Vaibhav Raj | Centers for Disease Control and Prevention (original) (raw)

Papers by Vaibhav Raj

As open pit mines continues to grow deeper and productivity continues to increase, the management... more As open pit mines continues to grow deeper and productivity continues to increase, the management of air pollution can become challenging. One of the challenges, common during winter in deep open pit mines operating in the Arctic, is the occurrence of atmospheric inversion. In itself, inversion is not hazardous. However, due to the emission of gases and particulates during the mining process, the air within the pit can be severely contaminated, rather quickly, leading to serious health and safety consequences. The problem is complex and any solution approach will require a good understanding of the interaction of the aerodynamic movement of air, the air inversion process, the meteorology, the pollutant sources, and the application of mechanical ventilators in open pit mines. Scientific literatures related to open pit mine ventilation, particularly with respect to air inversion, are practically non-existent in the English literature. This is perhaps the first account of a three dimensional computational fluid dynamics (CFD) model of pollutant transport in an actual open pit mine under an Arctic air inversion. Advanced technology has made computers faster and more powerful, which allows computational fluid dynamics (CFD) procedures to be applied to many air flow problems. Thus, a CFD approach can be used to understand the transport of contaminant in the pit during inversion by using several turbulence models. An array of data is required to develop CFD models for open pit mine ventilation. The meteorological conditions within deep open pit mines are significantly affected by temperature and roughness conditions, which ultimately generate complex dispersion phenomena including separation of air flow and its recirculation. For the application of CFD, various data such as pollutants concentrations, temperature, velocity, pit contours, equipment locations, and radiation (shortwave and longwave) were collected from the selected open pit mine and the weather stations located nearby. Analysis of the weather data showed that inversions are due to elevated inversions in the selected open pit mine. Because an exact flow situation in open pit mines is not known a-priori, open pit air flow simulation and pollution transport are often highly sensitive to the type of flow model employed. It is therefore necessary to investigate various turbulent models to identify the appropriate model that will simulate the flow phenomena with reasonable accuracy and predict the contaminant distributions within the pit. Dispersion models differ in their assumptions and structures as well as in the algorithm used and as a result, predictions vary from model to model. Furthermore, it is v

SME Annual Meeting, 2022

Underground stone mine ventilation is characterized by large openings with low resistances. These... more Underground stone mine ventilation is characterized by large openings with low resistances. These mines primarily face three challenges: moving adequate volumes of air, controlling and directing the airflow, and planning ventilation systems that work well with production requirements. Given these challenges, this paper examines the data collected by the Mine Safety and Health Administration (MSHA) to determine the extent to which respirable crystalline silica (RCS) and diesel particulate matter (DPM) are an issue in underground stone mines. Out of 522 sampled mines, there were 108 personal samples exceeding the RCS Permissible Exposure Limit (PEL) during 2000-2020. DPM were more prevalent than RCS in these mines with 382 personal samples exceeding the DPM PEL out of the 929 mines sampled during 2002-2020. Dilution of DPM is usually the defining parameter for design of mine ventilation systems in largeopening underground stone mines. With this knowledge, focused attention can be directed to these mines so that appropriate prevention and mitigation techniques can be utilized to prevent stone miners' exposure to RCS and DPM and subsequent respiratory diseases.

19th North American Mine Ventilation Symposium, 2023

Large-opening stone mines are characterized by entry sizes twice or thrice the size of typical un... more Large-opening stone mines are characterized by entry sizes twice or thrice the size of typical underground coal or metal/nonmetal mines. Due to the large openings, the volume of air need-ed to ventilate these mines is significantly higher than in coal or metal/nonmetal mines. This leads to low air velocities with low static pressure drop. Airflow in the mine mostly relies on natural ventilation and auxiliary fans at the working face. The National Institute for Occupational Safety and Health (NIOSH) is conducting research on the ventilation of large-opening stone mines to reduce worker exposure to dust and other contaminants such as diesel particulate matter (DPM). To understand airflow in a large-opening mine, we conducted a numerical modeling study using computational fluid dynamics (CFD). This paper presents the results from the CFD modeling of airflow in a large-opening stone mine. The CFD model is calibrated against the data previously collected at a large-opening stone mine. The team ran different scenarios with fan placement along with the movement of truck to simulate how effectively air is moving in the mine.

