Until reading the first article, I was unaware that one could get decompression sickness from free diving. The Wikipedia article on this dive also says that Nitsch passed out from nitrogen narcosis (and specifically not oxygen starvation) towards the end of the ascent, something else that I was unaware of being a risk (not that I have any intention of trying deep free diving.)
With regard to the hydreliox mix, I see it has a scant 0.8% oxygen, and needs to be less than 5% to avoid having an explosive mixture. Even the latter figure, I think, would lead to hypoxia in most people at atmospheric pressure, so I imagine these ratios are adjusted with pressure, and probably that these mixtures are only used in saturation diving.
Don't believe everything you read. While an extremely high PPN2 can cause unconsciousness due to narcosis, it wouldn't be possible to definitively identify that as the cause. There could have been something else going on physiologically.
Hydreliox has only been used in a few experimental or scientific dives, mostly with saturation procedures but at least once by cave divers. (It's possible that militaries could have done some secret dives as well.)
> While an extremely high PPN2 can cause unconsciousness due to narcosis, it wouldn't be possible to definitively identify that as the cause.
In a later post, I wondered (without any particular reason to think it might be so) whether the decompression sickness Nitsch experienced was manifest in neural tissue, and now I am wondering whether this 'nitrogen narcosis' was an early instance of the strokes which occurred during his treatment for that decompression sickness.
https://en.wikipedia.org/wiki/Herbert_Nitsch#Later_attempt_a...
With regard to the hydreliox mix, I see it has a scant 0.8% oxygen, and needs to be less than 5% to avoid having an explosive mixture. Even the latter figure, I think, would lead to hypoxia in most people at atmospheric pressure, so I imagine these ratios are adjusted with pressure, and probably that these mixtures are only used in saturation diving.