Models 1221-DOW and 1221-OW are "outside of wall" superior effectiveness mixture fire/smoke damper specially made for purposes in which the damper can't be installed throughout the aircraft on the wall or floor. They features Nailor’s special inter-locking double skin airfoil blade design that gets rid of combustible seals and supplies flame and smoke https://lorenzovmcqe.is-blog.com/43522284/the-5-second-trick-for-dampers-for-industrial-sector