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Nitrox, Skin Bends and Cozumel

Discussion in 'Ask Dr. Decompression' started by ljwillia, Feb 11, 2019.

  1. MaxBottomtime

    MaxBottomtime Divemaster

    # of Dives: 1,000 - 2,499
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    I found a post by DocVikingo that may help to explain this dilemma.

    "Diving nitrox to air tables bestows no demonstrated safety margin or edge.

    While the lower N2 loading achieved by diving EAN to air tables may be theoretically appealing as a "safety factor," at present there simply is no corpus of scientific evidence for this. It has not been shown that diving nitrox is "safer" than diving air in the sense of reducing the risk of DCS, the severity of DCS or any other aspect of the sphere of DCI.

    In fact, EAN is arguably less "safe" than air no matter what tables are being used. Several posters have raised the OxTox issue, and indeed diving nitrox greatly increases the likelihood of CNS oxygen toxicity if maximum operating depths or oxygen clock limitations are exceeded.

    As DrDeco stated, "In practice, the incidence of DCS is very low in recreational diving." It is in fact so low that based on statistical considerations alone it would be a monumental undertaking to show a safety edge for EAN even if it did exist.

    What diving EAN to air tables does do is reduce decompression obligations, required surface intervals & dive to fly times."
     
    Trailboss123 likes this.
  2. -JD-

    -JD- Eclecticist ScubaBoard Supporter

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    Do you have the ability to adjust the algorithm conservatism on your computer? If so, you would have the option to simply set and dive your actual mix and then adjust it to them more/most conservative setting to give yourself additional buffer on N2 loading.

    You can also stay "X" minutes short of your computer's profile. i.e. Start ascending before your computer's calculated NDL/RBT falls to "X" minutes." An approximate "X" for diving EANx on AIR setting should be be pretty easily determined by comparing AIR/EANx tables for a given planned depth.
     
  3. Jayfarmlaw

    Jayfarmlaw Divemaster

    # of Dives: 200 - 499
    Location: Tuttle, Ok
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    You will be fine. It would take a freak down current to present a problem. Keep in mind that there are safety margins built in to MOD's and exposure time at depth is a factor too. We have dove Nitrox on Coz for 4 years, 2 to 3 trips a year, several dives on Barracuda with the currents ripping, and not encountered the mythical killer downcurrent.

    Pay attention to your depths, stay close to your buddy and the DM if you drop into sporty currents, and enjoy your trip. If your uncomfortable with fast currents, let your DM know. A good operator will have multiple boats so divers can be divided by skill level.

    Safe travels,
    Jay
     
    ljwillia likes this.
  4. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
    Location: North Carolina
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    This is a quote somewhat taken out of context. He is refering to “the average diver” who's risk of DCS under normal circumstances is so exceedingly low that the slight edge of less N2 load, which he admits does occur, will have no significant impact on that divers safety.

    However, we are not talking about “the average diver” here. We are discussing a diver with one episode of skin bends that is at greater risk of recurrence then that average diver. Any steps an at risk diver can take may be worthwhile, depending on their risk tolerence. For some divers it might mean the difference between continuing to dive and hanging up the flippers.
     
  5. DandyDon

    DandyDon Old men ought to be explorers ScubaBoard Supporter

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    Well that was a nice siesta. I'm on Coz now, drying gear. I don't fly home for a couple of days tho. Taking a dry day tomorrow to drive around and explore the island some as I usually just eat, sleep, and dive here.
    Nope, I know you didn't. You said...
    Which is at best is an exaggeration of Nitrox guidelines. Then you twisted with this...
    Which is not what I said.
    Got a link? I know that old idea persists in the sport, even with some physicians experienced in treating bends. Preventing bends is a totally difference science. My statement was...
    Either of y'all know that not climbing the ladder with gear helps, or about the "silent safety stop"...?
    Ok, I don't buy that one, either. I don't know what all caused Lynn's near-hit, and I hope she never has another similar scare. Diving nitrox on air settings or diving a more conservative puter or puter setting can be a misunderstood buffer, like 55 mph driving is safer than 70 mph driving - which is great for gas mileage but not a guarantee of safety. If you want to add buffers, cool - but ignoring the other safe practices minimizes those.
     
  6. JamesBon92007

    JamesBon92007 Great White

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    Um, could you please elaborate on that? I've not heard that before but I have been on a couple of dive boats that require you to remove your gear before climbing the ladder so perhaps that's why. I just assumed in the past that's it's too difficult for some people so they make everyone remove their gear in the water.
     
  7. uncfnp

    uncfnp Solo Diver

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    Don. I sincerely do not understand your stance on this. Have you personally dealt with skin bends? I have. On multiple occassions. And I have since spoken or emailed with DAN, DDM and several cardiologists including Dr Ebersole. And no, I did not save the emails or record the conversations.

    And I agree, diving nitrox on air profiles or using a conservative computer is just one step that an at risk diver takes. I have also altered my dive style, avoid square profiles, extended safety stops, no longer carry my own gear (before or after the dive) and yes even took advance nitrox so I can use 100% O2 at my safety stop on some of my higher risk dives.

    So what is your story and which of us do you think has more “authority” to advise an similarly at risk diver?
     
    couv likes this.
  8. DandyDon

    DandyDon Old men ought to be explorers ScubaBoard Supporter

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    You're far more experienced than I, but one of the safety reasons for removing your kit in the water is to reduce exertion which can kick off a hit. I've read about some boats that even have mechanical lifts for divers.

    The silent safety stop I mention has to do with taking a floating break on the surface, resting for a minute or more there before exiting.

    Ok, fair enough.
     
  9. JamesBon92007

    JamesBon92007 Great White

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    This is why I read ScubaBoard :) It seems there was a thing or two they didn't mention in the dive courses 50 years ago.

    I usually have to float around for a few minutes waiting for the dive boat so I guess that's a plus I never thought of.
     
    aquacat8 likes this.
  10. ReefHound

    ReefHound PADI Pro

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    And hydration. I've seen studies that suggest dehydration may be the single biggest factor in unexpected hits. Since alcohol is dehydrating, that means not showing up hungover.
     
    muzikbiz22, krbailey and flyboy08 like this.

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