Narcosis in Scuba Diving: Understanding and Managing the Risk

Narcosis, a state of depressed mental function, is a phenomenon that can affect scuba divers, leading to confusion, drowsiness, or even coma. Commonly referred to as nitrogen narcosis, rapture of the deep, or inert gas narcosis, this condition results from breathing compressed air at increased pressures underwater. In this encyclopedia entry, we will explore the science behind narcosis, its symptoms, factors that influence susceptibility, and strategies for managing the risk.

Science of Narcosis

Narcosis occurs when divers descend to significant depths, typically beyond 30 meters (100 feet). At these depths, the increased pressure causes the partial pressure of inert gases, such as nitrogen and helium, to increase in the breathing mix. These gases can dissolve into the body tissues, leading to a change in the function of nerve cell membranes and, consequently, altered neurotransmission. This alteration in nerve cell function causes a reduction in mental faculties and can impair decision-making, problem-solving, and motor skills.

Symptoms and Manifestations

The symptoms of narcosis can vary in intensity and may present differently from one diver to another. Common symptoms include:

  1. Mild narcosis: Confusion, impaired judgment, mild euphoria, and overconfidence.
  2. Moderate narcosis: Slurred speech, dizziness, slowed reaction times, difficulty concentrating, and short-term memory loss.
  3. Severe narcosis: Hallucinations, extreme confusion, disorientation, unconsciousness, and coma.

Factors Influencing Susceptibility

Several factors may influence a diver’s susceptibility to narcosis:

  1. Depth: The risk of narcosis increases with depth. While some divers may experience mild symptoms at 30 meters (100 feet), most will be affected at depths beyond 40 meters (130 feet).
  2. Cold water: Cold water can exacerbate the effects of narcosis by increasing gas solubility in the tissues and impairing a diver’s ability to cope with the mental changes.
  3. Fatigue, stress, and anxiety: These factors may reduce a diver’s capacity to compensate for the mental impairment caused by narcosis.
  4. Alcohol or drug use: Consuming alcohol or drugs before diving can worsen the effects of narcosis and increase the risk of accidents.
  5. Individual differences: Divers vary in their susceptibility to narcosis, with some being more affected than others. This variability may be due to genetic, physiological, or psychological differences.

Preventing and Managing Narcosis

Narcosis is not entirely preventable; however, divers can take steps to minimize the risks:

  1. Limiting depth: By adhering to recommended depth limits, divers can reduce the likelihood of experiencing narcosis. Recreational divers should not exceed 40 meters (130 feet), while technical divers can venture deeper using specialized equipment and training.
  2. Gas mixes: Breathing gas mixes, such as trimix, that contain helium can help reduce narcosis risk. Helium, being less soluble than nitrogen, has a lower narcotic effect.
  3. Acclimatization: Gradually increasing depth exposure over time can help divers adapt to the narcotic effects of inert gases.
  4. Buddy system: Diving with a buddy can help divers monitor each other’s behavior for signs of narcosis and assist if needed.
  5. Proper training: Enrolling in advanced scuba diving courses can provide divers with the skills and knowledge to recognize and manage narcosis symptoms.

Recognizing and Responding to Narcosis

Divers should be aware of the signs of narcosis and know how to respond if they or their buddy experience symptoms:

  1. Ascend: If a diver suspects they are experiencing narcosis, they should signal their buddy and begin a controlled ascent to a shallower depth. As pressure decreases, the narcotic effect of the gas will diminish, and symptoms should improve.
  2. 2. Communicate: Divers should use hand signals to communicate any concerns about narcosis to their buddy. Regular check-ins can help ensure both divers are aware of each other’s condition.
  3. Monitor symptoms: If symptoms persist or worsen after ascending, divers should consider terminating the dive and returning to the surface. Narcosis symptoms can impair judgment and decision-making, so it’s essential to act conservatively.
  4. Log experiences: Divers should record their experiences with narcosis in their dive logs, including depth, symptoms, and factors that may have influenced their susceptibility. This information can be helpful for understanding individual sensitivities and planning future dives.

Safety Considerations

While narcosis is reversible and typically resolves upon ascending to shallower depths, it can pose significant risks if not managed appropriately. Divers experiencing narcosis may exhibit poor decision-making, which can lead to accidents, injuries, or even fatalities. In severe cases, a diver may lose consciousness or fall into a coma, necessitating emergency rescue and medical intervention.

Moreover, narcosis can mask or exacerbate other diving-related conditions, such as decompression sickness or oxygen toxicity. Divers should be cautious of these potential risks and prioritize their safety and well-being during dives.


Narcosis is a significant concern for scuba divers, particularly those venturing to deeper depths. By understanding the science behind this condition, recognizing the symptoms, and employing strategies to manage the risks, divers can enjoy their underwater adventures while minimizing the potential dangers associated with narcosis. Proper training, preparation, and adherence to safe diving practices are essential to ensure the well-being of both individual divers and the diving community as a whole.