46 CFR 108.455: Enclosure openings.

(a) Mechanical ventilation for spaces protected by a CO2 system must be designed to shut down automatically when the system is activated.

(b) Each space that is protected by a CO2 system and that has natural ventilation must have a means for closing that ventilation.

(c) Each space protected by a CO2 system must have the following means for closing the openings to the space from outside the space:

(1) Doors, shutters, or dampers for closing each opening in the lower portion of the space.

(2) Doors, shutters, dampers or temporary means such as canvas or other material normally on board a unit may be used for closing each opening in the upper portion of the space.