What happens if the compressed air cylinder is disconnected underwater? Can I open it again myself?

First of all, 2 separate controllers are always available (at least in Germany) (both on a self-closable valve). So if someone unnoticed turns the controller (soon happens for exercise purposes) then I simply change to the backup system. At the latest from the DTSA/CMAS**, part of the test itself is to come to its valves and can rotate them up and down accordingly.

As a technical diver, I am of course able to reach both valves as well as my bridge and turn them up and down. This is usually also regularly trained to not lose the ability and thus to sit the handles in emergency.

But someone turned the bottle so tightly to me that she couldn’t get up anymore. Then we had to help under water with a tool. This is, of course, nothing a normal sports diver has to afford.