CéCé,
In line with what Don was saying, blacking out at 20 meters is not likely. If you are having to retrieve someone at 20 meters, your most likely doing body recovery not life saving. About the only way someone is going to black out at that depth is if they totally lose track of time and have no contractions to remind them.
When a diver has to be retrieved from 20 meters, they most likely made it up part way, black out and then sunk back down. The chances of you being able to revive them after they spent some time on the bottom at 20 meters is bad, but it’s still better than nothing. Freedivers black out because of low oxygen, so they are starting with low oxygen to begin with, which makes death more likely than someone who blacks out from something else and starts with normal O2.
What’s far better than risking your life and having to deal with a fellow diver that may not live is to pay close attention and catch them on their ascent before they sink back to the bottom. Watch how long they are on the bottom and if 2 minutes goes by and they are not coming up, start your recovery dive.
If they do end up on the bottom and its below our ability to retrieve them, a lot of divers carry scuba tanks, pony bottles, or spareair on the boat and pray they never have to use it to recover a diver. It would not be difficult to attach a spareair to a float. Another good thing about having this capability is it can pay for itself in recovery of equipment, like a fish getting holed up with your shaft and gun if it’s attached.
Drew
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