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Thread: CO2 sensors for CCR units

  1. #1
    Muddiver Muddiver is an unknown quantity at this point Muddiver's Avatar
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    CO2 sensors for CCR units

    Does anyone have any experience in adding a CO2 sensor to their CCR? Except for the new Hollis SCR, I'm not aware of any rigs that come with CO2 monitoring capability. With most of the accidents on rebreathers occurring from scrubber issues, I would think a CO2 alarm would be a good idea. Any thoughts.


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    RBW Member 1Digger is an unknown quantity at this point 1Digger's Avatar
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    Re: CO2 sensors for CCR units

    As I understan Hollis Co2 sensor turns the unit on (according to Australian presentations).
    There are now a number or rebreathers fitted with CO2 sensors.
    Submatix have them as an option, Proteus P3 from Dive systems UK will have them and there are others.
    Also Techme.de have these as a add on item for most units.
    http://www.tecme.de/frame_start1.htm.
    Personally I think Co2 sensor acts as "the red light flashing you are almost out of fuel light".
    by then its too late.
    It is better to stick to manufactors' recomended time as soda lime is cheap compared to a life.

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    Muddiver Muddiver is an unknown quantity at this point Muddiver's Avatar
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    Re: CO2 sensors for CCR units

    I see any alarm that reads something you can't feel as an "Oh s**t!" Bail out! warning. I did see the tecme gear and that is one of the reasons I was asking the question. Thanks for the comment and I agree that one should stick with the manufacturer's specified scrubber duration.


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    Supporting Member Karl_H is an unknown quantity at this point Karl_H's Avatar
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    Re: CO2 sensors for CCR units

    The new X-CCR has CO2 detection too, although I'd completely agree with what 1digger says above that is simply a warning that may well be too late to respond to once it occurs.

    The other thing to consider is what would happen if the DSV/BOV one-way valves are the problem as opposed to the scrubber - The CO2 sensor is unlikely to show a problem in this case so could inadvertently keep the diver on the loop, the sensor would show no CO2 problem when there is actually a very serious one occurring.

    Given the problems above it still seems like a nice to have rather than an essential part of a unit.

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    RBW Member SlowDiver will become famous soon enough SlowDiver will become famous soon enough SlowDiver will become famous soon enough SlowDiver's Avatar
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    Re: CO2 sensors for CCR units

    Quote Originally Posted by Karl_H  View Original Post
    The new X-CCR has CO2 detection too, although I'd completely agree with what 1digger says above that is simply a warning that may well be too late to respond to once it occurs.

    The other thing to consider is what would happen if the DSV/BOV one-way valves are the problem as opposed to the scrubber - The CO2 sensor is unlikely to show a problem in this case so could inadvertently keep the diver on the loop, the sensor would show no CO2 problem when there is actually a very serious one occurring.

    Given the problems above it still seems like a nice to have rather than an essential part of a unit.
    If the one-way valves (mushroom) were the culprit would not the bad gas also be present in the unit where the CO2 sensor is located? I ask this question because I've had my mushroom valves fail due to duck weed blocking them from sealing completely. Did take a CO2 hit.


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    RBW Member Poltsi is an unknown quantity at this point Poltsi's Avatar
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    Re: CO2 sensors for CCR units

    Adding to 1digger's list:

    Sentinel. AFAIK for older models the CO2-module was optional (except for really old which did not have the place for it) and the Expedition model had it by default.

    The new Red Head seems to come by default with the CO2-module.

    A recent anecdote:

    I was doing a mine dive with my buddy, nothing fancy. I had a used scrubber in the unit for which the unit indicated a usage-% of ~50%. It should have been enough for our 100min dive.

    We were coming close to the turnpoint on 38m level and I had already passed a restriction. I turned around to see how my buddy is doing when I got a warning that the pCO2 was over 5mbar.

    My buddy was struggling with the restriction so I just noted the warning, and went to help him. After a couple of retries we gave up, showed the turn-around sign with the distinction that we now rose up to the 28m level so that the pCO2 would lower as it did. We later came to a Y-junction where we had originally planned to continue to another direction. I signaled that we will exit the mine.

    Later in the open water, while doing decompression, I got several times the pCO2-warning, with values between 5-9.3mBar.

    When I exited the water and brought in the unit in the warm (the air temp was around -15⁰Ĉ), the handset indicated that I still would have some 30% left of the scrubber.

    During the whole period from first warning to exiting the water, I kept a close eye both on the reading of the CO2-module as well as my breathing rhythm and based on that decided to not do a bailout.

    The initial decision to stay on the loop was also partially because I did not want to stress my buddy too much while he was trying to pass the restriction. I also did keep in mind what my instructors taught about hypercapnia under higher pressures.

    Anyhow, I think that CO2-module is a good addition to the CCR equipment, but the diver should, as Karl_H notes, not rely it to show when everything is ok. The unit may be showing false positives.

    FWIW I changed the sorb on the unit and completed another dive that day. No issue with CO2 then.

    Anyhow, I think knowing what the alert is, is quite essential. I would also recommend this video from DAN, especially from 10:45 forward.

    Poltsi

  7. #7
    Supporting Member Karl_H is an unknown quantity at this point Karl_H's Avatar
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    Re: CO2 sensors for CCR units

    Quote Originally Posted by SlowDiver  View Original Post
    If the one-way valves (mushroom) were the culprit would not the bad gas also be present in the unit where the CO2 sensor is located? I ask this question because I've had my mushroom valves fail due to duck weed blocking them from sealing completely. Did take a CO2 hit.


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    This all depends on the positioning of the sensor, the the sensor is located in the head or between the head and the inhale side counter lung as it normally seems to be positioned I wouldn't imagine it would pick up any notable rise in CO2 compared to what was leaving the mouthpiece.

    If air was traveling between the mouthpiece and exhale side of the loop I think the flow over the sensor on the exhale side would be minimal also. Even if some flow is still coming over the sensor it would be scrubbed air so shouldn't have a high CO2 content.

    The above info is based on what I can see from the sensor position as opposed to actual experience, however it does seem to potentially propose significant problem to any diver flying the unit with complete faith in such a sensor?

  8. #8
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    Re: CO2 sensors for CCR units

    I have the inspiration one but it is giving so many false-positives I don't listen to it anymore :-(

    The tempstick is great though, lets you get 8h from the scrubber in 29c.

    Matt.

  9. #9
    RBW Member jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner is a glorious beacon of light jturner's Avatar
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    Re: CO2 sensors for CCR units

    Quote Originally Posted by matthewoutram  View Original Post
    I have the inspiration one but it is giving so many false-positives I don't listen to it anymore :-(

    The tempstick is great though, lets you get 8h from the scrubber in 29c.
    On the other hand, I also have an APD one and it has never given me a false positive! Long may that continue!

  10. #10
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    Re: CO2 sensors for CCR units

    Quote Originally Posted by jturner  View Original Post
    On the other hand, I also have an APD one and it has never given me a false positive! Long may that continue!
    I've had a situation where this sensor did work, but since the 2020 it does not work.

    I'm pretty sure it's the sensor as the alarm was in the first 4 hours and the scrubber went on to do 8 without any symptoms!

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