# Hydrogen vs. Batteries: Comparative Safety Assessments for a High-Speed Passenger Ferry
## 5 Gas and Smoke Dispersion Analyses
### Battery Version-Smoke/Fire Simulation  
In this section, a quantitative risk assessment is presented using a fire dynamic simulator (FDS) on the battery-powered version of the high-speed ferry to indicate the smoke and fire paths under various scenarios. In the fire simulation, the key is to model the heat release rate per area (HRRPA), which is related to the heat release rate and surface area of the burner as shown in Equation (4).  
\[\mathrm{HRRPA}=\mathrm{HRR}/\mathrm{S} \tag{4}\]  
where HRRPA is the heat release rate per area (kW/m\({}^{2}\)), HRR is the heat release rate from the burning (kW), and S is the surface area of the burner (m\({}^{2}\)).  
For the firefighting system (FFS), there are two key factors, flow rate and control strategy. The flow rate of the system is calculated as shown in Equation (5).  
\[\dot{\mathrm{v}}=\mathrm{m}/\rho\cdot\mathrm{t} \tag{5}\]where \(\dot{\rm v}\) is the volume flow rate of the FFS chemical agent (m\({}^{3}\)/s), m is the total mass release of the agent (kg); \(\rho\) is the agent density (kg/m\({}^{3}\)), and t is the total release time duration (s). For the control strategy, the FFS is triggered when the temperature reaches 68 \({}^{\circ}\)C.  
The main deck of the ferry includes both the battery room and the passenger area. Following the provided geometry from the shipyard, the 3D geometry model was developed, as shown in Figure 6. The blue plate is the main deck with passengers and the red blocks are the battery packs. The dark yellow panels are the walls on the main deck; the brown objects in the passenger area are chairs.  
The battery room onboard the ferry includes the battery room walls, the battery packs, the sprayers of the FFS, and the inlet and outlet of the air ventilation system. The battery room was modelled and developed in PyroSim, and Figure 7 presents the developed model from the views from the top, bottom, and transparent inside:  
1. Two air outlets were designed on the ceiling and are shown in the top view.
2. Another two air inlets are shown on the floor of the battery room, which can be seen in the bottom view.
3. Four battery packs (red blocks in inside details) are equipped onboard the ferry.
4. Two sprayers are installed on the ceiling, and they are marked as SPRK01 and SPRK02.  
The battery fire heat released was provided by the manufacturer with a value of around 15,833 kJ/kWh obtained from a 14 min battery fire laboratory experiment; hence, the determined HRR was about 24,503 kW/kWh [41]. The dimension of the battery was also provided by the manufacturer: the width is 4 m, the depth is 0.5 m, and the height is 2.37 m [42]; hence, the surface area of the battery pack was determined as 25.33 m\({}^{2}\). With the heat release rate and surface area, the HRRPA can be derived on the basis of Equation (4): HRPA = 242 kW/m\({}^{2}\). The technical data for the batteries are shown in Table 6.  
Figure 6: Three-dimensional geometry model of the ferry in PyroSim ((**A**) battery room deck; (**B**) with superstructure).  
The FFS system onboard the ferry was Novec 1230 [43]. The data of the FFS were provided [44]; hence, the volume flow rate was able to be obtained on the basis of Equation (5): \(\dot{\mathrm{v}}=\)192 litre/min.  
The evacuation plan is summarised in Figure 8. The green arrows are the path of evacuation, and the green fishnet square is the evacuation exit.  
The wind profile targets the worst scenario on the River Thames according to the historical data from Met Office in the United Kingdom [45]. The strongest wind along the river was 38 mph (west) on 4 January 2018, and the average wind speed since 2011 is about 6.9 mph. These two data points were used for the analysis in the PyroSim simulation.