Using Portable Air Purifiers to Reduce Airborne Transmission of Infectious Respiratory Viruses – a Computational Fluid Dynamics Study
Aerosols and droplets generated from expiratory events play a critical role in the transmission of infectious respiratory viruses. Fine aerosols play a crucial role in airborne transmission of respiratory diseases including COVID- 19. Out-patient hospital activity moved to virtual clinics during the pandemic, making effective communication difficult and leading to increased isolation and staff dissatisfaction. Mitigations for aerosol-borne disease spread are needed to make healthcare spaces safer for doctors and patients to safely meet face to face again.
We used computational flow dynamic (CFD) modelling to investigate the efficiency of portable air purifiers containing HEPA filters as a retrofit mitigation strategy to reduce airborne aerosols in hospital consulting rooms. We modelled a single doctor patient interaction in a room with a chilled beam air conditioning system at 3 air changes per hour, 220C and 50% humidity. We generated a detailed computational mesh including 800,000 elements. We performed 3D transient simulations, with steps of 0.01 s, for 180 s. Both continuous phase (air flow) and discrete phase (aerosols) were taken into account. The discrete phase of aerosols was tracked in a Lagrangian manner, with representative populations of around 200,000 particles being tracked.
Aerosol particle number plateaued around 180 seconds. Clearance efficiency ranged from 25% to 62% depending on where the inlet/suction of the air purifier unit was placed. The best location for a single HEPA filter was on the desk between doctor and patient but highest efficiency was achieved using two devices, one on the desk and a second to the side of the room at the height where aerosols were generated.
This work provides practical guidance on a mitigation that can be rapidly implemented in an expedient, cost-effective manner, and may lead to more science informed strategies to mitigate airborne transmission of respiratory infections in hospitals.