# A Method for Generation of a Sizing System and Representative Models for a Facial Mask Design
## 4 Discussion  
The present study proposed a sizing system and RFMs of oxygen masks for KAF pilots with practical considerations including ease-of-use, ease-of-management, economic efficiency, accommodation ratio and representativeness. First, the initial sizing system consisting six categories formed by a combination of small, medium, and large sizes in SSL and narrow and wide sizes in LW. The size interval of 10 mm for SSL and LW and corresponding sizing cutoff criteria of 80, 90, 100, and 110 mm for SSL, and 40, 50, and 60 mm for LW in the initial sizing system were determined for ease-of-use of the sizing system. Second, based on stakeholders' considerations of economic efficiency (e.g., manu  
Figure 5: Representative face models for the proposed pilot oxygen mask sizing system of KAF pilots. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Face Dimension**} & \multicolumn{4}{c}{**Facial Measurements of the RFM Per Sizing Category**} \\ \cline{3-6}  & & **Small** & **Medium** & **Medium** & **Large** \\  & & **Narrow (11)** & **Narrow (307)** & **Wide (189)** & **Wide (139)** \\ \hline
1 & face length & 116.5 & 121.7 & 124.8 & 127.4 \\
2 & lower face length & 66.1 & 69.3 & 70.1 & 72.7 \\
3 & sellion-to-supramentale length * & 88.1 & 94.4 & 96.5 & 102.6 \\
4 & supramentale-to-mention length & 28.4 & 27.3 & 28.3 & 24.8 \\
5 & rhinion-to-mention length & 102.9 & 107.4 & 113.3 & 111.9 \\
6 & rhinion-to-promentale length & 85.7 & 95.0 & 99.4 & 98.0 \\
7 & promentale-to-mention length & 17.2 & 12.4 & 13.9 & 13.9 \\
8 & nose length & 50.4 & 52.4 & 54.7 & 54.7 \\
9 & nose protrusion & 17.2 & 17.0 & 17.6 & 18.7 \\
10 & face width & 144.8 & 150.5 & 157.6 & 156.1 \\
11 & chin width & 118.4 & 127.1 & 135.6 & 129.9 \\
12 & nasal root breadth & 19.1 & 18.6 & 20.5 & 21.3 \\
13 & maximum nasal bridge breadth & 26.4 & 34.4 & 32.8 & 30.3 \\
14 & nose width & 33.6 & 38.9 & 37.4 & 35.7 \\
15 & lip width * & 46.9 & 44.6 & 54.5 & 50.5 \\
16 & bitragion-menton arc & 293.4 & 305.7 & 323.3 & 320.6 \\
17 & bitragion-subnasale arc & 266.7 & 278.1 & 292.9 & 292.9 \\
18 & bizygomatic-menton arc & 285.2 & 296.6 & 306.5 & 314.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Selected representative face models (RFMs) of KAF pilots and their facial sizes (key dimensions of the sizing system are in bold; pilot identification numbers are indicated in parentheses; unit: mm). facturing and logistics costs) and equipment management (e.g., same sizing categories of the existing MBU-20/P), the number of sizing categories of the initially generated sizing system was reduced to four. Third, to increase the accommodation percentage with the reduced number of sizing categories, the sizing criteria for Small Narrow and Large Wide sizing categories were adjusted. The accommodation percentage of the adjusted sizing system (90%) showed 17% higher than that of the existing sizing system (73%) for KAF pilots. Lastly, the RFMs were found by considering the representativeness analysis methods (WSED and NED) proposed in this study. The proposed sizing system does not include the Extra Small Narrow size, because the anthropometric characteristics of female pilots who may include small faces in KAF had been considered. The Extra Small Narrow size of the existing MBU-20/P was created after the four sizing categories were defined to consider female pilots having smaller faces. In this study, the Extra Small Narrow was not necessary as a separated sizing category as the proportion (17%) of female KAF pilots was fully considered in the proposed sizing system. A usability evaluation conducted by [PERSON] et al. [27] on the new oxygen mask designs for KAF pilots designed based on the proposed sizing system [26] showed that the KAF female pilots were sufficiently accommodated by the Small Narrow size. The proposed RFM selection method considers multiple anthropometric dimensions rather than using only two key dimensions to increase the RFMs' representativeness.