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Comment by klodolph | Hacker News Reader

Wouldn’t hydrogen only work if it was atomic hydrogen? I thought molecular hydrogen gas was larger than helium.

Hydrogen is soluble in most metals. It will just diffuse right into it, like air flowing through a foam filter.

Added bonus: if the metals in question form chemical bonds with hydrogen, (titanium in particular) it will happily do so, even if it's deep inside the metal. The metal will turn very brittle very quickly if it's exposed to molecular hydrogen.

https://en.wikipedia.org/wiki/Hydrogen_damage

Even a single hydrogen atom is bigger than a single Helium atom. The charge of the helium nucleus is higher and thus "pulls" the two electrons further inward than Hydrogen's single proton pulls its single electron.

Hydrogen exists as H2 in its elemental form you’ll you’ll need to ionize it to separate it and keep it in an ionized or other way isolated form to prevent it from binding to other hydrogen atoms.

If you are talking about ionized hydrogen, you are no longer talking about a gas. If it’s ionized, it is a plasma.

And if it's a plasma...it's gonna melt whatever you're trying to leak-check :)

As a bonus hydrogen is higly explosive, helium is not.

Hydrogen is no more explosive than other flammable gasses when mixed with ambient air. To get the explosive effect, you need to mix it with oxygen in the right proportion (2:1, molecule-wise) and not have any filler gas such as nitrogen.

One of the dangerous things about hydrogen is its wide flammability range: from 4% to 75% concentration of hydrogen in air. Hydrogen will detonate in concentrations between 18% and 59%. In comparison, gasoline has a surprisingly small flammability range of 1.4% to 7.6%.

What drives this wide range of flammable concentrations? Is it just an issue of low activation energy?

Also the upper end is impacted by the low number of oxygen atoms each hydrogen molecule can react with, in this case it's just one, compared to gasoline with say 8 carbon and 18 hydrogen atoms which bounds to 25 oxygen atoms. Mind you, the size of a gas molecule doesn't affect how many you get per volume at a certain pressure and temperature. So 50% gasoline vapors and 50% hydrogen are both molecule counts, with the former requiring 25 times as much oxygen for full combustion, compared to the latter.

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