Analysis of risks related to maritime hydrogen-based propulsion solutions

Abstract

The maritime sector is actively investigating new solutions for zero emissions in
response to climate change. One of the promising options is hydrogen-based propulsion, but there are currently no prescriptive rules or legislation to approve the design of such innovative, unproven technology. The International Maritime Organization (IMO) requires a quantitative risk assessment to demonstrate that the safety level of hydrogen-fueled vessels is equivalent to that of conventional-fueled vessels. To address this challenge, a risk-based design approach is needed, and the quantitative risk assessment process plays a crucial role in the early design stage.

This research contributes to the technical understanding and potential of zero-emission maritime hydrogen propulsion solutions, by designing a quantitative risk assessment system for analyzing and evaluating risks associated with this innovative technology. The developed risk-analysis system could be a useful tool for future development. While compressed hydrogen design has matured and undergone relevant risk studies, its low volumetric energy density limits its sailing distance. Liquid hydrogen provides a more energy-dense solution, enabling longer-distance sea-going missions, but its application in the maritime industry lacks related risk studies. Therefore, this study aims to design a quantitative risk assessment system for maritime liquid hydrogen propulsion that can analyze and evaluate risks adequately.

The methodology of this study includes a conceptual design of a liquid hydrogen-fueled vessel, followed by hazard identification and scenario selection. The Bayesian theory was used to assess the leak frequencies of components operating with liquid and gaseous hydrogen from published literature, with adjustments made for the harsh maritime environment and mechanical systems. Ignition probability models were proposed, and validated consequence models were used to simulate hazards. Risks are presented as individual and societal risks and compared to acceptance criteria to determine the acceptability of the design. Mitigation measures were proposed and examined. The study also compared the risks associated with liquid and compressed hydrogen configurations.

The conclusion of this study shows that the risks associated with maritime liquid hydrogen-based propulsion solutions can be acceptably managed with appropriate mitigation measures. Specifically, the results indicate that for the FPS Rijn vessel, the risks are acceptable for up to 20% of the operational time without any mitigation measures, as long as the liquid hydrogen system is located at least 45 meters away from crew rooms. However, with the implementation of mitigation measures, such as those proposed in this study, it is possible to operate the vessel 100% of the time with acceptable risks. Additionally, a comparison of liquid and compressed hydrogen designs demonstrate that liquid hydrogen designs have a similar risk level as compressed hydrogen designs but offer advantages in terms of space-saving and longer-distance characteristics, making them a promising candidate for maritime zero-emission propulsion solutions in the future.

Nonetheless, it is essential to validate the consequences and liquid hydrogen leak frequencies more rigorously, as limited information is currently available for this innovative technology. Overall, this research explores the risks of maritime hydrogen-fueled applications and challenges the perception of hydrogen as an impossible and dangerous substance.