3D Facial Shape and Respirator Fit in Emergency Service Workers

Background: Emergency Service Workers (ESWs) are the first point of contact during medical emergencies and are frequently exposed to hazardous environments where respirators are the primary protection against bioaerosols. Respirator fit is evaluated through quantitative fit tests, which measure particle counts inside and outside the respirator as the wearer performs standardized slow movements, unlike typical ESW activities.

Methods: To assess the relevance of standard fit tests, we conducted a simulated work fit test using common ESW tasks, including CPR, intubation, patient lifting, stretcher handling, and movement with weighted bags. Tests were performed with three respirator types: N95, half-face, and full-face. Facial anthropometry was assessed with a high-accuracy handheld 3D scanner, supplemented by physical measurements (e.g., head width, face length).

Preliminary Results: Data were collected from 206 Ontario ESWs (Aug 2022 – Dec 2024). Forty-two facial landmarks were placed on 3D meshes. Generalized Procrustes Analysis (GPA) aligned landmark sets to a reference, producing a mean Procrustes shape. Principal components were extracted from this shape, with PC1 analyzed against simulated and standard fit factors using ordinary least squares with three knots. PC1 was a significant predictor for simulated work fit factors (R² = 0.234, model likelihood test) but not for standard fit factors.

Conclusion: Preliminary findings suggest that facial shape, as captured by PCA of 3D scans, is significantly associated with simulated work fit tests but not standard fit tests. These results indicate that standard fit tests may not fully represent respirator performance during actual ESW tasks. Further analysis is ongoing to confirm these findings and explore implications for respirator design and testing protocols.