# Hydrogen vs. Batteries: Comparative Safety Assessments for a High-Speed Passenger Ferry
###### Abstract  
Batteries and hydrogen constitute two of the most promising solutions for decarbonising international shipping. This paper presents the comparison between a battery and a proton-exchange membrane hydrogen fuel cell version of a high-speed catamaran ferry with a main focus on safety. The systems required for each version are properly sized and fitted according to the applicable rules, and their impact on the overall design is discussed. Hazards for both designs were identified; frequency and consequence indexes for them were input qualitatively, following Novel Technology Qualification and SOLAS Alternative Designs and Arrangements, while certain risk control options were proposed in order to reduce the risks of the most concerned accidental events. The highest ranked risks were analysed by quantitative risk assessments in PyroSim software. The gas dispersion analysis performed for the hydrogen version indicated that it is crucial for the leakage in the fuel cell room to be stopped within 1 s after being detected to prevent the formation of explosive masses under full pipe rupture of 33 mm diameter, even with 120 air changes per hour. For the battery version, the smoke/fire simulation in the battery room indicated that the firefighting system could achieve a 30% reduction in fire duration, with freedoors closed and ventilation shut, compared to the scenario without a firefighting system.  
I 2022 2  
Both emerging zero-emission technologies could be a potential solution for high-speed passenger ferries; however, the use of these novel propulsion methods and green technologies introduces new safety concerns and challenges in the design of ships, including weight limitations and internal arrangement restrictions. Regarding the safety issues, hydrogen gas leakage can lead to explosions under certain concentrations, while batteries are associated with fire risk. As far as the design of zero-emission high-speed vessels is concerned, substantial work has been carried out by the authors, within the TrAM project [4] and on alternative fuels [5], which is being extended through the work presented in this paper. Design optimisation has been beneficial for the performance improvement of various kinds of vessels [6; 7], including high-speed catamarans [8]. Recent studies on the hydrodynamic performance of high-speed catamarans in various operational conditions [9; 10] aim at reducing the energy requirements, resulting in more economical designs while mitigating the aforementioned challenges related to this kind of vessel.  
A brief overview of the existing literature, involving batteries and hydrogen applications on ships, is presented in Section 2. In Section 3, the proposed designs are discussed, including the considered systems for both versions. In Section 4, the most severe hazards and the most effective risk control options (RCOs) are presented after a hazard identification (HAZID) analysis was performed for the hydrogen and the battery versions of the ferry, following the formal safety assessment (FSA). In Section 5, materials and methods are presented, including quantitative risk assessments for both designs, using the PyroSim software. For the hydrogen version, a gas dispersion analysis in the fuel cell room is presented, while for the battery version, a smoke/fire simulation is performed in the battery room. In Section 6, the results are presented and discussed for various scenarios for both designs. The concluding remarks are presented in Section 7.