It’s an underwater “martini effect”: Breathing nitrogen under pressure produces an intoxicating effect known as nitrogen narcosis, which is sometimes called “rapture of the deep.”

“A lot of people compare nitrogen narcosis to drinking alcohol,” says Eric Douglas, who writes the Lessons For Life column for our sister magazine Scuba Diving. “For the same reasons that drinking and driving is a bad idea, nitrogen narcosis is dangerous. You make poor decisions — such as thinking, ‘I can go just a little deeper’ — or you don’t pay attention to your air supply or even realize you are in trouble until you are in real trouble. Even then, you might not respond to the emergency properly.”

A former colleague once described the first time he realized he was “narced”: “I was noticing all the pretty fishes,” he recalled. OK, that doesn’t sound too crazy; we divers love seeing fish. “But then I began waving at them, and feeling like I had just inhaled the propellent in a Reddi-Whip can,” he added. “It was fun, but I knew my judgment was impaired.”

He was at 120 feet, and he wisely chose to begin his ascent, signaling his dive buddy by using the hand signal for narcosis (see below). That’s when he noticed that his buddy was clearly grinning through his regulator.

As he ascended, his head cleared, and he felt mentally sharp again. “Once I got to about 90 feet, I lost that silly feeling. Afterward, I thought, ‘we could have gotten into trouble if we had stayed longer. We were both narced.’”

Narcosis isn’t usually serious or overly dramatic, like decompression sickness or an arterial gas embolism are. “Gas narcosis — a more proper name than ‘nitrogen narcosis’ because oxygen is likely narcotic — isn’t thought to be directly hazardous. It more commonly causes simple errors,” says Karl Shreeves, who designs and authors PADI’s training materials. “The risk is that these errors can compound into serious situations.”

Though you hear a lot about decompression illness, you should probably worry more about nitrogen narcosis when you dive deeper than 100 feet. At that depth, nitrogen narcosis is more likely than a DCI “hit.”

Related Reading: What Happens if You Miss a Decompression Stop?

The Martini Effect

Though most divers experience symptoms of nitrogen narcosis at depths greater than 100 feet, symptoms may occur in depths as little as 33 feet.

Symptoms include:

• Light-headedness
• Ringing in the ears
• Numb lips, hands or feet
• Inattention and/or difficulty concentrating
• Poor judgment
• Anxiety
• Decreased coordination
• Hallucinations

The Effects Of Nitrogen Narcosis

Though there is a constellation of symptoms, these three main effects are what should concern you:

1) You don’t think clearly. “It it like getting behind the wheel of your car when you’re drunk. You might ‘think’ you are doing great, but in reality you just drove your car into the side of a building,” says Douglas.

2) You are unable to multitask. You may become hyper-focused on one thing, like staring at one spot on a wreck. When you can’t process all the things you’ve been trained to do — such as monitoring your time and gas — nitrogen narcosis reduces your ability to manage risk and dive safely.

“Divers can tend to act irrationally when ‘under the influence’ of nitrogen narcosis and forget to do important things like check their air gauge and watch their bottom time," says Jo Mikutowicz, managing partner of Divetech on Grand Cayman.

3) You forget what the dive plan was. This happens especially to divers who have a specific task to complete during the dive, or to a diver who begins to dive deeper than planned. “It’s always acceptable to be more conservative than planned, but being less can lead to problems,” says Shreeves.

Adds Douglas: “There are dive accident reports where divers have made deep dives on air and simply kept swimming deeper and deeper without ever stopping to look around or check their depth or pressure gauge. It becomes a safety question as to whether you, as a rescuer, should attempt chase a diver who is descending without stopping. You are likely to get narced, too. Then, both of you are in trouble.”

Factors That Increase The Risk

While nitrogen narcosis is not completely understood, there are some factors that are thought to increase the risk:

• Cold water temperatures
• Rapid descent
• Anxiety
• Alcohol or sedatives
• Fatigue
• Carbon dioxide excess

“The primary variable affecting narcosis is depth,” says Shreeves. “But physiologists tell us that it can be variable in an individual. Also, any drug — prescribed or otherwise — that has cautions about possible impairment could combine its effects so that a diver experiences narcosis shallower.”

Avoiding The Effects

These four things can help you avoid — or at least manage — nitrogen narcosis.

1) Take a course in deep diving from a qualified instructor.

2) Be rested and sober. “Being fatigued probably makes you more susceptible,” says Douglas. “I am sure being intoxicated on drugs or alcohol would amplify the effects of nitrogen narcosis, but that just makes it an even dumber idea to drink and dive.”

3) Plan your dive, dive your plan. “Be cautious before deviating from your dive plan, especially when narcosis may affect your judgment,” says Shreeves.

4) Watch your buddy. “The main things to watch with a buddy — and yourself — that suggest narcosis is a concern is poor coordination and lack of attention to safety procedures,” says Shreeves. “Within recreational limits, narcosis is rarely extreme — its effects are milder, and therefore sometimes easier to overlook.”

Overlooking signs of narcosis can happen when your buddy is someone you don’t know or who you’ve never dived with before. “If you notice your buddy making fast, erratic movements, not paying attention to her depth or air gauges, or giving you a blank stare when asked if OK, she's probably narced,” says Miktowicz.

