Face mask fit modifications that improve source control performance

Abstract

Background: During the COVID-19 pandemic, face masks are used as source control devices to reduce the expulsion of respiratory aerosols from infected people. Modifications such as mask braces, earloop straps, knotting and tucking, and double masking have been proposed to improve mask fit however the data on source control are limited.

Methods: The effectiveness of mask fit modifications was determined by conducting fit tests on human subjects and simulator manikins and by performing simulated coughs and exhalations using a source control measurement system.

Results: Medical masks without modification blocked ≥56% of cough aerosols and ≥42% of exhaled aerosols. Modifying fit by crossing the earloops or placing a bracket under the mask did not increase performance, while using earloop toggles, an earloop strap, and knotting and tucking the mask increased performance. The most effective modifications for improving source control performance were double masking and using a mask brace. Placing a cloth mask over a medical mask blocked ≥85% of cough aerosols and ≥91% of exhaled aerosols. Placing a brace over a medical mask blocked ≥95% of cough aerosols and ≥99% of exhaled aerosols.

Conclusions: Fit modifications can greatly improve the performance of face masks as source control devices for respiratory aerosols.

Keywords: Face mask; Fit modification; Respiratory aerosols; Source control.

Fig 1

Source control performance of face masks (denoted by colors) with and without fit modifications. For comparison, source control data for an N95 respirator was included. Total particles blocked (%) by medical and cloth face masks with and without fit modifications following cough (top) and exhalation (bottom) simulations. Percentage blocked is based on mass of particles collected following unmasked source coughing and exhalation experiments. Asterisks (*) indicate the modification was determined to be statistically significant (p < .05) compared to the corresponding no modification control.

Fig 2

Percentage of particles in size fractions less and greater than 3.3 μm blocked by face masks with and without fit modifications. Particles blocked (%) in the size fraction ≤3.3 μm (white bars) and the size fraction >3.3 μm (black bars) following cough (top) and exhalation (bottom) simulations.

Fig 3

Exposure reduction (%) resulting from source masking (denoted by colors) in environmental chamber exhalation studies using both source and recipient respiratory simulators. Percent reduction is based on recipient exposures following unmasked source exhalation simulations. For comparison, expsoure reduction data for an N95 respirator was included. Asterisks (*) indicate the modification was determined to be statistically significant (P < 0.05) compared to the corresponding no modification control.