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By S. Sarac

In this study, a statistical model is suggested in order to determine the methane emission from a working seam. In the proposed method, methane concentrations which are systematically measured in return airway are the sample values, and the calculated statistical parameter is the upper confidence limit of the average of these values. At any given time, the probability of methane concentration in the return airflow to be lower than the calculated upper confidence limit value is 97.5%. The statistical method has been applied to the panel 206 of Armutcuk Mine, Turkish Hardcoal Enterprises. The calculated methane emission value for the considered shift was 15.18 m3/t.

Jan 1, 2003

By Dana C. Reinke

Water well drillers are exposed to high levels of noise while working. NIOSH researchers have found that water well drillers are exposed to levels above 85dB (A) while performing certain tasks during a typical drilling job. Noise levels consistently over 85dB (A) during an 8–hour work shift are hazardous and can lead to hearing loss in workers. Finding ways to reduce noise exposure is difficult because of many factors. The work environment is constantly changing due to the location of jobs and environmental factors. The types of drill rigs required for drilling are expensive. Equipment can range from new to used (10 to 30+ years old). Drillers and owners can work together to prevent noise–induced hearing loss, and measures can be taken to reduce exposure to hazardous noise.[ ] Preventing hearing loss occurs through three stages. The first stage is removing noise from the source (i.e., drill rig). Various parts of a drill rig create noise besides the drilling rod. NIOSH researchers have examined noise levels of drill rigs. Some of the loudest parts of the drill rig include the compressor, engine, and cooling fan (Fig. 1). While removing the noise source from a worksite is ideal, the process would be expensive and difficult.[ ]

Jan 9, 2005

Open pit mining has considerable damaging effects on the environment of the mining region. These harmful influences have to be controlled during mining operation until mine closure. Different sections of mined land, such as; pit(s), waste dump(s), tailing pond(s), roads, areas for onsite facilities and free land zones which are not mined, have to be reclaimed through treatment of environmental pollution and implementation of a permanent post mining land use (PMLU) after mine closure. Implementation of a permanent optimal post mining land use (OPMLU) is one the most decisive criterion which effects on reclamation procedure, mine closure and their costs. Therefore to define ultimate pit limit (UPL), mine closure and reclamation costs should be entered in the calculation iterations same as the other variable costs of the projects. Estimation of closure and reclamation costs of a mining project is carried out based on the attained OPMLU and the specifications of the mine site. In this paper, a model is developed to provide OPMLU for pit area through fuzzy multi-attribute decision making (FMADM) technique. The model was implemented on a hypothetical copper mine in northwest of Iran as a case study. Lumber production was selected as OPMLU for the pit area. It is finally concluded that through the developed model, OPMLU for different sections of mined land in an open pit mine project is defined. Also closure and reclamation costs are estimated based on the defined OPMLU to achieve a more accurate UPL.

Dec 6, 2010

By M. Steyn

[Zr(C9H6NO)4]?(HCON(CH3)2)?(H2O), where (C9H6NO) = 8-hydroxy quinoline (oxH), was synthesized and characterized. This tetrakis-coordinated zirconium complex crystallized in the triclinic crystal system (Pi, Z=2) along with water and N,N?-dimethylformamide(DMF) solvate in the asymmetric unit. The metal atom is surrounded by four N,O-donating bidentate ox-ligands that are arranged around the metal centre to give a square antiprismatic coordination polyhedron with a small distortion towards a dodecahedral geometry. Crystal packing is stabilized by intermolecular interactions of adjacent oxine ring systems in neighbouring molecules, as well as hydrogen bonding of the aqua and DMF solvate molecules, linking the molecular entities into a supramolecular three-dimensional network.

Jan 1, 2013

By Hebi Yin

A two-dimensional multi-scale solidification model was developed to study the heat transfer, fluid flow, and grain growth occurring in the molten pool during the laser engineered net shaping (LENS) process. This model coupled the finite element method to calculate mass, energy and momentum transport in the macroscale with the cellular automaton technique to calculate liquid/solid phase change at the microscale. The validation of the model was performed by comparing the simulation results with experimental data from previously published works, showing good agreement in temperature distribution and the dendrite morphology (size and shape). The simulation results showed that Marangoni convection, caused by the temperature gradient along the pool surface, played a critical role in determining the flow pattern in the molten pool and exerted influence on the pool size and shape. It was also found that columnar dendrites can be formed, with dendrite arm spacings as fine as a few microns due to the high cooling rate during the LENS process. In addition, the influence of fluid flow on the dendrite growth in the pool was discussed.

