# Hydrogen vs. Batteries: Comparative Safety Assessments for a High-Speed Passenger Ferry
## 7 Conclusions  
In this study, a comparative safety assessment of the battery and hydrogen version of the Stavanger high-speed catamaran ferry was presented. Placement of the LH2 tank at the upper deck and batteries at the aft of the main deck in the hydrogen and battery version, respectively, were considered the most suitable design solutions. In the hydrogen version, both fuel cell rooms were located within gastight enclosures in the main deck behind the passengers' area. The DC/AC converters were required to supply AC to e-motors in both hydrogen and battery versions. Both designs satisfied the HSC stability requirements. A qualitative HAZID approach was conducted for both versions to determine the most concerning hazards. For both designs, proper installation of alarm and firefighting equipment, as well as testing of the equipment prior to its use, were considered to be amongst the most effective RCOs in terms of safety. Leakage in the fuel cell room due to piping damage at the inlet of the fuel cell stacks, as well as fire in the battery room during construction/installation or operation were considered to be the most severe hazards for the hydrogen and battery version, respectively, and they were analysed in quantitative assessments using PyroSim software. A battery has more energy stored at any instant wherein an accident might occur compared to fuel energy in the hydrogen fuel cell, which constitutes an increased fire risk for battery applications. In other words, when hydrogen leakage is detected by sensors in the fuel cell stacks or the room, the supply can be automatically shut off by valves, reducing the fire risk, despite hydrogen's low ignition energy. In this study, in the case of hydrogen leakage, it was demonstrated that flow should be stopped within 1 s after gas concentrations higher than 0.4% are detected by any of the three sensors in the ceiling of the fuel cell room, in order to avoid explosive atmospheres under piping leakages from diameters of 16-33 mm. For the battery version, there is one sprayer of FFS in the ceiling of each battery room to reduce the smoke concentration and the probability of fire. The sprayer of FFS is activated when the temperature reaches 68 degrees Celsius, spraying with a volume flow rate of 192 litre/min. Minimising ignition sources in fuel cell and battery rooms is crucial for both designs so that potential gas or smoke released will not lead to fires. In the case of a fire, Novec1230 should be used as the firefighting system in fuel cell and battery rooms. Gastight bulkheads and firedors are essential for hydrogen and battery versions, respectively, in order to mitigate the escalation risk to adjacent places and especially in the passenger area in the middle part of the main deck. Ventilation can be effective before any ignition takes place in both designs, but in the case of a fire, vents need to be shut off. For the hydrogen version, leakages of 3 mm diameter did not constitute an ignition risk if leakage was stopped within 1 s after being detected. For 16 mm diameter of piping leakage, flammable masses, with 7.5% hydrogen concentration in air, were present in the room with 30 ACH for around 30 s. However, they were mostly concentrated near the ceiling, away from the stacks, resulting in low ignition risk. In the case of full pipe rupture (33 mm diameter), increasing the ventilation rates from 30 to 120 ACH can result in a significant reduction of time duration that flammable masses remain in the room. In the case where leakage was stopped within 1 s after being detected, the flammable masses were completely released after 18 s with 120 ACH, whereas with 30 ACH, flammable masses, with 4-9% hydrogen concentrations in air, remained near the ceiling, even after 40 s. In the case where leakage was stopped after 2 or more seconds, explosive atmospheres can be created with concentrations above 20% even with 120 ACH. For the battery version, it was demonstrated that the role of the FFS is crucial in cases of ignition.