published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Interpersonal transport of expiratory droplets and droplet nuclei constitutes a prerequisite for the transmission of pathogens as well as the transmission of respiratory diseases. This study modeled the physical process of interpersonal transport of droplets and droplet nuclei in a ventilated room. The impacts of a number of parameters in three length scales and three corresponding physical processes were analyzed, including dispersion and evaporation of droplets/droplet nuclei at 1 to 100 μm, human exhalation flows and body plumes at 0.1 to 1 m, and the indoor environment at 1 to 10 m. The strong hygroscopicity of the solutes in the droplet is capable of keeping the droplet with an equilibrium size in humid air, larger than that of a dried particle. Mathematical models were developed to predict the droplet nucleus size in both dry air and humid air, by simplifying the composition of one expiratory droplet to NaCl solution and suspended spherical particles. For a droplet with an initial diameter of 100 μm, initial NaCl concentration of 0.9%, and initial solids ratio of 1.8%, the droplet nucleus size was estimated to be 42 μm in an ambient relative humidity of 90% (25°C), which is 30% larger than it was in a relative humidity of 30% (25°C). A numerical model was also developed to predict droplet evaporation and dispersion in a constant turbulent buoyant jet. Droplets with initial sizes larger than 80 μm were predicted to deposit on the floor at a distance of ~1.25 m (~1.7 m for 60 μm) away from the mouth, while droplets with initial sizes less than 40 μm travelled to the end of the jet. A series of experiments was conducted to assess the characteristics of human exhalation airflows and thermal plume, using a full-scale test room and a breathing thermal manikin. The impacts of the ventilation system were illustrated by comparing the velocity distribution of the exhalation airflows and airflows induced by thermal plume. Further experiments employing two breathing thermal manikins were carried out to evaluate the interpersonal transport of the expiratory contaminants that were simulated by tracer gas. When the two manikins with the same heights were standing face to face at a mutual distance of 0.8 m, the exhalation airflows from the mouth of the source manikin could directly travel into the breathing region of the susceptible manikin, resulting in a high exposure. The high exposure decreased sharply with an increase in the mutual distance from 0.5 m to 1.0 m. Between 1.0 m to 3.0 m, the exposure by the susceptible manikin remained at a low and constant level. Numerical simulations considering droplet evaporation and droplet nucleus sizes were carried out; and the impacts of the parameters of droplet initial size, humidity, vicinity, ventilation conditions and synchronization of exhalation were evaluated. Fine droplets and droplet nuclei were predicted to travel toward the upper part of the test room, whereas large droplets tend to be deposited on the floor. With a high relative humidity, 95%, most of the droplets were deposited on the floor within 16 seconds. Meanwhile, all of the droplets evaporated to droplet nuclei and remained suspended in the air when the relative humidity was 35%. Mixing ventilation that supplied fresh air with a ventilation rate of 5.6 h-1 resulted in drafts and strong turbulence, which made droplets and droplet nuclei dispersed in the room. The average vertical position was higher than that when the ventilation rate was 3.0 h-1. Displacement ventilation led to the vertical temperature stratification in the room. The vertical temperature gradient could neutralize the buoyancy force and weaken body plumes and the vertical dispersion of droplets and droplet nuclei. The inhalation of the droplets and droplet nuclei by the susceptible person and the deposition of the droplets and droplet nuclei on the body surface of the susceptible person were investigated at mutual distances of 0.5, 1.0, 1.5 and 3.0 m. For one breath from the source person, 1,600 droplets were released. Three and 9 droplet nuclei were inhaled by the susceptible person at a mutual distance of 0.5 and 1.0 m, respectively. No droplet nuclei were inhaled at 1.5 and 3.0 m. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