Jan 1, 2010

By Stephen D. Smith

This chapter summarizes data on crude nonfuel mineral production for the United States, its island possessions, and the Commonwealth of Puerto Rim. Also included are tables that show the principal nonfuel mineral commodities exported from and imported into the United States and that compare world and U.S. mineral production. The detailed data from which these tables were derived are contained in the individual commodity chapters of Volume I and in the State chapters of Volume II of this edition of the Minerals Yearbook. Although crude mineral production may be measured at any of several stages of extraction and processing, the stage of measurement used in this chapter is what is normally termed "mine output." It usually refers to minerals or ores in the form in which they are first extracted from the ground, but customarily includes the output from auxiliary processing at or near the mines.

Jan 1, 1988

By M. E. Ryan, C. L. Hoebbel, E. J. Haas

DISCLAIMER The findings and conclusions in this paper are those of the authors and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. Mention of any company or product does not imply endorsement does not constitute endorsement by NIOSH. ABSTRACT It has been suggested that effective disaster prevention and response in mining requires that elements of emergency management be incorporated into everyday operations, planning, and decision-making, much in the same way that the industry approaches routine risk management. Since Congress passed the MINER Act in 2006, the newly mandated structural and technological advancements in mine emergency response preparation have been made and are apparent, but measureable improvement in mineworker emergency preparedness is difficult to ascertain. To begin exploring whether measurable indicators of mine workforce preparedness can or should be addressed within a risk management framework, NIOSH researchers examined the datasets from two separate research efforts—one which measured the organizational safety climate and self-reported safety performance, and the other which measured individuals’ perceptions of their own self-escape competency. INTRODUCTION In response to the mine disasters in 2006, the United States Congress passed the Mine Improvement and New Emergency Response Act (MINER Act), which strengthened existing regulations [30 CFR, Part 48] and introduced new provisions to improve mine emergency response. Since that time, new technological and structural features, such as mandated redundant communication systems, personnel tracking systems, and lifelines in primary and secondary escapeways, have been installed in underground coal mines across the country. Additionally, mine operators are required to develop emergency response plans, provide adequate supplies of breathable air throughout the mine, provide more frequent and realistic expectations training, and are required to immediately notify the Mine Safety and Health Administration (MSHA) in the event of an accident. While the structural and technological advancements in emergency preparedness are readily observable and easily measured, levels of individual mineworker preparedness remain difficult to assess. There is a general consensus that deficiencies in competence in the non-routine tasks required for individual miners to effectively respond to a mine emergency likely remain (e.g., National Research Council [NRC], 2013), and NIOSH research continues address this concern (Haas, et al., 2015; Hoebbel et al., 2018). To maximize an operation’s capacity to effectively prevent disasters and/or respond to emergency events, it has been suggested that individual and emergency management efforts be incorporated into everyday operations, planning, and decision-making in much the same way organizations manage routine risks to health and safety (Haddow et al., 2017). To the authors’ knowledge, the mindful intersection of routine risk management policies and practices and emergency prevention and response readiness have yet to be empirically studied within the mining industry.

Jan 1, 2019

By M. J. Papo, A. Muwila

Hercules? is a low nickel austenitic stainless steel developed at Mintek that has a typical composition of 9 wt% Mn, 0.05 wt% C, 2 wt% Ni, 0.25 wt% N and 16.5 wt% Cr. A more corrosion resistant version of Hercules? (Hercules? B) with 0.5 wt% Mo has also been developed. Potentiodynamic tests performed on Hercules? B in a 5 wt% sulphuric acid solution showed it to have improved corrosion resistance comparable to that of AISI 304. The effect of a varying Mn content on the corrosion resistance of Hercules? B has also been investigated and the results discussed in this paper. From the corrosion test results, it is clear that decreasing the Mn content of Hercules? B increased the corrosion rate while increasing it decreased the corrosion rate. KEYWORDS Austenitic stainless steel, %ferrite, molybdenum, manganese, nitrogen, electrochemical corrosion tests, potentiodynamic scans, microstructure, chemical analysis.

