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. 2022 Jan 21:17:e118.
doi: 10.1017/dmp.2022.23.

Experimental Measurement of the Size of Gaps Required to Compromise Fit of an N95 Respirator

Eugenia O'Kelly  1 , Anmol Arora  2 , Sophia Pirog  3 , James Ward  1 , P John Clarkson  1
Affiliations

Experimental Measurement of the Size of Gaps Required to Compromise Fit of an N95 Respirator

Eugenia O'Kelly et al. Disaster Med Public Health Prep. .

Abstract

Objective: The effectiveness of filtering facepiece respirators such as N95 respirators is heavily dependent on the fit. However, there have been limited efforts to discover the size of the gaps in the seal required to compromise filtering facepiece respirator performance, with prior studies estimating this size based on in vitro models. In this study, we measure the size of leak necessary to compromise the fit of N95 respirators.

Methods: Two methods were used to create a gap of specific dimensions. A set of 3D-printed resin spacers and hollow steel rods were used to generate gaps in N95 respirators while worn on 2 participants. Occupational Safety and Health Administration (OSHA) quantitative fit testing methods were used to quantify mask performance with gaps between 0.4 and 2.9-mm diameters.

Results: Gap size was regressed against fit factor, showing that overall, the minimum gap size to compromise N95 performance was between 1.5 mm2 and 3 mm2.

Conclusions: These findings suggest the fit of a N95 respirator is compromised by gaps that may be difficult to visually detect. The study also adds to the body of evidence supporting the routine use of quantitative fit testing to ensure that masks are well-fitting.

Keywords: COVID-19; SARS-CoV-2; coronavirus; face coverings; quantitative testing.

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Figures

Figure 1.
Figure 1.
The effect of the gap sizes on the fit factor of an N95 respirator. A: The effect of the gap sizes on the fit factor of an N95 respirator using a steel tube to hold open a hole in a mask. For each size, n = 10. The coefficient of determination, R was 0.86, indicating strong positive correlation. B: The effect of the gap sizes on the fit factor of an N95 respirator using a 3D-printed resin spacer to hold open a hole in a mask. The model indicates a 1.26 mm diameter gap compromises the fit of N95 respirators. For each size, n = 22. Some dots are not visible due to overlapping data points. The coefficient of determination, R was 0.61, indicating moderate positive correlation. C: The effect of gap sizes with combined spacer data. OSHA required fit was found to be compromised at 1.4 mm diameters. The coefficient of determination, R was 0.66, indicating moderate positive correlation.
Figure 2.
Figure 2.
Top: For visualizing the size of the gaps, 1.5-mm diameter and 2-mm diameter dots placed on an adult female finger. Bottom left: A steel rod spacer placed through the material of the mask. Bottom right: The 3D printed resin spacer held against the edge of the mask. A small hole in the middle of the spacers allowed air to flow through.
See this image and copyright information in PMC

References

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