For the bacterial reduction experiments, one of the authors irradiated the inner surface of his hands five times with and without gloves. In each case, both hands or gloves (models “nitrile white” from VWR (Radnor, PA, USA)) were first rubbed over the face and upper body to ensure a high concentration of microorganisms even on the sterile gloves. Subsequently, both hands were rubbed together to achieve an even distribution of microorganisms on both hands and gloves.
A filtered 222 nm far-UVC krypton-chloride excimer lamp from Ushio (Tokyo, Japan) was used as the radiation source. First, the distance from the lamp to the plane, where the irradiance was 1 mW/cm2, was determined with a photometer type X1-UV-3727 of Gigahertz-Optik (Tuerkenfeld, Germany). Then one contaminated hand was irradiated for 23 s to reach the dose of 23 mJ/cm2 (without gloves) and 100 s to reach the dose of 100 mJ/cm2 (with gloves). A maximum of one skin irradiation was performed per day to stay within the allowed limits in the EU. Three fingers of each of the irradiated and non-irradiated hands/gloves were pressed onto caso contact agar plates from VWR. The agar plates were then incubated for approximately 24 h at 37 °C. Afterwards, colonies were counted, and the ratio of colony numbers was determined.
For comparison, a similar disinfection study with contaminated gloves and fingers was performed with the commercial liquid alcohol-based hand disinfectant Sterilium of Bode Chemie (Hamburg, Germany). The application of the disinfectant was performed for 30 s according to WHO instructions [22 ], and with a following 2 min drying and waiting period before sampling.
In addition, the far-UVC transmission properties of some standard gloves were determined. First, pieces were first cut out of three different gloves. Among these glove models were the white nitrile gloves from VWR mentioned above, and also the “nitrile blue” models from Semperit (Vienna, Austria) and “latex white” from Braun (Schwalbach, Germany). Subsequently, the Gigahertz photometer was positioned in close proximity to the far-UVC lamp, and the irradiance on the detector was determined with and without a glove layer.
A filtered 222 nm far-UVC krypton-chloride excimer lamp from Ushio (Tokyo, Japan) was used as the radiation source. First, the distance from the lamp to the plane, where the irradiance was 1 mW/cm2, was determined with a photometer type X1-UV-3727 of Gigahertz-Optik (Tuerkenfeld, Germany). Then one contaminated hand was irradiated for 23 s to reach the dose of 23 mJ/cm2 (without gloves) and 100 s to reach the dose of 100 mJ/cm2 (with gloves). A maximum of one skin irradiation was performed per day to stay within the allowed limits in the EU. Three fingers of each of the irradiated and non-irradiated hands/gloves were pressed onto caso contact agar plates from VWR. The agar plates were then incubated for approximately 24 h at 37 °C. Afterwards, colonies were counted, and the ratio of colony numbers was determined.
For comparison, a similar disinfection study with contaminated gloves and fingers was performed with the commercial liquid alcohol-based hand disinfectant Sterilium of Bode Chemie (Hamburg, Germany). The application of the disinfectant was performed for 30 s according to WHO instructions [22 ], and with a following 2 min drying and waiting period before sampling.
In addition, the far-UVC transmission properties of some standard gloves were determined. First, pieces were first cut out of three different gloves. Among these glove models were the white nitrile gloves from VWR mentioned above, and also the “nitrile blue” models from Semperit (Vienna, Austria) and “latex white” from Braun (Schwalbach, Germany). Subsequently, the Gigahertz photometer was positioned in close proximity to the far-UVC lamp, and the irradiance on the detector was determined with and without a glove layer.
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