Jan 1, 2006

By A. Wright, P. Lacombe, R. del Villar, D. Hodouin, C. Sepulveda

"The data acquisition from industrial plants is a fundamental step for process modelling in process optimization, process analysis and automatic control.The introduction, some years ago, of modern distributed control and data acquisition systems in concentrators imposes a new approach in designing experimental schemes for data acquisition campaigns and new criteria for the treatment of the obtained discrete information.This paper presents the methodology applied to sample a zinc flotation circuit at Les Mines Selbaie, Joutel, PQ. Values of 85 process variables were obtained form the Distributed Control and Data Acquisition System (Bailey Network 90) and transferred to the DOS environment. Another 11 variables (flowrates and valve positions) were directly sampled using an IBM-PC compatible computer equipped with a data acquisition card and a signal processing circuit.All variables, under the vector form, were processed in the PC-MATLAB environment to either filter or eliminate the non-linear disturbances and noises, producing useful data for model development. The filtering algorithms are also presented.INTRODUCTIONProcess control does not need to be justified. Whether manual or automatic, any processing plant requires some form of control to accomplish its main objectives: a good quality product and a target throughput. Process control of mineral processing plants has steadily evolved from manual control, where the operator skills and/or experience play an important role, to some level of automatic control, usually considered better, as less human subjectivity is involved, at least when actions have to be taken.The design of these control systems requires the knowledge of the dynamics of the process it is deemed to control. Process modelling is therefore an essential step in the assessment and the design of a control strategy. The choice of model will depend on the available resources and manpower."

Jan 1, 1991

By J. Talja

Keywords: drying, steam drying, concentrates, copper, lead During the past twenty years steam drying has become a prominent technology for drying of non-ferrous metals concentrate. This is mainly because of its low energy consumption and very low emissions. The first applications of significant capacity were stationary steam dryers, which however, faced severe challenges in maintenance costs and availability. That technology was soon replaced by Kumera?s rotary steam drying technology, which has been the dominant technology in new dryer installations world-wide for the past ten years, ever since the first installation in Hamburg in 1999. There are ten Kumera steam dryers in operation today and five more to be commissioned during 2011. Practically every dryer is different owing to continuous development, new innovations and operational experience with continuous feedback from the operators. Most significant improvements relate to capacity increase with the Kumera steam-dryer family, new feeder systems at the wet end, a completely new design of the dry material discharge with increased availability, heating element design and material selection, and control systems. This paper discusses the modifications and improvements introduced which have enabled the Kumera steam dryer to become the global leader in new dryer installations.

Jan 1, 2011

By Maya Kamenetsky, Khoi Nguyen, Natalee Bonnici, Steve Walters, Claire McMahon, Julie Hunt, Ron Berry

"The analysis of meso- and micro-scale textural attributes has been undertaken on ore samples from the Ernest Henry iron oxide-copper-gold (IOCG) deposit in NW QLD. Quantified textural data including grain size, shape and mineral association have been extracted from classified images of core with the aim to better predict potential mineral processing behaviours such as comminution, liberation and flotation. Data have been extracted from images of intact core at meso- and micro-scales using high resolution continuous images collected using automated core-logger technology, SEM-based and optical microscopy platforms.The results of this study will show examples of quantified size, shape and mineral association data from meso- and micro-scale classified images. Analysis of the data shows that there are domains of variable grain size and mineral association that can potentially be related to crushing and liberation behaviour. The trends that are observed at the drill-core (meso-) scale are consistent with those at the micro-scale. The results from the micro-scale analysis show that the domains defined at the core-scale have clearly different chalcopyrite sizes and shapes as well as variable bulk mineralogy.INTRODUCTIONInnovations in technology have allowed automated extraction of information about mineral shape, grain size and mineral association, i.e., texture, from meso- and micro-scale images of intact rocks. The overall aim of this research is to investigate trends in quantified textural data that can potentially give an early view of processing parameters such as predicted grind size and liberation behaviour."

Jan 1, 2009

By Gary Anderson

??Privately Held Corporation ??Incorporated in Delaware, May of 2002 ??HQ in Malvern, PA (just outside Philly) ??Approx 40 employees ?9 Field Engineers ?MSHA Certified ?10 Development/NOC Engineers ?Site Survey/Site Design ?RF Engineers ??Standards Based ?IEEE 802.11 ??Commercial Off the Shelf (COTS) ?Gateworks, Ubiquity, Atheros, Linux Based ??Technology was developed and inspired by the lack of communications during the terrorist attacks of Sept. 11, 2001

