Jim
We know that cold shock can reduce the breath-hold capacity to less than 10 seconds - even for very experienced personnel.
In a recent conversation with an acknowledged expert in this field I gleaned 2 key pieces of information -
1. In cold water you have at most 5 seconds and probably less because of the body's reaction to immersion ie gasping/hyperventilation - it is not really a 'breath-hold'.
2. In order to escape promptly, you are far better off being on the air system before immersion rather than having to panic to find it afterwards.
Interestingly, it is possible to train yourself to improve breath holding time following cold water immersion but it involves (guess what) immersing yourself in cold water regularly - probably not that practical for oil workers I suspect.