Pressure-related injuries are caused primarily by breathing on _______.

The correct answer is compressed air. Pressure-related injuries, such as barotrauma or decompression sickness, primarily occur during scuba diving when divers are exposed to higher pressures than they are accustomed to at the surface. Compressed air is the air used underwater at greater depths, where the pressure increases significantly. The inhalation of compressed air causes the nitrogen in the air to dissolve more readily into the body's tissues due to the increased pressure, which can lead to nitrogen narcosis or decompression sickness if the diver ascends too quickly and the dissolved nitrogen forms bubbles in the bloodstream or tissues.

Understanding why compressed air is linked to pressure-related injuries is crucial for divers. As divers descend, the surrounding water pressure increases, affecting how gases behave in the body. This factor emphasizes the need for controlled ascent and proper dive planning. Other choices, while related to air mixtures in diving, do not specifically highlight the relationship to pressure-related injuries as clearly as compressed air does.