Which gas combination is commonly used for deep diving?

Trimix, which is a combination of helium, oxygen, and nitrogen, is commonly used for deep diving because it mitigates the risks associated with high-pressure environments. When divers descend to greater depths, the partial pressure of nitrogen can lead to narcosis, which impairs judgment and motor functions. helium, being less narcotic than nitrogen, is included in the mix to counteract this effect.

Another significant advantage of using trimix is that it reduces the risk of oxygen toxicity. At deeper depths, the partial pressure of oxygen becomes higher, which can become dangerous. By adjusting the amounts of helium and oxygen in the mix, divers can create a gas blend that provides adequate oxygenation without the hazard of toxicity, ensuring a safer diving experience.

The other combinations mentioned are less suitable for deep dives. Air, which is primarily composed of nitrogen and oxygen, does not adequately address the narcotic effects of nitrogen at depth and has a higher risk of oxygen toxicity. Carbon dioxide and nitrogen would not provide the necessary oxygen needed for breathing underwater, making it an impractical choice for diving.