Regulator gets harder to breath the deeper a diver goes
We took our regulators to the local dive center for their annual inspection and collected them when my husband and I took enriched air and dry suit classes. We used our regulators in a pool dive that day and then later they were used by me for a shallow water dive (less than 20 fsw / 6 msw) without incident. A couple of days later I was scheduled to make a deep dive along with another student. With us were three instructor candidates and the dive instructor. After some weight adjustments we descended to a depth of 60 fsw (18 msw), when I felt I wasn't receiving enough air from my regulator. I signaled to my instructor and pointed up. The instructor thought I was having a problem with my ears so we slowly started to swim to a shallower depth. Somewhere around the 50 fsw level (15 msw) my regulator was giving me very little air and I inhaled water. My instructor attempted to put my regulator back in my mouth because I had already spit it out because I was not receiving air from it, then I attempted to locate my secondary regulator which is integrated into my BCD power-inflator line and the instructor thought I was going to inflate my BCD and rapidly ascend to the surface so he attempted to stop me. I pushed him away and started to swim towards the surface and lost conscious at approximately 40 fsw (12 msw). My instructor caught up to me, inflated my BCD and sent me to the surface. At the surface the instructor administered mouth-to-mouth and yelled to my husband who was on shore. My husband called 911 and swam out to assist. After receiving rescue breaths from my instructor and husband I vomited and coughed up water repeatedly, then started to regain consciousness. I was pulled into shore by my husband and medical treatment was given to me by him and the arriving ambulance.
Later, after researching online about scuba regulator testing facilities, we took our regulators to have them inspected. The company put them in a pressure vessel to test gas flow and found the regulators were out of factory specifications. We were informed that the regulators were set so the deeper the dive the more difficult it was to receive air from them.
It sounds as though this diver was lucky not to have drowned. As with many near miss reports, a number of factors conspired to create the circumstances needed to enable this event to occur. First, the regulators were a particular type than can be set incorrectly to make it harder to breathe with increasing depth, then it sounds as though they may indeed have been incorrectly serviced, then the diver made some test dives but they were shallow so no problem was detected. During the actual dive the diver may not have given clear "OUT OF GAS" and/or "GIVE ME GAS" signals and, coupled with an unusual type of back-up second stage, the instructor mistook the diver reaching for the power inflator to indicate a desire to ascend. Even if the diver had tried this back-up second stage then it may not have worked, if it was the first stage that was malfunctioning. Rarely does a single issue lead to a near miss. The great majority of incidents involve many factors all coming together during the one dive. This is why to maximize safety it is essential for every diver to maintain current skills, (such as knowing standard dive signals), maintain personal dive gear and practice emergency procedures such as locating a back-up second stage, dropping weights and orally inflating the BCD at the surface.