“Aha. So this is only with scuba divers, not free divers...that the buoyancy thing becomes an issue?”
Not really, your lungs are a major component of your buoyancy. At normal depths you can you your breathing to help manage your depth.
At 300 feet your lungs are providing much less buoyancy than at 15 feet. If she blacked out she would not float up. If she can’t kick she also won’t be able to ascend.
I think they exhale on the way to the surface. Something to do with the re expansion of the air in their lungs.
So a naked human body stops floating when below a certain depth, right? When diving, you will reach a depth where you will start to sink like a rock. Is that how it works?