You know, breathing off the free-flowing regulator was way easy. That would not be a problem for me at all. Hm, well, I guess the main concern there is how long it would be before the air were exhausted altogether. Is this an easy-to-calculate number? I imagine it varies by depth...?
My understanding is that there are too many variables. Air is consumed faster at depth, yes - but also different divers use air at different rates (my SAC is about 22 litres a minute on average, and my wife is about 19). The same diver will use more air when exerting himself, or panicked, etc. I as looking at a profile graph of a recent dive (depth vs SAC) and I could see where some nervousness I was feeling at the start eased off and my consumption lowered. And of course the one big variable is how long you are into the dive at the time the free flow occurs.
I think from what I have read you only have a minute or minute and a half at most of air in a standard full tank if freely flowing.
My buddy and I practice air sharing, buddy ascents and so on on the way up at least once every day on a multi-dive day. We make sure to ascend with plenty more air than we need. I've learned I use circa 20bar going up including a stop, and the standard here is to be back on the boat with 50 in the tank. So we ascend on 80 bar to be extra conservative, and plan a turn around pressure accordingly (the half wy point between the starting tank pressure and 80bar). I'm detailing this because I'm at a similar experience level to you so it might be interesting to hear how we go about it. We are in the habit of regularly checking in about our pressures too.
One good tip I learned here was to get in the habit of guessing what your pressure should be before checking. I believe this habit is helping me get a gut feeling for it faster than I would otherwise.
It really does seem to me that if cared for and serviced properly the gear we all use is extremely safe and reliable. It does seem that the most likely reason you will run out of air is if you plan poorly or don't stick to your plan. And even if it all goes pear shaped, sharing air is not a technically demanding skill. This is one thing I feel pretty relaxed about, actually.
Now, if I can only get relaxed about removing my mask! For whatever reason, this is one little thing that freaks me out irrationally. It's how I'm spending time on my safety stops - taking the damn thing off and on again until the day comes when I don't dread it so much
I guess we all have our particular fears! Losing my mask and/or a runaway ascent are my two nervous scenarios, so I'm putting extra thought into ascending without holding the line and mask drills. Why don't you ask your next buddy to run a quick air share drill at the start or end of your next dive/s? Doing it over and over and seeing how easy it is might help relax you.
For now, I wonder if a pony bottle is a 'gear solution to a skills problem' as the old salts seem to put it.
