Model FLD-S-A is a Multi Blade fire damper with 3V style blades. It is designed for closure of the HVAC duct opening in emergency Fire situations. It is certified to withstand fire conditions for 2 hours as well as 4 hours, as per UL555 testing standards , tested by CBRI Roorkee. Model FLD-S-A can be installed vertically, with blades running horizontally with airflow in either direction. Suitable for Velocities up to 2000 fpm.