Article from COMEX Scientific Director on rebreathers, decompression and Penny Glover

MattDuke

OK, I am a complete CCR novice, but I have been diving a while, so I hope it's OK to reply to this thread, as I think this information is not just related to CCR diving.

One things for sure, I think we would all really like to see the tables that promise 0.01% chance of a bend, for a Bt of 40minutes at 80M.

Over the past 6 months I've done 10 OC trimix dives in the 60m range, all on VPM-B. None with BT longer than 25minutes. So I guess I'm in his safe zone! (Accept I should be using Air??) But I know that the dives have 10-15minutes less deco at 6M than proplanner. So being a cautious chap, I've done the extra 15 minutes anyway. My Tech 1 buddies regularly do 25 minutes less deco than me, and they seem pretty good topside.

In my opinion, the bottom line hasn't really changed since I did my mix course in the ninties. "This is dangerous. You are testing tables every dive. You should do all you can to minimise risk. You should understand the risks you take and explain that to loved ones." The only news is that they are suggesting they "Know a better way to reduce the risk" I find it impossible that they can do that, without telling!!

My move to CCR is driven by logistics. Not Bottom time. I am one of those who really is satisfied with 60m and 25 minutes. What i can't be bothered with anymore, is filling 2x12L with mix, and 2xalu80 with travel/deco for EVERY dive. When I've done enough hours to do the same dives on CCR, I'll still take 2 alu80's so I can complete the dive OC. But I'll be very glad not to have to fill them every time!

I had no idea people like Mark in the UK were pushing such extreme run times, (Both on OC and CCR it seems) the fact that so few bends have occurred in his team is a testimant to their skill, not just luck surely?

Anyway, very interesting reading from people that know a lot more than me! I just hope the article can be backed up with publishing the data!

Matt.

__________________
Born 1975
Started Diving 1984
Started CCR Diving 2006.
Stopped CCR Diving 2006.


CCR isn't for everyone, but it was a lot of fun trying.

SFM

Double misunderstanding here, my fault.
I told you I'm not a diver and I've tried to be very careful to only relay Dr Gardette's thoughts. When I read "bent", I thought it was some slang for inert/faint in the water, should have looked it up. My bad.
My line of work is predictive modelling, risk assessment etc. so what I meant is that as time passes you are more and more likely to know other divers who've had problems and further on that will decrease (you will hear about people with problems but likely not know them). Again no computation offered.

What are your sources? Why would he come out and say the opposite publicly if it was blantantly false? Why does he mention "the third possible cause of accidents, no doubt the most probable in the majority of the cases: the decompression procedure and profile" and back it up with "Dr (MD) Eric Bergman has noted that the number of tech divers treated for a decompression accident has been very high during the summer of 2005..."?

It's possible he may have a hidden agenda, but again it's hard to think he would ruin his reputation with obvious distortions of the facts.



Generally speaking a theoretical risk is an upper bound estimate, it's not the probability of something happening in the common sense. In other words, a risk is more akin to a probability for a worst-case scenario, at least that's what it represents in some other application domains. For example, when COMEX uses tables with a 1% theoretical risk they don't expect 1% of accidents (it would be tough for their business...)
Likewise I don't know how a theoretical accident is defined. It may not mean a guaranteed real-life accident. It could be physiological modifications that aren't noticed on the spot (or never even).
Plenty of other factors can come into play as well, like the representativity of your sample of divers (they may be more qualified than average) or the impact of your risk management for example.

You have to apply a mitigating factor that would be very hard to compute in real-life.
To give you an idea:
Let's say you use the 10% table and we use the same mitigating factor as the french Navy (70), your real-life number of accidents/incidents would be: 400*10%/70 = 0.57
THIS IS NOT A VALID COMPUTATION, it's only for the sake of the explanation. 0.57 being close to 1 (the real number) is pure coincidence.

