46 CFR §108.455

1. (a)Mechanical ventilation for spaces protected by a CO2 system must be designed to shut down automatically when the system is activated.
2. (b)Each space that is protected by a CO2 system and that has natural ventilation must have a means for closing that ventilation.
3. (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. (1)Doors, shutters, or dampers for closing each opening in the lower portion of the space.
   2. (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.