co2 hits? bov or not

[Brad_Horn]

I'm puzzled why the WOB on the shrimp is so much different breathing left-to-right vs. right-to-left? Or did I misread what you meant?

AFAIK the Shrimp WOB is around 1.44J/L at 75lpm at 40m on Air for the CC side. The OC performance is unknown.

though if there is no testing done on the shrimp how would you know an alternative is 2.5 times better?

The OSEL ALVBOV has a WOB of 0.57J/L under the same criteria at 75lpm https://www.opensafety.eu/datasheets/ALVBOV_40m_75lpm_air_081014.pdf and the OC WOB is comparable to a high performance OC reg.

In left to right flow you simply can't get as good a performing BOV as right to left. To see why just compare the R&D efforts of the different manufacturers and published testing.
It is a simple fact. Why is interesting! Most if not all folk would agree that Simon Mitchell is well educated and not debate this. Yet despite that, he has no idea what the actual WOB of the BOV he uses is and IF when he bails off this using his OCB, how much poorer performing the reg is, than his loops WOB. It is probably much worse but Simon has no idea - based on what APD have published.

If Simon doesn't know what the better and safer option is from a WOB standpoint what hope does the average diver? From openly published data the APD DSV has been tested as having a WOB of 2.13J/L and APD state that their OCB WOB is comparable as I understand it to their DSV.
If this is the case he can halve his WOB by instead bailing to a good conventional 2nd stage like an Apeks or Poseidon reg. Probably a good thing for CO2.
If he bailed to the OC side of his OCB how much has he raised his WOB by?
You can get a reg through EN250 with three times the WOB of a good 2nd stage. Is this good or safe to bailout to from a rebreather..... If I have read what Simon has written correctly, I am guessing that no it is not ideal.

but
If he was diving with a better BOV with a known performance. Noting this isn't commercial in any way as the ALVBOV isn't an option for him on his current unit of choice due to the flow direction being opposite. Then by how much does he improve his safety by first diving with a lower loop WOB and secondly bailing out to a known OC WOB, that is comparable to a good conventional 2nd stage!
IF Simon was to fit an ALVBOV to his Mk15.5 over the conventional DSV he would have then have the option of knowing what the OC WOB was when he wanted to bailout. and lower his units WOB at the same time.

 

[Mark Chase]

Oh right the holy grail lol

ISC tested a shrimp yrs ago (2007). WOB was not good.
http://www.megccr.com/wp-content/uploads/2013/10/Golem-Gear-BOV-Test-Results-Announcement.pdf
http://www.megccr.com/wp-content/uploads/2013/10/test-summary-extracts-on-the-Golem-Gear-BOV.pdf


I believe the check valves have since been changed to a different type, but these data are not as complete
http://www.golemgear.com/images/document/ShirmpWOBChart.pdf

Are you sure that test was on the shrimp? I thaught it was on the MK1 Golum BOV which was then upgraded with a low WOB kit (which we had to bloody pay for )

I can confirm the MK1 Golum pre upgrade was crap. I was diveing one till 2009 which is why I think you may have it wrong. I swapeed to a JJ breifly then on to the Shrimp in 2010 I think?

ATB

Mark

 

[Elmi]

@ Brad
Do you not see a market of the Osel ALV BOV for us rebreather divers who have loop direction flow from left to right?
If your figures are right, what i assume, i and sure many others would be interested
If i look at the GG shrimp, it goes like hot cake.
Is it really about the production ( engineering) cost not to offer left to right or is there some other reasoning (logic) behind?

 

[lizardland]

Why is interesting!

Unless I am missing something, the why is simply semantics and word play.

I am minded of a Raymond Chandler quote. Someone asked Marlowe why he calls him Hemingway.

"Because you keep saying the same thing over and over until you think it starts to make sense".

 

[GLOC]

Brad, whats the difference in WOB when using a Helium-based gas with something like 30%+ in it when considering your OC regulators.

