Diver dead on the Andrea Doria

[Jax]

If one goes to Doppler's Blog, to the 18 Nov 2010 listing, Steve discusses several issues with CCR statistics, but also says

At issue is poor initial instruction, diver complacency and a community ethos that sanctions, or at least ignores, bad habits and sloppy procedures.

I have no idea how much weighting or seriousness to give each of these issues because each is serious and each can lead some poor punter finding himself in a situation that has a better than average chance of a piss-poor outcome.

I remember reading a reasonably well put together article which suggested that the formulae:

(number of CCR fatalities)/(number of CCR dives) = 800 * (number of Open Circuit fatalities)/(number of Open Circuit dives)​

was accurate. Could probably find it again with judicious Google searching.

On this one, though . . . using what is in that 2008 article . . . Let's make up some reasonable numbers.

4500 divers, doing 1 dive a month = 54000 dives per year.

18 deaths / 54000 dives = .03.33%

That implies .000333 = 800 * (number of Open Circuit fatalities)/(number of Open Circuit dives)

So .000333 / 800 = % of fatalities based on dives . That just looks too tiny.

Besides, when you start talking numbers to the 4th significant digit when the sample size is only ~5000, I'm thinking it's not statistically relevant. And . . . who the heck really knows how many dives people do, anyway???

Remember, 78.64% of all statistics are made up, anyway!

 

[Thalassamania]

Jax, here are two posts that I think bear repeating at this point:

Experience changes perspective... as already mentioned.

An illustration from the CCR world is that after about 20 hours "on the unit" most individuals think of themselves as a newbie. After 50 hours, they are an expert. After 100 they achieve guru status. However, when they have logged 150 hours they understand they are still a novice; and after 200 they settle into the realization they are an experienced beginner.

And for what it is worth, Crush, I think this is a perfectly good question to provoke some thought.

An interesting analogy. For what it's worth I suspect that I was a much safer rebreather user back during my first 50 hours. I might not have been able to do much more than maintain position in the water and stay alive, but I was far more vigilant and safety conscious than I am now that I have settled comfortably into being an "experienced beginner." I don't think that open circuit/open water is quite the same.

When you add to this the more experienced CCR pilots' propensity to set their oxygen ever higher, as in: "what the hell, I've never had a problem and it shortens my deco," come on, admit it, we've all done it ... ever higher, until they get into trouble, and that trouble, when it finally happens, is big trouble, not just something that you can do a a hugely manly free ascent from and escape ... well, you get the idea. I've got a Mk15, and enough parts to build another and still have a good stock of spares, but I've also got a 15 year old ... so, like my Dunstall Norton, it is, at moment, hardware that is more enjoyed in the stroking (no pun intended) than in the regular use. Besides, I can't afford two Hammerheads at the moment.

Added Afterthought: The ever increasing set point issue is, I feel, one of the hidden secrets of the CCR world. It stems, like so many things, from overly conservative, hard and fast rules, that bear little or no relationship to reality (e.g., 130 foot depth, 24 hours to fly, etc.). If the diving world was more honest in it's rules, people would not have to incrementally push the limits to find out where the cliff really is.

 

[Jax]

No pun intended my azz.

 

[Ken Kurtis]

On this one, though . . . using what is in that 2008 article . . . Let's make up some reasonable numbers.

I'm personally OK with made-up numbers, especially when it's clearly indiciated that it's such. But . .

4500 divers, doing 1 dive a month = 54000 dives per year.

What's the basis for the 4500 and the 1 dive/month? If we're talking US/Canada numbers (basis of the DAN stats - and I've only occassionally been follwing this thread so I may be missing something here) I really would be surprised if there are 4500 rebreather divers in the US/Canada.

18 deaths / 54000 dives = .03.33%

OK.

That implies .000333 = 800 * (number of Open Circuit fatalities)/(number of Open Circuit dives)

Not clear on the 800 at all. If someone's saying there are 800 open-circuit fatalties US/Canada, that's too high. The average DAN number of ALL fatalties lately (which would include rebreathers) is around 90.

