An under-expanded hydrogen jet from high-pressure equipment or storage tank is a potential incident scenario. Experiments demonstrated that the delayed ignition of a highly turbulent under-expanded hydrogen jet generates a blast wave able to harm people and damage property. There is a need for engineering tools to predict the pressure effects during such incidents to define hazard distances. The similitude analysis is applied to build a correlation using available experimental data.

The "draft" report briefly discusses two distinctly different scenarios that create overpressure from an external release of hydrogen into an ambient air environment: Delayed ignition from a pressurized release and Delayed ignition of a flammable gas cloud.