Abstract: A workstation (10) includes a working area (12) inside an enclosure (11) to which an operative can gain access via an access aperture (13) beneath a transparent window, an air circulation system, including a fan (16), being provided for drawing air from the enclosure (11) and directing it back to the enclosure (11) via a filter (15), an outlet being provided downstream of the filter for diverting a proportion of the clean air from the filter (15), so as to cause a lowering of pressure inside the enclosure (11) sufficient to cause an inflow of ambient air via the access aperture (13). The outlet is connected to the atmosphere via a secondary fan (32) which is actuate by a contamination sensor (34).