My only experience with an OOA situation was ME. Before you dub me a dimwit for running out of air, hear me out. It was on a dive off Playa del Carmen to visit a site called Tortugas--an apt name since there were turtles everywhere! I flipped head down to take a picture of one of the creatures that was on the bottom feeding. When I righted, my first breath seemed a bit strange, sort of tight. I took another and realized there was real trouble brewing as the flow of air essentially stopped. While I was getting a bit of air, it was nowhere close to what was needed, perhaps 15-20 percent. I found that if I breathed VERY, VERY slowly (taking ten seconds to make one inhalation) I could eventually get a nearly complete breath. Checked my gauges--showed about 1800 pounds. Tried my octo--same effect. Hmmmm. Looked up and it was 65 feet to the surface. Sure, I can make that, I thought, but I don't WANT to do an EA. Looked for my buddy, who was an assigned partner, a fellow from Poland who had a total of 9 dives. He hadn't stopped when I slowed to take the picture, and now he was only about 15 feet away, but UP current. With the miniscule volume of air I was getting, kicking against the current was impossible. Hmmmmm again. I spotted the divemaster about ten feet below, so that seemed the best alternative. I dumped air from my bc, dropped in front of the dm, and got his attention. The hand signal conversation was quite funny in retrospect. He had a bit of trouble coming to the realization that I was having difficulties.
Cutting to the chase, I kept my regulator (after all, I was getting SOME air, just not enough to be effective) as we did a slow ascent. I did, however, have his octo in my hand just in case. He saw me to the surface and I boarded the boat while he re-descended.
The problem became evident when I dismounted the first stage from the tank. It was completely plugged with a white powder. It was an aluminum compound from the bottom of the rental tank. When I inverted, it slid to the valve and gummed up the works. (That means that even the "snorkle" attached to the tank valve had to be missing.) I don't dive with that service anymore. Tank maintenance doesn't seem to be a high priority.
So, there wasn't any "panic" on anyone's part. But then, it may not qualify as a true OOA experience since I was getting enough to survive, just not enough to do anything else.