The rise in hydrogen fuel cell electric vehicles (FCEVs) is expected to pose a variety of hazards on the road. Vehicles using hydrogen could cause significant damage, owing to hydrogen vapor cloud explosions, jet fires caused by leakage, or hydrogen tank explosions. This risk is expected to further increase in semi-enclosed spaces, such as underground parking lots and road tunnels. Therefore, it is necessary to study the fire safety of hydrogen vehicles in semi-enclosed spaces. In this study, an experiment on hydrogen tank explosion was performed. In addition, the CFD numerical model was verified using the experimental results, and the damaging effect due to pressure propagation during hydrogen tank explosions in underground parking lots and road tunnels was analyzed using numerical analysis. From the experiment results, the hydrogen tank exploded at about 80 Mpa, a maximum incident pressure is generated 267 kPa at a distance of 1.9 m. As a result of numerical analysis based on the experimental results, the limit distance that can cause serious injury due to the explosion of a hydrogen tank in a road tunnel or underground parking lot was analyzed up to about 20 m from the point of explosion.

Submerged tunnels are an innovative infrastructure solution for connecting roads and railways, especially in areas where conventional bridge or overland tunnel construction is limited by deep waterways, narrow straits, or dense urban development. In such regions, submerged tunnels offer an efficient and less intrusive alternative that overcomes geographical constraints. However, unlike conventional ground-level or subsea tunnels, submerged tunnels have unique structural and environmental characteristics, which necessitate the development of a dedicated evaluation system for responding to fire and other disasters. In this study, a quantitative fire risk assessment program (SFT_QRA) was developed by reflecting the specific characteristics of submerged tunnels. The program was applied to both road and railway tunnels to obtain evaluation results. First, to more realistically reflect the fire risk within submerged tunnels, the latest statistical data were used to update fire occurrence probabilities and the proportion of vulnerable users. In addition, the optimal smoke control mode for structural stop zones in ultra-long tunnels was analyzed to derive strategies for establishing a safe evacuation environment. Second, an Excel VBA-based assessment program was developed to improve user convenience and was structured to enable fire analysis and evacuation simulations. Third, in order to verify the accuracy and reliability of the developed program, a comparative analysis was conducted against commercial quantitative risk assessment programs. As a result, the total risk error rate was 0.4% for road tunnels and within 5.0% for railway tunnels, showing similar levels of results. This study advances quantitative risk assessment methods by incorporating the unique features of submerged tunnels and implementing them in a validated program. Through this approach, it presents a practical solution that can contribute to the advancement of tunnel fire safety technologies and the overall enhancement of tunnel safety.