Airflow and Particle Transport in Hospital Environments

QC 20251006

Abstract

In hospitals, it is essential to control the pathogen transmission for health aspects in addition to ensuring occupant comfort. High occupant density and frequent movement of staff and visitors accelerate pathogen spread, making hospitals at risk of airborne transmission. From the perspective of engineering controls, ventilation remains one of the most efficient and reliable strategies for mitigating airborne transmission. The key challenge, therefore, is not whether to ventilate, but how to design systems appropriately, operate them correctly, and ensure sufficient adaptability to varying indoorconditions in hospitals.This thesis examines two representative scenarios. The first scenario is surgical site infection in operating rooms, where maintaining an ultraclean environment is essential to prevent wound contamination. The second is respiratory infection in patient rooms, driven by human respiratory activities; here, the goal is early mitigation of exhaled particles to prevent onward spread.Computational fluid dynamics is employed to assess system performance across operating conditions. A literature review first characterizes emission sources in each scenario, with particular attention to particle size distributions. These characteristics inform the modeling strategy, either Lagrangian discrete-particle tracking or an Eulerian passive-scalar formulation. To preserve realism, the operating-room simulations replicate the actual room configuration, while the patient-room simulations implement the realistic human respiration model. Quantitative metrics are used to compare designs and sensitivities and to reveal how system behavior changes under different settings.For the hybrid operating room, the results demonstrate that the current Temperature-controlled Airflow installation establishes two distinct ventilation zones: a central zone with strong contaminant transport capacity and a peripheral zone where the short distance to the exhausts enables effective contaminant removal. In patient rooms, the work captured the full evolution of cough-generated air–particle mixtures, from an initial stage where particle motion is dominated by size, through an intermediate period of dispersion shaped by the thermal plume, and to a final stage of background ventilation removal. The intermediate period, typically between 5 and 23 s after a cough, was revealed as a critical window for local exhaust intervention. Simulations of different configurations showed that a ceiling-mounted system leveraging the body’s thermal plume offers a robust and effective solution. Furthermore, the analyses highlight the role of background ventilation in determining the optimal placement and performance of such ceiling-mounted systems, offering practical guidance for their application in patient care environments.Based on the analysis, this thesis advances the understanding of ventilationdriven contaminant transport in hospitals and establishes ventilation as a dynamic tool for infection control rather than a fixed design parameter. It emphasizes resilience and adaptability as key to creating safer healthcare environments.

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