Face masks and a good ventilation system are more important than social distancing for reducing the airborne spread of COVID-19 in classrooms, says a new study.
This study by the University of Central Florida is important at a time when schools and universities are considering returning to more direct classes in the fall.
The research has been published in the journal Physics of Fluids.
"The research is important as it provides guidance on how we are understanding safety in indoor environments," says Michael Kinzel, an assistant professor in UCF's Department of Mechanical and Aerospace Engineering and study co-author.
"The study finds that aerosol transmission routes do not display a need for six feet social distancing when masks are mandated," he says. "These results highlight that with masks, transmission probability does not decrease with increased physical distancing, which emphasizes how mask mandates may be key to increasing capacity in schools and other places."
In the study, the researchers created a computer model of a classroom with students and a teacher, then modelled airflow and disease transmission, and calculated airborne-driven transmission risk.
The classroom model was 709 square feet with 9-foot-tall ceilings, similar to a smaller-size, university classroom, Kinzel says. The model had masked students—any one of whom could be infected—and a masked teacher at the front of the classroom.
Masks were shown to be beneficial by preventing direct exposure of aerosols, as the masks provide a weak puff of warm air that causes aerosols to move vertically, thus preventing them from reaching adjacent students, Kinzel says.
Additionally, a ventilation system in combination with a good air filter reduced the infection risk by 40 to 50 per cent compared to a classroom with no ventilation. This is because the ventilation system creates a steady current of airflow that circulates many of the aerosols into a filter that removes a portion of the aerosols compared to the no-ventilation scenario where the aerosols congregate above the people in the room.
These results corroborate recent guidelines from the US Centers for Disease Control and Prevention that recommend reducing social distancing in elementary schools from six to three feet when mask use is universal, Kinzel says.
"If we compare infection probabilities when wearing masks, three feet of social distancing did not indicate an increase in infection probability with respect to six feet, which may provide evidence for schools and other businesses to safely operate through the rest of the pandemic," Kinzel says.
"The results suggest exactly what the CDC is doing, that ventilation systems and mask usage are most important for preventing transmission and that social distancing would be the first thing to relax," the researcher says.