Filmmaker Rob Stewart dies off Alligator Reef

[dmaziuk]

Statistics are irrelevant because each dive is an independent trial, not a series of repetitive events.

ITYM "statistics are irrelevant."

 

[PfcAJ]

Statistics are irrelevant because each dive is an independent trial, not a series of repetitive events.

...

You know not of which you speak.

 

[lionfish-eater]

I don't understand this.

It is just a clarification of the rules of probability.
For any individual dive, the diver will either live or die.
They cannot be 1/200,000 % dead.
For any single dive the outcome is 0 or 1, live or die.
We can never repeat the exact dive over and over, which is necessary for statistical analysis.
This is a technical point about how to interpret and apply probabilities.
Each dive is more like a case study than one in a series of repeatable events.
These are postulates of statistical analysis.
Statistical analysis of something as broad and varied as diving would require a much more indepth multi-variate analysis to be meaningful. Combining factors like training level, dive difficulty, dive support, equipment use and maintenance, etc. just makes statistical analysis difficult if not meaningless.
The method of analysis we are using in these threads (case study) is more appropriate than a mathematical approach.

 

[lionfish-eater]

...

You know not of which you speak.

In past years I taught stats at the University level.

I know little to nothing about rebreathers, but have learned much from these threads.

One thing I learned is that there are a lot of divers and instructors that vary from manufactures' recommendations.

Things like if you have a plane to catch, but want to get one more dive done, a diver can crank up the oxygen to speed up offgassing while diving, sometimes exceeding the MOD leading to serious results.

 

[doctormike]

The point of doing statistics in any field of study is to apply prior knowledge of independent variables to individual events so as to predict outcomes, and hopefully to modify outcomes by manipulating those variables. This is true for cancer chemotherapy, structural engineering and scuba diving.

To say that case reports are more appropriate than aggregate data because statistics are irrelevant makes no sense to me at all. To pick one example, most of our knowledge of decompression theory is based on statistical analysis of DCS injury rates in populations of divers.

In the present discussion, identifying the factors that lead to a given fatality rate for a given activity seems very relevant to me. But I'm no professor of statistics.

 

[cathal]

Statistical analysis of something as broad and varied as diving would require a much more indepth multi-variate analysis to be meaningful. Combining factors like training level, dive difficulty, dive support, equipment use and maintenance, etc. just makes statistical analysis difficult if not meaningless.
The method of analysis we are using in these threads (case study) is more appropriate than a mathematical approach.

About the only part of this post that is subject matter relevant. Unless you can highlight any other field where accident investigation requires statistical analysis to form a back bone of its cause? Have we forgotten the human in the system anyone? Plenty of accidents have occurred with perfectly functioning machines (cars, bikes aircraft etc) solely due to human error or malicious human interaction.

 

[Steve_C]

For any individual dive, the diver will either live or die.
They cannot be 1/200,000 % dead.
For any single dive the outcome is 0 or 1, live or die.
We can never repeat the exact dive over and over, which is necessary for statistical analysis.
This is a technical point about how to interpret and apply probabilities.
Each dive is more like a case study than one in a series of repeatable events.

So I am flipping a coin and it lands on the table. It will come up heads or tails. There is no way I can repeat the exact same flip. Are you saying that I cannot conclude after 1000 flips that if I am seeing heads 80% of the time that I have a weighted coin?

Are you saying that it is equally valid to do a case study? I flip the coin once.

If I had to bet $1000 on H or T and could use either the statistical analysis or a case study to inform how I bet I know how I would decide

 

[lionfish-eater]

I am just trying to make to point that to perform a meaningful statistical analysis, we would need account for a multitude of confounding variables. We would need repetitive data. That is, Stewart and Sotis would have had to repeat the series of dives using the same procedures over and over to collect data. To compare their dive accident with those of beginners or commercial/industrial divers would be cursory at best and would not lead to a further understanding of the circumstances in these cases.


Using your example of the deco tables is a perfect example. The tables were derived from a large data set of repeatable events collected from many subjects. The tables are great for describing the characteristics of the population of divers as a whole. For any one individual diver one any one particular dive, they may get an "undeserved hit" while well within the table limits, or they may grossly exceed the tables and be non symptomatic. Tables represent theoretical models of populations of divers, not any one diver.
I may be nitpicking a statistical interpretation, but identifying the factors that lead to this death is exactly what I am talking about.

