Browsing by Subject "Risk Assessment"
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Item A design approach to a risk review for fuel cell-based distributed cogeneration systems(Texas A&M University, 2004-09-30) Luthringer, Kristin LynA risk review of a fuel cell-based distributed co-generation (FC-Based DCG) system was conducted to identify and quantify the major technological system risks in a worst-case scenario. A risk review entails both a risk assessment and a risk analysis of a designed system, and it is part of risk engineering. Thorough literature reviews and expert interviews were conducted in the field of fuel cells. A thorough literature review of the risk engineering field was also conducted. A procedure for a risk review of the FC-Based DCG System was developed. The representative system design was identified by the current DCG design technology. The risk assessment was carried out, identifying the system components and potential failure modes and consequences. Then, using probabilities of failure for the various system components, the risk associated with a particular system design was determined. A Monte Carlo simulation on the total system reliability was used to evaluate the potential for system failure at a time of 1 hour, 5 hours, 10 hours, 50 hours, 100 hours and 500 hours of continuous operation. The original system was found to be acceptable at the initial times, but after 100 hours was predicted to fail. The components which consistently contribute significantly to the overall system risk are the membrane electrode assembly (MEA) and the nickel-metal foam flow fields. A revised system was analyzed with the reliability of the MEA and the Ni-foam set to 100%. After the revision, the components which contributed significantly to the system risk were the pumps. Simulations were run for several alternative systems to provide feedback on risk management suggestions. The risk engineering process developed with the design approach for this research is applicable to any system and it accommodates the use of many different risk engineering tools.Item A Risk-based Optimization Modeling Framework for Mitigating Fire Events for Water and Fire Response Infrastructures(2011-02-22) Kanta, Lufthansa RahmanThe purpose of this dissertation is to address risk and consequences of and effective mitigation strategies for urban fire events involving two critical infrastructures- water distribution and emergency services. Water systems have been identified as one of the United States' critical infrastructures and are vulnerable to various threats caused by natural disasters or malevolent actions. The primary goals of urban water distribution systems are reliable delivery of water during normal and emergency conditions (such as fires), ensuring this water is of acceptable quality, and accomplishing these tasks in a cost-effective manner. Due to interdependency of water systems with other critical infrastructures-e.g., energy, public health, and emergency services (including fire response)- water systems planning and management offers numerous challenges to water utilities and affiliated decision makers. The dissertation is divided into three major sections, each of which presents and demonstrates a methodological innovation applied to the above problem. First, a risk based dynamic programming modeling approach is developed to identify the critical components of a water distribution system during fire events under three failure scenarios: (1) accidental failure due to soil-pipe interaction, (2) accidental failure due to a seismic activity, and (3) intentional failure or malevolent attack. Second, a novel evolutionary computation based multi-objective optimization technique, Non-dominated Sorting Evolution Strategy (NSES), is developed for systematic generation of optimal mitigation strategies for urban fire events for water distribution systems with three competing objectives: (1) minimizing fire damages, (2) minimizing water quality deficiencies, and (3) minimizing the cost of mitigation. Third, a stochastic modeling approach is developed to assess urban fire risk for the coupled water distribution and fire response systems that includes probabilistic expressions for building ignition, WDS failure, and wind direction. Urban fire consequences are evaluated in terms of number of people displaced and cost of property damage. To reduce the assessed urban fire risk, the NSES multi-objective approach is utilized to generate Pareto-optimal solutions that express the tradeoff relationship between risk reduction, mitigation cost, and water quality objectives. The new methodologies are demonstrated through successful application to a realistic case study in water systems planning and management.Item Assessment of suspended dust from pipe rattling operations(Texas A&M University, 2006-10-30) Park, Ju-MyonSix types of aerosol samplers were evaluated experimentally in a test chamber with polydisperse fly ash. The Andersen sampler overestimates the mass of small particles due to particle bounce between stages and therefore provides a conservative estimate of respirable particulate mass and thoracic particulate mass. The TSP sampler provides an unbiased estimate of total particulate mass. TSP/CCM provides no information below ESD 2 ????m and therefore underestimates respirable particulate mass. The PM10 sampler provides a reasonable estimate of the thoracic particulate fraction. The RespiCon sampler provides an unbiased estimate of respirable, thoracic, and inhalable fractions. DustTrak and SidePak monitors provide relative particle concentrations instead of absolute concentrations because it could not be calibrated for absolute particle concentrations with varying particle shape, composition, and density. Six sampler technologies were used to evaluate airborne dust concentrations released from oilfield pipe rattling operations. The task sampled was the removal of scale deposited on the inner wall of the pipe before it was removed from service in a producing well. The measured mass concentrations of the aerosol samplers show that a Gaussian plume model is applicable to the data of pipe rattling operations for finding an attainment area. It is estimated that workers who remain within 1 m of the machine centerline and directly downwind have an 8-hour TWA exposure opportunity of (13.3 ???? 