Rebreather Discussion from Brockville Incident

[dreamdive]

THANK YOU. Not just "totally reasonable" but "normal scientific writing practice". It would appear that it is you who is much more familiar with critically appraising papers than the original poster.



And again, thank you. This paper is limited methodologically and is based on weak data (facts which the author freely admits), but it is the best data we currently have and, as you point out, are likely to have. The previous poster's suggestion that a randomized controlled trial is a pragmatic means of solving the question of relative safety of CCRs and OC is ludicrous. Under circumstances in which better data is unlikely to appear, papers like this do get published from time to time. It just needs to be interpreted in the context of all the caveats the author discusses.

Simon M



---------- Post added July 4th, 2013 at 11:51 PM ----------

Wow Simon, you actually have the galls to admit that this is based on weak data and yet promote this!!!

Just because you have "the best data....currently" available even though, as you admit, it is weak, does not mean it has to be promoted! I am disappointed at you for that. Weak data cannot support a strong conclusion and weak data suggests that further study is necessary and indicated prior to publication of such weak inference.

Let me give you this analogy:

You are having breakfast, and they are serving you dog crap. Are you going to eat it just because it is the "best currently available"????

 

[gianaameri]

Wow Simon, you actually have the galls to admit that this is based on weak data and yet promote this!!!

The data is not weak.

The fatality did happen. There is name and make and model of the rebreather.

It may contain omissions (rebreather fatalities have been kept secret by the industry and open internet forum discussions censored in some forums where this did not suit the commercial interest of the forum ownership), or bona fide errors (these can be corrected as Dr. Fock did where he was able to obtain more accurate information).

The difficulty is in establishing causality. You can associate the rebreather to fatalities, but you cannot prove the rebreather is the cause of death because we do not have the means to do so (we all die of hypoxia and a bit of hypercapnia and autopsies cannot discern between a fatality caused by rebreather and a fatality caused by natural death).

Where with certainty you can say rebreathers are more risky than OC is when you use an engineering methodology to calculate the Probability of Failure (and of a dangerous failure) of a machine.

Currently available electronic rebreathers have a "SIL level of less than 1" which means they exceed the Probability of Failure we normally accept for life-support equipment in the modern world.

There is no escaping that.

DAN and other insurers have a business interest in collecting denominator data... eventually denominator data will become available to reach more accurate statistical conclusions (but even intuitively it is clear rebreathers risk is far greater than OC risk).

 

[Dr Simon Mitchell]

Wow Simon, you actually have the galls to admit that this is based on weak data and yet promote this!!!

Claudia,

There is no need for me to "admit" anything in relation to the weakness or otherwise of the data. The quality of the data is clearly contextualised by the author in the paper, but a few readers are too busy reacting hysterically to notice this.

I drew attention to the paper on two rebreather forums, and why wouldn't I? The paper addresses a matter of extremely high relevance and interest, and it is published in a diving medicine journal. Are you suggesting that members of these forums should not have been told about it? What do you think these forums are for? This is not "promoting" the paper. Indeed, my original post linking to the paper on both forums said "The author is at great pains to point out that it (the data) is not perfect". This is a clear signal that the findings deserve a cautious interpretation in my opinion.

There has subsequently been a fair bit of debate about the paper; most of it reasonable and healthy. However, I have been forced to defend the paper against some criticisms that were just plain wrong (such as your own claims that Dr Fock obtained open circuit fatality data from Rebreather World and that he was promoting Jill Heinerth's mortality estimates). Such defence is not "promoting the paper".

Claudia, the data are honestly described by the author. They suggest that rebreather diving is more dangerous than open circuit diving. Yes, that conclusion could be confounded to some degree by inaccuracies in some of the assumptions, and the influence of differences in the type of diving performed using the two modalities. Dr Fock makes exactly these points in the paper. Nevertheless, his final conclusion based on his interpretation of the best data we have is that rebreather diving is more hazardous than open circuit scuba. I suppose the overarching message is that we need to strive for better safety. Is that a bad message?

