# Hydrogen vs. Batteries: Comparative Safety Assessments for a High-Speed Passenger Ferry
## 3 Proposed Designs
### Systems and Equipment Onboard  
#### 3.2.1 Hydrogen Version  
The connections from the hydrogen tank at the upper deck to the fuel cells at the aft of the main deck are shown in Figure 1. The catamaran's design provides sufficient stability, \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Main Particulars and Ferry Details** & \\ \hline Length overall (m) & 30.6 & route length & 23 nm \\ Length waterline (m) & 29.32 & service hours/day & Up to 20 \\ Draft (m) & 1.26 & round trips/day & Up to 15 \\ Breadth (m) & 9 & electric motors & 2 \(\times\) 550 kW \\ Demihull breadth waterline (m) & 2.44 & service speed & 23 knots \\ Demihull spacing (m) & 6.56 & crew & 3 \\ Displacement (c.m.) & 80 & passengers & 147 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Case ship specifications. enabling the placement of the hydrogen tank, piping, and vaporisers at the top deck. The type C double-walled LH2 tank has a pressure transmitter that will measure the pressure levels in the system. If there is a rapid pressure increase in the tank, there are two pressure relief valves mounted on top of it, as required by regulations, which will open immediately. The gas vents from these valves are led to the vent mast, which is located above tank connection space (TCS) adjacent to the tank, through gas vent piping. In this ventilated enclosure of TCS in which there are hydrogen sensors, fire detectors, vents, pipes, safety valves, vaporisers, etc., at least a 30 air changes per hour (ACH) ventilation rate is required. There is also a pressure building unit (PBU) that passively warms the liquid derived from the bottom of the tank and delivers it at its top in the cold gas space. Then, hydrogen is delivered to the vaporisers which convert cold hydrogen gas to room temperature hydrogen required for the fuel cells. After the vaporisers, there are pressure regulators to measure the pressure levels in the pipes, and if the pressure exceeds 10 bar, the pressure relief valves will open and gas will be vented to the vent mast. Then, there are three-way valves so that hydrogen is directed to the required fuel cell room even in case of damage/leakage in one of the pipes. The numerous master-gas valves, also called emergency shut-down (ESD) valves, throughout the whole gas distribution system should quickly shut off the flow of hydrogen once leakage is detected to avoid hazardous conditions by large accumulations of gas in the air. This arrangement with the cross-connected pipes and dual vaporisers was also utilised in the SF-Breeze high-speed ferry concept design and it provides redundancy of equipment in terms of safety [20]. The fuel pipes should either be gas-tight ventilated ducts or double-walled pipes, and they should not be led directly through control or accommodation spaces as required by regulations. Once hydrogen enters the fuel cell room through the gas supply piping, there are double block-and-bleed valves for each of the fuel cells, before hydrogen enters the stack (Figure 2). Double block and bleed valves are used to stop (block) the flow of hydrogen immediately after the hydrogen leakage is detected. Delay time for leakage to stop once detected should in general be around 0.5-2 s. The bleed valve will open to release (\"bleed\") any pressure that remains in the pipes and hydrogen gas will flow through the vent pipe to  
Figure 1: Onboard hydrogen systems. the vent mast. According to regulations inside each stack (gas consumer), there should also be double block and bleed valves. Fuel cell stacks used are Powercell MS-100, which are low-temperature PEM fuel cells [37]. They are placed at the aft of the main deck, behind the passengers' area as far away from the crew cabin as possible, in two separated spaces at the port and starboard within gastight enclosures as required by regulations. The technical data of the fuel cell stacks are presented in Table 3. Hybridisation with batteries is not required since MS-100 stacks have a very fast response time with a minimum operational lifetime of 20,000 h (high durability).