Stage Diving: What are you doing?

[jj1987]

Sometimes double is not enough. Sometimes six times is not enough.

There is no point where anyone has "enough" gas to protect them absolutely from an accident. There are accidents that are severe enough to overwhelm the most conservative gas reserve.

Theory is for every 100 psi more or less then thirds the chances of a fatal accident increase/decrease by a factor of 5-10.

Thirds gives about a 1 in 10,000 chance of fatal accident. Most would probably prefer to shift their chances in the direction of 1 in 100,000 or 1 in 1,000,000 than in the other direction (1 in 1000 or 1 in 100).

Amazing that 100psi in AL80's at 300ft increases the safety margin by the same amount as 100psi in LP104's at 20ft.

I admit I suck at statistics, so I'd love to see the study that produced those numbers if you wouldn't mind linking to it so I could give it a read over.

[rjack]

I get the normalized to 1 accident numerator, but where did this 10,000 (dive?) denominator come from???

I am also rather concerned that Exley's buddy, being a tad narked and not realizing that his own doubes were venting gas, and eventually losing backgas somehow is now turned into a "rule" for stages - which Exley HIMSELF didn't recommend even after being part of the accident in question. That kinda says somethin...

[Gary]

I admit I suck at statistics, so I'd love to see the study that produced those numbers if you wouldn't mind linking to it so I could give it a read over.

http://www.cavediver.net/forum/showthread.php?t=9180

[jj1987]

http://www.cavediver.net/forum/showthread.php?t=9180

Interesting, so the following factors don't really change the safety factor calculation?

• Solo vs non solo
• Scooter vs Swimming
• Depth (and as a result, time)
• High flow vs Low flow
• Silty vs Not Silty
• Low/Small/Tight vs Big Cave
• Diver Experience
• Equipment Shape (IE serviced regularly)
• Familiar vs Unfamiliar Cave
• Divers physical fitness level

[Meister481]

I would if I didn't have to leave them. Unfortunately as soon as you drop the stage, you're opening yourself up to people touching them, draining them, stealing them etc. Don't think for a minute that stages don't get drained, I've heard from a few people where multiple staged safety bottles were empty when they came back to dive the same area a few days later. This isn't the WKPP most of us are diving where everyone is on the same team, or indian springs where it's guided and safety bottles can be relied on, we're talking open access caves that it's happened in, including one that I bet most everyone on this board has dove.

I know if I were nearly OOA and about to die, I'd take a stage that wasn't mine. I bet 99.99999% of other cave divers would too, excluding the 0.00001% that would lie on the survey. It's worth considering that fact when you start planning stage dives.

I DO use that as a factor when considering reserves, If I'm at JB on the weekend I won't drop a stage until I'm past the trash room. If I'm alone during the week I might drop it just past kings bypass. In LR I will dump my stage and scoot at the end of the FL room. Heck, if the place is full enough I'll tow it a bit off the main line and then clip it off.

Interesting, so the following factors don't really change the safety factor calculation?

• Solo vs non solo
• Scooter vs Swimming
• Depth (and as a result, time)
• High flow vs Low flow
• Silty vs Not Silty
• Low/Small/Tight vs Big Cave
• Diver Experience
• Equipment Shape (IE serviced regularly)
• Familiar vs Unfamiliar Cave
• Divers physical fitness level

Among many others.... I see no basis for survivability. I get what he's trying to get at, but an odds based algorithm has to have many input factors and more data points than total # of dives and a fraction of PSI. Empirical testing like was done in the journal this quarter would be a requirement.

[aainslie]

http://www.cavediver.net/forum/showthread.php?t=9180

Exactly how much training do you have in probability theory and statistics?

Why is a Normal distribution appropriate? Why would probabilities be symmetric about 50% consumption?

Gauss would be rolling in his grave if he read that "theory".

Let me give you an example of why it doesn't work. According to your "theory", if I entered at 3000 psi and turned at 1350, I'd still have about a 10% chance of surviving.

Do you believe that? Try THAT empirically and see how it works out. heck, I'll even allow you a safety diver. Do 20 dives to 1350, and see if you survive 2, in a no flow cave.

Fitting a normal CDF the way you did is completely arbitrary and NOT based in any sensible model of air consumption distributions.

Next, the value of 1 in 10k is totally arbitrary. So you're fitting the curve to TWO points (already a dicey thing to do), one of which is a reasonable assumption and one of which is a total guess - and NEITHER of which are based on data. You simply can't do that in any adult audience with lukewarm IQ's.

Finally, there's no reason this would also apply to stages, or scooters, or anything other than backgas.

Sorry Gary - this just isn't either empirically or theoretically sound. It's total garbage.

[ARY]

I was always curious Andrew what would you do beyond the last stage depot. Lets say a cave becomes too small to carry stages and the only option is your two primary sm bottles. Lets say you are 2 stage legs after scootering in the cave at this point. What rule would you use for your "side gas" for penetration? Lets say up to this point you enjoyed the company of your buddy. Would you take him with your further, how does your gas plan change?

[atedeschi]

For a double scooter stage then drop and swimming, you would not only plan for a swimming exit but have safeties dropped along the way as well.

Kinda how they were doing exploreration dives past the hinkel.

[Gary]

According to your "theory", if I entered at 3000 psi and turned at 1350, I'd still have about a 10% chance of surviving.

Turning at starting at 3000 and turning at 1500 is assumed as 50% - a 10% chance of making it turning at 1350 doesn't sound at all unreasonable.

There is really nothing questionable about the general numbers. Using 3rds chances are about 1 in 10000 - turning at half in no flow 1 in 2 is as close to surety as one can get without actually running testing that would be illegal and unethical.

Depending on your tanks the difference between 3rds and half is about 400 to 500 psi. If you don't like normal distribution the only other way to divvy up the chances gives the same answer.

5 to 10 times the chance of fatality per 100 psi more/less than 3rds.

Solo/buddy, gear config, skills, dive difficulty, flow, etc of course all have their own contributions modifying the initial assumed risk at 3rds and the 1/2 point but it's not going to significantly change the basic answer: 5 to 10 times the chance of fatality per 100 psi.

[aainslie]

I was always curious Andrew what would you do beyond the last stage depot. Lets say a cave becomes too small to carry stages and the only option is your two primary sm bottles. Lets say you are 2 stage legs after scootering in the cave at this point. What rule would you use for your "side gas" for penetration? Lets say up to this point you enjoyed the company of your buddy. Would you take him with your further, how does your gas plan change?

I push cylinders - so I don't necessarily stop having stages past a tight restriction. It's rare that a thght restriction carries on for hundreds of feet - bu if it does, of course you can only do this so far.

So nothing really changes. I go to thirds in flow (less in no flow).

And I can rarely find anyonw dumb enough to join me so the second question doesn't really come into play.