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Thread: MX 90 Danger!!!

  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
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    MX 90 Danger!!!

    I was not sure whether to post this here or in accidents and incidents but here goes
    Our dear friend AG is advocating something that looks incredibly dangerous unless I am missing something...
    The interesting part is that I was unable to sustain a workload for 5 minutes to get it to drop more than 0.35. What I found was that after 5 mins, without adding any additional O2 or Diluent, the breathing loop volume had become so diminished due to the O2 metabolism that it become very difficult to breath, and by 7 minutes into the test it was impossible to breath and by 8 mins I had to bailout to open circuit because I could not breath the loop. In other words, I would run out of loop volume before significant or dangerous levels of PPO2 drop. This volume depletion is essentially an "alarm" of sorts that warns the diver that additional gas is needed. Adding O2 would both return the loop volume and the PPO2. Keep in mind we do dive standardized gases on the diluent side, so if the diver simply added dil at depth the PPO2 would still be very close to 1.0 or above, since the standard backgases have a PPO2 of approximately 1.2 at depth. Hence the advantage of using standardized mixes as diluent.
    OK so at 2 ata using a po2 of 1.0 you would have fo2 of 0.5. Let's say you have 9l counterlung volume that means you would have 4.5l of O2 in the CL and yes you would probably notice the loop volume decrease before you became hypoxic. If you were at 6ATA (165 ft) you would have 1.5l of O2 in your counterlung and you would be dead before your counterlungs bottomed out.
    Someone please tell me I am missing something
    Cheers,

    Dave....

    www.wedivebc.com

  2. #2
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    Re: MX 90 Danger!!!

    Assuming you supplement the gas in your loop back to 9L with something inert, so you have 1.5L O2 and 7.5L inert, you would still end up with 1.5/9*6ata=1.0 po2 So, no it doesn't seem you would be dead.

    I guess I'm missing the point of this discussion.

  3. #3
    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
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    Re: MX 90 Danger!!!

    Quote Originally Posted by Serge  View Original Post
    Assuming you supplement the gas in your loop back to 9L with something inert, so you have 1.5L O2 and 7.5L inert, you would still end up with 1.5/9*6ata=1.0 po2 So, no it doesn't seem you would be dead.

    I guess I'm missing the point of this discussion.
    AG is saying bottoming the CLs is a good indicator of low O2, I say if you only have 1.5l of O2 which is only 16% of the total loop volume the loop become hypoxic before it bottoms out or you even get a chance to add anything to the loop
    Cheers,

    Dave....

    www.wedivebc.com

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    Re: MX 90 Danger!!!

    Quote Originally Posted by wedivebc  View Original Post
    AG is saying bottoming the CLs is a good indicator of low O2, I say if you only have 1.5l of O2 which is only 16% of the total loop volume the loop become hypoxic before it bottoms out or you even get a chance to add anything to the loop
    Sure, but as you know, the metabolism does not work on O2 volume. It works on O2 pressure. So as you descent, the volume decreases, but the PO2 goes up. You don't really need a large volume of O2 to sustain life, but you do need enough gas volume to ventilate the CO2 out. Any time anyone feels like they cannot get a good satisfying breath due to volume, I would suspect CO2 buildup as the culprit. But then, I'm an engineer, not a doctor.

  5. #5
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    Re: MX 90 Danger!!!

    I'd like to see AG go 8 minutes without adding any oxygen to the loop in 300 feet of water. Sounds like a great way to go hypoxic and die. First time I heard of the MX rebreather I was surprised that ISC would build it and some insurance carrier would underwrite UTD for the training on the unit.

    Next I am waiting to hear that your can dive the MX rebreather without electronics. All you will need is minimum loop volume, a stop watch and SPG to know your PPO2.

  6. #6
    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
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    Re: MX 90 Danger!!!

    Quote Originally Posted by caverkevin  View Original Post
    I'd like to see AG go 8 minutes without adding any oxygen to the loop in 300 feet of water. Sounds like a great way to go hypoxic and die. First time I heard of the MX rebreather I was surprised that ISC would build it and some insurance carrier would underwrite UTD for the training on the unit.

    Next I am waiting to hear that your can dive the MX rebreather without electronics. All you will need is minimum loop volume, a stop watch and SPG to know your PPO2.
    Actually if you look at the picture here MX Series - mCCR Rebreather - Unified Team Diving you will see no ISC parts on that RB. I think Leon has pulled the plug on those guys
    Cheers,

    Dave....

    www.wedivebc.com

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    Re: MX 90 Danger!!!

    This thread will probably get locked out before too long. Which is too bad. This MX series is really a choice piece of work. The thinking seems to be that people can die in car wrecks. And nobody can decide on seat belts or air bags. So UTD just removed both of them.

    Dave's right on about the P02/F02 relationship. That will kill people quickly at depth.

  8. #8
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    Re: MX 90 Danger!!!

    Quote Originally Posted by wedivebc  View Original Post
    Actually if you look at the picture here MX Series - mCCR Rebreather - Unified Team Diving you will see no ISC parts on that RB. I think Leon has pulled the plug on those guys
    I "pulled the plug" on my participation months ago.....


    Tobin

  9. #9
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    Re: MX 90 Danger!!!

    Quote Originally Posted by wedivebc  View Original Post
    Actually if you look at the picture here MX Series - mCCR Rebreather - Unified Team Diving you will see no ISC parts on that RB. I think Leon has pulled the plug on those guys
    I'll be damned. Hard to be sure, but that HUD, and the loop sure ain't ISC.

  10. #10
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    Re: MX 90 Danger!!!

    Quote Originally Posted by caverkevin  View Original Post
    I'd like to see AG go 8 minutes without adding any oxygen to the loop in 300 feet of water. Sounds like a great way to go hypoxic and die. First time I heard of the MX rebreather I was surprised that ISC would build it and some insurance carrier would underwrite UTD for the training on the unit.

    Next I am waiting to hear that your can dive the MX rebreather without electronics. All you will need is minimum loop volume, a stop watch and SPG to know your PPO2.
    If he could find a way to make a class out of it I'm sure you would hear it.

    Why is anyone surprised by all this non-sense. What would you expect to see given the experience base all this is coming from?

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