It's the exactly 3 breaths thing that is the probem. The one and only time I will admit to doing this, I got all of breath number 3 and then fully exhaled to speed the descent and of course got absolulutely nothing from my regulator. (No warning of an impending OOA is the downside of a balanced high performance regulator.) This leaves the OOA diver with no air in his or her lungs and about 15 seconds to work the problem before things get interesting.Markdone:
That's an excellent point. As Rick points out, it is easy to detect with needle drop on the SPG when you inhale. It's also a excellent reason to be sure you can reach your tank valve(s) in the water.Markdone:
That skill is taught in virtually every tech course, but is seldom seen in OW or AOW courses with single tanks where it would be a potentially bigger problem.
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In the spirit of things that can possibly go wrong, you also want to note if your SPG reading does not change. For example at about 110 feet I noted I had 1870 psi left and then a few minutes later I noted that I still had 1870 psi left. In this case, I was using an air integrated computer with an uwatec quick disconnect attached to the first stage. The fitting had unscrewed just enough to stop the flow of gas and trap the pressure in the hose. If I had not noticed the "stuck" reading, and/or had not wondered why I had more gas left than expected, I could have breathed the tank dry and still had an 1870 psi reading. I don't use that model of quick disconnect anymore and Uwatec no longer sells them so I suspect mine was not the only occurrence.
Similarly, mechanical SPG needles can stick, especially if there is some corrosion going on inside, so you not only want to note your SPG reading but also remember it so you can tell if the next reading is different.
