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What is CNS in Scuba Diving?

Breathing oxygen at a partial pressure greater than 1.6 ATA exposes you to a toxic reaction that affects the lungs and the central nervous system (CNS).

The likelihood of CNS diving toxicity increases with oxygen partial pressure, exposure time, exercise, cold, anxiety, increasing carbon dioxide levels in the blood, and steroid therapy.

Precursor Symptom of CNS Oxygen Toxicity

In general, divers who breathe normal air from a scuba cylinder (21% oxygen content) will be avoiding the major risks of CNS in diving.

But, there is an increased risk of getting oxygen toxicity when (either):

Oxygen toxicity signs and symptoms vary in severity. But, grand mal convulsions are the first precursor of CNS oxygen toxicity.

Pro Tip: Recompression treatment with oxygen for decompression illness symptoms or carbon monoxide toxicity occasionally results in a toxic reaction.

Oxygen Toxicity Symptoms

CNS toxicity symptoms may first occur underwater or shortly after surfacing. The diver may be suffering any or all of the following manifestations:

Oxygen Toxicity Treatment

Special Considerations for Pulmonary Oxygen Toxicity

In most cases, pulmonary oxygen toxicity results from breathing 100% oxygen for an extended period at elevated partial pressures. Typical symptoms include:

Hence, it does not generally threaten air-breathing recreational divers, unless the diver requires recompression. If so, the oxygen level is reduced and monitored. However, divers breathing enriched air and technical divers need to monitor their use of high oxygen mixtures.

Related Information and Help Guides

Important: The tutorial video [16:21 seconds] presented by DAN explains how gas toxicities and pressure affect the human body during a dive.

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