pipelines in the informative (non-mandatory) Annex B portion that is applicable for the risk management of all aspects of the pipeline life cycle. Following the established international norms, the individual and societal risk criteria were published such that the societal risk criterion for the F-N curve to be applied over one kilometer of the pipeline. In contrast to the international standards such as IGEM/TD/2 “Assessing the risks from high pressure Natural Gas pipelines” (2015), there is little guidance to differentiate between use of the quantitative safety tolerance criteria for the purpose of permitting of new pipelines and land-use planning with the purpose of pipeline integrity management. This paper presents the differences in the use of available quantitative safety risk tolerance criteria for land-use planning and the pipeline risk management during the pipeline life cycle. The applicability of the risk tolerance as intended during the development of criteria, is critically reviewed when used in the context of risk management for the integrated asset management of the pipeline considering the life cycle performance. Additional considerations for interpreting the safety risk tolerance criteria during decision-making regarding risk mitigation actions are proposed. Furthermore, linear metrics used in risk measures established for other linear infrastructure, such as roads, and railways are compared with pipelines, and the differences between risk measures to establish tolerance criteria for point-source hazard infrastructure, such as chemical facilities, with the linear infrastructure, such as pipelines are highlighted.