Check your buddy for signs of nitrogen narcosis with our simple test.

I remember vividly the first time I was narced. The world was amazingly bright and warm. Every thought that passed through my mind was hilarious. I was convinced that this very moment was the best I'd ever had. Though some voice in the background was telling me, "Uh-oh, we could get in trouble here," I just didn't care. This was too much fun.

Oddly, I wasn't diving at the time. It was late at night in the dairy aisle of a big supermarket and there were these 12 cans of Reddi-Whip. See, if you don't shake the can, and you hold it upright, hit the nozzle and inhale the propellant ...

OK, I'm really embarrassed. It was a long time ago, I fell in with a bad crowd and I would never, ever do anything like that again, no siree, and don't you kids try it either, hear me?

This tale from my sordid past has more to do with diving than you might think. The stuff that pushes Reddi-Whip out of the can is the same stuff that gets dentists their party invitations — nitrous oxide, a general anesthetic. And while researchers don't know for sure what causes nitrogen narcosis in divers, they think it's the same process.

That's right: You're not getting high down there, you're getting comatose.

100 Percent at 100 Feet

Obviously, general anesthesia while surrounded by doctors loaded with malpractice insurance is one thing, and doing it to yourself while breathing through some artificial gizmo, under water and with your life depending on your wits, is another. Yet if you dive to 100 feet on air, your chance of getting narced is almost 100 percent.

Don't believe it? You've been that deep — and deeper — many times and never felt narced? You're like the guy who thinks he's able to drive home from the party because he's done it before without crashing. The first symptoms of nitrogen narcosis are subtle, and one of them is denial that anything is wrong ("I'm feeling great!").

"A lot of people have narcosis but don't ever know it because they're never called upon to do anything but breathe. It's when something happens that requires a response that they get in trouble," says Hal Watts, who has trained thousands of deep divers at Forty Fathom Grotto in Ocala, Fla.

Though you hear a lot about decompression illness, you should probably worry more about nitrogen narcosis 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.

In fact, the threat of nitrogen narcosis, not DCI, is the primary reason for setting the traditional recreational depth limit at 130 feet.

How Nitrogen Narcosis Messes With Your Mind

It resembles a lot of the entertaining drugs: First it makes you silly, then it makes you stupid.

That's a huge simplification, of course, and researchers can't agree on exactly how narcosis alters your thinking. Three effects have been generally recognized, however:

YOUR THINKING PROCESS SLOWS DOWN. Researchers frequently give subjects puzzles and math problems to do while narced. Often they can perform as well at narcotic depth as at the surface — if they take more time. If they rush, however, they make mistakes.

Diving requires clear thinking more often than quick thinking, but in an out-of-air emergency, for example, you're likely to rush, and if you're narced, you're more likely to make mistakes.

YOU LOSE MULTITASKING ABILITY. It becomes harder to think about several things at once, and you tend to become fixated on a single idea. Sometimes subjects in recompression chambers are able to solve puzzles better and faster at depth than on the surface. This drives researchers crazy. The explanation seems to be that they "cheat" the test by concentrating all their reduced mental power on one object, getting the right answer. But chamber "divers" don't have to worry about their gas supply, time, depth, etc.

Diving is a multitask activity. While thinking about where you're going and what you're looking at, you also have to be aware of your buoyancy, your depth, your tank psi, how you're feeling, your buddy, how he's feeling and more. If a problem arises, you have to be able to consider several options and switch to Plan B quickly if Plan A doesn't work. Narcosis, however, reduces your perception of danger and your options for dealing with it.

YOU LOSE SHORT-TERM MEMORY. Working divers who are narced often forget the tasks they were sent down to perform, and when they surface, forget that they forgot. They tend to lose first what they have learned most recently and practiced least.

Few of us practice emergency skills like weight ditching and air sharing. When narced we may forget how to do them, or forget to do them entirely. Likewise, a new BC or computer with unfamiliar controls may become confusing.

Wait, There's More!

Actually, there's some good news about how nitrogen narcosis affects your mind.

IT DOESN'T GET WORSE WITH TIME. After about two minutes at a given depth, you are as narced as you're going to get.

WHEN YOU ASCEND, IT GOES AWAY ALMOST IMMEDIATELY. Often, ascending only 10 feet or so is enough to clear your head.

