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Discussion Starter #1 (Edited)
Hello,

You may recall that one (of many) debates DL have had with others (including myself) has been over the issue of an appropriate end point for CO2 scrubber breakthrough testing. To summarise, DL have advocated a breakthrough threshold of 2% CO2 whilst others, including myself, have advocated 0.5%. My own recommendation of 0.5% has been based on extensive revision of the relevant diving physiology literature, the synthesis of which can be found here:

Doolette DJ, Mitchell SJ. Hyperbaric Conditions. Comprehensive Physiology 2011;1:163-201.

DL have argued their position largely on the basis of one paper containing no original data which was only ever designed as a "concept" document to provoke discussion. That can be found here:

Knafelc ME. Physiological basis for CO2 limits within semiclosed and closed circuit underwater breathing apparatus, NEDU TR4-00, Navy Experimental Diving Unit, Aug 2000.

The reason for posting today is that a relevant experiment has just been published from the NEDU group in the USA. It can be found here:

Shykoff BE, Warkander DE. Exercise and CO2 retention with inhaled CO2 and breathing resistance. Undersea and Hyperbaric Medicine 2012;39(4):815-828.

It is a complex study, but fundamentally demonstrates that working divers are prone to dangerous CO2 retention if the inspired CO2 is 2%. I quote from the conclusions:

"Other authors have suggested that divers may be able to compensate for 2% inspired CO2, at least in a low resistance circuit. With resistance like that of a rebreather UBA, particularly during oxygen breathing with heavy exercise, we disagree. In this study at heavy exercise, even without added resistance some air breathing subjects retained CO2, as did many of those who breathed oxygen. With 2% inspired CO2 and and resistance like that of the MK 16 UBA at 50 feet of seawater, ventilation was reduced and CO2 retention severe in some subjects. Further, subject recognition of hypercapnia was poor. For diver safety with the Mk 16 and other UBAs with both inspiratory and expiratory resistance, inspired CO2 must be maintained as close to 0% as possible".

My position has always been that DL have argued their beliefs from a position of poor understanding of both physiology and the relevant literature, and completely inappropriate reliance on a single discussion document. This latest publication from another authority on this subject, which presents arguably the most directly relevant original data published to date, strongly corroborates that view. Scrubber duration limits published by DL should be interpreted with particular attention to the CO2 breakthrough end point of the testing.

Simon M
 

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Hello,

My position has always been that DL have argued their beliefs from a position of poor understanding of both physiology and the relevant literature, and completely inappropriate reliance on a single discussion document. This latest publication from another authority on this subject, which presents arguably the most directly relevant original data published to date, strongly corroborates that view. Scrubber duration limits published by DL should be interpreted with particular attention to the CO2 breakthrough end point of the testing.

Simon M
The sole reason (in my opinion) that DL quoted the 2% figure as an endpoint was because their CE duration to the standard of 0.5% was less than 1 hour. Given the cost of the absorbent that makes for a very expensive dive.
However, if their CO2 sensing technology were to work as advertised (which according to Dave Sutton it does not) then I would think you could potentially squeeze a bit more time from that scrubber. However, the real question is not how long it takes to get to 0.5%, but how long it takes to get from 0.5 to 2%, then from 2% to 5% and above.
 

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Thanks simon, although frankly not a surprise.

If the target is expensive/difficult to hit, change the measurement metric. Its like politics. The harder route is to actually make something better.....
 

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Simon.

Cant get your two reference up, Google searching keeps popping up with the "Park Funeral Chapels" how bazaar.

However keeping on the subject of "raising the dead", I would suggest to get the "ducks" up first with proper references we can
all read for ourselves on the forum before commenting, and not just left to the folk with access to undersea and hyperbaric medicine.

You are going to have to post this latest document, a Pdf copy as most on the YD forum don't have UHMS access.

