Diving Impaired

By John Francis

Nitrogen narcosis and too much fun

It's true what they say, getting narced is fun--of a certain kind. Similar to drinking way too

Which should indicate the downside. Not to sound like your mother here, but nitrogen narcosis is, in fact, drunk diving. Though you hear a lot about decompression illness, getting narced should probably be a bigger worry, at least when you dive below 100 feet. At that depth, nitrogen narcosis becomes more likely than a DCI hit, and when it occurs it is more dangerous because it attacks your most important piece of life-support equipment: your brain. That, not DCI, is the primary reason for the traditional recreational depth limit of 130 feet. But there's good news too: You can manage this risk and still dive safely below 100 feet.

What Is Nitrogen Narcosis?

You probably know the term "rapture of the deep" and have heard stories of divers offering their regs to fish and so on. Inappropriate euphoria and general silliness are the best known symptoms of nitrogen narcosis, though narcosis can also trigger anxiety, even terror. The exact mechanism is not well understood, but it's probably no coincidence that the usual symptoms resemble the early stages of general anesthesia. Compare, for example, the effects of the common dental anesthetic nitrous oxide, called laughing gas. "The same kinds of mechanisms are involved," says Dr. Peter B. Bennett, author of the chapter on inert gas narcosis in Alfred Bove's Diving Medicine. "General anesthesia and nitrogen narcosis both occur when a given anesthetic gas--and I would include nitrogen as one--reaches a certain critical molar concentration." In fact, nitrogen narcosis "may be considered as a state of impending general anesthesia" according to the authors of Diving and Subaquatic Medicine. Not the best mental state, probably, with 100 feet of water over your head.

Nitrogen narcosis has also been compared to alcoholic intoxication, the so-called "Martini Law"--each 50 feet of descent is equivalent to drinking one martini. Your thinking slows down. Your inhibitions and self-control are reduced, allowing euphoria or anxiety to emerge. Perceptual narrowing and a tendency to become fixed on one idea are common. Nitrogen narcosis, like alcohol, also impairs your motor control and memory. If it progresses far enough, you become unconscious. Precisely which mental functions are impaired, in what order and to what degree are debated by researchers, and studies have yielded conflicting results. What everyone agrees on, however, is that nitrogen narcosis degrades your ability to react quickly to a crisis and reason your way out of it.

Not You? You Wish

You've been below 100 feet many times and you've never been narced? Maybe. Divers, like drinkers, vary widely in their susceptibility, and you may in fact be more resistant to narcosis than some others. But it's hard to know that for sure based on your subjective feelings. "One of the biggest effects of nitrogen narcosis is an amnesia of what happened when you were down there," says Bennett. "Divers don't even remember what they were like." So you may have been more narced than you remember. Add forgetfulness to overconfidence and recklessness, other important effects of nitrogen narcosis, and you're like the guy leaving the party after a few too many who insists he's OK to drive. He has done it before and may do it again, but only if he's not called upon to react to a sudden emergency like a sharp curve and a stout tree.

Nitrogen narcosis is related to the partial pressure of the nitrogen in your gas mix, so narcosis becomes more likely as you go deeper. You may as well say nitrogen narcosis is caused by going deep. The threshold for significant narcosis on air is often said to be 100 feet, but that's only a rough guide. Actually, narcosis probably begins to appear as soon as you leave the surface. For example, a Navy test found slight but measurable effects at only 33 feet. It's a lot like asking what blood alcohol level constitutes drunk driving. The law states a number, though everyone knows there is some effect on your reaction time at lower levels.

Nitrogen and alcohol are different in some ways too. Serious, noticeable narcosis comes on more quickly whenever you reach your personal threshold depth. Studies show it reaches a peak within two minutes, and does not get worse even after three hours at that depth. It goes away very quickly as you ascend, and totally disappears before you reach the surface. As far as anyone knows, nitrogen narcosis, unlike alcohol abuse, does not do long-term harm and leaves no hangover. However, it's not what narcosis itself does to you that you should worry about, it's the harm you can do yourself because you're too narced to think clearly.

