Investigations on the surface disinfection efficacy of far-UVC 222 nm germicidal irradiance device in a controlled environment and field test

The Covid 19 pandemic has significantly affected the health, economy, and social impact of humanity. The continuous mutations of the virus variants have accelerated the demand for scientific research on disinfection techniques for a safer indoor environment. Among all the available surface disinfection techniques, ultraviolet germicidal irradiance at 254 nm wavelength has been proven for its disinfection efficacy; however, its usage is limited to unoccupied conditions due to the risk of ultraviolet exposure. This study investigated the efficacy of far-UVC-222 nm experimentally in both controlled environment and field setting. Staphylococcus epidermidis and Mycobacterium smegmatis were employed for surface disinfection in both the laboratory and a meeting room. Total plate count was used to determine the disinfection efficacy by a 20 W unfiltered far-UVC lamp. At 1.1 µW/cm² far-UVC irradiation, a 1-log₁₀ reduction of Staphylococcus epidermidis and Mycobacterium smegmatis contamination on tabletop can be achieved by 31.3 min and 101.8 min of far-UVC irradiation, respectively. Other pathogens of interest such as Staphylococcus aureus, Mycobacterium tuberculosis, Legionella pneumophila, SARS-CoV-2, and the Measles virus were also referred and compared in this study. This study carefully examined how far-UVC irradiation performs effectively for surface disinfection in a real meeting room setting. The results offer useful recommendations for alternatives to upper-room ultraviolet germicidal irradiance for continuous disinfection within the ultraviolet threshold limit value, with the goal of preventing the spread of any diseases in the future.