Why is a good seal on the oral nasal assembly important?

A good seal on the oral nasal assembly is essential primarily because it prevents carbon dioxide buildup and limits dead air space. When divers are using surface-supplied breathing systems, there is a risk that exhaled carbon dioxide can accumulate in the breathing circuit if the seal is not effective. This accumulation can lead to hypercapnia, where the body retains too much carbon dioxide, resulting in serious physiological effects.

Additionally, limiting dead air space ensures that the diver is inhaling fresh, oxygen-rich air rather than rebreathing their expired gases. Dead air space refers to areas in the breathing system where exhaled air can linger without being exchanged for fresh air, and a good seal ensures that air circulation is maintained effectively within the assembly. Thus, the main purpose of a proper seal is to ensure the diver's safety and comfort by promoting efficient gas exchange during the dive.