Results from an assessment of face masks to prevent the spread of COVID-19 found that double masking and fit modifications significantly improved the performance of face masks as source control devices for respiratory aerosols. These findings were published in the American Journal of Infection Control.
This study was conducted between January and April 2021 by investigators at the National Institute for Occupational Safety and Health. The investigators assessed the performance of 3 cloth and 2 medical masks, as well as fit modifications including a mask bracket, an earloop strap, earloop toggles, and an elastic mask brace; all masks and fit modification devices were purchased online. Face masks with and without modifications were fit tested on patients (n=3-4 tests/modifications) and simulator manikins (n=4-5 tests/modifications). The investigators used a source control measurement system to assess the spread of respiratory aerosols via simulated coughs and exhalations.
The 2 medical masks included in the study were a 3-ply disposable protective mask made by Excellent Artisan (medical mask 1) and a 3-ply disposable surgical mask made my Winner Medical Co., Ltd. (medical mask 2). The 3 cloth masks were a 2-ply reusable polyester blend mask made by Lefty Productions, Co., a 3-ply defender cotton mask made by HanesBrands, and a 4-ply reusable cotton-polyester blend mask made by Badger-Smith.
On analysis of the 2 medical masks, the investigators found that medical mask 1 had a filtration efficiency of 82.0% and an airflow resistance of 45.4 Pascals (Pa), whereas medical mass 2 had a filtration efficiency of 96.4% filtration efficiency and an air flow resistance of 63.7 Pa.
Compared with medical masks, cloth masks had a 2- to 4-fold decrease in filtration performance and increased airflow resistance. The 2-ply mask had a filtration efficiency of 20.2% and an airflow resistance of 96.4. Further analysis showed that the 3-ply mask had a filtration efficiency of 21.0% and an airflow resistance of 45.1 Pa, and the 4-ply mask had a filtration efficiency of 36.0% and an airflow resistance of 92.2 Pa.
The average human fit factor without modification was 1.6 and 1.8 for medical mask 1 and for medical mask 2, respectively. Of note, crossing the earloops or the use of a mask bracket were both found to decrease the fit factor. In addition, the use of a mask brace was associated with the greatest increase in fit factor for both medical masks 1 (7.2) and 2 (13.3).
In source control simulations, the mean particle collection efficiency for medical mask 1 without modification was 56.0% for cough and 42.0% for exhalation compared with 63.0% and 55.0% for medical mask 2, respectively. Collection efficiencies were significantly improved by increasing the tension in the earloops. The best modification was double masking with the 3-ply cloth mask or using a mask brace. Double masking for medical masks 1 and 2 had a particle collection efficiency of 85.0% and 92% for experimental cough and 92% and 91% for exhalation, respectively. Of note, the use of a mask brace over medical masks 1 and 2 was associated with a mean particle collection efficiency of 95% for cough and 99% for exhalation.
This study was limited by the small number of masks tested compared with the large variety of masks commercially available. In addition, inconsistencies and discrepancies in individual mask quality may have occurred during production.
According to the investigators, “the results of these studies have broad applicability towards personal measures that can be taken to [decrease] the transmission of respirable infectious pathogens and are not limited to the SARS-CoV-2 virus.”
Blachere FM, Lemons AR, Coyle JP, et al. Face mask fit modifications that improve source control performance. Am J Infect Control. 2021;S0196-6553(21)00715-X. doi:10.1016/j.ajic.2021.10.041