How much you would take then for that dive? 3? Or do you advocate for 45l/min bailout calculations like some do?
I'll drop this as encouraged reading.
How Much Gas is Enough? Running on “Empty”
By Andrew Ainslie
I just had a rude awakening after a dive recently that has made me re-evaluate my attitude to gas management, and my ability to handle emergencies rationally. I thought that I’d write the case up as a short article, in the hopes that it will make others reconsider what constitutes adequate reserves, and to recognize the sort of mental spiral that almost killed me recently.
On my last trip to Florida, I decided to push an infrequently dived section of a cave section with a new sidemount rebreather setup that I had been playing with. While this is not the time to talk about the errors that I made in that configuration, it turned out to not be the right configuration for the task. At approximately 4800 feet of penetration, I tore a hose on the rebreather, instantly wetting the scrubber and flooding the rebreather to a level that made it fairly unusable. At that point, I had what I felt would be an outrageous amount of gas – I had a scooter, twin 85’s overfilled to 3600 psi in a sidemount configuration, a stage at 4000 feet, and a stage at 2000 feet. Under ideal conditions, a single one of those 85’s should have gotten me out.
My head, however, had different ideas. It took me approximately 10 minutes to get back through the restriction that I had just spent 10 minutes getting through in the other direction – and I really mean 10 minutes, I verified it afterwards on my computer log. During that 10 minutes I ultimately ended up completely removing one of the 85’s and pushing it ahead of me, then half removing the other 85 and pushing it ahead of me as I scrabbled behind it. The puffing and panting, together with my mounting concern, had my SAC up to an outrageously high level. By the time I got back to 4000 feet, I had emptied one of my 85’s – that’s over 100 cubic feet of gas in under 800 feet of cave, swimming with heavy flow assisting me. I was shocked when I saw the gauge so low – I hadn’t even considered swapping tanks yet, and I’d emptied one!
I went onto the second 85, attached my stage, and started heading out. I lost concentration at one point, and drifted off the “main” line (which is a white line) onto a side line, without noticing that I’d made a jump. This line led me almost immediately into a really low section of cave. I, together with my rebreather, 2x85’s and an 80, almost immediately got funneled into a mud-bottomed restriction that I couldn’t get past. My rapidly worsening mental state led me to try to force my way past the restriction, instead of slowing down and trying to work out what was going on. In the process, I created an outrageous mess, with a silt-out so bad that I now lost this new line. I finally stopped moving, and waited for what felt like an eternity (but was probably about 5 minutes) for the silt-out to subside, while I shone my light around, until to my huge relief, I found the line again. By now, my mental state was extremely poor, I was no longer thinking logically, and my SAC rate was beyond horrible.
Back on the line, I came to a restriction around 3500 feet that requires one to turn sideways when in a sidemount configuration. I turned on my side and squeezed halfway through when I felt my reg start to breathe hard. My immediate reaction (which turned out to be wrong) was that I had just finished my second 85 – that’s over 200 cubic feet of gas in just 1300 feet with flow! I stopped pulling through, moved backwards until clear of the restriction, and deployed and went onto my stage, now seriously concerned about my ability to get to my second stage at 2000 feet – i.e. another 1700 feet ahead of me – with no backup source of gas. I thought that I was now running on a single tank of gas.
