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November 09, 2007

Nitrogen Narcosis

I've been thinking more about nitrogen narcosis, the threat to divers when they dive too deep. Given that humanity knows so much about just about everything, from putting hundreds of millions of transistors onto microchips the size of a fingernail, to decoding the human DNA, to building giant bridges and tunnels to running remote-controlled vehicles on the planet Mars, it's amazing how little we know about nitrogen narcosis. Almost every dive book mentions it, yet there seems little agreement on it other than that it can be dangerous and divers are susceptible to it and react to it in different ways.

The most common explanation is that as we go deeper, the higher partial pressure of nitrogen has some sort of impact on our consciousness. It's conjectured that perhaps at these higher pressures nitrogen dissolves into nerve membranes and thus causes them to function differently, perhaps affecting the way signals travel inside our brain. Some view that as a cool thing. Jacques Cousteau called it "rapture of the deep," which has a nice ring to it and doesn't exactly sound dangerous. Others have mentioned looking forward to some pleasant buzz. But even Cousteau, of course, knew it could be dangerous.

Almost everyone agrees that nitrogen narcosis can lead to unanticipated feelings and thus behaviors, and that is not a good thing when you have a hundred feet of water above you and your well-being and survival depends on logical thinking and remembering what you have learned. But how can you deal with something when you don't know what to expect, when to expect it or what it'll make you do, if anything at all?

I am an avid reader, and for the past year or two it's been mostly dive books. Nitrogen narcosis is mentioned in almost every one of them. In older books, or when quoting older passages, nitrogen narcosis is often likened to having a dry martini (consisting of mostly gin (or sometimes vodka) and a bit of dry vermouth) for every 50 feet of depth. So if you're at 100 feet, that's supposed to be like downing two dry martinis, and 150 feet three of them. That is a lot of booze on an empty stomach, and poured down the hatch. Others use the "martini law" with different rules, like narcosis effect being like one additional martini for every 33 feet, starting when you reach 66 feet. Some writers describe the martini comparison as politically incorrect.

My friend Dave, a former diver who let his skills lapse and hasn't gone diving in many years, remembers his experience with narcosis. He said he was diving off the coast of some nice, sunny, friendly place when suddenly everything seemed to look really cool and colorful and he saw some irresistibly interesting things down deeper. So deeper he went to check it all out. Next thing he knew his dive buddy had grabbed him and brought him back up to the 70 feet or so where his narcosis had set in. So for him it definitely had been "rapture of the deep," even if it wasn't particularly deep.

One area where most experts and accounts appear to agree is that unlike alcohol induced impairment, you can get rid of narcosis simply by ascending. So the assumption is that the impact of nitrogen narcosis is directly proportional to water pressure, or depth. So if you have the experience and presence of mind (or the luck) to be able to recognize and control narcosis, you simply ascend a bit if the impact of narcosis becomes too much. However, there are dissenting opinions. At least a couple of authors stated that, no, the impact of narcosis lingers, just as does the impact of alcohol. Perhaps not for as long, but it definitely won't just vanish if you ascend.

Everyone seems to agree that nitrogen narcosis is hard to pin down as it affects different people in different ways, that it can manifest itself in different ways, and that its onset is unpredictable even within the same individual under similar diving conditions. Not even the depth at which nitrogen narcosis begins to show itself is a given. Some are affected at fairly shallow depths whereas the onset occurs much deeper for others, and some seem almost immune (or at least able to control it effectively).

The symptoms described in literature vary to a great extent. Narcosis may cause pleasant feelings such as exhilaration, happiness, thrill, giddiness, or negative ones like anxiety, depression, or general gloom. As a result, judgment becomes impaired, vision may become impaired, and things can go bad. Most texts state that nitrogen narcosis affects all divers, that its effects are rarely noticeable at depths of less than 60 feet, that serious impairment happens at around 100 feet, and extreme depths of 300 feet or so on air result in narcosis induced halucinations and loss of consciousness (using the various "martini" rules, that'd be six to eight of them; I'd definitely be unconscious!)

Almost every dive book describes examples of narcosis, and, as expected, they vary greatly. In one book, an experienced wreck diver was said to become "addled" and essentially unable to think and function at just 85 feet. In other accounts, deep dives to well over 200 feet on air describe narcosis as just a minor nuisance. Everyone agrees that environmental conditions have a big impact on narcosis. If it is cold and dark, it seems to affect people worse. Then again, it hit my friend Dave at just 70 feet in friendly, optimal conditions.

