What is the appropriate action when a diver exhibits symptoms of O2 toxicity?

When a diver exhibits symptoms of oxygen (O2) toxicity, the correct action is to shift both divers to air. Oxygen toxicity can arise in divers breathing high partial pressures of oxygen, leading to symptoms such as visual disturbances, tinnitus, or seizures. Reducing the partial pressure of oxygen is essential to mitigate these symptoms and safeguard the diver's health.

By switching to air, which contains a lower concentration of oxygen, divers can effectively lower the risk of toxicity and allow the body to gradually eliminate excess oxygen from the system. This immediate response is critical to managing the diver's safety and can prevent the situation from worsening.

The other options do not adequately address the urgency and nature of oxygen toxicity. While checking for breathing is an important standard response in emergency situations, it does not specifically tackle the underlying issue of O2 toxicity. Surfacing immediately could pose additional risks, such as decompression sickness, depending on the diver's current situation. Lastly, beginning a gas exchange protocol is not a recognized immediate action for addressing O2 toxicity symptoms; it is more related to managing other diving-related conditions. Therefore, shifting to air is the most appropriate and effective response in this scenario.