Another Great trip- need advice on nitrox cert.

[Tigerman]

The O2 exposure problem on 32% doing single-tank, 3-dive days is in my experience "not going to happen" even with 10-12 consecutive days of diving. Now If I upped it to 36% or even 40% that might change, but Ive been nowhere near clocking out with 32% and I have to admitt Im not neccesarilly the most conservative diver on the boat and I couldnt use a higher o2 mix than 32% on most of my dives either with regards to ppo2 and oxtox issues.
If I where diving shallower, maybe (longer NDLs, less air consumption) I could use a richer mix and try to get in trouble..

 

[boulderjohn]

The O2 exposure problem on 32% doing single-tank, 3-dive days is in my experience "not going to happen" even with 10-12 consecutive days of diving. Now If I upped it to 36% or even 40% that might change,

...probably not.

 

[Mossman]

...probably not.

Not to mention that O2 over tiime doesn't lead to CNS toxicity, only pulmonary toxicity. I'd much rather have burning lungs than a seizure underwater.

 

[Tigerman]

...so basically my experience that the o2 clock is a neglectable fact for most recreational diving is in line with others...
How bad IS that lung burn anyways?

 

[DandyDon]

When I accepted earlier above that diving Nitrox on air computers/tables couldn't hurt within reasonable MODs, I had simply forgotten about the O2 clock. My mistake, as it is a real consideration covered in the course. I dived Nitrox all week, 3 dives/day in Roatan a few years ago and it never amounted to much, but it's not to be ignored.

Not to mention that O2 over tiime doesn't lead to CNS toxicity, only pulmonary toxicity. I'd much rather have burning lungs than a seizure underwater.

Maybe so, I don't know, but I know that ignoring it is not within safe diving practices - and the origin of the thread was for safety, not to mention SB TOS.

...so basically my experience that the o2 clock is a neglectable fact for most recreational diving is in line with others...
How bad IS that lung burn anyways?

If you're going to get the card, get the computer, set it right, and dive it conservatively.

 

[Tigerman]

I have the card, I have the computer, I dive within the guidelines and the o2 loading simply dont get very high even with a week of 3-dive days followed by a 4-dive day..
Which is why Id gladly dive the computer set to 21% instead of 32% and just stay shallower than the 33m mod..

 

[halocline]

I have the card, I have the computer, I dive within the guidelines and the o2 loading simply dont get very high even with a week of 3-dive days followed by a 4-dive day..
Which is why Id gladly dive the computer set to 21% instead of 32% and just stay shallower than the 33m mod..

I've come fairly close on a 3 day trip to the flower gardens, but that's 5 deep dives/day, fairly square profiles.

Point is, I don't think it's appropriate to recommend on a public forum that the O2 toxicity issue be ignored simply because the risk of O2 exposure-related illness is low. Especially when it's really easy to not ignore; practically every dive computer sold these days is nitrox compatible.

I'm not one to typically rely too heavily on a computer; I'm a real believer in understanding your profile and using the computer for data, not profile direction. I just don't think it's advisable to deliberately have your computer record inaccurate or incomplete data when it's just as easy to set it correctly.

 

[boulderjohn]

If you took your nitrox class quite some time ago, as I did, you learned a lot about pulmonary oxygen toxicity. My PADI nitrox exam required me to do all sorts of calculations regarding that. It was the hardest part of the exam.

If you took your course recently, you don't know what I am talking about. It is barely part of the course now. That is not because the course has been "dumbed down." It is because of the realization that it really is not a matter the recreational nitrox user needs to be concerned about. You have to be doing some really serious diving to get into the danger zone, and even if you do, the consequences are not that bad.

 

[Tigerman]

That was kinda my point boulderjohn, not that everyone should throw away all knowledge of it. I did actually learn about the o2 clock and tables and how to use them in my nitrox course instead of just turning the computer on and listen to what it says - Which generally is <20% loading..

 

[Mossman]

It's really more a worry for tech divers, especially rebreather divers.

Symptoms of pulmonary oxygen poisoning begin slowly as a substernal irritation that becomes progressively more intense and widespread along with with increased coughing. Uncontrollable coughing occurs in severe cases, symptoms originating in the trachea and major bronchi associated with a constant burning sensation, which is worsened by inspiration. The most severe symptoms are associated with shortness of breath on exertion or even at rest. The onset of symptoms is variable among individuals but usually occurs after about 12 to 16 hours of exposure at 1.0 ata, 8 to 14 hours at 1.5 ata, and 3 to 6 hours at 2.0 ata. ( ata= 33 ft sea water)