Versions 1221-DOW and 1221-OW are "outside of wall" higher general performance combination fire/smoke damper exclusively created for purposes where the damper can not be mounted within the plane on the wall or ground. They functions Nailor’s exceptional inter-locking double skin airfoil blade style that eradicates combustible seals and delivers flame and smoke seal https://heavy-duty-stainless-stee80011.worldblogged.com/43074526/what-does-dampers-for-industrial-sector-mean