Comprehensive Literature Review of State of Safety (SoS) for Maritime Battery Management Systems (BMSs)

Battery-powered vessels can help reduce greenhouse gas emissions in the maritime industry, which is crucial to achieving the International Maritime Organization’s (IMO) ambition of net-zero emissions by 2050. However, batteries also introduce unique safety risks, since failures can lead to catastrophic outcomes such as thermal runaway and onboard fires. Effective Prognostics and Health Management (PHM) is essential for early detection of hazardous states to prevent critical failures or unsafe conditions. This paper investigates the emerging concept of state of safety (SoS), a metric for real-time quantification of battery safety, which is essential for ensuring safe operation of battery-powered vessels. A PRISMA-based literature review is conducted to address three research questions: (1) What are the current definitions of SoS in the maritime and other industries? (2) What are the existing methods to estimate SoS? (3) What gaps remain in defining and implementing SoS in the maritime industry? The review reveals recent advancements in SoS research from the automotive and energy storage domains, while identifying a notable lack of studies addressing SoS in maritime battery systems. Existing estimation approaches and key battery parameters relevant for SoS assessment are reviewed and critically discussed. To advance the practical implementation of SoS, the paper provides a structured overview of the battery parameters required for comprehensive SoS implementation, including measurement methods and associated challenges. Furthermore, safety hazards identified in the European Maritime Safety Agency (EMSA) battery guidance are systematically allocated across the battery management system, SoS, and design levels, thereby positioning SoS as a complementary layer to the safety functions ultimately governed by the Battery Management System (BMS). Finally, future research directions are outlined for advancing SoS estimation in marine applications, focusing on interpretability, granularity, ultrasound-based strain monitoring, and integration in the maritime environment.