Hydrogen fuel cell vehicles (HFCVs). Fire scenarios within confined spaces: road tunnels

In the current and future context, vehicles powered by alternative fuels are of increasing interest, being an option for the future zero-emission transport sector. In particular, hydrogen fuel cell vehicles (HFCVs), which represent the latest generation of electric vehicles, are spreading very rapidly in recent years. This revolutionary technology is powered by the chemical reaction that occurs between hydrogen and oxygen within fuel cells, rather than the typical combustion of fossil fuels that occurs in conventional engines. The issues related to safety and management of HFCVs connected risks must be thoroughly studied, especially in confined spaces, such as road tunnels, and indoor car parks. In fact, while in open environments an accidental hydrogen release is rapidly dispersed in the air, causing no particular safety concerns, in restricted ones the accumulation of hydrogen could lead to an explosion, in case of a delayed ignition, or to a hydrogen fire if an immediate ignition occurs. In the present study computational fluid dynamics (CFD) simulations of a hydrogen fire inside a road tunnel are carried out using PyroSim, a software program based on the Fire Dynamic Simulator (FDS) approach. The circumstances caused by the fire of a HFCV are critically analysed taking into consideration several parameters such as the heat release rate (HRR) during the burning process, the temperatures reached in the road tunnel, the visibility and concentration of hot smokes. Subsequently, this scenario is compared to the one produced by a traditional fossil fuels powered car, to make reference in the analysis of fire related safety hazards. In the end some mitigation techniques, such as longitudinal ventilation strategies, are investigated to try to reduce the critical issues triggered by the hydrogen fire inside the road tunnel.