Welding is a common metal fabrication process within industry. Epidemiology suggests that welders as an occupational group demonstrate slight, but significant, increased risks of respiratory ill-health. This might be expected as welding processes often present high levels of occupational exposure to oxidising gasses and weld fumes which are often inadequately controlled through local exhaust ventilation or personal respiratory protection because of high costs and the burden of worker participation. Fundamental control strategies of occupational hygiene encourage development and use of engineering controls as the best means to optimally control occupational exposure. However, engineering controls have not yet been successfully developed to control occupational exposure to welding fume and gases. This thesis investigates the interrelationships between ultra-violet radiation (UV). ozone (0:;). and hexavalent chromium (CrVI) in metal inert gas (MIG) welding in order to investigate possible methods to control occupational exposure to welding fume and gases by engineering contro!' Past studies of occupational ill-health in welders are reviewed as is the currently understanding of the physico-chemical principles by which the various components of welding fume evolves. Experiments were designed to investigate the mechanisms of formation of UV, 0 3 and CrVI formation from which a number of possible control strategies were developed further. Among these results emerge two process modifications with exciting potential to reduce two toxic components. 0, and CrVI , in stainless steel welding fume and gas. The addition of trace amounts of Zinc to chromium containing steel wires virtually eliminates all 0, and significantly reduces hexavalent chromium within the weld plume. As Zn is a volatile metal, it does not contaminate weld quality but increases the zinc oxide le\els in the fume slightly. A second method developed in this thesis involves the addition of a dual shield gas shroud containing reducing gases such as C2H .. to remove 0, and consequently. reduce Cr(VI) levels. Preliminary results suggest that these methods can be used separately. or in combination, to provide a practical means of controlling occupational exposure to two of the more toxic components of welding fume and gases. This thesis describes in details the experiments and results culminating in successful preliminary development of engineering controls for 0 3 and CrVI through process modification of the stainless steel MIG welding process. Further work for further development of these methods is outlined and funding to extend this area of applied research is being actively pursued with the support of major UK industry.

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Este artículo presenta un estudio acerca del riesgo percibido en el sector de la construcción. El estudio se realizó a partir del análisis de cuestionarios provenientes de una muestra de trabajadores de la construcción del sur de España. Se presenta el perfil del riesgo percibido obtenido según los enfoques del llamado paradigma psicométrico a través de atributos cualitativos y se analizan los resultados. El atributo relativo a como el trabajo afecta a la salud a largo plazo es el más puntuado. Lo cual representa una novedad con respecto a otros estudios previos. A su vez se analizan mediante un análisis de la varianza (ANOVA) los efectos de la variable sociodemográfica oficio con respecto a los distintos atributos del riesgo percibido del cuestionario. Se presentan las diferencias obtenidas entre el grupo de albañiles y estructuristas. / This article presents a study of the perceived risk in the construction sector. The study was conducted from the analysis of questionnaires from several samples of construction workers from southern Spain. We report the perceived risk profile obtained from the psychometric paradigm through qualitative attributes and then we analyze the results. Stands out the attribute regarding how work affects our own long-term health. This represents something new with respect to previous studies. Also analyzed by analysis of variance (ANOVA) the effects of socio-demographic variable craft with respect to the different attributes of the perceived risk of the questionnaire. It presents the differences obtained between the group of masons and framers.

Under certain conditions, reactive chemicals may proceed into uncontrolled chemical reaction pathways with rapid and significant increases in temperature, pressure, and/or gas evolution. Reactive chemicals have been involved in many industrial incidents, and have harmed people, property, and the environment. Evaluation of reactive chemical hazards is critical to design and operate safer chemical plant processes. Much effort is needed for experimental techniques, mainly calorimetric analysis, to measure thermal reactivity of chemical systems. Studying all the various reaction pathways experimentally however is very expensive and time consuming. Therefore, it is essential to employ simplified screening tools and other methods to reduce the number of experiments and to identify the most energetic pathways. A systematic approach is presented for the evaluation of reactive chemical hazards. This approach is based on a combination of computational methods, correlations, and experimental thermal analysis techniques. The presented approach will help to focus the experimental work to the most hazardous reaction scenarios with a better understanding of the reactive system chemistry. Computational methods are used to predict reaction stoichiometries, thermodynamics, and kinetics, which then are used to exclude thermodynamically infeasible and non-hazardous reaction pathways. Computational methods included: (1) molecular group contribution methods, (2) computational quantum chemistry methods, and (3) correlations based on thermodynamic-energy relationships. The experimental techniques are used to evaluate the most energetic systems for more accurate thermodynamic and kinetics parameters, or to replace inadequate numerical methods. The Reactive System Screening Tool (RSST) and the Automatic Pressure Tracking Adiabatic Calorimeter (APTAC) were employed to evaluate the reactive systems experimentally. The RSST detected exothermic behavior and measured the overall liberated energy. The APTAC simulated near-adiabatic runaway scenarios for more accurate thermodynamic and kinetic parameters. The validity of this approach was investigated through the evaluation of potentially hazardous reactive systems, including decomposition of di-tert-butyl peroxide, copolymerization of styrene-acrylonitrile, and polymerization of 1,3-butadiene.