Many Unknowns

Different divers feel different amounts of narcosis at the same depth. The same diver may feel different amounts of narcosis at the same depth on different days. Narcosis takes different forms, too. Just as there are happy drunks, sad drunks and angry drunks, some divers are euphoric when narced, but some are terrified and some are just confused.

Some of the variables affecting all divers are:

Interaction with drugs. It is well-known that several drugs can interact in surprisingly intense ways, so that 1 + 1 equals 3. Some drugs, including anti-motion sickness pills, may interact with nitrogen to increase your narcosis susceptibility and intensity. Not much research has been done, but Bennett suggests that if a drug would increase the effect of alcohol, it's a reasonable assumption that it might increase nitrogen narcosis.

Interaction with alcohol. Drinking and diving is never a good idea, of course, and some experts think the nitrogen/alcohol interaction may be especially strong because they have similar effects on your nervous system--1 + 1 may equal 5, in other words. Even a hangover can potentiate nitrogen narcosis.

Interaction with carbon dioxide. Among the intensifiers of nitrogen narcosis, "carbon dioxide is a big one," says Bennett. "High levels of carbon dioxide in your blood are going to work with nitrogen to make narcosis worse." Elevated carbon dioxide levels generally result from rapid, heavy breathing. You may be working hard--finning into a current, for example--or sucking on a poorly performing regulator. Anxiety is another cause of rapid breathing and therefore high carbon dioxide.

Fatigue. Doing heavy work at depth seems to bring on nitrogen narcosis, though whether that's because of the elevated carbon dioxide that usually goes with hard work or is an independent effect of being tired is not clear.

Task-loading, time stress. Trying to do too many things, or trying to do too much in a short time, also increases the narcosis effect. Again, whether this is a carbon dioxide effect caused by the anxiety of trying to cope with too many tasks or an independent effect is not clear.

Cold. Being cold is often mentioned as a contributing cause of nitrogen narcosis. The reasons aren't known, but some of the effects of hypothermia are similar to those of narcosis, including mental dulling, sluggishness and amnesia. In addition to the variables that affect all divers, some divers seem to be more susceptible to nitrogen narcosis than others. Obviously the relaxed, healthy diver with good breathing habits and a low air consumption rate has an advantage over the nervous, heavy breather. Also, some experts think highly intelligent and emotionally stable divers are less susceptible to nitrogen narcosis.

Adaptation to Narcosis

Most divers who regularly go very deep on air are convinced that they become adapted to it and after a while have less trouble with nitrogen narcosis. Is it true physical adaptation (meaning the divers are actually less narced) or have the divers just learned to compensate better for it? That's another unknown. The adaptation, if that's what it is, is temporary. Most say it wears off in about five days.

In any event, common practice among divers who must go very deep using air is to work up to the depth by making the first dive of each day progressively deeper. In 1989, Bret Gilliam set a depth record on air of 452 feet, and worked down to the depth with more than 600 dives, at least 100 of them deeper than 300 feet. As a result, Gilliam was not so narced at 452 feet that he could not do a series of math problems and, more to the point, return to the surface alive.

How Deep Is Too Deep?

Gilliam's 452 feet on air is off the chart for the rest of us. Various studies have described the narcotic effect of air at 300 feet as "stupefaction," "severe narcosis," "marked impairment of practical ability and judgment," and even unconsciousness. Other reports: "severe impairment of intellectual performance" at 230 feet; "sleepiness, illusions, impaired judgment" at 165 feet; and "idea fixation, perceptual narrowing and overconfidence" in the 100- to 132-foot range. Probably the customary 130-foot limit for recreational diving in the U.S. is a good one until you know better your personal susceptibility to nitrogen narcosis and have trained yourself in coping with it. For diving much deeper than that, trimix (in which most of the nitrogen is replaced with less-narcotic helium) is probably a safer gas.

