Fire resisting ductwork is generally used when protection from the spread of fire from one compartment to another cannot be achieved using conventional thermally-actuated (fusible link) fire dampers
Ventilation and Smoke Control systems which need to continue to operate under emergency / fire conditions cannot use thermally actuated, fusible link type dampers.
In such applications, the closing of dampers due to elevated temperatures would prevent the system from supplying air to, or extracting air from, the required zones.
In addition, Kitchen Extract systems should not incorporate fire dampers, as the inherently high operating temperatures within a commercial kitchen duct would persistently trigger the fire dampers during normal use.
The build-up of grease and carbon deposits resulting from the cooking process over time is also likely to prevent the damper from closing fully.