Comment by jsjohnst
7 years ago
> Helium isn't toxic but it displaces oxygen.
While technically correct in theory, in any real world environment Helium will not displace Oxygen unless you are dumping orders of magnitude more helium than in this scenario.
> Heliox still contains enough oxygen to breathe (at sea level it's 21% oxygen just like normal atmosphere, and when diving the partial pressure of oxygen is the same as oxygen in normal atmosphere).
There’s so much wrong with this (and the rest of your post) I can’t think of a polite way to respond, so I’ll just wish you a good day.
I’ll admit I haven’t gotten that far in my diving certs yet, but isn’t the point of Heliox so that you can have less than 21% O2 at high depths to avoid narcosis and a fatal ppO2?
To simplify it a bit.
The point is to keep partial pressure of oxygen below that of maximum safe limit of 1.2 to 1.6. For example, 100% oxygen at surface is 1.0 and thus safe but will very fast reach maximum when you increase the pressure just by a few meters. Regular air with 21% oxygen will start to be a problem at 50 meters, so divers that need to go deeper need to use mixes that has less than 21% oxygen. When a mix is less than 18% oxygen they become hypoxic and cannot safely be used at shallow depth.
So the point is not to get "the same as oxygen in normal atmosphere". It is to keep the partial pressure of oxygen within safe limits, usually between 0.18 pp02 and 1.4 pp02 depending on a multitude of factors and safety margins.
The only point I was trying to convey with that statement was that there might be much less oxygen by volume in deep-diving heliox but the partial pressure of oxygen is still maintained so that cellular respiration can continue normally. Was that the only thing you thought was outrageously wrong with my comment?
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Kind of, a fatal ppO2. But in a hospital room you have the other kind of fatal ppO2, the kind where you pass out and need an O2 mask.