Risks in Cave Diving

[Gary]

I took some simple assumptions an looked at risk involved in choosing a safe air reserve. The results were fairly sobering... I realize this could be bashed and twisted in any number of ways but the idea is still worth considering.

I took a rough estimation on cave diving risk is 1 death per 10000 events. And for the risky end a rough guess on the order of a 50% chance of surviving a dive to half gas (whether or not an accident/silt out or whatever may or may not occur).

In the range of gas reserve from 2/3s to 1/2 we are looking at a factor of 5000 times the chance of dying on a per dive basis. 2/3 of 3000 = 2000 psi, 1/2 of 3000 = 1500 psi. For every hundred pounds difference might increase or decrease risk by a factor of 10 times!

I ran the theory over a fitted normal distribution curves and it seems to agree with this general theory. With these assumptions the risk factor is predicted closer to 15 times per 100 psi in the vicinity of 2/3 reserve.

In the graph the 2/3's reserve being the assumed basis for the 1 in 10000 ratio we get the predicted 50% chance of death after 10000 dives. But the cumulative effect of additional risk or safety is clearly evident in repetitive diving as any 10 times risk is multiplied over a larger number of dives.


Whatever the assumptions used for the comparison the risk factor of 10 times per 100 psi would seem to be fairly universal. The cumulative effect of additional risk/safety over multiple dives could well decide your lifetime as a cave diver (or lifetime in general). Even over as little as 10 to 100 dives the tiniest violations of 1/3s has a noticeable effect on survival chances. And for those planning for a long career in cave diving additional safety margins might be worth considering.

<disclaimer: I'm neither a mathematician nor a dive instructor but figured this was interesting enough to share>

[MengTze]

Interesting concept. What is missing in this set of assumptions is that with each 100 dives (or pick a number), experience increases, comfort increases and thus the chances of survival increase all things being equal.

Can you add that to the numbers machine and pump a new graph?

[cloudboy55]

Reading this reminds me of those speeding signs that I used to see up north where they posted the fines for each level of violation. The discerning speeder could choose his level of risk...

Seriously, though, it would appear that some speculation went into producing this graph, although I'm not sure how one would produce such a graph without these methods.

-- cloudboy55

[jj1987]

I took a rough estimation on cave diving risk is 1 death per 10000 events. And for the risky end a rough guess on the order of a 50% chance of surviving a dive to half gas (whether or not an accident/silt out or whatever may or may not occur).

50% chance surviving a dive to half gas? I've yet to have a reg/post failure in a cave. Even in my one silt-out incident, it didn't take more gas coming out than going in. My Apprentice class in JB where we had portions lights out, sharing air, and portions just lights out, we didn't use more gas coming out than going in, though it was very close. Thinking about it, I don't know of many people who have had a failure such that they required their reserve air. That means that every dive, I could have gotten away with diving to 1/2. I guess this would qualify as a proof by counter example?

I would also say that it's fairly obvious that the calculation of risk would HAVE to factor in things like silt, low flow, new system, new buddy, new cave diver, frequency of dives leading up to the dive you're calculating, how well the system is marked (IE Ginnie with arrows every 100ft or a rare system), siphon or spring, etc. One thing that cave training makes VERY clear, is that diving to 1/3 in JB/LR/Manatee/Ginnie has a much greater safety reserve than diving to 1/3 in Peacock. You can easily prove that by looking at a dive log of someone who records dive end pressures, and I can almost guarentee that they end with less gas from a peacock dive than a Ginnie dive.

