I haven't been in an actual OW OOA event yet, thank goodness.
The on OOA event I was involved with was in a pool during, yes, OOA training, which I have decided is the worst time to "run out of air".
There were ~12 people in the class on the bottom of the pool in two rows. Everyone was set up with the bungied backup/donate primary method (no long hose though
). The instructor was at the other end of the line watching them do air shares. I was hovering around watching the rest of the group--they weren't supposed to do anything until the instructor showed up. I noticed one girl at the end of the line giving the OOA signal, so I'm thinking "Why is she practicing without the instructor?"
Her buddy must have been thinking the same thing, but after about 3 repeated signals I realized it was real, so I stuck my primary in her face. One of the other volunteers noticed it as well, so she really had 3 regulators to choose from, but by this time she had already ripped her buddy's out of her mouth. Thankfully her buddy remembered her backup was around her neck.
We had only been down perhaps ~10 minutes, with full tanks, so there was absolutely no way she was out of air already sitting at the bottom of an 11ft dive well. Right after the ripping of regulators, I swam by and checked the girl's tank valve. Turns out it was only about half a turn open, so I opened it fully and signaled them it was ok for the "OOA" girl to get back on her own reg. She didn't realize it was her tank valve, she kept pointing to her regulator, as if saying "It just stopped giving air!" I explained to her on the surface that her tank valve was essentially closed.
While she "panicked", I believe she learned an important lesson the hard way--make sure you check your equipment completely, before hopping in.
Something tells me she won't make that same mistake again.