I'd love to dive there someday.
assuming it's in similar range, that's serious depth. Way into hypoxic trimix zone (ie: you'll be breathing gas that'd kill you if you were breathing it on the surface)
Looks fascinating, but almost certainly out of reach for all but the most extreme technical divers.
It’s seriously non intuitive to a layman the whole pressure thing.
> DCS [Decompression Sickness] is best known as a diving disorder that affects divers having breathed gas that is at a higher pressure than the surface pressure, owing to the pressure of the surrounding water. The risk of DCS increases when diving for extended periods or at greater depth, without ascending gradually and making the decompression stops needed to slowly reduce the excess pressure of inert gases dissolved in the body.
DCS > Prevention > Underwater diving: https://en.wikipedia.org/wiki/Decompression_sickness#Underwa... :
> Decompression time can be significantly shortened by breathing mixtures containing much less inert gas during the decompression phase of the dive (or pure oxygen at stops in 6 metres (20 ft) of water or less). The reason is that the inert gas outgases at a rate proportional to the difference between the partial pressure of inert gas in the diver's body and its partial pressure in the breathing gas; whereas the likelihood of bubble formation depends on the difference between the inert gas partial pressure in the diver's body and the ambient pressure. Reduction in decompression requirements can also be gained by breathing a nitrox mix during the dive, since less nitrogen will be taken into the body than during the same dive done on air. [85]
Is there an issue with the above explanation?
[0] https://en.m.wikipedia.org/wiki/Nitrogen_narcosis [1] https://en.m.wikipedia.org/wiki/Oxygen_toxicity
Consequently, the partial pressure of oxygen you are breathing is doubled, to .42. This continues, until you reach a partial pressure which is incompatible with life. That danger-zone is generally considered to be between 1.4 and 1.6, so air cannot be safely breathed below about 60 meters (1.6/.21 - 1 = about 6 atmospheres). Similarly, pure O2 cannot be breathed safely below about 6 meters (1.6/1 - 1 = about .6 atmospheres).
Your description of nitrogen narcosis is correct. To dive deeper than your nitrogen narcosis limits you start replacing some of the nitrogen with helium in the gas you breathe. This works up to the limits of even the most technical recreational diving, after which you will get symptoms of something called HPNS which could mean replacing the helium itself with hydrogen.
Both helium and nitrogen will get stored in your inert tissues and will bubble out catastrophically if you ascend too quickly. With either inert gas you must carefully plan your ascent to avoid the bends.
I'm not going to link to the Byford Dolphin incident, because it would need a [TW] and I hate that shit, so you can just google it yourself. The 30-second rundown is that on the surface divers live in a very strong steel tank pressurised to the same degree as they would be on the seabed, so maybe make sure you close the door properly.
Incidental, and didn't get the chance.
Crammond opened the clamp that was keeping the trunk sealed before Diver 4 (Hellevik) could close the door to the chamber.
The equipment did have interlocks to prevent it being opened incorrectly but nobody used them because they were annoying and fiddly.
Diving that deep isn't going to become easier anytime soon. But have a look at the consumer-grade "underwater drones", formerly called ROVs. I wouldn't be surprised to see people in small boats doing youtube videos of such wreaks in a couple years.