The operation of tandem loading/offloading is associated with a high level of uncertainty because it usually operates in a dynamic environment in which both technical, and human and organisational, malfunctions may cause possible accidents. There is a lack of approaches for dealing
with uncertainty and vagueness in expert judgements in assessment of safety of the operations. This paper proposes a framework for modelling the safety of offshore and marine engineering systems using fuzzy reasoning and evidential synthesis approaches. The proposed method is capable of dealing
with uncertainties, including ignorance and vagueness, which traditional methods or frameworks for multiple criteria decision analysis, such as expected utility theory, cannot handle. A case study of the collision risk between a floating production, storage and offloading unit (FPSO) and a
shuttle tanker due to technical failure during a tandem offloading operation is used to illustrate the application of the proposed model.