407.1 General.

407.1.1 All supply-air, return air, and exhaust-air sys- tems shall be mechanically operated and such systems for areas listed in Table 4-A shall be operated continu- ously. Natural ventilation through windows or other openings such as louvers will be considered as supple- mental to the required mechanical ventilation systems.

Exceptions: (1) Natural ventilation shall not be used in airborne

infection isolation rooms and protective environment rooms. (2) The number of air changes may be reduced to 25

percent of the indicated value in Table 4-A, when the room is unoccupied, if provisions are made to ensure the following: (1) The number of air changes per hour indicated

is reestablished whenever the space is occupied. (2) The pressure relationship with the surrounding

rooms is maintained when the air changes per hour are reduced. In areas requiring no contin- uous directional control as identified in accor-

68 2022 CALIFORNIA MECHANICAL CODE

dance with Table 4-A, ventilation systems may be shut down when the space is unoccupied and ventilation is not otherwise required. Ventilation shall not be reduced in rooms specifically used for airborne infection control, such as waiting rooms, triage rooms, corridors, reception areas, areas adjacent to waiting areas, airborne infec- tion isolation rooms, negative pressure exam room, negative pressure x-ray treatment rooms, and protective environment rooms. All operat- ing and delivery rooms shall maintain a mini- mum of six air changes per hour of total air when not in use. 407.1.2 Fans serving exhaust systems shall be located at the discharge end of the system. The ventilation rates shown in Table 4-A shall be considered as minimum acceptable rates and shall not be construed as precluding the use of higher ventilation rates if they are required to meet design conditions. 407.1.3 Services/Systems and Utilities. (Refer to Sec- tion 1224.4.1 of the California Building Code).