I am sure that Simon mitigates his lack of knowledge of the WOB for the OC aspect of the BOV by using a less-dense gas (trimix) than required for the CE which means the WB will be automatically less...

Regards

 

[Ben Field]

Do you not see a market of the Osel ALV BOV for us rebreather divers who have loop direction flow the right way?

Fixed that for you ;-)

 

[rjack]

In left to right flow you simply can't get as good a performing BOV as right to left. To see why just compare the R&D efforts of the different manufacturers and published testing.
It is a simple fact. Why is interesting!

I'd like to know why actually, I snipped off the rest of you post because it goes off on a bit of a tangent. Does not seem like a simple fact to me that L to R and R to L would be fundamentally different.

Are you sure that test was on the shrimp? I thaught it was on the MK1 Golum BOV which was then upgraded with a low WOB kit (which we had to bloody pay for )

I can confirm the MK1 Golum pre upgrade was crap. I was diveing one till 2009 which is why I think you may have it wrong. I swapeed to a JJ breifly then on to the Shrimp in 2010 I think?

ATB

Mark

That might be, its not clear to me exactly which units were tested and if they are even sold now.

 

[Elmi]

Fixed that for you ;-)

 

[Mike Ferguson]

sorry Brad you lost me. can you explain what gas flow direction has got to do with WOB?

if you put your BOV in your mouth upside down and breathe from it so the gas is now flowing left to right instead of right to left does the WOB change?

 

[Randy Thornton]

Nonsense! All else being equal, there is no difference in WOB going from L/R or R/L. To say otherwise is just marketing spin!

 

[Andy Del]

The luckiest man in the world is the one who is prepared mentally and physically, who has carefully and methodically prepared and tested his equipment, and has the necessary redundancy in place to respond appropriately when things still go pear shaped. I suspect that your diligence has prepared you to win the lotto!

Please tell the newsagent I buy my Lotto tickets from!

 

[Johan Isaksson]

I had CO2 issues a week or so ago. Mine diving at approx 60 meters. Retained CO2 due to bad OC habits when taskloaded. Basically I tend to skip breathe when I get too much on my plate and doing tricky reel work in low vis with the equipment I brought was obviously too much. I've had similar experiences before both on OC and CCR and the buildup was the same. Slowly building sense of unease up until the five minute mark (I timed it) were I decided that the increase in breathing rate made it time to call it quits. I finally found a decent tie-off, passed the reel to my buddy and thumbed the dive. We switched positions and I bailed and started moving back towards the entrance on OC. CO2 symptoms faded in just over three minutes. Sac was around 18 which is roughly a 50% increase from normal. I went back on the loop after five minutes and we finished the dive without any further incidents. I was probably cognitively impaired on some level but not to a degree were I or my buddy could notice it. Identifying bailout regulators and dealing with the situation at hand was not a problem at least. I do not dive with a BOV which for me is a personal choice based on the belief that I notice the symptoms before they escalate. Others obviously react differently so I won't be making that choice for anyone else.

 

[Mark Chase]

I agree with early bailout allowing the switch to a conventional OC regulator possable but from my personal experiance it seems to take a LOT of personal diciplin to decide to go for full on OC bailout

I found having to flip a lever on the BOV increased my inclination to bail early.


The second issue is narcosis. C02 being massivly narcottic the level of motor skills necessary to conduct a full OC bailout mey present too much of a chalange.

Third issue is buddy bailout.

If I see a buddy acting odd then I'd be inclined to bail him to OC if I suspected c02. Doing this via an OC from a CCR loop would present a significant chalange on a zoaned out diver. If he's on a BOV I just flip the switch for him


Tghe narcossis isse with C02 is even more significant on CCR because we pay pennys for trimix and tend to dive 30m or less ENDs. I personaly do 20mEND on 70M + depth dives

As a result my narcosis tolerance built up from my OC days of running 40 or even 50m ENDs to keep gas cost down has vanashed. Last time I was on Air at 30m on a single 12 I could feel I was narked. I used to sware I could do 40 nark free no problem whan I was deep dived up on OC.

