Investigations and Improvement of Aerosol Distribution for Effective Protection of Healthcare Workers in Negative Pressure Airborne Infectious Isolation Room

Abstract

Thesis TitleInvestigations and Improvement of Aerosol Distribution for Effective Protection of Healthcare Workers in Negative Pressure Airborne Infectious Isolation RoomAuthorMiss Thanchanok KaeophetMajor ProgramChemical EngineeringAcademic year2023ABSTRACTThe negative pressure airborne infectious isolation room (AIIR) is the primary healthcare facility air contamination control systems used in the treatment of severe respiratory infectious patients. The present study aims to study the effect of configurations of the ventilation systems including size, position, number of air supply and exhaust panes, and ventilation conditions on air flow pattern, aerosol distribution and ventilation performance using computational fluid dynamics (CFD) simulation. Verification and validation of CFD simulations in a negative pressure AIIR was performed to determine accuracy. The agreement between simulation and experimental results were all acceptable. Therefore, CFD technique is possible to use to study and improve the air flow pattern, aerosol distribution and ventilation performance in a negative pressure AIIR. The field measurement by SARS-CoV-2 environmental surface test was also conducted and analyzed by RT-PCR method to ensure simulation results. The cycle threshold values from RT-PCR method showed inversely related to the simulated results of number of particles trapped on the surfaces including exhaust wall and patient�s beds. The present case was modified to be symmetrical supply and exhaust air with sizing ratio of Width (W): Height (H) = 1:1 (Improved case#1). The aerosol number concentration in healthcare workers (HCWs) working areas with a residence time higher than 300 s in the Improved case#1 reduced by ~96.7% from the present case. The exhaust size affected the air flow pattern and aerosol distribution. The velocity magnitude of exhaust air reduced when the opening areas of the exhaust were enlarged, causing an increase the aerosol accumulation. The average aerosol number concentration in the working areas of HCWs for the Improved case#2 (W: H =2:1) and Improved case#3 (W:H = 3:1) were 23.5% and 67.8% higher than for the Improved case#1 (W:H = 1:1). Also, an increase in the number of air exhausts led to large swirling air, resulting in more aerosols being trapped and suspended in the swirling air. Hence, this finding suggests that a symmetrical of supply air at the ceiling and exhaust air with a sizing ratio of W:H = 1:1 at the wall over the patient�s head is the suitable configuration of negative pressure AIIR to maximize the ventilation performance and minimize exposure risk to HCWs. The differential pressure value should be at least -5 Pa and the air supply rate should be 12 ACH, which was suggested for effective protection of HCWs in negative pressure AIIR.Keywords: Airborne transmission, CFD, Infectious respiratory diseases, Aerosol, AIIR

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