Before I fall for this too hard...I'm not sure if your post was serious or stirring the pot? I mean, you've got a graph and spreadsheet and haven't mentioned any confirmed source of data, so maybe I'm taking this way too serious

[cloudboy55]

...you've got a graph and spreadsheet and haven't mentioned any confirmed source of data, so maybe I'm taking this way too serious

[FW]

50% chance surviving a dive to half gas? I've yet to have a reg/post failure in a cave. Even in my one silt-out incident, it didn't take more gas coming out than going in. My Apprentice class in JB where we had portions lights out, sharing air, and portions just lights out, we didn't use more gas coming out than going in, though it was very close. Thinking about it, I don't know of many people who have had a failure such that they required their reserve air. That means that every dive, I could have gotten away with diving to 1/2. I guess this would qualify as a proof by counter example?

Before I fall for this too hard...I'm not sure if your post was serious or stirring the pot? I mean, you've got a graph and spreadsheet and haven't mentioned any confirmed source of data, so maybe I'm taking this way too serious

You may be mis-reading Gary's intent. If you turn at half gas, in a no-flow cave. there is a good possibility that you would exit with zero gas, if you got out at all.

[cloudboy55]

In the range of gas reserve from 2/3s to 1/2 we are looking at a factor of 5000 times the chance of dying on a per dive basis. 2/3 of 3000 = 2000 psi, 1/2 of 3000 = 1500 psi. For every hundred pounds difference might increase or decrease risk by a factor of 10 times!

I think we can all agree with the extreme danger of turning at halfs in a no flow cave, but I'm not sure that danger approaches a 50% risk of death. I do think the risk would be very high, especially for an inexperienced cave diver.

What I'm really wondering about is the quoted text above, and the methodology used to reach the dramatic conclusion that using an extra 100 psi for penetration (over thirds) increases your risk of death by 10 to 15 times.

[Daedalus]

If you aren't reaching the place you want to go on 1/3rds either add more gas or improve your SAC rate. If you are conducting multiple long distance exploration dives and using safety bottles then maybe you have another option.

It used to mean that breaching 1/3rds meant no-one would dive with you. Now people are using controversial gas planning methods used by a solo diving explorer to justify cheating thirds in their everyday diving because "I'm experienced, the rules don't apply to me" and no-one seems to be concerned. What is happening in cave diving today?

[MengTze]

If you aren't reaching the place you want to go on 1/3rds either add more gas or improve your SAC rate. ..

Adding more gas would still require to turn at 1/3rd..... Just a tad further.

It used to mean that breaching 1/3rds meant no-one would dive with you. Now people are using controversial gas planning methods used by a solo diving explorer to justify cheating thirds in their everyday diving because "I'm experienced, the rules don't apply to me" and no-one seems to be concerned. What is happening in cave diving today?

If you break your gas rules/plans (any rule) that were in place and could get you and I out safely, I would not dive with you. The buddy is basically playing with my life.

On the other hand, if you feel comfortable and plan according to your comfort levels, who are we to judge? As long as the risks are known, accepted and not transposed (i.e accountability stops with the diver). The issue is that this is not reality.................

[Daedalus]

Adding more gas would still require to turn at 1/3rd..... Just a tad further.

I was thinking in terms of adding a stage or increasing the size of your tanks.

If you break your gas rules/plans (any rule) that were in place and could get you and I out safely, I would not dive with you. The buddy is basically playing with my life.

That is the way it should be. I have a very good friend from high school I took my cavern and intro classes with that I stopped diving with because I caught them cheating on 1/3rds when I dove with them. I asked them why after the fact and they said it was because they did not want to be the one to turn the dive. We are still good friends, but this person does not cave dive anymore.

On the other hand, if you feel comfortable and plan according to your comfort levels, who are we to judge? As long as the risks are known, accepted and not transposed (i.e accountability stops with the diver). The issue is that this is not reality.................

It is not reality. A lot of people do not know the risks or lie to themselves and underestimate the risks. The problem is not with experienced people who have run up against a wall in terms of how many tanks they can bring in and out of the cave at one time. The problem is the buddy team who has 50 cave dives, think they are experts, and go 100-200 psi over thirds to reach whatever B.S. destination they read about on the internet because it is the most important thing in the world and "the flow will carry me out".