So the big nark deep from C02 is a signifcant issue in the bailout decision process.


I have thaught about it a lot and concluded thers more evidance to suport a BOV than there is hassel owning one.

 

[uwxplorer]

I agree with early bailout allowing the switch to a conventional OC regulator possable but from my personal experiance it seems to take a LOT of personal diciplin to decide to go for full on OC bailout

I found having to flip a lever on the BOV increased my inclinsation to bail early.


The second issue is narcosis. C02 being massivly narcottic the level of motor skills necessary to conduct a full OC bailout mey present too much of a chalange.

Third issue is buddy bailout.

If I see a buddy acting odd then I'd be inclined to bail him to OC if I suspected c02. Doing this via an OC from a CCR loop would present a significant chalange on a zoaned out diver. If he's on a BOV I just flip the switch for him


Tghe narcossis isse with C02 is even more significant on CCR because we pay pennys for trimix and tend to dive 30m or less ENDs. I personaly do 20mEND on 70M + depth dives

As a result my narcosis tolerance built up from my OC days of running 40 or even 50m ENDs to keep gas cost down has vanashed. Last time I was on Air at 30m on a single 12 I could feel I was narked. I used to sware I could do 40 nark free no problem whan I was deep dived up on OC.

So the big nark deep from C02 is a signifcant issue in the bailout decision process.


I have thaught about it a lot and concluded thers more evidance to suport a BOV than there is hassel owning one.

After being brainwashed during my Fundies class about CO2 narcosis based on the flimsiest shred of evidence (to the eye of a skeptical scientist), I have developed a serious case of allergy to the term "CO2 narcosis".
Would someone mind providing first hand description of CO2 narcosis versus incapacitation due to CO2 buildup in the bloodstream, which to me is physiologically different: there are a lot of ways CO2 can apparently affect our normal state, with some capable apparently to result in panic (which can hardly be assimilated to "narcosis").
But my point is not so much to argue about semantic, than to figure out whether or not ways of detecting CO2 build up can be learned (and therefore taught).
The recent study let by Simon Mitchell about prebreath stopped short of addressing this issue at the surface, by not testing subjects who had failed to detect a missing scrubber (or a missing O-ring) several times after their initial failure, to check whether subtle symptoms could be learned. Maybe after all, besides detection by fancy medical gizmos, it is possible to become aware of something abnormal going on in our physiology, thought process or bladder function, which we could use to anticipate those cases of high internal CO2.
To me the arguments of the kind "I got a CO2 hit and I survived because I had a BOV, therefore anyone without a BOV, however good their reasons are, will die when they suffer a CO2 hit [implicitly suggesting that everyone doing challenging enough dives will experience one]" are getting tiresome and are not fundamentally helpful without a thorough introspective analysis of what led to the event. If what led to the event was a series of bad decisions, but the ego of the person prevents him or her to clearly state that, then I am not learning anything.
Surely driving without a seatbelt, above speed limit and passing cars in curves with no visibility raises you chances to die in a car accident?

 

[Jeff Pack]

I have always been very in tune with my body, from martial arts, to exercise, to healthy lifestyle. I have always believed I'm in tune enough to feel something coming. Yet I took a hypoxic hit on my Meg from a stupid mistake (hence rectified), and never felt anything out of place, just bang, lights out. So I now question whether I may even feel a CO2 hit coming on.

 

[Mark Chase]

After being brainwashed during my Fundies class about CO2 narcosis based on the flimsiest shred of evidence (to the eye of a skeptical scientist), I have developed a serious case of allergy to the term "CO2 narcosis".
Would someone mind providing first hand description of CO2 narcosis versus incapacitation due to CO2 buildup in the bloodstream, which to me is physiologically different: there are a lot of ways CO2 can apparently affect our normal state, with some capable apparently to result in panic (which can hardly be assimilated to "narcosis").

