In this research the ability of the ventilation system in an operating room to keep the operating table and the instrument tables free from airborne bacteria has been evaluated in an experimental mock-up for different ventilation systems under various static circumstances. To accomplish this, the VDI 2167 particle test has been used as a basis. In this test particles are released on the floor and smoke concentrations are measured on the operating table. The VDI 2167 method was able to distinguish the different systems, but did not provide for a complete evaluation. The thermal balance in the room plays a major role in whether a laminar downflow system works and the VDI method does not incorporate this into the tests in an adequate manner. Moreover, the influence of surgical lighting is not included in the test method in an effective way.