Given infinite air and infinite time to acclimatise, how deep could you actually dive? Assume that you’re naked apart from special pressure proof googles (presumably they’re pressurised as you dive) and some kind of way of breathing.
Well, if you had organs of steel, I think its the point where the water pressure overcomes your bone structure’s strength. However, from wikipedia:
Although people have been able to dive for under 2000ft with specialized suits, with a whole suite of health problems afterwards.
The problem is not that your bones will fail, the problem is that air starts to dissolve in your blood, effectively poisoning you.
(According to this the record stands at 330m)
Don’t divers use different gas mixes to compensate for problems like this?
AINA diver.
As far as I can tell, there is a point where the oxygen itself becomes the problem.
I’m not a professional diver but I don’t think there’s a limit. The human body is mostly liquid so is incompressible, air spaces have to be equalized even in shallow dives. As others have stated Oxygen becomes toxic at pressure, although being naked the cold would kill you first. BTW, googles (masks) aren’t pressure proof, the gas in them has to be equalised as well.
Various Googling (one link is Wiki) suggests that oxygen becomes a problem when its partial pressure is significantly higher than in air at normal atmospheric pressures. The problem can be managed during deep dives by using gas mixtures that contain smaller than normal proportions of oxygen, so the partial pressure remains within safe limits.
Isn’t that nut (Pippin Ferraras) trying for 600 feet? I think a free diver faces collapse of the chest cavity, if he/she goes too deep. Of course, free diving is just an elaborate duicie scheme, IMHO.
I usually dive on Nitrox, which is sort of the generic term for air with a non-standard oxygen content. Typically I’ll use a 36% O2 mix, but because of the potential dangers of oxygen toxicity, one has to be careful to make sure the mix is safe for the depths you’re planning to dive. Most recreational divers will plan the dives in order to keep the partial pressure of O2 above 1.4 atm for the duration of the dive. Technical divers will go higher under other circumstances, but once you get around 1.8 atm things get dicey (time at depth factors into this as well, but let’s just stick to pressures to keep it simple).
I assume there’s some practical lower limit to the O2 content of a potential breathing gas, so using that and a partial pressure of 1.6 atm, one should be able to rough out a max. depth for a human, no?
As long as you’re allowed to switch gases on the way down, which is what really deep divers do, I don’t think that would be your limiting factor. The Marianas trench is 10900 meters deep, so given 1 atm/30 meters, pressure would be 363 atm. 1.6/363 gives a gas of 0.44% oxygen.
Of course, you’d need a tank that could be pressurized beyond 363 atm, or else you couldn’t get your fancy breathing gas out. A standard scuba tank at 3000 psi wouldn’t cut it.
I dont know the number off hand (and its not an exact one anyway), but no matter WHAT mix of gases you use, the limit is somewhere between 1000 and 2000 feet. Unless of course some navy somewhere is keeping a big secret. I THINK the 2000 foot barrier may have been broken by some heavily funded commerical divers.
You can dilute the 02 WAY down percentage wise to keep the O2 partial pressure safe. But at some depth, the partial pressure of nitrogen causes one type of halucination/convulsions. So, you use helium instead of nitrogen to dilute the oxygen. But at great depths helium causes another kind of convulsion. so you mix back in a little bit of nitrogen which interestingly enough seems to counteract the Helium problems (kinda like lightly drinking to control the shakes due to a pain medication). But at some depth, even that doesnt work.
I do know that a few cave divers have gone to about a 1000 feet with mixed gases for short periods and survived.
In theory, using hydrogen rather than helium increases your depth limit, but not surprisingly not many people are excited by the thought of mixing up high pressure mixes of hydrogen and oxygen. Other much heavier noble gases have been considered IIRC, but those are so “thick” that at extreme depths you are going to have a hell of time working your breathing gas in and out of your lungs.
The book and film The Abyss proposed using liquid breathing to dive to great depths.
I think you mean “plan to keep the ppO2 below 1.4 atm” etc. Maximum recommended depth for a rec diver is 30 meters, at which point the ppO2 will be about 0.8 atm won’t it? (Been a while since I dived). 
Addendum: 0.8 ppO2 on air. 1.44 on your 36% nitrox mix.