SME Annual Meeting, 2022

Diesel particulate matter (DPM) is a common and well-known health hazard in the mining environmen... more Diesel particulate matter (DPM) is a common and well-known health hazard in the mining environment. The current approved method for monitoring both the organic and elemental carbon (OC, EC) portions of DPM is a laboratory method with a turnaround time of approximately one week. In order to evaluate exposure levels and take corrective action before overexposures occur, a portable real-time device capable of quantifying both OC and EC is needed. To that end, researchers from the National Institute for Occupational Safety and Health (NIOSH) designed and tested a device based on narrow bandpass optical filters that is capable of targeting infrared absorbance bands associated with DPM. Five optical bandpass filters were chosen based on previous work quantifying DPM using Fourier-transform infrared (FT-IR) spectrometry. The resulting device, referred to as a filtometer, is optimized to exclusively determine DPM and could serve as a cost-effective, field-portable alternative to laboratory-grade FT-IR analysis and instrumentation. The performance of the filtometer was investigated by calibrating FT-IR data from DPM (dependent variable) to the filtometer spectra (predictor variables) using a partial least-squares (PLS) and ordinary least squares (OLS) approach. The square of the correlation coefficient and root-mean-square error of cross validation measures were used to assess individual model performance.

Mining, Metallurgy & Exploration, Apr 22, 2019

Diesel particulate matter (DPM) has been classified as a carcinogen to humans by the Internationa... more Diesel particulate matter (DPM) has been classified as a carcinogen to humans by the International Agency for Research on Cancer. As a result of its potential carcinogenic nature, DPM exposure is regulated by the Mine Safety and Health Administration. Currently, diesel emissions in the workplace are monitored by collecting the aerosol onto filters, which are then sent to a laboratory for thermal-optical analysis using the NIOSH method 5040. This process can take days or even weeks, and workers can potentially be exposed to excessive levels of DPM before the problem is identified. Moreover, the delay involved in getting the loaded filter to the lab inevitably means the loss of some of the more volatile organic carbon. To remedy this delay, researchers from the National Institute for Occupational Safety and Health are seeking to develop a field-portable, real-time method for measuring elemental and organic carbons in DPM aerosols. In the current study, the use of mid-infrared spectrometry was investigated. It is believed that mid-infrared spectroscopy is more suitable for use in a real-time field-portable device than thermo-optical analysis methods. This article presents a method for measuring organic carbon (OC) and elemental carbon (EC) in DPM for a broad range of OC/EC ratios. The method has been successfully applied to laboratory-generated and mine samples.

Mining, Metallurgy & Exploration, Oct 6, 2020

Conveyor systems persist in being a source of injuries and fatalities in the mining industry. To ... more Conveyor systems persist in being a source of injuries and fatalities in the mining industry. To reduce these incidents, better methods are needed to enhance the monitoring of probable hazards and improve situational awareness during the normal operation and maintenance of conveyor systems. To address these issues, researchers from the National Institute for Occupational Safety and Health (NIOSH) continue to investigate emerging technologies that show the potential to improve miner safety around conveyors. This paper presents a feasibility assessment by NIOSH researchers of a fully integrated, commercially available wireless Internet of Things (IoT) system to improve situational awareness around conveyor systems. Included are discussions of a full-scale laboratory test bed that was designed to simulate a working conveyor system as well as the challenges and successes of integrating the IoT system with the test bed.

