KABOOM!
Many of us are old enough to remember the transition from coal gas to natural gas. One of the big issues was that coal gas can be smelled when it leaks, while natural gas is odourless. The solution adopted (and in place to this day) as to add smelly stuff to natural gas. This is what you notice when there's a gas leak and it's smelly enough that you notice it at gas concentrations way below explosive.
Hydrogen isn't even a molecule, there are no smelly molecules that'll do any more than settle out of it.
Couple that with the fact that Hydrogen is the very devil to get to stay inside anything (let alone underground pipework - that's just sheer insanity) and the Kaboom is a "when, not if" issue.
Biting the hand that feeds IT