However I can help for the Knafelc Navsea document NEDU TR4-00 August 2000 Try this:


http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA383684


And to get the post off to a flying start I would like to add the prequel to the main attraction that of TA 08-06 April 2010 Effects of CO2 and UBA Here:


http://www.dtic.mil/dtic/tr/fulltext/u2/a549670.pdf


Iain Middlebrook
 

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(SNIP) However, the real question is not how long it takes to get to 0.5%, but how long it takes to get from 0.5 to 2%, then from 2% to 5% and above.
Matthew.

I couldn't agree more. That, and that alone is the solid foundation from which to build.

Iain Middlebrook
 

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Iain,

As you know, there are rules and regs about posting reports from journals without prior permission of the editor. Not sure if Simon is going to be able to get this permission.

Regards
 

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Iain,

As you know, there are rules and regs about posting reports from journals without prior permission of the editor. Not sure if Simon is going to be able to get this permission.

Regards
Then try harder, it's not like it's written in latin now is it, besides if we are required to discuss in open forum these matters we should have equal access to the documentation.
It's not like it's going to be a best seller in "Waterstones" last seen flying off the shelf at every Airport bookstore. Now is it?

Besides I have posted two of the three reference already how hard can it get? It's not "Wikileaks" for goodness sake Iain Middlebrook
 

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Iain,

Having fallen foul of an editor in the past about quoting from a paper that wasn't just the citation, I can see the reticence. I was also surprised that when I submit my thesis to Cranfield, they own the copyright on the material and I have to apply to them for permission to reproduce.

If you are that interested, why not join UHMS? Its only $100 or so...its why I joined SPUMS to get access to the latest journals...

Regards
 

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more weaselly than a weaselly thing
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Then try harder
I seem to recall someone else who posts on the forums and keeps referring to gagging clauses in contracts. Maybe he should try harder ;)

iain/hsm said:
It's not "Wikileaks" for goodness sake
Shame, Im told ecuador is a good time ;)
 

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Iain,

Having fallen foul of an editor in the past about quoting from a paper that wasn't just the citation, I can see the reticence. I was also surprised that when I submit my thesis to Cranfield, they own the copyright on the material and I have to apply to them for permission to reproduce.

If you are that interested, why not join UHMS? Its only $100 or so...its why I joined SPUMS to get access to the latest journals...

Regards
$100.................. A HUNDRED DOLLARS are you insane?

This is YD a divers forum, do you expect every diver to pay $100 to read a copy of this pamphlet?
For most on here $100 would keep them in lime and cells till 2015

I'm also sorry you need to apply to them permission to reproduce Gareth.
This is not China, you and your wife can do this with or without there permission.

But joking aside Simon has brought up a real interesting point here it would do well for
every diver to get a read of this information.

It is of critical importance but they are just not going to pay $100 to get it.

Matthew also with his comments these a pivotal to the whole rebreather ethos.
We are almost back to base. The "Unless or Until" of CO2 detecting is in place
Nailed down, limit set, all agreed.

I guess now, some 20 years later would be a good a time as any to make a start.

We all just need to read ALL these references then debate. Iain Middlebrook
 

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I seem to recall someone else who posts on the forums and keeps referring to gagging clauses in contracts. Maybe he should try harder ;)
Shame, Im told ecuador is a good time ;)
This is different EBT

A gagging clause forbids both discussion and or publication.

However the kicker here is that with

Shykoff BE, Warkander DE. Exercise and CO2 retention with inhaled CO2 and breathing resistance. Undersea and Hyperbaric Medicine 2012;39(4):815-828.

This anyone can read, Knock yourself out. Just fork out $100 for the privilege.
You see the difference? Iain Middlebrook
 

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Honestly? No.

You're asking him to give away something he does not own and thus risk professional damage and possible litigation. Sounds the same in principle as a gagging clause. Both are designed to protect a commercial interest and prevent someone publishing something that belongs to another party.
 

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Honestly? No.

You're asking him to give away something he does not own and thus risk professional damage and possible litigation. Sounds the same in principle as a gagging clause. Both are designed to protect a commercial interest and prevent someone publishing something that belongs to another party.
EBT

Rubbish, stop this nonsense. Simon and Warkander are as tight as a drum. :) there great friends I cannot even imagine the possibility.
No this has the makings of a decisive publication, It may be the best publication you and I will ever read on the subject.
I just don't want to wait 20 years before we get to discuss it again or have you lot pay $100 for the privilege that's all.
 

