Originally Posted by
turbidus
At 16m or even to 50m...you can dive supplied air however long you want....
At extended times (think hours) this become saturation dives which need much more support and safety equipment compared to normal open water equipment, since you can not decompress to surfaces pressure in short times. You will need chambers and pressurised living compartments. Problem is the nitrogen saturation of your blood and it will take days for decompression after you are fully saturated.
The homo sapiens physiology is not good adapted for long stays below 10m ( 2000mbar absolute pressure) under water level.