This is my standard response to someone who asks how I feel about using a pony bottle:
There are 3 rules that I have come to live by in my 16 years of emergency work, including many operations in extremely hazardous environments:
“Never say never”:
You can greatly reduce the risk of bad things happening through training and planning, but you cannot completely eliminate the unexpected. Those who say that they will never have an out of air emergency because they are well trained/experienced or good at planning are asking for trouble. Just because it has not happened to you yet, does not mean that it never will. Always plan for the worst, to lessen the chance that a problem at depth will become a fatal one. As a confined space rescue instructor, I will never make entry into a low oxygen or toxic environment without my bail out bottle. It is not a crutch, but a safety tool in the event of a catastrophic failure of my main system.
“It ain’t over till its over”:
If I ever find myself in an OOA situation underwater, I will use every tool that I have to get to the surface. If I was at 130 fsw, I’d sure as heck try the ascent with a 6 cu ft pony bottle, or even a Spare Air if that’s all I had, over an ESA any day, and I have little doubt that I’d make it to the surface. It may not be a safe 60’ per minute ascent and I would be risking other, treatable dive maladies, but it is far better than the alternative. DCI is treatable, remaining underwater with no air to breathe is 100% fatal. That being said, I would never depend on a bottle that small at that depth. But to those who say that you would be better off with nothing at all on rec dives, I must disagree.
“Simpler is safer”
The less complicated something is, the less likely you (as a human) are to screw things up, and the less humans you have in your "chain of survival", the less likely things are to go wrong. If you or your buddy end up in an OOA situation, it is almost always better to resolve the situation yourself rather than ascend connected to a buddy. The rate of double accidents on shared air ascents testifies to this. Some divers here say that they train regularly with their buddies on sharing air, etc, and this is certainly the right thing to do, as long as you practice with everyone you dive with. But most people don’t do this, and it will not help with the unknown dive buddy that you are paired with on the boat against your will. But of even greater concern to me is the fact that you never know how someone is going to react when faced with a sudden emergency until they are actually faced with it. Training and practice certainly help, but at least twice now I’ve seen divers bolt toward the surface with eyes as big as saucers. I certainly don’t want to be attached to that person when he runs out of air. And I’ve seen several more do it from hazardous environments on land, despite literally hundreds of hours of training. You simply do not know for sure when someone is going to panic.
Anyway, don't let anyone tell you that you are less of a diver because you choose to use a pony bottle. The bottom line is self sufficiency. You can enjoy buddy diving, be a good dive buddy, and still be self sufficient. If your buddy needs you, you are there. But if he can resolve the problem using self sufficiency, even better. Safe diving involves planning, and that means planning for the unexpected. A fully redundant air supply is a valid part of that equation.
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