Turn pressure in the recent incident

[aainslie]

1) Why would you swim out in an emergency with yoru scooter? Especially if you begin to get behind schedule? Dump the bloody thing!

2) Some things are self evident. Aruithmetic as simple as the stuff I proposed doesn't need empirical testing. Sheesh.

OK, I'm done on both these threads.

For those of you who care, DON'T DIVE THIRDS. DIVE DOUBLES.

Seriously. Find ways to make sure that you reserve double or more teh gas erquired to exit under all scenarios. With stages, you might change this to reserving (n+1)/n where n is the total number of tanks (I could provide a proof of why this makes sense but I've come to realize that mathematical sophisticaion is viewed as a form of dark magic around here - so instead I'll leave it to those willing to use their noggins), i.e. with 3 tanks, reserve 1 1/2 x the gas needed to exit in EACH tank; with 4, reserve 1 1/3 - and of course use this as an absolute minimum, i.e. add a nice margin. This is a way safer rule than the conventional one of diving stages to 1/2 + 200. This is where I intended to go next, Richard, after your example of recalcing thirds with stages. I'll hold it for an article I've decided to write - assuming anyone is willing to print it. We'll see.

This has been fun. Be careful who you buddy up with. A lot of them will, to quote myself from another thread, run like a girl at the first sign of toruble. So make sure whether your'e diving with a girl (Gary comes to mind) or a real diver (Cindy comes to mind).

[Burke]

I voted for 800 PSI for several reasons...
- I drop my stage beyond the H400 jump. So if I can swim against the flow to that point on an AL 80, I know I can make it out with the flow on 800 PSI from 104s. No math is necessary in this instance.
- I always place an O2 bottle so I don't have to deco on BG and don't need to allow anything extra for deco. I dive with O2 on every dive and a stage on most. That extra redundancy should be SOP for cave diving. In an emergency, you don't have to make it back to the entrance, but only to the first bottle, which might be 700ft in. That's a HUGE safety factor.
- With 800 PSI that close to the entrance, there's gas for a slow exit, stopping to look behind, frequently.
- If I find my buddy on the way out, more than likely he'll have about the same amount of gas as I do. We'll greet each other and make a quick exit. He's buying lunch...
- If something else happend and he needs gas, we'll share what I have and skip breathe to the exit if necessary. What else can you do at that point, turn your back on him? At what point during the exit do you say to yourself, "I'll stop looking for my buddy now because I don't have enough gas left for the both of us?" If I happen to have that stage with me, all the better...
- 800 PSI is a lot of gas in 104s, but as someone else mentioned, I've noticed that gas isn't exactly linear, meaning the 1,000 PSI going from 3,000 to 2,000 lasts longer than the 1,000 PSI from 1,500 to 500, but maybe that's just my imagination...

I agree that in most instances your lost buddy can exit by himself with no problems, and it certainly doesn't make sense to kill yourself trying to find him when he may have already exited. That said, this isn't OW diving. No one wants an additional, and unnecessary fatality, but if you're not willing to take on some additional risk to help your buddy, you need to find some other type of diving, maybe one where it's expected that you surface after one minute to look for your buddy and yell to the DM for help when you can't find him. If I got back to the surface with 1,000 PSI left and my buddy wasn't there, I would probably have to go back in, and that could be an even worse situation. I prefer to use that 1,000 where it's most effective - in the immediate area of separation.

[RN]

1) Why would you swim out in an emergency with yoru scooter? Especially if you begin to get behind schedule? Dump the bloody thing!

Because it was a test and my scooter wasn't busted! In a real emergency, the scooter would have been left in the cave for later retrieval.

2) Some things are self evident. Aruithmetic as simple as the stuff I proposed doesn't need empirical testing. Sheesh.

Arithmetic is fine, but I believe in empirical testing...at least once. Once I've verified the numbers I'm okay with using the math to figure out all subsequent dives. You want science, then that's how it works. You can't leave a hypothesis untested.

[quarrydiver]

"Burke"

Cuft of gas is linear with psi from 0 to 3000 psi, it is only above 3000 psi that the relationship is no longer linear owing to the fact that the gas molecules are not infinitely compressible. So if you notice that 3000 to 2000 psi lasts longer than 1500 to 500 psi it is for 1 of 2 reasons: either you are consuming more gas owing to fatigue towards the end of the dive or your SPG doesn't read accurately at low psi. Both are quite possible.

Marius

[Meister481]

Because it was a test and my scooter wasn't busted! In a real emergency, the scooter would have been left in the cave for later retrieval.



Arithmetic is fine, but I believe in empirical testing...at least once. Once I've verified the numbers I'm okay with using the math to figure out all subsequent dives. You want science, then that's how it works. You can't leave a hypothesis untested.

I'm with you there, just because it works on paper doesn't mean I trust it. If I'm betting my life on it, I'm going to test it more than once.

[MORGAN]

Empirical testing of any hypothesis is necessary, not to confirm that the math works (math always works), but to identify aspects of the operational situation that we didn't take into account in our mathematical calculations.

Mike