Quantitative risk assessment of medium-sized floating regasification units using system hierarchical modelling

Currently there are no sufficiently detailed and specific regulations and guidelines applicable to Floating Regasification Units. In view of the fact that these units are likely to become more popular in the near future, their safety needs to be examined urgently. During the design of the world's first medium-sized floating regasification unit a qualitative risk assessment was carried out. Although the results are useful, they cannot be used for developing rules and regulations directly. For such purposes some detailed quantitative studies are essential. This paper addresses this gap and introduces a hierarchical system modelling method to overcome the problem of the lack of direct statistical accident data of novel systems. The method was implemented in IQRA (integrated quantitative risk assessment), a piece of software developed in-house for quantitative risk assessment. The safety of the floating regasification unit mentioned above was assessed using this software and the results were compared against the results obtained from conventional qualitative and the quantitative risk assessment. It was found that the qualitative risk assessment had a tendency to overestimate the frequency of the accidents but to underestimate their consequence, while the quantitative risk assessment based on the result of the qualitative assessment inherently underestimated both the frequency and the consequence of hazards. The hierarchical modelling was found to be an excellent method of dealing with complex systems with short operational history.