This study proposes a design method for half-face masks shape and sizing using an existing 3-D head database, aiming at air-tightness of faceseal and minimization of dead-space volume. The design procedure consists of two phases: extraction of 3-D faceseal contour and construction of mask body. In the extraction phase, the samples were divided into sizes L and S based on face-length (nasion-to-menton). Then mask boundary contour was determined from the middle sample. This boundary contour was projected onto every sample to extract 3-D faceseal contours and they were superimposed. The lateral side dispersion is a measure of air-leakage. Since the dispersion were greater than the design allowance of material elasticity and flesh deformation limit, sizing were further divided into “LS (shallow)”, “LD (deep)”, and “SS” and “SD”. Within each size group, the sample with the deepest faceseal was selected as the final representative 3-D faceseal contour.
The 3-D face surface (of the final representative sample) encircled by the faceseal was used to construct the mask body. The central longitudinal ridge-rib of the mask was constructed from the mid-sagital line. It was elevated above 10 mm at mid-nasion, 20 mm at nasal-tip and 10 mm at menton levels. Next, a series of horizontal contours were drawn crossing these reference points and were further interpolated to form a 3-D surface of the mask. The space bounded between the mask body and the face surface is the dead-space volume. The dead volume each for SS, SD, LS, and LD size was 168.3 cm3, 176.8 cm3, 174.2 cm3, and 185.1 cm3 respectively, which is smaller than most existing masks (with a mean of 224.3 and S.D of 28.5)