2.2.3. UV Irradiation
UV rays were radiated from 16.5 cm away from the tray using a UV sterilizer (KRS-A1, KARIS, Gyeonggi-do, Korea). The wavelength of 253.7 nm UV ray was irradiated through the inner area of the sterilizer in 42 cm × 32 cm × 32 cm. The power consumption of UV light bulb was 10 W and the irradiation was conducted for 1 h for inner side and another 1 h for outer side of respirators.