An Investigation of Headforms Representing Japanese Facial Features Using an Elastic Material for Adequate Respirator Fit Testing.

Introduction: Respirator fit is significantly impacted by facial features, which can differ greatly due to the diversity of race and ethnicity. In our previous study, we reported on a “Specified PCA panel for Japanese” that better represented the Japanese facial features, along with five corresponding digital headforms. Objective: This report describes the construction of digital headforms into “soft headforms” with softness and elasticity parameters similar to a human face, and evaluates their respirator fit. Methods: Using a skin softness and elasticity meter, the skin deformation curves at 10 facial points on each subject were measured to obtain softness and elasticity parameters. Subsequently, based on the information obtained from the subject test, five soft headforms were developed using an elastic material. Finally, the fit factors of the soft headforms for the six respirator models were compared with those of hard headforms (plastic) with identical shapes. Results: In the subject test, the softness parameter values varied across various points, including the cheek and chin, whereas the elasticity parameter values were almost constant, regardless of the points. The softness and elasticity parameters of the five soft headforms were also measured, and confirmed that both parameters were close to the target value ranges based on the subject test. For the fit factor evaluation, while the fit factors of all respirator models on hard headforms were below 100, soft headforms could achieve 100 or more, depending on the combination of headform type and respirator model. Conclusion: The soft headforms showed higher fit factors, confirming the efficacy of elastic material for respirator fit. However, further research is required to assess the effect of headform type and respirator model on fit factors by comparing subject groups in the corresponding facial category in the Specified PCA panel for Japanese.