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

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    New Member SFM is an unknown quantity at this point SFM's Avatar
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    Article from COMEX Scientific Director on rebreathers, decompression and Penny Glover

    Hi everyone,

    I confess I don't dive. But I was graced to have met Penny Glover while she was training one of my best friends on the Evolution. A truly exceptional person, like you meet only a few in one's life. Not only did Penny have a deep knowledge and a total dedication to rebreathers, she was an outstanding professional in an amateur world and more than that she was an enlightening soul.
    Despite having met her only one week, I was truly shocked to learn of her fate. And because she was so dedicated to safety, because she trained tens if not hundreds of divers who are now diving safely with their rebreathers, my friend among them, I wanted to contribute (very modestly) to her legacy.

    So I translated this article from the scientific director of COMEX, Bernard Gardette, from the March-April 06 edition of french magazine Subaqua. He makes VERY IMPORTANT POINTS about (not so) deep dives with rebreathers. And with his experience and knowledge of her case, he explains what is likely to have happened to Penny and Jacques. The original article can be found here in french: http://www.comex.fr/suite/news/franc...06/article.pdf
    I'm not a translator, nor a diver and english is not my mothertongue. But I've done my best, hopefully you'll find it acceptable. I know Penny would have liked tech divers to be aware of this.

    Rest in peace Penny, you won't be forgotten.

    Read on !
    Last edited by SFM; 25th May 2006 at 04:31.

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    Interview: Bernard Gardette in Subaqua #205 (March-April 06)
    “Regarding decompression, truth is not available for download”.

    The recent passings of Penelope Glover and one of her students add to the already lengthy list of victims of trimix rebreather diving accidents. Is this type of gear under question? Do extreme uses lead to errors? It’s precisely those questions we asked physiologist Bernard Gardette, PhD, scientific director of COMEX and uncontested specialist in the most advanced decompression procedures.
    Interview conducted by Pierre Martin-Razi.

    PMR: You reacted quite vehemently after reading an article from Dr (MD) Andre Grousset publised in Subaqua #204 which related Penny Glover’s death. And you felt the need to express yourself in the federal newspaper. Why?
    BG: The sad death of Penny Glover was a triggering factor, the last drop. I don’t have precise statistics but as of today there have been around 30 deaths of divers using rebreathers on trimix like the Buddy Inspiration. That figure calls for some reflections. In this very advanced domain, experience comes from the military. The (French) Navy has conducted thorough studies on the topic. In 20 years, 96 incidents have been reported with rebreathers of all kinds. Around 60% of those are biochemical (40% hypercapnia, 30% hypoxia, 30% hyperoxia). Also noted are pressure-related lung traumas and 15% decompression accidents. These decompression accidents never happen with gear using pure oxygen of course. They happen with nitrox at depths often greater than 35m and it’s interesting to note that no decompression accident has happened with devices using trimix (O2, H2, He) in 60-80m depths… I don’t make any definitive conclusions because one should only compare what’s comparable, but let’s admit that if the Navy doesn’t experience such accidents, it’s likely because the diving procedures they use are extremely thorough, both on logistics and decompression profiles.
    Last edited by SFM; 25th May 2006 at 23:35.

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    PMR: Shall we deduct that the Buddy Inspiration is a dangerous device?
    BG: Objectively nothing proves it. And COMEX is not a specialist on the matter, even if we devised an emergency rebreather during Operation Hydra VIII. This “Bell Out System” gave divers an autonomy of 20 minutes at a depth of 500m versus 2 minutes with standard bottles. The device had been validated at 530m and has been commonly used between 220m and 340m in the 90s in Brazil. Today it’s not actualized (used?) anymore. That said this rebreather, like the Navy’s rebreathers, is a mechanical type when the Buddy is an electronical type with all the risks that go along. That reserve should nonetheless be alleviated with the circuits’ redundancy. Oxygen captors for example are tripled and the reliability of the Inspiration is apparently not contested… At least neither in its conception nor its build quality. One should look instead into its applications and uses…
    There’s a fundamental difference between civilian professional diving and leisure/hobby diving which is not managed from the surface whereas in the first case, a 1974 law mandates this precaution. For this we use communication systems, video, Rovs… Decompression and gas reserves alike are managed from the surface. This obligation has considerably increased security for divers but it cannot apply to autonomous diving. The counter-example of coral divers, who are an exception to the 1974 law, is eloquent. Disappearances are numerous… Whereas for the military, we’ve said it, their procedures, notably the regulator strap and the obligation to dive in attached pairs, contribute to the security improvement. On the 96 mentioned accidents, there has been only 3 deaths, 2 with pure oxygen and one with trimix beyond 80m. It represents 1 death for 200,000 exposures which in purely statistical terms is really very low.

