+ Reply to Thread
Page 1 of 3 1 2 3 LastLast
Results 1 to 10 of 25

Thread: WOB difference between air and trimix

  1. #1
    Dave Tomblin wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc's Avatar
    Join Date
    Feb 2005
    Location
    Vancouver Island BC Canada
    Posts
    3,789
    Hollis Prism 2, Megalodon

    CCR Instructor Trainer

    WOB difference between air and trimix

    Has anyone seen a direct comparison between WOB effort in a rebreather using helium vs straight air diluent?
    I am hoping for some numbers if it has in fact been studied.
    Cheers,

    Dave....

    www.wedivebc.com

  2. #2
    RBW Member michael-fisch is on a distinguished road michael-fisch is on a distinguished road michael-fisch's Avatar
    Join Date
    Feb 2006
    Location
    Germany
    Posts
    333
    SF2, IDA76, Flex

    AH1

    Re: WOB difference between air and trimix

    no numbers, but I only did 1 dive using air in my SF2. Filled with 797 the WOB was, for me, unacceptable. Since then I've done over 150 dives using at least 35% He in my diluent and find the WOB acceptable.
    The best way to check is by using a long thin sorb cannester (non radial) filled to the lid with small grained sorb, without He everything listed is working against you.

    Michael

  3. #3
    RBW Member tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining's Avatar
    Join Date
    May 2005
    Location
    Asia, Europe & Mexico
    Posts
    1,144
    Hammerhead, SF2, Megalodon, JJ

    Boris, Sentinel, Inspiration,

    Re: WOB difference between air and trimix

    I have never seen any data sheets but i really cannot notice it on any of the rigs i dive currently and try to avoid CCR that i like sucking treacle though a straw in the first place

  4. #4
    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
    Join Date
    May 2005
    Location
    New Zealand
    Posts
    683

    Re: WOB difference between air and trimix

    Quote Originally Posted by wedivebc  View Original Post
    Has anyone seen a direct comparison between WOB effort in a rebreather using helium vs straight air diluent?
    I am hoping for some numbers if it has in fact been studied.

    Dave,


    There is no doubt that such a measurement would reveal a lower work of breathing for helium. All other things kept equal, the degree of WOB reduction would be entirely dependent on the density of air vs the helium mix which in turn is dependent on the depth at which the gases are used and composition of the helium-based gas.


    The most relevant question, therefore, is what gas density is acceptable in rebreather diving. With this knowledge, divers could plan the composition their gases appropriately for their target depth. Gavin Anthony from QinetiQ and I are about to publish an article which is the first (to my knowledge) that substantially addresses this question. It presents Gavin's data from hundreds of test dives at QinetiQ, and will appear in the Proceedings of the Rebreather Workshop run by NOAA and the US National Parks Service at Catalina just over a year ago. Neal Pollock is the editor. I will link to the article as soon as it is published. I'm virtually certain the proceedings will be made available on line. Neal is visiting our lab here in NZ on Monday so I will ask him how it is going.


    Basically, to put it as simply as possible, Gavin found a sharp inflection in the risk of dangerous CO2 retention in working immersed divers when the gas density exceeded 6g/L.


    I will provide more detail when the article is published, but these are very important data that will (for the first time) provide an objective guideline for planning gas mixes to minimise the risk of CO2 retention.


    Simon M

  5. #5
    RBW Member matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram's Avatar
    Join Date
    Aug 2007
    Location
    london
    Posts
    738
    inspiration

    Re: WOB difference between air and trimix

    Quote Originally Posted by Simon Mitchell  View Original Post
    Basically, to put it as simply as possible, Gavin found a sharp inflection in the risk of dangerous CO2 retention in working immersed divers when the gas density exceeded 6g/L.
    Did you find 6g/L surprising, Simon? It's quite low:

    Air - 37m - 6.05g/L
    10/52 - 75m - 6.05g/L
    6/72 - 113m - 6.05g/L

    Look forward to the output, as always.

    Do you make any comparison/variation to the limits that Dan Warkander proposed?

    http://www.dtic.mil/dtic/tr/fulltext/u2/a550047.pdf

    Cheers
    Matt.

  6. #6
    RBW Member ECho is an unknown quantity at this point ECho's Avatar
    Join Date
    Jun 2014
    Location
    Marina del Rey, CA
    Posts
    98
    rEvo Micro FT

    Meg

    Re: WOB difference between air and trimix

    Quote Originally Posted by matthewoutram  View Original Post
    Did you find 6g/L surprising, Simon? It's quite low:

    Air - 37m - 6.05g/L
    10/52 - 75m - 6.05g/L
    6/72 - 113m - 6.05g/L
    Anyone feel free to correct me if I'm wrong on this, but wouldn't being on a rebreather, potentially, exacerbate gas density related CO2 retention? The above numbers would be for the diluent, yes? It seems to me that adding, relatively, denser O2 to maintain PO2 would skew the gas density value upwards, making the depth at which 6g/L occurs just that much shallower? Depending on the exact shape of the inflection, couldn't that mean that even a small shift in depth might create a significantly greater shift in CO2 retention?

