This thesis is concerned with the experimental determination of the fundamental flame characteristics in a dust-air mixture and the influence of turbulence on flame propagation. Experiments were carried out in a tube having a 0.19 meter inside diameter and a length of 0.93 meter, and 1.86 meter with both ends closed. A dispersion system was developed giving a good quality uniform dust suspension. A comparative method for the estimation of dust flame characteristics, based on well defined methane-air flame characteristics, was developed and employed to estimate the characteristics of a flame propagating in a cornstarch dust-air mixture. A systematic study of the influence of dispersion-induced turbulence on the dust flame propagation was carried out. The influence of obstacles on flame propagation also was investigated. Some mechanisms of flame propagation in a cornstarch dust-air mixture have been proposed and discussed. In the conclusion, general remarks concerning the dust flame characteristics and the influence of turbulence on flame propagation are made. The future direction of research is also indicated.

To ensure safety regarding dust explosion hazards, it is important to study the dust lifting process experimentally and identify important parameters that will be valuable for development and validation of numerical predictions of this phenomenon. A new shock tube test section was developed and integrated into an existing shock tube facility. The test section allows for shadowgraph or laser scattering techniques to track dust layer particle motion. The test section is designed to handle an initial pressure of 1 atm with an incident shock wave velocity up to Mach 2 to mimic real world conditions. The test section features an easily removable dust pan and inserts to allow for adjustment of dust layer thickness. The design allows for the changing of experimental variables including initial pressure, Mach number, dust layer thickness and characteristics of the dust itself. A separate vacuum manifold was designed to protect existing equipment from negative side effects of the dust. A study was performed to demonstrate the capabilities of the new facility and to compare results with experimental trends formerly established in the literature. Forty-micron limestone dust with a layer thickness of 3.2 mm was subjected to Mach 1.22 and 1.38 shock waves, and a high-speed shadowgraph was used for flow visualization. Dust layer rise height was graphed with respect to shock wave propagation. Dust particles subjected to a Mach 1.38 shock wave rose more rapidly and to a greater height with respect to shock wave propagation than particles subjected to a Mach 1.22 shock wave. These results are in agreement with trends found in the literature, and a new area of investigation was identified.

No description available.

No description available.

Per and polyfluorinated compounds (PFCs) include a large group of chemicals which are known to be toxic, bioaccumulative and resistant to hydrolysis, photolysis, microbial degradation and metabolism. However, human exposure pathways and toxic effects to humans are still widely unknown and more data is needed over time. The concentrations of 7 PFCs were measured in indoor air from homes in Winnipeg, Manitoba using gas chromatography-mass spectrometry. 16 PFCs were measured in house dust from Winnipeg, Manitoba using on-line solid phase extraction coupled with liquid chromatography mass spectrometry. For commonly detected PFCs in indoor air and dust, concentrations were found at pg/m3 and ng/g levels, respectively, similar to that observed in other recent studies. Appropriate statistical tests and principal component analysis were used to evaluate possible associations between PFC concentrations and home characteristics. PFCs in indoor air and dust were associated with each other and home characteristics but not with indoor ambient temperature nor type of room (child room or the most used room). Furthermore PFCs did not show significant association with infant wheezing. None of the neutral PFCs in indoor air showed an association with seasonal temperature variation, except 8:2 FTOH and MeFOSE that had significantly higher concentrations in winter than summer.

Current methods for the detection and quantitation of airborne asbestos are either tedious, time consuming, subjective, or too expensive for routine analysis. A FT-IR spectroscopic method for the identification and quantitation of airborne asbestos samples provides a relatively inexpensive, fast, and non-subjective alternative for routine analysis.Three methods are investigated for the separation of the asbestos fibers from the matrix of the collection filter, (a mixed cellulose ester) for infrared analysis: spectral subtraction, chemical digestion, and ashing. Problems associated with the handling of asbestos (sample loss and contamination), and band anomalies encountered during spectral subtractions are discussed.Calibration curves are presented using the asbestos Si-O absorptions to quantitate the amount of asbestos. The spectral subtraction method yields linear calibration curves down to 0.3% asbestos by weight (6 mg) for tremolite asbestos. Tremolite and amosite asbestos calibration curves are linear down to 8 µg and 3 µg asbestos respectively using the ashing method.The spectral subtraction method and the ashing method are applied to NIOSH prepared PAT samples previously analyzed by phase contrast microscopy.The spectra are analyzed for asbestos by band identity, and once identified, quantitated from the appropriate calibration curve. / Department of Chemistry