C02 is so narcotic, its just above materials used for general anasthetic

https://www.youtube.com/watch?v=AOqrKX3cb-g

But my point is not so much to argue about semantic, than to figure out whether or not ways of detecting CO2 build up can be learned (and therefore taught).

The on set of C02 varies so much its not really possable to tie down a pre hit state. My general concensus is If i dont feel right bailout first and ask questions later but in the events where I have "not felt right" I sadly have not folowed my own advice.

Proof that armchair diveing is easier than the real thing

To me the arguments of the kind "I got a CO2 hit and I survived because I had a BOV, therefore anyone without a BOV, however good their reasons are, will die when they suffer a CO2 hit

Id say your chances are significantly improved by having a BOV but nothing is 100%

Howard didnt understand he was having a C02 hit at 70m. He was just off his face. Janos tried to coax him back to the shot (realising something was wrong) but he was litraly scootering off into the blue

Then Janos got him back and tried to get him to ascend but he was so out of it he lost controll and polarised up.

He in his own words "woke up" in 15m of water and went back down to do deco at which point his breathing was so hard he said he couldn't have switched to OC without a BOV

I had a deep air narcosis hit many years ago at about 60m. I too remember "waking up" hugging a rock in shalow water

Thers a piece in the incident in Diver Mags archives under Narcosis. After this experiance Howards experiance rang a bell with me.

[implicitly suggesting that everyone doing challenging enough dives will experience one]" are getting tiresome and are not fundamentally helpful without a thorough introspective analysis of what led to the event

.

Sorry thats rubbish. I have been deep diveing CCR since 2004 1500 something hours underwater pushing the scrubber to 6 hours + and working at depth and I have never had a C02 hit

If what led to the event was a series of bad decisions, but the ego of the person prevents him or her to clearly state that, then I am not learning anything. Surely driving without a seatbelt, above speed limit and passing cars in curves with no visibility raises you chances to die in a car accident?

Howard was on a fresh scrubber but was strugling with scootering at depth something he doesent normaly do. (he doesent own a scooter) and hes not a raceing snake.

We put it down to task loading and poor breathing but we dont know this for a fact.


The fella who had no BOV and went for the surface had a deformed mushroom valve in his mouthpiece which was letting by.

He hadn't done a flow check on his unit but it had passed pos neg no problem

ATB

Mark

 

[uwxplorer]

C02 is so narcotic, its just above materials used for general anasthetic

https://www.youtube.com/watch?v=AOqrKX3cb-g

Precisely: N2 is not raising your blood pH and making you pass out. It's narcotic influence is separable from the rest (in fact there is apparently no other effects, besides DCS if you go back to the surface to quickly).
CO2 might make you goofy and incapacitated, but is that because it affects your brain function or because your whole body metabolism is thrown upside down? One doesn't go without the other, therefore saying that CO2 is narcotic is like saying that strangulation is a better treatment of erection dysfunction than Viagra because of the speed of the effect... The curve shown in the video is known for a while to have no value whatsoever to predict the narcotic effects of a molecule BTW.
During Fundies, I was particularly upset by the exploitation of Dave Shaw's video to illustrate the narcotic effect of CO2. Dave Shaw died of narcosis! (at 900 ft trying to pull a corpse, maybe?). But I digress...

To reiterate my point: I am not accusing anyone to brush off their own mistakes, but if indeed hypercapnia is such a rampant possibility for even the most experienced divers, shouldn't it be our common interest to try and learn as best as possible from those lessons? That's what I am trying to do. I know that if I kick furiously, I will be at risk. I am not monitoring my breathing pattern when task loaded, but probably I should. Heck, maybe I should sign up for a yoga class?
Are you not the one who despises automation because it makes you complacent? Isn't there a risk that the BOV, unconsciously does the same to a diver, and will stop him from worrying to much about overexertion or a failed stereo check?