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    PMR: Are these incidents related to the mixes per se?
    BG: It’s hard to express an opinion for all the accidents, but in Penny Glover and her student’s case, neither the nature of the trimix nor the control are questioned. On the other hand, three sources can be at the origin of their fate.
    A gear problem obviously, but it’s unlikely since the divers reached the 6m decompression stop. Even if the Navy is reluctant to adopt electronic rebreathers despite their advantages, we can dismiss this hypothesis.
    The second cause could be a training issue. There’s a reason why at the National Professional Diving Institute, the training sessions are done by Navy instructors. Some training centers for amateurs are serious, some not so much. I think that to be on top in this domain, one has to get out of his amateur diver “bubble”. One needs to be confronted to other realities than leisure/hobby diving, like Anglo-Saxons use to say, because with a trimix rebreather we’re very far away from it… Penny Glover was considered a very accomplished diver. I’m still astonished by the parameters of her ultimate dive. 40 minutes at 80m constitutes a major error for such a competent individual, especially with a student. Those values have to be confirmed, but if they are then the initial reason for their demise has likely been established.

    PMR: Meaning?
    BG: This leads me naturally to the third possible cause of accidents, no doubt the most probable in the majority of the cases: the decompression procedure and profile. In theory and because it delivers a mix with variable PPO2, the electronic trimix rebreather optimizes the dive perfectly. Viewed like that this type of gear is the ultimate weapon. Paradoxically the problem resides in the amazing performances of these devices. Their autonomy is such that divers need decompression procedures that are not always mastered.

    PMR: Do divers disrespect decompression procedures?
    BG: In general no, except for incidents. At this level, one should consider that divers are technically capable of managing their ascent, speed and stops. The main problems stems from the tables that are used… As long as one stays within durations not exceeding 15 minutes at 80m there isn’t any problem. The MN-78 tables are perfectly adapted and they’re available in “Diving physiology and medicine” by B. Broussole published by Ellipses. Beyond those 15 minutes, it’s an entirely different matter….

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    PMR: Isn’t there any table available for longer durations?
    BG: Of course there are. But some are dangerous! I’ll give only one example. For a duration of 40 minutes at 80m, the Heliox table from the Labor ministry (MT 92) gives 4 hours and 2 minutes of decompression. For the same parameters, there are tables from the US on the internet which state only 2 hours of ascent! The difference isn’t in minutes, it’s halved. It’s unreasonable, even more so that the difference doesn’t lie in the initial ascent, somewhat too slow in the incriminated tables, but in the last stops. Missing almost 2 hours at 6m and 3m stops, it’s pure madness!

    PMR: Following your reasoning, divers have decompression accidents because of nitrogen, not helium?
    BG: Exactly. The slow ascent speed from the bottom is required to eliminate helium, but when ascending too slowly there’s more nitrogen saturation. And if one skips part of the decompression in the last stops there’s an accident… I think this is the cause for the majority of deaths with trimix rebreathers. A major depth, too long a stay and insufficient stops at 9m, 6m and 3m. I have in mind the example of a diver who had a massive accident after 20 minutes at 100m. Such a dive requires 3 hours of decompression with the 1992 tables from the Labor ministry and around the same from extrapolated IAMTD tables. That diver had done only one and a half hour of decompression after looking up the procedure from an american software on the internet. Resulting in brain bubbles with lasting and severe consequences…. One has to be convinced that for decompression, truth is not downloadable from the internet.

    PMR: Would that be the error that was fatal to Penny Glover?
    BG: Alas… One can think so. Penny was a good diver who knew herself well and it’s very likely she didn’t experience the initial triggering problem. It wasn’t the case for her student. Conditions weren’t optimal, strong currents and important drift... At the time of the accident, the pair was 500m away from the entry point… One can imagine that the decompression stops haven’t been enjoyable... It’s very likely her student who had a faint/dizziness. We know it because she lightened him by removing the emergency O2 and deep mix bottles, as prescribed by the Inspiration procedure, which were burdening him. Was it a dizziness/faint caused by exhaustion, by a decompression accident? Likely both… Let me remind you that with a rebreather, buoyancy of the counterlung has to be compensated and that in case of a faint, the diver sinks. Penny must have tried to catch him, didn’t have the time to purge the loop from O2 and experienced hyperoxia… Consequences can happen very quickly. We’re still at the supposition stage but the scenario is plausible.
    Last edited by SFM; 24th May 2006 at 10:12.

