Throughout your diving career you have been told that nitrogen is an inert gas, which has no biological purpose in the human body, and serves only to dilute oxygen. While this is true when air is breathed on the surface, nitrogen can have an adverse, and potentially narcotic effect when breathed under a higher partial pressure. This is called nitrogen narcosis.
Nitrogen narcosis can manifest in many different ways depending on the severity. Symptoms of nitrogen narcosis may include feeling intoxicated, euphoria, and lowered inhibitions. A diver experiencing nitrogen narcosis may act strangely, and ignore the predetermined parameters of the dive plan. Divers experiencing nitrogen narcosis have been observed removing their regulator form their mouth and making erratic actions under water.
Deeper depths may bring on more serious symptoms such as nausea, loss of memory, auditory and visual hallucinations, and potential loss of consciousness.
Divers affected by nitrogen narcosis may become disoriented and make an uncontrolled ascent to the surface, potentially resulting in decompression sickness or a gas embolism.
The exact cause of nitrogen narcosis is not known; however, the most accepted theory, based on recent studies, is that nitrogen under increased partial pressure dissolves into the myelin sheaths of nerve fibers changing their permeability and altering their nerve impulse conductivity properties.
The onset and symptoms of nitrogen narcosis are subjective. Some divers will experience symptoms between 24 and 30 meters / 80 and 100 feet. The onset of symptoms is rapid; though, the treatment is as equally rapid; simply ascend in a controlled fashion until the symptoms have subsided. The decrease in the partial pressure almost immediately reduces the effects of nitrogen.
It’s not always possible to determine the depth at which nitrogen narcosis will manifest, as it varies based on individual physiology and the diver’s overall condition. In fact, the depth at which it manifests for a particular diver often changes.
The best guideline to help prevent nitrogen narcosis is to avoid diving deeper than 30 meters / 100 feet. Though, it is possible to experience nitrogen narcosis at any depth. Also, recent research suggests that there may be a physiological adjustment process in regard to higher partial pressures of nitrogen. This means that diving in shallow depths may actually prepare a diver’s nervous system for deeper depths, which may help prevent nitrogen narcosis.
For this reason, it is recommended that divers who have not dived for a long period of time should perform shallow dives in the days before diving deeper.