Comprehensive list of all accidents

York

Clear answer: yes and no!
Just because statistics is not understood by 60 out of 100 people (over 80%!!!) doesn't mean that it can't be applied to condense data. It is certainly correct to critique that there are too many assumptions. These assumptions however have been argued (which does of course not make them necessarily right), and, based on these premisses the conclusions are valid. What is missing is the introduction of further/differing/opposing assumptions to be tracked to other conclusions. By making the raw data available, and documenting any steps taken Alex gave everyone the possibility to do so - a valid and scientific approach. I for one played with the data and used different assumptions, but the ballpark of the outcome appears similar. The alternative to this approach is to wait until a few more thousand people die to then feel confident that the statistical data is sufficient to commence an evaluation - I hope you agree that this is not desireable. For the time being, based on insufficient data, the current approach certainly was an eye-opener for me. I may disagree with aspects of Alex's argumentation, but cannot disagree with the direction it is pointing. There is no doubt in my mind that Alex is wrong - the question is by how much?

Instead of arguing objections of general nature I suggest that we take the lack of data for granted (because there is nothing we can do about it) and focus on individual points.

This is not meant as an attack but as a contructive contribution.

Joerg

solocavediver

It is a generally accepted feature of statistics that usually they can only prove things that are already obvious.

The main exception is if you're prepared to do extensive and repeated experiments in controlled conditions, as when a new drug is tested for harmful side-effects. This is really hard to do with rebreathers, because it would be very expensive to do it without killing people. That's true of drug testing too, but the profits are high enough that the tests nonetheless get done.

It seems obvious enough, though, that rebreathers are extremely dangerous compared to (say) solo cavediving.

Cheers,

Charles.

AM

Since we are discussing statistics...

There seems to be a lot more accidents on the rebreather fatal accident list from heart attack than I would expect compared to Open Circuit figures.As part of a data compilation exercise, some time ago I requested the Work Of Breathing (WOB) figures from Deep Life for the Megalodon and Inspiration rebreathers.

1) WOB for the Inspiration rebreather under EN14143:2003 conditions is 5.67J/L, or 6.29J/L on a human.

2) WOB for the Megalodon rebreather with Cis-Lunar scrubber is 2.8J/L, compared to 1.9J/L claimed. It may explain the lower figure: ADV freeflow at very high negative pressures – which can be seen clearly on the plots.

Therefore in respect of the EN14143:2003 limit being 2.75l, accordingly this means Inspiration would result in more CO2 retention that on a rebreather complying with the limit, i.e. Ouroboros. Meg is close to the pass limit, with the CIS Lunar Radial Scrubber.

Please see corresponding attached files, along with calibration data.

Initial analysis of WOB figures would indicate that unless WOB testing is conducted on all sports diving rebreathers in *identical conditions which replicate the diving environment*, the data is unreliable. I understand this is why AD_Ward9 reiterated that the calibration data had to be published with the figures, and the figures should include the complete set of curves such as they are represented in the attached files.

CCRB Ltd have highlighted in their chart at DEMA that most rebreathers have a WOB well *above* safe limits (that is, not in accordance with safe limits) - these figures from Deep Life confirm that. If that is the case, then it is not surprising to see so many heart attack cases on the rebreather fatal accident list.

It seems that WOB is the third corner of a triangle of three hazards on current rebreathers:

a. Hypoxia from electronics or mechanical failure
b. Hypercapnia from scrubber failure
c. Hypercapnia from WOB, resulting in CNS events, heart attacks and strokes above the rate expected.

The obvious inference to draw from the statistical breakdown of heart attacks on closed circuit equipment, compared to heart attacks on open circuit equipment, is that the number on closed circuit is higher. The physiological implication is that the WOB characteristics inherently related to closed circuit diving *could* be a factor in the high rate of heart attacks while rebreather diving.

Regards

AnneMarie

Attached Images

	APDBuddy_WOB_75-90lpm_90pitch_air.pdf (275.4 KB, 28 views)
	ISCMegalodon_WOB_75-90lpm_90pitch_air.pdf (283.4 KB, 26 views)
	BM_calibration_080422-2.pdf (118.1 KB, 15 views)

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EBT

Heart attack is the easy diagnosis, given that most life threatening events eventually result in that outcome. Personally Im bored of the stats, whats interests me more is the data and the analysis I can personally conduct upon that. Naturally its not 100% right, but it seems a huge improvement on the chinese whispers we had before

Anyway, this is boring bollox.... i need to fix about 200 problems with gear before a caving week. Its a sod when you've had a year off as a result of working abroad.

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Dutchy

Do drowning (out-of-air) and hyperoxia fall in that category? What (diving related issues) apart from hypercapnia lead to a heart attack? You make it sound trivial but I'd be interested in what does (ultimately?) lead to a heart attack.

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AM

My dearest Zak

With the greatest of respect, whether or not most life threatening events do eventually result in a heart attack is not the point. The point is that the higher heart attack statistics for closed circuit indicate a correlation with closed circuit. If it is the case that WOB issues can indeed *potentiate* a heart attack then that is a different proposition altogether from the proposition that a heart attack would be the eventual outcome anyway after a specific physiological event.

PS - I sympathise with the gear issues. Working away from home in the week creates "Friday night fettling syndrome" where you drink beer on a Friday evening and curse all the gear faults then stay up late fixing them!

Regards

AnneMarie

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EBT

like everything dutchy, its not black and white. If you look hard you can find a root cause, sometimes people dont look hard because its hard work/complicated/hard to beleive it wasnt a simple incident.

<shrugs> welcome to human beings, complex sods, arent we

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AM

Zak

I would be very interested in your information relating to a specific physiological event (not related to hypercapnia/WOB issues) that can occur and then trigger a heart attack underwater?

Regards

AnneMarie

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doug allen

Amen Ben...each accident is different.

UWSojourner

Wouldn't you expect, if it was simply a CCR correlation, to be seeing heart attack deaths on mCCRs as well? Any ideas on why this isn't the case? I thought the WOB for mCCRs was no better than the other eCCRs.