Mailing List Archive Mailing List Archive
The topic of "oxygen narcosis" has come up, and I thought I'd share an experience I had which leads me to believe that nitrox might be MORE narcotic at depth than air. Now, this anecdote involves some diving practices which are no longer considered "acceptable" in technical diving circles, but please bear in mind that this happened before nitrox made it to the big-time - back when we used to think the USN PPO2 limit of 2.0 ATM was acceptable for a working dive. In order to understand my conclusion, I need to explain a bit of background....This incident happend back in the late 80's - in a period in my life when I used to do a LOT of 200+fsw air dives, and a fair number of 300+fsw air dives. I had got to know my response to nitrogen narcosis very well over a range of depths. For me, something I call "warm" narocsis would start to become noticable at depths of anywhere between 150 and 220 fsw. The symptoms of this "warm" narcosis are, I believe, what most people think of when the think of narcosis - fuzzy thinking, reduced short-term memory, reduced ability for "parallel" processing in the brain, inebriation, etc. The onset of these symptoms occured at different depths, depending upon a wide variety of factors (how much deep diving I'd been doing, work load, personal condition, etc.). Whenever I descended below 275', however, the narcotic feelings would change to what I call "cold" narcosis. The symptoms (for me) included tingling in the extremities, strong paranoia, tunnel vission, etc.; but most importantly, instead of a "warm fuzzy" feeling, it would be a "cold, scary" feeling. The odd thing about this "cold" narcosis is that it happened consistently on air at a depth of about 275' - regardless of other factors. In other words, there was very LITTLE variation in the onset of these symptoms. Now, the incident I wanted to describe happened a number of years ago, during one of my trips to Rarotonga. One day, I made an air dive to 200' to a ledge I had been to several times before. All conditions were ideal (warm clear water, no current, etc.), and the "warm" narcosis came on just as it had on hundreds of previous dives to similar depths under similar conditions. The very next day, under identical conditions, I made the same dive to the exact same ledge. Every aspect of the second dive was identical (as far as can be determined) to the previous days' dive except one thing: this time I was breathing nitrox-29 (29% oxygen, balance nitrogen). On this second dive, I was hit with "cold" narcosis as soon as I got to the ledge. Basically, I felt like I was at 275', even though I was only at 200'. I have NEVER experienced those "cold" narcosis symptoms at a depth that shallow while breathing air. I am now convinced that the "cold" narcosis is related in some way to oxygen. If you work out the partial pressures, you'll see that the PPO2 was roughly 2 ATM on the nitrox-29 dive to 200' - essentially the same as air at about 275'. One explanation, therefore, is that the "cold" narcosis symptoms are not narcosis at all - but have something to do with oxygen toxicity. However, I have been much deeper than 275' on air many times, and although the "cold" narcosis symptoms increase in intensity with increase depths, I have never experienced any of the classic oxygen toxicity symptoms on any of these dives (e.g. twitching of facial muscles, etc.). Another complication is that I've never experience "cold" narcosis when breathing pure oxygen at high partial pressures. I've breathed 100% oxygen at a simulated 60fsw in a chamber for many hours without any sign of "cold" narcosis. I've even breathed O2 at 220' in a chamber (as a result of a mistake), again with no "cold" narcosis symptoms. Thus, it seems there is some sort of a synergistic effect with high PPO2's & PPN2's that causes intense (i.e., "cold") narcosis symptoms. Of course, there are other explanations for my "cold" narcosis other than actual "narcosis" (as it is with nitrogen) - things like constriction of perhipheral circulatory system, etc. But my main point is that nitrox is not necessarily a "less narcotic" breathing mixture at a given depth than air is. My one experience would suggest that, in fact, I become MORE impaired on nitrox at a given depth than air. Is this true of everyone? Who knows? But it's interesting to think about. I'd love to get involved with controlled chamber experiments to probe the question more carefully. I'm sorry this message was so long and hastily written. I just wanted to throw it out there while on the topic of narcosis. Gotta run.... Aloha, Rich
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]