Abstract: Disclosed is a system for assisting in preventing over heating of the internal electrical components of a computer in the event of a failure of one of the adjacent fans of an array of fans employed to circulate cooling air over the components. The fans include openings through which air is forced from their inlet sides to their outlet sides. The system includes a vent for each fan arranged adjacent to and aligned with the fan opening at its outlet side. The vents are open and closed by vanes, having hinged slats construction to allow them to fall downwardly by their own weight or additional assistance. The vanes are kept open by the airflow created by the fans. Upon the failure of a fan, the absence of airflow through the opening thereof allows the slats of the vane to drop to close off the fan opening and prevent airflow into the fan opening from its outlet side.