Dr Dorit Aviv of the University of Pennsylvania and Dr Jovan Pantelic of KU Leuven tell HEQ about optimising space design to incorporate UVC disinfection technology.
In a March 2021 study titled ‘Spatial analysis of the impact of UVGI technology in occupied rooms using ray‐tracing simulation’, published in Indoor Air, the International Journal of Indoor Environment and Health, a group of researchers assessed and analysed the optimum design-based solutions for implementing ultraviolet germicidal irradiation technology (UVGI) in indoor spaces.
The team comprised University of Pennsylvania Stuart Weitzman School of Design Assistant Professor of Architecture and Thermal Architecture Lab Director Dr Dorit Aviv; Dr Jovan Pantelic, Associate Professor at Katholieke Universiteit Leuven; and Miaomiao Hou, a visiting scholar at the University of Pennsylvania and first author on the study. Drs Aviv and Pantelic tell HEQ about the findings and implications of their research.
What are the main benefits of ultraviolet-C (UVC) radiation as a tool for indoor space disinfection?
UVC in the spectrum from 200nm to 280nm is the most potent part of ultraviolet germicidal irradiation (UVGI) for microorganism disinfection. When infectious microorganisms receive sufficient doses of radiation, they become inactivated and do not pose threat to human health anymore.
The upper room UVGI which we discuss in our paper addresses virus release within the room where the infected person is. This represents one of the most effective engineering strategies for prevention of airborne mode of infection transmission. Upper room UVGI protective effectiveness is equivalent to delivering up to 20 air exchange rates of clean air to the indoor space. This is very challenging to achieve with any other engineering control measure.
What are the key factors that need to be taken into account when installing UVC disinfection technology in clinical settings?
Frist et al have written guidelines for upper room UVGI installation that should be followed (see reference here and here).
In clinical settings such as patient rooms, where patients stay in the same location for a very long period of time, it is especially important to confirm that they are not placed at risk of overexposure from the UVGI device because of radiation leakage from the upper zone, since the risk of overexposure is dependent on both the irradiation rate and the duration of exposure. The area around the patient bed should be clear of dangerous levels of UVC radiation leakage.
Another consideration in a clinical setting is that the upper ‘kill’ zone of the room must have a high enough level of irradiation to deactivate high concentrations of microorganisms, because those are the settings in which sick patients are spreading the virus.
Are there ways in which existing indoor spaces could be adapted to optimise the efficacy of UVC disinfection technologies, while maintaining safety for users?
Our study shows that one of the key factors to maintain safety for people in occupied spaces where UVGI devices are installed is the properties of materials in the room. The UVC range has different reflectance properties than visible light; and so the reflectance of the walls, ceiling, and any other large surfaces in the upper zone, must be kept to a minimum in order to avoid leakage of UVC radiation into the occupied zone.
To optimise the efficacy of the germicidal irradiation, the location and height of the device are very important. In an existing room, it is important to consider the airflow pattern in conjunction with the location of the UVGI devices to ensure a sufficient dose of irradiation to the polluted air. Additionally, it is important to consider the layout of the room furniture to identify where people stay for long periods of time and prevent UVC leakage creating hotspots in those locations.
In the course of your research, did you observe any significant limitations or challenges associated with UVC disinfection?
There are known challenges with upper room UVGI. One is the additional space requirement: floor to ceiling height has to be large enough to incorporate a kill zone where microorganisms receive UVC radiation. The second limitation is that the UVC tends to degrade materials where it is installed, usually in grade A office buildings. The last significant limitation is that leakage of UVC radiation into the occupied zone must be controlled, in order to avoid damage to human skin and eyes.
The simulation process that we developed aids in finding a design with an optimal set of these parameters, so that the system becomes as effective and compact as possible.
What are some other potential applications for UVC disinfection?
Upper room UVGI has been applied in hospitals and clinics. Infection isolation rooms are one of the types of space where this technology can be applied very successfully to prevent known infectious cases from spreading infectious aerosols; another important application is in waiting rooms within hospitals and clinics.
The challenge is how to design this technology effectively so it can have wider applications that might include densely occupied public spaces, like indoor train stations or metro stations. The challenge is to have an effective kill zone while controlling UVGI leakage in order to avoid overexposure for the people occupying these environments.
Dr Jovan Pantelic
Associate Professor
Katholieke Universiteit Leuven, Belgium
Department of Biosystems
Dr Dorit Aviv
Assistant Professor of Architecture, University of Pennsylvania Weitzman School of Design
Director, Thermal Architecture Lab
https://thermal-architecture.org/
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