Hospital bed ventilation: impact of operation mode on exposure

Full-scale measurements were performed in a climate chamber set as a two-bed hospital room with overhead ventilation. Air temperature was kept constant at 22 °C. Two breathing thermal manikins were used to mimic a sick patient lying sideways in one of the beds and a doctor. A thermal dummy mimicked a second patient lying in the other bed. The doctor stood up 0.55 m from the bed facing the sick patient. Two pairs of localized ventilation units were attached near the heads of both patients alongside the beds to capture, clean and release the captured exhaled air from the lying patients. When the bed units were not operated the room was ventilated at 3, 6 or 12 ACH. The background ventilation was kept at 3 ACH when the units were used. 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 3 μm aerodynamic diameter. Two modes of operation of the bed incorporated ventilation unit were tested: releasing the cleaned air upwards (pull mode) or supplying it sideways over the lying patient (“push and pull” mode). The strategy to exhaust pollutants close o release proved to be efficient. The bed incorporated ventilation unit was effective in capturing the air exhaled by the sick lying patient and performed significantly better than the overhead ventilation at 12 ACH. The exposure for the doctor and the second patient was further reduced when the bed incorporated ventilation unit was operated in the “push and pull” mode compared to the pull mode.