May 1, 2009

By Sylvain Létourneau

Help organizations maximize the benefits of the data that they collect ? perform scientific research in: machine learning, data mining, statistics, artificial intelligence, soft computing, information retrieval, information systems, and natural language processing ? preferred application areas: Equipment Health Management, Bioinformatics, Health, Web Mining ? today?s talk limited to Equipment Health Management While the aircraft is still in the air, IDS: ? clusters relevant WRN, FLR, and snag (pilot) messages ? identifies probable causes based on TSM and provide links to corresponding TSM pages ? assesses MEL conditions (GO, NOGO, GOIF, ?) ? displays relevant maintenance history, suggests fixes based on similar cases ? Commercialization with MxI Technologies Ltd and Air Canada in 2000

May 1, 2008

By S. L. Gerhard

In the United States the performance characteristics of permissible explosives are controlled by routine tests, which include firing the explosive into a gallery filled with a methane-air mixture. These tests are made by the staff of the Explosives Division of the Bureau of Mines and, are similar, in general, to those employed in other countries. This control has helped to reduce the frequency of accidents involving the ignition of firedamp by explosives but has not clarified the basic causes, of the ignition. To advance this control and to minimize potential hazards further, this fundamental knowledge is needed. Some of the results of recent research on the causes of the ignition are described herein. NATURE OF THE PROBLEM When an explosive ignites firedamp in the gallery tests, the source of the ignition must be one or more of the emissions from the steel borehole. It has been accepted generally that these emissions are (1) particles, (2) the shock wave, and (3) hot gases and flames. Photographs show that the shock wave emerges from the borehole first, followed closely by hot gases. At first the velocities of these are high and approximately equal, but the velocity of the gases decreases more' rapidly than that of the shock wave, and by the time the reactions causing the flame are complete the shock wave travels in an otherwise undisturbed medium. The particles are originally enveloped in the hot gases but some soon begin to break through and eventually out-distance the shock wave. The approximate geometry of these emissions about I millisecond after the shpt is fired is illustrated in figure

Jan 1, 1939

"Research on the control of exposure to respirable contaminants in mine atmospheres is conducted in five areas; 1) control of dust generation, 2) dilution, dispersion and collection of dust in mine airways, 3) characterization of dust particles, 4) interaction of dust and lungs, 5) relationship of mine environment, geology, and seam characteristics to dust generation and mobility. The distribution of research findings to the mining industry, to government agencies, and to scientists at other universities is accomplished in several ways.A data bank of respirable dust samples displaying a wide range of characteristics (low volatile, medium volatile, high volatile, silica fireclay, rockdust) has been established by the Center. This data bank is being utilized by Center researchers in a suite of medical, scientific, and engineering tests (FIGURE 26).The Center has honored requests for educational and informational materials from several sources, including MSHA and CANMET who received information on Center generated software and used the Center's expertise in developing a computer program for particle distribution model (DISFIT).The Generic Mineral Technology Center for Respirable Dust has organized two dust conferences on respirable dust, the Coal Mine Dust Conference, held at West VirginiaUniversity, Morgantown, West Virginia from October 8-10, 1984 and Respirable Dust in the Mineral Industries: Health Effects, Characterization and Control, an international symposium on Respirable Dust in the Mineral Industries held at The Pennsylvania State University, University Park, Pennsylvania from October 14-16. 1986. These conferences were co-sponsored by the U.S. Bureau of Mines, Mine Safety and Health Administration, National Institute for Occupational Safety and Health (NIOSH), and the American Conference of Governmental Industrial Hygienists (ACGIH). On August 23-26, 1988, the VIIth International Pnuemoconioses Conference was held in Pittsburgh, Pennsylvania. While not a sponsor of this conference, researchers in the Generic Mineral Technology Center for Respirable Dust had significant participation with sixteen (16) papers presented (see Volume 8 of this series for abstracts and papers). These conferences provided a significant forum for the exchange of ideas on dust research and the interchange of research findings. The proceedings from these conferences are available from NTIS and ACGIH.In sum, significant benefits to mine worker health have resulted and should continue to result from the synergistic scientific, engineering, and medical research in respirable dust (FIGURE 27). As always, an important objective is the rapid dissemination of the results of this research to industry. Video tapes and the Bureau's Technology News series have been a very effective means of USBM technology transfer. Individual no-cost subscriptions to the Technology News series are available from the U. S. Bureau of Mines, Branch of Technology Transfer, 2401 E Street, N.W., Washington, DC, 20241."