It has been suggested that this paper harms the rebreather industry by giving an ungrounded perception that rebreather diving is dangerous. Is that really a revelation? Don't these devices have messages like "this rebreather can kill you instantly and without warning" emblazoned all over them and their related training materials? Do you really think a prospective rebreather diver who is prepared to accept that "this rebreather can kill you instantly and without warning" is going to be discouraged by a paper in a medical journal which suggests that the warning might be correct?

I do agree that papers like this are vulnerable to being misquoted by people pursuing various agendas. If I see that happening then I will certainly comment.

Just because you have "the best data....currently" available even though, as you admit, it is weak, does not mean it has to be promoted! I am disappointed at you for that. Weak data cannot support a strong conclusion and weak data suggests that further study is necessary and indicated prior to publication of such weak inference.

I have dealt with your "promotion" allegations above. Your comment about "further study" and your observation that this issue would require a randomised trial to resolve (from an earlier post) reveal a degree of naivety in relation to these matters. You could never do a randomized study large enough, even if it was practical to do so in other respects (which it would not be). Indeed, it is difficult to envisage in a pragmatic sense (and for the foreseeable future anyway) how Dr Fock's methodology is likely to be improved. Under these circumstances journals will sometimes publish weak or indicative data, so long as it is properly contextualised. That is what appears to have happened here. The New England Journal of Medicine sometimes publishes studies with relatively inferior methodology if that is the only way the data is likely to be obtained.

Let me give you this analogy:

You are having breakfast, and they are serving you dog crap. Are you going to eat it just because it is the "best currently available"????

I don't find your analogy to be particularly sophisticated or relevant. I would not eat dog crap under any circumstances. But weak data does not necessarily give me indigestion so long as it coated in heavy servings of honest contextualisation.

Simon

 

[doctormike]

Wow Simon, you actually have the galls to admit that this is based on weak data and yet promote this!!!

Just because you have "the best data....currently" available even though, as you admit, it is weak, does not mean it has to be promoted! I am disappointed at you for that. Weak data cannot support a strong conclusion and weak data suggests that further study is necessary and indicated prior to publication of such weak inference.

Let me give you this analogy:

You are having breakfast, and they are serving you dog crap. Are you going to eat it just because it is the "best currently available"????

Gotta say, Claudia - I couldn't agree with Simon more. When you use a term like "promotion", it sounds like you are characterizing a peer reviewed scientific study in a medical journal as if it were a cable news talking point. It's a paper that was written to help answer a very important question, a question that certainly can NOT be answered by a randomized controlled trial.


Yes, an RCT is necessary for level one or two conclusions in evidence based medicine (EBM). I can't even imagine how someone would ever be able to publish even a single RCT (let alone, a meta-analysis of multiple RCTs) on this topic, as we have mentioned before. Remember, "weak data" has been responsible for the vast majority of the medical literature, and has not only contributed to clinical breakthroughs but has laid the groundwork for further advances as well.


What would you propose? That we just leave the question of the additional risk of CCRs as eternally unanswerable? That no one should ever do research on this topic, since by definition, it will all be "dog crap"? Seriously, that analogy alone does not suggest to me a good understanding of the scientific process.


I would caution all of you to avoid approaching the scientific literature with a preconceived conclusion- that is the exact opposite of the scientific method. You may feel that CCRs are safe, you may feel that they have been mischaracterized by the OC community, and you may be right! But you should not approach research with the attitude that "this paper refutes something that I believe, so let me see what methodological critique I can construct so that I can dismiss the conclusion".

 

[mathauck0814]

I would caution all of you to avoid approaching the scientific literature with a preconceived conclusion- that is the exact opposite of the scientific method. You may feel that CCRs are safe, you may feel that they have been mischaracterized by the OC community, and you may be right! But you should not approach research with the attitude that "this paper refutes something that I believe, so let me see what methodological critique I can construct so that I can dismiss the conclusion".

I suppose the bigger question is, "Does it matter?"

Let's say rebreathers are more dangerous - so what? Are you insinuating that those of us who do dive them should stop immediately? Fat chance.

Personally, I could care less if YOU dive a rebreather. I could care less if YOU die doing just about anything. The remedies and procedures for stupidity that get people killed on CCR have been exhausted here. Some feel that stupidity is pervasive and will overcome even the best designed procedures. I disagree. You seem to have a study that supports your hypothesis. I still disagree.