9.7) mg/m3 for the Mud Lake pipe scale and (11.4 ???? 9.7) mg/m3 for the Lake Sand pipe scale at 95 % confidence. At distances more than 4 m downwind from the machine centerline, dust concentrations are below the TWA-TLV of 10 mg/m3 for the worker in both scales. At positions crosswind or upwind from the machine centerline there is no measurable exposure. Available data suggest that the attainment area for the public starts at about 9 m downwind from the machine centerline in both scales, as 24 hour average concentrations at these distances are smaller than the 0.15 mg/m3, the NAAQS for unrestricted public access. The PSD of the suspended plume is dominated by particles smaller than ESD 50 ????m.Item Bayesian Networks and Geographical Information Systems for Environmental Risk Assessment for Oil and Gas Site Development(2013-04-03) Varela Gonzalez, Patricia YsoldaThe objective of this work is to develop a Bayesian Network (BN) model to produce environmental risk maps for oil and gas site developments and to demonstrate the model?s scalability from a point to a collection of points. To reach this objective, a benchmark BN model was formulated as a ?proof of concept? using Aquifers, Ecoregions and Land Use / Land Cover maps as local and independent input variables. This model was then used to evaluate the probabilistic geographical distribution of the Environmental Sensibility of Oil and Gas (O&G) developments for a given study area. A Risk index associated with the development of O&G operation activities based on the spatial environmental sensibility was also mapped. To facilitate the Risk assessment, these input variables (maps) were discretized into three hazard levels: high, moderate and low. A Geographical Information System (GIS) platform was used (ESRI ArcMap 10), to gather, modify and display the data for the analysis. Once the variables were defined and the hazard data was included on feature classes (layer shapefile format), Python 2.6 software was used as the computational platform to calculate the probabilistic state of all the Bayesian Network?s variables. This allowed to define Risk scenarios both on prognostic and diagnostic analysis and to measure the impact of changes or interventions in terms of uncertainty. The resulting Python ? ESRI ArcMap computational script was called ?BN+GIS, which populated maps describing the spatial variability of the states of the Environmental Sensibility and of the corresponding Risk index. The latter in particular, represents a tool for decision makers to choose the most suitable location for placing a drilling rig, since it integrates three fundamental environmental variables. Also, results show that is possible to back propagate the information from the Environmental Sensibility to define the inherent triggering scenarios (hazard variables). A case of study is presented to illustrate the applicability of the proposed methodology on a specific geographical setting. The Barnett Shale was chosen as a benchmark study area because sufficient information on this region was available, and the importance that it holds on the latest developments of unconventional plays in the country. The main contribution of this work relies in combining Bayesian Networks and GIS to define environmental Risk scenarios that can facilitate decision-making for O&G stakeholders such as land owners, industry operators, regulators and Non-Governmental Organizations (NGOs), before and during the development of a given site.Item Modeling toxic endpoints for improving human health risk assessment(2009-05-15) Bruce, Erica DawnRisk assessment procedures for mixtures of polycyclic aromatic hydrocarbons (PAHs) present a problem due to the lack of available potency and toxicity data on mixtures and individual compounds. This study examines the toxicity of parent compound PAHs and binary mixtures of PAHs in order to bridge the gap between component assessment and mixture assessment. Seven pure parent compound PAHs and four binary mixtures of PAHs were examined in the Salmonella/Microsome Mutagenicity Assay, a Gap Junction Intercellular Communication (GJIC) assay and the 7-ethoxyresorufin-O-deethylase assay (EROD). These assays were chosen for their ability to measure specific toxic endpoints related to the carcinogenic process (i.e. initiation, promotion, progression). Data from these assays was used in further studies to build Quantitative Structure-Activity Relationships (QSARs) to estimate toxic endpoints and to test the additive assumption in PAH mixtures. These QSAR models will allow for the development of bioassay based potential potencies (PPB) or toxic equivalency factors (TEFs) that are derived not only from bioassay data, but also from structure, activity, and physical/chemical properties. These models can be extended to any environmental media to evaluate risk to human health from exposures to PAHs.Item Prevention and Management of Aquatic Invasive Plants in Texas(2014-12-04) Edgerton, Elizabeth ADetermining which non-native aquatic plants have the greatest potential to invade a new