Ear-loop-type Korean Filter 94 masks (KF94 masks, equivalent to the N95 and FFP2) are broadly used in health care settings in Korea for the COVID-19 pandemic. However, no studies have assessed the adequacy of respiratory protection. In this prospective randomized open-label study, the investigators aimed to evaluate the fitting performance of ear-loop-type KF94 masks by the quantitative fit test according to the occupational safety and health administration (OSHA) protocol. In addition, by quantitatively comparing the "tight-fitting" method using a clip and the "general-fitting" method, the investigators tried to evaluate whether the tight-wearing method improves the fitting performance of KF94 masks.

Sample size: The sample size was calculated based on a pilot study of 10 participants, which examined the FF of general-fitting. The mean FF was 20.3, and the log-transformed FFs were assessed due to skewed data, which was 1.98 (standard deviation 1.34). We assumed that the FF for tight-fitting would increase by 50%, with an α value of .05, and a β error of .10 (power = 90%) for two-sided hypothesis testing. The estimated sample size calculation revealed a required sample of 24 participants. Therefore, 30 participants were enrolled to account for a 20% dropout rate.

Data analyses: Repeated-measures analysis of variance or generalized estimating equations were used to compare the FFs or passing rate of the QNFTs for the three mask types according to the wearing method. Paired t-tests or Wilcoxon signed-rank tests were used to compare the FFs according to the wearing method for each mask type. McNemar's test was used to compare the passing rate of the QNFT according to the wearing method. Bonferroni's correction was performed for all results of each subgroup analysis. SAS ver. 9.4 software (SAS Institute, Cary, NC) was used to perform all statistical analyses.

Inclusion Criteria:

• healthcare workers with experience in wearing filtering facepiece respirator working in the hospital

Exclusion Criteria:

• Individuals with expected difficulties in wearing masks or undergoing OSHA fit tests because of factors such as a facial anomaly, lung disease, or lower back disorder