@gr8jab
what we have learned from accident analysis is that there have been exceptionally few incidences of death due to equipment failure on open circuit scuba *maybe one a decade.....*
Is this BSAC data or another source?
@gr8jab
In terms of trying to quantify a probability of failure, the probability of failure is highest immediately after service, usually due to faulty parts from the manufacturer or bad service in the first place.
I'm assuming that designers/manufactures have extensively studied wear-out mechanism and chosen service intervals recommendations with huge safety margins. This post-service infant mortality was on my mind, but again don't know
where to get enough data to put into a model.
@gr8jab
It is functionally impossible to compile that data to get any sort of realistic data.
Although I think I could do something with less detail than you suggest, your point is still valid. The nature of the source of the data and how it is (not) reported limits the data set and skews what is reported.
@gr8jab
We can SWAG it fairly quickly.
...
that's 1/2.7m which is IMO irrelevant.
Although I respect this back-of-the-napkin guestimate, and acknowledge that the sheer order of magnitude alone makes the implied large confidence interval moot, I still wish there was better data.
TANGENT/RATHOLE WARNING: pony bottle efficacy
Let's say we generally trust a guestimate of 1/2.7m, and agree it is irrelevant to the overall OOA occurrence rate. Therefore what is the primary cause of OOA? Human error?
An individual can minimize human error through training, mindset, vigilance, planning. A logical conclusion that many here have espoused is that a pony bottle is a crutch for those who don't want to bother. I forget Tbone, are you in that camp? No judgement, just inquiry, all this is meant in 'conversational tone'.
So how does an individual honestly assess their own chances of making a mistake? We all know people on both ends of the spectrum, who are extremely over cautious or over confident. Measured introspection is difficult. Some divers may realize they are at risk and work to reduce that risk. Others may be unable to assess their own risk. Still others may over compensate by avoiding all but the most innocuous dives, or excessively train and plan well beyond the marginal utility thereof.
If we dismiss the pony bottle as a crutch for those unaware or unwilling to address their own inadequacies (chance of a human error induced OOA), are we not suffering from our own form of extremism? Are we really prepared to say "if you need a pony bottle, you obviously are deficient in some other area, and therefore should not dive until you can do so safely without a pony bottle."?
What that tends to create is an all-or-nothing paradigm, where if you are a diver, you must do it all the time, take every class you can, and constantly train and practice. If you can't, and you realize you don't have the time/money/interest to go all-in, and therefore realize you are at a higher risk of human error, you can't be a diver. That seems extreme to me.
So why isn't a pony bottle a good risk mitigation tool? Yes, we should be introspective enough to acknowledge our own shortcomings and attempt to correctly minimize them. But why can't a pony bottle be
part of that mitigation plan?
Of course the problem is that the existence of the pony bottle may change the behavior of the diver, incurring additional risk that offsets or exceeds any mitigation by the bottle. This scenario, when applied to a diver without self awareness or enough introspection, is real and meaningful. But, I think to extrapolate this scenario to everyone who chooses a pony bottle is disingenuous and harmful to the aggregate risk of the diving community.
Many divers can self-evaluate and determine their risk for human error leading to OOA, and make a choice to mitigate the risk. Many divers are smart enough to mitigate by improving dive skills and vigilance. But for those unable to acceptably reduce the risk to personally tolerable levels, a pony bottle is a good addition.
Obviously, all this comes from my own struggles with risk. Since we've (above) determined that mechanical failure OOA is extremely rare, I have to consider my own chances of human error. Am I going to do something stupid? Have I done something stupid in the past? How will I react when faced with a stressful situation? Where is my own personal risk tolerance, and how can I move below that threshold?
Am I a moron? Let's hope that since I'm asking, I'm probably not. Therefore I can work to ensure I don't modify my diving behavior, and will not dismiss prudent training and practice. So, for me, pony bottle = less risk. I just hope my self-evaluation is reasonably accurate
But, sometimes I second guess that decision. Mostly when I look at the hassle of the pony bottle. It is one more piece of gear to maintain, transport (vacation diving), setup/teardown, and dangle from my gear. How much risk does it really mitigate? How likely am I to make a mistake? What dives won't I do without the bottle? Oh! Wait! I've already been here, feeling like I'm circling back on myself, with conflicting logic...
Boy am I frustrated with this struggle...
