During exhalation, what happens to the diaphragm in the MMR?

During exhalation, the diaphragm in the MMR (Manual/Mixed-Mode Regulator) rises toward the regulator cover. This movement is a crucial part of the breathing process. As you exhale, the pressure in the lungs decreases, allowing the diaphragm to move upward. This upward motion effectively helps push the exhaled air out of the SCBA and into the atmosphere. The diaphragm's rising motion plays an integral role in creating the necessary pressure differential that facilitates proper ventilation.

This action also ensures that the air supply is controlled and that the user can maintain an adequate flow of air. It is important to understand the mechanics of how the diaphragm functions within the SCBA to ensure effective and safe breathing in hazardous environments. Other options—such as the diaphragm lowering into the seating area, remaining flat, or disconnecting from the piston lever—do not accurately reflect the physiological movement associated with exhalation and, therefore, do not pertain to the correct sequence of operations in the MMR during exhalation.