Methodology for Consequence-based Setback Distance Calculations for Bulk Liquid Hydrogen Storage Systems

Updates to the separation distances between different exposures and bulk liquid hydrogen systems are included in the 2023 version of NFPA 2: Hydrogen Technologies Code. This work details the models and calculations leading to those distances. The specific models used, including the flow of liquid hydrogen through an orifice, within the Hydrogen Plus Other Alternative Fuels Risk Assessment Models (HyRAM+) toolkit, are described and discussed to emphasize challenges specific to liquid hydrogen systems. Potential hazards and harm affecting individual exposures (e.g., ignition sources, air intakes) for different unignited concentrations, overpressures, and heat flux levels were considered, and exposures were grouped into three bins. For each group, the distances to a specific hazard criteria (e.g., heat flux level) for a characteristic leak size, informed by a risk-analysis, led to a hazard distance. The maximum hazard distance within each group was selected to determine a table of separation distances based on internal pressure and pipe size, rather than storage volume, similar to the bulk gaseous separation distance tables in NFPA 2. The new separation distances are compared to the previous distances, and some implications of the updated distances are given.