+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 10 of 13

Thread: A helium in CCR question

  1. #1
    RBW Member Mike_Eitel is an unknown quantity at this point Mike_Eitel's Avatar
    Join Date
    May 2006
    Location
    Switzerland
    Posts
    220
    MeCCRxWi

    MeRAY, MeTravox,MeCCRV"x,Inspi

    A helium in CCR question

    Hi
    I'm not an expert in He diving. But since longer time I'm wondering the mixture behavior in a closed loop:

    a. Lets make it easy and use f.x. 0/50 trimix = 50 N2 & 50% He.
    b. have an perfect CCR, nit loosing any diluent to environment.
    c. now diving to f.x 40m.

    As I understand HE is going faster in and out of my body than N2. And in my understanding, this must change the mix in my loop. pp of He will degrade and N2 will have a higher percentage than He.

    As my body consumes gas from the loop, finally II have to inject the equal mix diluent…
    It will rise the He part in the loop.

    That way I’m loading my body with more He then in OC with the same mix ???

    I’m aware that this example might be academic, but I’m wondering if anybody ever tried to measure this in real diving and had a look into the eventual outcome for decompression calculations.

  2. #2
    RBW Member trakrat is on a distinguished road trakrat is on a distinguished road trakrat's Avatar
    Join Date
    Oct 2008
    Location
    the peoples republic of yorkshire
    Posts
    164
    rEvo

    Re: A helium in CCR question

    Quote Originally Posted by Mike_Eitel  View Original Post
    Hi
    I'm not an expert in He diving. But since longer time I'm wondering the mixture behavior in a closed loop:

    a. Lets make it easy and use f.x. 0/50 trimix = 50 N2 & 50% He.
    b. have an perfect CCR, nit loosing any diluent to environment.
    c. now diving to f.x 40m.

    As I understand HE is going faster in and out of my body than N2. And in my understanding, this must change the mix in my loop. pp of He will degrade and N2 will have a higher percentage than He.

    As my body consumes gas from the loop, finally II have to inject the equal mix diluent…
    It will rise the He part in the loop.

    That way I’m loading my body with more He then in OC with the same mix ???

    I’m aware that this example might be academic, but I’m wondering if anybody ever tried to measure this in real diving and had a look into the eventual outcome for decompression calculations.
    this is something that should show up in the appoc when it is released!
    it has a he sensor so will monitor this and log it !
    try asking brad or dave as they have there hands on the appoc !

  3. #3
    RBW Member Wol is just really nice Wol is just really nice Wol is just really nice Wol is just really nice Wol is just really nice Wol is just really nice Wol is just really nice Wol is just really nice Wol is just really nice Wol's Avatar
    Join Date
    Oct 2007
    Location
    UK
    Posts
    433

    Re: A helium in CCR question

    It would be interesting to get a feel as to what volume of free He or N2 is absorbed into the average human body when saturated. This would give a gauge as to what volume of inert gases we are talking about and whether this is of any consequence to the diver decompressing and holding a perfect loop with no flushing. - Any bidders out there?

  4. #4
    Jakob Selbing jaksel will become famous soon enough jaksel will become famous soon enough jaksel will become famous soon enough jaksel's Avatar
    Join Date
    Oct 2008
    Location
    Stockholm
    Posts
    178
    AP Evolution+

    Re: A helium in CCR question

    EDIT: I realized I made a mistake, I will redo the math...
    Last edited by jaksel; 23rd November 2009 at 17:14.

  5. #5
    RBW Member Kermit has a spectacular aura about Kermit has a spectacular aura about Kermit has a spectacular aura about Kermit has a spectacular aura about Kermit has a spectacular aura about Kermit has a spectacular aura about Kermit's Avatar
    Join Date
    Apr 2007
    Location
    Hexham, Northumberland
    Posts
    176
    Submatix mCCR

    Re: A helium in CCR question

    A typical human, fully saturated at 1 atm holds about a litre of N2.

    Quote Originally Posted by Wol  View Original Post
    It would be interesting to get a feel as to what volume of free He or N2 is absorbed into the average human body when saturated. This would give a gauge as to what volume of inert gases we are talking about and whether this is of any consequence to the diver decompressing and holding a perfect loop with no flushing. - Any bidders out there?

  6. #6
    RBW Member nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh's Avatar
    Join Date
    Mar 2005
    Posts
    1,382

    Re: A helium in CCR question

    Quote Originally Posted by ianfirmin  View Original Post
    A typical human, fully saturated at 1 atm holds about a litre of N2.
    Woo....
    Where did that come from?
    I spent ages trying to come up with a number and ended up at about 1.2L but with very little confidence in the factors I'd used. Finding somebody else is within a factor of 10 would be good. This is cool. :D

    Certainly if this is the case we aren't going to see much loop change as we gas on and off.
    I got similar final volumes for helium but just about three times as fast.

