What action should be taken if a diver experiences excessive carbon dioxide levels while under water?

Improving ventilation of the surface-supplied helmet is crucial when a diver experiences excessive carbon dioxide levels while underwater. Carbon dioxide buildup can lead to various complications, including impaired cognitive function, increased respiratory rates, and potentially life-threatening situations if not addressed swiftly. By enhancing the ventilation of the helmet, the diver can expel the exhaled carbon dioxide more effectively and allow for a greater influx of fresh air.

This action is vital, especially if the diver is using a surface-supplied breathing system, as it directly addresses the issue of elevated CO2 levels. Enhanced ventilation ensures that the air the diver breathes is more adequately oxygenated and less contaminated by exhaled gases, reducing the risk of hypoxemia and hypercapnia.

While decreasing depth might seem beneficial, it does not directly resolve the issue of carbon dioxide accumulation unless the diver is experiencing signs of distress related to depth. Avoiding ascent could lead to further trouble, especially if the diver is feeling unwell due to elevated CO2 levels. Switching to a different gas supply might not be practical or possible in many scenarios, and it doesn't guarantee immediate improvement in CO2 levels while still submerged.