[Jim Noble]

Hydrogen has two challenging characteristics. One is the extraction of hydrogen from other sources, as there are no hydrogen mines or hydrogen wells around. Another is, hydrogen is notoriously hard to store, as it leaks out through most EVERYTHING, and it is highly corrosive of most metal connectors

Three challenging characteristics:

[Ozark Tom]

Fourth, it migrates through the walls of containers unless lined with amorphous alumina.