  7. #7
    Normal people worry me jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap is a name known to all jaap's Avatar
    Join Date
    Jun 2005
    Location
    Stockholm Sweden
    Posts
    634

    Re: A helium in CCR question

    Quote Originally Posted by nigelh  View Original Post
    Woo....
    Where did that come from?
    I spent ages trying to come up with a number and ended up at about 1.2L but with very little confidence in the factors I'd used. Finding somebody else is within a factor of 10 would be good. This is cool. :D

    Certainly if this is the case we aren't going to see much loop change as we gas on and off.
    I got similar final volumes for helium but just about three times as fast.

    Sounds about right.

    This link is perhaps of interest:
    Rubicon Research Repository: Item 123456789/2892

    Looks like helium has about 70% the solubility of nitrogen in blood.

    Parts of this thread might also be interesting:

    http://www.rebreatherworld.com/showthread.php?t=29410

    /Anders

  8. #8
    Jakob Selbing jaksel will become famous soon enough jaksel will become famous soon enough jaksel will become famous soon enough jaksel's Avatar
    Join Date
    Oct 2008
    Location
    Stockholm
    Posts
    178
    AP Evolution+

    Re: A helium in CCR question

    OK, I made an initial post which I instantly realized was completely wrong. Here's a new one.

    If you look at the constant in Henry's law, dealing with concentration of inert gases at equilibrium, assuming T=298 K and solutant is water:
    K_N2 = 0.01492
    K_He = 0.009051
    At equilibrium your loop (with volume V_loop) will have some unknown pN2_loop, and unknown pHe_loop. The molecular concentrations of N2 and He in your body (volume V_body) will be K_N2 x pN2_loop and K_He x pHe_loop, respectively.

    Since we know that we inject a diluent with equal fractions N2 and He, the total amount (loop + body) of N2 must be equal to total amount of He:

    V_loop x pN2_loop + V_body x (K_N2 x pN2_loop) =
    V_loop x pHe_loop + V_body x (K_He x pHe_loop)

    What you get if you rearrange is:

    pHe_loop = pN2_loop x Q

    where Q = (V_loop + K_N2 x V_body )/(V_loop + K_He x V_body)

    If we assume V_loop = 10 L and V_body = 80 L, we get:

    Q = (10 + 0.01492 x 80)/(10 + 0.009051 x 80) = 1.044

    So the ratio pN2_loop/pHe_loop will be 1/1.044, or 0.4892/0.5108, i.e. N2 contents will be 48.9% and He contents 51.1% at saturation at any depth.

    However this is at equilibrium (i.e. saturation). Since He diffuses more rapidly than N2, the He fraction might initially drop below 50% as He rushes into your body, then rise back up above 50% as N2 slowly diffuses into your body and He is near equilibrium.

    Actually you could use the formula for Q from above to get a worst-case estimate if we assume He reaches equilibrium instantly and N2 has not diffused into body at all:

    Q = (10 + 0)/(10 + 0.009051 x 80) = 0.9325

    so ratio is now 1/0.9325 or 0.5175/0.4825, i.e. 51.75% N2 and 48.25% He. Again, note that this is just a worst-case estimate.

    Please correct me if I'm wrong.

  9. #9
    Jakob Selbing jaksel will become famous soon enough jaksel will become famous soon enough jaksel will become famous soon enough jaksel's Avatar
    Join Date
    Oct 2008
    Location
    Stockholm
    Posts
    178
    AP Evolution+

    Re: A helium in CCR question

    Quote Originally Posted by nigelh  View Original Post
    Woo....
    Where did that come from?
    I spent ages trying to come up with a number and ended up at about 1.2L but with very little confidence in the factors I'd used. Finding somebody else is within a factor of 10 would be good. This is cool. :D
    Just use Henry's law:

    pN2_body = K_N2 x pN2_loop = 0.01492 x 0.79 bar = 0.01179 bar

    Total amount of N2 in body = V_body x pN2_body = 80 L x 0.01179 bar = 0.94 L x bar, i.e. about 0.94 litres of N2 at 1 atmosphere.

  10. #10
    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
    3,787
    Hollis Prism 2, Megalodon

    CCR Instructor Trainer

    Re: A helium in CCR question

    Quote Originally Posted by nigelh  View Original Post
    Woo....
    Where did that come from?
    I spent ages trying to come up with a number and ended up at about 1.2L but with very little confidence in the factors I'd used. Finding somebody else is within a factor of 10 would be good. This is cool. :D

    Certainly if this is the case we aren't going to see much loop change as we gas on and off.
    I got similar final volumes for helium but just about three times as fast.
    That number is also referred to in the PDIC OW manual. They don't say how they derived it though.
    Cheers,

    Dave....

    www.wedivebc.com

+ Reply to Thread
Page 1 of 2 1 2 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