Nitrogen narcosis is a temporary, reversible impairment of the nervous system that affects divers breathing compressed air at depth. This phenomenon is often referred to as “the rapture of the deep,” or the “Martini effect,” due to its intoxicating effects. The altered state of consciousness poses a threat to safety in underwater diving. The condition occurs because increased pressure forces the nitrogen component of the breathing gas to act as an anesthetic.
How Pressure Affects Nitrogen in the Body
The mechanism behind nitrogen narcosis is directly tied to the physical principles of gas behavior under pressure. As a diver descends, the surrounding water pressure increases proportionally with depth, which in turn increases the pressure of the air being breathed from the tank. This increase in ambient pressure causes the partial pressure of nitrogen, which makes up nearly 78% of the air mixture, to rise substantially.
The elevated partial pressure of nitrogen causes more of the gas to dissolve into the body’s tissues and bloodstream. Nitrogen is an inert gas, meaning the body does not metabolize it, but it is highly soluble in fatty tissues, particularly those of the central nervous system (CNS). The dissolved nitrogen disrupts nerve cell membrane function by dissolving into the lipid (fatty) portions of these membranes.
The effect is similar to that of a general anesthetic, slowing down the brain’s processing speed and reducing neuronal excitability. This interference disrupts the transmission of electrical signals between neurons. The severity of this anesthetic effect is directly correlated with the depth and the resulting partial pressure of nitrogen, becoming more pronounced as the diver continues to descend.
The Cognitive and Physical Effects
Nitrogen narcosis manifests as a decline in cognitive function, resembling alcohol intoxication. The symptoms are subtle at first, often beginning around the 30-meter (100-foot) depth mark. Early signs include mild light-headedness, a sense of euphoria, and poor judgment, which can lead to inappropriate behavior or overconfidence underwater.
As the diver goes deeper, cognitive impairment progresses to include difficulty concentrating, short-term memory loss, and delayed reaction time. More severe narcosis, which can occur at depths greater than 50 meters (165 feet), can lead to profound mental decline, including hallucinations, stupor, and impaired motor skills and coordination. This impairment of decision-making ability is the primary danger, as it can cause a diver to ignore established safety protocols or make errors with life-support equipment.
Prevention and Management Strategies
The most straightforward strategy for preventing nitrogen narcosis is to limit the depth of the dive. Recreational diving agencies commonly recommend a maximum depth limit of 30 to 40 meters (100 to 130 feet) when breathing compressed air. Proper pre-dive planning, which includes adhering to established depth limits, is a foundational safety measure.
Immediate management of narcosis is simple and highly effective because the condition is instantly reversible. If a diver recognizes the onset of symptoms while at depth, the appropriate response is to ascend slowly to a shallower depth until mental clarity returns. Ascending by just 5 to 10 meters (16 to 33 feet) is often enough to significantly reduce or eliminate the symptoms within minutes.
For dives that must exceed recreational depth limits, an advanced preventative measure involves substituting some of the nitrogen in the breathing gas mixture with helium. Gas mixtures such as Trimix, composed of oxygen, nitrogen, and helium, are used by technical divers because helium has no narcotic effect at these depths. Other contributing factors, such as fatigue, anxiety, cold, and a buildup of carbon dioxide from heavy exertion, can also increase a diver’s susceptibility to narcosis and should be managed through careful dive planning.