Risk Sensitivity Study as the Basis for Risk-informed Consequence-based Setback Distances for Liquid Hydrogen Storage Systems

A quantitative risk assessment on a representative liquid hydrogen storage system was performed to identify the main drivers of individual risk and provide a technical basis for revised separation distances for bulk liquid hydrogen storage systems in regulations, codes, and standards requirements. The framework in the Hydrogen Plus Other Alternative Fuels Risk Assessment Models (HyRAM+) toolkit was used, and multiple relevant inputs to the risk assessment (e.g., system pipe size, ignition probabilities) were individually varied. For each set of risk assessment inputs, the individual risk as a function of the distance away from the release point was determined, and the risk-based separation distance was determined from an acceptable risk criterion. These risk-based distances were then converted to equivalent leak size using consequence models that would result in the same distance to selected hazard criteria (i.e., extent of flammable cloud, heat flux, and peak overpressure). The leak sizes were normalized to a fraction of the flow area of the source piping. The resulting equivalent fractional hole sizes for each sensitivity case were then used to inform selection of a conservative fractional flow area leak size of 5% that serves as the basis for consequence-based separation distance calculations. This work demonstrates a method for using a quantitative risk assessment sensitivity study to inform the selection of a basis for determining consequence-based separation distances.