Analysis of Published Hydrogen Vehicle Safety Research

Flamberg, Stephanie; Rose, Susan; Stephens, Denny · 2010 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This report, commissioned by the National Highway Traffic Safety Administration (NHTSA) and conducted by Battelle Memorial Institute, addresses the need to synthesize existing safety research for hydrogen-fueled vehicles (HFVs). As HFV technologies differ significantly from conventional fuel systems, ensuring equivalent safety levels presents unique engineering challenges. The study aims to identify technical documents related to HFV safety performance, organize this research to avoid redundancy in future NHTSA planning, and highlight opportunities for cooperative research. The review analyzed nearly 100 technical papers and presentations from national and international organizations, categorizing findings into eight major themes: leak/dispersion/ignition, fire test methodologies, container rupture, general safety, cylinder design, fast-fueling, liquefied hydrogen storage, and compressed natural gas (CNG) incident data. The methodology involved a systematic review and categorization of published literature to assess its relevancy to current vehicle designs. Key findings from the leak, dispersion, and ignition research indicate that with adequate ventilation, hydrogen concentrations in vehicle interiors can remain below the 4% lower flammability limit. A post-crash maximum leak rate of 131 NL/min was identified as ensuring sufficient safety. Computational fluid dynamics modeling was validated as a reliable tool for predicting safety in scenarios lacking experimental data. Regarding fire testing, researchers found that standard engulfing bonfire tests produce variable results and may not represent real vehicle fires; consequently, substitutive gases like helium were deemed inappropriate for testing due to differing pressure relief device (PRD) activation characteristics. Research on container rupture consequences revealed that 35 MPa Type III and Type IV cylinders without PRDs fail after approximately 12 and 6 minutes of fire engulfment, respectively. Blast waves from such failures can cause eardrum rupture at 50 feet and break windows at 65 feet. Notably, vehicle interiors became untenable due to heat and carbon monoxide four minutes into tests, well before tank rupture. For fast-fueling 70 MPa containers, thermal loads pose significant risks; pre-cooling hydrogen to -40°C was identified as an optimal balance for energy consumption, while increasing temperature limits was deemed impractical due to material degradation. Liquefied hydrogen storage faces challenges regarding boil-off, though BMW’s dual-fuel vehicle demonstrated no leaks in crash tests. Finally, CNG incident data highlighted that localized fires often prevent PRD activation, suggesting current engulfing bonfire standards may be inadequate for larger pressure vessels. The significance of this review lies in its support for the development of performance-based safety codes and standards. The findings emphasize the need for harmonized international standards and improved test repeatability. By identifying that hydrogen vehicles are not inherently more dangerous than CNG or gasoline vehicles in fire scenarios, and by providing specific data on leak rates and rupture consequences, the report guides NHTSA in drafting Federal Motor Vehicle Safety Standards. It underscores the importance of addressing localized fire risks and thermal management in high-pressure storage to ensure HFVs are safe, practical, and viable for everyday use.

Key finding

Standard hydrogen vehicle fire tests may be inadequate for larger pressure vessels, and substitutive gases like helium or nitrogen do not accurately replicate hydrogen behavior during thermal events.

Methodology

review

Provenance

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