Marek Brand

Exposure of health care workers and occupants to coughed airborne pathogens in a double-bed hospital patient room with overhead mixing ventilation

The exposure of a doctor and a second patient was studied in a simulated two-bed hospital isolation room. The room was ventilated at three air change rates (3 h−1, 6 h−1, and 12 h−1) by mixing air distribution keeping at 22°C (71.6°F). The effect of the distance between the doctor and the coughing person, the posture of the coughing patient (lying sideways facing the doctor or on back), and the position of the doctor (facing the coughing patient or standing sideways) was examined with respect to exposure to coughed air. A thermal manikin with realistic body shape and surface temperature distribution was used to resemble the doctor. A coughing patient (equipped with cough generator) lying in one bed and another patient in the second bed were simulated by two heated dummies with simplified geometry. The cough consisted of 100% CO2. The peak cough time was 4 s, when the doctor was closest to the sick patients bed, and more than doubled for the exposed patient. The level of exposure (peak concentration level) depended strongly on the positioning and distance of the doctor from the infected patient and posture of the coughing patient. Peak concentration level varied widely from 194 to 10,228 ppm. Ventilation rates of 12 h−1 (recommended by present hospital standards) resulted in background velocities exceeding 0.5 m/s (98.43 fpm), suggesting elevated risk from draught discomfort.