(68e) The Use of Quantitative Risk Assessments (QRA) for Lng Plants

Application of quantitative risk assessment (QRA) becomes more common during early phases of LNG projects instead of deterministic methods, such as worst-case or maximum credible event approaches. Among other reasons, it is mainly due to the fact that deterministic methods are heavily relied on "over-sized" scenarios, and may result in wasting sources on over-confident LNG-terminals in some cases. Deterministic methods are also unfavourable from the viewpoint of project owners who attempt to build LNG terminals more compactly with minimum sufficient separation distances, but still complying with applicable codes and regulations and without compromising on safety aspects. QRA is an integrated approach and has many advantages in comparison to deterministic methods. Evaluating up to hundreds of scenarios, it provides an in-depth understanding and valuable input to decision-makers. QRA also indicates the risks related to components or sections in an LNG plant dominating the overall risk picture and thus enabling that the resources for risk-reducing measures are allocated correctly. Another benefit of QRA is that, once quantifying the risks for a specific LNG plant, the change of risk level due to a future expansion project or any modification can easily be implemented and communicated. However, QRA has some limitations. An important limitation of QRA is encountered while identifying and treating the uncertainties, introduced during different stages of the risk assessment. The objective of this paper is to describe the application of QRA for LNG terminals and discuss various types of uncertainties in QRA for LNG terminals. This is achieved partly based on a case example from an ongoing Swedish LNG terminal project in the Stockholm region. It is the authors opinion that today, the QRA method, notwithstanding the problems regarding mapping out and treating uncertainties, is the most powerful tool available for safety evaluation of LNG terminals. When applied properly and the uncertainties treated well, QRA allows decision-makers to design LNG terminals cost-effectively with very high level of safety.