RACA Journal August 2020 | Page 13

International News indoor bacterial communities and create communities that are more similar to outdoor-associated bacteria than air delivered through a centralised HVAC system. In some buildings, this can be accomplished through distributed HVAC units, such as packaged terminal air-conditioners (PTAC) frequently found in hotels, motels, senior housing facilities, condominium units and apartments or through perimeter passive ventilation strategies such as perimeter dampered vents. However, for most buildings, the easiest way to deliver outside air directly across the building envelope is to open a window. Window ventilation not only bypasses ductwork but increases outside air fraction and likely increases total air change rate as well. Administrators and building operators should discuss a plan for increasing perimeter, and specifically window, ventilation when outdoor temperatures are adequate for this practice without substantial comfort or energy implications. Light is another mitigation strategy for controlling the viability of some infectious agents indoors. Daylight, a ubiquitous and defining element in architecture, has been shown in microcosm studies to shape indoor bacterial communities in household dust to be less human associated than in dark spaces. Moreover, daylight in these microcosm spaces reduced the viability of bacteria compared to dark controls. Further research is needed to understand the impact of natural light on SARS-CoV-2 indoors; however, daylight exists as a free, widely available resource to building occupants. Some electric lighting is already implemented as engineering controls for disinfection indoors. Ultraviolet light in the region of shorter wavelengths (254nm UV-C) is particularly germicidal and fixtures tuned to this part of the light spectrum are effectively employed in clinical settings to inactivate infectious aerosols. However, ultraviolet germicidal irradiation (UVGI) has potential safety concerns if the high-energy light exposure occurs to room occupants. For this reason, UVGI is safely installed in mechanical ventilation paths or in upper-room applications to indirectly treat air through convective air movement. More recently, far-UVC light in the 207-222nm range has been demonstrated to effectively inactivate airborne aerosolized viruses. While preliminary findings from in vivo rodent models and in vitro 3D human skin models appear favourable to not cause damage to human skin and eyes, further research must be conducted to verify the margin of safety before implementation. If implemented safely, UVC light offers a range of potential disinfectant strategies for buildings. Administrators and building operators should encourage blinds and shades to be opened when they are not needed to actively manage glare, privacy or other occupant comfort factors to admit abundant daylight and sunlight. Implementing targeted UVGI treatment may be prudent in spaces where individuals that tested positive for COVID-19 All photos by IMD were known occupants, but routine treatment may have unintended consequences and should be implemented with appropriate precaution. Spatial configuration of buildings can encourage or discourage social interactions. In recent years, Western society has valued design that emphasizes visual transparency and a feeling of “spaciousness” indoors, whether at home through the use of open plan concepts or at workplaces that harness open office concepts with spatial layouts that intentionally direct occupants to nodes of “chance encounters,” thought to enhance collaboration and innovation among employees. While these spatial configurations are culturally important, they may inadvertently enhance or reduce opportunities for transmission of viruses through human interaction. For example, large, densely populated open office spaces may increase connectivity while private offices may decrease connectivity. Space syntax analysis demonstrates a relationship between spatial disposition and degrees of connectivity and has been shown to correlate with the abundance and diversity of microbes within a given space. Understanding these spatial concepts could be part of the decision-making process of whether to implement socialdistancing measures, to what extent to limit occupant density, and for how long to implement the measures. Increasing evidence indicates that humidity can play a role in the survival of membranebound viruses. www.hvacronline.co.za RACA Journal I August 2020 11