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Can some explain to me what PPO2 is?

Discussion in 'Basic Scuba Discussions' started by 911_abuser, Jan 15, 2004.

  1. 911_abuser

    911_abuser Angel Fish

    I am confused as to what this is and in what applications it would be used.
  2. archman

    archman Marine Scientist

    # of Dives: 200 - 499
    Location: Florida
    It's partial pressure oxygen you goof! You DID learn this in basic scuba didn't you?
  3. DeepScuba

    DeepScuba Manta Ray



    Do you guys know each other???? This sounds like a quarrel between friends!!!!

    If not, this is gonna get juicy REAL quick!!!

    Man that's funny.

    Uhm, getting back to it, I'm not sure if I learned this in OW.
  4. roturner

    roturner ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Rotterdam, Netherlands, Netherlands
    It means "partial pressure of oxygen". It's calculated by multiplying the percentage of O2 in your gas mix by the pressure it's under.

    For example, at 33ft you're at 2ata (2x atmospheric pressure). That's 2x 0.21% if you're calculating the PPO2 of air at this depth, so at 33ft air has a PPO2 of .42

    It's important because oxygen becomes toxic above 1.6 or so. That means that the maximum operating depth (MOD - something else you'll eventually see here) is determined to be the depth at which you hit the 1.6 PP02 boundary.

    If you take a Nitrox class you'll learn more about this too.

    hope that helps (or at least more than being called a goof).

    Gruber likes this.
  5. AzAtty

    AzAtty Instructor, Scuba

    You probably learned about "Dalton's Law," but the instructor may not have explained it very well or might have said you really wouldn't need to know much about it--besides not to breathe oxygen below a certain depth or not to dive on air below a certain depth. PADI taught the concept back in the 80's when I certified, but I don't see any reference to it in their new book (but I didn't look too hard).
  6. Scubaroo

    Scubaroo Great White

    This is explained in a nitrox course - I don't think it gets covered in OW classes. PPO2 is the "partial pressure" of oxygen. Briefly, at the surface, you're breathing 1 ATA of air, 21% oxygen (O2), 79% nitrogen (well approximately anyway). The PPO2 is 0.21. At 33', you are still breathing 21% oxygen if you're diving air, but the ambient pressure is now 2 ATA, so the PPO2 is 0.21 * 2 = 0.42. At 66', your PPO2 is 0.63. It is generally felt that a PPO2 of 1.4 (roughly the equivalent of breathing air at 187') is the safe working maximum PPO2 you should expose yourself to, and a PPO2 of 1.6 is the safe MAXIMUM PPO2 you should expose yourself to (roughly 218' depth), before oxygen toxicity becomes a concern. At these depths however, nitrogen narcosis is probably the limiting factor.

    PPO2 becomes of real concern when diving nitrox - say you're breathing a mixture of EAN40, which is 40% oxygen, 60% nitrogen - a PPO2 of 1.6 is as shallow as 99' - which is within the recreational depth limits for air. So by diving a tank of nitrox and treating it like a tank of air, without regard to the PPO2 of the mixture at depth, is a receipe for tragedy.
    gdawg20001 likes this.
  7. MikeS

    MikeS Divemaster

    It's not something easily explained in a post. The best thing to do is to take a Nitrox course where it should be explained. Short of that read Nitrox course ware. In reference to diving, above a certain partial pressure (PP), oxygen (02) becomes toxic and below a certain PP02 you will pass out. But again, this is not an issue diving air at recreational depths.

    I don’t think that it’s covered in OW training as it’s not a concern diving air at recreational depths.

  8. Walter

    Walter Instructor, Scuba

    "I don't think it gets covered in OW classes."

    "I don’t think that it’s covered in OW training"

    It is covered in YMCA OW courses.
  9. Scubaroo

    Scubaroo Great White

    Unfortunately not everyone has access to YMCA courses Walter :)
  10. matt_unique

    matt_unique Solo Diver

    # of Dives: 200 - 499
    Location: Massachusetts
    Yeah PP02 is the partial pressure of 0xygen. Oxygen becomes toxic at certain depths at certain mixes. This PP02 number provides a way to measure that potential for toxicity. When the PP02 reaches 1.4 or above there are potential hazzards including CNS toxicity (Central Nervous System). This could "ruin you whole day" because the worst possible outcome is passing out without any other symptom.

    You will first learn about this in a Nitrox course. If you are breathing compressed air you don't have to worry about PP02 or CNS toxicity until you are approaching 218 feet.


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