Final answer:
Oxygen levels in high-altitude environments must be maintained, and functional pressure suits must be worn when cabin altitude surpasses a certain threshold. These measures are necessary to ensure the well-being and safety of occupants.
Step-by-step explanation:
In high-altitude environments, it is necessary to maintain a sufficient level of oxygen for the well-being of occupants. The question asks that the cabin altitude should not exceed a certain value unless occupants are wearing functional pressure suits. The specific value is not provided in the question text.
For instance, Mount Everest climbers need bottled oxygen to prevent altitude sickness, as the partial pressure of oxygen decreases with increasing altitude.
At extremely high altitudes, the level of oxygen in the air becomes insufficient to sustain bodily functions without supplemental oxygen. In such cases, climbers wear functional pressure suits to ensure their safety and well-being.
Overall, the question highlights the importance of maintaining the proper oxygen levels in high-altitude environments, and the need for protective gear when those levels become dangerously low.