Silica is a common silicon dioxide (SiO2) that can be crystalline or non-crystalline (amorphous). Amorphous silica is considered to be less hazardous than crystalline silica. Three dominant crystalline polymorphs exist, with silica quartz being the most common. Exposure to respirable crystalline silica (quartz) causes silicosis, a lung scarring disease. The aim of this study was to identify and quantify the silica exposure in respirable dust personal exposure samples, as well as in representative bulk samples which are large samples taken from the sources of airborne dust obtained from different mining and production plants involved in the production of titanium dioxide from beach sand. This is needed to determine the degree of risk of developing silicosis. Forty five workers employed in different mining and production plants participated in this study. Their eight-hour personal exposure to respirable particulate was determined. Personal respirable dust exposure samples and bulk samples were analyzed for silica by an accredited laboratory by means of X-ray diffraction based on NIOSH method 7500. Silica quartz was detected in personal respirable dust samples and bulk dust samples obtained from the mining and production plants, but amorphous silica was only detected in three personal exposure samples at the Slag plant and in the bulk sample obtained from the Roaster plant. All the silica quartz and amorphous silica concentrations in personal exposure samples were well below their respective exposure limits of 0.1 mg/m3 (quartz) and 3 mg/m3 (amorphous). No significant differences were found between the silica quartz concentrations in personal respirable exposure samples obtained from the mining ponds and the production plants, although a practical significance was found between some mining and production area personal exposure samples. The non-significant differences found between exposure concentrations and a practical significance suggest the necessity of involving a larger sample group in future. Other studies done in non-mining industries showed that some workers were over exposed to respirable silica dust. Compared to these findings the results of the present study showed the opposite, with respirable silica dust levels being below the South African action level and OEL. Further research, involving more samples, spread over a longer period of time, would probably be able to show a clear trend as to how quartz structures and exposure profiles change from the mining to the various production processes. Overexposure to silica quartz anywhere at the mine and production processes is considered unlikely, with the risk of developing silicosis being low. / Thesis (MSc (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2013

Silica is a common silicon dioxide (SiO2) that can be crystalline or non-crystalline (amorphous). Amorphous silica is considered to be less hazardous than crystalline silica. Three dominant crystalline polymorphs exist, with silica quartz being the most common. Exposure to respirable crystalline silica (quartz) causes silicosis, a lung scarring disease. The aim of this study was to identify and quantify the silica exposure in respirable dust personal exposure samples, as well as in representative bulk samples which are large samples taken from the sources of airborne dust obtained from different mining and production plants involved in the production of titanium dioxide from beach sand. This is needed to determine the degree of risk of developing silicosis. Forty five workers employed in different mining and production plants participated in this study. Their eight-hour personal exposure to respirable particulate was determined. Personal respirable dust exposure samples and bulk samples were analyzed for silica by an accredited laboratory by means of X-ray diffraction based on NIOSH method 7500. Silica quartz was detected in personal respirable dust samples and bulk dust samples obtained from the mining and production plants, but amorphous silica was only detected in three personal exposure samples at the Slag plant and in the bulk sample obtained from the Roaster plant. All the silica quartz and amorphous silica concentrations in personal exposure samples were well below their respective exposure limits of 0.1 mg/m3 (quartz) and 3 mg/m3 (amorphous). No significant differences were found between the silica quartz concentrations in personal respirable exposure samples obtained from the mining ponds and the production plants, although a practical significance was found between some mining and production area personal exposure samples. The non-significant differences found between exposure concentrations and a practical significance suggest the necessity of involving a larger sample group in future. Other studies done in non-mining industries showed that some workers were over exposed to respirable silica dust. Compared to these findings the results of the present study showed the opposite, with respirable silica dust levels being below the South African action level and OEL. Further research, involving more samples, spread over a longer period of time, would probably be able to show a clear trend as to how quartz structures and exposure profiles change from the mining to the various production processes. Overexposure to silica quartz anywhere at the mine and production processes is considered unlikely, with the risk of developing silicosis being low. / Thesis (MSc (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2013

