LAUSR

Wearing protective face mask has been demonstrated as one of the most effective COVID-19 prevention measures. The breathability measurement of surgical masks is normed by the UNI EN 14863:2019. This study aims at evaluating the uncertainty and reproducibility in the breathability ( $\Delta P$ ) measurement, as well as understanding the effects induced by the number and location of the measurement points. A total of 300 surgical masks were tested for breathability. For each mask, 15 measurement points have been considered. Results showed that more than 60% of the tested masks do not satisfy the standard requirements in terms of breathability, with the lower percentage of compliant mask associated with type II. Repeatability was found comparable to the instrument uncertainty related to the digital resolution of the device. A relative percentage variability related to the reproducibility up to 21.2% was found for the mask type II, thus allowing to affirm that different areas of the same mask can lead to different results in terms of breathability. The reproducibility error was found as the main source of uncertainty, leading to an underestimation or overestimation of the breathability value and, consequently, of the number of compliant masks. Finally, the number and location of measurement points represent a further source of uncertainty influencing the final value of the breathability also among the masks produced by the same manufacturer.