Masks and ventilation systems are more effective at preventing indoors COVID-19 transmission than physical distancing, a new study has found.
With places hit hard by COVID-19 such as the UK looking to reopen schools and businesses, the findings could point to a safe way to increase classroom, workplace and store capacities back to pre-pandemic levels.
"The research is important as it provides guidance on how we are understanding safety in indoor environments," said study leader University of Central Florida engineering professor Michael Kinzel.
Using state-of-the-art computer models, his team simulated what would happen if a student or teacher in a 65 square metre classroom with 3m-high ceilings - typical for universities - was infected with the virus, but everyone wore masks.
With proper ventilation, they found no correlation between distance and infection risk.
"The study finds that aerosol transmission routes do not display a need for six-feet social distancing when masks are mandated," he said.
Six feet is just under two metres, the distance the Unite Against COVID-19 campaign recommends people maintain when in public.
"These results highlight that with masks, transmission probability does not decrease with increased physical distancing, which emphasises how mask mandates may be key to increasing capacity in schools and other places."
In other words, if everyone's wearing masks there's little to be gained by enforcing physical distancing.
"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."
Masks not only stopped people infected with the virus from expelling droplets onto others, but also prevented their breath from spreading around the room. What little breath passed through the mask was slow and warm, so followed "the thermal plume vertically rather than being projected forward" onto others.
Having a good ventilation system reduced the risk of infection overall by up to 50 percent, the study also found.
"The ventilation system creates a steady current of air flow 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," the researchers said in a statement.
Dr Kinzel said it showed "ventilation systems and mask usage are most important for preventing transmission and that social distancing would be the first thing to relax".
The research was published in journal Physics of Fluids on Monday.