Hydrogen safety for systems at ambient and cryogenic temperature: A comparative study of hazards and consequence modelling

Transport and storage of hydrogen as a liquid (LH₂) is being widely investigated as a solution for scaling up the supply infrastructure and addressing the growth of hydrogen demand worldwide. While there is a relatively well-established knowledge and understanding of hazards and associated risks for gaseous hydrogen at ambient temperature, several knowledge gaps are yet open regarding the behaviour in incident scenarios of cryogenic hydrogen, including LH₂. This paper aims at presenting the models and tools that can be used to close relevant knowledge gaps for hydrogen safety engineering of LH₂ systems and infrastructure. Analytical studies and computational fluid dynamics (CFD) modelling are used complementarily to assess relevant incident scenarios and compare the consequences and hazard distances for hydrogen systems at ambient and cryogenic temperature. The research encompasses the main phenomena characterising an incident scenario: release and dispersion, ignition, and combustion. Experimental tests on cryogenic hydrogen systems are used for the validation of correlations and numerical models. It is observed that engineering tools originally developed for hydrogen at ambient temperature are yet applicable to the cryogenic temperature field. For a same storage pressure and nozzle diameter, the decrease of hydrogen temperature from ambient to cryogenic 80 K may lead to longer hazard distances associated to unignited and ignited hydrogen releases. The potential for ignition by spark discharge or spontaneous ignition mechanism is seen to decrease with the decrease of hydrogen temperature. CFD modelling is used to give insights into the pressure dynamics created by LH₂ vessels rupture in a fire using experimental data from literature.