I agree that if it is the only gas you have, it is a no brainer of a decision. From research I have read regarding WWII O2 rebreather development, you may have 10 minutes or so at 50' on 100% O2 before you tox - with a lot of varaibles such as CO2 levels, activity levels, water temp, physical differences between individuals etc. Could be more, could be a lot less, but if it were me, I'd roll the dice and use whatever extra time it gave me to try to get myself out.Any chance of knowing if the right post had pressure?
If it's the only bottle with the needle off the peg.... I've read that it doesn't hurt, but I myself can't imagine that decision.
Willem