Thinking of upgrading unit with a BOV after reading some of the posts about co2 hits, now my question is how many have ever had a hit? did you get to understand why and did/would a BOV have made any difference. I've had one fubar moment and whether it was a hit or not I'm not sure but managed to come of the loop and onto bailout without a great problem, the ascent was another thing but happy my buddy was on twin 12s and had a reg on a long hose to assist me to the surface. I'm still trying to shake of the minimalistic OC style I used to dive in and not sure if I see a BOV as a solution to a possible problem or an additional problem/maintainance issue.
co2 hits? bov or not
- Thread starter jas kev
- Start date
Might be worth starting a survey on here, so you can actually track the responses numerically.
Simon Mitchell
Well-Known Member
Hello,
There are arguments for and against, but I am a BOV advocate (and use one), largely because of the issue you raise. Ten years ago Barbara Trytko and I published what I believe was the first report of a diver who knew he should change to an open circuit supply but could not bring himself to do it because he was so short of breath during a CO2 hit.
The reference is:
TRYTKO B, MITCHELL SJ. Extreme survival: a deep technical diving accident. SPUMS J 35, 23-27, 2005
The paper can be downloaded from this page:
http://archive.rubicon-foundation.org/xmlui/handle/123456789/9573
Subsequently similar stories have emerged. It is certainly possible that a diver can become so incapacitated / short of breath during hypercapnia that they will refuse to remove their DSV to change to an open circuit supply. A BOV is likely to mitigate that problem. There are several caveats though. Depending on the reason for the CO2 hit, changing to open circuit might not help. If it is due to CO2 rebreathing, open circuit is definitely the answer. If, however, the hypercapnia is due to CO2 retention (simply not breathing enough to eliminate the CO2 that is being produced in the body) then open circuit will only help if the work of breathing on the open circuit reg is lower than the work of the breathing in on the rebreather loop. In that regard, there have been some BOVs with poor work of breathing over the years. Such a device could even make a CO2 hit due to CO2 retention worse. So you need to do some research, and make sure your BOV is a good one.
Simon M
There are arguments for and against, but I am a BOV advocate (and use one), largely because of the issue you raise. Ten years ago Barbara Trytko and I published what I believe was the first report of a diver who knew he should change to an open circuit supply but could not bring himself to do it because he was so short of breath during a CO2 hit.
The reference is:
TRYTKO B, MITCHELL SJ. Extreme survival: a deep technical diving accident. SPUMS J 35, 23-27, 2005
The paper can be downloaded from this page:
http://archive.rubicon-foundation.org/xmlui/handle/123456789/9573
Subsequently similar stories have emerged. It is certainly possible that a diver can become so incapacitated / short of breath during hypercapnia that they will refuse to remove their DSV to change to an open circuit supply. A BOV is likely to mitigate that problem. There are several caveats though. Depending on the reason for the CO2 hit, changing to open circuit might not help. If it is due to CO2 rebreathing, open circuit is definitely the answer. If, however, the hypercapnia is due to CO2 retention (simply not breathing enough to eliminate the CO2 that is being produced in the body) then open circuit will only help if the work of breathing on the open circuit reg is lower than the work of the breathing in on the rebreather loop. In that regard, there have been some BOVs with poor work of breathing over the years. Such a device could even make a CO2 hit due to CO2 retention worse. So you need to do some research, and make sure your BOV is a good one.
Simon M
SlowDiver
Member
Also a BOV advocate and wonder why not have one. They are now a lot smaller and the WOB between the new BOV's and DSV's I can't tell the difference. A machine maybe can, and I have both.
I have heard the story's of divers taking a caustic cocktail hit and switching there BOV over to OC and the acidity mix is still in the mouthpiece. This I can understand why a diver would want a completely different second stage. But with a CO2 hit you want and need fresh gas in a hurry and I know no faster way than moving a knob from one position to another.
After reading numerous reports from divers that have had a CO2 hit it seems that it affects divers differently. When I took my CO2 hit my vision went and everything was a blur. Next day I had a very bad headache.
