Should you be diving NITROX if you can not answer these questions?

[scubadiver888]

FWIW, the DAN report cited above (which in part is a roundtable of PADI, SSI, TDI, NOAA, USN, IANTD, and NAUI hyperbaric medicine experts, amongst others) cites the number of recreational divers taking an ox-tox hit ("seizure") at 1.6 ppO2 or less from single exposures in recorded history as zero.

I assume you are referring to the portion, "AMERICAN ACADEMY OF UNDERWATER SCIENCES' NITROX USE" starting on page 61.

First, "at 1.6 ppO2 or LESS". How many dives were at 1.6? How many were at 1.4? How many were at 1.0? Hard to say from the article.

Page 62 notes, "Organizations most commonly use a PO2 of 1.4 atm, and 1.6 atm was the second most common limit. Several organizations reported that the impose different partial pressure limits depending on depth, mixture, and operation."

Basically, this article tell me there is no data for greater than 1.6 atm and they don't have any break down for how many dives are at 1.6, 1.4 or another other ppO2 levels. The article was written in November 2000. The data is from 1987 to 1999. So not only is it vague but it does not include the last 9+ years.

I think the importance of this article is (a) to understand all the studies and that there is a risk of CNS hit at even 1.4 but that the odds of that are probably lower than a DCS hit and (b) read the rest of the article starting on page 65 and watch as they massage the numbers.

It should also be noted that although the article I believe you are citing indicates no recreational divers having a CNS hit, this is different from all scuba divers who dive to recreational limits. There were some reported cases of CNS hits at as low as 1.4 atm for commercial divers operating within recreational limits.

 

[DandyDon]

Not sure I understand all of the post?

First Post - "I was diving ... at 1.6 ppo (130)

That was me. I don't remember what my mix was on that tank 5 years ago I think; they were partial pressure blended and I tested & marked each one carefully all week; what I do remember is that I followed the others down until I was hovering in the column at 1.6 but would not go deeper in pursuit - and by the question mark I meant that it might have been 130 that I hit the 1.6 and stopped to watch.

FYI, I do know how to calculate MODs from formulas, but I usually just use my dive computer as it's less likely to make a mathematical mistake than I. For that discussion, I'm not sure what the mix or stop depth was, just that I stopped at 1.6.

The next post quoted did strike me as odd, but then his often do.

 

[halocline]

I have noticed recently, PADI is pushing all divers should go to Rescue Diver (on the PADI website and at all the LDS in my area). This is one stop short of Master Diver (currently their highest non-professional level) or Dive Master (first level of dive professional). Cynical people will assume it just another case of Put Another Dollar In but I think they also want to have more people with rescue knowledge as recreational divers push the limits more and more.

Count me as one of the cynical ones. PADI's mission is to make money on diver training. They have NEVER been shy about using implied safety factors, even when those factors are completely unprovable, as sales tactics. In this economic climate, I'm sure they see current divers as a better market option than recruiting new divers.

 

[ScubaSteve]

Yeah I think many are confused as to the purpose of this thread but that is not unusual around here. I think it was just to prove that it is possible to backwards calculate one part of an equation so long as you have the other parts...but I am not sure.

Not sure I understand all of the post?


That was me. I don't remember what my mix was on that tank 5 years ago I think; they were partial pressure blended and I tested & marked each one carefully all week; what I do remember is that I followed the others down until I was hovering in the column at 1.6 but would not go deeper in pursuit - and by the question mark I meant that it might have been 130 that I hit the 1.6 and stopped to watch.

FYI, I do know how to calculate MODs from formulas, but I usually just use my dive computer as it's less likely to make a mathematical mistake than I. For that discussion, I'm not sure what the mix or stop depth was, just that I stopped at 1.6.

The next post quoted did strike me as odd, but then his often do.

 

[Buoyant1]

Come to think of it, the best way to avoid O2 toxicity is by not diving at all.

the K

That's about the only thing you can bank on in this thread!