According to recommendations from the Facility Guidelines Institute (FGI) of the American Institute of Architects (AIA), World Health Organization (WHO) and Center for Disease Control and Prevention (CDC), a common engineering approach to isolation room design is to maintain the air ventilation rate at a minimum of 12 air changes per hour (ACH) for mixing and dilution, and a negative pressure in the room to direct airflow inwards, instead of leaking outwards. / In collaborations with physicians in the Respiratory Division and the Intensive Care Unit (ICU) at the Chinese University of Hong Kong (CUHK), a series of experiments were carried out to verify the ventilation performance of an All room at the Princess Margaret Hospital (PMH). Experiments investigated the effects of ACH, the control of airflow direction, the air tightness of the automatic swing door and the application of positive pressure ventilation procedures, such as high flow rate oxygen masks, jet nebulizers and NPPV. These were extensively tested in two different isolation rooms of the Prince of Wales Hospital (PWH) and PMH, under common clinical circumstances and environmental conditions. / Many patients with severe respiratory infection require supportive therapy for respiratory failure. Common interventions involve supplemental oxygen to improve tissue oxygenation. In the worst scenario, mechanical ventilation via non-invasive positive pressure ventilation (NPPV) may be required. Since a large amount of aerosols is generated during these interventions, there is a great risk of spreading infectious aerosols from the respiratory tract of the patient to the surrounding environment. / The aerodynamic data in this thesis infonns architects and engineers on how to improve the hospital ward ventilation design so as to avoid aerosol and ventilation leakage. Ultimately, it is hoped that this work may play a role in preventing devastating nosocomial outbreaks in the future. / The design of airborne infection isolation (AII) room has become one of the major research domains following the emergence of the global concern of acute respiratory diseases in this century. These include severe acute respiratory syndrome (SARS) in 2003, H5N1 avian influenza, and pandemic influenza H1N1 in 2009. All of which have claimed thousands of lives. Even with the current stringent design and practice guidelines, nosocomial infection of healthcare workers (HCWs) and inpatients continues to occur. This implies that there might be limitations in current isolation ward designs. / The experiments implemented a high-fidelity human patient simulator (HPS) which could be programmed with different lung breathing conditions and oxygen flow rate settings. The patient exhaled air dispersion distances and airflow patterns were captured in detail with a non-intrusive, laser light sheet, smoke particle scattering technique, designed for this thesis. Thin laser light sheets were generated by a high energy YAG laser with custom cylindrical optics. Smoke concentration in the patient exhaled air and leakage jets was estimated from the intensity of light scattered, which was then expressed as nonnalized particle concentration contours using computer programs developed for this study. / The study quantitatively revealed the distinctive patient exhaled airflow patterns and the extent of bioaerosol, generated directly from the patient source with the application of different oxygen delivery interventions for different patient lung conditions and oxygen flow rates. It was found that contamination was more critical during the administration of oxygen therapies, which is common in clinical circumstances. Source control is therefore the most efficient and effective approach to the reduction and even elimination of patient exhaled bioaerosol contaminants. Thus, when working in an isolation room environment, full preventive measure should be taken and it is essential to consider the location of mechanical vents and the patient exhaled airflow patterns. It has also been shown in experiment that applications of bacterial viral filter could be a solution to the problem. / Chow, Ka Ming. / Advisers: Puay Peng Ho; Jin Yeu Tsou. / Source: Dissertation Abstracts International, Volume: 73-09(E), Section: A. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 115-147). