These requirements and methods of tests apply to ceiling dampers and ceiling air diffusers intended for installation in hourly rated fire resistive floor-ceiling and roof-ceiling assemblies. Fire resistive assemblies are investigated in accordance with the Standard for Fire Tests of Building Construction and Materials@ UL 263. Ceiling dampers are intended for use in sheet metal air duct outlets which penetrate the ceilings of hourly-rated fire resistive assemblies. Ceiling air diffusers are intended for use with Class 0 and Class 1 air duct connectors@ or for ductless installation in the ceilings of hourly rated fire resistive assemblies. Ceiling dampers and ceiling air diffusers are designed for use as alternatives to previously tested hinged-door sheet metal type dampers installed at the bottom of sheet metal air ducts over each duct outlet. Ceiling dampers and ceiling air diffusers intended for installation in other types of fire resistive assemblies@ such as assemblies without penetrations@ are investigated in accordance with the Standard for Fire Tests of Building Construction and Materials@ UL 263@ in place of the Fire Endurance Test@ Section 6@ described in this standard. The investigation of ceiling dampers and ceiling air diffusers for use in floor/ceiling assemblies previously rated with a hinged-door sheet metal damper involves a comparison of the fire resistance performance of the ceiling damper or ceiling air diffuser with that of a hinged-door sheet metal damper. This is done to confirm that the substitution of the ceiling damper or ceiling air diffuser does not reduce the hourly fire endurance rating of an assembly previously rated with the hinged-door type damper. Ceiling dampers and ceiling air diffusers for use in floor/ceiling assemblies not previously rated with a hinged-door sheet metal damper shall be tested as a component of the proposed floor/ceiling assembly in accordance with the Standard for Fire Tests of Building Construction and Materials@ UL 263. Ceiling dampers and ceiling air diffusers are not assigned hourly ratings@ but rather are assembly components designated for use in specific hourly rated fire resistive assemblies incorporating air duct outlets penetrating protective ceilings. The fire performance measured by ANSI/UL 263 is based upon air movement being stopped at the start of a fire. Ceiling dampers and ceiling air diffusers intended for use in HVAC systems where the airflow is operational at the time of a fire@ such as in a smoke control system@ or from other situations in which the fan system is operational at the time of a fire are investigated for dynamic closure. Ceiling dampers and ceiling air diffusers intended for use where the air movement is effectively stopped at the start of a fire are not required to be investigated for dynamic closure. Tests conducted in accordance with the test methods described herein are intended to develop data to enable regulatory authorities to determine the acceptability of ceiling dampers and ceiling air diffusers for use in floor-ceiling and roof-ceiling assemblies having hourly fire endurance ratings of the specified or shorter duration.