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I have heard the story's of divers taking a caustic cocktail hit and switching there BOV over to OC and the acidity mix is still in the mouthpiece. This I can understand why a diver would want a completely different second stage. But with a CO2 hit you want and need fresh gas in a hurry and I know no faster way than moving a knob from one position to another.
After reading numerous reports from divers that have had a CO2 hit it seems that it affects divers differently. When I took my CO2 hit my vision went and everything was a blur. Next day I had a very bad headache.
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Cheers Simon, any clue which BOVs are poor performers?
Cheers for reply, having just read Simon's report it appears the fault was due to human error, any clue as to the cause of your hit? My fubar was human error, rushed incorrect build which led to me feel like I was trying to draw air through a solid oobject.
Simon Mitchell
Well-Known Member
Hi again,
Not really my areas of expertise, and unless there is an obvious safety issue I try to stay away from equipment comparisons, even when I think I know something about it. In this case I don't really. Its not something I have kept up with. There are probably many more knowledgable than I around here who can advise you on BOV performance.
I had a quick read of that paper again.... its interesting how things evolve as research is done. Barb and I made an issue of the fact there was no prebreathe, but if I wrote that paper again today (and based on our recent study),[1] I would have to acknowledge that even with a prebreathe there would have been a high likelihood that the diver would have continued with the dive (25% of subjects in the study who breathed on a circuit with absolutely no CO2 scrubbing at all completed the prebreathe and said they would be happy to dive the unit).
Simon M
1. DENG C, POLLOCK NW, GANT N, HANNAM JA, DOOLEY A, MESLEY P, MITCHELL SJ. The five minute prebreathe in evaluating carbon dioxide absorption in a closed-circuit rebreather: a randomised single-blind study. Diving Hyperbaric Med 45, 16-24, 2015
Simon M
Mike Ferguson
WTF is that?
couple of old threads on BOV's that might be worth reading if you haven't found them yet
http://www.ccrexplorers.com/showthread.php?t=14022
http://www.ccrexplorers.com/showthread.php?t=14094
http://www.ccrexplorers.com/showthread.php?t=14022
http://www.ccrexplorers.com/showthread.php?t=14094
SlowDiver
Member
Mine was also human error. Diving in a cave with a lot of duck weed and took the mouthpiece out while at the surface to talk to my dive partner. The small duckweed seeds got into my mouthpiece which then got around my mushroom valves causing them to not seal correctly.
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What are you adding that you do not already need in order to bailout?
Recommend in addition to the BOV you investigate adding a retaining strap as well. If your diving a CE certified CCR that already comes with the required retaining strap ensure its moved over even if the BOV is supplied without.
Usually, only if you do not want better performance. Kind of a two edged sword this one.
If your talking about DSV/BOVs from the same manufacturer having the same WOB, then you probably won't be able to identify any difference. AFAIK the BOVs/DSVs from JJ, APD or ISC are near as identical, or at least in one notable case, they say they are anyway. This however is not the same as saying they offer the diver good WOB.
It is also quite different to there not being any WOB difference between BOVs & BOVs and DSVs & DSVs and BOVs & DSVs. If you do some research on it you will identify that there can potentially be significant differences in performance capability between options.
What effect that has on the divers ability to bailout safely is over to guys like Simon to analyse.
Kind of an irrelevant but still million dollar question....
Irrelevant not because it is a bad question but because you are comparing unknowns with unknowns as most that are poor haven't bothered with offering any WOB data. The same can be said for a number of manufacturers that only ship units with a DSV whose component WOB is unknown.
Some are advertised as being good performers until you benchmark them against alternatives. The Shrimp being a case in point.
At best for comparison, you might be able to tabulate if a bunch of BOVs pass as a minimum the CE requirements for both OC and CC use.... Not really good enough but all you have to work with until divers make manufacturers supply comparable WOB data from unmanned testing before sales occur.
If it helps from my research, for left to right gas flow the better performers are probably:
Poseidon or Hollis BOVs but with the caveat that neither at the last time I bothered to look have published WOB test data for both OC and CC WOB.
