A Model for Assessing the Risk of Liquid Hydrogen Transport through Road Tunnels

Among the new energy carriers aimed at reducing greenhouse gas emissions, the use of hydrogen is expected to grow significantly in various applications and sectors (i.e., industrial, commercial, transportation, etc.) due to its high energy content by weight and zero carbon emissions. The increasingly widespread use of hydrogen will require massive distribution from production sites to final consumers, and the delivery by means of liquid hydrogen road tankers may be a suitable cost-effective option for market penetration in the short-medium term. Liquid hydrogen (LH2) presents different hazards compared to gaseous hydrogen, and an accidental release in confined spaces, such as road tunnels, might lead to the formation of a flammable hydrogen cloud that might deflagrate or even detonate. Nevertheless, the potential negative effects on users in the event of accidental leakage of liquid hydrogen from a tanker in road tunnels so far have not been sufficiently investigated. Therefore, a 3D Computational Fluid Dynamics model for the release of LH2 and its dispersion within a road tunnel was developed in this study. The proposed model was validated by a comparison with certain experimental and numerical studies found in the literature. Such modeling is demanding for long tunnels. Therefore, the results of the simulations (e.g., the amount of hydrogen contained within the cloud) were combined with established simplified consequence methods to estimate the overpressures generated from a potential hydrogen deflagration. This was then used to evaluate the effects on users while evacuating from the tunnel. The findings showed that the worst scenario is when the release is in the middle of the tunnel length and the ignition occurs 90 s after the leakage.