COMMENT:It must have been disconcerting to suddenly be unable to breath at 55 feet (16 meters) depth. This diver kept a cool head, signaled "out-of-air" to her buddy, secured the alternate air source and made a controlled ascent. This is exactly what is taught in entry-level diver courses worldwide.
This incident also highlights a topic we are so concerned about that we wrote an article in Alert Diver in 2014: Tank valves and out of air emergencies.
The days when we needed to turn our valve back half-a-turn are long gone, but still some instructors teach divers to do this. Why? The safest way to ensure you have adequate gas for any dive is to open your tank valve all the way, then look at your SPG while taking a couple of breaths.
If your needle does not move then your valve must be open and if your needle goes down towards ‘Zero' then your valve must be closed. If you are in the habit of turning it back half-a-turn then, like this diver discovered, you might have enough gas to breath normally at the surface but you could find yourself short of breath at depth. Remember, the safest way is to turn your tank valve all the way open or all the way closed.
~ Peter Buzzacott, MPH, PhD