Risk assessment of Hydrogen fueling stations for 70 MPa FCVs

People are placing their hopes on the future of fuel-cell vehicles (FCVs) to replace today's gasoline-fueled vehicles. To encourage the widespread use of FCVs, however, these vehicles must be able to drive a distance of at least 500 km, mileage comparable to today's gasoline-fueled vehicles. To achieve this distance, automobile manufacturers are focusing their efforts on developing new hydrogen fuel tanks that will raise pressure to 70 MPa from the current 35 MPa. At the same time, hydrogen stations will also have to be able to provide 70 MPa compressed hydrogen gas to service these improved FCVs. Regulations for hydrogen fueling stations where pressure is no higher than 40 MPa were established in 2005 in Japan but it goes without saying that these regulations are inadequate for hydrogen fueling stations of 70 MPa.To assist in the drafting of new regulations for hydrogen stations capable of 70 MPa, the authors in this study undertook risk assessments of hydrogen stations. However, there is little existing safety data concerning hydrogen leakage, ignition, and explosions at 70 MPa, as well as high-pressured hydrogen equipment.Therefore, the authors undertook a risk assessment of hydrogen fueling stations for 70 MPa FCVs using data on hydrogen behavior at 70 MPa which was extrapolated from existing 35 MPa hydrogen data. This study made it possible to identify outstanding safety issues that need to be resolved to maintain the safety of hydrogen fueling stations in the future. Results of the study also suggested that a safety distance of 6 m, the same as for 35 MPa hydrogen stations, was sufficient for 70 MPa hydrogen stations. In the future, the authors intend to resolve the outstanding issues identified in this study. As part of their study, they plan to conduct field experiments on hydrogen explosions and jet flames at 70 MPa or more and reflect their findings in their risk assessment.