April 26, 2021

Study: 6-ft rule inadequate to mitigate indoor airborne transmission of COVID-19

Editor's Note

This study by researchers at the Massachusetts Institute of Technology, Cambridge, finds that the transmission risk of COVID-19 is reduced in large rooms with high air exchange rates, increased with vigorous respiratory activities, and reduced with face masks.

The researchers developed a method of calculating exposure risk to COVID-19 in an indoor setting that factors in issues that could affect transmission, including the amount of time spent inside, air filtration and circulation, immunization, variant strains, mask use, and respiratory activity such as breathing, eating, speaking, or singing.

Among their findings:

  • The risk of being exposed to COVID-19 indoors is as great at 60 feet as it is at 6 feet, even when wearing a mask.
  • The longer someone is inside with an infected person, the greater the chance of transmission.
  • Opening windows or installing fans to keep the air moving could be as effective or more effective than installing expensive new filtration systems.
  • Guidelines capping indoor occupancy should depend on the size of the room and ventilation, not number of people. Often a space is large enough and the ventilation is good enough that it can be operated at full capacity.

The researchers conclude that their study makes clear the inadequacy of the 6-foot rule in mitigating indoor airborne transmission of COVID-19.

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