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Thesis (M. Tech. (Environmental health: Food safety )) - Central university of Technology, Free State, 2013 / Food processing plants and agricultural environments have a long-standing history of being known to provide a conducive environment for the prevalence and distribution of microorganisms which emanate as a consequence of activities undertaken in such premises. Microorganisms in the aforementioned environments may be found in the atmosphere (airborne), and/or on food contact surfaces. Airborne microorganisms from food handlers and in food products and raw materials (as part of bioaerosols) have in the past been implicated as having a potential to cause adverse health effects (especially in indoor environments) and therefore also to have economic implications. Recently their effect on food safety has received increased interest. The recent international interest in bioaerosols in the food industry has played a role in rapidly providing increased understanding of bioaerosols and their effects in different food processing environments. However, there is still a lack of research on the actual impact of bioaerosols over time in most of the food premises especially in Southern Africa and other developing countries. The overall purpose of this dissertation was to assess possible microbial contaminants and the role of selected environmental parameters on these microbes at a dairy farm plant in central South Africa. In relation to the purpose of the study, the objectives of this dissertation were to investigate and establish the food handler’s food safety knowledge, attitude, behaviour and practices. The sub-objective was to investigate the prevalence and distribution of microbial contaminants (both airborne and food contact surface populations), and concomitant environmental parameters. The microbe isolates from both investigations (i.e. air samples and food contact surfaces) were identified to strain level using matrix-assisted laser desorption ionization – time of flight mass spectrometry (MALDI-TOF MS). The findings of this study in relation to food handlers’ food safety knowledge, attitude, behaviour and practices indicated a dire need for training of employees as well as improved health and hygiene measures as emphasised by some of the identified strains. The environmental parameters (both indoor and outdoor) were similar, with no relationship established between airborne microbes’ prevalence and environmental parameters. The samples of the airborne microbial populations in both indoor and outdoor environments were similar. Airborne microbial counts at the dairy farm plant over the entire duration of the study ranged between 1.50 x 101cfu.m-3and 1.62 x 102cfu.m-3. Microbial counts on food contact surfaces ranged between 2.50 x 102 cfu.cm-2 and 1.10 x 105 cfu.cm-2 over the entire duration of the study. A wide variety of microorganisms (from air and food contact surfaces) such as the Gram-positive bacteria, Gram-negative bacteria, as well as fungi were present at the dairy farm plant. A number of the isolated genera have previously been associated with agricultural environments whilst others are associated with hospital environments. The positively identified strains were from genera such as Aeromonas, Arthrobacter, Candida, Pseudomonas, Pantoea, Citrobacter, Staphylococcus, Bacillus, Escherichia, Rhodococcus and Rhodotorula, amongst others. The isolation of microorganisms associated with food spoilage and foodborne disease outbreaks, which are known as indicator organisms such as Escherichia coli, Staphylococcus and Bacillus from both air and surface samples, signified possible faecal contamination and could be attributed to poor health and hygiene practices at the dairy farm plant. Despite the isolation of microorganisms associated with food spoilage and foodborne disease outbreaks, the isolation of microorganisms not usually associated with the food processing industry (usually associated with hospital environments) was an enormous and serious concern which suggested a need for further investigations at dairy farm plants as the implications of these pathogenic microorganisms in food is not known. The isolation of similar microorganisms from both the air samples and surface swabs suggests that airborne microbes have a potential of settling on food contact surfaces, therefore having a potential to contaminate dairy products which are known to be more prone to contamination and which, because of their nutritional status, serve as a good substrate for the growth of microorganisms.

