Minki Sung

Estimating the germicidal effect of upper-room UVGI system on exhaled air of patients based on ventilation efficiency

Abstract Upper room (UR)-ultraviolet germicidal (UVGI) systems, one of several disinfection applications of UV, target airborne infectious diseases in rooms of buildings such as healthcare facilities. Previous studies have introduced many experiments showing the germicidal effect of UR-UVGI systems. In this study, a novel numerical method of estimating the germicidal effect of UR-UVGI systems for air exhaled by ward patients was introduced. The method adopts and modifies the concept of ventilation efficiency because the germicidal effect depends upon how the air containing airborne infectious particles flows and stays within UV-radiated area. A case study based on a four-patient ward showed that UV doses were correlated with the age of the air exhaled by a source patient, as expected. Moreover, the UV doses were considerably affected by the position of the UR-UVGI system. Inactivation rates of the influenza virus estimated using the UV doses, were in the range of 48–74%, and those of Mycobacterium tuberculosis were 68–90% in the breathing area of a neighboring patient. The results indicate not directly the decreased concentration of airborne infectious particles, but the possibility of inactivation caused by the UR-UVGI system, which is useful for system optimization.

Disinfection performance of ultraviolet germicidal irradiation systems for the microbial contamination on an evaporative humidifier

Humidifiers have been used not only to maintain a comfortable indoor environment, but also to prevent respiratory diseases from worsening due to extremely low humidity. Some evaporative humidifiers (EH) that were considered to be energy efficient have been reported to have problems with microbial contamination. In this study, the microbial contaminations of an EH were verified, and both the germicidal effects and limitations of in-duct ultraviolet germicidal irradiation(ID-UVGI) systems against the contaminations were investigated. A numbers of bacteria and fungi were isolated from the surfaces and drain water of the EH, and airborne microbes that were likely dispersed from the contaminated EH were also detected. Based on the results of monitoring microbes for approximately six months for an ID-UVGI operation, it was found that microbial contamination was reduced but that microbes could still consistently be isolated from the surfaces and drain water. This was likely due to internal contamination of the EH in locations beyond the reach of the ultraviolet C-band (UVC) irradiation. Methods to overcome the limitations of this ID-UVGI system for EH disinfection are thus required.

Development of a Fungal Biosensor for Field Verifying the Surface Disinfection of Ultraviolet Germicidal Irradiation Systems for Air Handling Units

This study developed a fungal biosensor to verify the germicidal effect of ultraviolet germicidal irradiation (UVGI) systems in the field from a biosensor originally developed to assess indoor climate. A UVC ray was irradiated on the fungal spores of the biosensors at various doses, and the differences in hyphal length after subsequent incubation were observed to verify the susceptibility of the fungal biosensor to C-band ultraviolet (UVC). The results showed reasonable correlations between UVC dosage and hyphal length. These fungal biosensors were thereafter attached to the coil and the drain pan of an air handling unit with a UVGI system installed and exposed to UVC for 1 h to test the effectiveness of the biosensors on the UVGI systems in the field. The hyphal lengths observed after incubation corresponded with UVC doses of 468–1620 J·m−2 at each sampling point as shown in the previous susceptibility experiments. The extended experiments to confirm the susceptibility of the fungal spores showed that the spores were more sensitive to UVC ray than those of the fungal biosensor and had similar susceptibility to the same UVC doses even at different UVC intensities.