The Impact of Hospital-Ward Ventilation on Airborne-Pathogen Exposure

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime

“…Further experiments have been carried out in several operational buildings in which localized dilute clouds of CO 2 are released at a point in a room or corridor, and the subsequent spreading of this cloud is then measured over time; the CO 2 acts as an analogue for the small aerosols in that it moves with the air flow in the space [73]. Comparisons have been made between the rate of dilution and flushing of the CO 2 from the space in the case with people moving and with no people moving in the space.…”

“…In the case of a ventilated corridor, for example, the impact of the people moving along the corridor is to drive additional mixing of the cloud of CO 2 into the new ventilation air, thus delaying the flushing of the CO 2 from the space. Figure 3 a illustrates the results of an experiment, which was carried out in a ventilated corridor in the cystic fibrosis ward of the new Royal Papworth hospital in Cambridge [73]. A small pulse of CO 2 gas was released at the end of the corridor, and the evolving concentration of the CO 2 was measured at three locations along the corridor using an array of sensors.…”

“…Now, the mixing driven by the movement of the person resulted in additional dispersal and mixing of the CO 2 tracer, as illustrated diagrammatically in figure 3 b . As a result, the residence time of the CO 2 in the corridor increased by about five times [73]. This illustrates how the internal mixing processes of the air in buildings, and especially people movement, can lead to greater residence times for small aerosols.…”

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Figure 3( a ) Time series of the concentration of CO 2 as recorded by three sensors located in a ventilated but empty corridor in the cystic fibrosis ward of the new Royal Papworth Hospital in Cambridge (UK), after the local release of a pulse of CO 2 at one end of the corridor (black lines). The experiment was repeated with one person continuously walkingback and forth along the corridor, and the red lines show the CO 2 concentration obtained in this second experiment [73]. ( b ) Schematic illustrating the effect of the mixing associated with the wake of a person walking along the corridor.

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Healthcare-acquired clusters of COVID-19 across multiple wards in a Scottish health board

“…15 This would have exacerbated inadequate air change in clinical areas, thus impeding removal of any infectious aerosols. 16 , 17 , 18 …”