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  • Michael Strahan
    replied
    Just saw this thread and thought I would chime in. For background, I used to manage a dive shop in Hawaii, before we moved here to Alaska, and in that capacity ended up with a PADI Divemaster certification. That was back in the 1980's. There didn't seem to be much money in instructing in our case (we had 10 instructors working for us at the time, and I knew what they were doing and how much they made), so I took a different fork in the PADI trail that was more in line with my goals. I've done a little diving in Alaska and would love to do more. Deepest dive here was 130' in Seward; basically a bounce dive off a pinnacle out toward Fox Island.

    In all this discussion the focus has been on getting "the bends", but I'm not seeing anything about dysbaric osteonecrosis. That's the one where nitrogen comes out of solution (reverts to a gas) in bone tissue and, over time, causes bone tissue to die and become brittle. It's the bane of commercial divers especially. It's possible to experience it without getting the immediate joint pain you get when gas bubbles develop in the joints. As I'm sure you guys are aware, bone tissue has a slower absorption / release rate than joint tissue. So just because you don't get bent / feel immediate pain, doesn't mean there's no damage. You just don't see the results for several years.

    Never occurred to me that there were limits under 33 ft. That makes tons of sense, of course. Just one of those things I never thought of. I think my longest recreational dive was over two hours; it was on a shallow reef at night near Blowhole on Oahu (to the right of Sandy Beach). We were hunting lobsters and shells. Full moon, and totally flat seas; you almost didn't need lights. An unforgettable dive. We never even made it to 30' on that one; our average depth was 15'. I was using a steel 104, which allowed me a ridiculously long bottom time.

    Anyway, I thought I'd toss that log on the fire for rumination...

    -Mike

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  • AGL4now
    replied
    This thread wins the 2017 Alaska Outdoors Forum thread of the year award for "Painful Constipation".

    Leave a comment:


  • Cheeser
    replied
    Originally posted by Grizzly 2 View Post
    You're mixing apples with oranges here. It isn't 1 atmosphere, it's the atmosphere. Higher, it becomes the stratosphere, the ionosphere, etc. None of those terms relate to air pressure values.

    As one dives to 30-feet (actually 29.4 feet), he may ascend without decompression. At any depth below that, he will require decompression. This exemplifies and supports the the 1/2 ATM rule.

    An interesting aside: around 1969, SCUBAPRO came out with its first "Decom Meter". Worn on the wrist, this cumbersome gadget included "Mystery Element X", and was designed to aid in dive calculations as they related to decompression needs.

    I didn't say either of those terms (stratosphere, ionosphere) applied to pressure because I never used those terms. And as far as our entire atmosphere being 1atm of pressure that wasn't me who discovered that, it was a fellow named Torricelli hundreds of years ago.

    Your statement of being able to dive to 30 feet and ascend without decompression was proven by the Navy to be false. The Navy also disproved your statement about going below 30 feet requiring decompression. Because decompression is determined not by one factor (pressure) as you seem to imply but by two factors - time and pressure. Stay at 30 feet for more than Navy dive table no decompression limits (approx 3 hours at 30 feet) and you are in decompression mode. Again, you can't change physics so whether you believe that or not means nothing.

    So your two statements, both of which the Navy proved are false, do you not support this phantom "1/2 atm" rule you keep citing.

    I'll ask again - please post any documentation proving this phantom '1/2 atm' rule. Because the Navy disproved everything you stated above about how pressure affects us when diving. Documentation - post it. Stop making things up and post your proof. I did. Why can't you?

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  • Grizzly 2
    replied
    Originally posted by Cheeser View Post
    Please cite where I discussed oxygen levels at altitude. Yeah, I didn't. Your entire comment above is about something that no one said in this entire thread.

    My comment was about atmospheric pressure and everything I stated is 100% correct. Our entire atmosphere, from sea level to 300 miles up, is referred to as 1 atmosphere of pressure. A fellow named Evangelista Torricelli discovered that back in the 1600's so that knowledge has been around for a long, long time.