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    PMR: Isn’t it too easy to blame tables found on the Net when none is available on the market in France?
    BG: It’s true it’s a real conscience issue. Let me state that the tables from Buddy are totally valid as long as the dive durations are short. Let me repeat: around 80m all the problems arise for durations over 15 minutes. As well, all-in-all, one must be aware that the deeper one dives, the riskier it becomes…

    PMR: On this point, in statistical terms, do we have any idea of accidents risks with existing tables?
    BG: Jean-Pierre Imbert, when he used to work for COMEX, realized a thorough study on the topic. Divers must know that one has to consider the amount of gas(es) to eliminate, an amount that is a function of the depth and the square root of the time spent at the bottom. One’s organism has to eliminate that(those) gas(es) and by nature it has its physiological limits. It requires time which cannot be reduced with impunity. Tables that can be downloaded like Varying Permeability Model (VPM) or Reduce Gradient Bubble Model (RGBM) correspond to decompression times we were using more than 30 years ago. The risk was then evaluated at 10%. With the current COMEX tables, for any depth and duration, we divided this risk by 10, meaning less than 1% accident rate. For comparison purposes, the risk for leisure/hobby diving is around 0.01% to 0.001% as long as one stays within the security curve… As soon as one reaches 20 to 30 minutes at 40m, the risk climbs to 0.1% and for 20 minutes at 60m we reach the 1% ratio, identical to what we currently have in our trimix tables… To sum up, one should be reasonable and be content with diving for less than 20 minutes at 60m on air and for trimix, less than 15 minutes at 80m. Ten more minutes yield a huge price to pay in terms of decompression. 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…
    Last edited by SFM; 24th May 2006 at 10:14.

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    PMR: You mentioned for comparison sake the problems related to depth and duration for air dives. But today every diver has a decompression computer…
    BG: Yes but those computers aren’t adapted to extreme dives. For 20 minutes at 60m, they may still be ok, after that the indications make no sense anymore. In those situations, haldanian models require very lengthy tissues that have not been integrated in computers and we meet again the physiological elimination limits we discussed earlier…

    PMR: Back to rebreathers and trimix. Since they allow for deep dives, why not diffusing the validated tables which truly ensure divers’ security?
    BG: It’s a matter of responsibility that didn’t likely exist 15 years ago. The root of the problem is the absence of control for their possible uses. A table is a marching order and does not condition the entire security of the dive. Diffusing tables officially is an official responsibility commitment. The Navy refuses to do so and COMEX, after hesitations, had to renounce as well. It’s possible to dive securely 40 minutes at 80m but it requires very consequent means that don’t fit leisure/hobby diving. Believing that a rebreather is the panacea, as stated in a show broadcasted on La Cinq (French TV channel), constitutes a crude mistake. That said and at a personal level, I’m willing to give the tables but I need to know the divers who will be using them, know their motivations, trust them. I have done it for a few, among them Pascal Barnabe in the framework of his record attempt. I warned him about the suicidal aspect of his endeavor but he was so determinated, he would have done it anyway. He’s an exceptional diver… So in those conditions let’s maximize his security…

    PMR: Then you are opposed to trimix use in rebreathers?
    BG: No, it’s the opposite. It’s an extraordinary tool for pros mention B, movie makers, biologists, archeologists who plan and organize their dives rigorously. But one has to keep in mind that the exceptional performances of rebreathers can turn against him/her. During dives the limit is Man, and amateurs shall limit themselves to short dives who don’t require excessive decompression times.

    PMR
    : Divers can contact you then?
    BG: Yes of course. A few months ago, FFESSM started a process in that direction. We wished for a study to be launched. We have Doppler bubble detectors, compact and very simple to use. Developped by Jean-Claude Dumas from Aqualab System, they cost only 1500 euros each. Their use on the ground (Translator: in the water that is…) would allow us to refine our work. With a study on ten divers, we know already perfectly if we’re at 1%, 0.1% or 0.01% risk level. In short, we know if it’s a risky dive or not. It would be a pertinent experience for trimix diving done by sporty divers and for which we lack data…

    Contact: Bernard Gardette
    Last edited by SFM; 24th May 2006 at 10:17.

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

    May I suggest the admins/moderators close this thread & open a seperate thread for replies/comments.

    Cheers

    Giles

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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Gl

    Better still - post it as an article in the library

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    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
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    Re: Article from COMEX Scientific Director on rebreathers, decompression and Penny Glover

    Still waiting for the reply thread but I am sure they can move this...


    Its a very interesting piece but if you research the deaths there have been on CCR there are very few related to long deep exposure dives. Most have been shallow limited or no deco dives so is this really relevant?

    40mins at 80m ?? I understood that Penny's dive was to 70m not 80 but I could be wrong. I have regularly done 45mins at 60m+ and occasionally done 60mins on dives of 60-65m. The divers i dive with will carry out probably 25 -30 65m+ dives a year with bottom times of around 45mins and yet we are not aware of any great number of DCI incidents in the teem.

    Interestingly I haven't noticed a big increase in run times using CCR? On OC we would load up with twin 15's or even twin 18's and still do 40 -45mins at 70m?

    For most deep dives the controlling element of the run time is tide and deco commitment. Most people just cant stand dives with more than 2 - 2 1/2 hours deco in the open ocean

    Where the CCR is pushing the limits is dives of 100m+ That said the DIR teems (if they are to be believed) claim to have done 25min run times on the Britannic at 125m on OC?

    So its a very interesting article but I cant quite see it as a revelation in the fight to manage CCR risk.

    ATB

    Mark Chase

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