Furnish and install, at locations shown on plans or in accordance with schedules, backdraft dampers that meet the following minimum construction standards: Frame shall be 16 gage galvanized steel with windstops to reduce back flow all around. Blades shall be non-combustible neoprene coated fiberglass mechanically locked into blade edge for low noise operation. Each blade shall operate independently without bearings or linkage. Dampers shall be designed for maximum 1200 fpm spot velocities and up to 4" w.g. back pressure depending on damper size. Dampers shall be in all respects equivalent to Ruskin model NMS.