Risk prioritization in autonomous ship operational modes using FMEA and interval numbers

The Maritime Safety Committee of the International Maritime Organization named autonomous ships as Maritime Autonomous Surface Ships. For Maritime Autonomous Surface Ships, it is of utmost importance to remain at a required safety level, or acceptable risk, in ad hoc operational modes. Recently, the concept of risk has been increasingly adopted to measure the safety of socio-technical systems. In the case of Maritime Autonomous Surface Ships, a continuous risk assessment may be required, with respect to a predefined set of unwanted events associated with a corresponding operational modes. Despite the growing number of research works related to autonomous ships and their safety, an approach to compare the operating regimes from the point of risk assessment is still lacking in literature. Therefore, this paper proposes a three-step framework, aiming to assess the risk index and its uncertainty for a Maritime Autonomous Surface Ships in a given scenario, in three operational modes: Manual Control, Remote Control, and Autonomous Control. The applicability of the proposed framework is demonstrated on conventional ship grounding accidents, assuming the ships as being Maritime Autonomous Surface Ships. The results reveal that in a same scenario, the risk of Maritime Autonomous Surface Ships grounding and the inherent uncertainty vary across the operational modes.