Which gas is primarily responsible for the risk of decompression sickness?

The risk of decompression sickness primarily arises from the behavior of nitrogen during dives. When divers descend, the pressure increases, allowing nitrogen, which is a component of the air we breathe, to dissolve into the body's tissues and fluids. As they ascend, the pressure decreases, leading to a reduction in the solubility of nitrogen in the body. If the ascent is too rapid or not controlled properly, nitrogen can come out of solution too quickly, forming bubbles in the tissues and bloodstream. These bubbles can cause various symptoms and potentially serious complications related to decompression sickness.

While oxygen, carbon dioxide, and helium are important gases in diving, they do not primarily contribute to the risk of decompression sickness in the same way nitrogen does. Oxygen can lead to toxicity at high partial pressures, and carbon dioxide is more related to other physiological effects like hypercapnia. Helium is often used in technical diving to reduce the risk of nitrogen narcosis and is less likely to cause decompression sickness compared to nitrogen. Therefore, nitrogen is uniquely responsible for the occurrence of decompression sickness as a result of its behavior during pressure changes in diving.