A presente pesquisa tem como objetivo avaliar a eficiência de diferentes sistemas de ventilação no controle da transmissão aérea de agentes infecciosos em sala cirúrgica e em quarto de isolamento hospitalar. Para isso, foram desenvolvidos estudos experimentais e numéricos a partir de dados gerados em um hospital brasileiro de referência no tratamento de doenças respiratórias. Em uma sala cirúrgica, comparou-se o sistema de climatização existente (sistema de ventilação unidirecional) com um sistema split, adaptado na sala especialmente para este estudo. Em um quarto de isolamento compararam-se diferentes arranjos com ventilação natural (porta e janelas) e/ou mecânica (ventilador axial e unidade de descontaminação - filtro e exaustor). Em ambos os ambientes foram medidos parâmetros ambientais (velocidade do ar, temperatura do ar e intensidade de turbulência) e se realizou um estudo da concentração de partículas, mediante o uso de um gerador de partículas monodisperso. A partir dos dados gerados por meio desses procedimentos experimentais, para a sala cirúrgica, obteve-se o fator de proteção e, para o quarto de isolamento, a probabilidade de infecção utilizando o equacionamento proposto por Wells e Riley, bem como a taxa de decaimento de partículas. Os resultados experimentais subsidiaram a realização de um estudo numérico, que consistiu na avaliação dos campos de velocidade, temperatura e intensidade de turbulência do ar para os diferentes tipos de ventilação estudados e no estudo da dinâmica de partículas nos dois ambientes. Embora o sistema unidirecional seja, teoricamente, mais eficiente no controle das partículas, a metodologia de análise adotada evidenciou ineficiência do sistema na remoção de partículas devido a problemas na instalação e operação. Quanto ao sistema split, o presente estudo, como outros assemelhados, evidenciou a inadequação de seu uso em salas cirúrgicas. No quarto de isolamento a ventilação natural mostrou-se o método mais eficiente para a remoção de partículas e, consequentemente, o que mais reduz o risco de contaminação cruzada, conforme o equacionamento original de Wells-Riley. Para a sala cirúrgica foram obtidos valores experimentais do fator de proteção variando entre 0,10 e 0,52 e de -0,9 a +2,5 na análise numérica. Para o quarto de isolamento foram obtidos experimentalmente riscos de infecção entre 0,25 e 2,65%. Finalizando, este trabalho visa contribuir na proposição de uma metodologia experimental e numérica para a avaliação da dinâmica das partículas e, consequentemente, do risco de infecção por via aérea em ambientes hospitalares. / This research aims to evaluate the efficiency of different ventilation systems to control airborne transmission of infectious agents in a hospital operating room and isolation room. Experimental and numerical studies were carried out based on data generated in a Brazilian reference hospital for the treatment of respiratory diseases. In an operating room, an existing unidirectional air conditioning system (i. e., laminar air flow - LAF) was compared to a split system, adapted in the room especially for this study. In a respiratory isolation room, comparisons were drawn between different arrangements with natural ventilation (door and window) and/or mechanical ventilation (axial fan and decontamination unit - filter plus exhaust fan). In both rooms, environmental parameters (air speed, air temperature and turbulence intensity) were measured, and a study of particle concentration was developed employing a monodisperse aerosol generator. The data generated by these experimental procedures were used to calculate the protection factor for the operating room and the probability of infection for the isolation room, using the equation proposed by Wells and Riley, as well as the rate of particle decay. The experimental results were then used in a numerical study, which included evaluation of the fields of air velocity, temperature and turbulence intensity for different types of ventilation under study, as well as the analysis of particle dynamics in both environments. Although the unidirectional system is theoretically more effective for particle control, the methodology of analysis adopted revealed an inefficiency of this system in removing particles, due to installation and operation problems. Concerning the split system, this research - similarly to analogous studies - emphasizes the inadequacy of its use in operating rooms. In the isolation room, natural ventilation proved the most effective method for removing particles and, consequently, the one which reduces the most the risk of cross-contamination, according to the original Wells-Riley modeling. In the operating room were obtained experimental data for the protection factor ranging from 0.10 to 0.52 and from -0.9 to +2.5 in the numerical analysis. In the isolation room were obtained probabilities of infection between 0.25 and 2.65%. Finally, this work aims to contribute in proposing an experimental and numerical methodology for assessing the dynamics of particles and hence risk of airborne infection in hospital settings.

