During a Sur 'D' dive, what is the protocol if a diver experiences CNS O2 toxicity?

In the context of a Sur ‘D’ dive, when a diver experiences central nervous system (CNS) oxygen toxicity, the immediate response is crucial to prevent further complications. Shifting the diver's breathing gas to air during ascent effectively reduces the partial pressure of oxygen that the diver is inhaling. This action helps to alleviate the symptoms of CNS oxygen toxicity, which can include seizures and other neurological disturbances.

Using air allows the diver to breathe a gas mixture that has a much lower oxygen concentration compared to what they were inhaling during the dive. This reduction in oxygen can help to mitigate the toxic effects that arise from elevated levels of oxygen in the system.

Increasing oxygen flow would exacerbate the situation, as it would lead to higher levels of oxygen intake, posing greater risks of toxicity. Performing emergency CPR is not an initial response unless the diver is unresponsive or in need of revival; continued diving should never be an option if CNS O2 toxicity is suspected, as it could lead to severe and potentially fatal consequences.

Overall, transitioning to air is a standardized procedure in diving safety protocols when dealing with CNS oxygen toxicity, making it the appropriate action to take.