o2pp 1.4ata+?

[Atticus]

Nitrox divers. Do you or will you ever exceed 1.4ata?

I regularly use 1.6 for deco.

Would you bop down to 1.6 to get a picture?

If I was comfortable with my conditions and it was for a limited amount of time, then yes.

Or 1.8 to get the light you dropped?

Probably not for a light, though as was said by others, I would do this for a life.

Or maybe you don't have a problem planning dives to 1.5.

I usually plan a bottom ppO2 of 1.2 and a deco ppO2 starting at 1.6.

Would you dive 32% to 120' (I have, and will)?

I have. Light trimix is better.

Why? Why not?

Time at a particular ppO2 is important. Conditions are important. I don't mind a higher ppO2 during deco because the goal portion of the dive is over and I am relaxed.

 

[Uncle Pug]

How many incidents of Ox Tox have occured at a PO2 of 1.6?

 

[Albion]

I have heard one story related to me by a friend of the concerned diver who toxed, he got a momentary warning and basically locked his arms and legs around a line a hoped for the best, it did work out for him. I also know of another incident (RB) the exact cause is unknown but it was a possible tox, luckily (hmm) he was buoyant and floated up not down, unluckily he floated up fast and was badly bent and is still in a wheelchair.

A better choice is to Plan your dives accurately for the max possible depth not the depth you are diving too. if you plan to dive to the deck of the wreck consider what depth the sand is, if diving a reef then make a decision before you go in what is the max! I use 1.4 for the dive 1.6 for deco, at least in deco you and your buddy are pretty much in each other faces. I know of people who spike their PO2 during deco to open the oxygen window more, they have experience and training i would not try it myself or advocate anyone else to do so.

It may be a remote chance that you tox just above 1.6 but if you do and your buddy is not close your chances are slim to nil.

 

[Kim]

The point is - exposure. Dive 1.6 for 30 minutes and it shouldn't be a problem. Dive 1.6 for 50 minutes - Russian roulette. It's your CNS clock that you have to watch.
Liveaboard diving can be tricky. Especially diving a single tank it would be quite hard to break through the 1.6/45min barrier. However, doing 4 or 5 dives using Nitrox all the way, it would be a lot easier to cross the 1.6/150min line.

 

[Mike Veitch]

The point is - exposure. Dive 1.6 for 30 minutes and it shouldn't be a problem. Dive 1.6 for 50 minutes - Russian roulette. It's your CNS clock that you have to watch.
Liveaboard diving can be tricky. Especially diving a single tank it would be quite hard to break through the 1.6/45min barrier. However, doing 4 or 5 dives using Nitrox all the way, it would be a lot easier to cross the 1.6/150min line.

Not sure about the logic on your 4 or 5 dives a day on liveaboards. Are we talking a 32% recreational mix found on most liveaboards? I worked on liveaboards with nitrox for 5 years. There are two ways to look at your 1.6/150 line. Using the silly tables (insert the agency name here)for O2 exposure you would certainly be dead, but those tables take into account only max depth and total time. HOwever, using a computer on 4 or 5 dives a day every day for 5.5 days week after week my percentage was never more than 15%. Unless of course i had to drop down to 150 ft+ to grab some dimwit who wandered down there on nitrox...And to answer that question, no i never felt any symptoms and have been down to 160+ (not a brag but again grabbing some dimwit)
Looking at nitrogen time there is no chance, and i mean no chance, unless doing serious deco time, to come anywhere close to the 45 mins or 2.5 hours at 130ft needed to put you into the theoretical o2 time problem (note the word theoretical)
The allowed bottom time at 130 (or even 100) is going to put you into nitrogen problems loooong before the O2 becomes a problem.
Tech diving is another story so please don't bring in higher O2 arguments here, i am discussing purely recreational nitrox.

 

[Kim]

There is an interesting article about OxTox and the research done into it on the DAN website. One quote from the article:

During a nitrox dive done at Duke University's F.G. Hall Hypo/Hyperbaric Center at 100 feet / 30 meters, breathing 1.6 ata pO2 (oxygen partial pressure) during heavy exercise, a convulsion occurred after 40 minutes. Perhaps this would not have occurred had there been a lower level of exercise, but it does seem to indicate that the NOAA limit of 45 minutes for 1.6 ata nitrox diving is not overly conservative.

Breathing 100 percent oxygen during the 20-foot / 6.1-meter decompression stop is common practice, and at this depth, the partial pressure will be about 1.6 ata. At this shallow depth, under conditions of rest, the chance of CNS oxygen toxicity should be very low. But, like most things in life, this is not certain, as evidenced by a recently reported oxygen convulsion at 20 feet / 6.1 meters during decompression by a technical diver after completing a dive on the Lusitania.

The full article can be found here:
http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35

 

[Mike Veitch]

hmmm just re read my post, i guess going to 160 to grab a dimwit makes me a dimwit too eh?! he he

 

[Kim]

Maybe this depends where you do the liveaboard? In Thailand I could have any mix I wanted - although I agree 32% was probably the norm. However we were doing quite a number of deep dives and I had my computer up to 70% on two of the 6 days. Sure I was spending a lot of time deep (photographing Leopard sharks), but I had a large 15ltr tank so it would have been easily possible to push it too far.

 

[cameron]

It seems as though everyone is just following the rules without knowing where the rules came from and why they are there. Look what military divers have been doing for years, look at the ppo2 of a patient in a table 6. They don`t tox...welll some due but.... The rules are there because over many years of trial and error this is the best guess the dive comunity has. It is not a hard and fast rule, it is a hard and fast guidline

 

[jonnythan]

They don`t tox...welll some due but....

Well, I don't want to be one