Challenges to improve confidence level of risk assessment of hydrogen technologies

Making large-scale distribution and use of hydrogen successful will require adequate risk control. In turn, control requires risk assessment. Despite many years of experience, in general, methods to determine risk lack still robustness: results being much too dependent on choices made by the analyst due to uncertainties, lack of data and different views. This can create frustration amongst people dependent on results. HySafe and other groups work in the right direction. This paper will review existing methodological weaknesses, current improvements in e.g. the context of developing risk-informed standards and emphasize the challenges to raise quality further. The Standard Benchmark Exercise Problems, SBEPs, were a good start but shall produce recommendations for CFD use or even certification of models. Scenario generation shall take advantage of historical incident data and newer methods such as Bayesian belief nets, and cover the entire hydrogen distribution system and not only garages and refueling stations; the analyses shall more explicitly present confidence intervals on results. Knowledge gaps on e.g. ignition probability shall be defined and filled.