Your specific mitigating factor is unknown, but you can directly influence it (by not allowing people with hangovers to dive for example ).

rdmmdr

comex tables reflect the nature of commercial diving, nobody gets hurt and we all go home. for the boss this means that he is not getting sued every five minutes. when I need a prop cleared on one of our tugs, a job i had done twenty times before. i call a pro outfit for support because my gear was on another boat. Three guys showed up with surface comms and supplied air, and still took four hours. Was the job done safer then the way i always did it ?yes. Was the job done better that i did it? no. but it was done according to OSHA and the rules the commercial guys have to play with.


Are the recreational tables inherently dangerous? No. Are they as safe as they could be? That is the question. Without putting in some kind of sensor to determine the physiological factors involved in dci hit, all tables use a fudge factor for the conservatism. The current drive to deeper, longer. and quicker decos that some are pushing scares me. This is not the way to go home at the end of the day. The push to see who has the biggest set of brass balls will get someone killed. can you really tell me that 200 meters on a meg is sane. If you want to go to 200 meters rent a rov.

on this forum there are several who are quick to blame the units after a failure, others who are quick to blame the training. But most of us just want to know what happened so we can incorporate an other unfortunate lesson in our own training. Guessing is not going to teach anyone anything, we all need to wait until all of the info comes out. The only good thing to come out of this tragedy is avoiding the next one, and that takes real info not speculation.

rip. penny

rick m

MHD

http://www.btinternet.com/~madmole/D...e/DMDanger.htm

have a read, here is 25 of the 30 inspiration deaths listed. You'll so start to see a trend. Also review the accident section here and again you get a lot more of an idea about what is actually killing people on Rebreather’s.

I don't doubt that the numbers of tech divers presenting with bends is increasing, (both due to the increased number tech divers i.e. the population is getting bigger and the sport more popular and some poor information out there in both training and profiles). I won't be surprised if sone of the current available tables are not accurate and present a high risk, but I do doubt that deco issues is the main culprit for Rebreather deaths.

Matt

jasondrake

I suspect that most Rebreather deaths, like most OC deaths, result from divers screwing up. Bends really don't kill very many divers at all. Most divers drown because they find themselves with nothing to breathe, for whatever reason.
The reason commercial operations are so much safer is not because they have better tables, it's because they have better procedures and they stick to them. The thought of sending a diver to 100 m without having him on the end of a rope, with comms, and with a chamber and paramedics and a helicopter on standby would make commercial outfits shudder.

Amateur divers dive often untested units, with untested tables, in untested environments, take care of their own maintenance (and modification), mixing and filling, undergo no medical screening, etc. etc. etc. And training is often less than exacting. (I've done commercial and amateur mixed gas training, both with instructors with good reputation and I have to say the amateur training was laughable.)
Amateur deep diving is risky. People will die.

Mark Chase

Don't thing I am trying to hide behind numbers because i am not and i deeply appreciate all and any information and debate on issues that could potentially see my daughters father live to a ripe old age.

However

With the BSAC incident reports showing a worst case total of 144 incidents of DCI (as reported by the hyperbaric chamber centers across the UK) across the range of all divers in the UK doing all levels of diving. I would suggest that were looking at approximately 144 incidents of DCI across 10,000 divers doing some 50,000 dives in the UK every year.

So thats a DCI rate of 0.28%

Now i gave the example of myself suffering shoulder pain after loading and unloading 300Kg of kit over the w/end. I kid you not, I would have gone for treatment due to the pain in my shoulder. A lot of divers will do the same thing so the 144 incidents of reported DCI incidents don't actually represent 144 actual incidents of DCI so the figure is lower than 0.28%

As a result of my fag packet calculations I struggle to accept the 10% figure put forward.

I sincerly hope you see this as logic and not denial.

ATB

Mark Chase

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SFM

Matt,

Dr Gardette said "I don’t have precise statistics but as of today there have been around 30 deaths of divers using trimix rebreathers like the Buddy Inspiration"
I regret that my translation is not of the quality I'd like it to be but in french it really looks like he mentions 30 deaths of CCR divers who were using mixes, not air. I edited the translation to make it more clear (I hope). There's always the possibility of him using the expression as a generic term for rebreathers but it *doesn't sound* like it.
I don't know how extensive is the list you linked and how many of those had been included by Mr Gardette. The general emphasis of the article is on trimix, not air.


