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Types of Oxygen Toxicity

Types of Oxygen Toxicity

Oxygen toxicity happens when divers expose themselves to high concentrations of oxygen when they five to extreme depths or use gas mixtures. Oxygen toxicity affects two types of persons and this article looks at the two major types of oxygen toxicity common among divers:


Central nervous system toxicity occurs when the cells in a diver’s central nervous system (primarily the brain) gets damaged or experiences cell death. This often occurs when a diver breathes partial pressures of oxygen over 1.6 ata, such as taking in EANx32 beyond 130 feet. For this reason, a partial pressure of 1.4 ata is recommended by most training organizations.

The symptoms of CNS toxicity often manifests as uncontrollable unconsciousness and convulsions. This convulsion occurs suddenly as once minute, a diver is perfectly healthy and the next he is convulsing. Underwater, a diver who’s a victim of CNS toxicity risks losing his regulator and drowning or pulmonary barotrauma if the convulsions commence while his airway is closed.

Although the usual effect of CNS toxicity is a sudden convulsion, an alert diver sometimes notices other signs and symptoms, and this includes visual disturbances, auditory anomalies, nausea, dizziness, twitching- especially of the facial muscles and mood changes such as euphoria or irritability.

Once a diver suspects CNS oxygen toxicity, he should immediately ascend to a shallower depth to reduce the partial pressure of oxygen. A conscious, non-convulsing diver can do this independently but a diver experiencing more severe effects of oxygen toxicity must depend on his buddy to make the ascent. One training body recommends holding a convulsing diver with his regulator in place for as much as 15 seconds while waiting for the convulsion to cease (attempting to dive while convulsing places the diver at risk of pulmonary barotrauma). After 15 seconds or when the diver has stopped convulsing, he should slowly be taken to the surface.


This toxicity occurs when the cells in a diver’s lungs are damaged or undergo apoptosis. This toxicity is most common with technical divers when they breathe elevated partial pressures of oxygen for extended periods, such as breathing oxygen on a series of decompression stops. Most divers can inhale a partial pressure of oxygen of between 1.4- 1.5 ata for 8-14 hours before experiencing the effects of pulmonary oxygen toxicity.

Divers affected by pulmonary toxicity experience a progression of symptoms which begin with a burning sensation in the trachea, then breathing difficulties, tightness in the chest, shortness of breath, and uncontrollable coughing. If no immediate action is taken, a diver’s lungs cease to work, and he dies from a lack of oxygen.

Dealing with pulmonary oxygen toxicity calls for some smart and to do this, technical divers that plan on decompressing with high partial pressures of oxygen for extended periods avoid pulmonary oxygen toxicity by taking air breaks. For every 20-25 minutes in which the diver breathes the decompression gas, he takes in air for at least 5 minutes. This allows his lung cells to remove any accumulated oxygen free radicals before they become problematic.

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