How helpful would a CO2 monitor really be?

abowie · 10th August 2006, 06:54

I believe that any device that reliably tells you that the PCO2 in your loop has gone above a predetermined level is a very useful device indeed. It would remove some of the uncertainty in the "I feel terrible all of a sudden" scenario.

To be useful though, a monitor needs to be reliable, accurate and robust. It needs to give you the data loudly and correctly the instant it is triggered.

Equally importantly, it must NOT not go off when it shouldn't, or fail to when it should. A monitor that isn't reliable is worse than no monitor at all.

Tim Cashman · 10th August 2006, 08:17

If a CO2 detector were fitted to the stack outlet, it has been argued that the time between CO2 breakthrough, and the alarm activating, would be too short for the diver to react, before being overexposed to CO2?

So rather than placing the CO2 detector at the stack outlet, could it be placed in a cavity, say 3/4ths up the stack, so when CO2 breakthrough ocurred at that point, the alarm would sound, but the diver would still have a "reserve" of stack he could keep using before being overexposed to CO2?

Tim

jasondrake · 10th August 2006, 09:03

I'm not convinced about the speed of 'hits'. I've had various co2 hits on open and closed circuit and while all disconcerting none knocked me out, or even close. Try breathing into a plastic bag. It takes several breaths before you start feeling woozy, and several more before you want to sit down. While ppco2 obviously changes things I suspect that a rapid reacting sensor which was reliable would be a huge plus.

Woz · 10th August 2006, 09:49

Quote: (Originally Posted by Mdemon)

I think there is more to it than that. Ever tried this? Drink half a large bottle of coke. Give it a gentle swirl to get some bubbles going then squeeze the bottle and inhale at the same time (not the coke!). That's pretty much neat CO2 and it's effects are almost instant. But!!!! We never get that, since we will always have O2 and N2 in the loop and the O2 being in fairly constant amounts. Remember my "non-scrubber" test above - a million miles from the 'coke' hit.

Just tried that with a bottle of Tescos Cranberry Kick. Cor.

Scubascooby · 10th August 2006, 12:55

A few days ago I was watching a repeat of that TV programme where they
built a replica of a wooden submarine that was orignally rowed along under
the River Thames.

In the reconstruction, two guys rowed it. Inside the sub they had a CO2
alarm. They were still rowing stringly when the alarm went off. Similarly in
early lab trials one of them was using a rowing machine and breathiing in/out
of a large bag to replicate the volume of the sub. The alarm went off but
he was still rowing strongly.

From this I infer that the safe limit is much lower than the level at which we
become aware of CO2 in our breathing gas and so well below the level at
which any severe hit would occur.

The rebreather hyperbaric situation is slightly different but I would still expect
a CO2 alarm to occur before I felt any effects, allowing the diver to bail-out
safely.

**Gill Envy** · 10th August 2006, 18:28

i appreciate all the input. maybe someone with more specific knowledge of PCo2 limits could tell us what the agreed upon thresholds are and how fast a winded diver could cuase breakthrough in a standard inspiration size canister still well within it's rating, substantial enough to cause symptoms and ultimately loss of consciousness. It think it would be helpful to have spelled out what percent of gas mix change that would represent at say 40 fsw, 100fsw and 200fsw respectively. I'm thinking that the change in gas ratio is minute compared to the O2 and nitrogen in the loop. I still have my doubts that we are capable of making a reliable instrument that can detect such minute fluctuations quickly enough to catch a dangerous breakthrough. but i'm all ears.
;~)

Mdemon · 10th August 2006, 18:36

Quote: (Originally Posted by Gillenvy)

i appreciate all the input. maybe someone with more specific knowledge of PCo2 limits could tell us what the agreed upon thresholds are and how fast a winded diver could cuase breakthrough in a standard inspiration size canister still well within it's rating, substantial enough to cause symptoms and ultimately loss of consciousness. It think it would be helpful to have spelled out what percent of gas mix change that would represent at say 40 fsw, 100fsw and 200fsw respectively. I'm thinking that the change in gas ratio is minute compared to the O2 and nitrogen in the loop. I still have my doubts that we are capable of making a reliable instrument that can detect such minute fluctuations quickly enough to catch a dangerous breakthrough. but i'm all ears.
;~)

Not wishing to be picky, but AP have tested the Inspo cannister at some incredibly high RMVs within its rating. You're talking about an out-of-tolerance event here...

Do you need to know exact values? Wouldn't "there is CO2 in the loop" be enough? IIRC, there is zero CO2 with a functioning Inspo scrubber.

E-man · 10th August 2006, 23:15

While the tested limits of rebreathers is 0.5% (pco2 0.005) it is not until 10% (pco2 0.1) that most will likely loose consciousness (lower levels for longer periods of exposure).

...........DEPTH.......................0.5% SEV............unconsciousness.......