 

[doctormike]

I suppose the bigger question is, "Does it matter?"

The bigger answer is - of course it matters. The only way that rebreathers have progressed to the point that they are now is a lot of scientific and engineering investigation to optimize design, grounded in a thorough understanding of human physiology. That means that efforts to understand specific modes of failure are crucial in making them better and better.

Let's say rebreathers are more dangerous - so what? Are you insinuating that those of us who do dive them should stop immediately? Fat chance.

I have no idea where you came up with that "insinuation" on my part, but I assure you I do not care at all whether you or anyone else here dives a CCR, OC or a Mark V helmet.

You seem to have a study that supports your hypothesis. I still disagree.

I'm really not sure what to make of this. Do you mean that you have other studies which suggest that CCR and OC have similar fatality rates for matched dives, and therefore you feel that this study is not significant? Or do you mean that you like your CCR and have no interest in any new research that might ultimately lead to improvements in overall dive safety?

The funny thing is, the only way that you can ever improve a process - CCR or otherwise - is to always be open to new information and modifications of existing gear and techniques.

I could care less if YOU die doing just about anything.

Nice.

 

[mathauck0814]

The bigger answer is - of course it matters. The only way that rebreathers have progressed to the point that they are now is a lot of scientific and engineering investigation to optimize design, grounded in a thorough understanding of human physiology. That means that efforts to understand specific modes of failure are crucial in making them better and better.

But the physiology is understood, thousands and thousands of dives are being done every year quite safely on rebreathers. So the obvious follow up is it matters to who? To the scientific community that bends their brains around questions for fun? Matters to rebreather divers who have already decided that the benefits outweigh the risks? Matters to the evangelicals like gianamarie who pound their pulpits?

I have no idea where you came up with that "insinuation" on my part, but I assure you I do not care at all whether you or anyone else here dives a CCR, OC or a Mark V helmet.

Agreed.

I'm really not sure what to make of this. Do you mean that you have other studies which suggest that CCR and OC have similar fatality rates for matched dives, and therefore you feel that this study is not significant? Or do you mean that you like your CCR and have no interest in any new research that might ultimately lead to improvements in overall dive safety?

I suppose of the choices you've provided I believe that what I am diving is safer than open circuit for the dives I am doing. Do I think everyone should dive a rebreather? No, I've stated that much. But a common thread is that rebreathers aren't killing people - people making mistakes are killing themselves through their stupidity. You can attempt to engineer the idiot out of the machine, I prefer to remain meticulous and use it as incentive not to screw up.

The funny thing is, the only way that you can ever improve a process - CCR or otherwise - is to always be open to new information and modifications of existing gear and techniques.

Obviously, but what is gained from people like gianamarie pounding the bully pulpit decrying rebreathers and telling us all how we're going to die? Especially when the very vast majority of us aren't dying - we're diving quite frequently, quite successfully. This does not represent an intelligent conversation.

Nice.

My point remains - do as you like, I'll do as I like. Rebreathers are not death machines one straps to one's back in a game of subaquatic Russian Roulette. Attempts by the anti-rebreather evangelists to "save me" (or others) are not appreciated or required.

 

[HIGHwing]

gianaameri -

I believe you have to allow divers the opportunity to come to their own conclusions. The data and data quality concerns have run rampant on the forums for years.

You decided rebreathers are outside of your risk tolerance except when it makes sense for you to use it in a very hostile environment. If I understand your position correctly, you believe using a CCR in a cave is okay for you because logistics (read the CCR diving advantages) warrant CCR technology and you mitigate the risk (read eventuality of failure) by bringing copious OC gas on the dive. Not to be rude, but that’s the whole strategy of CCR diving for the majority of us, too. I do see value in less intense CC dives as a means of practice in OW and we seem to diverge on the topic of practice, which I find intriguing. You seem to argue less time on the loop is less likely to die, whereas I feel that I benefit from workup dives in OW before taking on overhead environments. Noted.

