What is the ideal gas used in recreational diving tanks?

The ideal gas used in recreational diving tanks is compressed air, which is primarily made up of nitrogen and oxygen. Compressed air is suitable for recreational diving for several reasons.

First, it provides a breathable mixture for divers at the depths typically encountered in recreational diving. The ratio of nitrogen to oxygen in air is well-tolerated by the human body under pressure, allowing for safe breathing at various depths. The presence of nitrogen is crucial because it helps prevent hypoxia, a condition that arises when there is not enough oxygen available to the body.

Additionally, compressed air is more available and economical compared to other gases. It is easy to fill tanks with compressed air using dive shops and filling stations, making it a practical choice for divers.

In contrast, while helium is used in specific technical diving scenarios, such as deep dives to reduce narcosis and improve breathing efficiency, it is not typically used in recreational diving tanks. Carbon dioxide is not suitable for breathing because it is a waste gas, and oxygen only would not provide sufficient pressure at depth and could lead to toxicity issues at higher concentrations. Thus, compressed air stands out as the most suitable option for recreational diving.