Transactions of the Society for Mining, Metallurgy & Exploration, 2018

In underground metal/nonmetal mines, repeated localized short-term exposure to high levels of air... more In underground metal/nonmetal mines, repeated localized short-term exposure to high levels of airborne contaminants can become a serious health issue. Currently, there are no common mechanisms to control or mitigate these short-term high exposures to contaminants. To improve miners' health and safety, the U.S. National Institute for Occupational Safety and Health's Spokane Mining Research Division (SMRD) is developing a smart monitoring and control (SMAC) system for the real-time monitoring of mine air quality, with integrated countermeasures to reduce high concentrations of airborne contaminants in localized sections of mines. To develop and test a SMAC system capable of being implemented in an underground mine, SMRD researchers built a test apparatus incorporating a fan, louver, ducting and sensors combined with atmospheric monitoring and control software. This system will institute effective countermeasures to reduce contaminant levels, improving miner safety and health.

Mining Engieering, 2015

The control of fugitive dust in high-latitude openpit mines is challenging due to unique atmosphe... more The control of fugitive dust in high-latitude openpit mines is challenging due to unique atmospheric phenomena resulting in complicated flow regimes as well as atmospheric inversion due to the lack of adequate insolation during prolonged winter seasons. In this study, two idealized (one conical and one trapezoidal) three-dimensional openpit mine geometries were simulated for different seasonal conditions using a computational-fluid-dynamics package from Software Cradle. The airflow was solved by Reynolds-averaged Navier-Stokes equations
using the standard kappa-epsilon turbulence model. The concept of particle tracking was used to predict the flow patterns of dust particles.
For various climatic conditions and two different pit geometries, fugitive dust particles varying in size, from PM0.1 to PM10, and concentration were generated at various locations and dispersed by the airflows inside the openpit mine. The amount and location of dust particles inside the pit were reported at various time intervals. In the summer season, airborne dust particles were quickly transported outside the openpit domain. In the winter season, however, the development of atmospheric inversion significantly affected the amount of dust retention inside the openpit domain.

Transactions of the Society for Mining, Metallurgy & Exploration, 2015

The air flow problems in openpit mines are complex. Computational fluid dynamics (CFD) models can... more The air flow problems in openpit mines are complex. Computational fluid dynamics (CFD) models can provide detailed information regarding air flow pattern, velocity distribution, temperature, and pollutant concentration in an enclosed domain of an openpit mine. A range of turbulent models can be selected with varying complexity and accuracy. Pollutant transport models, however, differ in their assumptions and structure as well as in the algorithms they use. As a result, predictions vary from model to model. This paper presents a study of pollutant transport in an actual openpit mine under a stable boundary layer. The objective was to test two turbulence models using similar geometry and the same input conditions and model constants. Measured data were used to compare the results of the two CFD models, namely, the kappa-epsilon (к-є) model and the Large Eddy Simulation model. Despite the complex synoptic situations, different meteorological input data and fast-changing conditions, the simulation results from both the models were in good agreement regarding the dispersion of pollutants.

Mınıng Engineering, 2013

This paper highlights the use of an innovative mine production scheduling scheme for grade-contro... more This paper highlights the use of an innovative mine production scheduling scheme for grade-control planning tasks that take into consideration grade-model uncertainty. The scheduling exercise has been carried out with the help of a multiobjective genetic algorithm (MOGA) for the production scheduling operations. The underlying motive behind the use of MOGA has been the generation of a set of Pareto optimal solutions to meet the goals of the target-grade specifications for the considered multiple grade attributes. Several new concepts related to MOGA formulation, in particular the mutation operation and the convergence criteria of this algorithm, are proposed in this paper. The modeling of grade uncertainty into the scheduling outputs has also been incorporated through a set of conditional simulated grade maps. The proposed scheme of production scheduling operations has been applied for the grade-control planning operations in an iron ore mine to meet the targeted grade specifications of iron, silica and alumina, and a risk analysis has been performed to this end.