The OP was maybe hoping that everyone would tell him: go for a BOV, this will save you in all situations, even though it is an additional pain in the rear to handle underwater and maintain above water.
I just wanted to point out that some very experienced divers (which I am not) do not think so, and they probably have good reasons for their choice. I suspect that they are investing in more pre-emptive action, checks and cross-checks, and would all the same be grateful if an exhaustive list of all cases of hypercapnia fully analyzed by their victims were available to all to learn from.
Statements of the kind "s***t happens to the best" are self-defeating. It also will happen with BOV (if of a different kind) and maybe the kind of problems that only happen to divers with a BOV.

 

[Johan Isaksson]

I firmly believe that what people describe as a CO2-hit - panic, extreme respiratory stress and cognitive impairment, is due to respiratory acidosis after a prolonged time of increased CO2 exposure. The question is if there are preceding symptoms and if you notice them.

I know for a fact that I can tolerate very high pCO2 levels without noticeable cognitive impairment since we did some breathholding experiments measuring end-tidal CO2 during a dive medicine course. We did this pre-breathing pure O2 and I hit CO2 levels around the 10,5 kPa mark with no immediate side effects (roughly double normal levels). From that experiment I also know that high oxygen concentrations will mask some of the symptoms of increasing CO2 which up until now has been my biggest fear in regards to CO2 and CCR-diving.

Basically I've wondered whether or not I would be able to notice the symptoms as they develop even at a high pO2. Previous incidents have been shallow at moderate pO2 or on OC. It seemed unlikely to me that there would be no symptoms before it spiralled out of control due to the tightly regulated functions in play but you never know. For my part I now know that my reaction is the same at depth and at 1.3 pO2 so I'll stick to my DSV. I tend to be quite zoned in when I dive. I notice when something is slightly off, from gear to general balance and I also routinely monitor my breathing rate (habit from work, it's a reflex) which I am sure makes it easier to detect. Without those characteristics I would definitely dive with a BOV.

I still might get one if I see a hassle free solution that is properly tested and provides a ccr wob that is as good as what I get from the DSV. Mainly because of Marks point with the buddy assist in case of loss of consciousness.

 

[Johan Isaksson]

I have always been very in tune with my body, from martial arts, to exercise, to healthy lifestyle. I have always believed I'm in tune enough to feel something coming. Yet I took a hypoxic hit on my Meg from a stupid mistake (hence rectified), and never felt anything out of place, just bang, lights out. So I now question whether I may even feel a CO2 hit coming on.

The body regulates CO2 very tightly and has multiple checks in place to warn you when it's out of range. Not so for oxygen levels. In addition the main symptoms would add in making it harder to notice. Furthermore the highest risk of it happening will be at times when you're distracted and might easily forget the monitoring of equipment needed to catch it.

I would not expect to notice hypoxia by symptoms before it's too late and I don't think a BOV alone would help either, perhaps with a buddy switch to OC but you'd probably need a gag strap too. Personally hypoxia is my main paranoia, mainly upon entering the water and at the start of the dive. I've already shared my take on CO2 and plan to deal with hyperoxia by the simple rule of bailing out in case any cell shows a non viable pO2.

 

[rjack]

Precisely: N2 is not raising your blood pH and making you pass out. It's narcotic influence is separable from the rest (in fact there is apparently no other effects, besides DCS if you go back to the surface to quickly).
CO2 might make you goofy and incapacitated, but is that because it affects your brain function or because your whole body metabolism is thrown upside down?

You can test this yourself. Just assemble your unit without a scrubber, set it at 0.21 ppO2. Then go for a walk (a reasonable proxy for light swimming) with a nose clip on. Have a friend along make sure you don't hurt yourself.

In my limited experience with O2, the respiratory drive goes sky high and the anxiety matches it. Which leads to massive perceptual narrowing. Is that "narcosis" in the same sense as other gases? I don't know, but on a practical level its debilitating - as most victims of a CO2 hit here are validating.