These days technical divers use special breathing gas mixes to reduce the impact of nitrogen narcosis. For relatively shallow dives Nitrox, the breathing gas with more oxygen and less nitrogen, reduces the risk of narcosis, though it is primarily used to extend bottom time due to less nitrogen being absorbed into the diver's body. Nitrox is unsuitable for deeper dives because then the oxygen becomes the limiting factor as high partial oxygen pressures result in seizures. The answer is Trimix where oxygen, nitrogen and helium are mixed for optimal results (or least potential for damage) at deeper depths. A certain Trimix concoction may contain the proper percentage of oxygen to give the diver enough to sustain life but not so much as to cause seizures; a percentage of nitrogen that will result in enough bottom time for a given depth without the penalty of excessive decompression stops; and the rest in helium, a costly gas that has its own issues, some of them poorly understood and hotly debated.

There are examples of deep divers who used air and simply learned to cope with the impairment, others who switched to Trimix and praised the sudden clarity of thought they had during their deep dives where they'd become used to having to muddle through, and yet others who paid dearly for avoiding the cost of Trimix gasses in favor of plain compressed air.

So how does nitrogen narcosis affect me? Up to recently I simply did not know as my deepest dives had taken me only down to just under 70 feet. My high altitude dives in Lake Tahoe were different. The visibility was good, but several other factors might well have affected the onset of narcosis. I had never gone nearly that deep. The water was cold, down to 48 degrees. And then there was the impact of high altitude diving where equivalent depth is even deeper than actual depth.

So did it affect me? Well, on the first dive I felt a bit uneasy because it had been several months since I'd been diving and because, following my dive buddy Carol, I quickly found myself deeper than I had ever been before. We stopped around 80 feet or so and I felt uneasy. I looked up, knew I had 80 feet of water on top of me, and suddenly felt a slight onset of panic, the kind where you feel not quite right. When that happens on land, you may lay down or drink a glass of water or whatever. At 80 feet that isn't possible, but I knew I did not want to stop and needed to keep moving to keep the uneasy feeling from grabbing a hold of me. So I slowly swam around Carol, and the feeling passed. When she gave me the Ok? sign, I answered back. Ok. And followed her deeper. I had never expected the dive to be so deep and so impressive, but it was. Carol showed me the depth reading on her dive computer every ten feet and stopped to take pictures of it with her underwater camera. I'd taken mine along as well, the Olympus 770SW.

We were now pretty deep and Carol, who was a few feet below me, motioned for me to come down to her. I checked my dive computer and saw 94 feet. She had wanted me to experience 100, but for now 94 felt enough to me. I did not feel compromised or disoriented or buzzed in any way. On the way down to 94 feet I did realize that I had probably flooded the camera. The 770SW has a depth rating of 33 feet without deepwater housing, and I'd taken it down to 67 and Carol to 77. So it was not that I had simply forgotten about the camera; I simply expected it to continue to work. I did not write that off to narcosis, as in I'd completely forgotten that I had the camera with me. I hadn't.

The second Lake Tahoe dive was the Rubicon wall dive. Here we knew we were probably going to go deep, just not how deep. We didn't even know at what depth the wall started. This time we used hoods and gloves so that we'd be less affected by the cold. Despite the unfortunate flooding episode, this time I took two cameras along, both Sealife Reefmasters. We found the wall at 70 to 80 feet. I'd wondered how I'd feel one I came face to face with the wall, where there suddenly would no longer be a bottom. Once I got there, I felt neither elation nor uneasiness, but simply followed Carol over the wall and down. It quickly got much colder, and Carol, who wore only a 4mm wetsuit stopped at 100 feet. I wore my hefty 7mm suit and felt fine. To the best of my recall, I still felt neither anxiety, giddiness or anything else unusual. I just felt good and in awe of everything I saw, as I always do on dives.

I was proud that I had finally reached 100 feet, but all seemed so well that I decided I wanted to push a little farther. So I motioned to Carol that I intended to go down to 110 feet. I didn't use the proper hand signals. Instead, I pointed at my depth reading, then signaled a number as I would on land. I pointed down, then showed five fingers, five fingers again and then one, for 11, or 110 feet. Then I slowly descended, watching my depth gauge. Once I reached 110, I was satisfied (well, very pleased is more like it), and ascended again to 100 feet where Carol hung. By now she was very cold and we began our ascent.

Had I experienced nitrogen narcosis? Was narcosis what made me feel uneasy for a minute or two on the first dive and also flood my camera, and then brave enough to descend another ten feet once I had reached the magic 100 mark on the second? I don't know. I don't think so as I never felt compromised and never did anything that either Carol or I felt was irrational or out of control.

So I don't know. Maybe I am one of the lucky ones who have a fairly high tolerance for nitrogen narcosis. Maybe it just didn't happen on those two first deep dives. Maybe it did happen and I just didn't notice. I don't know. Most likely I'll eventually find out.

Posted by conradb212 at November 9, 2007 11:21 PM