Air handling is a key element to cleanroom operation to maintain a particulate-free working area. Fresh outside air is brought in filtered and dehumidified to the cleanroom plenum, where it is lead/pushed through fine filter units (FFUs) into the working area (white area). Particles that are may be in the air get trapped by the laminar air flow generated by the FFUs and are driven through the perforated floor panels. Via the grey area the whole air inside the cleanroom recirculates through the FFUs, while it is supplemented with outside air.