If we could get good data, it would be helpful to know things like,
what percent of divers dive above their training level. What percent still do trust me dives even at advanced levels of training. What percent modify their equipment, etc.

 

[Brad_Horn]

You say ALARP, in 1981 when I first heard the term it was ALARA, As Low As Reasonably Achievable. Had Open Safety understood this, they would probably have not pissed off half the rebreather world (not the website, but them too) and understood that Reasonably means just that. It is not reasonable to "Diver proof" a rebreather. Diving cannot be made safe, but it can be done safely. Risks can be mitigated. Good training is a huge part of that. Experience is the rest. I believe that good training and experience is exactly what this thread is all about. Even if you try to make it about the rebreather, I will drag the conversation back to training and experience.

Frank, Exactly but your take on how rebreathers should be designed is just using the training as duct tape to fix any underlying issues...
It is quite reasonable and achievable, to add a trigger to a BOV that closes the loop when the mouthpiece is removed. You and others might not agree with this, but it is still reasonable and achievable.
Done based on the experiences of divers who have not closed off their loop... and it means that valuable training time can then be focussed on what the diver actually needs to learn to stay alive. Rather than to learn a workaround to fix a basic design issue.
This is not "diver proof”ing the rebreather, as the diver can still make plenty of other mistakes, inclusive of diving without the associated gag/retaining strap or doing 3 x 70m dives on a single scrubber.

It is quite reasonable and achievable to supply a Rb with a BOV to enable rapid bail out.
It is quite reasonable and achievable to offer the lowest WOB rebreather.
It is quite reasonable and achievable to test for scrubber duration at the mouth.
It is quite reasonable and achievable to offer a rebreather certified to the CE standard.
etc etc for a long list!

Something I want to make perfectly clear. A rebreather never ever ever killed a diver. The Open Safety minions have expertly testified a number of times about the failure of the rebreather to keep the diver alive, and y'all have been stomped every time. Rebreathers don't kill divers. Divers lack of training and experience kill divers. Every time.

Others have found this to not be the case, inclusive on the developers of the Voyager, Nicola Donda and Marco Panico who were fined a total of 800k Euro and one year in prison, each, for their actions which were judged to be culpable manslaughter. The Voyagers were constructed by Rojano "Hbt", which Donda owned. See http://ilpiccolo.gelocal.it/cronaca/2012/05/31/news/sub-morti-istruttori-condannati-1.5185349 Examination found a hypercapnia situation as well as hypoxia. And lack of training and supervision by the attending instructors.

The Coroner concluded the death of Jillian Smith was a tragic accident. "I am surprised that in this day and age dive equipment can be made in such a way that it allows any incorrect assembly." – DEPUTY VISCOUNT, MARK HARRIS Equipment blamed for diver's death

As far as the court cases Alex Deas has been associated with, I have not yet ever seen him proven wrong based on testing of the rebreathers in question. Noting that the court is interested in determining liability and not fatality root cause. Liability being something that is irrelevant in determining the root cause.

There have been what over 400 rebreather fatalities in the last 15 odd years and less than 10 court cases ....

 

[lionfish-eater]

So I am flipping a coin and it lands on the table. It will come up heads or tails. There is no way I can repeat the exact same flip. Are you saying that I cannot conclude after 1000 flips that if I am seeing heads 80% of the time that I have a weighted coin?

Are you saying that it is equally valid to do a case study? I flip the coin once.

If I had to bet $1000 on H or T and could use either the statistical analysis or a case study to inform how I bet I know how I would decide

You are totally correct in that we cannot reproduce the exact same coin toss due to the minute differences in force, wind, etc. However, for the level of precision that we assign to coin tossing, we assume that these are identical repetitive events because they are close enough.

In the case of a diver fatality, the differences between individual events is orders of magnitude different than those between coin tosses.

Can you compare this event to other cases where an instructor and student attempted three deep dives with similar missteps, with similar equipment, with the same number of people on board, with the sun at the same angle, with the same dinner reservations for that night, etc.