Transactions of the Society for Mining, Metallurgy and Exploration, 2013

In the mining industry, computational fluid dynamics (CFD) modeling is used extensively to simula... more In the mining industry, computational fluid dynamics (CFD) modeling is used extensively to simulate air flow in underground mines. CFD modeling of pollutant transport in openpit mines is relatively new. Modeling the actual pit geometry of an openpit mine and the open domain is complex. The complexity is primarily due to the faceted geometry of an openpit mine with its numerous associated sharp features. Important issues that are not considered carefully at the geometry level are generally propagated to the subsequent processes. Several challenges and pitfalls are encountered in modeling pollutant transport in openpit mines. These challenges and pitfalls are related to the geometry, meshing, boundary conditions and turbulence modeling parameterization. An appropriate mesh selection is critical. A detailed discussion of the meshing of the domain of an openpit mine is presented in this paper. The selection of an appropriate turbulence model, such as kappa-epsilon (κ-ε), large eddy simulation (LES), Reynolds stress model (RSM), etc., to obtain the best possible solution is equally significant. This paper discusses the various challenges in modeling the pollutant transport process in an openpit and some of the approaches adopted to address these challenges.

Mining Engineering, 2012

As openpit mines continue to grow deeper and productivity continues to increase, the management o... more As openpit mines continue to grow deeper and productivity continues to increase, the management of respirable dust and noxious gases can become a challenge. The natural wind flow in openpit mines is often recirculatory. This recirculation traps dust and gases in deep openpit mines. This problem is particularly acute in high-latitude openpit mines, due to a phenomenon known as atmospheric inversion. In the winter, arctic and subarctic regions experience short days and long nights. This deficit of solar radiation creates a situation in which cold, still air accumulates near the bottom of the pit. In openpit mines, this can result in unhealthy accumulations of gases and other contaminants. In this study, the natural wind flow patterns in and around openpit mines were investigated using a computational fluid dynamics (CFD) program. Two-dimensional models were created for a variety of pit geometries. The effect of depth, slope angle and wind speed on the recirculation pattern in the pit was examined.

Conference Presentations by Vaibhav Raj

14th United States/North American Mine Ventilation Symposium, 2012

As open pit mines continue to grow deeper and productivity continues to increase, the management ... more As open pit mines continue to grow deeper and productivity continues to increase, the management of air pollution can become challenging. The natural wind flow in open pit mines is generally recirculatory. This recirculation can trap harmful aerosols and gases in open pit mines. This problem is exacerbated as the depth of the pit increases. Maintaining a safe and healthy atmosphere in open pit mines can present a particular challenge at high latitudes due to atmospheric inversion. Air inversions are common during the winter months in arctic regions. Arctic winters are characterized by extremely short days. During winter months, a deficit of solar radiation incident upon the bottom of the pit can result in a negative surface energy balance. This results in heat flow from the air to the pit surfaces. Under these conditions, the convection currents that normally keep the atmosphere in the pit well mixed do not exist, resulting in stagnant and polluted air. Developing predictive models for air quality in open pit mines under conditions of arctic inversion is complex. The quality of air in the pit is determined by a coupled relationship among mesoscale meteorological processes, topography, the air inversion process, and the sources and extent of pollution. The influence of pit geometry on wind flow patterns within open pit mines under neutral atmospheric conditions and the effects of Earth's diurnal cycle significantly influence the stability and height of the boundary layer, and, thus, impact the retention of contaminants in an open pit mine. Two-dimensional models were created for several different pit geometries to analyze the transport of contaminants in the pit under arctic air inversion. This paper will present the effects of pit depth, wind speed, and inversion strength on the contaminant concentrations within the pit. The results of this study indicate that the concentration of air pollutants in open pit mines will increase with increasing pit depth and inversion strength. Natural ventilation alone is not sufficient to mitigate the inversion problem.

