Which action should be taken immediately if a diver shows signs of lung overexpansion?

When a diver shows signs of lung overexpansion, the immediate action to take is to remove them from the water. This is because lung overexpansion injuries can occur when a diver ascends too quickly without exhaling properly, leading to air expanding in the lungs and potentially causing ruptures or life-threatening conditions such as an arterial gas embolism.

By removing the diver from the water, you minimize the risk of further ascent and prevent the possibility of worsening the injury. After successfully getting them out of the water, medical assistance should be sought immediately, as this condition requires prompt treatment.

While administering oxygen, checking diving gear, or performing CPR are all important actions in different contexts, they are not immediate responses specifically for lung overexpansion. Administering oxygen can be beneficial afterward, particularly if the diver is experiencing symptoms related to gas embolism, but it is not the first step. Checking diving gear does not address the immediate risk of lung injury, and performing CPR is only necessary if the diver shows signs of cardiac arrest, which is not the immediate concern in the case of lung overexpansion. Therefore, the most critical first step is to remove the diver from the water urgently.