What type of breathing gas is commonly used in DLSS?

The commonly used breathing gas in Diver Life Support Systems (DLSS) is indeed compressed air or specific gas mixtures such as nitrox or trimix. This is because these gas mixtures are tailored to suit the conditions and requirements of underwater diving.

Compressed air, which consists primarily of nitrogen and oxygen, provides a suitable breathing environment for divers at shallower depths. However, as divers go deeper, the partial pressure of nitrogen can increase the risk of nitrogen narcosis and decompression sickness. To counter these risks, gas mixtures like nitrox, which has a higher oxygen content and lower nitrogen percentage, are employed to enhance safety and extend bottom time.

Trimix, on the other hand, is used in even deeper diving scenarios. This mixture includes helium, oxygen, and nitrogen, allowing for safer breathing at greater depths where nitrogen narcosis can be a significant issue. The inclusion of helium helps reduce the risk of narcosis and also addresses the density of the gas at high pressures.

In summary, the option referring to compressed air or specific gas mixtures is correct because it acknowledges the use of a variety of breathing gases that enhance safety and performance for divers across different depths and conditions.