For right to left gas flow the best performer is OSELs ALVBOV by a significant margin.
lizardland
Active Member
How many contenders are thrre in the right to left category? Not hard being best when the field is non existent or tiny.
Anyway, I'm always uncomfortable with human error or not making co2 hits avoidable. If it was avoidable then it would've been avoided. The idea that you can avoid co2 because you wont get something wrong strikes me as hubristic in the extreme.
All my co2 hits were user error. I have no doubt that I will probably have a user error hit again at some point because that's human nature. You never know you are making a mistake til you've made it.
The case Simon cites reminds me of one of mine. The idea of holding my breath to switch regs was completely ridiculous. It genuinely was one of the hardest things I've done underwater. After 2, I think the calmly swap regs drill is dangerous and irresponsible. The actual strength of will it took me to get off the loop really shocked me. You know exactly what you need to do but everything tells you not to do it.
Anyway, I'm always uncomfortable with human error or not making co2 hits avoidable. If it was avoidable then it would've been avoided. The idea that you can avoid co2 because you wont get something wrong strikes me as hubristic in the extreme.
All my co2 hits were user error. I have no doubt that I will probably have a user error hit again at some point because that's human nature. You never know you are making a mistake til you've made it.
The case Simon cites reminds me of one of mine. The idea of holding my breath to switch regs was completely ridiculous. It genuinely was one of the hardest things I've done underwater. After 2, I think the calmly swap regs drill is dangerous and irresponsible. The actual strength of will it took me to get off the loop really shocked me. You know exactly what you need to do but everything tells you not to do it.
Andy Del
still causing trouble!
If it helps the OP, I've been diving rebreathers since about 2005 (I've forgotten!) and never had a CO2 hit. I have also dived with a BOV on every rebreather I have ever dived. These days with a gag as well. I use a checklist to prep my units each and every time.
What does this mean? I've been lucky so far. Luck due to diligence? Possibly...
cheers
Andy
What does this mean? I've been lucky so far. Luck due to diligence? Possibly...
cheers
Andy
Mark Chase
ATB=AlwaysTalkingBollocks
I convinced my mate Howard to buy a BOV
In Mallin Head in 2009 he had a C02 incident and had to bailout. Post dive he thanked me for the BOV sugestion and said biling without one would have been impossable
Another friend had a C02 hit and couldent bailout on to the reg he was holding in his hand and looking at. Instead he inflated his BCD and shot to the surface as he felt it was his only option.
Its a no brainer for me
ATB
Mark
In Mallin Head in 2009 he had a C02 incident and had to bailout. Post dive he thanked me for the BOV sugestion and said biling without one would have been impossable
Another friend had a C02 hit and couldent bailout on to the reg he was holding in his hand and looking at. Instead he inflated his BCD and shot to the surface as he felt it was his only option.
Its a no brainer for me
ATB
Mark
Mark Chase
ATB=AlwaysTalkingBollocks
Stuart, Re-look at it without bias. A fair number of BOVs have been designed such that you can reverse the loop flow.
In one recent notable instance in the Channel Is, an element of this on a non CE'd prototype unit was perhaps seen to not be the best design decision...
but reversible flow BOVs seem to be quite popular. IIRC a quote attributed to the GG Shrimp was they can't keep them on the shelves, they are selling so well.
That BOV on a left to right flow unit, probably performs nearly as well as some of their competition. We will never know how well until GG, Poseidon and Hollis bother to conduct and publish unmanned WOB testing on their BOVs to the same criteria.
On a right to left flow unit, like your Mk15, it in comparison to an alternative, performs quite poorly. As in the CC WOB of the BOV alone is in the order of 2.5 times as much!
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!
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? Making an inlet valve an exhaust and vice versa seems like it wouldn't change anything as the actual flappers are exactly the same (on most DVSs and BOVs as far as I know). Can you elaborate here?
Mike Ferguson
WTF is that?
you misread it. I suspect Brad means that it's not as good as his BOV which is only available right to left.
though if there is no testing done on the shrimp how would you know an alternative is 2.5 times better?
though if there is no testing done on the shrimp how would you know an alternative is 2.5 times better?
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