The Myth of Air Purifier in Mitigating the Transmission Risk of SARS-CoV-2 Virus

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly infectious disease that emerged in December of 2019, threatening human health and leading to global public health crises. Airborne transmission via droplets and aerosol has been recently recognized as one of the infection modes for the SARS-CoV-2 virus. Hospitals have deployed/incorporated indoor air purifiers with the hope to minimize the transmission risk of SARS-CoV-2 virus. Nevertheless, the effectiveness of the indoor air purifier in reducing the transmission risk remained unknown. This study uses computational fluid dynamics to model the dispersion of the aerosol particles exhaled from the patient under the influence of an air conditioner, exhaust fans and air purifier. The numerical model showed that airflow from the diffusers, exhaust fans and placement of the air purifier significantly influenced the dispersion pattern of the aerosol particles in the common ward. Multiple air purifiers placed at 1 meter above the floor and next to a patient can increase the total efficiency from 37.14 to 59.91% for weak exhalation and from 36.44% to 48.81% for medium exhalation. No aerosol particles flew out from the door for weak and medium exhalation when multiple air purifiers were deployed in the common ward. Location and matching the clean air delivery rate with the size of the room are the important factors that affect the performance of the air purifier.

An overview of SARS-CoV-2 transmission and engineering strategies to mitigate risk

“…The effects of different ventilation conditions, as studied through CFD modelling, can help prevent the transmission of SARS-CoV-2. For instance, in a hospital setting, the turbulence caused by the air conditioning system can promote the dispersion of the virus in the room, thereby increasing the risk of transmission [ [26] , [27] , [28] , [29] , [30] , [31] , [32] ]. Li et al used CFD simulation and tracer gas measurements of ventilation to confirm the airborne transmission of SARS-CoV-2 during the first outbreak in a restaurant in Guangzhou, China [ 26 ].…”

“…Therefore, an aerosol arrestor is proposed to mitigate the transmission risk in isolation wards. Saw et al also investigated the effectiveness of indoor air purifiers (APUs) in mitigating the transmission of the SARS-CoV-2 virus in hospital common wards [ 29 ]. It was found that placing multiple APUs near the source at an elevated level increased the overall effectiveness of the APUs.…”

“… (Saw et al, 2021) [ 28 ] To investigate the SARS-CoV-2 transmission through aerosol using CFD CFD simulation Indoor simulation Temperature, ventilation rate, particle mass flow rate, mesh size 70nm–10 μm N/A 5 days, 48 hours interval Southeast Asia (Malaysia) Dispersion of SARS-CoV-2 virus–laden aerosol throughout the room is affected by strong exhalation and airflow. (Saw et al, 2022) [ 29 ] Effectiveness of the indoor air purifier in controlling SARS-CoV-2 virus transmission RT-qPCR Indoor measurement, simulation Temperature, ventilation rate, particle mass flow rate, mesh size 70nm–10 μm Less than 40 (air sample) 10 days, 48 hours interval Southeast Asia (Malaysia) Single air purifier only has a minimum impact in reducing particle dispersion (Ren et al, 2021) [ 31 ] The effects of different ventilation on a prefabricated COVID-19 inpatient ward snappyHexMesh and blockMesh grid measurement Indoor, simulation Wind speed, turbulence, kinetic energy 3 μm, 6 μm, 12 μm, 20 μm, 45 μm and 175 μm N/A N/A Asia (China) The ‘U’ type inlet and outlet ventilation have the highest removal efficiency for small particles (<20 μm), whereas the ventilation outlet near the pollutant source has the highest removal rate of big particles (>45 μm) (Prajapati et al, 2022) [ 32 ] Simulation of Covid-19 transmission in an ICU room ANSYS Fluent CFD software Indoor, simulation Temperature, wind speed, transition ration N/A N/A N/A Asia (India) The contaminated droplets travelled along a specific streamline along with airflow, hence posing an infection risk to the ICU workers. ...…”

Removal of indoor aerosol particles generated in a medically relevant space using a portable airborne particle filtration device

“…[26][27][28][29] It is important to note that the effectiveness of an air purifying system for a given application will depend on its location and properties. 30 PF devices designed for point-source decontamination have recently been used to reduce airborne concentrations of volatile organic compounds (VOCs) emitted from electrosurgical plume 31 and bone cement fumes. 32 Despite heightened awareness and the promise of PF devices to improve safety in nosocomial settings, their use in reducing bioaerosols in ORs has received little attention.…”