And if you take thje ratio for (number Open Circuit fatalties)/(number of Opemn Circuit dives) it's going to be 90/25,000,000 (2.5 million divers doing 10 dives/year - another made-up number) would would equal 0.00036%. Based on comparing the two rates, you could say then that diving a rebreather is 100 times more likely to produce a fatality than diving open circuit or - probably more accurately - the rate is 100 times greater.

And . . . who the heck really knows how many dives people do, anyway???

Excellent point. As we've said frequently, we know the numerators but we don't know the denominator and that makes a "rate" at best an educated guess that may have no bearing on reality.

Remember, 78.64% of all statistics are made up, anyway!

I'm 100% certain I saw something that said 93% of the time the stats are 85% made up by 50% of those making 89% of the claims.

- Ken

 

[Thalassamania]

That implies .000333 = 800 * (number of Open Circuit fatalities)/(number of Open Circuit dives)

comes from an earlier post by Rhone Man:

I remember reading a reasonably well put together article which suggested that the formulae:

(number of CCR fatalities)/(number of CCR dives) = 800 * (number of Open Circuit fatalities)/(number of Open Circuit dives)
​

was accurate. Could probably find it again with judicious Google searching. ]

e.g., the article he was remembering suggested that a CCR dive came with a built in risk factor that was 800 times that of an OC dive.

 

[Ken Kurtis]

e.g., the article he was remembering suggested that a CCR dive came with a built in risk factor that was 800 times that of an OC dive.

No one will ever accuse me of being a rec-tech proponent but the 800 number sounds way too high in terms of the increased risk factor, especially given the numbers (assuming they're close to accurate) that I posted above. 800 might have been used more as a scare tactic than a real number. Are the original numbers upon which he based the 800 in the original article (if anyone knows)?

- Ken

 

[Dodger23]

another item that may need to be considered is CCR units are not necessarily measured per dive. Often they are measured by hours on a unit. This will need to be clarified in your equation, or you may not be using apples to apples either. 2 more worthless cents...

 

[Garth]

I'd just like to say that 60% of the time, it works all the time,..

 

[jkaterenchuk]

True . . . my point was from MY perspective -- and that "moment" of inattention could be longer, of course. As you say, an experienced CCR diver would notice all those things.

*I* simply am incompatible with the amount of attention such a machine requires. I'm afraid the period to get to the point of experience would be quite dangerous for me. Lastly, as a computer engineer, I don't have the faith in the electronics. Just me.

Just as a point of reference regarding ppO2 levels and time of exposure(or what you call a moment). Most CCR divers select a 1.0 to 1.3 ppO2 set point. Technical divers on OC routinely deco on pure O2 at 20ft (ppO2 of 1.6). Depending upon the dive depth and time they can be doing this for an hour or more. The normal recompression chamber treatment for a type 2 DCI is a Navy Table 6 which involves subjecting the patient to a ppO2 more than 1.6 for greater then 4 hours and a ppO2 of 2.84 for three 20 minute blocks during the total treatment time.

I am glad you have come to the decision that you are not compatible. Better to self select out then have Darwin make the selection.

John

 

[jkaterenchuk]

Interesting comment. I have dived with a very large number of CCR divers over the years and I would not be able to name a single diver that has expressed this perspective or pushes the ppO2 during a dive above the normally accepted set points. In fact I would say that CCR divers are much more aware of the O2 short and long term exposure limits and oxygen toxcity in general. Also, with the readily available deco planning software any CCR diver can easily see the rather small decrease in deco time versus the rather large increase in CNS% that increasing the ppO2 above normal limits does not justify.

And no we have not all done it. I dive at a ppO2 of 1.0 and know many CCR divers the dive lower then the generally accepted level of 1.3.

I am sure divers have done what you express but my experience is the opposite of yours in that it is a rather isolated occurence and any ccr diver submitting a dive plan with a high dive ppO2 would be looked at in much the same way as someone showing up in a single tank with a BCD for a Doria dive.