Curious why they don't have emergency unmanned drones with the crew or why they don't have emergency tanks at their work site (which he was able to get back to)
(1) - Not sure how well it has aged (https://en.wikipedia.org/wiki/The_Abyss)
There was a UUV in the water, which helped to locate the casualty but wasn't capable of performing a rescue.
Bailing out to open-circuit SCUBA doesn't help for very long, because of the immense pressures involved. As you go deeper, you need more pressure to inflate your lungs. A cylinder that lasts for an hour near the surface will only last for a couple of minutes at 100m. Tethered divers do carry bailout gas cylinders, but they're very much a temporary fix for brief losses of gas supply.
There are major logistical problems with portering dozens of gas cylinders to a job site that may actually increase the overall risk, because of the far greater time spent in the water. That pile of cylinders won't help you a jot if you lose the job site or you're incapacitated. Saturation divers are increasingly switching to closed-circuit rebreather bailout systems, which recirculate the breathing gas and so are far less affected by depth.
Even that is only a partial help because of the effects of hypothermia - if you lose your umbilical, you lose the warm water supply that stops you from freezing to death. You also lose your lighting and communications, which substantially impedes your ability to self-rescue.
https://www.jfdglobal.com/products/commercial-divers-equipme...
And unfortunately for saturation divers, you can't pressurize cylinders on-site to make up for the difference.
Pressurizing your tank to 210 bar (which puts the same stress on the cylinder walls as 200 bar at the surface) doesn't change the factor-of-10 increase on the other side of your P1V1=P2V2 balance.
Not to mention that you need even more air for decompression time...
fun facts about the abysss.
1. it's a version of the divine comedy, particularly the inferno.
2. the set still exists as of a several years ago
https://io9.gizmodo.com/take-a-tour-of-the-abandoned-remains...
Also, it's staggering how much oxygen can be dissolved into your system at depth. The Navy did some experiments where they put pigs in a chamber, pressurized them to something obscene, like 300 feet, and replaced their blood with water. The oxygen diffused so well the pigs were still conscious and walking around. Source: I work with a lot of Navy dive medicine officers.
I was just saying though, if he did have more oxygen down there he would have had to be awake for that freezing experience...