Comment by kijin
7 years ago
Moreover, helium floats to the top and escapes through any opening (staircases, HVAC ducts, gaps in ceiling tiles) because it is lighter than air. This makes it much less dangerous than a heavier gas such as CO2 even if there's enough of it to displace a significant amount of air.
Not just any opening: just about any microscopic crack would let it out and most non-metal materials are effectively porous when trying to contain helium under pressure. It's even used to detect leaks in high vacuum chambers.
You don’t even need cracks. Helium (and hydrogen) can diffuse through metal, especially at high temperatures. Hydrogen embrittlement is a problem for processes that use high temp hiydrogen like the Haber process.
how is it typically dealt with? regular annealing?
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That is not true by any stretch of the imagination. If gases behaved like that then we'd all be choking on a layer of argon with all of the oxygen out of reach above us. No, gases diffuse and mix easily.
Gases diffuse and mix given enough time. There's not enough time when you have a massive indoor gas leak.
Even outdoors, large amounts of CO2 tend to sink to the ground and suffocate people in low-lying areas. Look up Lake Nyos for a particularly grizzly example of that.