A corridor in a hospital, which is required to be of fire-resistive construction per the California Building Code, is being used to convey return air from several patient rooms back to a central air handler. According to CMC Section 407.4.1.3, under which of the following conditions would this be permitted?

• It is permitted if the air transfer is a result of pressure differentials required for specific rooms by Table 4-A.
• It is permitted if the corridor serves only administrative offices.
• It is permitted if the return air grilles have a minimum MERV 6 filter.
• It is never permitted for corridors of fire-resistive construction.