EaNX and PPO2 of 1.6

[Oside Jimc]

Just curious and wanting to learn, but why not just go to tri-mix for a dive like this? Seems like a safer mix all around for such a deep dive.

 

[String]

Just curious and wanting to learn, but why not just go to tri-mix for a dive like this? Seems like a safer mix all around for such a deep dive.

The huge increase in cost and skills needed. Trimix will cost roughly 8x per dive than nitrox here at least.
Also you need to be proficient in stage handling for decompression and various other things.

 

[jviehe]

Hey guys,

I'm going to be diving the Oriskany in a few weeks with a dive group and we will be diving nitrox. I've been certified to use it for over 2 years but have never found the opportunity to use it (air has worked fine for all my ocean dives since we'd do a deep dive then a shallow dive, shallow cavern diving etc.) . My computer can handle nitrox and I'm familiar with the rules etc. but I think maybe during my classes I misunderstood my teacher and just would like some clarification.

My instructor said the limit for PPO2 is 1.6. Now is that limit tied to the same limit as your O2 clock? Let me see if I can explain what I thought he meant and then what my confusion is.

When I first took the class, my understanding was PP02 1.6 was THE limit. If you hit 1.65 you instantly black out from OxTox. This was seperate from your O2 clock where if you reached 100%+ of your O2 clock limit, you'd black out from OxTox. They were two seperate ways to croak....for lack of a better term lol.

Now that I'm thinking about it. What if it's your first dive of the day on nitrox and you go straight to the bottom and hit PPO2 1.65 for say 1 minute and come back to a level where your PP02 is 1.3 or so. Is what my instructor was trying to say was "If you go below PP02 1.6 your O2 clock is used up much much faster so you consider it "instantly" using up 100% of your O2 clock because it only takes maybe 10 minutes to use it up at PP02 1.6?"

The reason I ask is we will be diving 29% O2 and at the beginning of the dive we're planning on touching the deck at 137'. This puts me at a PP02 of 1.58. We would only stay for a minute or two and then go hang out around 110' and shallower. Now I can have my computer beep at me if I were to hit PP02 1.6, but if something goes wrong (heaven forbid) and I get distracted for a second or take a second to become neutrally bouyant and accidentlly go slightly over PP02 1.6 I'm not going to black out right?

Sorry if it's a stupid question, just like to be very prepared for things (taking my rescue diver classes this weekend, I guess it's rubbing off on me already ).

Thanks for your responses in advance!
Jim

The 02 clock is to protect you from pulminary toxicity, damage to your lungs. But, I would recommend rereading your nitrox book.

 

[Charlie99]

The 02 clock is to protect you from pulminary toxicity, damage to your lungs. But, I would recommend rereading your nitrox book.

I see that you are a scuba instructor.

Are you qualified to teach nitrox classes, and if so, is this what you teach ??

For which agency?

Do teach about CNS toxicity calculations in addition to pulmonary toxicity calculations? If the "O2 clock" is pulmonary-related, what do you call the CNS related calculations, if anything?

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[jviehe]

I see that you are a scuba instructor.

Are you qualified to teach nitrox classes, and if so, is this what you teach ??

For which agency?

Do teach about CNS toxicity calculations in addition to pulmonary toxicity calculations? If the "O2 clock" is pulmonary-related, what do you call the CNS related calculations, if anything?

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Yes, yes, PADI, and yes. CNS calculations are called maximum operating depths. This is all in the nitrox book. Are you disagreeing, testing my knowledge, or interested in learning about nitrox? I am simply trying to reinforce to ALL students that you have books for a reason. They are a reference if you forget something.

 

[Tomeck]

I often dive at 1.6. I find 1.6 is very reasonable, because we can stay at 1.6 during 45 minutes, it is enough long.

 

[Scubakevdm]

I think that Charlie is the cleverest guy I've ever met. For real.

 

[Bismark]

CNS calculations are called maximum operating depths. .

So are you saying that CNS is only a function of your MOD?? Are you then implying that staying within your MOD is sufficient to ward off CNS???

 

[Charlie99]

Yes, yes, PADI, and yes. CNS calculations are called maximum operating depths. This is all in the nitrox book. Are you disagreeing, testing my knowledge, or interested in learning about nitrox?

A bit of all three. I can only disagree once I know for sure what you are saying. And when I am in disagreement with someone, I often find that figuring out why we disagrees leads to further enlightenment.

It does appear that what I consider to be a CNS O2 clock you say is controlled by lung/pulmonary considerations.

For example, I consider the 300 minutes max at 1.0ata ppO2, 210 minutes max at 1.2ata ppO2, and 150 minutes max at 1.4ata ppO2 to be CNS limits, not pulmonary. When I refer to CNS clock, I refer to using these sorts of limits, but expressed in %/minute terms to calculate the "% of CNS clock" that has been consumed. (For example 300 minute limit at 1.0ata turns into 0.33%/ minute, 150 minute limit at 1.4ata becoms 1/150 = 0.67%/minute).

Is the above sort of calculation what you are calling lung/pulmonary toxicity calculations? I call the above the O2 clock or CNS clock, and don't believe it has anything to do with pulmonary effects such as lung damage, edema and breathing difficulty. I've never had to calculate OTUs for any recreational dive.

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The MOD of 1.4ata is indeed a CNS-related calculation, but it is simply a very quick and dirty way of keeping the CNS clock in limits, since it is unlikely that a non-technical open circuit diver will exceed the 150 minute per dive CNS limit for 1.4ata ppO2.

 

[jviehe]

So are you saying that CNS is only a function of your MOD?? Are you then implying that staying within your MOD is sufficient to ward off CNS???

THere are some other physical factors such as workload, drugs, and c02 levels, but yes, CNS is a result of depth, and not time for recreational divers. Staying below recomended partial pressure limits (1.4 for PADI) will ward off CNS in most cases. We dont need to get into disclaimers.

Pulminary toxicity however is a result of time at above normal pressures and is tracked using the 02 clock.