Nitrogen Narcosis

A reversible, anesthetic-like impairment caused by breathing nitrogen at high partial pressure, typically noticeable below about 30 m (100 ft) on air.

Nitrogen narcosis is the intoxicating effect of breathing nitrogen under pressure. As depth increases, the rising partial pressure of nitrogen acts on the nervous system much like an anesthetic gas, slowing thinking, dulling judgment, and narrowing focus. On air, most divers notice something around 30 m (100 ft), and the effect strengthens rapidly beyond that. Divers describe euphoria, anxiety, tunnel vision, or simply doing dumb things, like misreading a gauge or forgetting the plan. The old rule of thumb compares each 15 m to one martini.

The danger is not narcosis itself but what an impaired diver does: blowing past planned depth, ignoring gas supply, or fumbling a simple task. The fix is beautifully simple, because narcosis is entirely reversible: ascend a few meters and the fog lifts within moments, with no lasting effects. Cold, darkness, exertion, CO2 buildup, and anxiety all make it worse, so the same depth can feel very different from one dive to the next.

Susceptibility varies between divers and between days, and you cannot train it away, only learn to recognize it. Technical divers manage narcosis by replacing part of the nitrogen with helium, breathing trimix to keep an equivalent narcotic depth around 30 m or shallower. A simple habit on deep dives is to run periodic self-checks: read your gauges, restate the plan to yourself, and treat any unusual feeling as a signal to get shallower.