At approximately what depth on air does nitrogen narcosis typically begin?

• A. 130 fsw
• B. 200 fsw
• C. 50 fsw
• D. 300 fsw

Answer: (A)

Nitrogen narcosis happens because dissolved nitrogen under pressure affects the nervous system. On air, the narcotic effects typically begin at about 130 feet of seawater (fsw). At that depth, ambient pressure is high enough that the nitrogen you’re breathing has a noticeable narcotic effect, leading to symptoms like altered judgment, slowed thinking, or impaired coordination. The exact depth can vary between divers, but 130 fsw is a common reference point for when narcosis may start to appear. If symptoms show up, ascending to shallower depths usually reduces or stops the effect. Using gas mixes with less nitrogen or including helium can delay onset for deeper dives.