The distributions of physical properties, such as the temperature, mass, or density of the dust grains in molecular clouds near Galactic massive star forming regions are relatively poorly understood. These properties are significant in characterizing the early stages of high-mass star formation. The major goal of this thesis is to study the dust properties using continuum emission to learn about the effect on the dust of the extreme environments around high-mass star formation. For this we estimate mass, temperature and luminosity of the hot (??? 100 K), cool (20-40 K) and cold (??? 20 K) dust in the environs of Galactic H??? regions using Infrared Astronomy Satellite (IRAS) and James Clerk Maxwell (JCMT) Submillimeter Common User Bolometer Arrays (SCUBA & SCUBA-2) data.??????A total of 83 clouds has been examined using IRAS data. A two-component model Spectral Energy Distribution (SED) of hot and cool dust is used to fit the IRAS data. A three-component model SED is fitted to combined SCUBA and IRAS data for 15 clouds near H??? regions to measure the cold dust component. Surprisingly, the ratio of the bolometric luminosity of the cool dust to the hot dust appears to have the same value 2.8 in virtually all objects. The cool dust has typically four to five orders of magnitude greater mass than the hot dust. However, the mass in cold dust is much greater than the mass in cool and hot dust. These results may prove useful for using IR observations for estimating gas masses in extragalactic systems with active high-mass star formation.??? ???The clouds in the environments of H??? regions are modelled assuming a thermal equilibrium in large grains, ignoring small grains and polycyclic aromatic hydrocarbons (PAHs). A number of different models having varying density distributions and external stellar radiation are compared to the IRAS SEDs. The model results suggest that the assumptions are not valid. We need a larger amount of dust at 30 K than the models produced and in this thesis we propose a solution to this problem, which we have not yet tested. ??????The JCMT Submillimeter Common User Bolometer Array-2 (SCUBA-2) data of six complexes is used to analyze the cold dust near Galactic H??? regions. Dust physical property maps such as the temperature, optical depth, column density and visual extinction are constructed from the SCUBA-2 data at 450 and 850 ??m wavelengths. All of the molecular cloud cores are found to be at very low temperatures, down to 6 K at the centres, with increasing values toward the periphery. This is surprising because we expected some internal heating at the centre. The column densities at the centres of the clouds exceed 10???? cm????? and the derived peak visual extinction values of most of the cloud cores are above 100, indicating a highly opaque cloud centre. The observed clouds are massive with gas masses ranging from 10?? to over 10??? M???. All of these properties together suggest that the cores are high-mass starless cores (HMSCs), which are not hosting any massive stars at the centre. Note that there are only a few such observations, on these potential precursors of high-mass proto-stellar objects, by others. From the derived physical properties such as high column densities, high visual extinction and the cold temperatures toward the centres of the cores, we speculate that the all the sample cores are in a state of collapse. Note that the Jeans masses of the clouds are much less than their real cloud masses and the free fall times range from 10?? to 10??? years, confirming the potential state of the cores.

We have used broad-band near infrared photometry in combination with optical Johnson-Cousins photometry to study the dust properties in the line of sight to the Galactic globular cluster M4. These data have been used to investigate the reddening effects in terms of absolute strength, distribution and variations across the cluster field, as well as the shape of the reddening law defined by the type of dust. All three aspects were poorly defined for this system and therefore there has been controversy about the absolute distance to the globular cluster which is closest to the sun. Here, we introduce a new method to determine the ratio of absolute to selective extinction (RV ) in the line of sight toward resolved stellar populations, which is known to be a useful indicator for the type of dust and therefore characterizes the applicable reddening law. This method is independent of age assumptions and appears to be significantly more precise and accurate than existing approaches. In a first application, we determine AV /E(B − V ) = 3.76 ± 0.07 (random error) for the dust in the line of sight to M4 for our set of filters. That corresponds to a dust-type parameter RV = 3.62 ± 0.07 in the Cardelli, Clayton & Mathis (1989) reddening law. With this value, the distance to M4 is found to be d = 1.80 ± 0.05 kpc, corresponding to a true distance modulus of (m − M)0 = 11.28 ± 0.06. These uncertainties do not include possible systematic errors in the theoretical isochrones. A reddening map for M4 has been created which reveals a spatial differential reddening of δE(B − V ) ≥ 0.2 mag across the field within 10′ around the cluster centre; this is about 50% of the total mean reddening, which has been determined to be E(B − V ) = 0.37 ± 0.01. In order to provide accurate zero points for the extinction coefficients of our photometric filters, a computer code has been written to investigate the impact of stellar parameters such as temperature, surface gravity and metallicity on the extinction properties and the necessary corrections in different bandpasses. Using both synthetic ATLAS9 spectra and observed spectral energy distributions, we found similar sized effects for the range of temperature and surface gravity typical of globular cluster stars: both cause a change of about 3% in the necessary correction factor for each filter combination. Interestingly, variations in the metallicity cause effects of the same order when the assumed value is changed from the solar metallicity ([Fe/H] = 0.0) to [Fe/H]=-2.5. Our analysis showed that the systematic differences between the flux of a typical main-sequence turnoff star in a metal poor globular cluster and a Vega-like star are even stronger (∼ 5%). We compared the results from synthetic spectra to those obtained with observed spectral energy distributions and found significant differences in detail for temperatures lower than 5 000 K. We have attributed these discrepancies to the inadequate treatment of molecular bands in the B filter within the ATLAS9 models. Accordingly, for those cooler temperatures we obtained corrections for temperature, gravity and metallicity primarily from the observed spectra. Fortunately, these differences do not affect our principal astrophysical conclusions in this study, which are based on stars hotter than 5 000 K. / Graduate