Deepest safe depth on air?

[do it easy]

I have always used the 1.4 limit, you are saying symptoms are "probable" over 1.3? Probable to me is more than a 50% chance.

The NOAA O2 exposure tables are built around a time-depth assumption:

1.3 is "safe" for 180 (???) minutes
1.4 is "safe" for 150 minutes
1.6 is "safe" for 45 minutes

Check my times, since I'm making this up from my head.

with O2 partial pressures above 1.0 ATA there is no "safe" limit; it's only a matter of time before symptoms become more likely- similar to the dive tables.

Edit: corrected exposure times

 

[H2Andy]

Wanna play it safe? Stay within Recreational Limits, ie: 130 ft.

sweet!! i'll dive a 40% Nitrox mix to 130 feet

i should be ok since i'm within recreational depth limits



(THE ABOVE IS IRONY... DONT NOBODY DO THIS)

 

[cummings66]

I'd say worry about narcosis first, before worrying about your PPO, because, most likely, you will feel narced long before your PPO becomes a problem....BUT: don't ignore the PPO factor either.

Divers who use Nitrox know or should know the requirements for the dive and it's not hard, but it is more difficult than a non nitrox diver is aware of as far as what you keep track of. The o2 adds up just as the nitrogen does and can definitely cause toxing well before being narc'd.

With one foot in the tech world so to speak I'm sure you know this, but I wanted to clarify it for others. A nitrox diver keeps tabs on his O2 and Nitrogen levels, most of the time the O2 level isn't a problem because you adjust things to suit the dive, but it can be an issue if you don't pay attention to it.

 

[wedivebc]

If you do some research you will find that each agency supports diferent levels and exposure time. Padi and SSi recomend a maximum of 1.4 but include a grey area up to 1.6 ATA. Dan research director proposed a limit of 1.2 on a Oxygen Exposure paper that he wrote. NOAA set a limit of 1.3 ATA for 3 hours of exposure but allows exposures up to 1.6 ATA.

Actually I teach though 4 different agencies and they all follow NOAA guidelines as far as oxygen exposure limitation, and all seem to be in agreement with what I said earlier. Exposures above 1.4 do provide a non-zero risk factor but the incidence of O2 tox below 1.6 are so rare that there is little information about these levels. Mathmatical modelling is nice on paper but with so few data points it has little meaning in the real world.

In summary, only exposure up to 1.3 ATA will assure you that OXTOX won't be a problem. Over 1.6 ATA something most likely will happen and in between, there is always a posiblity. Why do you think that most agencies consider the 1.4 to 1.6 ATA range a grey area.

I take exception to your use of the expression "crap shoot" with regard to exposures above 1.3. That is why I asked where you got your information from. Are those your words or from some report you read?

 

[wedivebc]

Anyway I hope everybody reads the article and gets some good info out of it.

Just a quick scan of your article reveals some errors
At this depth the 50 percent oxygen would have the same physiological effect as 100 percent oxygen at the surface. Breathing a 100 percent oxygen mix at a depth of 33 feet / 10 meters (2 ata total pressure) would be equivalent to breathing the 50 percent mix at 132 feet / 40 meters (4 ata total pressure).

 

[wardric]

Your study stated narcosis CAN have effects as shallow as 30. He might not have had problems at 87 because he had no problems and he might not have had problems because it wasn't effecting him.

I occasionally dive to the 125fsw range and have no problems. I have helped people that did have problems though. Narcosis affects everybody differently and at different depths. I have not personally had any problems that I had to handle with myself, but I have been diving with people that developed problems that I had to handle for them.

I do know what being narced feels like also, as the only time that I felt it was when I dove to about 105fsw once. The water was cooler than normal (about 72 F versus 77-82 F) and I didn't feel 100% that day either. I handled it though and ascended slightly to relieve the effects. I then went back down and had no problems.

I made a bad translation of the article. It in fact does not state it CAN but that it DOES have effects even at 30 ft. Sorry about that.

Narcosis is not always an effect you can sense but at depth, everyone have narcosis in a form or another. Narcosis is not always a "drunk" effect. It can be paranoia, unfounded fears or most of the time, just slower thinking process and less awareness.

My deepest dive on air was at 171 ft. I did not feel any narcosis effect, I did not feel drunk or paranoid or any other. During this dive, at the bottom, I had a freeflow and then my mask got bumped and so flooded. We did all the correct procedures but I can tell you that even the simple thinking process to clear the mask took much more time that on surface. It was like in slow motion. Try doing simple math or other tests at 30 ft and then at 100 ft. You will see that the time to resolve it is much longer at depth.

Most of my dives are below 80 ft in cold 40-45 F waters (I so envy you with your 72 F waters ), a good proportion are below 100ft and did many below 130. I only "felt" narcosis once, at only 90ft. I could not stop laughing and a little voice in the back of my head said: you are experiencing narcosis, be aware. Ascended a bit and it went away. So I could say I experienced Narcosis only once. But I know that rapidity and efficiency are affected at depth even if you dont notice it and that is also a narcosis effect. It does not mean it always have a debilitating effect, it can strike at a different degree and in different ways. But it is always there.

So the diver in our example had no problems not because it wasn't effecting him but because it had no debilitating effect on him and he did not have any major problems to resolve. If you consider narcosis only the effect of losing awareness and feeling like being drunk, I agree that it does not strike that way all the time (not even often) but narcosis is much more than that.

 

[tehach]

If you have not read the books "The Last Dive" and "Shadow Divers", go to your local library and check them out. The dives recounted in those books will blow your mind. Chip

It's been a while since I read it, but didn't Chatterton, Kohler, and others regularly dive to 230' on air in "Shadow Divers"?

 

[H2Andy]

It's been a while since I read it, but didn't Chatterton, Kohler, and others regularly dive to 230' on air in "Shadow Divers"?

yes.... also the Rouses, on U-869


of course, the Rouses didn't make it. thosed depths are a very real gamble
with air.

 

[StSomewhere]

I take exception to your use of the expression "crap shoot" with regard to exposures above 1.3. That is why I asked where you got your information from. Are those your words or from some report you read?

That is an almost direct quote from this book. The author's premise is that there are no indications you'll ever tox at 1.3 and almost certain indications you will tox at some point at 1.7. The area inbetween is the place you should be careful, taking into account additional factors like cold water, whether its a working dive, etc. Take exception all you want but do it with the author.

 

[DiverBuoy]

The 1.3 is just a conservative approach that's all ...

Folks please don't dive deep on air ... if you are diving regularly deeper than 4 atm sw give thought to alternatives, there are just too many risks on air and better solutions available.