An experienced open-circuit diver was trying the “latest, greatest” rebreather during an introductory dive experience. After a few minutes of cursory instruction, she entered the water and began her grand adventure. Descending gradually to 15 fsw (5 msw), she kept close watch on her gauges.
After a few minutes, she felt that things “just weren’t right.” She started to switch to her bailout bottle and passed out. Safety divers brought her to the surface and back to shore. She woke up just a few moments after the rebreather mouthpiece was removed from her mouth so she could begin breathing surface air.
What happened? It was determined that she was monitoring the submersible pressure gauges of the constant PO2 rebreather, and not the oxygen sensor gauge. Thus, even though she was continuing to breathe, her PO2 had dropped to a level incapable of sustaining consciousness. If your rebreather has oxygen sensors, you must monitor them on a frequent basis.
Learn more about rebreather diving in the best selling book by Jeff Bozanic, "Mastering Rebreathers"