Cumene hydroperoxide (CHP), a type of organic peroxide, is widely used in the chemical industry for diverse applications. However, it decomposes and undergoes highly exothermic runaway reactions under high temperature because of its unstable peroxide functional group. The risk of runaway reaction is intensified by the fact that operation temperature of CHP is close to its onset temperature in many cases. To ensure safe handling of CHP in the chemical industry, a lot of research has been done on it including theoretical research at the microscopic level and experimental research at the macroscopic level. However, the unstable radicals in the CHP decomposition reactions make it difficult to study its reaction pathway, and therefore lead to incomplete understanding of the reaction mechanism. The slow progress in theoretical research hinders the application of the theoretical prediction in experimental research. For experimental research, the lack of integration of operational parameters into the reactivity evaluation limits its application in industrial process. In this thesis, a systematic methodology is proposed to evaluate the reactivity hazards of CHP. This methodology is a combination of theoretical research using computational quantum chemistry method and experimental research using RSSTTM. The theoretical research determined the dominant reaction pathway of CHP decomposition reaction through the study of thermodynamic and kinetic stability, which was applied to the analysis of experimental results. The experimental research investigated the effect of CHP concentration on runaway reactions by analyzing the important parameters including temperature, pressure, self-heat rate and pressure rate. This methodology could also be applied to other organic peroxides or other reactive chemicals. The results of theoretical research on reaction mechanism show that there is a dominant reaction pathway, which consumes most of the CHP in decomposition reaction. This conclusion agrees with the experimental results that 40 wt% is a critical point for almost all important parameters of runaway reactions. In the high concentration range above 40 wt%, some unknown reaction pathways are involved in decomposition of CHP because of lack of cumene. The shift of reaction mechanism causes the change of the effect of concentration on runaway reactions.

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Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 141-146).

In-vitro mutagenicity assays have traditionally been used for first line identification of potential genotoxic hazard, purporting to chemical carcinogenesis and heritable genetic damage. The recent advances m combinatorial chemistry and high throughput screening technologies have led to a massive explosion in numbers of possible therapeutic candidates being produced at the early stages of drug discovery. This rapid increase in the number of chemicals to be classified results in a greater need for to acquire alternative methods for the prediction of toxicity. Quantitative StructureActivity Relationships (QSAR) can till this need for early hazard identifications by elucidating the physicochemical basis of biological activity. The assumption with predictive QSARs for toxicity is that "biological activity may be described as a function of chemical constitution". This thesis focuses on the Ames mutagenicity assay data for two compound sets; one of 90 compounds, with limited structural flexibility, comprising a range of chemical classes (non-congeneric series), the second, a set of 30 flavonoid compounds. Three physicochemical descriptor sets were generated: EV A, a theoretical molecular descriptor based on the normal co-ordinate modes of vibration; WHIM, derived from weighting functions applied to the 3D-structural molecular co-ordinates; and TSAR, a series of hydrophobic, electronic and steric parameters traditionally associated with the production of biological QSARs. Various "unsupervised" data pre-treatment methods were adopted, to reduce the level of degeneracy within the individual descriptor sets, prior to the calculation of stepwise linear discriminant classification functions. Good predictive models for Ames mutagenicity, as determined by leave-one-out (jackknife) cross-validation, were obtained with each of the three physicochemical descriptor sets. An increase in the predictive ability was observed following the combination of variables from the individual descriptor sets, inferring that some unique information associated with mutagenic activity is contained within each descriptor set. The predictive stability of the models produced was assessed via independent compound predictions, with a poor overall success rate determined. This failure in external prediction was investigated and fundamental differences in physicochemical data space occupancy revealed. Conclusions on training set composition and general model applicability are made with consideration to individual model physicochemical data space coverage.

Under certain conditions, reactive chemicals may proceed into uncontrolled chemical reaction pathways with rapid and significant increases in temperature, pressure, and/or gas evolution. Reactive chemicals have been involved in many industrial incidents, and have harmed people, property, and the environment. Evaluation of reactive chemical hazards is critical to design and operate safer chemical plant processes. Much effort is needed for experimental techniques, mainly calorimetric analysis, to measure thermal reactivity of chemical systems. Studying all the various reaction pathways experimentally however is very expensive and time consuming. Therefore, it is essential to employ simplified screening tools and other methods to reduce the number of experiments and to identify the most energetic pathways. A systematic approach is presented for the evaluation of reactive chemical hazards. This approach is based on a combination of computational methods, correlations, and experimental thermal analysis techniques. The presented approach will help to focus the experimental work to the most hazardous reaction scenarios with a better understanding of the reactive system chemistry. Computational methods are used to predict reaction stoichiometries, thermodynamics, and kinetics, which then are used to exclude thermodynamically infeasible and non-hazardous reaction pathways. Computational methods included: (1) molecular group contribution methods, (2) computational quantum chemistry methods, and (3) correlations based on thermodynamic-energy relationships. The experimental techniques are used to evaluate the most energetic systems for more accurate thermodynamic and kinetics parameters, or to replace inadequate numerical methods. The Reactive System Screening Tool (RSST) and the Automatic Pressure Tracking Adiabatic Calorimeter (APTAC) were employed to evaluate the reactive systems experimentally. The RSST detected exothermic behavior and measured the overall liberated energy. The APTAC simulated near-adiabatic runaway scenarios for more accurate thermodynamic and kinetic parameters. The validity of this approach was investigated through the evaluation of potentially hazardous reactive systems, including decomposition of di-tert-butyl peroxide, copolymerization of styrene-acrylonitrile, and polymerization of 1,3-butadiene.