Hydrogen is once again assuming significant importance in national energy strategies. In a dynamic but uncertain context, there is a need to delve into security issues which, due to the peculiar characteristics of this energy carrier, are especially relevant in
case of accidental release and/or combustion, the latter with possible explosion. In order to outline a research activity in this context and with the aim of supporting the development of methods for the analysis of accidental scenarios, the report presents the main
phenomena of interest and some useful calculation tools to simulate the dispersion and combustion of hydrogen following release. These phenomena are presented in order to highlight their influence on the risk of release/leakage and ignition of the hydrogen-air mixture. Numerical simulations were performed with calculation codes against some benchmarks, and focused on the comparison with experimental data. They showed the potential of the
calculation tools in the analysis of accidental scenarios, an activity within the broad context of Risk Engineering.