A Backblast Damper or Isolation Flap is a passive isolation device used to prevent a deflagration from propagating back upstream in ductwork in the event of a dust collector explosion. It is installed on the ductwork upstream of a dust collector.
The unit contains a flap that is held open by the normal process airflow. Should a pressure wave from an explosion in the collector propagate through the ductwork in the reverse direction of the normal airflow, it will force the flap down to prevent the deflagration from passing further upstream.
Isolation Flaps are to be used in applications where the dust collector is properly vented.