Nitrogen narcosis is rare in diving, and even rarer in freediving compared to scuba diving. It can best be avoided by training well, building up freediving experience, being well-rested and both physically and mentally healthy, and ensuring that there is no alcohol or other intoxicant in your bloodstream while diving. Static and dynamic apnea, cardio, strength and mental training are all important disciplines for a freediving training program.
If you are a complete beginner, you should not be diving to depths where nitrogen narcosis is likely to affect you. Whatever your level of experience, exercise caution if you are unsure about your wellbeing while underwater and ascend towards the surface at a steady pace if you feel physically or mentally unwell during a freedive, signaling any distress to your diving buddy.
Nitrogen narcosis is a state of altered consciousness and disrupted neuromuscular function caused by inert gases passing into the bloodstream under pressure. It is most commonly caused by nitrogen and found in scuba divers but can also occur in freedivers during dives below approximately 30-40 meters. Good training and apnea practice are the best ways to avoid nitrogen narcosis and other health risks.
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Nitrogen narcosis, also known as depth intoxication or “rapture of the deep”, is an intriguing subject. If you’re a freediver you might be wondering about its causes and risks. Our article explains some of the background around nitrogen narcosis and freediving including symptoms, risks and how best to avoid the problem.
Can you get nitrogen narcosis freediving?
While nitrogen narcosis is more commonly found in scuba divers, it can also occur in freedivers below depths of around 30-40 meters. As a beginner attempting supervised freedives ranging from a meter or two up to 10-15 meters, you would be unlikely to be diving deep enough to experience nitrogen narcosis.
In deeper dives, any freediver may begin to feel some effects of nitrogen narcosis, with risk and intensity of narcosis increasing with depth.
Nitrogen narcosis is more likely to occur in less experienced divers or those who have taken a break from freediving (e.g. over the winter). It seems likely to occur in colder water and if the diver is tired, hypothermic or affected by other intoxicants (e.g. alcohol, cannabis).
Freediving training and experience are probably the best ways to avoid nitrogen narcosis or to recognize and respond to it quickly. You should always return to the surface to recover if you suspect you are feeling the effects of nitrogen narcosis.
What is nitrogen narcosis in freediving?
Nitrogen narcosis is an altered state of consciousness which can occur while diving to deeper depths due to intoxication of the brain by inert gases, especially nitrogen.
The effect is reversible and symptoms generally resolve within minutes when a diver returns to the surface. Some of the symptoms, however, including disorientation, reduced analytical ability and poor judgment, might cause divers to continue their descent, leading to more serious symptoms, along with possible injury and death.
For further details on the effect diving has on your body, check out our article; what happens to your body when you freedive (opens new tab).
What is the cause of nitrogen narcosis?
While the process of nitrogen narcosis is not completely understood, the explanation may lie in considering the freediving breath-hold, the forces exerted on the body at depth and the subsequent compression of air spaces including the lungs.
During a freedive your body is under massive pressures from the water around you, even when diving only to a few meters depth. At a depth of 10 meters, the pressure will be double that experienced on land at sea level, and pressure will continue to increase at a rate of one bar (one normal air atmosphere) for every further 10 meters of descent.
Physical laws mean that gas volumes decrease at the same time in inverse proportion with the increasing water pressure. Airspaces in the human body including the lungs are therefore gradually compressed during diving descent. At a depth of 10 meters, lung volume will be only 50% of its usual level.
Freedivers take a full breath of air before diving, with this air containing 78% nitrogen, 21% oxygen and 1% other gases. These gases are compressed within our lungs, with lung exchange surface area being vastly reduced, and more nitrogen dissolved into our blood.
Physiological diving responses also cause peripheral vasoconstriction, directing blood flow largely to the brain and other key organs with a corresponding rise in nitrogen partial pressure, while blood is diverted from arms and legs.
