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Post-Crash Hydrogen Leakage Limits and Fire Safety Research

Product #: 811 816

Federal Motor Vehicle Safety Standards (FMVSS) for fuel system integrity set limits for fuel spillage during and after crashes to reduce the occurrence of deaths and injuries from fire. FMVSS 301 and 303 respectively specify post-crash limits for liquid fuels and compressed natural gas (CNG). These limits have been used as a benchmark for setting leakage limits for hydrogen, based on energy equivalence, in industry standards and proposed or enacted international regulations. However the properties of hydrogen with regard to leak behavior and combustion are very different from those of liquid fuels or CNG. Gasoline will pool and dissipate slowly. CNG and hydrogen will rise and dissipate more rapidly. Hydrogen has a much wider range of flammability in air than most fuels, including CNG: 4% to 75% for hydrogen versus 5% to 15% for CNG. Therefore, a research program was developed and executed to assess the safety of the proposed allowable leak rate for hydrogen, through leak and ignition experiments in and around vehicles and vehicle compartment simulators.