What type of gas is used in standard recreational scuba tanks?

The use of compressed air in standard recreational scuba tanks is essential because it consists primarily of nitrogen and oxygen, which closely matches the composition of the air we breathe at the surface. This makes it suitable for divers as it allows them to breathe naturally underwater without causing significant physiological complications.

Breathing gas mixtures that deviate from this standard composition, such as pure oxygen or helium, have specific applications and limitations in diving scenarios. Pure oxygen, for instance, is generally not safe for diving beyond shallow depths due to the risk of oxygen toxicity. Helium is often used in technical diving setups for deep dives or in specific gas mixes to reduce narcosis but is not typically found in standard recreational setups. Lastly, carbon dioxide is not used in scuba tanks as it is a waste product of respiration and can be harmful if inhaled directly from a tank. Thus, compressed air remains the go-to choice for recreational divers.