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Why extra air when solo?

Discussion in 'Solo Divers' started by pauldw, Jul 11, 2019.

  1. johndiver999

    johndiver999 Manta Ray

    # of Dives: 500 - 999
    Location: Gainesville FL
    I did not verify the volumetric data, but I assume they are mathematically correct. However, your lungs are not
    simply balloons.

    It is my understanding that, portions of the lungs can be isolated or cut off on a hard exhale and this could result in an over expansion injury, even though the total lung volume capacity has not been exceeded. The vulnerability is associated with a portion of the lung that might be isolated from the hard exhale.

    I used to do a similar calculation and remember thinking that if you just exhale completely at the bottom from x feet, that it is impossible to have a barotrama because the volume would go from residual to less than maximum volumetric capacity upon reaching the surface. I don’t think this overly simplistic conceptual model is necessarily valid.

    So the advice of keeping the airway open and releasing air in a somewhat relaxed and continuous manner is still the best.
    John C. Ratliff likes this.
  2. Linke Seitentasche

    Linke Seitentasche Angel Fish


    Rapidly expanding air in your lungs is a bad idea. Parts of your lungs might be clogged because of smoking or an illness.
  3. AfterDark

    AfterDark Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Rhode Island, USA
    Sure is when you have air to release. Otherwise yaguta wait until a little expansion happens, like happened to me.

    Yes sir, you are correct about " this overly simplistic conceptual model " I wouldn't bet my life on for sure.
    Bob DBF and John C. Ratliff like this.
  4. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    Actually, this applies to regular ascents too, not just CESA (controlled emergency swimming ascents). Note that the most rapidly expanding air in the lungs occurs in the last 33 feet of ascent. That was the point of the discussion.

  5. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    Yes, that is possible (an isolated part of the lung being cut off) but not probable, and is possible with any ascent.

    I highlighted one section of your comment above, to note that it is not correct. If only the residual volume of the lungs, say 2 liters of air, were in the lungs at 70 feet, this would represent over 6 liters of air at the surface. My vital capacity is somewhere just over 5 liters (which is greater than most adult males), and that amount would cause barotrauma in my lungs at the surface if not exhaled during the ascent. Those AL 50 tanks have since been mothballed due to the problems of sustained load cracking in these tanks. I now had my twin steel 45s with this type of valve on it. Take a look at the U.S. Navy Lung Volume chart below. You will see that it shows a residual volume of 1-1.5 liters, but also an expiratory reserve volume of about 0.5 liters. I think my estimate of 2 liters remaining in the lungs after an exhalation is therefore very close to reality.

    In the U.S. Navy School for Underwater Swimmers, we needed to do a "blow and go" buoyant ascent from 33 feet. This was supervised by instructors, and consisted of us getting out of a compressed air dome, holding onto the edge while one instructor in scuba inflated our vest, looking up and exhaling hard, then releasing and commencing the buoyant ascent to the surface. It was important that we empty our lungs, as the volume of air in our lungs would double in that brief time buoyantly ascending to the surface.

    Now, getting back to the original idea of this thread, by having a second air source, this whole discussion of whether or not an embolism or other barotrauma would occur upon a CESA from 70 feet would have been avoided. This could have been a small bailout bottle, or a duel valve on the tank (I have one set of doubles set up this way. This setup allows me to "test" old vintage double hose regulators, like the Healthways Scuba regulator shown in the photo below, with a completely redundant regulator sitting right beside it. I have since mothballed these AL 50 tanks, as they are made of the aluminum which has a sustained-load cracking issue with the threads. My steel 45s have the same Sherwood manifold that allows two regulators to be mounted on the set of doubles.


    Attached Files:

    dead dog and AfterDark like this.
  6. dead dog

    dead dog Solo Diver

    # of Dives: 2,500 - 4,999
    Location: SoCal via Pittsburgh, Pa.
    Exhaling from the other end. :rofl3:
    AfterDark likes this.
  7. kensuf

    kensuf Cave Instructor

    I got some duckweed in the exhaust valve of my primary second stage on a dive a few months ago. 20 minutes into the dive it was sucking water heavily with every single breath. With a second second stage, I could simply switch to that reg and clean out my primary second stage without having to abort the dive / chew through the bailout gas.
    dead dog likes this.
  8. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: New York City
    OK, that's a pretty unusual situation, but I guess if you want to carry two second stages on your primary gas supply in addition to your redundant gas supply so that you don't have to end the dive in that unique case, it make sense.

    If I was single tank diving with a pony and had that problem, I would probably just clean out my primary regulator while breathing from my RGS. If that process took so long that it was going to use up a significant percentage of my RGS, I would probably abort the dive.

    But good to have options!
  9. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    You might look at the design of your primary regulator too. The older single hose second stages were pretty well protected from this type of problem (duckweed, or other "stuff" from the water being stuck in the exhaust mushroom). These older regulators, such as the Aqualung (then U.S. Divers Company) Calypso had a larger exhaust "T". These have been reduced to almost nothing to save weight for traveling divers, and allow bubbles to the front of your mask too. The older style second stages may be less prone to allowing the milkweed and other stuff to compromise your exhaust valve.

    dead dog likes this.
  10. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    I picked up a reg with one of the small exhaust T, I went to the dealer and found they also made a larger T and ordered one. I doubt that saving weight is more important than making money, otherwise titanium would cost the same as brass.


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