SME Annual Meeting, 2018

Workers at mineral processing facilities are often exposed to high levels of dust generated when ... more Workers at mineral processing facilities are often exposed to high levels of dust generated when ores are processed. Crushing, grinding, screening, and other processes generate large quantities of dust, which can exceed the threshold values prescribed by the Mine Safety and Health Administration (MSHA). Many ores contain quartz (silica), which has been known to cause serious health problems in workers over time. Given the structure of mineral processing plants, the airflow regime is not coherent inside the building, which may lead to multiple recirculation zones. These recirculation zones can trap dust, and concentrations of dust can then rise over time. Therefore, there is a need to understand the airflow phenomenon that occur inside of mineral processing facilities and how these occurrences interact with the dust generation processes to identify zones of potentially high dust concentration. Computational fluid dynamics (CFD) modeling can give a better understanding of the airflow and help recommend designs and methods to mitigate the high dust concentrations in a mineral processing plant. This paper presents the CFD modeling of airflow inside of a mill building to demonstrate airflow patterns that will affect the generation and subsequent dispersion of dust due to crushing, grinding, and other activities. This study was conducted by researchers from the National Institute for Occupational Safety and Health (NIOSH).

SME Annual Meeting, 2019

Diesel particulate matter (DPM) has been shown to contribute to various adverse health effects on... more Diesel particulate matter (DPM) has been shown to contribute to various adverse health effects on underground miners. In order to reduce worker exposures, it is critical to measure the levels of DPM in the active work settings and in real time. However, the 5040 method, developed by the National Institute for Occupational Safety and Health (NIOSH), which quantifies the mass of elemental carbon (EC) and organic carbon (OC) in the samples, is based on full-shift samples, and can take days or even weeks for results. Use of real-time monitors could significantly reduce the risk of DPM exposure to miners, and available monitors have been shown to quantify DPM, mainly using the EC and other surrogates. The NIOSH Spokane Mining Research Division is conducting research aimed at developing a field-portable DPM monitor that is able to quantify both EC and OC. One part of this work is to understand the effect of OC on currently available real-time DPM monitors. This paper will present the results from experiments that were designed to observe the effect of OC on real time monitors and compare the results with the NIOSH 5040 method.

SME Annual Meeting, 2020

Advanced data science techniques have been applied in a verity of fields to improve health and sa... more Advanced data science techniques have been applied in a verity of fields to improve health and safety and reduce accident and fatality rates. Similar to other industries, the mining industry requires the adoption and implementation of modern research methods to continue boosting safety in mine operations. Text analytics, in general, is one of the essential methods used to analyze unstructured data that is in text format. Using text mining and Natural Language Processing (NLP) techniques to extract patterns with incidents and identify insightful information from contents and reports is extremely valuable to produce actionable recommendations and strategies for applying text mining and NLP to accident text data. In this research investigation, advanced text mining techniques and NLP were applied to the U.S. Mine Safety and Health Administration (MSHA) final fatality reports in metal and nonmetal operations (surface and underground) to perform preprocessing, Exploratory Data Analysis (EDA), and various statistics to discover insightful word relation patterns in the reports. For this purpose, the final fatality reports from 2010 through 2017 were collected and cleaned. In addition, topic modeling was done to group the reports with similar underlying themes or topics.

16th North American Mine Ventilation Symposium, 2017

Air inversion is a natural meteorological phenomenon. Mitigation of pollutants in deep open-pit m... more Air inversion is a natural meteorological phenomenon. Mitigation of pollutants in deep open-pit mines in the Arctic is a challenging task. Release of pollutants below the inversion height in an open-pit mine during periods of weak winds and consequently weak vertical mixing may result in very high concentrations of primary and secondary pollutants, causing serious consequences for human health. For continued mining operation, the levels of pollutants must be below the TLVs. If no significant synoptic meteorological situation changes during an inversion, a warm air mass sits over the cold air mass within the open pit. Artificial ventilation is required to dilute the pollutants to an extent that mine workers can safely resume work. Studies of the turbulence parameters suggest that effective ventilation of the pit and removal of pollutants can be accomplished if a large enough mixing length in the open pit can be created. Turbulent mixing by eddies of different scales in the SBL is produced by wind shear and dissipated by molecular viscosity and buoyancy destruction. The main result of turbulence is mixing of the atmospheric profile and transport of momentum. Several approaches that may create a large mixing length are examined. Computational Fluid Dynamics Simulation results of various mitigation approaches using fans in forcing and exhaust modes as well as a push-pull ventilation system are presented. Mitigation by creating mechanical turbulence using large fans in forcing and exhaust modes is not effective for dilution of pollutants in the pit to a safe level. A push-pull ventilation system is similarly ineffective.

