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In this study, hydrogen was leaked using a nozzle that simulated an actual leak port (with varied materials and diameters), and the possibility of ignition was verified to collect data useful for establishing standards for the allowable flow rate of hydrogen leakage on receptacle. With the flow rate of a hydrogen leak set at 250 mL/h(NTP) (hereinafter mL/h is NTP condition) or less, ignition of leaked hydrogen with an electric spark and a small methane-fueled flame was attempted. The results confirmed that ignition of 200 mL/h of hydrogen was not achieved under tested conditions. In some cases, hydrogen at a flow rate of 250 mL/h was ignited. Tissue paper placed in contact with the flame at a flow rate of 250 mL/h combusted, resulting the flame went out almost immediately. Therefore, it was determined that a hydrogen leak at approximately 200 mL/h that occurred in this test is a very low possibility of ignition or spreading.

To determine the appropriateness of specifying the allowable amount of hydrogen leakage upon collision based on the amount of leakage with generated heat equivalent to that of gasoline vehicles and CNG vehicles, we investigated the safety of each type of fuel when flame ignites. Our results confirm that the flame lengths for hydrogen and methane are almost equal, and there is no remarkable difference between them in terms of the distance for assuring safety. Furthermore, we confirmed that the irradiant heat flux from the mixed burning of hydrogen flame with liquid flammable materials is almost equal to that of the spray flame of gasoline. Thus, no clear difference was found between various types of fuel. Therefore, it is appropriate to specify the allowable amount of hydrogen leakage based on the amount of leakage with generated heat equivalent to that of other types of fuel.