These higher levels of blood nitrogen under pressure exert a narcotic effect once in the central nervous system (i.e. brain and spinal cord) with the mechanism for this still a subject of research and discussion.
Symptoms of nitrogen narcosis when freediving
Nitrogen narcosis during freediving can produce a range of symptoms at levels of greater or lesser severity. It is also sometimes known as “the martini effect” or “Martini’s Law” because some divers compare it to the effects of drinking one martini on an empty stomach for every 15 meters of diving depth.
Symptoms experienced may include:
- feeling “drunk”,
- sudden euphoria or anxiety,
- numbness,
- mild hallucinations,
- poor coordination and difficulty with precise movements,
- limited analytical ability and poor judgement,
- tunnel vision,
- failing consciousness and short term memory loss.
At what depth do most divers experience nitrogen narcosis?
Some level of nitrogen narcosis may occur from depths of around 30-40 meters. More sensitive divers could experience it even earlier at 25-30 meters. The deeper you dive, the greater the chances of nitrogen narcosis occurring and the more severe the narcosis is likely to be.
Serious symptoms may begin from around 90 meters depth. If you continue to descend while suffering from nitrogen narcosis (e.g. because your decision-making is impaired), it’s possible that this could eventually result in coma or death.
How to avoid nitrogen narcosis when freediving?
While nitrogen narcosis and its causes are not completely understood, we can identify some common factors associated with the condition (lack of experience, cold, tiredness, alcohol etc)… Considering these factors leads to a range of steps you can take to reduce the risk of serious nitrogen narcosis.
Train well and practice regularly.
Better trained and more experienced divers appear to be less likely to suffer from nitrogen narcosis, and may able to recognize and react to its symptoms more quickly. Their bodies and minds may be better adapted to high pressure underwater conditions, more efficient in using oxygen and tolerating carbon dioxide, and/or less sensitive to the intoxicating effects of nitrogen.
Exercises to include in a regular freediving training program may include:
- Dry static apnea: breath-hold exercises on land to gradually increase apnea capacity and familiarity with the physical sensations of breath-holding, while training your body to use oxygen more efficiently.
- Wet static apnea: breath-hold exercises in the water without movement, to boost lung function and capacity, and freediving competence.
- Dynamic apnea: strength or cardio exercises on land or in the water while breath-holding.
- Cardio: any type of cardio exercise which suits an individual freediver, including running, cycling, HIIT and circuit training.
- Strength training: working out with weights to increase muscular strength in arms and legs for improved ability to propel the body through the water under apnea conditions.
- Mental training: yoga, meditation or mindfulness practices which promote calm, clear thinking and good control over body and mind.
Limit diving depth
If diving below a certain level triggers symptoms of nitrogen narcosis you should return to the surface to recover. Once symptoms have resolved, you can continue to dive and but should remain above the level where the narcosis occurred for the remainder of your diving session. In future freedives, you should exercise caution on descent and increase diving depth gradually as your experience and mastery of technique increases.
Avoid alcohol and other intoxicants
You should completely avoid consuming any intoxicating substances on the day you freedive. As alcohol and other intoxicants may remain in the bloodstream for hours or even days, you may wish to avoid them entirely for the period immediately before your diving trips.
Stay rested, warm and calm
Since nitrogen narcosis is more likely when someone is hypothermic, tired or anxious, you should make sure that you get sufficient sleep, have a normal body temperature, and feel relaxed before getting in the water.
Learn about nitrogen narcosis
Make sure that both you and your diving buddy know all about nitrogen narcosis and its symptoms before you freedive. This will enable either of you to recognize the signs and take quick corrective action if it occurs.
References
https://www.freedivewire.com/freediving-narcosis-an-interesting-interplay-of-gases
https://repository.si.edu/bitstream/handle/10088/21621/SCMS39_Lang_03.pdf
https://www.ncbi.nlm.nih.gov/books/NBK470304/
https://www.sciencedirect.com/topics/medicine-and-dentistry/nitrogen-narcosis