I guess I dive a lot with just buddys; not known, competent people who subscribe to a briefed and followed plan like I do. I've been the junior diver on too many dives where I wound up leading some confused buddy.
No offense taken. Just meant "first stage failure." Rare, true, but possible. I tend to worse-case scenarios.
If you're diving with poor buddies, and you expect an expensive regulator to mitigate the risks involved, you're fooling yourself. The nice thing is that, as I said, recreational diving is generally very safe...look how many bad divers survive every day! (I'm not calling you a bad diver by any means!)
Again I have to ask, what do you mean by "first stage failure" and how does it cause loss of air? I have a feeling you're just repeating something you heard or read someplace, maybe in connection with buying a new regulator.
If you would like to have a slightly better understanding of how regulators work, you could check out Vance Harlow's excellent book on regulator repair. You'd learn a lot about the basic function of regulators. A short and simple bit is this: 1st stages are 'normally open' valves, meaning that they only close when air pressure in the stage reaches a certain threshold, at which point it closes and is holding back the pressure from the tank. As soon as that pressure drops even 1 or 2 PSI, it opens and sends air out. Any leak in a hose or 2nd stage would cause this pressure drop, BTW. 'Failure' of the 1st stage results in it not being able to contain the pressure from the tank, sending HP air to the 2nd stages and a resulting freeflow. I.E., too much air, not 'no air.'
Since the entirety of the 1st stage is under pressure, there is no way it can flood as long as the tank valve is open and there's air in the tank. There is an ambient pressure chamber in all 1st stages, but if the seal between that chamber and the interior of the 1st stage were to fail, air would leak out but no water could get in unless the tank was empty. So it's a physical impossibility for a 1st stage to send water instead of air to the 2nd stages, unless there was a large quantity of water in the tank.
A blockage could theoretically occur, most likely at the inlet filter if there were large pieces of crap in the tank that somehow made it past the dip tube in the tank. I'm sure this has happened to someone at sometime. But the best regulator in the world expertly maintained wouldn't matter in that case; it's a blockage in the tank.
There could be a possibility that the 1st stage could crack apart, possibly at the turret on 1st stages equipped with one, or at the yoke connection. This did happen on some SP piston firsts where the technician severely over-torqued bolts holding the stage together. In each case, SP responded with a recall and modified parts to make servicing a bit more idiot-proof. However, in this extremely rare scenario of a 1st stage literally flying apart, it's most likely to happen immediately on pressurization; turn the air on, and boom! Not likely while diving, because it's already experienced it's highest pressure threshold when first pressurized. I suspect that the odds of this happening are substantially less than one-in-a-million, given the number of documented times it's happened (a very few) compared with the number of actual scuba dives that have taken place on earth (many millions.) You'd be far more likely to simply die of health problems, drowning, giant octopus attack, be run over by a submarine, or lured into the abyss by an imaginary mermaid. (my personal favorite)
As I learned more about regulators, two rather sobering bits of knowledge have come into my head. One is that most of what is bantered about in dive shops (that I've been in) and advertising copy about regulators is misleading, irrelevant, or outright wrong. The other is that despite ANY best efforts, a regulator is a mechanical device and could conceivably fail at any moment. 2nd stages can and do flood occasionally, and freeflows do occasionally drain the tank quickly. The appropriate response to this is not to simply spend more on a regulator (or servicing) but instead to dive in such a way that you ALWAYS have access to another air source or the surface.
