They are set up from the HVAC ductwork and they are activated to close after they sense smoke. Smoke dampers are usually made of aluminum and also have a motorized actuator that closes the damper. Backdraft dampers are either gravity or motorized. Gravity backdraft dampers use the force of gravity https://air-control-dampers-for-e91233.newbigblog.com/43028451/the-definitive-guide-to-air-control-dampers-for-engine-sheds