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Shallow Diving and flying

Discussion in 'Decompression Theory' started by PinkPADIgal, Jan 20, 2008.

  1. PinkPADIgal

    PinkPADIgal PADI Master Instructor

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    I have to do checkout dives for open water students. If I do 2 dives in less than 20 feet of water for about 15 minutes each, (1 hour surface interval between) what kind of risk do I take flying 6 hours later? Would hitting up my O2 bottle help me?

    Thanks for the input.
     
  2. fisherdvm

    fisherdvm Solo Diver

    # of Dives: 200 - 499
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    I don't know about you, but my dive computer allows me to fly only about 6 hours after 4 dives. Two in the morning to 44 ft, and two in the afternoon to about 20-30 ft ending about 4 pm. By 10 pm, it said I could fly.

    Based on what your profile is, my guess is, you likely could fly within 1 or 2 hours of your short shallow dives. Can you borrow a dive computer, a conservative one, and test it out?

    I think someone posted a table that allows you to figure it out manually on another thread, and this topic has been discussed in the very recent past.

    Based on this article, you likely can fly almost immediately after your dives:

    www.scuba-doc.com/fad_web.pdf

    Table 3 suggests 0 hr waiting for Cat A, 2 hrs, for B, and 8 hrs for C. Based on your profile, you are likely B or A.
     
  3. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
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    I would definitely not worry about flying a couple of hours later following these short, shallow dives.
     
  4. ce4jesus

    ce4jesus Manta Ray

    # of Dives: 100 - 199
    Location: Denver
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    Knowing that DCS isn't an exact science and often involves variables that can't be measured, why would you make this recommendation?

    What computer is that?



    How did you figure that the dives would be catagory A or B?
    Sorry for the questions but reading this thread just popped my bubble.
     
  5. PinkPADIgal

    PinkPADIgal PADI Master Instructor

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    To quote PADI OW manual, "...to be reasonable safe, you should wait 12 hours after a single dive, and 18 hours or more after mulitple dives..."

    I know I should wait to be safe, and flying 6 hours later isn't setting a good example. However, I am looking at all options and while I don't want to suffer a DCS hit, I need to weigh all options. If I stayed 20 feet or shallower, it isn't much deeper than being in a pool.

    I looked at the tables as well and while the tables are not an exact science, they are more conservative than a dive computer. I am sure my Wisdom or even my conservative Cobra would allow me to fly. While you should obey a dive computer, people have gotten a DCS hit, even diving well within the limits of their computer.

    One of my options was being well-hydraded, and hitting up my O2 bottle to help make sure I stayed reasonable safe for my short flight. Yet, I still have the flying after diving rule ingrated into my head.

    So, I wanted to ask this question to weigh all my options. Please keep posting on this subject. Thank you!!!
     
  6. fisherdvm

    fisherdvm Solo Diver

    # of Dives: 200 - 499
    Location:
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    If you just used a standard dive table from ssi, padi, etc, you would have to round up to 35 or 40 ft, and round up to 19 minutes or more, which will put you at cat B. In reality, she was at 20 minute, for 15 ft. Likely, if the table was extrapolated, she would even be at a lower cat.

    Assuming a surface interval of 1 hour, even if you conservatively put her at a cat B, she would drop down to A....

    But if she were using a computer, I am guessing that she likely can fly even within 30 minutes of her dives.
     
  7. DocVikingo

    DocVikingo Senior Member

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    Hi ce4jesus,

    "Quote: Originally Posted by Dr Deco

    I would definitely not worry about flying a couple of hours later following these short, shallow dives."

    "Quote: Originally "osted by ce4jesus

    Knowing that DCS isn't an exact science and often involves variables that can't be measured, why would you make this recommendation?"

    Given 2 dives in less than 20' of water for about 15 minutes each with a 1 hour surface interval between, it isn't humanly possible to take on enough nitrogen to cause DCS.

    Regards,

    DocVikingo
     
  8. Gene_Hobbs

    Gene_Hobbs Instructor, Scuba

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    I am careful about absolutes such as this.

    We had a diagnosis of DCS following a small series of breath hold dives to 33 fsw in a study of oxygen enhanced breath hold diving for SPECWAR. (Diagnosis was made by Ed Thalmann, study phase IV, If memory serves, pain resolved in second O2 period of USN TT6.) The rapid ascent likely influenced bubble growth but the point was that it is possible though highly unlikely in the case given.

    As Ed was fond of saying (and not sure where he got it from - always sounded like he was quoting someone.), "there is only two ways to absolutely avoid DCS while diving, 1) don't get in the water or 2) don't come back up."

    According to our testing for the USN (later NOAA) Flying after diving tables, it is also safe to assume that this exposure would be EXTREMELY safe. The tables are found online in the current USN manual Rev 5. The new FAD tables do not change much in the next revision but the standard air decompression tables have some significant changes (due out in a few months).
     
  9. lamont

    lamont Photographer

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    Keep in mind that the 18 hours after multiple dives recommendation was determined via a test where subjects were taken to 60 fsw in a chamber for 60 minutes and then taken directly to the surface at 60 fpm, then with a 1 hour SI they repeated that same dive and then took them up to an equivalent of 8,000 ft altitude and they found DCS occuring up to 11 hours later.

    On my PADI table that exceeds the tables for the first dive and gives at best a 30 minute NDL after a 1 hour SI for the second dive which was blown completely and avoids the recommendations for mandatory safety stops and longer SIs for the large amounts of gas loading incurred.
     
  10. gcbryan

    gcbryan One Bad Hombre

    # of Dives: 1,000 - 2,499
    Location: Seattle
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    Since you ongas and offgas at roughly the same rate and since the process is measured in half lives then for any dive that is less than one hour you should be free of excess nitrogen after 6 half lives which in this case would be 6 hours.

    In your case you should be clear well before that since you are only talking about being down for 30 minutes total. You should be clear in 3 hours.

    If I'm incorrect someone please correct me.
     

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