THERE'S NO LONG-TERM DAMAGE. Once you've surfaced it leaves no after-affects or permanent harm (as far as anyone knows).

How to Beat Narcosis

Yes, the exact mechanism of nitrogen narcosis is a mystery, but we've learned enough about it (often the hard way) to understand how to manage the problem.

Start by assuming you will be narced. The amount of narcosis you'll experience on a given day is a function of depth, but it's hard to predict what depth is "unsafe." To add to the uncertainty, some divers are more susceptible than others, and all divers are more susceptible on some dives than on others.

As a rule of thumb, most divers have some slight impairment at 60 feet, though it might not become noticeable until, say, 100 feet. At 130 feet, virtually all divers will have significant, though still manageable, narcosis. They might not realize it themselves, but it would be clearly detectable by a non-narced observer or by an objective test.

Bottom line: You could probably avoid all detectable nitrogen narcosis by staying above 60 feet, but you'd miss a lot of good diving for no good reason. Instead, assume you will be narced to some degree, take it seriously, minimize it and compensate for it. Here's how:

AVOID TASK LOADING. Remember the K.I.S.S. principle, because stupid is what you'll be. If you've got a new and confusing camera housing, get familiar with it at shallow depths. And it's not just the picture you might screw up at 130 feet. You've got a diminished amount of attention to devote to everything, and if you concentrate almost all of it on f-stops, you won't have enough left for the little things like, say, how much air you have left. Diving with only one piece of new equipment at a time is always a good rule. Below 100 feet, it's a rule to live by.

OVERLEARN SKILLS. This is, in effect, similar to reducing task loading, but it applies especially to emergency skills. You and your buddy should actually practice skills like weight ditching and air sharing. They seem too simple to need practice, but if they don't feel instinctive you may not do them when you're narced. Don't depend on doing anything you have to think about.

USE A SLATE. Free up RAM by using your slate. Don't rely on remembering your dive plan; write it down. Don't try to remember what the fish looks like or how the camera controls work; write it down. A slate is also useful in detecting narcosis — see below for "Are You Narced? Tests for Nitrogen Narcosis."

SCHEDULE GAUGE CHECKS. When you're going deep, agree with your buddy on gauge checks at specific intervals--say, every two minutes. (Air goes fast at 100-plus feet.) Does one of you consistently miss the two-minute deadline? He may be narced.

SCHEDULE BUDDY CHECKS. Agree to look for each other at specific intervals, say, every three breaths. Less often (say, at the two-minute gauge check), make eye contact and exchange OK signs.

DESCEND SLOWLY. There is some evidence that rapid compression causes more narcosis.

STAY CLEAN AND SOBER. Sounds obvious, but even over-the-counter medications can promote nitrogen narcosis. It is well-known that several drugs can interact in surprisingly intense ways (so that 1 + 1 equals 3), and nitrogen can be considered a drug in this case. Many drugs, including motion sickness pills and cold preparations, seem to interact with nitrogen to increase narcosis susceptibility and intensity.

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). A hangover can also promote nitrogen narcosis. Here's some real bad news for dive resort bars and those who love them: One authority, Dr. Lawrence Martin, has written that total abstinence for 24 hours before diving is a "reasonable recommendation." Better dial back those margaritas if you're diving deep tomorrow.

BE WARM, RESTED AND CONFIDENT. Cold, fatigue and anxiety have all been shown in experiments to increase nitrogen narcosis, though the cause is unknown. This is another reason why the last dive of the day should not be deep.

High levels of carbon dioxide in particular seem to increase narcosis. That can be caused by fatigue — by finning hard into a current, for example — or by a hard-breathing regulator, or by the shallow breathing that often accompanies anxiety. Try to take slow, deep breaths with complete exhalations.

ASCEND SLIGHTLY. Often, narced divers find that their heads clear if they ascend only 10 feet or so. And sometimes they can descend again with less narcosis than before.

BE POSITIVE AND MOTIVATED. Again, experiments have shown that divers who have a strong desire to conquer narcosis and believe they can, actually do.

What's In a Name

Nitrogen narcosis has been called everything from "compressed air intoxication" to "rapture of the deep." More properly, it's "inert gas narcosis" because any inert gas — and even some non-inert gases — can cause it. Nitrogen just happens to be the major inert component in air, and therefore the main cause of narcosis in recreational diving.

