Development and evaluation of “Safe, Affordable, Friendly, and Effective” UVC sterilizer for reusing N95 medical masks

Prasita Jakthreemongkol; Peerapong Pornwongthong; Phakkhaphum Lethaisong; Pollawat Jamparuang; Suparuj Lueangarun; Premjit Juntongjin

Authors

Prasita Jakthreemongkol Division of Dermatology, Chulabhorn International College of Medicine, Thammasat University, Pathum Thani 12120, Thailand
Peerapong Pornwongthong Scientific Instrument and High-Performance Computing Center, Faculty of Applied Science, King Mongkut’s University of Technology North, Bangkok 10800, Thailand
Phakkhaphum Lethaisong Scientific Instrument and High-Performance Computing Center, Faculty of Applied Science, King Mongkut’s University of Technology North, Bangkok 10800, Thailand
Pollawat Jamparuang Radiometry Laboratory, Light and Color Group, Thermometry and Optical Metrology Department, National Institute of Metrology, Pathum Thani 12120, Thailand
Suparuj Lueangarun Division of Dermatology, Chulabhorn International College of Medicine, Thammasat University, Pathum Thani 12120, Thailand
Premjit Juntongjin Division of Dermatology, Chulabhorn International College of Medicine, Thammasat University, Pathum Thani 12120, Thailand

Keywords:

COVID-19, ; filtering facepiece respirators (FFRs), N95 medical masks, ultraviolet germicidal irradiation (UVGI), UVC germicidal cabinet, UVC sterilizer

Abstract

Shortage of NIOSH-approved N95 filtering facepiece respirators (FFRs) has made healthcare workers concerned during the COVID-19 pandemic. CDC has recommended ultraviolet germicidal irradiation (UVGI) for medical mask reuse. This study aims to develop UVC germicidal cabinet to sterilize N95 FFRs with four to five log reduction without losing protective properties. UVC germicidal cabinet is fitted with two low-pressure mercury discharge lamps (UVC T8,40W) at the top and bottom. Radiometric performance tests were conducted and exposure time for decontamination was calculated targeting 1 J×cm^-2 or 10000 J×m^-2. Four samples of 1870+N95 3M™ were selected to be tested after decontamination. The peak wavelength of UVC light source was 253.89 nm ± 0.60 nm with UVC irradiance value in the range from 6.56 W×m^-2 at P#9 to 17.9W×m^-2 at P#5. The result showed no ozone production from the lamp after one-hour monitoring with ≤1 percent instability after six minutes of lamp operation. The calculated time is 564.961 sec or 10 minutes according to maximum UVC irradiance at P#5 (17.9W×m^-2), resulting in UVC dose of 3463.21 J×m^-2at minimum UVC irradiance at P#9, which still exceeds D₉₀ values. No visible change and unfavorable odor were detected up to 12 cycles. The SEM showed no significant change up to 10 cycles, the distortion and fusion became obvious at cycle 15 and totally damaged at cycle 16, which correlated with the percentage filtration efficiency, which was lower than 95 percent, more specifically, 90.4070 percent at 16 cycle at the maximum point "P#5". This study demonstrated decontamination of N95 FFRs in dose 1 J×cm^-2 up to 10 cycles without losing properties and recommended placing masks at the center of UVC germicidal cabinet to gain targeted dose. Prospective studies with additional models of N95 FFRs are required and performing strength tests on respiratory coupons and straps is recommended.

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