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Saturation Diving

Discussion in 'Ask Dr. Decompression' started by Iguana Don, Oct 18, 2000.

  1. Iguana Don

    Iguana Don Guest

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    "Practicioner of Abyssal Medicine", aka Dr.Deco

    What is meant by the term saturation diving? I've heard it used several times & know that rainreg does it for the Navy.
    Could you please explain this term to me.


    Looking to you for knowledge & wisdom
     
  2. BillP

    BillP Senior Member

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    Hi don:

    I imagine Dr. Deco is pretty busy with the current space shuttle mission. I hope you don't mind if I jump in.

    Saturation diving means that you've reached the point on the dive where your tissues can absorb no further inert gas. Sitting at your desk right now your tissues are saturated with nitrogen at your current partial pressure of nitrogen (that is at the ambient pressure with the current % inspired nitrogen.) Your tissues cannot possibly absorb more nitrogen unless you increase the partial pressure of nitrogen by either increasing the concentration of nitrogen in the gas you're breathing or increasing the ambient pressure you're sitting in. If you were to say breathe pure oxygen at your desk for awhile, you would be decreasing the partial pressure of nitrogen in your breathing gas so your tissues would begin to off-gas nitrogen. When you take the O2 mask off, your tissues will reabsorb nitrogen until they again reach saturation.

    If you were to climb a mountain but still breathe air, you would be decreasing the partial pressure of nitrogen in your inspired gas and and would be super-saturated with nitrogen. You would then off-gas nitrogen until you reached the saturation point at the new ambient pressure on top of the mountain. If you come down the mountain and go home, you'll reabsorb nitrogen until you're again at saturation.

    When you dive, your tissues will absorb nitrogen (or whatever inert gas you're breathing) until they reach saturation. The longer you stay down, the more nitrogen you absorb (until you do reach saturation), and the more time you need to spend in deco before you can return to the surface. If you're doing a saturation dive, once you reach saturation it doesn't matter for decompression purposes if you stay down even longer. Your deco time will be the same since you won't be absorbing any additional inert gas. It takes many hours at depth- probably more than a day- to reach saturation.

    I hope this makes sense,

    Bill
     
  3. Walter

    Walter Instructor, Scuba

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    How long you stay at a given depth to become saturated depends on what model you are using. If you use only a 5 minute compartment in your model, you'd consider a diver saturated after 30 minutes. If your longest compartment is 60 minutes, you reach saturation after 6 hours, a 120 minute compartment would saturate a diver after 12 hours and using a model with a 480 minute compartment would require 2 days to reach saturation.

    Actually, in theory, a diver can not ever become totally saturated without increasing the pressure beyond the point at with you desire saturation. In general use a compartment is considered saturated after 6 times the half time of the compartment. A 5 minute compartment is 50% saturated after 5 minutes, 75% saturated after 10 minutes, 87.5% after 15 minutes, 93.75% after 20 minutes, 96.875% after 25 minutes and 98.4375% after 30 minutes. As long as the diver remains at the same pressure, the compartment continues to approach 100% without ever reaching it. After 6 times the half time, at 98.4375% most models consider it close enough to figure as if it was 100% as little progress toward that unattainable 100% is made after that (of course it also makes it easy to figure saturation points for compartments of 10 minute increments which would <B>not</B> be the case if 7 times the half time or 99.21875% were used).

    HTH,

    Walter
     
  4. 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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    As the other writers have indicated, saturation loads the body with nitrogen after about 24 hours at a given pressure. The main advantage of this is in commercial diving where the decompression time does not increase after this 24 hour period. As a rough rule of thumb, decompression from saturation on helium is at 4 fsw/ hour or approximately 100 fsw/day.
    - - - - - -
    When divers are saturated, they can make limited excursions from the habitat depth either downward or upward. In cases of aviators or astronauts , all decompressions are upward excursion decompressions from saturation . How about that.

    [Edited by Dr Deco on 10-23-2000 at 01:56 PM]
     

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