Abstract: A clean room is supplied with air at a controllable velocity from a blower with a variable damper mechanism. The ceiling of the clean room is comprised of a plurality of panels of particulate filter material Associated with at least some of the panels are air dampers comprised of first, second, and third adjacent perforated plates. The first plate is fixed and the second plate is mounted for translational movement relative to the first. The third plate is interposed between the first and second plates as a gasket to reduce air flow between the plates. By moving the second plate relative to the first, the perforations therein are selectably opened or occluded, permitting the air passing through each panel to be regulated. Air flow through the room as a whole is controlled by the variable air flow feature of the blower.