There are two sorts of mouthpiece/valve on a CCR. A bailout value (aka BOV or OCB) or a dive/surface valve (DSV). They both have levers. Since a lot of dive gear is black they may look very similar.
If you turn the lever on a BOV you will probably be doing the right thing, so long as they have bailout gas available. This may not be true, especially if using their backgas dil as bailout, running out of dil is not an emergency, or maybe it is plumbed in externally but they lost it or gave it away. So, usually good but not always.
If you turn the lever on a DSV you will drown them.
The only way to be sure what is going on with a CCR diver's kit is to be briefed.
If you find a motionless non-responsive CCR diver and are in a position to go directly to the surface then give a lift a go. But if you have a ceiling then the lift may be too risky.
If you turn the lever on a BOV you will probably be doing the right thing, so long as they have bailout gas available. This may not be true, especially if using their backgas dil as bailout, running out of dil is not an emergency, or maybe it is plumbed in externally but they lost it or gave it away. So, usually good but not always.
If you turn the lever on a DSV you will drown them.
The only way to be sure what is going on with a CCR diver's kit is to be briefed.
If you find a motionless non-responsive CCR diver and are in a position to go directly to the surface then give a lift a go. But if you have a ceiling then the lift may be too risky.