Exposure to Exhaled Air from a Sick Occupant in a Two-Bed Hospital Room with Mixing Ventilation: Effect of Posture of Doctor and Air Change Rate

Full-scale measurements were performed in a climate chamber set as a two-bed hospital room, ventilated at 3, 6 and 12 ACH with overhead mixing ventilation. Air temperature was kept constant at 22 °C. Two breathing thermal manikins were used to mimic a sick patient lying on one side in one of the beds and a doctor. A thermal dummy mimicked an exposed patient lying in the second bed. The doctor either stood up or sat in a chair 0.55 m facing the sick patient. The ‘sick patient’ was exhaling through the mouth and inhaling from the nose. Tracer gas (R 134A) was mixed with the exhaled air to mimic airborne droplets and droplet nuclei of less than 5 μm aerodynamic diameter. Important finding of this study is that airflow distribution and interaction in rooms, position of the recipient with respect to the source, etc. may have greater impact on the exposure to exhaled air by a sick patient than the ventilation rate itself. Furthermore, increase in ventilation may affect adversely the exposure to exhaled air and thus enhance the risk from airborne cross infection.