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Causes Of Hyperoxia in Scuba Diving and How Divers Avoid It

We understand the causes of hyperoxia, or excess oxygen in the blood. Keep in mind that this can be both an ally and an enemy for divers. On one hand, it is used as a medical treatment in hyperbaric chambers to combat decompression sickness, fight infections, and accelerate healing.

However, during diving, the causes of hyperoxia can have serious health consequences, and it is essential to know how to prevent it. In this article, we will explore the factors that trigger hyperoxia in diving and the strategies divers use to avoid it. Keep reading!

causes of hyperoxia in Diving - causas de hiperoxia en el buceo (1)

1. What is Hyperoxia

The word hyperoxia is a scientific term formed from:

  • The Greek prefix “hyper,” which means “a lot,”
  • The English word “oxygen,” and
  • The Latin suffix “-ia,” which means “phenomenon” or “quality.”

Knowing this, you don’t have to be the brilliant scientist who coined the term to deduce that hyperoxia refers to an excess of oxygen and the qualities of cells, tissues, or organs exposed to this excess.

Therefore, if we talk about normoxia, we are referring to the state of our body exposed to normal oxygen conditions. Note that normal oxygen (about 21%, which is the oxygen percentage at sea level with a partial pressure of 0.21 ATA) is suitable for pressures between 0.17 ATA and 0.5 ATA.


2. Causes of Hyperoxia in Diving

The causes of hyperoxia in diving should be sought in the ways we can be exposed to high levels of oxygen.


Causes of Hyperoxia While Diving

But let’s see, you might say. If the air mix we use while diving has oxygen levels similar to those on the surface.

That’s true; the most commonly used mix contains 21% oxygen, 78% nitrogen, and 1% other gases. But what if…

The partial pressure of oxygen exceeds certain limits.

Diving beyond depths of 66 meters / 216 feet (with compressed air), our body can suffer the effects of hyperoxia, in diving specifically called: oxygen toxicity, acute hyperoxia (or Paul Bert syndrome).

This is why recreational diving does not exceed 40 meters/131 feet.

We are spending too much time breathing oxygen at a high partial pressure.

This is another cause of hyperoxia in diving. When there is a prolonged excess of oxygen, the alveolar membrane becomes inflamed, making gas exchange difficult and irritating the lungs. This condition is known as pulmonary hyperoxia or the Lorraine-Smith syndrome. In recreational diving, dive times are short. This type of pulmonary oxygen toxicity is mainly a concern for divers who perform very long technical dives, lasting between six and twelve hours, as well as for those who perform repetitive technical dives over several days or weeks.

We use an air mix above 21% oxygen.

Remember that Nitrox mixes contain 32% oxygen and can have up to 36% and even 40% oxygen. Is Nitrox a cause of hyperoxia? NO. Neither is oxygen itself. What causes hyperoxia is misusing it. That’s why training is necessary to dive with Nitrox.

A hyperoxic air mix, like Nitrox, must be used within a specific depth range. Outside of that range, it is no longer useful and another gas mix must be used.

Apart from these causes of hyperoxia related to diving, there are also other factors related to the diver.

Causes of Hyperoxia Related to the Diver’s Physical Condition

Why are some divers unaffected no matter how deep they go, while others are quickly affected?

Note that it’s not just the amount of oxygen, the partial pressure at which you breathe it, and for how long that matters. Other factors must be considered, and they have to do with you, the diver.

  • Intense physical exercise: In this case, your body needs more oxygen, making it easier for excess to affect you.
  • Cold: Cold also increases oxygen demand, so be careful with cold water!
  • Fever: Needless to say, if you have a fever, you shouldn’t dive. Your body is already stressed, and the extra oxygen could be the final straw.
  • Stress: Stress also makes you more vulnerable to oxygen.
  • Lack of vitamins E and A: These vitamins are important for protecting cells from free radicals, so make sure they are in your diet.
  • Corticosteroids: Some medications, like corticosteroids, can increase sensitivity to oxygen.
causes of hyperoxia in Diving - causas de hiperoxia en el buceo (8)

3. Effects of Hyperoxia

Breathing too much oxygen (this is called hyperoxia) can intoxicate us and cause some health problems.

How does it work? Oxygen releases tiny bombs called free radicals in our bodies. It always does this, even when we are on the surface, where we eliminate them without much problem. But when we breathe too much oxygen for too long or at high pressure, free radicals accumulate and can damage our cells.

Which organs are affected? Mainly the lungs and the nervous system.

  • Lungs: If we breathe oxygen at high pressure for a long time, it can irritate our lungs and cause breathing problems, resulting in what is called Lorraine-Smith syndrome or chronic hyperoxia. Symptoms of chronic hyperoxia include itching, burning, and chest pain, as if you had swallowed a cactus. Then, dry cough, chest pain, and difficulty breathing. If you don’t stop, things get worse: convulsions, loss of consciousness.
  • Brain: In divers who go to great depths, excess oxygen can affect the brain and cause dizziness, convulsions, and loss of consciousness, known as acute hyperoxia (Paul Bert syndrome). Symptoms: Tachycardia, tremors, nausea, vomiting, vertigo, ringing in the ears, nervousness, irritability, blurred vision, and… convulsions! It’s very dangerous, and you need to act as soon as symptoms appear.


