A comparison of performance metrics for cloth face masks as source control devices for simulated cough and exhalation aerosols

Lindsley, William G.; Blachère, Françoise M.; Beezhold, Donald H.; Law, Brandon F.; Derk, Raymond C.; Hettick, Justin M.; Woodfork, Karen; Goldsmith, William T.; Harris, James R.; Duling, Matthew G.; Boutin, Brenda; Nurkiewicz, Timothy R.; Noti, John D.

doi:10.1101/2021.02.16.21251850

Cited by 14 publications

(38 citation statements)

References 40 publications

(41 reference statements)

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“…ASTM standardized tests for filtration efficiency and inhalation airflow resistance measurements from unmodified medical and cloth face masks were performed using automated filter testers (Models 8130 and 8130A, TSI) as previously described. 10 Briefly, medical and cloth face masks were secured to a test plate using beeswax. Pleats on the unmodified medical face masks were expanded prior to measurement.…”

Section: Methodsmentioning

confidence: 99%

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Face mask fit modifications that improve source control performance

Blachère¹,

Lemons²,

Coyle³

et al. 2021

Preprint

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

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Section: Methodsmentioning

confidence: 99%

“…6, 7 Face masks provide a physical barrier to the expulsion of both aerosols and droplets, and offer limited personal respiratory protection against aerosols that may enter through the nose and mouth. 8-10…”

Section: Introductionmentioning

confidence: 99%

Face mask fit modifications that improve source control performance

Blachère¹,

Lemons²,

Coyle³

et al. 2021

Preprint

Self Cite

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“…The source simulator was based on a system used to test masks as source control devices for respiratory aerosols. [19,20] The simulator uses an elastomeric bellows driven by a computer-controlled linear motor to reproduce human coughing and breathing airflows. The source simulator includes a manikin headform that has pliable skin mimicking the elastic properties of human skin in order to create a realistic simulation of how each source control device would fit a human face.…”

Section: Respiratory Aerosol Source Simulatormentioning

confidence: 99%

“…[18] Two quantitative source control studies by our group using an aerosol simulator found that cloth face masks and medical masks typically blocked 40%-60% of coughed and exhaled aerosol particles and were more effective as the particle size increased. [19,20] In a subsequent study, we found that if a medical mask was knotted and the pleats were tucked to improve the fit of the mask, the mask blocked 77% of the aerosol particles, and the aerosol blocking could be increased to 85% by wearing a cloth mask over a medical mask (double masking). [21] We examined the efficacy of universal masking by placed a respiratory aerosol simulator (simulating a "source" person coughing or exhaling respiratory aerosols) and a breathing simulator (simulating a "recipient" person inhaling the aerosols) in a small room with aerosol particle measurement instruments.…”

mentioning

confidence: 99%

Efficacy of universal masking for source control and personal protection from simulated cough and exhaled aerosols in a room

Lindsley¹,

Beezhold²,

Derk³

et al. 2021

Preprint

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Face masks reduce the spread of infectious respiratory diseases such as COVID-19 by blocking aerosols produced during coughs and exhalations (“source control”). Masks also slow and deflect cough and exhalation airflows, which changes the dispersion of aerosols. Factors such as the directions in which people are facing (orientation) and separation distance also affect aerosol dispersion. However, it is not clear how masking, orientation, and distance interact. We placed a respiratory aerosol simulator (“source”) and a breathing simulator (“recipient”) in a 3 m x 3 m chamber and measured aerosol concentrations for different combinations of masking, orientation, and separation distance. When the simulators were front-to-front during coughing, masks reduced the 15-minute mean aerosol concentration at the recipient by 92% at 0.9 and 1.8 m separation. When the simulators were side-by-side, masks reduced the concentration by 81% at 0.9 m and 78% at 1.8 m. During breathing, masks reduced the aerosol concentration by 66% when front-to-front and 76% when side-by-side at 0.9 m. Similar results were seen at 1.8 m. When the simulators were unmasked, changing the orientations from front-to-front to side-by-side reduced the cough aerosol concentration by 59% at 0.9 m and 60% at 1.8 m. When both simulators were masked, changing the orientations did not significantly change the concentration at either distance during coughing or breathing. Increasing the distance between the simulators from 0.9 m to 1.8 m during coughing reduced the aerosol concentration by 25% when no masks were worn but had little effect when both simulators were masked. During breathing, when neither simulator was masked, increasing the separation reduced the concentration by 13%, which approached significance, while the change was not significant when both source and recipient were masked. Our results show that universal masking reduces exposure to respiratory aerosol particles regardless of the orientation and separation distance between the source and recipient.

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“…Many factors that impact the efficiency of masks in reducing exposure to aerosols including the pressure difference across the mask, the direction of flow through a mask (inhalation versus exhalation), filter efficiency, pliability of mask material, and the fit of the mask on the user's head (Lindsley et al 2021;Pan et al 2021). The last two factors can influence the amount of leakage around the mask.…”

Section: Masksmentioning

confidence: 99%

Single-zone simulations using FaTIMA for reducing aerosol exposure in educational spaces

Ng¹,

Poppendieck²,

Polidoro³

et al. 2021

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On March 11, 2020, the World Health Organization declared the novel coronavirus (COVID-19) outbreak a global pandemic. Following this announcement, school closures around the United States began, and starting in June 2020, many schools decided to reopen for the next academic year or were planning to reopen. Guidance from ASHRAE and other organizations for reoccupying school buildings include wearing masks, increasing ventilation, increasing filtration, and using portable air cleaners (PAC).This report describes a simulation study that: (1) compares the relative reduction in aerosol exposure in education spaces as a result of changes to the operation of heating, ventilating, and air conditioning (HVAC) systems and inclusion of non-HVAC controls (e.g., wearing of masks and operating PAC) and (2) estimates the uncertainties in effectiveness associated with these controls and combinations of controls.

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A comparison of performance metrics for cloth face masks as source control devices for simulated cough and exhalation aerosols

Cited by 14 publications

References 40 publications

Face mask fit modifications that improve source control performance

Face mask fit modifications that improve source control performance

Efficacy of universal masking for source control and personal protection from simulated cough and exhaled aerosols in a room

Single-zone simulations using FaTIMA for reducing aerosol exposure in educational spaces

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