    Please re-read my reply and address any points I actually made that you're having issues with.
    You're mixing apples with oranges here. It isn't 1 atmosphere, it's the atmosphere. Higher, it becomes the stratosphere, the ionosphere, etc. None of those terms relate to air pressure values.

    As one dives to 30-feet (actually 29.4 feet), he may ascend without decompression. At any depth below that, he will require decompression. This exemplifies and supports the the 1/2 ATM rule.

    An interesting aside: around 1969, SCUBAPRO came out with its first "Decom Meter". Worn on the wrist, this cumbersome gadget included "Mystery Element X", and was designed to aid in dive calculations as they related to decompression needs.

    Leave a comment:


  • boneguy
    replied
    Cheeser
    Have you looked at that table yet? Shayno and others are trying to help but you are stuck on the Recreational Dive Tables. Nothing wrong with them or the mandatory 10 ft stop. From a recreational standpoint keeping it simple is easier/safer, however, you can still get bent or have other issues even if you follow the conservative tables. As for hot air, show me the medical data of all the long or short term diving injuries from the Nome divers!!
    DENNY

    Leave a comment:


  • Cheeser
    replied
    Show me your dive profile, the dive tables you used and your math of nitrogen absorption based upon your dive profile. We can put the whole thing here for everyone to see.

    I'm willing to learn if you show me the proof. So far all I hear back from those making claims is hot air.

    Leave a comment:


  • boneguy
    replied
    Try US NAVY table 9-7
    DENNY

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  • shayno
    replied
    Ok cheeser I'm back. I just spent 3 weeks at 380', 1 week travelong from 380' fsw to the surface and i never got bent... huh.. That's weird...
    Just kidding. I was just sick. But I gotta hedge my bet here a little, as I don't really want to do any work for some random scuba guy on the internet; but, if I post a bona fide dive log (over 8 hours without blowing a table-proprietary info blacked out) , I gotta win something other than me saying -told ya so... So what's in it for me? How about 24 cold coors and 2 large hawaiin pizzas from dominoes Delivered to me! Oh, and you gotta smile the whole time and call me "dark overlord". I always wanted a cool nickname.
    I was even so kind as to give a very accurate hint!

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  • fuhrerak
    replied
    Originally posted by Cheeser View Post
    And I am still waiting
    That's a long safety stop!

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  • Cheeser
    replied
    I'm still waiting for someone to post a link to this "1/2 atm reduction rule" for scuba divers a couple people have referred to. I have yet to find any reference to it anywhere on the interweb. And if it really exists I'd definitely like to read about it.
    And I am still waiting for the link to the Navy dive table showing you can dive for 8 hours without going past NDL.

    Leave a comment:


  • Cheeser
    replied
    Originally posted by boneguy View Post
    Cheeser
    It is all about the pressure. It does not matter if you are in the water or not. The physics are the same for pilots as for divers. Air Force jet training in tweets (small trainer jets) can go to 18,000 Ft (.5 atmosphere buy the way) without prebreathing O2 to prevent the bends. Yes pilots get the bends just like divers. So following your logic anytime you lower the pressure you are in DCS in or out of the water.

    Part of the issue may be your terminology, How do you define decompression mode? Are you saying once you reach the no decompression limit you start to form bubbles while you stay at that depth?

    DENNY
    Thanks for the aviation info. That makes sense. I've heard of the Armstrong effect where as you go higher the pressure gets so low water boils at body temperature. It's interesting there is an aviation version of DCS.

    If you stay at depth you're fine as your body has already equalized to that pressure. It's changing pressure too fast and releasing that dissolved nitrogen from your blood that's the issue. NDL means the pressure difference going directly to the surface has been shown (Navy dive tables) to cause DCS. The pressure difference causes the body to want to equalize as fast as possible so it creates microbubbles. In reality any return to the surface creates microbubbles but going into NDL means more and bigger bubbles. That's why we teach a 3 minute safety stop for every dive. It gives the body time time to off-gas at an intermediary pressure so the off-gassing is reduced when you return to the surface.

