What is the first action to take if a diver shows symptoms of an oxygen convulsion?

In the event that a diver exhibits symptoms of an oxygen convulsion, the immediate and most critical action is to shift both divers to air. This is because breathing high concentrations of oxygen under pressure can lead to increased risk of oxygen toxicity, which can trigger convulsions. By transitioning to air, the diver's exposure to oxygen in a hyperbaric environment is reduced, thus decreasing the likelihood of convulsions continuing or worsening.

Moving to air effectively mitigates the acute risk associated with oxygen toxicity. It is important to promptly act to prevent further complications and ensure the diver's safety. Other options, like waiting for symptoms to subside or administering first aid on site without addressing the underlying cause, do not prioritize the diver’s immediate respiratory needs and can result in severe consequences.

Therefore, the correct course of action emphasizes the importance of managing oxygen levels and ensuring the safety and well-being of the diver during a critical situation.