Exactly why compressed inert gas makes divers loopy is still a matter of speculation, but as far back as 1899, H.H. Meyer noted that the more easily an inert gas is absorbed by fat, the more narcotic it is. For example, helium is about one-fourth as soluble in fat as nitrogen, and about one-fourth as narcotic. Xenon, which is used for surgical anesthesia, is about 25 times as soluble as nitrogen and about 25 times as narcotic.

This "Meyer-Overton Hypothesis" led A.R. Behnke, R.M. Thomson and E.P. Motley to the conclusion, in 1935, that it was the absorption of nitrogen by fat in nerve cells that causes narcosis. Just what happens then is unknown, but the leading theory of the moment is that narcosis occurs when fat structures in the nerve cells, possibly the cell membrane, swell with nitrogen to a certain "critical volume." This swelling disrupts nerve impulses by interfering with chemical neurotransmitters as they cross the synapses, the tiny gaps between nerve cells that form the circuitry of the brain.

Are You Narced? Tests For Nitrogen Narcosis

Dizziness, ringing in the ears, numb lips, air tasting sweet or metallic, difficulty reading small numbers on instruments, anxiety, short-term memory loss, numbness and tingling of lips, limbs or feet — all these have been cited as symptoms of nitrogen narcosis. Unfortunately, they can also indicate DCI or other problems or nothing at all and, if caused by nitrogen narcosis, they are not often early signs. You feel these, if at all, well after you're narced.

There are, however, a few tests that are more useful:

THE FINGER TEST. Bret Gilliam, a depth record holder on air, takes credit for inventing this one: 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). "If you really wanted to screw a guy up," writes Gilliam in Deep Diving, "you gave him all five fingers and then he had to use both hands to come up with a six-finger response."

THE SLATE TEST. Every few minutes, check your depth and psi and write them on your slate. Check your buddy's depth and psi and write them on your slate too. 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. It has the added value of promoting gauge checks.

APPROACH YOUR LIMITS GRADUALLY. Each diver experiences narcosis differently and at different depths. Some are more susceptible than others. Don't go directly from your last open-water certification dive to a 130-foot dive. Instead, test your personal envelope cautiously. Increase your maximum depth by increments of 10 feet or so. How did you feel at 60 or 80 or 90 feet? Any symptoms of narcosis? Did you stick to your dive plan? Did you make any mistakes or feel confused at any point? If all was well, try that depth again with more task loading on another day. When you're comfortable with 90 feet, go to 100. It's not a race to 130 feet.

THE BEHAVIOR TEST. Inappropriate behavior in your buddy is difficult to pin down, harder when it's in you. Is he (or are you) acting silly or euphoric, zooming around like a sea lion for minutes on end, for example? Diving is supposed to be fun, of course, but this much fun?

Sometimes narcosis takes the form of anxiety instead of euphoria, and this can be easier to detect. Do you find yourself constantly holding your reg in your mouth with your hand, or holding your pressure gauge in front of your face? Assuming no objective reason for this exaggerated caution, you may be narced.

Can You Adapt To Nitrogen Narcosis?

Scientists are doubtful, but many divers who frequently go deep believe that they become less susceptible to narcosis.

That belief was behind Bret Gilliam's training for his then-record dive to 452 feet on air in 1989. He worked down to that depth with more than 600 dives over the course of a year, and at least 100 of them were deeper than 300 feet. That's why, he believes, he was not so narced at 452 feet that he couldn't do a series of math problems and, more to the point, return to the surface alive.

However, many researchers believe this apparent resistance to narcosis may not be a true physical adaptation. It's more likely that divers who routinely dive deep have developed ways to offset the mind-clouding effects of narcosis. As a result, they have less anxiety and more practice at performing certain tasks. And the adaptation (if that's what it is) is short-lived: It goes away after five to seven days without deep dives.

In any case, the practice of approaching a deep dive in gradual steps is a prudent one. If your resort's star attraction is a deep wreck, make that dive later in the week. Work down to it with a couple of progressively deeper dives and you'll be better prepared to handle any bout of narcosis.

Ed.'s note: Divers differ. Some will experience these effects shallower or deeper.