Which type of gas is primarily used in the MK-20 diving system?

The MK-20 diving system primarily uses compressed air as the breathing gas. Compressed air is utilized due to its availability and suitability for various diving conditions. It is a mixture of approximately 21% oxygen and 79% nitrogen, which aligns well with physiological requirements for a wide range of recreational and professional diving activities. In the case of the MK-20 system, using compressed air enables divers to operate efficiently in water depths typically associated with recreational diving.

Other gases like helium and nitrox are often used in specialized diving situations, such as deep dives or in environments where nitrogen narcosis could be a concern. However, for the general use in the MK-20, compressed air remains the standard gas due to its effectiveness and safety profile for most diving scenarios. Oxygen, while crucial for breathing, is typically not used in pure form within a standard surface supplied system like the MK-20 since it can present toxicity concerns at deeper depths.