# A Method for Generation of a Sizing System and Representative Models for a Facial Mask Design
## 2 Development of a Sizing System of a Pilot Oxygen Mask for KAF Pilots
### Existing Sizing System of MBU-20/P Pilot Oxygen Mask  
The existing sizing system for the MBU-20/P was not applicable to KAF pilots due to the differences between KAF pilots and USAF personnel in the key facial dimensions, SSL and LW. The average SSL of KAF pilots (97.1 \(\pm\) 5.2 mm) was 6.5 mm longer than that of USAF personnel (90.6 \(\pm\) 7.0 mm) measured by [PERSON], [PERSON], [PERSON] and [PERSON] [10]. The average LW of KAF pilots (49.1 \(\pm\) 3.8 mm) was 6.5 mm narrower than that of USAF personnel (51.6 \(\pm\) 3.3 mm). The accommodation percentage of the existing sizing system for KAF pilots was 73%. The scatter plot of KAF pilots' faces in the existing MBU-20/P's sizing system showed a highly unbalanced distribution in the existing sizing categories (Extra Small Narrow: 0%, Small Narrow: 3%, Medium Narrow: 61%, Medium Wide: 5% and Large Wide: 4%) (Figure 2).  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Face Dimensions**} & \multirow{2}{*}{**\(n\)**} & \multirow{2}{*}{**Mean**} & \multirow{2}{*}{**SD**} & \multirow{2}{*}{**Min**} & \multirow{2}{*}{**Max**} & \multicolumn{4}{c}{**Percentile**} \\ \cline{5-10}  & & & & & & & **1 st** & **5 th** & **95 th** & **99 th** \\ \hline
1 & face length & 336 & 123.4 & 6.1 & 106.7 & 140.4 & 108.0 & 113.1 & 133.2 & 136.6 \\
2 & lower face length & 336 & 69.1 & 4.5 & 57.5 & 83.6 & 58.6 & 61.8 & 76.3 & 79.4 \\
3 & sellion-to-supramentale length & 336 & 97.1 & 5.2 & 80.7 & 114.1 & 85.3 & 88.3 & 104.7 & 109.4 \\
4 & supramentale-to-menton length & 336 & 26.4 & 3.0 & 18.6 & 36.2 & 19.7 & 21.4 & 31.0 & 34.6 \\
5 & rhinion-to-menton length & 336 & 109.1 & 5.5 & 93.2 & 124.3 & 95.8 & 99.8 & 117.7 & 120.8 \\
6 & rhinion-to-promentale length & 336 & 95.8 & 5.6 & 78.2 & 108.9 & 83.7 & 86.7 & 104.9 & 108.1 \\
7 & promentale-to-menton length & 336 & 13.3 & 2.5 & 4.9 & 20.6 & 7.9 & 9.5 & 17.6 & 19.1 \\
8 & nose length & 336 & 54.3 & 3.4 & 43.2 & 62.2 & 46.6 & 48.6 & 60.3 & 61.9 \\
9 & nose protrusion & 336 & 18.4 & 1.9 & 12.9 & 23.9 & 14.2 & 15.3 & 21.6 & 23.0 \\
10 & face width & 336 & 154.8 & 6.4 & 132.4 & 171.5 & 138.6 & 144.0 & 164.2 & 168.2 \\
11 & chin width & 336 & 130.3 & 8.6 & 105.4 & 156.7 & 112.5 & 116.5 & 144.6 & 150.8 \\
12 & nasal root breadth & 336 & 20.0 & 2.8 & 12.3 & 27.7 & 14.0 & 15.2 & 24.6 & 26.8 \\
13 & maximum nasal bridge breadth & 336 & 30.5 & 2.8 & 22.3 & 37.7 & 24.2 & 25.6 & 35.3 & 36.7 \\
14 & nose width & 336 & 37.6 & 2.7 & 30.3 & 45.8 & 31.8 & 33.4 & 42.4 & 43.8 \\
15 & lip width & 336 & 49.1 & 3.8 & 38.5 & 58.2 & 40.7 & 42.6 & 55.5 & 57.4 \\
16 & bitragion-menton arc & 336 & 313.7 & 16.2 & 269.0 & 361.1 & 273.5 & 284.1 & 339.1 & 347.3 \\
17 & bitragion-subnasale arc & 336 & 283.0 & 12.9 & 234.9 & 319.6 & 252.1 & 263.1 & 304.5 & 312.1 \\
18 & bizygomatic-menton arc & 336 & 304.8 & 14.5 & 261.3 & 339.6 & 267.0 & 277.8 & 327.6 & 336.2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Descriptive statistics of face dimensions derived by [PERSON] et al. [5] (unit: mm).  
Figure 2: Scatter plot of Republic of Korea Air Force (KAF) pilots in the existing MBU-20/P’s sizing system (acommodation percentage = 73%; dots: 336 KAF pilots).