Face Mask Fit Modifications to Reduce the Expulsion of Respiratory Aerosols

FRANCOISE BLACHERE, William Lindsley, Raymond Derk, Jayme Coyle, Angela Lemons, Matthew Duling, Brenda Boutin, Theresa Boots, James Harris, Donald Beezhold, John Noti, National Institute for Occupational Safety and Health

     Abstract Number: 99
     Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept

Abstract
Wearing a face mask or respirator to protect others from potentially infectious respiratory aerosols and droplets, called source control, can help limit the transmission of COVID-19. The efficacy of a face mask at blocking expelled respiratory particles depends on how well it fits the user’s face. To improve the fit of a face mask and minimize face seal leaks, fit modifications have been proposed but the data on source control are limited. Using manikin-based respiratory simulations, the efficacy of face masks at blocking expelled aerosol particles was examined. The mass and size distribution of particles that pass through or around different face masks were measured by aerosol impactors and optical particle sizers. Medical masks without fit modification blocked up to 57% of aerosols ≤3.3 μm in size. Improving the fit of a medical mask with an elastic brace, knotting the ear loops and tucking in excess material, or adding a cloth mask over the medical mask (double masking) increased the blocking efficacy for smaller sized aerosols. Results show that double masking or using the knot and tuck fit modification blocked up to 83% of cough aerosols and 92% of exhaled aerosols ≤3.3 μm in size. The most notable results were demonstrated with the face mask brace modification, where ≥99% of expelled aerosols were blocked. Simulated exposure studies, where particles were exhaled by a masked source simulator and the mass of the particles reaching the mouth of an unmasked recipient breathing simulator was measured, further demonstrate that a well-fitted face mask can limit recipient exposure. Aerosol exposure was reduced by nearly 100% when the source wore a medical mask fit modified with an elastic brace. The results of these studies highlight personal measures that can be taken to reduce the transmission of respirable airborne pathogens and are not limited to SARS-CoV-2.