area and prohibiting those species prior to their introduction is the key to preventing future injurious invasions. Once introduced however, prioritization and effective control is important to managing infestations. This study focused on identifying potential new aquatic invasive plant species and prioritizing existing infestations in Texas, via two aquatic plant models. An aquatic plant risk assessment was the first model. While other risk assessments of this type currently exist, a model suited to the varied environmental conditions in the State of Texas was not available. In addition, many existing models cover large geographic areas, leading to decreased accuracy on a more localized scale. This new model, referred to as the Texas Aquatic Plant Risk Assessment, was based on previous aquatic plant risk assessment and serves as a pre-entry screening tool for testing non-native plant species and identifying those which are likely to be invasive and should therefore be excluded. The model uses a series of weighted questions to give a score to each plant species tested; the higher the score, the more likely the plant is to be invasive in the State of Texas. We tested the model against 100 known non-native species within the state and subsequently ran a series of statistical tests on the results to determine the model?s accuracy and find the best threshold to separate major invaders from minor and non-invaders. When model results were compared to known species invasiveness and a threshold of 50 was set between high risk major invaders and non-invaders, 100%, 87%, and 94% accuracy was achieved in classifying major invaders, minor invaders, and non-invaders, respectively. Other, more precautionary thresholds were also explored during analysis. The second model, the Lake Conroe Invasion Model, simulates growth and senescence of hydrilla in Lake Conroe, and the plant?s response to control efforts using grass carp (Ctenopharyngodon idella). The model was developed using reported data from previous hydrilla infestations and control attempts at Lake Conroe, and serves as a prototype for future simulated invasion modeling. A series of simulations were run to calibrate the model, based on previously reported data, and to demonstrate the model?s use. Results from the simulations accurately reflected reported growth and senescence rates of hydrilla within the lake; growth rates for grass carp in the model were also comparable to rates reported in the literature. Simulations of various management strategies showed that increasing numbers of grass carp were needed to control a hydrilla infestation as the time lag between initial hydrilla invasion and stocking of grass carp increased. However, the number of grass carp needed to control an infestation decreased as the amount of time allowed for control increased. In addition grass carp mortality rates may be significantly impacted by grass carp stocking rates relative to the number of vegetated hectares. If smaller stocking rates are preferred in order to avoid removing all aquatic vegetation from the lake, higher mortality rates likely need to be accounted for as increased mortality due to a decreased predator to prey ratio may occur.Item Risk Framework for the Next Generation Nuclear Power Plant Construction(2012-12-11) Yeon, Jaeheum 1981-Uncertainty can be either an opportunity or a risk. Every construction project begins with the expectation of project performance. To meet the expectation, construction projects need to be managed through sound risk assessment and management beginning with the front-end of the project life cycle to check the feasibility of a project. The Construction Industry Institute?s (CII) International Project Risk Assessment (IPRA) tool has been developed, successfully used for a variety of heavy industry sector projects, and recently elevated to Best Practice status. However, its current format is inadequate to address the unique challenges of constructing the next generation of nuclear power plants (NPP). To understand and determine the risks associated with NPP projects, the goal of this thesis is to develop tailored risk framework for NPP projects that leverages and modifies the existing IPRA process. The IPRA has 82 elements to assess the risks associated with international construction projects. The modified IPRA adds five major issues (elements) to consider the unique risk factors of typical NPP projects based upon a review of the literature and an evaluation of the performance of previous nuclear-related facilities. The modified IPRA considers the sequence of NPP design that ultimately impacts the risks associated with plant safety and operations. Historically, financial risks have been a major chronic problem with the construction of NPPs. This research suggests that unstable regulations and the lack of design controls and oversight are significant risk issues. This thesis includes a consistency test to initially validate whether the asserted risks exist in actual conditions. Also, an overall risk assessment is performed based on the proposed risk framework for NPP and the list of assessed risk is proposed through a possible scenario. After the assessment, possible mitigation strategies are also provided against the major risks as a part of this thesis. This study reports on the preliminary findings for developing a new risk framework for constructing nuclear power plants. Future research is needed for advanced verification of the proposed elements. Follow-on efforts should include verification and validation of the proposed framework by industry experts and methods to quantify and evaluate the performance and risks associated with the multitude of previous NPP projects.