Oxygen toxicity and air diving depth records

[Gene_Hobbs]

In the old days (and maybe still today) prior to training with oxygen rebreathers you did a standard oxygen tolerance test, which was 20 minutes (?) at 60 feet on pure oxygen. If you convulsed, you were out of the training. In a 1986 paper it is noted that, “The U.S. Navy standard Oxygen Tolerance Test was not sensitive enough to produce symptoms in the three oxygen-susceptible divers identified ...”

In any case, 60 FSW is 2.82 ATA of oxygen which is like 410 feet on air.

BTW: The Navy Transit with Excursion Limits for poure oxygen are 20 FSW with an excursion to 40 FSW for 15 min or 50 FSW for 5 min for a total dive not to exceed 240 min.

Refs for everyone else who did not just KNOW this.

Central nervous system oxygen toxicity in closed circuit scuba divers II.
Butler and Thalmann, 1986
RRR: 3045, PMID: 3727183
Abstract: Central nervous system oxygen toxicity is currently the limiting factor in underwater swimming/diving operations using closed-circuit oxygen equipment. A dive series was conducted at the Navy Experimental Diving Unit in Panama City, FL, to determine whether these limits can be safely extended and also to evaluate the feasibility of making excursions to increased depth after a previous transit at a shallower depth for various lengths of time. A total of 465 man-dives were conducted on 14 different experimental profiles. In all, 33 episodes of oxygen toxicity were encountered, including 2 convulsions. Symptoms were classified as probable, definite, or convulsion. Findings were as follows: symptom classification is a useful tool in evaluating symptoms of oxygen toxicity; safe exposure limits should generally be adjusted only as a result of definite symptoms or convulsions; the following single-depth dive limits are proposed: 20 fsw (6.1 msw)--240 min, 25 fsw (7.6 msw)--240 min, 30 fsw (9.1 msw)--80 min, 35 fsw (10.7 msw)--25 min, 40 fsw (12.2 msw)--15 min, 50 fsw (15.2 msw)--10 min; a pre-exposure of up to 4 h at 20 fsw causes only a slight increase in the probability of an oxygen toxicity symptom on subsequent downward excursions; a pre-exposure depth of 25 fsw will have a more adverse effect on subsequent excursions than will 20 fsw; a return to 20 fsw for periods of 95-110 min seems to provide an adequate recovery period from an earlier excursion and enables a second excursion to be taken without additional hazard; nausea was the most commonly noted symptom of oxygen toxicity, followed by muscle twitching and dizziness; dives on which oxygen toxicity episodes were noted had a more rapid rate of core temperature cooling than dives without toxicity episodes; several divers who had passed the U.S. Navy Oxygen Tolerance Test were observed to be reproducibly more susceptible to oxygen toxicity than the other experimental divers.

Since the topic of oxygen tolerance testing has come up again, these might be worth a look.

Symptoms of Oxygen Poisoning and Limits of Tolerance at Rest and at Work.
Yarbrough et.al., 1947
RRR: 3316, NEDU: AD0755472

Screening for oxygen intolerance in U.S. Navy divers.
Butler and Knafelc, 1986
RRR: 3046, PMID: 3705251
"Conclusions from this paper are: Screening for oxygen intolerance is complicated by intraindividual variation in oxygen tolerance; U.S. Navy diving using 100percent oxygen during the period studied has had an acceptable safety record according to the data on record at the Naval Safety Center; the OTT as currently administered by the U.S. Navy does not identify all individuals who are relatively susceptible to oxygen toxicity; those individuals who do fail the OTT are unusually susceptible to oxygen toxicity; and because of the need to continue to identify these unusually susceptible individuals, the OTT should continue to be administered to U.S. Navy diver candidates"

Screening for oxygen sensitivity in U.S. Navy combat swimmers
Walters et.al., 2000
RRR: 2358, PMID: 10813436
"Many factors other than individual sensitivity to HBO2 may contribute to the occurrence of O2 toxicity episodes during combat swimmer operations. The authors conclude that O2 tolerance testing of U. S. Navy SEAL candidates is not a useful screening test and recommend discontinuation of this test."

These papers are available for download from: http://archive.rubicon-foundation.org/

 

[Thalassamania]

Thanks.

 

[Gene_Hobbs]

Here are some others that Saturation recently pointed out that were VERY nice from 2003.

