Methods, systems and apparatus for monitoring the state of a reticle by providing a reticle having a device exposure region in an imaging tool, defining one or more image fields across the device exposure region, and transmitting energy through the device exposure region. The blow-through sluice includes a supply chute in the top area and a cylindrical housing which is disposed below the supply chute and in which a cellular wheel is arranged. The screen unit can move laterally, relative to the mounting frame, putting the foam in shear, in response to an edge or corner impact.