4. Treatment of Hyperoxia

The Lorraine-Smith syndrome or pulmonary hyperoxia can be prevented by not exceeding the safety doses indicated for each gas. If we ignore the guidelines and lung damage occurs, a doctor will have to intervene. DAN describes pulmonary hyperoxia as similar to the flu, while other sources mention a sensation similar to asthma. However, everyone agrees that in rare cases it results in permanent damage.

But how do you act in the face of acute hyperoxia (great depths)?

A diver with hyperoxia may realize their body is intoxicated and ascend, but if they don’t recognize the symptoms, they will depend entirely on their partner. To act appropriately, it is essential to know the different stages of the intoxication process.

Phase 1: Prodromal. You might not notice it because the symptoms are very mild or because they don’t occur.

Symptoms: Tachycardia, tremors, nausea, vomiting, vertigo, ringing, irritability, and tunnel vision.

Solution: Ascend NOW! ⬆️ Up, up, as the oxygen is getting to your head.

If not detected, the diver will suffer a convulsive crisis.

Phase 1: Prodromal. You might not even notice it because the symptoms are very mild or because it might not happen at all.

Symptoms: Tachycardia, tremors, nausea, vomiting, vertigo, ringing in the ears, irritability, and tunnel vision.

Solution: Ascend NOW! ⬆️ Up, up, the oxygen is getting to your head.

If we don’t detect it, the diver will suffer a convulsive crisis, which has 3 more phases.

Phase 2: Tonic. (less than 1 minute)

Symptoms: Faints, becomes rigid, and stops breathing.

Phase 3: Clonic. (2 or 3 minutes)

Symptoms: Convulsions and relaxation of sphincters.

Phase 4: Post-crisis depression.

Symptoms: The diver is sleepy and disoriented, with no memory of the event.


In 2012, Dr. Simon Mitchell signed a document titled “Recommendations for rescue of a submerged unresponsive compressed-gas diver,” which compiled the action recommendations from prestigious organizations such as the Diving Committee of the Undersea and Hyperbaric Medical Society, Divers Alert Network (DAN), the University of Washington, the University of California, and the U.S. Navy Experimental Diving Unit, among others.

His summarized recommendation was as follows:

  • Convulsing WITHOUT mouthpiece: Ascend NOW!
  • Convulsing WITH mouthpiece: Hold them, and when they stop convulsing, ascend.

However, recently Divers Alert Network (DAN) has published new articles regarding the treatment of hyperoxia during diving, recommending an ascent even if the mouthpiece is in place. (In this case, it explains the steps with a rebreather diver, but they can be applied to open system diving) We summarize the steps below:

  • Position yourself behind the diver.
  • Release the weights: Remove their weight belt unless they are wearing a dry suit. In that case, leave it on to avoid them flipping face down upon reaching the surface.
  • Mouthpiece: If the mouthpiece is in place, don’t touch it. If it falls out, don’t try to put it back, just ensure it is in the surface position.
  • Hold the diver by the chest, above the regulator, or between the regulator and their body. If you can’t control them this way, use the best method at hand.
  • Controlled ascent: Ascend slowly to the surface, maintaining slight pressure on the diver’s chest to help them exhale.
  • Extra buoyancy: If you need more buoyancy, activate the diver’s BCD, but not yours, and don’t remove your weight belt.
  • On the surface: Once on the surface, if you haven’t already, inflate the diver’s BCD.
  • Remove the mouthpiece: Once on the surface, remove the diver’s mouthpiece and switch the valve to the surface position.
  • Emergency signal: Alert everyone! Make the emergency signal to get help.
  • Clear the airway: Tilt the diver’s head back to open their airway and ensure they are breathing. If they are not, a trained diver can initiate mouth-to-mouth resuscitation.
  • Monitoring and decompression: Monitor the diver for signs of decompression sickness.

5. Prevention of Hyperoxia in Diving


Preventing hyperoxia in recreational diving

Preventing hyperoxia in recreational diving is simple. It mainly involves staying within the indicated limits of time and depth, even when diving with Nitrox. The only key is to dive within the indicated depths for each mix because no tank lasts long enough for hyperoxia to develop.

The Professional Association of Diving Instructors (PADI) limits open-circuit diving with Nitrox to 1.4 ATA. Since open-circuit diving would not continuously expose divers to this level, the levels are 1.3 ATA maximum for the diving phase with a rebreather and 1.4 ATA during decompression.

Therefore, cases of hyperoxia are rare in recreational diving.

Preventing hyperoxia in technical diving

In technical diving, there are ways to prevent it. The main way to prevent hyperoxia is to use hypoxic gas mixes (low in oxygen).

Among them are:

  • Hypoxic trimix: Reduces the amount of oxygen to a maximum of 17%, helium, and nitrogen.
  • Heliox: Does not include nitrogen. It is primarily used in professional diving, performed at great depths and usually with reabreathers. When using this mix, the oxygen proportions vary according to the depth.

Other important points for preventing hyperoxia in diving are:

  • Knowing the symptoms of hyperoxia to recognize and act on them if they occur;
  • Preventing cold during dives, as well as avoiding stress and muscle overexertion while diving;
  • Lastly, following health recommendations: eating healthy, exercising, and staying hydrated.

In summary, diving safely involves knowing the risks and causes of hyperoxia to take appropriate preventive measures. Hyperoxia is a reality, but with the necessary knowledge and responsibility, we can enjoy diving with complete peace of mind.