Where ductwork penetrates a fire-rated or smoke-resistant assembly, it can't compromise that rating — so IMC Chapter 6 requires dampers. Fire dampers close on heat to maintain a wall or floor's fire-resistance rating; smoke dampers close on smoke detection to maintain smoke barriers; combination fire/smoke dampers do both. The chapter also covers duct construction, insulation, and support. Which damper is required depends on what assembly the duct crosses and its rating.
The common mistake is a duct running through a rated corridor or shaft wall with no damper — or a fire damper where a smoke or combination damper is actually required by the assembly type. This is a classic coordination gap between the mechanical and architectural sets, because the ductwork designer and the person defining the rated walls have to agree on every penetration.
Reviewers overlay the duct routing on the rated-assembly plan and confirm the correct damper at each penetration. Catching these early avoids field cutting-in of dampers after the ducts are hung.
This guide describes the model code for general understanding and is not a substitute for the adopted code and amendments enforced by your local authority having jurisdiction. Verify all figures against your jurisdiction's codes of record.