Assessment of Fabric Masks as Alternatives to Standard Surgical Masks in Terms of Particle Filtration Efficiency

Amy V Mueller; Loretta A Fernandez

The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10. 1101 /2020 Calibration. Two PortaCount Plus instruments were used to report particle counts in air sampled from inside the mask (Mask PortaCount) and ambient air just outside the mask (Reference PortaCount) ( Figure 1 ). Because these instruments were not recently calibrated, nor last calibrated at the same time, an intercalibration was conducted to allow calibration adjustments on collected data. Each sampling day, calibration data (a minimum of three one-minute time series, n=180) were collected by recording readings simultaneously on both instruments while sample tubes were side-by-side (within 3 cm), open to the air (no mask), and a minimum of 1m from any person and 2m from the particle generator (as recommended by the manufacturer). The Mask PortaCount consistently reported higher particle counts; however, correlation coefficient between the readings from the two instruments was consistently above 0.9. Therefore day-specific linear regressions were used to normalize particle counts from the Reference PortaCount to equivalent particle counts from the Mask PortaCount. Data collection and processing. Each mask test consisted of three one-minute runs while wearing the mask as designed (Figure 2(a) ). To simulate a face-hugging fit like that used for N95 masks, each mask was also tested for one minute while pressing the material to the face around the breathing zone (across the bridge of nose, cheeks, and around the chin) using two hands. In addition, a more practical method of holding the mask material against the face was tested by adding section of nylon stocking over the entire mask area following recommendations from Copper et al. (1983a) (Figure 2(b) ). The N95 was not tested using either of these additional methods as this is already a tight-fitting mask. Tests were run on at least three replicate sample masks whenever possible, however for many masks only one sample was available.