10th International Mine Ventilation Congress, Aug 8, 2014

In a deep open pit mine, the management of air quality can become challenging due to atmospheric ... more In a deep open pit mine, the management of air quality can become challenging due to atmospheric inversion. During inversion, the natural ventilation cycle is absent and the pollutants emitted from various mobile sources in the pit accumulate over time at the lower levels. The growth of inversion descent is a function of sensible heath flux, atmospheric pressure, density of air, solar heat flux, pit potential temperature lapse rate at sun rise and warm air advection rate above the pit. The problem is complex and any solution requires an extensive understanding of the interactions of the aerodynamics movement of air, air inversion, meteorology, pollutant source, transport phenomena, and fan applications in the pit. In the Arctic air inversion phenomenon is presented with a discussion of the various factors that influence the air quality. The mathematical modeling of the pollutant flow in the open pit is discussed in general with the identification of the issues in modeling and in specific, under inversion conditions. A three-dimensional CFD model of contaminant transport in a deep open pit mine under arctic air inversion is presented along with the result from its application to an operating mine. The three dimensional model was validated using data from the selected open pit mine. In order to understand the turbulent behavior of the flow during the inversion for the mitigation of the pollutants in the pit, plots of the turbulent kinetic energy and turbulent intensity with time are analyzed. Challenges encountered during data collection as well as areas requiring further research are discussed.

SME Annual Conference, 2017

Air inversion is a meteorological phenomenon generally occurs during winter times. Release of pol... more Air inversion is a meteorological phenomenon generally occurs during winter times. Release of pollutants below the inversion height in an open-pit mine during periods of weak winds and consequently weak vertical mixing may result in very high concentrations of primary and secondary pollutants, causing serious consequences for health and safety of miners. Mine operations cease if the concentration of NOx or CO exceeds the threshold limit value (TLV) of the pollutants. Artificial ventilation is required to dilute the pollutants to an extent that mine workers can safely resume work. Studies of the turbulence parameters suggest that effective ventilation of the pit and removal of pollutants can be accomplished if a large enough mixing length in the open pit can be created. Turbulent mixing by eddies of different length scales under an inversion layer is product of wind shear, thermal gradient and buoyancy. The main result of turbulence is mixing of the atmospheric profile and transport of momentum. Computational fluid dynamics (CFD) Simulation results of a novel mitigation approach using cloud cover will be presented in this paper.

SME Annual Conference, 2016

The development and advancement of computational fluid dynamics (CFD) has made it possible to bet... more The development and advancement of computational fluid dynamics (CFD) has made it possible to better understand pollutant flow and distribution in deep open pit mines. Open pits located at higher latitudes, especially in the Arctic and sub-Arctic, face a unique problem due to atmospheric temperature inversion, which is prevalent during much of the winter. A three-dimensional CFD model of an actual open pit mine in the Arctic was developed to analyze the problem of pollutant growth during inversion, and mitigation of the pollutants through improved ventilation schemes. Due to the availability of mine-specific data, such as contaminant concentrations and coordinates of sampling locations, the actual 2013 pit geometry was used for model validation Concentrations predicted by the selected realizable κ-ε turbulent model are compared to measured pollutant concentrations at the open pit. Pollutant concentrations at selected locations showed differences, but remained within the same order of magnitude in most cases.

