# Hydrogen vs. Batteries: Comparative Safety Assessments for a High-Speed Passenger Ferry
## 2 Background
It was demonstrated that jet fires caused by hydrogen leakage could not be extinguished but fire field temperature could be reduced by setting the appropriate spray velocity and droplet size values, preventing fire spread and damage to adjacent equipment/structures. [PERSON] et al. [19] presented a consequence assessment using the FLACS CFD model to estimate the fatality risks during operation and at night, related to various hydrogen systems, including high-pressure piping, vent mast, and high-pressure storage tanks, onboard a hydrogen-fuelled high-speed ferry. It was demonstrated that the design was equivalent in terms of safety with conventionally fuelled ferries. [PERSON] and [PERSON] [20] presented a preliminary HAZID risk assessment for another concept design, the SF-Breeze high-speed catamaran, with hydrogen stored in liquefied form. In this assessment, bunkering was also considered, and it was demonstrated that collision during operation and fuel spill during bunkering were the most severe hazards (highest risk indexes). Another safety analysis was conducted to assess the hydrogen diffusion using ANSYS Fluent software in the SF-Breeze by [PERSON] et al. [21], but it was assumed that hydrogen is stored in compressed gas form at 200 bar. It was assessed how hydrogen was concentrated in space depending on the leakage position for different ventilation and hydrogen detection systems' arrangements. The highest hydrogen concentrations were observed in the corners of the fuel cell rooms. Similarly, there are very few research studies related to the risk assessments on marine battery power plants. One study carried out by [PERSON] et al. [22] developed a multi-criteria decision-making approach for a hybrid battery-engine system focusing on cost-environment-risk issues. In their study, the qualitative risk assessment conducted could be further expanded to a quantitative risk assessment. There are also classification societies' guidelines providing risk assessment and safety design for the maritime batteries' application [23; 24]. In the TrAM project, a safety level evaluation was carried out including HAZID, fault tree analysis (FTA), event tree analysis (ETA), and cost-benefit assessment on RCOs [25]. Currently, most studies are focused on the design/efficiency, as well as the cost or emission analysis, of hybrid arrangements including both batteries and fuel cells for the propulsion [26; 27; 28; 29]. In this work, two zero carbon emission designs are proposed. For the design of the hydrogen ferry, hydrogen is stored as a cryogenic liquid (LH\({}_{2}\)), since it is more gravimetrically and volumetrically effective, enabling larger amounts of fuel to be stored onboard and used for propulsion, without requiring frequent refuelling [20]. LH\({}_{2}\) is used as the only fuel source for the catamaran ferry. Batteries are used only for emergency situations in case of severe failure of hydrogen systems. In the battery version, the ferry is fully electric, powered solely by electricity. The novelty of this paper is twofold. First, two novel zero-emission solutions are proposed and compared for a catamaran ferry, showcasing the possibility of a pure hydrogen solution, with hydrogen stored in liquefied form, and a pure electric alternative. Secondly, a detailed safety comparison is performed for these zero-emission solutions for the high-speed passenger vessel including HAZID analysis but also gas and smoke dispersions in the fuel cell and battery rooms, respectively. As was derived from the literature review, this is the first work to perform such an in-depth safety assessment for these decarbonising solutions for passenger ferries.