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Thread: who can explain ppo

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    RBW Member adam0321 is an unknown quantity at this point adam0321's Avatar
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    who can explain ppo

    I am an instructor for the marine corps and teach open thru rebreathers. Well Now I have to teach boyles, gay lusaks, henerys and daltons law. Although I know them and can teach them I am struggling with a way to convey partial pressure and absorbtion to a bunch of young marines. Any thought?

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    Re: who can explain ppo

    You have a blender that at the surface will fit 21 oranges and 79 apples in it. When you blend it up you have juice containing 21% orange and 79% apple. It all mixes together to make the juice.

    Now you take that blender 33 feet under water. The blender remains the same volume/size but the apples and oranges squish down to half their size so you can now fit 42 oranges and 158 apples into the same blender. The percentage of juice is still 21% orange and 79% apple but the density is 2 times what it was on the surface. Go to 66 feet the oranges and apples are now a third of their size on the surface so you can now fit 3 times as many in the blender. Percentage of each juice is still the same but the density is now three times as much yet still fits inside the same blender.

    Sometimes marshmellows and puff cakes are easier for some people to get their head around the density end of it. I have used both examples in the same class to get understanding from everyone.

    The blender is our lungs and will break if pressure is exerted on it from the rising pressure of the juice or marshmellows when we come to the surface so we need to let the contents out as we come up due to the increase in volume.

    Hope that helps,

    Bobby

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    RBW Member adam0321 is an unknown quantity at this point adam0321's Avatar
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    Re: who can explain ppo

    I have come up with the idea of using a seal a meal in class to show them how a bag(lungs) filled with marshmellows(gas) is full on the surface but at depth becomes compressed and therfore alowing more room for more marshmellows. and how at surface the preasure the marshmellow exerts on the bags(lungs) is not that great but how at depth they are pushing harder on the bag therfore becoming absorbed into the tissues more rapidly. this way I cover boyles.henerys,and daltons law all at once.

    I am having a hard time showing how 32% nitrox is .76ppo2 at 45' but 1.58ppo2 at 130'. so 32%on surface is like 132% at 100'(just an estimate not actualy doing the math) I can do the equation and show them but its hard to explain and visualize why it is

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    Re: who can explain ppo

    Quote Originally Posted by adam0321  View Original Post
    I have come up with the idea of using a seal a meal in class to show them how a bag(lungs) filled with marshmellows(gas) is full on the surface but at depth becomes compressed and therfore alowing more room for more marshmellows. and how at surface the preasure the marshmellow exerts on the bags(lungs) is not that great but how at depth they are pushing harder on the bag therfore becoming absorbed into the tissues more rapidly. this way I cover boyles.henerys,and daltons law all at once.

    I am having a hard time showing how 32% nitrox is .76ppo2 at 45' but 1.58ppo2 at 130'. so 32%on surface is like 132% at 100'(just an estimate not actualy doing the math) I can do the equation and show them but its hard to explain and visualize why it is

    Maybe in addition of using percentages on your nitrox explanation you could explain the density of the gas.
    example
    32% at the surface gives you 1000 molecules of oxygen in a cubic inch. This is equivalent to 1ATM

    at 3ATM(66') that same cubic inch of space now has 3000 molecules of oxygen and so on.

    Our lungs are therefore exposed to so many more molecules of oxygen as we descend that our blood oxygen content naturally increases.
    Our physical use of these molecules remains the same regardless of depth (pressure) provided same exertion.

    Unused molecules of O2 in our blood actually damage tissues (freeradicals) and our body can only repair this damage at a steady rate which is equivalent to a density (PPO) less than 1.6

    this may open some minds as the the need to control the ppo to whitin safe rate.

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    Re: who can explain ppo

    I hit that problem a couple of years ago with some friends.
    This is what I came up with.

    It might help.
    Last edited by nigelh; 24th August 2010 at 21:28.

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    Re: who can explain ppo

    What agency are you certifying them through or is it a military internal class?

    The course materials and slides have fairly good examples. I always find it best to work through those and then check for understanding by using real examples on actual dives they have done / are about to do.

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    RBW Member adam0321 is an unknown quantity at this point adam0321's Avatar
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    Re: who can explain ppo

    our students dont even leave with a basic ow qual or card even though our class is 10 weeks of scuba certified to a depth of 190,searches,dive medecine,two types of rebreathers(pure o2 and heo2) underwater demo, sub lock outs, chamber treatments and over the course navigate at night a total of about 34 miles underwater

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    Re: who can explain ppo

    Quote Originally Posted by bobby  View Original Post
    You have a blender that at the surface will fit 21 oranges and 79 apples in it. When you blend it up you have juice containing 21% orange and 79% apple. It all mixes together to make the juice.

    Now you take that blender 33 feet under water. The blender remains the same volume/size but the apples and oranges squish down to half their size so you can now fit 42 oranges and 158 apples into the same blender. The percentage of juice is still 21% orange and 79% apple but the density is 2 times what it was on the surface.

    um.....if the juice is a liquid then it wont be compressed 2x.... :)

    liquid is usually considered incompressible (although its not fully)

    If the above were true our brains would also be compressed when we dive...oh, hang on that explains a lot :)

  9. #9

    Re: who can explain ppo

    Quote Originally Posted by Drmike  View Original Post
    um.....if the juice is a liquid then it wont be compressed 2x.... :)

    liquid is usually considered incompressible (although its not fully)

    If the above were true our brains would also be compressed when we dive...oh, hang on that explains a lot :)
    No no Mike that is a myth. Truth be told it was my head and the blender that really made it bad.

    Bobby

  10. #10
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    Re: who can explain ppo

    Partial pressure is a numerical expression of percentage that allows more than 100 percent of molecules to fit into a given space than would fit at standard surface pressure.

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