Probably, but not always. I have taken 10's of thousands of divers in the water. I have had exactly one full out of air situation (client, not me). It was in the first five minutes of the dive, and their first stage failed closed. SPG still read full, but zero gas was coming out of either second stage. One breath was fine, next breath was nothing. They fortunately were 3 feet behind someone that had their octopus hanging free behind them, so just switched to that before I even got to the diver.Even a catastrophic failure would provide some gas for at least a few breaths.