Three-Dimensional Facial Geometry and Its Impact on N95 Respirator Fit Factor in Hong Kong Chinese Adults: An Integrated Experimental and Computational Approach

The current study investigated the impact of facial three-dimensional shape geometry and respirator-face interface mechanics on the fit of N95 respirators in 21 Hong Kong Chinese adults. Three-dimensional facial scanning, quantitative fit testing of four N95 respirators (3M 1860, 1870+, 9105, and 9502+), and facial dimensions extraction using Geomagic Wrap were conducted in this study. The seven fit test exercises were performed in the current investigation, while finite element analysis (FEA) was used for studying respirator-face contact mechanics in a stratified subset of 14 participants wearing 3M 1870+ geometry. Among all evaluated models, 3M 1870+ had the highest pass rate. Pearson correlation analysis showed only nominal, uncorrected associations between the fit factor and nose length (r = 0.574, p = 0.007) as well as neck circumference (r = 0.434, p = 0.050). None of the anthropometric correlations remained statistically significant after Bonferroni correction for multiple comparisons (n = 38) (adjusted alpha level = 0.00132). Threshold post hoc observations of the bitragion coronal arc, neck circumference, nose height and nose length should therefore be considered as hypothesis generation and not as screening criteria. Fit factors decreased in dynamic movements, especially when bending. FEA-predicted contact area correlated strongly with experimental fit factor (r = 0.974, 95% CI: 0.918 to 0.992, p < 0.001), thus confirming the association of simulation and fit performance measurement but not serving as independent validation of the model. These preliminary results could be helpful for future respirator fit studies and respirator design for Hong Kong Chinese adults.