Yep. Maybe a function of the area and the prevalence of quasi-techies here or the diver population with whom I have regular contact... but yes, I would say that 40s are more popular here by an order of magnitude.
Not sure what you mean. Primarily, one can make a good argument that once a dive has been conducted below 30 metres, a stop is less optional more "Best Practice" if not actually required. A gas emergency does not make any "decompression obligation" or "Best Practice" dissolve, therefore having sufficient gas to meet those needs -- emergency or not -- seems like good contingency planning.
Of course one could make an argument that in an emergency, a diver should shoot to the surface and get outta the water... but that kind of goes against everything I teach and write about.
If a diver becomes too freaked out by -- let's say a freeflow -- that she is unable to deploy her backup and execute a normal controlled ascent, she needs remedial training and does not belong below 30 metres... in my considered opinion, but others feel differently. By the same token, I believe that a dive below 30 metres requires the diver to carry a redundant gas source and regulator... again, your mileage may vary.
Which is why I write articles... teaching is about modifying behavior. In this case, my belief is that a having enough gas to ascend properly and the skillset to use that gas in a fashion that's prescribed by best practice, is the goal.
Life is not black and white, and frankly, any amount of back-up gas is better than none... but if someone is going to the bother of carrying a redundant gas source, why not make sure it is going to function in the most extreme circumstances on a pinnacle dive for the diver.
What I mean is that a diver has to balance safety versus convenience. I completely agree that the addition of a pony bottle can increase the safety of a diver, even at depths well less than 100 feet. I kinda demand that people who dive with me use one..
However, it seems as if you are arguing that everyone needs to buy a Volvo station wagon to drive over 50 mph, while I am perfectly happy with a corrolla and an air bag....
Having more air might make things easier, but (a 40 cu-ft bottle) is just too much trouble to get most people to even consider it. I see a lot more people using no pony bottle than people using 40 cu-ft bottles.
I've used a pony bottle for maybe 25 years and have had to use it once... On a solo dive a few years ago where I ran out of air at maybe 120 feet while chasing a wounded fish. Incredibly stupid. I was using a 6 cu-ft pony bottle and made a somewhat quick ascent from depth up to shallow and then once at 20 feet, I sipped my main tank for a long time and completed a safety stop with zero issues.
I think that if it is a choice of taking no pony bottle or a small one, the little bottle is a much better choice.
I think we need to acknowledge that most people will NEVER need the pony.
Most rec divers will probably NEVER go into deco.
The probablity that a diver will run out of air completely AND go into DECO AND will be delayed for 3 minutes on the bottom AND be unable to control their breathing rate to a manageable level (for 120 seconds) AND will feel the need to perform a 5 minute safety stop AND will have no air remaining in their main tank to help out on an ascent...... is.. pretty unlikley to occur simultaneously on the same dive.
For myself, for no-deco... I am perfectly willing to assume that I will begin my ascent the second it gets hard to breath from my tank. I am willing to assume that I will be able to add enough air to the BC, to allow me to gently float up and eliminate all kicking and exertion, I am willing to assume that I will be able to control my breathing rate for 2 minutes, I am willing to ascend at 60 feet per minute for the first 30 or 60 feet (depending on depth) and I am willing to forgo a safety stop at 20 feet if I run out..
And with all those assumptions, a 13 cu-ft bottle is a reasonable compromise; so is the new Corolla.
