What is the most critical sign of CNS Oxygen Toxicity that can result in severe danger for divers?

The most critical sign of CNS Oxygen Toxicity is convulsions. When a diver is exposed to high levels of oxygen, particularly beyond partial pressures of 1.4 ATA (atmospheres absolute), the risk of CNS oxygen toxicity increases. Convulsions are particularly dangerous because they can occur unexpectedly and without warning, potentially leading to loss of consciousness or controlled buoyancy. If a diver experiences convulsions while underwater, it could result in choking, rapid ascent, or other serious accidents that may compromise the diver's safety.

Dizziness, nausea, and blurred vision can also indicate oxygen toxicity or other issues, but they do not pose the immediate and severe risk associated with convulsions. Convulsions can incapacitate a diver and lead to life-threatening situations, making them the most critical sign to recognize and respond to in the context of diving safety.