One of the things that seems to have been kept very quiet about hydrogen is its ability to self-ignite when leaking from high pressure into air. The jury is out

One of the things that seems to have been kept very quiet about hydrogen is its ability to self-ignite when leaking from high pressure into air. The jury is out on the exact mechanism but most seem to think it creates a wavefront that has high enough energy content to auto ignite. This seems to be why automotive hydrogen refueling is relatively slow. At very high pressures there is no reason why refueling should take longer than gasoline refueling. They made the nozzle so small (less than a millimeter) because if a valve fails open and the hydrogen vents to air, it will limit the length of the invisible flame that probabilistically results to a meter or two. The temperature limit of the tank is one reason to rate-limit as well, but I don’t think it explains the whole picture.