“A sure sign of nitrogen narcosis is if you signal to your buddy, you are sure he or she sees you, and there is no acknowledgment,” says Douglas. “They look at you and there is no recognition that you are even there. That is likely tunnel vision.”

Also look for silly behavior. “Euphoria or uncontrolled laughter is sign of nitrogen narcosis, like the feeling of laughing gas,” says Douglas. “If your buddy starts taking his regulator out of his mouth and smiling at you or taking his mask off for no good reason — things he wouldn’t normally do at 30 feet — you have a good reason to be concerned.”

Adds Miktowicz: “When your buddy thinks it is funny to take her regulator out and give the fish some air, you need to move to a shallower depth.”

Two simple tests to administer while you’re underwater are the finger test and the slate test. Make these a part of your agreed-upon dive plan, and make them a part of your underwater buddy-check when diving deep.

In the finger test, one of you holds up a certain number of fingers to the other, and the buddy flashes back the same number plus one. In the slate test, every few minutes, jot down your depth and psi. Your buddy does the same on his slate. If the numbers are wildly different, one of you may be narced.

Finally, monitor your instruments. The slate test above promotes this. “Stay as shallow as you can on a deep dive,” advises Shreeves. “It helps keep you clear-headed and increases your bottom time.”

Related Reading: How Do I Stay Comfortable in Cold Water?

READ A PADI INCIDENT REPORT ON TWO DIVERS IMPACTED BY NITROGEN NARCOSIS

Reversing The Effects

Ascent reverses the symptoms of nitrogen narcosis. Often, an ascent of only 10 or 20 feet will clear the fogged feeling in your brain.

“If someone seems affected by narcosis, ascend to a shallower depth,” says Shreeves. “End the dive if you must, but often simply coming up to a shallow level to finish the dive is all you need to do. A good rule of thumb is that while diving, never revise the dive plan in a liberal direction — conservative is OK. In other words, if you plan a max depth of 80, don’t change it to 100 while you’re at 80 — but it’s OK to decide 70 is deep enough. That way, you stay within limits set without narcosis being a factor.”

Once you’ve reached your agreed-upon depth, will the effects of nitrogen narcosis worsen? After about two minutes at a given depth, you are as narced as you’re going to get, but can your body adapt and become immune to the effects of nitrogen narcosis?

“With experience, we compensate for narcosis, but physiologists tell us that we don’t truly adapt,” explains Shreeves. “Diving the USS Monitor in the early years of tec diving, we were using air at 220 feet. I was hammered on the first dive I made and remember very little of it. A couple days later, I was functioning relatively normally — but recall that even so, passing 80 feet on the way up, my head would clear markedly.”

Editor’s note: If symptoms fail to resolve after ascent, narcosis is not the cause of the symptoms.

Anxious Moments

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? You may be narced.

I can remember the first time I dived to 130 feet, as part of my Advanced Open Water dive training. My instructor had me perform a few simple mental tasks on the boat — on his slate, he had me write my name backwards and do a few simple math tests, and then he timed me. I performed the exact same tasks once we were at 130 feet, and he timed me.

At the time, I remembered knowing that I had been cautioned that I might feel euphoric, but instead, I remember feeling very uncomfortable — I was cold, the water seemed dark and scary, and I just wanted to get back to the boat. I also experienced perceptual narrowing. I was focused on the slate, and performing the tasks as quickly as I could. I barely glanced around, and I was relieved when my instructor signaled that we’d begin our ascent. At about 60 feet, I remember the water felt warmer, and the reef was dappled by sunlight. I began to relax and realized I had felt cold, extremely nervous and tight.

Back on the boat, my instructor told me I had actually performed my simple tasks faster than I had on the boat before the dive. “You didn’t seem narced at all,” he said.

“No, it wasn’t at all like that,” I told him. “I think I was anxious — I couldn’t wait to finish those slate tests.”

“Oh, you were narced,” he said. “It just wasn’t a pleasant feeling for you — being narced can present as anxiety for some people.”

Eric Douglas has experienced both the silly and serious side of narcosis. “My two best narcosis stories are both in a hyperbaric chamber. The first time I went to 165 feet in a chamber was an experience dive. There was a group of us. Everyone was quiet during the compression phase, equalizing our ears and watching each other. When we got to depth, and the chamber got silent, someone spoke for the first time. Because of the air pressure, his voice sounded like Donald Duck. Everyone inside broke out into hysterical laughter. It was only then that we all realized that we were all narced. It was difficult to stop laughing and everything and everyone was funny for the few minutes we were at depth. As soon as they began reducing the pressure in the chamber, we all calmed down and stopped giggling.

“The second time was more serious. We were doing a US Navy Treatment Table 6A for a diver with an air embolism. That treatment begins with a descent to 165 feet of pressure. I was doing chest compressions on the diver. I remember the tunnel vision. I really couldn’t see more than the back of my hands, the diver’s chest and the sweat dripping off my nose onto the back of my hands. I was so focused, I wasn’t aware of anything going on around me.”

Editor’s note: Divers differ. Some will experience the effects of nitrogen narcosis shallower or deeper.