1 ata............0fsw............0.5%.......0.005pco 2........10%........0.1pco2
3 ata............66fsw...........0.167%...0.005pco2. .......3.333%....0.1pco2
5 ata............132fsw.........0.1%.......0.005pco2 .........2%........0.1pco2
6 ata............165fsw.........0.83%......0.005pco2 ........1.67%.....0.1pco2
10 ata...........297fsw.........0.05%......0.005pco2. .......1%........0.1pco2

E-man · 10th August 2006, 23:20

Quote: (Originally Posted by Mdemon)

Not wishing to be picky, but AP have tested the Inspo cannister at some incredibly high RMVs within its rating. You're talking about an out-of-tolerance event here....

What really high RMV rated duration testing done by AP are you refering to? Other than the 40RMV?

**Gill Envy** · 10th August 2006, 23:51

Quote: (Originally Posted by E-man)

While the tested limits of rebreathers is 0.5% (pco2 0.005) it is not until 10% (pco2 0.1) that most will likely loose consciousness (lower levels for longer periods of exposure).

...........DEPTH.......................0.5% SEV............unconsciousness.......

1 ata............0fsw............0.5%.......0.005pco 2........10%........0.1pco2
3 ata............66fsw...........0.167%...0.005pco2. .......3.333%....0.1pco2
5 ata............132fsw.........0.1%.......0.005pco2 .........2%........0.1pco2
6 ata............165fsw.........0.83%......0.005pco2 ........1.67%.....0.1pco2
10 ata...........297fsw.........0.05%......0.005pco2. .......1%........0.1pco2

awsome, thanks for that. indeed it is sobering to see that as little as 1% CO2 on a deep dive can be the end of you. It's kind of unfathomable to me to think that anyone can, and apparently has, designed something that sensitive and compact enough to fit into the electronics package of your average rebreather... It's an even more seemingly insurmountable challenge to detect even smaller amounts which would be necessary to give someone time to react. I'm still a bit dubious, but mostly intrigued. very interested to see this thing when it comes out.

