Abyss Scuba Diving

Understand Nitrogen Narcosis


Understanding Nitrogen Narcosis: Essential Tips for Safe Scuba Diving

What if, mid-dive, you start to feel disoriented, almost drunkenly euphoric, with your judgement clouded? This phenomenon, known as narcosis, can strike divers at depths typically beyond 30 meters. Narcosis affects your consciousness and can dangerously impair your motor skills and decision-making abilities underwater. This article delves into the causes, symptoms, and preventive strategies for narcosis, arming you with essential information for safer diving experiences.

Key Takeaways

  • Nitrogen narcosis, often called ‘the rapture of the deep’ or ‘the martini effect,’ affects scuba divers at depths exceeding 30 meters, impairing judgment and neuromuscular functions due to breathing compressed inert gases.

  • The onset of nitrogen narcosis is related to increased solubility of gases under pressure, leading to more nitrogen absorption in the bloodstream and tissues; understanding gas solubility, the impact of pressure, and the concept of partial pressures is crucial for divers.

  • Preventing nitrogen narcosis involves careful dive planning, selecting the right breathing gas like helium or trimix for deeper dives, adherence to ascent rules, and specialised training for managing the effects of narcosis.

Understanding Narcosis in Scuba Diving

Image of a scuba diver experiencing nitrogen narcosis

Imagine diving into the mesmerising underwater world, exploring the vivid marine life, when suddenly you start feeling a bit tipsy, almost drunk. Nitrogen narcosis is characterised by a change in consciousness, as well as alterations in neuromuscular function and behaviour. It is caused by breathing compressed inert gases, such as nitrogen, at depth. This intoxication-like effect, also known as ‘the rapture of the deep’ or ‘the martini effect,’ can impair a diver’s judgment and decision-making capacity. Some symptoms of nitrogen narcosis include:

  • Euphoria

  • Impaired judgment

  • Loss of coordination

  • Dizziness

  • Confusion

  • Hallucinations

It is important for divers to be aware of these symptoms and take appropriate precautions to ensure their safety while diving.

Interestingly, this “martini effect” isn’t instantaneous but gradually sets in as you dive deeper. Divers often begin to experience the effects of nitrogen narcosis at depths exceeding 30 meters. This depth correlation is humorously referenced as “Martini’s law,” suggesting that descending every additional 10 meters underwater is akin to consuming one more martini, thus relating depth to the progressively intoxicating effects of narcosis.

The Science Behind Nitrogen Narcosis

But why does nitrogen, a gas that makes up almost 78% of our atmosphere, cause such effects under water? The science behind nitrogen narcosis involves increased solubility of gases under pressure, the impact of pressure on gas absorption, and the understanding of partial pressures in a gas mixture. Let’s dive deeper into these aspects.

Not just compressed nitrogen, but other inert gases like neon, argon, krypton, and xenon can also induce inert gas narcosis when breathed under pressure. The narcotic effects of these gases increase under pressure, affecting consciousness and neuromuscular function. As a rule of thumb, the risk of impairment due to nitrogen narcosis begins at approximately 30 meters, with depth being the primary factor affecting narcosis. Additionally, volatile substances induce narcosis, which further highlights the importance of understanding the effects of various gases on the human body.

The Role of Gas Solubility

When diving, as we inhale compressed air, the inert gases we breathe can dissolve in our body tissues and trigger narcosis symptoms. This solubility of gases in our body tissues is a key factor in the onset of narcosis.

The concept of gas solubility is fundamental in understanding narcosis. All gases are soluble to some degree in body tissues. Under normal conditions at sea level, these gases remain in a balanced state. However, as we dive deeper, the pressure increases, leading to a higher volume of gases getting dissolved in our body tissues, thereby triggering narcosis symptoms.

Impact of Pressure on Gas Absorption

The effect of pressure on gas absorption plays a critical role in nitrogen narcosis. As divers descend underwater, the surrounding pressure increases proportionally with depth. This increased pressure leads to a higher volume of inert gas dissolving in a scuba diver’s bloodstream and tissues.

This greater absorption of inert gases into the bloodstream associated with deeper depths can contribute to the risk of narcosis and other diving-related complications. Thus, understanding the relationship between pressure and gas absorption is crucial in managing the risk of nitrogen narcosis.

Understanding Partial Pressures

To fully grasp the science behind nitrogen narcosis, we need to understand the concept of partial pressures. According to Dalton’s law of partial pressures, each gas in a mixture of gases exerts its own pressure as if the other gases were not present. This plays a significant role in narcosis as depth increases.

As divers go deeper and the total pressure increases, the partial pressure of nitrogen in the blood increases correspondingly. This can lead to impairments in manual dexterity and is a contributing factor to narcosis. Understanding this principle of partial pressures is key to managing the risks associated with nitrogen narcosis.

