For thimble ducting Class II, Type A2 Biosafety Cabinets. Canopy provides an air gap to allow room air to enter the ductwork and mix with the filtered air being exhausted to the outside. Inadequate exhaust activates the switch in less than one second and signals the LCD to display an alarm and the motor to increase to maximum speed for personal safety. Adds only 1.25" to the overall height of the cabinet. Exhaust connection is required. Damper and Remote Blower are recommended (not included).