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Thread: Deep dives with rich He mix - do you change to another mix or not?

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    Deep dives with rich He mix - do you change to another mix or not?

    Hello guys,

    I am trying to get an idea of what other fellow ccr divers do in such circumstances.

    When you dive with a high Helium mix, and when the time comes to ascent, what do you do? Do you prefer to change to a mix with less or even no He and complete the deco, or do you stay on the initial mix?

    I personally stay on the initial mix, mainly because i worry that if you change mix, there will always be He in the mix due to exhaling, and that gas stays in the loop...

    Even if you dil flash, there will continue to be He in the loop. I would hate to flash every 5-10 minutes.

    BUT, i would like to hear from people who do this frequently, and what syptoms or signs they have felt...

    Thanks all

    Spyros

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    Hi Spyros,

    I stay on the same dil all the way to the surface. Less task loading, smoother mix transitions, and I can run it in O2 mode when I am in the shallows.

    Regards,
    Randy

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    Quote Originally Posted by Mixaddict  View Original Post
    Hi Spyros,

    I stay on the same dil all the way to the surface. Less task loading, smoother mix transitions, and I can run it in O2 mode when I am in the shallows.

    Regards,
    Randy
    Same for me! My Deep dive was at -240mt, 4' on bottom And first stop at -189mt, Only one dil!

    Just my cent.
    Mario

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    Deepest Iv dived is 100 meters and I ride the same dill all the way up for pretty much for the same reasons as you stated. Kind of the old school method doing dil switches.

    Cam

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    Thanks guys,

    I am even more anxious to find out how many would change mix.

    I believe this can be educating. Searching for knowledge is never wrong.

    Hope many would take a minute and take part so we have a bigger picture.

    Spyros

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    I do not many deep dives. But if, i do not change the DIL. the way up.
    Best Ossi Italy

    Quote Originally Posted by Outlaw  View Original Post
    Thanks guys,

    I am even more anxious to find out how many would change mix.

    I believe this can be educating. Searching for knowledge is never wrong.

    Hope many would take a minute and take part so we have a bigger picture.

    Spyros
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    Last edited by gerstl_ossi; 16th September 2012 at 20:41.

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    This has been discussed on different forums many times but I am still very interested in it as we do switch and it is always told to be very dangerous. In the article of Simon Mitchell etc. there is an example that most natural change around 40m is the most dangerous thing to do as you may get Inner ear DCI. With this info we do the switch deep but not immediately but while ascending 10m and still get most of the advantage for the deco time.
    I know many cases when diver have done it more shallow and got the ear problem and vomitting… but still survived. I hope I never get that experience.
    All who are making comments we are crazy, are diving in warm water compared to us. We are seeking for a balance to survive if we have to surface and skip 1+h of deco.
    We just did 6h, 132m, 5C dive, switching dil around 110m. Hoping to know more about the issue in the future.

    Jukka

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    Quote Originally Posted by jukkao  View Original Post
    This has been discussed on different forums many times but I am still very interested in it as we do switch and it is always told to be very dangerous. In the article of Simon Mitchell etc. there is an example that most natural change around 40m is the most dangerous thing to do as you may get Inner ear DCI. With this info we do the switch deep but not immediately but while ascending 10m and still get most of the advantage for the deco time.
    I know many cases when diver have done it more shallow and got the ear problem and vomitting… but still survived. I hope I never get that experience.
    All who are making comments we are crazy, are diving in warm water compared to us. We are seeking for a balance to survive if we have to surface and skip 1+h of deco.
    We just did 6h, 132m, 5C dive, switching dil around 110m. Hoping to know more about the issue in the future.

    Jukka
    Thank you very much Jukka,

    I would be interested in viewing some of your planning, gases and generally info on some dives you guys made.

    I have had to change mix from deep, (130m) due to a problem i faced, but ended up fine.

    Although i wouldnt do it if not an SOS matter, i would like to know more on this, and compare data with people who have done it..

    Thank you again. I am sure others would find this topic interesting.

    Spyros

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    This is just one example,
    The dive included three parts as the deep part starts from an air chamber:
    0 – 32 - 0m
    0 – 132 – 0m, Diluent switch 9/65 -> 10/55 between 116…111m
    0 – 32 – 0m
    Our strategy has always been to do all the deco and move over the air chamber without any delay.
    We feel cutting deco obligation is really important for safety.

    We put the new diluent in through O2 manual feed in our Inspirations.
    In the future we would like to do a smooth continous change while ascending but we just do not know what is the optimal mix?

    Plura Cave Deep Exploration 2012, depth 132m on Vimeo

    Jukka

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    Re: Deep dives with rich He mix - do you change to another mix or not?

    In my opinion, the greatest risk comes from a bailout situation and depends what the mix is in your loop at that time compared to what bailout gasses you have chosen. Add in the reduced deco obligation you get by adding some nitrogen into the loop and you can see why there are different opinions.

    You should be able to calculate your actual loop contents at any depth based on your dil. Then compare that to the bailout gasses you have and see if there is a significant ICD risk. If so, you might want to do a partial flush before reaching that point to add some N2 into the mix.

    I know this goes against what many people I respect believe. But in a real bailout situation such as a CO2 hit, slamming your cells with N2 could invite more trouble when you are already compromised. And if you choose bailout gasses that do not have that high risk of ICD at the worst possible depth, then there is really no reason to flush.

    BTW, if you change diluent during the dive, a flush is appropriate because I believe that is what the software in most computers would assume.

    Just my opinion. YMMV.
    Ken

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