They shouldn't experience hypoxia. That's what the air supply is for.

1970-01-01 3 days ago | parent [-]

It's not so simple. Check this out: https://en.wikipedia.org/wiki/Freediving_blackout#Ascent_bla...

Barring really traditional (and now very rare) pearl/scallop divers, professional divers aren't doing it by holding their breath.

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PaulHoule 3 days ago | parent | prev [-]

I never got "deep" into it but everybody told me that breath holding diving can be really dangerous.

I know part of the SCUBA story is that phenomena like nitrogen narcosis are particularly dangerous because you need your cognitive capacity to survive in the underwater environment.

In the surface world I can go to a party and drink eight beers and maybe throw up and act like a dumbass and embarrass myself and then wake up with a headache the next morning. That level of incapacitation under water would likely be fatal.

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nradov 3 days ago | parent | next [-]

Nitrogen narcosis isn't usually a significant factor in breath hold freediving. They do feel it on extremely deep dives but most aren't going past about 100 ft / 30 m where it becomes really noticeable.

https://alchemy.gr/post/429/dealing-with-narcosis-when-freed...

Technically it's not just nitrogen. Most breathable gasses other than helium have some narcotic potential. This includes oxygen, although the magnitude is unclear. Elevated CO2 levels (hypercapnia) can also seriously reduce your cognitive capacity via multiple mechanisms.

	▲	foxyv 2 days ago \| parent \| next [-]
		At very high pressures, helium is actually the opposite of a narcotic. This is why it is introduced in Trimix for deep dives. It kind of offsets the narcotic effect of the high pressure oxygen. However it can also cause trembling if there is too much of it. https://pmc.ncbi.nlm.nih.gov/articles/PMC7478267/ To offset this problem, world record divers are introducing Hydrogen to their mixtures at extreme depths. https://en.wikipedia.org/wiki/Hydrox_(breathing_gas)
	▲	PaulHoule 2 days ago \| parent \| prev [-]
		It's not so much about nitrogen and narcosis from other gases, it's that underwater is a dangerous environment where you can get in trouble quickly if anything goes wrong.

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ceejayoz 3 days ago | parent | prev | next [-]

Yeah, when I learned scuba, I was told the rule with freediving is your buddy stays on the surface while you dive; that way they can rescue you if you can pass out.

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Hnrobert42 3 days ago | parent | prev [-]

While ascending, the air in your lung expands. If it can't go out your mouth/nose, then it expands your lungs or is forced through membranes. Either way, the results are not good.

Nitrogen narcosis is another risk of SCUBA diving, but it is not really related to breath holding.

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nradov 3 days ago | parent [-]

Lung over expansion issues can only happen when ascending after breathing compressed gas under pressure. That isn't a problem with breath hold freediving.

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