Nitrogen narcosis is a temporary condition that can affect divers, primarily those venturing into deeper waters. It is characterized by an altered mental state resulting from breathing compressed gases at elevated pressures. This phenomenon is a significant consideration for underwater safety, as it can impair a diver’s judgment and physical performance.
What Nitrogen Narcosis Is
Nitrogen narcosis is a change in consciousness, neuromuscular function, and behavior caused by breathing compressed inert gases, most commonly nitrogen, at depth. Divers often call it “rapture of the deep” or the “Martini effect,” as it produces a state similar to mild intoxication. It occurs because nitrogen in the breathing gas becomes more soluble in body tissues under increased underwater pressure. Symptoms resolve quickly upon ascending to a shallower depth.
How It Affects Divers
The effects of nitrogen narcosis vary among individuals and with increasing depth, generally becoming noticeable around 30 meters (98 feet) and more pronounced at greater depths. Divers may initially experience subtle changes in cognitive functions, such as impaired judgment, reasoning, and concentration. This can progress to difficulty with complex tasks, short-term memory impairment, and a sense of euphoria or overconfidence. Some divers might instead feel anxiety or fear.
As a diver descends further, symptoms can escalate to include disorientation, loss of coordination, and reduced manual dexterity. In severe cases, divers may experience idea fixation, hallucinations, stupor, and even unconsciousness. These cognitive and motor impairments pose significant dangers in an underwater environment, leading to poor decision-making regarding dive planning, equipment, or emergency responses. The inability to recognize one’s own impairment is a particular risk, potentially leading to accidents.
The Science Behind It
Nitrogen narcosis occurs due to the increased partial pressure of nitrogen when breathing compressed air at depth. As divers descend, ambient pressure increases, causing more inert gas, including nitrogen, to dissolve into the bloodstream and body tissues. This increased solubility is relevant for lipid-rich tissues, especially in the central nervous system, including the brain. Nitrogen is approximately five times more soluble in fat than in water or blood.
The precise mechanism by which dissolved nitrogen affects the nervous system is not fully understood, but it involves interference with nerve impulse transmission. One long-standing theory, the Meyer-Overton hypothesis, suggests narcotic gases dissolve into nerve cell lipid membranes, causing a physical disruption that alters their function. This can lead to changes in ion permeability or affect specific receptors within the nerve cells. This interference slows brain activity and neural communication, producing the narcotic effects.
Prevention and Management
Several strategies help divers prevent or manage nitrogen narcosis for safer underwater experiences. Limiting dive depth is a primary method, as narcosis severity increases with pressure. Most recreational dive training recommends a maximum depth of 30 to 50 meters (98 to 164 feet) when breathing compressed air. Gradual descent rates also help the body adapt to increasing pressure more smoothly.
Avoiding factors that exacerbate narcosis, such as fatigue, anxiety, cold water, and alcohol or drug consumption before diving, is important. For deeper dives, experienced divers may use alternative gas mixtures like nitrox (enriched air) with lower nitrogen, or heliox/trimix (helium and oxygen/nitrogen mixture), as helium has no narcotic effect. If narcosis symptoms occur during a dive, the most effective management is to slowly ascend to a shallower depth until symptoms subside. It is crucial for divers to recognize the signs in themselves and their buddies and dive within their training and experience limits.