I was taught that 1.6 was a contingency depth.

I know what gas I'm diving, I don't push the limits, in fact most of the guys I dive with err on the very conservative side. Most of the time I'm breathing 29 or 30% on a hard bottom of about 115-120 ffw Sure I could stick with a standard mix, but why push it?

 

[lamont]

FWIW, the DAN report cited above (which in part is a roundtable of PADI, SSI, TDI, NOAA, USN, IANTD, and NAUI hyperbaric medicine experts, amongst others) cites the number of recreational divers taking an ox-tox hit ("seizure") at 1.6 ppO2 or less from single exposures in recorded history as zero.

there was a suspected case of oxtox last year in a cave dive that was within the NDL limilts which was at 1.4

there was also at least one case of a technical diver that had seizures at 1.6 while on deco due to increased exertion (diving the USS monitor i think?).

 

[lamont]

FWIW, the DAN report cited above (which in part is a roundtable of PADI, SSI, TDI, NOAA, USN, IANTD, and NAUI hyperbaric medicine experts, amongst others) cites the number of recreational divers taking an ox-tox hit ("seizure") at 1.6 ppO2 or less from single exposures in recorded history as zero.

there was a suspected case of oxtox last year in a cave dive that was within the NDL limilts which was at 1.4

there was also at least one case of a technical diver that had seizures at 1.6 while on deco due to increased exertion (diving the USS monitor i think?).

 

[elan]

I usually breathe a mix with a PPO₂ of 0.21 during surface intervals to help off-gassing. Am I being too conservative?

As long as you do not exceed the oxygen load for 24hours

 

[cowdog77]

Originally Posted by pittyyofool
PPO limits are different for every one. I can run 1.8 all day and be fine, at almost 2.0 I start getting a few small signs of TOX and I know it is time to back off a bit. On the other hand I know someone that starts having TOX symptoms at 1.6 and anther that is 2.1."
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Lordy, lordy.......spooky stuff here.:depressed:

 

[diverdowndude]

Originally Posted by pittyyofool
PPO limits are different for every one. I can run 1.8 all day and be fine, at almost 2.0 I start getting a few small signs of TOX and I know it is time to back off a bit. On the other hand I know someone that starts having TOX symptoms at 1.6 and another that is 2.1."

I think the point of most of these discussions are to educate divers as to not earn a Darwin award and the bad press that follows- Looks like you and your buddies are well on your way to earning your own Darwin.

Just a dumb question: why would you be diving beyond 1.6 PPO knowing full well that a O2 hit will render you totally unconscious without warning?

What's frightening about Nitrox is the page of studies in my Rec Triox workbook . . . The variability between individuals and with the same individual on different days is enormous. It makes it quite difficult to propose a ppO2 above 1.0 that could be considered to be "safe". For a long time, 1.4 was felt to be pretty benign, but I know of two incidents where people seized on 1.4, and one died. It is extremely difficult to manage a seizing person underwater, and rarely successful even if the divers involved have extensive training. I don't want to risk it, myself.

There is a difference, too, in the motivations of recreational and technical divers. For a tech diver, reducing the ppO2 means doing more deco -- which in the majority of cases, is quite possible. Although hanging in cold water isn't fun, the people who do it are trained to do it, and the risk of more deco is substantially less than the risk of toxing. Most of the people I know who do staged decompression diving are very respectful of that risk.

But recreational divers have a motive to push ppO2s . . . more bottom time. Since they don't intend to go into deco (as a general rule) they are constrained by that pesky NDL. So it becomes attractive to use the hottest mix that will permit keeping ppO2s to whatever the diver has decided is safe FOR HIM. One hopes that's the agency's chosen standard, because the recreational diver is least likely to have a buddy who can recognize oxygen toxicity and manage a seizing diver to the surface.

I couldn't have said it better.... just my opinion.