What physiological effect should a diver watch for during prolonged exposure to high partial pressures of oxygen?

During prolonged exposure to high partial pressures of oxygen, divers are particularly at risk for experiencing seizures, which is a significant physiological effect associated with oxygen toxicity. High concentrations of oxygen can lead to a condition known as Central Nervous System (CNS) oxygen toxicity. This occurs when the partial pressure of oxygen exceeds safe levels, typically above 1.6 ATA (atmospheres absolute) when diving.

Seizures in this context are often the most severe manifestation of CNS oxygen toxicity and can occur suddenly and without warning. They can be life-threatening and may lead to loss of consciousness and potentially a loss of control while underwater, which can be extremely dangerous for a diver.

Other effects can occur with high oxygen exposure, such as loss of equilibrium, headaches, and fatigue; however, these symptoms do not present the same level of immediate danger and severity that seizures do. Thus, monitoring for seizures is critically important in diving, as it indicates that the diver is experiencing dangerous physiological changes due to elevated oxygen levels.