Which of the following shall not serve as supply, return, exhaust, relief, or ventilation air ducts?

In the context of mechanical code regulations, corridors are designated pathways that serve as important elements in building egress and fire safety. They are not intended to function as air ducts because using them in this capacity can impede movement and create complications during emergencies, such as evacuations.

By maintaining corridors free from obstructions including airflow systems, it ensures that these spaces remain accessible and clear for occupants at all times. This creates a safer environment in the event of a fire or evacuation scenario, as proper ventilation and air distribution must be maintained through dedicated ductwork designed for that purpose.

In contrast, bathrooms, janitor closets, and smoking lounges have specific designs and purposes that allow for the installation of ducts, either for ventilation to remove moisture or odors or to control air quality. Therefore, the regulation prohibits the use of corridors for air distribution to uphold safety and compliance with building codes.