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IF warkander has the rights to publish/distribute your opinion may be valid. If he doesnt the previous statement stands.

Lets agree to disagree, i do so hate dragging father ted out of retirement on a friday ;) (and its really simons discussion to have)
 

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The Rubicon Foundation Rubicon Foundation is a fabulous resource for scientific information about diving. If you search for CO2 or Warkander, for example, you will get pages of results.

You aren't allowed to publish the reports yourself, but as far as I understand it, you may even post a link to the article if you like. It is a resource I use frequently.

Bruce
 

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The rubicon does have lots of articles but they have a prohibition notice that prevents publication of journal articles inside 12-24 months depending on the journal.

This is standard academic process. Simon and Warkander do not get that money.

When I signed up to do my PhD with Cranfield, part of the T&C's were that they have the copyright for any material, but wouldnt necessarily asking for it to be released elsewhere. Same for journal articles, once published, the journal holds the copyright.

Regards
 

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Discussion Starter #17
Iain,

Simon.

Cant get your two reference up, Google searching keeps popping up with the "Park Funeral Chapels" how bazaar.
The search engine probably thinks you are diving a rebreather whose scrubber breakthrough was tested to 2%, so it takes you to an appropriate site.

I couldn't agree more. That, and that alone is the solid foundation from which to build.
No its not "that alone". I do agree that the time course to development of even higher levels of inspired CO2 is important because if this time course is short (which I understand it is) then this implies an even greater hazard. But the point of this paper is that 2% inspired CO2 (forget about the levels getting even higher) is dangerous during rebreather diving at any time. Put another way, even if the scrubber was magically able to allow breakthrough up to 2% but then prevent any further increase, it would still be dangerous. I have made this point many times in the past.

I think the segment of the conclusion I posted verbatim is fairly explicit. Nevertheless, I do agree that being able to read the entire document would be ideal. I have emailed the Managing Editor of UHM to ask permission to provide a pdf to those of you who request it. I will let you know the response. Regarding the other publications, your links do not work for me. I would be happy to provide a copy of our review (Doolette and Mitchell) to anyone interested, and the Knafelc report is in the public domain and can be accessed via Rubicon I think. I would also provide that to anyone interested (pm me with a private email address).


Simon M
 

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Discussion Starter #18
simon mitchell said:
I have emailed the Managing Editor of UHM to ask permission to provide a pdf to those of you who request it. I will let you know the response.
I got a super quick response.

I have permission to send a copy of the Shykoff and Warkander pdf to divers interested in this issue. So, Iain and others, please pm me a private email address and I will send it to you.

Simon M
 

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No its not "that alone". I do agree that the time course to development of even higher levels of inspired CO2 is important because if this time course is short (which I understand it is) then this implies an even greater hazard. But the point of this paper is that 2% inspired CO2 (forget about the levels getting even higher) is dangerous during rebreather diving at any time. Put another way, even if the scrubber was magically able to allow breakthrough up to 2% but then prevent any further increase, it would still be dangerous. I have made this point many times in the past.
The time from 0.5% to 2% was (IIRC) somewhere around 25 minutes, and from 2% to 5% somewhere south of 10 minutes. Very scary stuff to be playing around with given that the promised CO2 sensor (which was supposed to negate this concern by forewarning the diver well before 2%) has yet to materialize. Are they still quoting 2+ hours duration, even without the CO2 monitor? Quite a tightrope for end users to be walking if they are unaware of exactly what these numbers truly mean.
 

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Discussion Starter #20
EBT

Rubbish, stop this nonsense. Simon and Warkander are as tight as a drum. :) there great friends I cannot even imagine the possibility.
Iain, just for your information, it is not nonsense. It is not Dan Warkander I have to deal with. When we publish manuscripts in scientific journals we almost always sign over the copyright to that journal. That is why I needed permission from the journal.

Simon M
 
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