46 CFR §32.56-60

1. (a)Each duct for ventilation of Category A machinery spaces that passes through accommodation, service, or control spaces must be:
   1. (1)Constructed of steel and insulated to “A-60” Class; or
   2. (2)Constructed of steel, fitted with an automatic fire damper at each boundary where it enters and leaves the Category A machinery space, and insulated to “A-60” Class for a distance of 5 meters (16.4 feet) beyond each machinery space boundary.
2. (b)Each duct for ventilation of accommodation, service, and control spaces that passes through Category A machinery spaces must be constructed of steel and be fitted with an automatic fire damper at each Category A machinery space boundary.