I have been so shocked for Penny that I looked around quite a while, believe me, actually I looked earlier as well when my friend started. I looked at the list you linked and others, and of course I made myself an opinion on CCR accidents (air or mix) but from a data analyst perspective I urge you to be careful and not jump to conclusions:
-most of the reports are very incomplete (ex: air, mix?)
-tech divers population is changing, for example there's an age poll in this forum and someone mentioned today's tech divers are younger
-this is a fast evolving discipline in its infancy, I don't know the history but I'm sure the training you would get today has not much in common with what you would have been taught 8-10 years ago (if you'd been taught anything)
-devices are improving over time
-families have a vested interest in the certification of the deaths (life insurance...)
-manufacturers have vested interests as well (lawsuits, reputation...)
-ccr divers are passionate and some outcomes (ex:health problems) could be favored over others

In the link you provided the author is well aware of the potential traps including the small size of the sample. Still he seems to conclude that solo diving is more dangerous. I cannot concur because we don't know the ratio of solo dives on all dives without accidents. It could be totally imaginable that because of the rarity of rebreathers, it's hard to find a buddy and maybe also annoying to dive with OC divers so there's a relatively high ratio of solo dives (especially in the early days when rebreathers were even rarer). What I'm saying is that it's inconclusive and from the data on the page you cannot make that conclusion, it's only speculation and it could be false.

A lot of people seem to think that most CCR deaths are caused by human errors (and maybe lack of training, especially in the past). It's very possible but again as far as data is concerned, there's no way to prove it yet and here as well it could not be true.
Personally, looking at that list and other places, I found it odd that there's almost no report of hardware failure. It's not consistent with the application (tough environment/conditions) IMHO, but maybe it's because of my very limited knowledge of the topic and there's a good (read objective) reason for it.

All this to explain that one should be very cautious in making strong assumptions because a false sense of confidence is detrimental to security: there's the danger of overemphasizing some security aspects at the expense of others, or instinctively discard a fundamental hypothesis in the very short time left to react when there's a problem underwater.

Drmike

can you really tell me that using (inherently dangerous) CCRs for shallow 20 meter reef dives is sane? If your only doing <50m non overhead dives rent a twin set.

Personaly I think doing a 200m dive on a well tested professionaly designed Rebreather is about as risky as you jumping in the water as a crash test dummy on a homebuild youve knocked up in your garage out of bits from home depot.

Is this opion based on your extensive experience after diving since 2006 and being advanced open water certified?

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

MHD

I think you are mis-readig it, the following list is not conclusive but comes from my memory from 4 years of following Rebreather's and hopefully other people can correct as required

Deaths by model (these are from my memory only)

Cis lunar MK4/5 - 3 (could be more)
meg - 7
Prism - 0 (I don't remember any but there could be some)
Inspo/Evo - about 30 (33-35?)
CCR1000/ Mk15 - 1
SMI 1600 / Mk15.5- 2 (I think, Dave Shaw and thought I'd heard of another)
Kiss (classic) - 0 (I can't remember any, not not to say there hasn't been one or more)
Kiss Sport - 0 as above
Rebreather-80 - 1 at least
EDO-04 and other clones- 1 at least
halcyon fridge - ??
Ouroboros - 0

This is pretty much the entire trimix capable CCR market over the last 10 years by model thats made some market impact. As you can see we are talking a minimum of 50 deaths on trimix capable units, the most common cause of death are hyperoxia, hypoxia and hypercapnia. There are not 30 deaths as a result of deco problems on these units.

The guy has an angle or has been mis informed. Most likely the later. When people like Dr Mike say Deco has nothing to do with deaths, they know as they have been involved directly with these events.

Matt

divetheworld

B&Q not Homedepot. They do the clear ducktape instead of that yucky grey stuff when patching your leaks.
I dont know what your trying to say

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