SME Annual Meeting, 2022

19th North American Mine Ventilation Symposium, 2023

SME Annual Meeting, 2022

Mining, Metallurgy & Exploration, Apr 22, 2019

Mining, Metallurgy & Exploration, Oct 6, 2020

Transactions of the Society for Mining, Metallurgy & Exploration, 2018

Mining Engieering, 2015

Transactions of the Society for Mining, Metallurgy & Exploration, 2015

Mınıng Engineering, 2013

Transactions of the Society for Mining, Metallurgy and Exploration, 2013

Mining Engineering, 2012

14th United States/North American Mine Ventilation Symposium, 2012

As open pit mines continue to grow deeper and productivity continues to increase, the management ... more As open pit mines continue to grow deeper and productivity continues to increase, the management of air pollution can become challenging. The natural wind flow in open pit mines is generally recirculatory. This recirculation can trap harmful aerosols and gases in open pit mines. This problem is exacerbated as the depth of the pit increases. Maintaining a safe and healthy atmosphere in open pit mines can present a particular challenge at high latitudes due to atmospheric inversion. Air inversions are common during the winter months in arctic regions. Arctic winters are characterized by extremely short days. During winter months, a deficit of solar radiation incident upon the bottom of the pit can result in a negative surface energy balance. This results in heat flow from the air to the pit surfaces. Under these conditions, the convection currents that normally keep the atmosphere in the pit well mixed do not exist, resulting in stagnant and polluted air. Developing predictive models for air quality in open pit mines under conditions of arctic inversion is complex. The quality of air in the pit is determined by a coupled relationship among mesoscale meteorological processes, topography, the air inversion process, and the sources and extent of pollution. The influence of pit geometry on wind flow patterns within open pit mines under neutral atmospheric conditions and the effects of Earth's diurnal cycle significantly influence the stability and height of the boundary layer, and, thus, impact the retention of contaminants in an open pit mine. Two-dimensional models were created for several different pit geometries to analyze the transport of contaminants in the pit under arctic air inversion. This paper will present the effects of pit depth, wind speed, and inversion strength on the contaminant concentrations within the pit. The results of this study indicate that the concentration of air pollutants in open pit mines will increase with increasing pit depth and inversion strength. Natural ventilation alone is not sufficient to mitigate the inversion problem.

SME Annual Meeting, 2018

SME Annual Meeting, 2019

SME Annual Meeting, 2020

16th North American Mine Ventilation Symposium, 2017

10th International Mine Ventilation Congress, Aug 8, 2014

SME Annual Conference, 2017

SME Annual Conference, 2016

15th North American Mine Ventilation Symposium, 2015

In extreme climatic conditions, deep open pit mines trap pollutants as a result of the developmen... more In extreme climatic conditions, deep open pit mines trap pollutants as a result of the development of air temperature inversion. Management of the air quality becomes challenging with the disruption of natural ventilation cycles. Surface-based inversion (SBI) is formed as result of radiative cooling of the ground surface. The formation of this temperature inversion layer is common during the winter months in the Arctic and sub-Arctic. However, a temperature inversion can also develop above the SBI, depending on the synoptic meteorological conditions, commonly known as the elevated inversion (EI). Depending on the altitude, location and geometry of an open pit mine, different types of air inversion may occur. The growth of inversion descent is a function of sensible heat flux, atmospheric pressure, density of air, solar heat flux, and potential temperature. Better understanding of the air inversion type, frequency and vertical structure of air inversion is important in order to design pollution mitigation measures in an open pit mine. In this paper, various types of inversion that can develop in open pit mines are discussed. Impacts of air inversions in open pit mines from various regions including mines from lower latitudes are analyzed.

SME Annual Meeting, 2014

As open pit mines continues to grow deeper, managing air pollution can become challenging. During... more As open pit mines continues to grow deeper, managing air pollution can become challenging. During arctic air inversion, the temperature of the air over the mine increases with altitude, and the cold, heavy, surface air is trapped in the pit. This problem is complex, and any solution will require an extensive understanding of the interactions between the aerodynamic movement of air, air inversion, meteorology, pollutant sources, and transport phenomena in the open pit mines.
The availability of computational fluid dynamics (CFD) has elucidated the pollutant flow mechanism in open pit mines. Very few CFD studies have been published, especially the Large Eddy Simulation (LES), on the contaminant transport in deep open pit mines under arctic air inversion. The contaminant transport in an open pit mine under arctic inversion is due to a stable or nocturnal boundary layer in micro-meteorological terms. Understanding the physics of the stable boundary layer (SBL) is relevant to air flow and pollutant transport in deep open pit mines. This paper focuses on a Large Eddy Simulation (WMLES as Sub-Grid Scale Model) modeling of the SBL and pollutant transport in a large open pit mine.

