Discussion in 'Basic Scuba Discussions' started by 911_abuser, Jan 15, 2004.
I am confused as to what this is and in what applications it would be used.
It's partial pressure oxygen you goof! You DID learn this in basic scuba didn't you?
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.
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).
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).
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.
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 dont think that its covered in OW training as its not a concern diving air at recreational depths.
"I don't think it gets covered in OW classes."
"I dont think that its covered in OW training"
It is covered in YMCA OW courses.
Unfortunately not everyone has access to YMCA courses Walter
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.
Roturner is correct but there is a little more to it and discussing the maximum PPO2 that is considered acceptable is normally a good way to start an argument.
PPO2's far lower than 1.6 or 1.4 are still toxic given enough time and PPO2's well above 1.6 can be tolerated for short times. The specific times are where it gets interesting as they can vary from diver to diver, from day to day, with workload and with other confounding variables such as elevated CO2 levels and the amount of nitrogen in the mix.
A PPO2 of 1.6 is considered the acceptable max for sport diving and many people feel the more conservative limit of 1.4 is better for portions of the dive where you are exerting yourself. But as a rule, the higher the PPO2, the shorter the period of time you can be exposed to it without potential problems.
Short term problems with high PPO2 include central nervous sysytem problems up to and including convulsions where the diver is likely to lose his reg and then drown. Longer term exposures to high 02 levels can cause pulminary problems due to oxygen at high partial pressures damaging lung tissue. (This can even occur with 100% O2 at 1 ATA given enough time.) Really long term problems can also occur such as bone necrosis but this is not an issue in sport diving.
Walter is 100% correct. I know it is covered in YMCA OW certification because we teach it in every single class I have ever attended, taught, or sat in on.
Not to piss anyone off, but I did let two of my friends go through other agencies for their OW training so they could finish faster and go on a dive trip with me (this ended up a mistake on my part). One went through PADI and the other through SSI. I hate to say it, neither one knew anything about Daltons Law or partial pressures the day after they finished.
They both are very intelligent people with plenty of common sense, but neither one knew how to properly use dive table after going through the class. When I asked them why they didnt cover this more in depth in the class, I got a response that the LDS's instructors basically didnt think it was necessary since they would end up using a computer anyway (that they'd sell them I'm sure). Now that is asinine to assume that. It turns out that I ended up totally re-training both on the trip which sucked for me (paying for my mistake of sending them to other agencies). This was two competing shops around Nashville that basically skimmed dive tables.
Thank god they are diving with me, otherwise they would have made some very unsafe divers (no cockiness intended).
All right everybody, you can start your flaming now.....
Required per standard or is it just something you present? The WRSTC (of which YMCA is a member) is not clear. The just say an understanding of pressure/gas laws.
http://www.wrstc.com/downloads/Open Water Certification.pdf
I guess Wendigo it was a fault of theirs OR the instructor, as Dalton's law and tables are obviously taught in PADI. Partial Pressures, in as much it coincides with Dalton, wasn't taught as such RE Oxtox etc in our OW. Of course it's standard in Nitrox when it actually starts to become relevant.
I don't see too many people toxing out @ 60ft on air, which is to say, teaching it (PP's) in OW isn't really necessary.
Well, all I can say is that I have been in these shops and if they did skim the info *they* deem not necessary, it would not suprise me. I have been appalled at some of the carelessness of several LDSs. I must be in the minority in thinking having an overly cautious new diver is the only way to train.
Oh and perpet1, The newest version of the YMCA student book has partial pressures and all the laws used for SCUBA in it, and we cover every page of that manual.
It is also quite a nice reference book for me. We just started using it not long ago. It is also a requirement on the part of the instructor. I basically follow a lesson plan that is revised every so often by the agency.
You are allowed freedom to teach in a different order than is planned out, but you must cover everything in it.
When I took basic open water, Dalton's Law had not been invented yet. Neither had nitrox. Back then, the main thing you learned was Martini's Law, of 1 martini per every 50 ft.
Back in those days, there were no SPGs either, and everyone had J valves, or else they used their watch carefully.
Today we teach Dalton's Law in basic open water. But I swear the students' eyes glaze over at the mention of it. Since they are not diving nitrox, they cannot relate very well.
I'm afraid partial pressure is not tought at the OW by many agencies these days. There is often mention of oxygen toxicty on air at depths beyond recreational limits and thats it.
Take a mixed gas class and you'll learn it though.
Long before you have to worry about air in your tanks becoming toxic at or above 1.6 ATAs ppO2, you will have run into the problem of the N2 in your air becoming extremely intoxicating, starting at 130 ft, and getting progressively worse, until you become a zombie around .... hmmm ... should I tell him/her?
ppO2 is a major limitation whenever you are diving nitrox. When you take a nitrox class, hopefully they will teach you about it then.
EAN50... ahhh well thats ADvanced Nitrox
Do any of you really think that it is a good idea to skim these lessons just because it isn't absolutely critical at OW depths?
I truly hope not. Having more information can do nothing to harm a diver, however it can be a great detriment to have too little. Besides, if they do go on to nitrox classes, they will be just that much further ahead.
"Required per standard or is it just something you present?"
Required per standard. How do you explain the theory of decompression without discussing Dalton's Law of partial pressures?
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