Identifying Symptoms of Nitrogen Narcosis

Illustration of a diver experiencing vertigo and confusion underwater

Now that we’ve understood the science behind nitrogen narcosis, let’s look at how it manifests itself. Symptoms of nitrogen narcosis include:

  • Cognitive impairment

  • Decision-making difficulties

  • Physical manifestations such as vertigo

  • Emotional reactions

These symptoms can vary among divers and may be influenced by factors like alcohol consumption, fatigue, and high carbon dioxide levels.

As a precursor to more severe symptoms, divers may experience a sense of euphoria or mild intoxication, impaired manual dexterity, and mental decline. Nitrogen narcosis can severely affect diver cognition, leading to impaired judgment, difficulty with short-term memory and concentration, and eventually idea fixation, hallucinations, and stupor with increased depth.

Cognitive Impairment and Decision Making

Just like a few martinis can impair your decision-making skills at a party, nitrogen narcosis can compromise a diver’s ability to make rational decisions and respond to unforeseen challenges underwater. Cognitive abilities such as arithmetic and reaction time progressively decline under the influence of nitrogen narcosis as pressures increase.

A study utilising the Iowa Gambling Task revealed decision-making impairments in divers at 30 meters, suggesting that higher cognitive functions are significantly affected by nitrogen narcosis. Understandably, these cognitive impairments can pose serious risks to a diver’s safety, making early detection and management of nitrogen narcosis crucial.

Physical Manifestations of Narcosis

While nitrogen narcosis primarily affects cognition, it also leads to noticeable physical symptoms. One of the key physical symptoms exhibited by divers experiencing narcosis is vertigo. Divers may also encounter visual or auditory disturbances as part of the physical manifestations of narcosis.

Physical symptoms of narcosis can further include a range of emotional reactions, such as:

  • excitement and giddiness

  • extreme anxiety

  • depression

  • paranoia

Being aware of these physical manifestations can help divers and their buddies quickly recognize the onset of narcosis and take appropriate action.

Strategies to Avoid Nitrogen Narcosis

 selecting the right breathing gas for a deep dive, a technical diving lable

Having understood the science and symptoms of nitrogen narcosis, let’s now explore strategies to avoid it. These strategies include selecting the right breathing gas, planning your dive depth, and adhering to your dive plans.

For dives greater than 50 meters, the use of helium or helium-nitrogen gas mixtures, such as heliox, can reduce the risk of nitrogen narcosis. Also, divers can lower their risk of experiencing nitrogen narcosis by ensuring they are well-rested and relaxed and refrain from consuming alcohol prior to diving.

Selecting the Right Breathing Gas

Choosing the appropriate breathing gas plays a significant role in narcosis prevention. For instance, helium, which doesn’t have an anesthetic effect at depth, is often used instead of nitrogen in deep diving to prevent narcosis. For dives deeper than 50 meters, divers are advised to use gases other than breathing air, such as helium or helium-nitrogen mixtures called trimix, to prevent nitrogen narcosis.

These helium-based mixes help in mitigating the narcotic effects of nitrogen, and helium helps reduce breathing resistance at depth. For dives deeper than 60 meters of seawater, helium-oxygen mixtures are required to avoid nitrogen narcosis. However, using these specialized gas mixtures introduces challenges like higher costs for helium and the need for specialized gas blending equipment.

Planning Your Dive Depth

Another crucial strategy to prevent nitrogen narcosis is careful depth planning. To prevent nitrogen narcosis, divers are advised to:

  • Keep their dive depth within 30 to 50 meters when using compressed air

  • The deeper a diver goes, the shorter the duration they can stay at that depth without requiring decompression

  • Exceeding the limits of a dive plan can lead to serious problems.

These guidelines emphasise the importance of careful depth planning and adherence to dive plans as key strategies to avoid nitrogen narcosis. A well-thought-out dive plan can be the difference between a delightful deep dive and a dangerous dive!

Handling Narcosis During a Dive

Despite all preventive measures, if a diver suspects they are experiencing nitrogen narcosis, there are ways to handle it during the dive. The immediate response to symptoms is critical, as is the management of severe narcosis if necessary.

If a diver suspects they are experiencing nitrogen narcosis, they should signal their dive buddy and ascend to a shallower depth following regular ascent rules; likewise, if a diver notices symptoms in their buddy, they should signal for them to ascend and stay close, providing assistance as necessary.

Immediate Response to Symptoms

Recognising the early symptoms of nitrogen narcosis is crucial, and it’s essential to ascend to shallower depths if symptoms are detected. Upon experiencing symptoms of narcosis, divers should immediately ascend, as symptoms typically resolve within minutes at shallower depths.

