CFD Modelling of Pathogen Transport due to Human Activity

Health-care Associated Infection is a major concern with 1 in 11 patients affected each year. There is evidence that some pathogens may be transported by an airborne route, and hence fluid modelling tools, such as Computational Fluid Dynamics (CFD), are increasingly used to aid understanding of the transport mechanisms of infection. These models tend to only consider respiratory infections that are released from a single point, such as a person coughing. However there is substantial evidence that certain pathogens, such as MRS A, may be released from the skin during regular routine activities (e.g. undressing, walking). An observational and air sampling study carried out on a respiratory ward found that certain activities correlated to greatly increased numbers of large particles (> 5µm), and bioaerosols. The increased concentrations of bioaerosols also corresponded to sampling of potentially pathogenic Staphylococcus aureus. It is therefore necessary to be able to represent these releases ofbioaerosols within CFD models used in design and risk assessment. Bioaerosol transport is modelled in CFD simulations usmg passive scalar transport and Lagrangian particle tracking models with the DRW model to simulate turbulent diffusion. These are validated for the first time using spatial variation of airborne and deposited bioaerosols generated under controlled conditions. Simpler multi-zone models are compared to CFD and found to perform well at simulating the bioaerosol decay within large spaces that can be assumed to be well mixed, however they are not refined enough to simulate the detail required to study the transfer of infection between individual patients. A zonal source model is introduced and validated with the aim of representing the time average dispersion from a transient source in a steady state model. This enables the dispersion of bioaerosols from activities occurring in hospital wards to be represented within CFD models. The zonal source model is shown to give a good representation of the average dispersion and total deposition of a transient source, whereas a point source is not. Point sources produce different dispersion patterns to zonal sources and so it is recommended that both are used to simulate bioaerosols produced due to activities or respiratory diseases. Point sources are found to be highly sensitive to the injection position, whereas the zonal source is found to produce relatively similar patterns of dispersion for varying size definitions. CFD is a useful tool for studying pathogen transport in indoor spaces, and when doing so it is recommended that the potential bioaerosol release from the skin is considered which can be taken into account within a steady state model using a zonal source model

Natural ventilation : an evaluation of strategies for improving indoor air quality in hospitals located in semi-arid climates

PhD ThesisThis thesis is an investigation into improving natural ventilation in low rise hospital wards in Northern Nigeria. The climate of this region is semi-arid, during the dry season, sub-Saharan fine dust (Harmattan dust) is blown into the region from the North East and during the wet season, Mosquitos are prevalent. The energy infrastructure in the whole of Nigeria is under resourced; hence ventilation strategies’ based on mechanical extraction are not possible. Five wards within low rise hospital buildings were studied; these were purpose designed hospital buildings, not converted buildings. Questionnaire surveys of health care workers in the hospitals was conducted and revealed dissatisfaction with the buildings’ ventilation and Indoor Air Quality. The questionnaires were then followed up by Tracer Gas measurements and during the period of measurement there was only one occasion when a ward achieved an air change rate of 6-ach-1, the ASHREA Standard requirement for hospital buildings. To investigate methods of improving natural ventilation in these wards, a CFD model was developed of a representative ward, the model was validated against the Tracer Gas measurements; with an acceptable agreement of ≤ 15%. Using the CFD model, achievable ventilation strategies within the context of the location, were investigated, and a combination of cross ventilation utilizing windows on the windward and leeward sides of the ward together with a roof ventilator on the leeward side proved the most successful. All openings were screened to prevent the entry of mosquitos. This best case was further investigated with the wind direction at an oblique angle to the ward side. The oblique angle of wind attack reduced the air change rates but improved air circulation/mixing within the ward. With the exception when the wind direction was parallel to the ward side. To reduce the ingress of Harmattan Dust, was problematic given the energy restrictions, a low energy solution of introducing screened plenums on both the windward and leeward sides of the building proved successful. Larger dust particles were detained within the windward plenum and the smaller dust particles were exhausted into the leeward plenum. With the mosquito screens located on the large surface area of the plenum, the window screens were removed resulting in higher air change rates. Thus, it is recommended that, openings should be provided on the windward and leeward walls and on the roof toward the leeward side for efficient ventilation and airflow circulation at the occupancy level. The longer sides of the wards should be oriented toward the North-South to capture the North-East trade winds and South-West monsoon winds with oblique angle of attack. Plenums should be incorporated to the windward and leeward facades and Insect screen should be installed on the plenums instead of the wards’ openings to increase ventilation rates while excluding mosquitoes and decreasing dust particle concentration in the hospital wards. Openings should be at the middle of the windward and leeward walls and on the roof toward the leeward to avoid airflow short-circuiting. It is recommended to use insect screen with the porosity of 0.2 and when the outdoor local wind speed is ≤ 1.26 m/s (2 m/s: airport value), the ventilation should be supplemented with fan.Ramat Polytechnic Maiduguri, Borno State Government and Tertiary Education Trust Fund (TETFUND

