PO2 limits...

[Charlie99]

If you are using air, narcosis becomes a problem a depths much shallower than where ppO2 becomes a problem.

 

[nereas]

Nah, only the Greeks can drink that stuff.

Yes exactly! That's why the retsina is in it, so nobody else will drink it!

I was with a beautiful Italian woman at a table in a restaurant overlooking the Saronic Gulf of the Aegean Sea, with a nice large bottle of Peloponnesian retsina wine, the strongest kind, that smells and tastes like old basketball sox.

I offerred her a glass of it, and she shrivelled her pretty nose and said, "I cannot drink that, you go ahead."

So I did, and in a matter of a few moments, since it was a very hot day in September, and we had spent the entire morning hiking around the archaeological ruins of Mycenae in the Argolid, I was very thirsty and so finished the bottle quickly. Then she said, in amazement, "You drank that whole bottle!"

And I smiled at her, then looked closely at the bottle, and replied, "Yes, you're right, it is gone. Did you want some more?"

 

[nereas]

Ill plug PADI a bit here. Pick up the Encyclopedia of Recreational Diving for more info, AND of course take a nitrox class. They physics behind diving is pretty interesting, including deco theory.

And I will plug the National Oceanic and Atmospheric Administration.

Get a copy of the NOAA Diving Manual. It contains excellent explanations of nitrox and nitrox diving. After all, NOAA invented nitrox diving.

 

[divermatt]

Nereas, Great explanation!

Seriously dude. Good explanation.

 

[nereas]

Actually, if you go through the numbers, using the NOAA Exceptional Exposure limits, with EAN32 I will always run out of gas first when diving an AL80. With EAN36 or EAN40, that's not always true. For a buddy that is worth saving, I'd have no qualms about going to 2.0 or even 2.5 for 5 minutes or less.

For you I'd go to 1.4.
For your DPV I would go to 1.6ata, but for no longer than 45 minutes.

To put things into perspective, with EAN36, ppO2 of 2.0ata is 150'. With EAN32, ppO2 of 2.0ata is 173'. Even when diving nitrox, my true absolute rock bottom is the limiting factor in an emergency rescue, not MOD.

NDL recreational students are normally taught not to exceed 1.4 ATAs PO2.

Technical students are normally taught to manage their oxygen clock by setting their bottom mix at MOD for 1.2 to 1.3 ATAs PO2, and deco max at 1.6 ATAs PO2. V-Planner gives you a yellow warning if you exceed 80% of CNS exposure time. When that shows up, then you need to redetermine your mixes, leaning out something or other, to reduce the CNS exposure. Not everyone worries about this, as some plan back-gas breaks.

If you were some unknown joe-diver on the same boat, I would watch you descend below 1.6 ATAs PO2, and send up a marker bouy at where I last saw you descening. Then weight it with something off my rig, such as the knife or a caribiner.

If you were my buddy, I would stay close to you, and grab your fins if you started to head deeper than 1.6. With EAN36, my favorite nitrox blend, this happens at 114 fsw. I myself am comfortable with 1.6 for short periods since I hang out at this level during deco often enough.

If someone has good buddy skills there is no need to anticipate any kind of "rescue" where you would be wandering into 2.0 or 2.5 territory. And for just some ordinary joe-diver on a boat, why would you care? Why would you risk the loss to your own family?

When you teach a class to new students, you must keep it simple. Therefore 1.4 ATAs PO2 is very simple.

 

[nereas]

Seriously dude. Good explanation.

Thanks, Matt.

 

[nereas]

ummm.....yeah...thanks? I really appreciate all the info and I'm sure one day it'll all make sense. I guess what I'm concerned about is....as a recreational diver who has yet to break the triple digit ft. barrier, do I need to worry about this yet?

With air, no.

Breathing air will not pose a PO2 problem for you as long as the ambient pressure at which you are breathing it is equal to or less than 6.7 ATAs. This is beyond your 130 ft recreational scuba limit, so with air it is something that you do not need to worry about.

With nitrox, yes, then you do need to worry about it.

 

[nereas]

...

I do think that Charlie has a very valid point though in that some (many?) divers think that 1.4 is the limit and they will immediately die if they drop below this for a couple of minutes.

Thats fine, if they believe that. They really have no business going deeper than 1.4 ATAs PO2 anyway.

With new students, you need to keep everything simple. The human brain does not remember complex stuff the first time around. And the way that scuba diving is taught these days, the students only get one relatively fast first time around, for everything, anyway.

Unless they enroll in a D/M course or a tech course, in which case they then get a great scuba education.

 

[ianr33]

ummm.....yeah...thanks? I really appreciate all the info and I'm sure one day it'll all make sense. I guess what I'm concerned about is....as a recreational diver who has yet to break the triple digit ft. barrier, do I need to worry about this yet?

Diving single Al 80's. Using no more than 32% nitrox and going no deeper than 110 feet you can basically forget about oxygen toxicity.

If you are diving air dont even think about it,just have fun.

 

[razorseal]

some real good info here