While it's compelling to read "Study A", "Article B", and "NEDU Result C", and anecdote Q from paragraph seven page 143, it's also reasonable [necessary] to understand [realize] people with money and time will find ways to off themselves. Anyone attaching a rebreather to their respiratory system should fully comprehend they have essentially left planet Earth. The diver has fundamentally mechanically extended their body and will be the only person anywhere breathing the precise atmosphere they're blending. We could agree that two rebreather divers on the same dive will have slightly different gas fractions, humidity, etc. in the loop at all times.

Properly trained CCR divers know what they should do to mitigate risks, the real issue here becomes are they doing it. If not, can we cause that change in the community via peer-pressure, best practices, or perhaps more fatalities - whatever else motivates change. I think what you’re asking for is everyone to agree with, "These things are as dangerous as I say they are." /pound table If that’s your objective, we get it loud and clear. Rebreathers are dangerous, especially when coupled with inadequate training, bad behaviors [plural on purpose], and lack of recent experience. You can’t decide how people will use a gizmo, or more importantly misuse a widget.

I remain interested in your thoughts, ideas, and opinions, but I think you're finding resistance here when you say - I dive a rebreather in [arguably] the most hostile environment possible, and its okay for me because I accept the risk for logistics purposes. A sentence or paragraph later you somewhat condemn your fellow divers for accepting the risk of selecting a rebreather in a less harsh environment. I recognize you may have a training/experience advantage, but these two factors, even when paired have not prevented previous fatalities as you repeatedly point out. We know that diver behaviors and disciplines have been factors in many accidents. As a community of CC divers, let’s agree to at the bare minimum eliminate bad behavior and bad discipline root causes from the list of fatalities. I acknowledge best practices will not eliminate a diver being overcome by a problem s/he could not have reacted to, or anticipate, but I do believe we can stem the tide of divers overcome by overall poor execution.

I don't want to see anyone off themselves, and I would prefer to live without ever having to pull a lifeless body out of the water again. Because of this, I take your position seriously, and with consideration, but please allow me the opportunity to make my own decisions about risk and my pursuit of diving enjoyment much as you've done. You’re not the only diver who has turned to a CCR because of logistics or environmental considerations.

 

[tridacna]

I don't want to see anyone off themselves,

What did you mean to say? (I'm not being facetious...I appreciate your post).

 

[doctormike]

But the physiology is understood, thousands and thousands of dives are being done every year quite safely on rebreathers. So the obvious follow up is it matters to who? To the scientific community that bends their brains around questions for fun? Matters to rebreather divers who have already decided that the benefits outweigh the risks? Matters to the evangelicals like gianamarie who pound their pulpits?

You think that our understanding of physiology is complete, and that there is no point in any further research other than for scientist to have "fun"? Try saying that in the DCS forum!


But seriously, the only reason why you are able to dive at all today is thanks to thousands of brilliant people who devoted their careers to figuring out the basic physics and physiology of breathing gas underwater - Boyle, Henry, Haldane, Cousteau, Buhlmann, etc… No real scientist would ever assume that our understanding of anything is complete, without need for further inquiry. If you really think that we have reached the end of this journey, ask yourself if the CCR you will be diving in 20 years will be the same as the one you have now.


As far as rebreather divers deciding about the benefits and the risks, it sounds like you aren't very curious regarding new research about risks (you dismissed the paper out of hand), so I'm not sure how you make those calculations. Remember, I'm not telling you not to dive a CCR, but if you are going to make a risk-benefit analysis, you should at least make sure that you know as much as you can about the risks and the benefits.

Obviously, but what is gained from people like gianamarie pounding the bully pulpit decrying rebreathers and telling us all how we're going to die?

Dunno. He seems to have some experience but seems to be dealing in controversies and technical details that are far beyond what I understand about CCRs. You would need to bring that up with him.

Especially when the very vast majority of us aren't dying

That's a pretty low bar for safety!

My point remains - do as you like, I'll do as I like. Rebreathers are not death machines one straps to one's back in a game of subaquatic Russian Roulette. Attempts by the anti-rebreather evangelists to "save me" (or others) are not appreciated or required.

I think that you have me confused with someone else.