Exposure to exhaled air from a sick occupant in a two-bed hospital room with mixing ventilation: effect of distance from sick occupant 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 h-1. Air temperature was kept constant at 22 °C. Two breathing thermal manikins were used: a sick patient lying on one side in one bed and a doctor. A thermal dummy mimicked an exposed patient lying in the second bed.

The doctor stood 0.55 m or 1.1 m facing the sick patient. The breathing mode of the “sick patient” was: exhalation mouth/inhalation nose. Tracer gas (R-134a) was mixed with the exhaled air. Important finding of this study is that airflow distribution and interaction in rooms, distance between the source and recipient, etc. may play more important role for the exposure to the air exhaled by the sick patient than the ventilation rate.

Increase in ventilation may affect adversely the exposure to exhaled air and thus enhance the risk from airborne cross infection.