New research shows physical distancing alone may not be enough to stop the spread of COVID-19 indoors.
Two meters (about six and a half feet) of distance between unmasked people isn’t enough to avoid infectious aerosols, according to researchers at the Penn State Department of Architectural Engineering.
The researchers looked into how building ventilation and physical distancing affect airborne transport of virus particles released from infected people in buildings.
The study looked into three factors:
- the amount and rate of air ventilated through a space
- the indoor airflow pattern associated with different ventilation strategies, and
- the aerosol emission mode of breathing versus talking.
The aerosol sizes they studied are in the range of those that can carry the coronavirus.
Displacement vs. mixed-mode ventilation
Results show virus particles from an infected person speaking without a mask can travel to another person’s breathing zone within one minute, even at a distance of two meters and in rooms with sufficient ventilation.
“The results suggest that physical distance alone is not enough to prevent human exposure to exhaled aerosols and should be implemented with other control strategies such as masking and adequate ventilation,” said Donghyun Rim, author and associate professor of architectural engineering.
In their tests, aerosols traveled farther and more quickly in rooms with displacement ventilation, where fresh air continuously flows from the floor and pushes old air to exhaust vents near the ceiling. This type of ventilation system is installed in most residential homes and can result in a breathing zone concentration of aerosols seven times higher than in mixed-mode ventilation.
Many commercial buildings use mixed-mode systems, which incorporate outside air to dilute the indoor air and result in better air integration and lower aerosol concentrations, according to the researchers.
Displacement ventilation can be improved by operating mechanical fans and stand-alone air cleaners to reduce the chance of infection.
Rim says increasing the ventilation and air mixing rates can reduce the transmission distance and number of aerosols.
Physical distancing, ventilation and mask wearing should be used together for best results, according to Rim.
The researchers are continuing their study by analyzing various occupied spaces such as classrooms and transportation hubs.
The study was published online ahead of the October print edition of Sustainable Cities and Society.