Effects of hydrogen concentration, number of obstacles, and blockage ratio on vented hydrogen-air explosions and its consequence analysis

With the swift advancement of commercial hydrogen fuel cell vehicles (HFCVs), accident risks of hydrogen explosions are heightened, especially in enclosed or semi-enclosed areas such as tunnels and underground parking lots. To prevent and control these accidents, experiments are conducted in a 1 m-long cylindrical tube at 1 atm and 286 K to study the impacts of hydrogen concentration, number of obstacles, and blockage ratios on vented hydrogen-air explosions. As the number of obstacles rises, there is a gradual rise in the maximum internal overpressure for a hydrogen concentration of 20 vol%. However, a reverse trend is observed for hydrogen concentrations of 30 vol% and 50 vol%. The size of the external flame gradually expands as the hydrogen concentration increases, but diminishes gradually with increasing in the number of obstacles and blockage ratio. The maximum external overpressure decreases as the distance to the vent increases. The maximum temperature experiences an increase with increasing in hydrogen concentration and blockage ratio but undergoes a decrease with an increase in the number of obstacles. Furthermore, the safety radii are determined using thermal radiation criteria to ensure the absence of thermal radiation hazards for humans, and PROBIT equations to ensure the absence of overpressure and impulse hazards for humans and buildings. The safety radii for humans based on thermal radiation criteria are smaller compared to those based on the corresponding overpressure and impulse hazards.