Liquid hydrogen (LH2) storage is a viable approach to assuring sufficient hydrogen capacity at commercial fuelling stations. Presently, LH2 is produced at remote facilities and then transported to the end-use site by road vehicles (i.e., LH2 tanker trucks). Venting of hydrogen to depressurize the transport storage tank is a routine part of the LH2 delivery process. However, the behaviour of cold hydrogen plumes has not been well characterized because empirical field data are essentially non-existent. The National Fire Protection Association (NFPA) Standard 2 Hydrogen Storage Safety Task Group, which consists of hydrogen producers, safety experts, and computational fluid dynamics modellers, has identified the lack of understanding of hydrogen dispersion during LH2 venting of storage vessels as a critical gap for establishing safety distances at LH2 facilities, especially commercial hydrogen fuelling stations. To address this need, the National Renewable Energy Laboratory sensor laboratory, in collaboration with the NFPA 2 Safety Task Group, developed the Cold Hydrogen Plume Analyzer to empirically characterize the hydrogen plume formed during LH2 storage tank venting. A prototype analyzer was developed and field deployed at an actual LH2 venting operation. Critical findings included:

• Hydrogen (H2) was detected as much as 2 m lower than the release point, which is not predicted by existing models.

• A small and inconsistent correlation was found between oxygen depletion and the hydrogen concentration.

• A negligible to non-existent correlation was found between in-situ temperature and the hydrogen concentration.

The analyzer is currently being upgraded for enhanced metrological capabilities, including improved realtime spatial and temporal profiling of the plume and tracking of prevailing weather conditions. Additional deployments are planned to monitor plume behaviour under different wind, humidity, and temperature conditions. The data will be shared with the NFPA 2 Safety Task Group and ultimately will be used support theoretical models and code requirements prescribed in NFPA 2.