LENGTH: I can reach my valve (with a bit of effort) when diving dry and a 24" PST HP 100 (3,500 psig) single. I cannot reach my valve in this situation if I switch out the 100 for a 20" PST HP 80 (3,500 psig).
WEIGHT/BUOYANCY: I use a 3/2 mm when diving wet, with ~6 lbs on my weight belt in freshwater when using an old-school steel 72 and plastic backpack or Scubapro Stab Jacket and no additional weight. So the HP 100 is too negatively buoyant (and the HP 80 even more so) to use.
---------- Post added September 22nd, 2014 at 04:04 PM ----------
lemke,
I described elsewhere on SB, a Great Lakes solo ascent where I did just as you describe, but from ~135 ffw and a bit off the anchor line. Too much drama! Much easier to reach over one's shoulder, shut down the valve, and go to bailout. Of course, I knew all this at the time, but I chose to dive the way I did anyway!
EDIT: I just looked. The post I was referring to is here:
http://www.scubaboard.com/forums/ad...475964-free-flow-incidents-4.html#post7035602. However, the details are absent. Those I wrote on a Facebook post. Here they are:
"
Another view of a free-flow. Taken from my air-integrated computer after an actual recreational dive in Lake Huron, June 28, 1996. First graph shows the depth (blue line, left axis) and *temperature* (green line, right axis). Run time is on horizontal axis. Max depth is ~130 ffw. Water was cold at the surface (~48 F) and colder at depth (colder than 39 F, as tank was still cooling when I began my expeditious ascent at run-time ~05:45 mm:ss).
"
Second graph shows depth (blue line, left axis) and *tank pressure* (green-yellow line, right axis). Tank (HP 80) is full (82 cu ft) at 3,500 psig, so dive was begun with a partially used tank (~2,500 psig). Free-flow began at run-time ~05:45 when tank still contained ~1,800 psig. Although ascent was begun almost immediately, and despite some "creative" measures taken toward the end, I ended the dive at the surface with a virtually empty tank. I was using a single Poseidon Odin (1st stage) + Scubapro D400 (2nd stage) regulator. This illustrates just how fast a free-flow through a high-performance reg can empty a tank!
"[There]
were three of us in single file going to inspect something that had blipped the fishfinder. Lead diver had tied his reel to the anchor line, and we were venturing away from the anchor. I was at the rear. I felt my reg getting a little wonky--often you'll get some small hint if you're paying attention--and then swam forward to signal the others what was up and that I was going to ascend. I had traveled back just a few yards as the other two continued on their way, when the reg cut loose completely. I still remember thinking: 'Don't screw this up, Ronald.'
"
Okay. The rest of the story: As I was ascending among all the noise and vibration and bubbles and monitoring my remaining air supply, I saw that I might run empty before I reached the surface. Rather than increase my ascent rate, I pulled off my Scubapro BC, swung it around in front of me, and then eventually began alternately turning off the valve, and then turning it on again (when I needed to take a breath)--while continuing to ascend while venting air from my BC and drysuit. This explains the blips that can be seen toward the end of the pressure curve. No big deal given our ... training, though you should have seen the Captain's eyes when I surfaced cradling my gear! (People on board can very readily see evidence of a free-flow at depth. The surface virtually boils, since air released at depth increases volume tremendously as it rises.)
"[My]
HP 80 is such a short tank (~20 inches) and sits so low on my back in my Scubapro BC that I cannot reach my tank valve when I'm wearing it (especially when I'm wearing my drysuit), which is why I doffed my BC during the above incident. If I had been wearing a longer tank (e.g., a 25" steel 72, or a 26" Al 80, or, especially, a 28" HP 120 or 29" LP 126), then I would have simply reached over my shoulder to turn the valve on and off as neededthe way we all did, ad infinitum, throughout [our] training. The upshot: (1) A freeflow at depth can leave you empty incredibly quickly, so it must be managed without hesitation, and (2) there are so many ways my dive could have been done so much better (beginning with a better gear choice) so that this type of not-improbable incident could have been handled so much easier and without so much drama."
