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Requesting Validation in My Understanding of a Concept from Mark Powell's "Deco For Divers"

Discussion in 'Decompression Theory' started by Ryan Neely, Feb 22, 2021.

  1. ofg-1

    ofg-1 Course Director

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    All of you hard scientists need to lay off the Viagra.
     
    OTF, No_Stress, rjack321 and 2 others like this.
  2. Storker

    Storker ScubaBoard Supporter ScubaBoard Supporter

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    They most definitely are. IMNSHO, your error is that you seem (to me) to demand the same exact standards from a high-quality pop sci publication like "Deco for divers" as we should demand from a scientific journal article. Allow me to disagree about that.

    In other news, water is wet, the Pope is Catholic and bears shít in the woods (and up here, we have scientific evidence for the latter). Film at 11.

    EDIT: Like @Angelo Farina and @tursiops I'm a bona fide scientist. In the field of natural science/technology. And I've read Powell's "Deco for divers" with great satisfaction. No, it isn't a proper scientific publication. But that book does an awesome job at explaining rather advanced deco theory to non-scientists. I can only hope to be able to do as good a job as that, but I most probably won't be.
     
  3. Ryan Neely

    Ryan Neely ScubaBoard Supporter ScubaBoard Supporter

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    Thanks for all the help, folks! (. . . and for the additional insight into SI units, I didn't mind one bit.)

    For additional clarification, I think the lack of a label on the graph combined with Powell's passing reference to tissues being saturated with nitrogen at the surface was what threw me. (As in, What do you mean we're saturated already? How are we not suffering decompression sickness just by going swimming then?)

    I do understand now. Partial pressures are important. Everyone here has totally helped in that regard. Thanks!
     
  4. Neilwood

    Neilwood Contributor

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    It is an important concept for divers to get - after the relevant time (allowing for on gassing/ off gassing), we are all saturated at whatever the ambient pressure is at whatever height/depth we are at. At depth we on gas as we go down at a certain rate depending on tissue category and after a certain time we will be fully saturated for that depth and pressure. As we return to the surface, we off gas at a certain rate and eventually will return to surface saturation levels.

    With swimming, we are generally shallow enough and not down long enough for us to absorb enough gas at depth for decompression illness to be an issue.
     
  5. Ryan Neely

    Ryan Neely ScubaBoard Supporter ScubaBoard Supporter

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    Right, and we're also holding our breath or breathing atmospheric air, so the saturation levels don't change due to pressure differences. (. . . and am I recalling correctly that it's not just ambieny pressure but the partial pressure of the inspired gas that affects this? . . . I'll need to read the book a second time, it seems.)
     
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    Almost....the important quantity is the ambient partial pressure of the gas you are wondering about saturation of, in this case Nitrogen.
     
  7. dmaziuk

    dmaziuk Regular of the Pub

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    They do and if you quickly drive up Mt. Kea on the Big Island, you'll very much feel it. But under normal circumstances changes in atmospheric pressure are too small, and/or too gradual (if you walk up Mauna Kea instead of driving), to be a concern.
     
  8. Storker

    Storker ScubaBoard Supporter ScubaBoard Supporter

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    One of the better science-y books I've read rather lately is Edward Tufte's "The Visual Display of Quantitative Information". Tufte has this thing about data/ink ratio, and in my opinion he goes a bit off the rack about that. But he has some very good points about how to communicate data without too much superfluous and/or confusing information, and it just might be that Powell follows some of the same principles.

    As has been mentioned upthread, if you want to show superaturation, the actual units (bar, atm, psi or whatever) are rather irrelevant to the message. Get the message through without confusing the audience with irrelevant info. Scientist geeks needing to know about all the dots over the is and all the slashes across the ts be damned.
     
  9. jadairiii

    jadairiii Solo Diver

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    One comment, that book was written in 2008, since then there has been some interesting studies done as it relates to on/off gassing of HE by the US Navy experimental diving unit and, specifically, Dr. David Doolette.

    If you ever get a chance look up some of his lectures at diving symposiums, really interesting guy.
     
  10. Neilwood

    Neilwood Contributor

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    Originally released in 2008 but revised in 2014.

    Most of the concepts are still valid but anyone who is interested in He on/off gassing (ie tech divers or instructors) should be keeping themselves up to speed on general developments in thinking such as gradient factors etc.

    I would agree about Dr. Doolette - very good to listen to.
     
    chillyinCanada and jadairiii like this.

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