As open pit mines continue to grow deeper and productivity continues to increase, the management ... more As open pit mines continue to grow deeper and productivity continues to increase, the management of air pollution can become challenging. One of the challenges, common during winter in deep open pit mines operating in the Arctic, is the occurrence of atmospheric inversion. In itself, inversion is not hazardous. However, due to the emission of gases and particulates during the mining process, the air within the pit can be severely contaminated, rather quickly, leading to serious health and safety consequences. The problem is complex and any solution approach will require a good understanding of the interaction of the aerodynamic movement of air, the air inversion process, the meteorology, the pollutant sources, and the application of mechanical ventilators in open pit mines. Scientific literature related to open pit mine ventilation, particularly with respect to air inversion, is practically non-existent in the English literature. This is perhaps the first account of a three dimensional computational fluid dynamics (CFD) model of pollutant transport in an actual open pit mine under an Arctic air inversion. Advanced technology has made computers faster and more powerful, which allows computational fluid dynamics (CFD) procedures to be applied to many air flow problems. Thus, a CFD approach can be used to understand the transport of contaminant in the pit during inversion by using several turbulence models. An array of data is required to develop CFD models for open pit mine ventilation. The meteorological conditions within deep open pit mines are significantly affected by temperature and roughness conditions, which ultimately generate complex dispersion phenomena including separation of air flow and its recirculation. For the application of CFD, various data such as pollutants concentrations, temperature, velocity, pit contours, equipment locations, and radiation (shortwave and longwave) were collected from the selected open pit mine and the weather stations located nearby. Analysis of the weather data showed that inversions are due to elevated inversions in the selected open pit mine. Because an exact flow situation in open pit mines is not known a-priori, open pit air flow simulation and pollution transport are often highly sensitive to the type of flow model employed. It is therefore necessary to investigate various turbulent models to identify the appropriate model that will simulate the flow phenomena with reasonable accuracy and predict the contaminant distributions within the pit. Dispersion models differ in their assumptions and structures as well as in the algorithm used and as a result, predictions vary from model to model. Furthermore, it is also important to investigate the behavior of a CFD model when simulating complex phenomena, such as the transport and distribution of contaminants in an open pit mine under an Arctic air inversion. The simulation of an enhanced period of turbulence in the stable boundary layer (SBL) is of particular interest because traditional air pollution dispersion models cannot explicitly treat intermittent turbulence events, and yet the SBL is often the worst-case scenario in open pit pollution transport. Realizable κ-ϵ and Large Eddy Simulation (LES) models were used for understanding flow of gaseous contaminants. The 2010 pit configuration was used to develop models for understanding the gaseous transport under air inversion. During an inversion, turbulence is dominant at the bottom of the pit, while in the middle portion of the pit turbulence is intermittent and flow over the upper portion of the pit is mostly laminar. The realizable κ-ϵ model tends to over-predict the contaminant concentration, whereas, the LES model under-predicts the level of pollutant concentrations. Validation of the developed model was performed using the 2013 pit configuration. Despite the complex synoptic situations, the different meteorological input data and the fast changing conditions, the simulation results from the validation model were in good agreement regarding the dispersion of pollutants and other turbulent variables. Pollutant concentration values in the selected locations showed differences, but remained within the same order of magnitude in most cases. Removal of the harmful pollutants from the pit is significantly important for the health and safety of the mine workers. The mitigation models were developed for both the 2010 and the 2013 pit configurations. Several remedial measures such as the use of mechanical ventilators in forcing and exhaust mode, push-pull ventilation and a novel approach of using cloud cover were considered. Mitigation efforts employing mechanical means were unsuccessful in removing or diluting the contaminants to a safe level. The novel approach of using cloud cover over an open pit mine showed promise. With this approach, the model showed that the inversion could be lifted and pit could be cleared of all pollutants.