How To Tell If You Are Narced

That's tough because your judgment, the faculty you depend on to tell you if you are affected, is the first to be attacked by the narcosis. Returning to the analogy to alcohol, it's like asking how you can tell if your driving is affected after you've had a few drinks. In both cases, you should probably just assume it.

Some divers experienced with deep water like Gilliam have developed their own versions of roadside sobriety tests. Not foolproof, but better than nothing:

Every few minutes, check your depth and tank pressure, and write them on your slate. Check your buddy's depth and pressure and write them on your slate. Your buddy does the same on his slate. Now each of you has to point to your own and your buddy's numbers on both slates, and the slates have to agree. This test automatically compares both divers, which can be valuable if one diver is narced and the other is not.

Every few minutes, hold up a number of fingers to your buddy (say, three fingers). He has to respond with the same number plus one (four fingers). These "roadside" tests aren't foolproof because many of the effects of mild to moderate nitrogen narcosis can be overcome, or at least masked, if you try hard enough. Your mind can be impaired, but if you devote all your diminished resources to one job, you can do it well. This can drive researchers crazy. In one case, subjects in a chamber at a "depth" where they should have been narced performed the tests better than at the surface. In other studies, narced divers have often been able to attain good accuracy at the expense of speed, or vice versa. This means you might be able to perform the match-slates test or the count-fingers test and still be narced. So watch your responses (and your buddy's) for both accuracy and speed.

You are like the drunk driver who, by fierce concentration, is able to keep his car between the white lines. Obviously, the greater danger for both of you is the unexpected, not the routine. It's the entanglement or a regulator free-flow, the sharp curve and the tree. So leave the nitrogen party early and dive carefully. Mom's right: There is such a thing as too much fun.

How To Beat Narcosis

Start by assuming you will be narced if you go deeper than 100 feet. You can't prevent nitrogen narcosis entirely, but you can minimize it and compensate for it.

Be clean and sober. Avoid over-the-counter meds like Sudafed and Dramamine if you can, because they may potentiate the narcotic effect. It goes without saying that you shouldn't drink and dive, but even a hangover from last night's drinking can make narcosis worse and reduce your ability to cope with it.

Be rested and confident. Fatigue and anxiety may help trigger narcosis, and certainly are stresses that diminish your ability to solve problems.

Use a high-quality regulator in good condition. High breathing resistance elevates your carbon dioxide level, which potentiates narcosis.

Avoid task-loading. Don't try to do too much, because that causes stress and anxiety. Your first excursion below 100 feet is not the time to figure out a new camera housing, for example, because it will divert your diminished mental capacity from what's most important—diving safely. Keep it simple, stupid, because stupid you will be.

Be overtrained. Most of us never practice the basic safety skills like air sharing and weight dumping because they seem so simple. But under the influence of narcosis, the simplest tasks become more difficult. If you have to think about it, you may not be able to do it, and your repertoire of skills may be stripped down to those made automatic by frequent rehearsal.

Approach limits gradually. Don't go to 130 feet until you've been to 110 a few times, seen how you react and become comfortable with the depth. And descend slowly, as there is some evidence that rapid compression makes narcosis more severe.

Use a slate. Don't depend on remembering the dive plan or the camera controls; write them down. That frees up mental RAM for coping with the dive itself. And a slate is useful for narcosis tests like writing down depth and tank pressure.

Schedule gauge checks and buddy checks. Don't check your tank pressure only when you think of it. Plan to check at stated intervals, say every two minutes. Likewise, plan to look for your buddy and make eye contact on a schedule, like every minute. Discipline helps keep you focused, and if either of you consistently misses appointments, suspect narcosis.

Be positive and motivated. Experiments have shown that divers who want to conquer narcosis and believe they can, actually do. At recreational depths, narcosis is fairly mild and controllable. The key is to be optimistic but prepared, confident but prudent.

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