Hydrogen would also be .. interesting ...
ASME Boiler and Pressure Vessel Section V
Helium leak detection sensitivity is 3 orders of magnitude higher.
Memory is fallible, but the code doesn't lie.
Why?
It's used in power station generators. Why would a hard disk be interesting?
https://en.wikipedia.org/wiki/Hydrogen-cooled_turbo_generato...
Larger amounts handled in the manufacturing process, OTOH...
I'm curious how the shaft seals for generators manage to seal the hydrogen. Perhaps the hydrogen is contained within the the generator and not exposed to the seals, though I thought one of the reasons for its use (along with cooling) was reduced windage losses.