The key words for a search in the future to this link would be 02 toxicity, P02, oxygen tolerance, CNS toxicity

http://www.scubaboard.com/showpost.php?p=258723&postcount=31

http://www.scubaboard.com/showpost.php?p=261187&postcount=37

http://www.scubaboard.com/showpost.php?p=261612&postcount=41

http://www.scubaboard.com/showpost.php?p=1696798&postcount=14

 

[drbill]

I somewhat routinely dive to the 180 to 200' level on air, but my exposure times at those depths are brief (rarely more than a few minutes). My computer (Uwatec Aladin Pro) calculates the percentage of my CNS O-2 limit reached (I've never exceeded 5%, although I also would never rely entirely on the computer).

I'm glad previous posters emphasized the point that is a combination of the ppO2 AND duration of exposure to that level that must be considered. I consider 200 ft my max depth on air...besides, there is just enough light at that depth to film. And filming "deep ecology" is the only reason I go there in the first place.

 

[Mako Mark]

depth records are stupid IMHO, and I have dived deep air before it became politically incorrect to do so or even talk about it as it is now. The limits are not real limits, they are just guidelines based on probability, and unfortunately in diving when you finally discover where your limits are, it is because you have exceeded them and are about to die.

 

[scubak]

Like Dr. Bill, I have dived to 200ft on air for a purpose, not for a depth record. I have had dive buddies that have wanted to go deep on air (140 +/-)...I won't go there unless it is for some specific purpose. It is my understanding that your physiology changes day to day so what is "safe" for me today might not be safe for you (my buddy)...do I want to test those limits? NO!!! Do I want an "accident" or situation at that depth. NO!! I am trying to get further training to do those depths on the "correct" gas and with proper deco procedures.
Just my .02PSI...
Kirsten

 

[drbill]

I should add that there are very few buddies I would dive to those depths with. I know their capabilities and their experience. I can accept responsibility for myself, but cannot for someone else since I may have no idea of how they respond to narcosis at those depths. I'm the only one I'm willing to accept the risks for.

 

[Sundiver]

Each individual will has a different susceptibility to oxygen toxicity that actually will varies for that person.

In recreational diving using Nitrox it is generally accepted that 1.4 is the max PPO2 to plan for (sometimes you'll hear 1.6) These limits were chosen because for the average person on a average day keeping your exposure to those limits are very unlikely to cause oxygen toxicity.

Just like sometimes exceeding a PPO2 of 1.4 can cause trouble, sometimes you can exceed 1.4 and not have problems. Once you get above 1.6 it really is like playing Russian Roulette.

By the way CNS O2 tox, will go away when you ascend. The problem is if you have convulsed there is a large likelihood that your regulator came out of your mouth and you drowned. Thats hard to fix underwater.

It's not impossible just well on the crazy side.

Yes, well...
As a commercial diver, I frequently worked at 240-260 FSW on air. That is working, not floating. Many people have dove air on scuba past the 325 FSW (2.2 or so?) that used to be the O2 tox limit for commercial and military. I've supervised a guy working at 280 FSW on air for 120 minutes BT! BUT! Individual physiology is a determining factor. And the only place to determine that is in a chamber.

I would disagree that the limits have anything to do with averages. Those limits are set for the RECREATIONAL diver who has never seen the inside of a chamber and doesn't know what his/her susceptibility to O2 is. The are set there to hopefully insure that 0% will have tox problems.

So to rephrase the quote- sometimes SOME PEOPLE will have problems above 1.6. SOME PEOPLE will convulse at 1.7 or maybe even 1.5. If you don't know that you're not one of them, it would be prudent to follow the guidelines.

 

[Crazy Fingers]

Perhaps someone can answer this for me...

I was told by someone that there were no recorded instances of fatal/near fatal oxtox for young, male, in shape divers below 2.0 atm PPO2. Is this true?

Usually I set my limit at 1.5 atm, but wouldn't mind knowing my statistical odds. As it is now, I know the rec limits are set for Fred & Fran Fatass, the 50 year old, smoking, half-drunk vacation diving couple. I just don't know what's realistic for people of my age and fitness group, so I have been unwilling to go past the recommendation.

 

[Cheekymonkey]

Thank you for asking this question and for all the wonderful answers, this was something I was wondering about myself, and I found it very helpful.