Dude the majority of divers don't wear any pony whatsoever......
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Very much so. It is an argument of convenience. Of course a 40 would be "safer" than a smaller tank, but does the inconvenience justify the marginal safety? The answer is right in your face and the answer is "NO"! Look at the diving population.. are they wearing 40 cu-ft pony bottles for 65 ft dives????
Lynne, I totally agree with that. I agree that a well-trained, vigilant buddy is by far the safest bet. However, I can't say that that's always possible. I was buddied with a HORRIFYINGLY poor diver in Mx. Had anything have happened to my gear, it would've been at least me dying. A pony wouldn't have been unwelcome.
One thing about carrying a tiny pony, like the Spare Air, is that it may cause a false sense of security. Too many people purchase one without doing any thinking other than "the ad says it'll save my life" and then don't train anywhere beyond "I'll just breathe off of this if everything goes badly." A pony bottle of any size is a tool in the arsenal of a diver, not the answer to all safety concerns. It requires practice, discipline, and forethought....both in its deployment and in its utilization (taking it with you in the first place). SafeAir has marketed itself as an insta-fix for bad training, and as an automatic solution. It is neither of those things.
However, if you ARE carrying a pony bottle for redundancy it is unrealistic to think that in the case of something actually going wrong that 3 cubic feet is enough for any reasonable depth. In the vast majority of scenarios, this happening would be relatively unexpected. Immediate and flawless deployment of the pony would be FAR from the norm. Breathing rates would be elevated drastically. Even if everything happened quickly and smoothly, there's no way to start an ascent at the same instant your gear fails while transitioning to a pony. The paradigm set forth under DumpsterDiver's post regarding the need for a minute at depth before responding, and then SAC rates noticeably higher than 1ft3/min is inaccurate. My numbers depicting a 25 second ascent time from 100ft was using a SAC rate of 1.2 and no excessive wait time at the bottom. The figure I calculated for the "standard" ascent rate was 60ft/min below 30ft and 30ft/min above 30ft. At 100ft, a SAC rate of 1ft3/min would mean less than 45 seconds total at depth. This doesn't take into account purging the regulator or a short fill/leak or any reserve (using every single molecule). This ignores all effects that aren't a perfect-world scenario.
What exactly do you need to accomplish on the bottom (say when you can't breath anymore)?
Realistically, and following safe diving practices and training you are given:
How low would you draw down your main 12L air cylinder at 232 b diving solo with a 2.7L pony bottle at 200 b diving in the ocean. Without the spare air you'd normally surface with 50 b.
Realistically, and following safe diving practices and training you are given:
1) Comprehend that you actually have a problem.
2) Analyse what is wrong.
3) Conclude what the problem is.
4) Calculate what resources you have available.
5) Consider options to solve the problem.
6) Decide upon the optimum solution.
7) Communicate your problem and intention to your buddy.
8) Co-ordinate and confirm your buddy understands
9) Enact your solution.
What you seem to be suggesting is:
1) Bolt to the surface.
...which is odd; from a former dive instructor...