Weak signals in Science and Technologies: 2019 Report

JRC has developed a quantitative methodology to detect very early signs of emerging technologies, so called "weak signals of technology development". Using text mining and scientometrics indicators, 257 of these weak signals have been identified on the basis of scientific literature and are reported in the present report.JRC.I.3-Text and Data Minin

The Emerging Threat of Drug Resistant Tuberculosis

Cite: Academy of Science of South Africa (ASSAf), (2011). The Emerging Threat of Drug Resistant Tuberculosis. [Online] Available at: DOI http://dx.doi.org/10.17159/assaf/0013An estimated 2 billion people, one-third of the global population, are infected with Mycobacterium tuberculosis (M.tb.), the bacterium that causes tuberculosis (TB) (Keshavjee and Seung, 2008). Spread through the air, this infectious disease kills 1.8 million people each year, or 4,500 each day (WHO, 2009a). TB is the leading killer of people with HIV, and it is also a disease of poverty—the vast majority of TB deaths occur in the developing world (WHO, 2009a). Exacerbating the devastation caused by TB is the growing threat of drug-resistant strains of the disease in many parts of the world. The development of drug resistance is a predictable, natural phenomenon that occurs when microbes adapt to survive in the presence of drug therapy (Nugent et al., 2010). Although antibiotics developed in the 1950s are effective against a large percentage of TB cases, resistance to these first-line therapies has developed over the years, resulting in the growing emergence of multidrug-resistant (MDR) and extensively drugresistant (XDR) TB, and even totally drug-resistant (TDR) TB (see Box 1-1 for definitions). In recognitionUS Academy of Science

Prediction of bioparticles dispersion and distribution in a hospital isolation room

Removal of bioparticles from hospital isolation room is important in reducing the transmission risk of infectious diseases. An effective ventilation system is necessary to protect the patient, doctor and nurses from catching infectious diseases. The goal of this study was to select the most effective ventilation scenario for the investigated isolation room among the defined scenarios. To select the most effective ventilation scenario, the effect of air exchange rate (ACH), injection angle (Ɵ) and exhaust position on removing the exhaled bioparticles from a patient mouth during coughing process, was investigated. Computational Fluid Dynamic (CFD) was used for predicting the air flow pattern and bioparticle transmission. Bioparticle dispersion and deposition was modelled by an Eulerian-Lagrangian approach. The mathematical model for air flow was the Reynold Averaged Navier Stokes (RANS) equations with k-ɛ turbulence model. Code-Saturne was chosen as the CFD program and validated by numerical results and empirical equations. The numerical results obtained by Code-Saturne were compared to results publish in the literature. To investigate the Code-Saturne capability to predict particle deposition, particles with different diameter in the range of 1 μm to 10 μm, were injected in a channel. Non dimensional deposition velocity obtained using Code-Saturne was compared to the empirical results available in the literature. The results showed that Code-Saturne has the capability of predicting the air flow pattern, particle dispersion and particle deposition. For analyzing the results and choosing the most effective ventilation system, particle removal efficiency (PRE) and normalized particle concentration in the inhalation zone were compared. Among the six ventilation scenarios with different ACH and Ɵ, scenario with ACH=15 and Ɵ=45° was selected as the most effective. Finally, effect of exhaust position was investigated. Three scenarios were defined. The first one with an exhaust mounted on a wall near the ceiling, the second one with an exhaust mounted on a wall near the floor and the last one with an exhaust mounted on the ceiling. It is observed that the exhaust position has great influence on the air flow pattern and particle removal. It is found that an exhaust mounted on the ceiling scenario has the best particle removal efficiency

The detection and prevention of airborne tuberculosis transmission

Imperial Users onl