Nitrogen narcosis is a reversible alteration in consciousness occurring in scuba divers at depth. Jacques Cousteau described it as the “rapture of the deep”. As divers descend, the increased partial pressure of nitrogen in the compressed air in their tanks produces a state similar to alcohol intoxication. The effect occurs at any depth, but does not usually become noticeable until depths of around 30–40m.
The precise mechanism that causes “the narks” is not known, but appears to be a direct effect of nitrogen dissolving into nerve membranes and causing temporary disruption of nerve transmission. Other gases, including argon, krypton and hydrogen, cause similar effects under raised atmospheric pressure.
Because of its perception-altering effects, the onset of nitrogen narcosis can be hard to recognise, its severity unpredictable, and its outcome sometimes fatal as a result of the subsequent illogical behaviour in a dangerous environment. Its effects disappear quickly following ascent to shallower water.
Nitrogen narcosis causes a loss of decision-making ability and a loss of focus. It impairs judgement, multitasking and co-ordination. The syndrome can cause exhilaration, giddiness, extreme anxiety, depression or paranoia depending on the individual. All divers are affected but some less so than others.
The relationship between depth and narcosis has been referred to as “Martini’s law”, based on the concept that narcosis results in the feeling of having drunk one martini for every 10m descended below 20m.
Cold, stress, heavy work and fatigue all increase the risk and severity of nitrogen narcosis. It is additive to the effects of drugs such as alcohol, marijuana, opiates and benzodiazepines.
A hangover makes narcosis more likely, as well as increasing the risk of decompression sickness (the “bends”) through the associated dehydration. Experts recommend total abstinence from alcohol for at least 24 hours before diving and a longer period still for marijuana because of its longer half life.
Nitrogen narcosis can be reduced by replacing a portion of the nitrogen in the gas mixture with helium, thus reducing the partial pressure of nitrogen at depth. But the simplest way to avoid getting “narked” is to limit the depth of dives.
