What ppO2 do you use and why?

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Mr Carcharodon

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On a recent live aboard to the Cocos I found that everyone excepting myself was using a ppO2 of 1.6 ATA as a hard limit. Most of the divers onboard were from Europe or the Near East. In practice there was little prolonged diving below a ppO2 of 1.4 ATA.

What do you use as your limit? Does it make a difference to you if your peak ppO2 is significantly above your average. Do you treat ppO2 as a hard limit, or as a dose limit where both pressure and time come into play? If you are using something less than the NOAA limits what is your rational?
 
I aim at 1.2 to 1.4 allowing for a planned unexpected of 1.6 if needed. I dont have a problem with a very quick bounce to > 1.6 (camera drop ect.). Have only done this 2 times. If i do hit a 1.6 or greater, I (whether it makes sence or not) will retreat to less than 1.0 for the duration of the dive and cal it a wash. If i think there may be any symtoms i call it a day/trip/week.
 
I dive 1.3

I think I set it to 1.4 maybe once because my MOD on 1.3 was too shallow and was on a trip that the dive operation always takes on running EANx 30 at 1.4 so I knew it was probably going to be just fine and it was. I know I can do 1.4 but I just add a cushion then stay away from the adjusted MOD by 5 ft as well so it's extra conservative. Rather be safe than sorry!
 
ANDI has a really good manual on Nitrox diving that explains why a ppO2 of 1.4 should be your planned exposure for your dive. Statistically your far more likely to take a hit at 1.6 and if you are diving a traditional scuba regulator you risk losing the regulator during convulsions. The ANDI manual also covers CNS loading really well as opposed to the PADI form of watered down education. You should know the cumulative CNS clock is increased at a higher ppO2.
 
If you use a Suunto computer, I would recommend planning for 1.4 for the bottom section of the dive and setting your computer for 1.5. The Suunto computers add more conservatism and if you dial 1.4, it will give you the MOD for something like 1.37 instead (and you may end up with a beeping alarm for the deepest part of the dive without exceeding your real MOD)... I like to know exactly what the machine is telling me and how it gets there!
That being said a PO2 of 1.4 for recreational/no-deco profiles on open circuit is extremely conservative. I haven't heard of convulsions with this type of profiles... It would take a lot of diving (and therefore a lot of deco) to reach 80%+ on the CNS Clock.
 
I dive air and stick to 1.4/1.6 deco generally, but I'm willing to push what I view as a relatively recent increase in conservatism within my own not entirely arbitrary limit of 240'/pO2 1.7. If there's something I want to see down there and I believe the dive can be executed with a minimum of exertion on the bottom, I'll push past 187' and take whatever the additional quantum of risk of a CNS hit that is.
 
I set my computers and do all math based on a 1.6. My reason is the same reason that I have for all of my clocks being set to real time. I really know the actual level and know to dive my plan. If all is set to less then I have found people are more likely to "fudge" their plan. Just how I do it.
 
I rarely go to 1.4 . . . I dive 32% with a hard deck of 100 fsw due to narcosis issues, so ppO2 rarely comes into it. On technical dives, I tend to run even lower, just because of the standard gases and the depths to which I am willing to dive. Deco, I'll do 1.6, but that's resting and brief.
 
Usually 1.3. Sometimes up to 1.4 if dive requires it.

Reason: I am 67 and one cannot always predict the amount of exertion on a dive. It's all statistics. But if you loose on this one it is probably the end.

In NC I dive a variety of depths but probably half the dives are canceled. So a given tank may be used on a different dive then the next scheduled one. So I use a mix that will work for any of my upcoming dives which is 30%. Also what my LDS banks.
 
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