Nitrogen narcosis: when deep air feels like a drink
In short
Nitrogen narcosis is a reversible, alcohol-like effect of breathing nitrogen under pressure. Most divers notice it around 30 m (100 ft), some shallower: slow thinking, overconfidence, poor judgment, sometimes anxiety. It varies from diver to diver and day to day. The fix: signal your buddy and ascend a few meters together. It fades quickly.
You read your gauge three times and still can’t take it in. You feel oddly cheerful, and the reef looks wonderful. At 30 m (100 ft), that’s probably narcosis, and it can cloud the next decision you make.
What is nitrogen narcosis?
Nitrogen narcosis is a temporary change in how your brain works, caused by breathing nitrogen at high pressure. NOAA describes it as a reversible alteration in consciousness, caused by the anesthetic effect of some gases under pressure and usually noticeable around 30 m (100 ft). It isn’t a lack of air, and it isn’t permanent: it comes and goes with depth.
Why does depth cause narcosis?
Depth raises the partial pressure of the nitrogen you breathe. Air is about 79% nitrogen, counting the trace gases with it. At 30 m (99 ft), the absolute pressure is 4 bar (4 ata), so nitrogen’s partial pressure is 0.79 × 4 = 3.16 bar (ata), four times the surface value. Your body responds to partial pressure, not percentage: that’s Dalton’s law.
What are the signs of nitrogen narcosis?
Narcosis feels a bit like a drink or two. Signs taught to divers, and listed by NOAA and DAN, include:
- slow thinking, trouble reading or making sense of your gauges;
- overconfidence, euphoria, giggling;
- poor judgment, tunnel vision or fixing on one task;
- anxiety or fear instead of euphoria;
- memory gaps: you may not remember what happened at depth.
The danger lies in the mistakes it leads to: missing your turn pressure, drifting deeper, losing your buddy. Narcosis can also hide another problem. In a case reported by DAN, a diver at 35 m (115 ft) dismissed the burning pain of a jellyfish sting as part of his narcosis.
What makes narcosis worse?
DAN lists fatigue, depth, a personal history of susceptibility, alcohol before the dive and cold water. Anxiety, hard work, carbon dioxide buildup, a fast descent and dark or murky water are commonly taught factors too, though the evidence varies. Experience helps you recognize narcosis and plan around it, but nobody becomes immune.
Try a question from the app
narcosis and experience
True or false: with enough deep dives, a diver becomes immune to narcosis.
Show the answer
Answer B. Experience helps you recognize narcosis and plan around it, but nobody becomes immune, and the same diver can feel it more on some days than others.
What should you do if you feel narced?
Go up a little, together. Narcosis fades quickly as you ascend.
- Signal your buddy that something feels wrong.
- Ascend together a few meters (feet) and see if it clears. DAN notes that it typically resolves once you’re above the depth where it started.
- If it doesn’t clear, or if either of you feels uneasy, end the dive with a slow, normal ascent and your safety stop.
- Never make a fast ascent to make it go away, and never let a diver who seems narced swim off alone.
If your buddy drifts deeper, grins and ignores your signals, reach them, make contact and ascend a little together. End the dive if it doesn’t clear.
Try a question from the app
response to narcosis
At 30 m (100 ft), you read your gauge three times without taking it in, and you feel oddly cheerful. What do you do?
Show the answer
Answer A. These are signs of narcosis, and it fades when you ascend a little. Do it together: alone, you split the team. Staying at depth keeps the narcosis, and a fast ascent adds other risks.
How do you limit narcosis on deep dives?
You can’t switch it off, but you can plan around it:
- Plan before the dive. Agree on a maximum depth, a time and a turn pressure, and write them on a slate, as NOAA advises, so you don’t have to work them out at depth.
- Stay within your training. The limit of recreational diving is 40 m (130 ft), and your certification may set a shallower one.
- Arrive rested, sober and warm. Dress for the temperature at the bottom, not at the surface.
- Descend slowly, along a line if there is one, and avoid hard swimming at depth.
- Check your gauges and your buddy on a schedule, rather than when you remember.
Which dive training levels cover narcosis?
Open Water Diver introduces narcosis next to decompression sickness. Advanced Open Water covers it in detail, with deep diving. Divemaster adds the physiology, with oxygen, carbon dioxide and carbon monoxide. The Advanced Open Water practice questions include one on narcosis.
Frequently asked questions
At what depth does nitrogen narcosis start?
Most divers notice it around 30 m (100 ft), and some feel it shallower. NOAA describes it as usually noticeable around that depth. There’s no fixed threshold: the effect builds gradually with depth and changes between divers and from one day to the next, so plan for it rather than waiting for a number. The idea of a switch at 30 m (100 ft) is one of the dive theory myths.
Is nitrogen narcosis dangerous?
The feeling itself is temporary, but it impairs judgment where mistakes cost the most. DAN warns that narcosis makes diving dangerous because divers may make poor decisions, such as missing a turn pressure or drifting deeper. That’s why you ascend a little with your buddy as soon as either of you notices it.
How long does narcosis last after you ascend?
It fades quickly as you ascend. DAN notes that it typically resolves once the diver is above the depth where the symptoms first appeared. NOAA lists memory loss among the signs, so a diver may not remember what happened at depth. If symptoms don’t clear, end the dive.
Can you build a tolerance to narcosis?
No. Experience helps you recognize the signs early and plan around them, but nobody becomes immune, however many deep dives they’ve logged. The same diver can feel it strongly one day and barely the next, depending on fatigue, cold, effort and stress.
Does nitrox reduce narcosis?
Don’t count on it. Nitrox has less nitrogen, but oxygen is probably narcotic too, so dive nitrox as if your narcosis were the same as on air. Its benefit is longer no-stop times. Its oxygen also sets a maximum depth, explained in oxygen toxicity and nitrox.
