Can building’s ventilation substitute mask wearing and social distancing while preventing COVID-19 transmission?

REMARK: This Q&A was part of the AIVC special COVID-19 newsletter published in February 2021. To subscribe to the newsletter please click here.

No. One cannot rely solely on a strategy of dilution through building ventilation to reduce the risk of COVID-19 transmission to a low level.

Social distancing is a measure to prevent transmission considering that large particles will follow a ballistic trajectory and are not influenced very much by airflow. In this case, ventilation cannot replace masks and social distancing because these are dealing with this ballistic trajectory.

Some experts of physics of respiratory emissions consider that “droplets of all sizes are trapped and moved by the exhaled moist and hot turbulent gas cloud that keeps them concentrated as it carries them over metres in a few seconds. After the cloud slows sufficiently, ventilation, specific patterns of airflow (…) become important" (Jones et al. 2020) (1). As a result, Covid-19 aerosol transmission depends on building ventilation rates but also on several other factors: emission and inhalation rates are crucial issues which depend on occupants (for instance, “super-emitter”) and their activities (silent and calm, speaking, singing, sport training, …), the mask wearing and the efficiency of the mask, the occupancy of the space (low/medium/high), the duration of the contacts between occupants, environmental conditions, etc. An illustration of this multifactor approach has been provided by (Jones et al. 2020) in order to replace a fixed value of social distancing. Even if this is mainly a qualitative approach with no modelling, the results suggest that if people don’t wear any mask in a room for meetings over a prolonged time, even if they keep a 2m-distance and irrespective of occupancy level (high or low), ventilation alone would not be able to decrease the risk of SARS-CoV-2 transmission to a lower level than medium or high risk.

In a conclusion, the nature of respiratory emissions indicate that ventilation alone cannot replace masks and social distancing.

Authors

Gaëlle Guyot, Cerema, Univ. Savoie Mont Blanc, Jelle Laverge, UGent & Willem de Gids, VentGuide

References

1. N.R. Jones, Z.U. Qureshi, R.J. Temple, J.P.J. Larwood, T. Greenhalgh, L. Bourouiba, Two metres or one: what is the evidence for physical distancing in Covid-19?, BMJ. 370 (2020). https://doi.org/10.1136/bmj.m3223. 
2. AIVC. AIVC Newsletter Special Issue on COVID-19. February 2021.