Oxygen toxicity (CNS, pulmonary)

Oxygen toxicity happens when high partial pressures of oxygen damage your body. This risk comes in two forms: Central Nervous System (CNS) and pulmonary. CNS toxicity affects your brain while you dive. It often causes sudden seizures because the oxygen levels become too high for your nervous system. Pulmonary toxicity targets your lungs after long exposures. You might feel a burning chest or a cough during your deco stops.

Watch your depth carefully. I saw a diver in Koh Tao hit 40 m on air in 2018 and nearly suffered a seizure. Always track your CNS clock on your dive computer. Do not exceed the limits set by your training agency, such as PADI or SSI. Staying within safe oxygen limits prevents life-threatening emergencies.