What is really interesting is that at depths below 65m the real danger isn't running out of air, but that air itself becomes toxic due to the higher partial pressure of oxygen and it's effect on the nervous system.
Tech and commercial divers breathe exotic air mixtures which are hypoxic and include helium to mitigate this.
Dive science is pretty fascinating and is still a developing field.
Nitrogen narcosis is usually called "drunkenness of depth" (if I translate this correctly), because it produce effect like you are drunk.
I've seen and heard many stories of experienced divers that would do silly things due this effect; that is why you always have to have partner with you and the rest of the crew near by.
This effect is highly dependent of person and I've seen guys goes beyond 40m without getting this at all.
I'm no professional diver, but did a bunch of dives between 60-100ft, and it seems like it can start happening to me around 70-80ft. Experienced divers will be more conscious about when it happens to them, and will plan their actions accordingly.
It's pretty eerie. It's _literally_ like being drunk, but you happen to be strapped to an oxygen tank with 100ft of water over your head, and could get extremely sick if you did something too stupid.
It's actually a pretty safe activity, given you follow safety rules. It's however pretty easy to stray from them.
Yep, especially for inexperienced divers. This is why one of the cert qualification dives is a "deep" dive, usually in the 90-110ft (30ish meters), and why that dive is usually just a really simple descent + a few elementary tasks at the bottom while maintaining neutral buoyancy.
Experience provides no protection against narcosis. There is no adaptive effect. Experienced divers who think they can somehow handle it are just fooling themselves.
When teaching students about the effects of depth on cognition, one fun trick is to give them a couple of combination locks attached to a slate (with the combinations written on the slate). Time each of them opening the locks on the surface, then time them opening another slate with the same sort of locks at 60 feet -- a depth not normally associated with awareness of cognitive changes.
I usually have my students come up with a couple secret handshakes that we practice on the surface beforehand.
I like the combination lock too, but I've found that a lot of people struggle with the locks regardless of depth and it can throw some false positives.
Much of the differential narcosis effect is actually due to carbon dioxide rather than nitrogen. CO2 will interfere with your ability to think clearly even worse than nitrogen. If you're relaxed and breathing deeply then you generally won't accumulate much CO2, but then if you have to exert yourself it suddenly hits you and can have severe effects.
The solution to both N2 and CO2 narcosis is the same: put more helium in the mix.
Calculating your maximum operating depth and the time you can spend there before experiencing oxygen toxicity is an important part of advanced diving training.
For deep dives I really enjoy the planning phase, it requires a high degree of technical expertise and a thorough understand of your bodies physical limits.
Tech and commercial divers breathe exotic air mixtures which are hypoxic and include helium to mitigate this.
Dive science is pretty fascinating and is still a developing field.