What must separate the corridor from a return air plenum?

The requirement that separates the corridor from a return air plenum is focused on fire safety and prevention. Fire-resistance-rated construction is essential in this context because it helps to limit the spread of fire and smoke between spaces, thereby protecting occupants and facilitating safe evacuation during an emergency.

In the case of a return air plenum, which is used for airflow in a heating, ventilation, and air conditioning (HVAC) system, having a fire-resistance-rated barrier means that it can withstand fire exposure for a specified amount of time. This is crucial in corridors, which often serve as primary escape routes. By utilizing fire-resistance-rated construction, the integrity of these escape routes can be maintained, reducing risks associated with smoke and fire spread into areas where people are present.

This practice aligns with codes and standards that prioritize safety in building design and management, particularly concerning how air movement and fire resistance are handled in occupied spaces.