A presente pesquisa tem como objetivo avaliar a eficiência de diferentes sistemas de ventilação no controle da transmissão aérea de agentes infecciosos em sala cirúrgica e em quarto de isolamento hospitalar. Para isso, foram desenvolvidos estudos experimentais e numéricos a partir de dados gerados em um hospital brasileiro de referência no tratamento de doenças respiratórias. Em uma sala cirúrgica, comparou-se o sistema de climatização existente (sistema de ventilação unidirecional) com um sistema split, adaptado na sala especialmente para este estudo. Em um quarto de isolamento compararam-se diferentes arranjos com ventilação natural (porta e janelas) e/ou mecânica (ventilador axial e unidade de descontaminação - filtro e exaustor). Em ambos os ambientes foram medidos parâmetros ambientais (velocidade do ar, temperatura do ar e intensidade de turbulência) e se realizou um estudo da concentração de partículas, mediante o uso de um gerador de partículas monodisperso. A partir dos dados gerados por meio desses procedimentos experimentais, para a sala cirúrgica, obteve-se o fator de proteção e, para o quarto de isolamento, a probabilidade de infecção utilizando o equacionamento proposto por Wells e Riley, bem como a taxa de decaimento de partículas. Os resultados experimentais subsidiaram a realização de um estudo numérico, que consistiu na avaliação dos campos de velocidade, temperatura e intensidade de turbulência do ar para os diferentes tipos de ventilação estudados e no estudo da dinâmica de partículas nos dois ambientes. Embora o sistema unidirecional seja, teoricamente, mais eficiente no controle das partículas, a metodologia de análise adotada evidenciou ineficiência do sistema na remoção de partículas devido a problemas na instalação e operação. Quanto ao sistema split, o presente estudo, como outros assemelhados, evidenciou a inadequação de seu uso em salas cirúrgicas. No quarto de isolamento a ventilação natural mostrou-se o método mais eficiente para a remoção de partículas e, consequentemente, o que mais reduz o risco de contaminação cruzada, conforme o equacionamento original de Wells-Riley. Para a sala cirúrgica foram obtidos valores experimentais do fator de proteção variando entre 0,10 e 0,52 e de -0,9 a +2,5 na análise numérica. Para o quarto de isolamento foram obtidos experimentalmente riscos de infecção entre 0,25 e 2,65%. Finalizando, este trabalho visa contribuir na proposição de uma metodologia experimental e numérica para a avaliação da dinâmica das partículas e, consequentemente, do risco de infecção por via aérea em ambientes hospitalares. / This research aims to evaluate the efficiency of different ventilation systems to control airborne transmission of infectious agents in a hospital operating room and isolation room. Experimental and numerical studies were carried out based on data generated in a Brazilian reference hospital for the treatment of respiratory diseases. In an operating room, an existing unidirectional air conditioning system (i. e., laminar air flow - LAF) was compared to a split system, adapted in the room especially for this study. In a respiratory isolation room, comparisons were drawn between different arrangements with natural ventilation (door and window) and/or mechanical ventilation (axial fan and decontamination unit - filter plus exhaust fan). In both rooms, environmental parameters (air speed, air temperature and turbulence intensity) were measured, and a study of particle concentration was developed employing a monodisperse aerosol generator. The data generated by these experimental procedures were used to calculate the protection factor for the operating room and the probability of infection for the isolation room, using the equation proposed by Wells and Riley, as well as the rate of particle decay. The experimental results were then used in a numerical study, which included evaluation of the fields of air velocity, temperature and turbulence intensity for different types of ventilation under study, as well as the analysis of particle dynamics in both environments. Although the unidirectional system is theoretically more effective for particle control, the methodology of analysis adopted revealed an inefficiency of this system in removing particles, due to installation and operation problems. Concerning the split system, this research - similarly to analogous studies - emphasizes the inadequacy of its use in operating rooms. In the isolation room, natural ventilation proved the most effective method for removing particles and, consequently, the one which reduces the most the risk of cross-contamination, according to the original Wells-Riley modeling. In the operating room were obtained experimental data for the protection factor ranging from 0.10 to 0.52 and from -0.9 to +2.5 in the numerical analysis. In the isolation room were obtained probabilities of infection between 0.25 and 2.65%. Finally, this work aims to contribute in proposing an experimental and numerical methodology for assessing the dynamics of particles and hence risk of airborne infection in hospital settings.