Structure of Fire Damper Distribution Box

A fire damper distribution box consists of a metal sleeve housing the damper blades, fusible link or actuator, and mounting flanges, designed to fit within fire-rated walls or floors while allowing proper airflow and inspection access. Components and Structure1. Damper Sleeve or Box: The main body of the distribution box is a galvanized or stainless steel sleeve that fits into the wall or floor opening.

It provides structural support for the damper blades and ensures the assembly maintains its fire-resistance rating when installed. The sleeve must be square, free of twist, and aligned with the duct or opening. 2.

Damper Blades: Inside the box are single, multi, or interlocking blades that close automatically in response to heat or an electrical signal. Blades are typically spring-loaded and held open by a fusible link or fail-safe actuator. The blades must be protected from damage during handling and installation.

3. Fusible Link or Actuator: A fusible link melts at a predetermined temperature, releasing the blades to close and block airflow, preventing fire spread. In some systems, an electrically actuated damper may close in response to a fire alarm signal.

4. Mounting Flanges and Retaining Angles: The box includes mounting flanges that secure it to the wall or floor. Retaining angles overlap the opening by at least 1 inch to maintain fire integrity.

Clearances between the damper and sleeve allow for thermal expansion: typically 1/8 inch per foot for galvanized steel and 3/16 inch per foot for stainless steel, with minimum and maximum limits. 5. Access Panels and Identification: Fire damper boxes must provide inspection access large enough to test and maintain the damper without compromising the fire barrier.

Access points are permanently labeled to indicate the type of damper (fire, smoke, or combination),.

Installation Considerations

Orientation: Dampers are labeled for horizontal or vertical installation, and the indicated orientation must be followed.

Wall/

Floor Integration: The box is framed with studs or concrete, and gypsum board or other fire-rated materials are fastened around it to maintain the fire-resistance rating. Clearances: Proper gaps between the damper and opening accommodate thermal expansion while ensuring the damper can close fully. Compliance: Installation must follow UL 555 standards and NFPA codes (NFPA 80, 90A, 105) for fire and smoke protection.

Summary

A fire damper distribution box is a metal housing that integrates damper blades, actuators, and mounting hardware within a fire-rated wall or floor. Its design ensures automatic closure during fire events, maintains fire-resistance integrity, and provides access for inspection and maintenance. Proper installation, orientation, and compliance with NFPA and UL standards are critical for effective fire protection.