At which distance upstream and downstream must linings in ducts be interrupted relative to fire dampers?

The correct answer relates to the specific requirements set forth in the North Carolina Mechanical Code regarding the installation of fire dampers within ductwork. Fire dampers are critical components used to prevent the spread of fire through the duct system and must be installed correctly to ensure their effectiveness.

The code specifies that linings in ducts must be interrupted at a distance of 6 inches both upstream and downstream from the fire dampers. This requirement is in place to ensure that the fire damper is able to operate effectively without obstruction, allowing it to fully close and preventing any passage of smoke or flames through the ducts. Interrupting the duct linings at this distance minimizes the risk of any materials in the ductwork interfering with the damper's function, thus enhancing fire safety in the building's ventilation system.

Maintaining this specified distance also contributes to proper airflow dynamics and minimizes turbulence, which can otherwise affect the performance of the fire damper during an emergency. Therefore, complying with this requirement is essential for both safety and code adherence.