10th August 2006, 06:54	#11 (permalink)
abowie Fighting Girl Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: May 2005 Location: Land of Oz Posts: 573	Re: How helpful would a CO2 monitor really be? I believe that any device that reliably tells you that the PCO2 in your loop has gone above a predetermined level is a very useful device indeed. It would remove some of the uncertainty in the "I feel terrible all of a sudden" scenario. To be useful though, a monitor needs to be reliable, accurate and robust. It needs to give you the data loudly and correctly the instant it is triggered. Equally importantly, it must NOT not go off when it shouldn't, or fail to when it should. A monitor that isn't reliable is worse than no monitor at all. __________________ Andrew Bowie Rebreather-friendly Buddy Last edited by abowie : 10th August 2006 at 12:15. Reason: removed allusions to ancient Greek mythology. Happy now are we Steve?
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10th August 2006, 08:17	#12 (permalink)
Tim Cashman New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Aug 2005 Location: Wales Posts: 55	Re: How helpful would a CO2 monitor really be? If a CO2 detector were fitted to the stack outlet, it has been argued that the time between CO2 breakthrough, and the alarm activating, would be too short for the diver to react, before being overexposed to CO2? So rather than placing the CO2 detector at the stack outlet, could it be placed in a cavity, say 3/4ths up the stack, so when CO2 breakthrough ocurred at that point, the alarm would sound, but the diver would still have a "reserve" of stack he could keep using before being overexposed to CO2? Tim __________________ Iechyd da
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10th August 2006, 09:03	#13 (permalink)
jasondrake New Member Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Nov 2005 Location: Completely homeless Posts: 75	Re: How helpful would a CO2 monitor really be? I'm not convinced about the speed of 'hits'. I've had various co2 hits on open and closed circuit and while all disconcerting none knocked me out, or even close. Try breathing into a plastic bag. It takes several breaths before you start feeling woozy, and several more before you want to sit down. While ppco2 obviously changes things I suspect that a rapid reacting sensor which was reliable would be a huge plus.
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10th August 2006, 09:49	#14 (permalink)
Woz Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Jun 2005 Location: Nottingham Posts: 185	Re: How helpful would a CO2 monitor really be? Quote: (Originally Posted by Mdemon) I think there is more to it than that. Ever tried this? Drink half a large bottle of coke. Give it a gentle swirl to get some bubbles going then squeeze the bottle and inhale at the same time (not the coke!). That's pretty much neat CO2 and it's effects are almost instant. But!!!! We never get that, since we will always have O2 and N2 in the loop and the O2 being in fairly constant amounts. Remember my "non-scrubber" test above - a million miles from the 'coke' hit. Just tried that with a bottle of Tescos Cranberry Kick. Cor. __________________ Still punting shiny diving tatt to gullible divers www.kitfondle.co.uk
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10th August 2006, 12:55	#15 (permalink)
Scubascooby Better Off Out of the EU Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Nov 2005 Location: Great Britain Posts: 367	Re: How helpful would a CO2 monitor really be? A few days ago I was watching a repeat of that TV programme where they built a replica of a wooden submarine that was orignally rowed along under the River Thames. In the reconstruction, two guys rowed it. Inside the sub they had a CO2 alarm. They were still rowing stringly when the alarm went off. Similarly in early lab trials one of them was using a rowing machine and breathiing in/out of a large bag to replicate the volume of the sub. The alarm went off but he was still rowing strongly. From this I infer that the safe limit is much lower than the level at which we become aware of CO2 in our breathing gas and so well below the level at which any severe hit would occur. The rebreather hyperbaric situation is slightly different but I would still expect a CO2 alarm to occur before I felt any effects, allowing the diver to bail-out safely. __________________ "dove" is NOT the past tense of "dive" Better off OUT of the EU !
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10th August 2006, 18:28	#16 (permalink)
Gill Envy Shearwater Copis Diver Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,302	Re: How helpful would a CO2 monitor really be? i appreciate all the input. maybe someone with more specific knowledge of PCo2 limits could tell us what the agreed upon thresholds are and how fast a winded diver could cuase breakthrough in a standard inspiration size canister still well within it's rating, substantial enough to cause symptoms and ultimately loss of consciousness. It think it would be helpful to have spelled out what percent of gas mix change that would represent at say 40 fsw, 100fsw and 200fsw respectively. I'm thinking that the change in gas ratio is minute compared to the O2 and nitrogen in the loop. I still have my doubts that we are capable of making a reliable instrument that can detect such minute fluctuations quickly enough to catch a dangerous breakthrough. but i'm all ears. ;~) __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
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10th August 2006, 18:36	#17 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,906	Re: How helpful would a CO2 monitor really be? Quote: (Originally Posted by Gillenvy) i appreciate all the input. maybe someone with more specific knowledge of PCo2 limits could tell us what the agreed upon thresholds are and how fast a winded diver could cuase breakthrough in a standard inspiration size canister still well within it's rating, substantial enough to cause symptoms and ultimately loss of consciousness. It think it would be helpful to have spelled out what percent of gas mix change that would represent at say 40 fsw, 100fsw and 200fsw respectively. I'm thinking that the change in gas ratio is minute compared to the O2 and nitrogen in the loop. I still have my doubts that we are capable of making a reliable instrument that can detect such minute fluctuations quickly enough to catch a dangerous breakthrough. but i'm all ears. ;~) Not wishing to be picky, but AP have tested the Inspo cannister at some incredibly high RMVs within its rating. You're talking about an out-of-tolerance event here... Do you need to know exact values? Wouldn't "there is CO2 in the loop" be enough? IIRC, there is zero CO2 with a functioning Inspo scrubber. __________________ www.southwestmafia.com "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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10th August 2006, 23:15	#18 (permalink)
E-man On the loop! Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Titan Join Date: Sep 2005 Location: Eastern Coast ;) Posts: 212	Re: How helpful would a CO2 monitor really be? While the tested limits of rebreathers is 0.5% (pco2 0.005) it is not until 10% (pco2 0.1) that most will likely loose consciousness (lower levels for longer periods of exposure). ...........DEPTH.......................0.5% SEV............unconsciousness....... 1 ata............0fsw............0.5%.......0.005pco 2........10%........0.1pco2 3 ata............66fsw...........0.167%...0.005pco2. .......3.333%....0.1pco2 5 ata............132fsw.........0.1%.......0.005pco2 .........2%........0.1pco2 6 ata............165fsw.........0.83%......0.005pco2 ........1.67%.....0.1pco2 10 ata...........297fsw.........0.05%......0.005pco2. .......1%........0.1pco2 Last edited by E-man : 10th August 2006 at 23:18.
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10th August 2006, 23:20	#19 (permalink)
E-man On the loop! Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Titan Join Date: Sep 2005 Location: Eastern Coast ;) Posts: 212	Re: How helpful would a CO2 monitor really be? Quote: (Originally Posted by Mdemon) Not wishing to be picky, but AP have tested the Inspo cannister at some incredibly high RMVs within its rating. You're talking about an out-of-tolerance event here.... What really high RMV rated duration testing done by AP are you refering to? Other than the 40RMV?
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10th August 2006, 23:51	#20 (permalink)
Gill Envy Shearwater Copis Diver Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,302	Re: How helpful would a CO2 monitor really be? Quote: (Originally Posted by E-man) While the tested limits of rebreathers is 0.5% (pco2 0.005) it is not until 10% (pco2 0.1) that most will likely loose consciousness (lower levels for longer periods of exposure). ...........DEPTH.......................0.5% SEV............unconsciousness....... 1 ata............0fsw............0.5%.......0.005pco 2........10%........0.1pco2 3 ata............66fsw...........0.167%...0.005pco2. .......3.333%....0.1pco2 5 ata............132fsw.........0.1%.......0.005pco2 .........2%........0.1pco2 6 ata............165fsw.........0.83%......0.005pco2 ........1.67%.....0.1pco2 10 ata...........297fsw.........0.05%......0.005pco2. .......1%........0.1pco2 awsome, thanks for that. indeed it is sobering to see that as little as 1% CO2 on a deep dive can be the end of you. It's kind of unfathomable to me to think that anyone can, and apparently has, designed something that sensitive and compact enough to fit into the electronics package of your average rebreather... It's an even more seemingly insurmountable challenge to detect even smaller amounts which would be necessary to give someone time to react. I'm still a bit dubious, but mostly intrigued. very interested to see this thing when it comes out. __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
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