Safety integrity level (SIL) determination for a maritime fuel cell system as electric propulsion in accordance with IEC 61511

This study investigates the safety integrity levels for an electric propulsion system based on a molten carbonate fuel cell in a liquefied hydrogen tanker. The electric propulsion system necessitates multiple electronic and electric elements; thus, the functional safety of the system should be considered. Additionally, a maritime fuel cell system is nonconventional propulsion machinery. This system should follow a risk-based ship design framework, and IEC 61511 is a suitable standard for evaluating the functional safety of the system. Hazardous operability studies provide basic information for determining the safety integrity. In this work, a safety layer matrix and calibrated risk graph are generated, and a layer of protection analysis is conducted for a molten carbonate fuel cell stack. Eight guidewords are used to describe accidental scenarios and compare the results of the three methods in an unbiased manner. The most severe consequences are fire and explosion caused by overflows or a control failure in the stack, and the safety integrity levels are mutually different.