Additional stress factors like anxiety can exacerbate the symptoms of narcosis, increasing the risk of impaired diving ability. The overarching management strategy for narcosis involves ascending to shallower depths to alleviate the effects of increased pressures on gas absorption.

Managing Severe Narcosis

A diver ascending to shallower depths due to severe narcosis

Severe nitrogen narcosis can result in mental decline, hallucinations, stupor, coma, and death, particularly due to accidents resulting from impaired judgment. Signs of severe narcosis include loss of consciousness and severe impairment of judgment, indicating an urgent need to abort the dive.

If symptoms of narcosis do not subside at shallower depths, divers must terminate the dive and safely ascend to the surface. The management of severe narcosis is a critical aspect of diving safety and should be a key focus in all diver training programs.

Advanced Diving Techniques to Manage Narcosis

Beyond the basic strategies, advanced diving techniques can further help in managing narcosis. These techniques include utilising multiple gas mixtures and specialised training for deep divers.

Specialised training is essential for divers planning to engage in technical and deep dives to manage narcosis. The PADI Advanced Open Water Course is recommended for divers going deeper than 18 meters.

Utilising Multiple Gas Mixtures

A rebreather diver using specialised gas mixtures for deep dives

Technical deep diving often involves using specialised gas mixtures like nitrox, trimix, or heliox to reduce the risks of nitrogen narcosis and oxygen toxicity, especially on dives beyond 60 meters. Divers add helium to their breathing gas to create mixtures such as trimix or heliox, mitigating the narcotic effects of nitrogen.

These mixtures are tailored for different diving conditions, with factors such as depth and decompression requirements taken into consideration. However, using these gas mixtures introduces challenges like higher costs for helium and the need for specialised gas blending equipment.

Specialised Training for Deep Divers

Specialised training, like the PADI Advanced Open Water and Deep Diver Specialty courses, can help divers enhance their skills in deep-sea diving and manage narcosis. This training instructs divers in planning deep dives, managing gas supply, and identifying and handling narcosis up to a depth of 40 meters. To dive deep safely, it is crucial to undergo such training.

These courses provide a comprehensive understanding of the risks associated with deep diving and the effective management of nitrogen narcosis. They ensure that divers are well-equipped to safely explore the depths of the underwater world.

Insights from Divers Alert Network (DAN)

The Divers Alert Network (DAN), a renowned diving safety organization, provides valuable insights on nitrogen narcosis. According to DAN, nitrogen narcosis symptoms include feelings of intoxication, impaired judgment, and difficulty concentrating. Risk factors for nitrogen narcosis include fatigue, depth, personal history of susceptibility, alcohol intake prior to diving, and cold water exposure.

DAN emphasises the importance of understanding risk factors associated with nitrogen narcosis and having discussions with dive buddies to mitigate these risks. They recommend immediate termination of a dive if symptoms of nitrogen narcosis develop.


In conclusion, nitrogen narcosis, while potentially hazardous, can be effectively managed with a good understanding of its causes, symptoms, and preventive strategies. Selecting the right breathing gas, careful dive depth planning, prompt response to symptoms, and specialised training are all essential elements in the safe management of nitrogen narcosis. As we continue to explore the underwater world, let’s remember to dive safely, respect our limits, and enjoy the beauty of the deep.

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Frequently Asked Questions

What happens during nitrogen narcosis?

Nitrogen narcosis can cause symptoms like lightheadedness, euphoria, numbness, and slowed manual dexterity, with severe cases possibly leading to convulsions and unconsciousness. This occurs as a result of increased nitrogen levels in divers at depths below 70 feet of sea water.

What is the main cause of narcosis?

The main cause of narcosis, specifically nitrogen narcosis, is the high partial pressures of nitrogen, which leads to anesthetic effects when breathing compressed gas at depth. Breathing gases under elevated pressure is the overarching cause.

At what depth does nitrogen narcosis typically occur?

Nitrogen narcosis typically occurs in divers at depths exceeding 30 meters.

What are the symptoms of nitrogen narcosis?

The symptoms of nitrogen narcosis include cognitive impairment, decision-making difficulties, vertigo, and emotional reactions. These can impact the diver's ability to function effectively underwater.

What is gas narcosis?

Gas narcosis, also referred to as inert gas narcosis, occurs when divers breathe in compressed gases at significant depths. The term has evolved from the more specific "nitrogen narcosis" to acknowledge that a variety of gases, not just nitrogen, can cause narcotic effects under pressure. This updated terminology reflects the expanding scope of gases used in modern diving practices, including various gas mixtures that have become more common, especially in technical diving. While helium is often used to mitigate the effects of nitrogen, it too can produce narcotic effects under certain conditions. Therefore, the term "gas narcosis" more accurately describes the phenomenon as it relates to the range of gases that divers may encounter.