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  • boneguy
    replied
    Cheeser
    It is all about the pressure. It does not matter if you are in the water or not. The physics are the same for pilots as for divers. Air Force jet training in tweets (small trainer jets) can go to 18,000 Ft (.5 atmosphere buy the way) without prebreathing O2 to prevent the bends. Yes pilots get the bends just like divers. So following your logic anytime you lower the pressure you are in DCS in or out of the water.

    Part of the issue may be your terminology, How do you define decompression mode? Are you saying once you reach the no decompression limit you start to form bubbles while you stay at that depth?

    DENNY

    Leave a comment:


  • Cheeser
    replied
    Originally posted by Grizzly 2 View Post
    Hey, Cheeser, I-atmosphere does NOT hold out for 18,000 feet! If that were true, the airlines wouldn't have to pressurize their cabins above six thousand feet; nor would all pilots be required to use oxygen above 12,000 ft. I would note that PADI instruction was, and maybe still is, a little shy on the direct and indirect effects of pressure.

    Please cite where I discussed oxygen levels at altitude. Yeah, I didn't. Your entire comment above is about something that no one said in this entire thread.

    My comment was about atmospheric pressure and everything I stated is 100% correct. Our entire atmosphere, from sea level to 300 miles up, is referred to as 1 atmosphere of pressure. A fellow named Evangelista Torricelli discovered that back in the 1600's so that knowledge has been around for a long, long time.

    Please re-read my reply and address any points I actually made that you're having issues with.

    Leave a comment:


  • Grizzly 2
    replied
    Originally posted by Cheeser View Post
    I'm not a pilot so you'd have to ask someone trained in aviation. I do know that our entire atmosphere, all 300 or so vertical miles of it, is 1 atmosphere. 1 atmosphere underwater is 10 meters. So trying to link it with diving is quite the stretch. If you have information addressing your question by an aviation person, please post the link as I'm always interested in learning new things.

    I'll request the same from you as I did from the other fellow - post a link with that 1/2 pressure reduction rule. I've searched quite a bit for it and have found nothing.

    Seeing as I've provided the Navy dive tables to prove what I've stated and no one challenging what I've said, including you, have provided anything, I'd say its rather clear that I'm not the one doing the trolling.

    Please, post links backing up what you're stating so everyone can learn.
    Hey, Cheeser, I-atmosphere does NOT hold out for 18,000 feet! If that were true, the airlines wouldn't have to pressurize their cabins above six thousand feet; nor would all pilots be required to use oxygen above 12,000 ft. I would note that PADI instruction was, and maybe still is, a little shy on the direct and indirect effects of pressure.

    Leave a comment:


  • Cheeser
    replied
    Originally posted by boneguy View Post
    Cheeser
    So do the pilots flying from sea level to the Ruth Glacier in non-pressurized aircraft also get DCS? The have full Nitrogen saturation at seal level but have reduced the atmospheric pressure so they will be off gassing Nitrogen. If PADI did not teach you the 1/2 pressure reduction rule you should go get your money back, they ripped you off. It is a important bit of information especially from a historic viewpoint.
    Throwing out the acronym DCS is very simple, understanding what is happening is very complex. If you are trolling be carefull it is very deep water and your boat of knowledge seems to be limited to the shallow stuff. If you really want to have a discussion about the effects of inert gas absorption, micro bubble formation, and ways to mitigate tissue damage. It sounds like some of the people here could help.
    DENNY
    I'm not a pilot so you'd have to ask someone trained in aviation. I do know that our entire atmosphere, all 300 or so vertical miles of it, is 1 atmosphere. 1 atmosphere underwater is 10 meters. So trying to link it with diving is quite the stretch. If you have information addressing your question by an aviation person, please post the link as I'm always interested in learning new things.

    I'll request the same from you as I did from the other fellow - post a link with that 1/2 pressure reduction rule. I've searched quite a bit for it and have found nothing.

    Seeing as I've provided the Navy dive tables to prove what I've stated and no one challenging what I've said, including you, have provided anything, I'd say its rather clear that I'm not the one doing the trolling.

    Please, post links backing up what you're stating so everyone can learn.

    Leave a comment:

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