H2 is a very small molecule. From a practical standpoint, this means it really, really wants to escape containment. And to store enough of it to do useful things, it must be stored a high pressures. This makes it really, really likely to leak! It’s hard to make it not leak!
What are the practical results of a hydrogen leak?
Well, this example from history is illustrative:
https://www.youtube.com/watch?v=fURATK5Yt30
“And to store enough of it to do useful things, it must be stored a high pressures.”
Some facts:
Hydrogen can be stored as a liquid.
Hydrogen can be stored as a metal hydride.
It can also be stored underground.