    Apologies, if I'm way off base... Just trying to be a bit smarter about my diving.

  7. #7
    RBW Member matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram's Avatar
    Join Date
    Aug 2007
    Location
    london
    Posts
    738
    inspiration

    Re: WOB difference between air and trimix

    Quote Originally Posted by ECho  View Original Post
    Anyone feel free to correct me if I'm wrong on this, but wouldn't being on a rebreather, potentially, exacerbate gas density related CO2 retention? The above numbers would be for the diluent, yes? It seems to me that adding, relatively, denser O2 to maintain PO2 would skew the gas density value upwards, making the depth at which 6g/L occurs just that much shallower? Depending on the exact shape of the inflection, couldn't that mean that even a small shift in depth might create a significantly greater shift in CO2 retention?

    Apologies, if I'm way off base... Just trying to be a bit smarter about my diving.
    Correct, the calculation above is for OC. The depth at which a 10/52 diluent would be 6g/L with a SP of 1.3 is 69m.

    e.g.:

    10/52 @ 69m SP=1.3 is actually 16/48.

    The depth at which 16/48 is 6g/L is 69m.

    16.5/48.3 - 69.4m - 6.05g/L

    The 6/72 is reduced to 100m also at SP=1.3.

    Matt.
    Last edited by matthewoutram; 9th April 2016 at 21:45.

  8. #8
    RBW Member Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1 has a reputation beyond repute Gobfish1's Avatar
    Join Date
    Apr 2005
    Location
    on the grassy knoll
    Posts
    1,455
    ybod

    Re: WOB difference between air and trimix

    Quote Originally Posted by matthewoutram  View Original Post
    Correct, the calculation above is for OC. The depth at which a 10/52 diluent would be 6g/L with a SP of 1.3 is 69m.

    e.g.:

    10/52 @ 69m SP=1.3 is actually 16/48.

    The depth at which 16/48 is 6g/L is 69m.

    16.5/48.3 - 69.4m - 6.05g/L

    The 6/72 is reduced to 100m also at SP=1.3.

    Matt.
    In a older post by simon im sure i read 8g/L as the line the sand maybe i read it wrong , Think it was in a wet mules thread ,

    also this is WORKING divers , so how hard are we working them ,

    6/72 Bangs on 20/30min,s more deco ,
    Last edited by Gobfish1; 10th April 2016 at 06:20.

  9. #9
    Escaped... Lab Rat is an unknown quantity at this point Lab Rat's Avatar
    Join Date
    Oct 2005
    Location
    Memphis, TN, USA
    Posts
    62
    Meg Driver

    Re: WOB difference between air and trimix

    Maybe just new data?

    Either way, thanks for putting this out Simon!

    Also, know that Brett Stolp has a bunch of data on this from the early 80s dives at the chamber, but, as I recall, it is all about max tolerable density and not density at which CO2 retention increases. They did pull blood gasses at depth though and that included the workup dives if I remember right.


    -Richard


    Is it a laminar flow thing through smaller bronchiols and disrupted gas flow into alveoli due to increased density alone?



    where:
    inlet pressure
    outlet pressure
    is the length of tube
    is the viscosity
    is the radius
    is the volume of the fluid at outlet pressure
    is the velocity of the fluid at outlet pressure

  10. #10
    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
    Join Date
    Jan 2005
    Location
    Kent
    Posts
    5,205
    JJ Hybrid

    Inspo, Hammer Head, KISS rEvo

    Re: WOB difference between air and trimix

    Quote Originally Posted by Lab Rat  View Original Post
    Maybe just new data?

    Either way, thanks for putting this out Simon!

    Also, know that Brett Stolp has a bunch of data on this from the early 80s dives at the chamber, but, as I recall, it is all about max tolerable density and not density at which CO2 retention increases. They did pull blood gasses at depth though and that included the workup dives if I remember right.


    -Richard


    Is it a laminar flow thing through smaller bronchiols and disrupted gas flow into alveoli due to increased density alone?



    where:
    inlet pressure
    outlet pressure
    is the length of tube
    is the viscosity
    is the radius
    is the volume of the fluid at outlet pressure
    is the velocity of the fluid at outlet pressure

    Ocasionaly I find myself thinking I am quite intelegent then somone posts something like this and i railise I am not even close :D

+ Reply to Thread
Page 1 of 3 1 2 3 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts