46 C.F.R. § 131.899 Fire dampers.
Title 46 - Shipping
Each fire damper installed within the boundary of a space protected by a fixed fire extinguishing system must be fitted with an indicator showing whether the damper is open or closed and must be marked with red letters at least 13 millimeters (
Title 46: Shipping
PART 131—OPERATIONS
Subpart H—Markings for Fire Equipment and Emergency Equipment
§ 131.899 Fire dampers.