Aug 31, 1989

By A. Frits van Tol, Rodriaan Spruit, Jan H. van Dalen

"Abstract In recent years, there have been major problems with deep excavations in urban areas supported by diaphragm walls. In some cases, like the fatal Nicoll Highway collapse in Singapore the quality of the D-walls was not the cause. However in other projects, like the problems with the major leak in the walls of the Boston Big Dig and with leakage in a few projects in Belgium and The Netherlands was related to poor D-wall quality. Leakage through the D-walls at the joints in deep excavations led in these cases to very serious settlement behind the walls, in the case of the North- South line in Amsterdam, there was severe damage to historical buildings. This paper describes ongoing research that focusses i on acquiring more knowledge on and improvement of D-wall installation, in particular the flow process prior and during casting ii on the detection of anomalies prior to excavation and iii on the composition of the concrete mixture in view of a better and more sustainable concrete quality of D-walls.INTRODUCTIONIn the case of deep excavations in urban areas close to neighbouring buildings, diaphragm walls are one of the best feasible solutions for the retaining structure. Although the costs of D-walls generally exceed the costs of alternative wall solutions, the advantages are decisive in many situations. The main advantages of D-walls are the limited impact of the installation on the built environment, the high stiffness and bearing capacity and the retention of water, even at considerable depths. This makes Dwalls often the preferred solution for deep excavations Sometimes the D-walls are the temporary support while for the final stage a complete concrete box is constructed in the excavation. In many other cases the D-wall has the permanent function of retaining soil as well as groundwater.In the last ten years, there have been major problems with deep excavations in urban areas supported by diaphragm walls. In some cases, like the fatal Nicoll Highway collapse, 2004 , the quality of the Dwalls was not the cause. In other important failures like the collapse of the Archives in Cologne, 2008 and Dubai Infinity Tower Flooding, 2007 a combination of design and quality issues played a role. However, the major leak in the walls of the Boston Big Dig was related to poor D-wall quality (McNichol, 2000). Van Tol et al, (2010) describe a number of case studies in Belgium and the Netherlands, with leakage through the D-walls at stop end joints. In several cases with deep excavations these leakage caused serious surface settlements behind the walls. In the case of the North-South line in Amsterdam, there was severe damage to historical buildings. All these cases have generated considerable additional costs and delays, and subsequently public and political concern. Van Tol et al. (2010) present several possibilities to improve the quality of D-walls.Other disputes related to D-walls deal with the quality of the concrete and the sustainability of D-walls applied as a permanent wall. In particular the porosity of the concrete cover is sometimes problematic."

Jan 1, 2014

By S. M. Spottiswoode

Much as one hopes to predict whether damaging seismicity might occur somewhere in the next shift, this is not possible at present. Recently, an analysis of seismicity at two mines has shown that a small increase in seismicity occasionally occurs before both large and small events. This analysis is extended here to five mines, with the same results. Earthquake seismologists forecast hazard in terms of the average incidence of earthquakes over the last 50 years, adjusted on an hourly basis according to the possibility of aftershocks of events that have happened. The rate of seismicity in any area remains approximately constant when expressed as seismicity per area mined, or better still, per unit of elastic strain energy released. It is suggested that seismic hazard in mines be estimated using historical seismicity and forward modelling, adjusted according to the possibility of aftershocks. In summary, medium-term forecasting of seismicity is viable; short-term prediction of large events is not.

Jan 1, 2010

By D Craw, D Wilson, D Chappell

Gold is extracted by cyanidation of a sulphide-rich concentrate at Macraes mine, and after cyanidation, the concentrate is discharged to tailings impoundments. The concentrate tailings were discharged to a dedicated concentrate impoundment from 1989 to 1993, afterwhich they were blended with the flotation tailings. Since mid-1998, concentrate tailings have been redirected to the dedicated concentrate impoundment. The concentrate tailings contain up to 1 ppm gold, and will be reprocessed in the future. However, it is a regulatory requirement that a contingency plan be in place to rehabilitate the concentrate tailings should the mine operation cease for any reason. Initial predictions suggested that the sulphide-rich tailings would oxidise and acidify, creating a potential long term environmental problem. Investigations of the state of the tailings after 4 years show that these predictions were overly conservative. Only minor oxidation has occurred in the upper 2 metres of the tailings where the pH has locally dropped from 10 (discharge condition) to between 7 and 8. Below 2 metres, the tailings are essentially unchanged from their deposition state. The low rate of change in the tailings is due to their very low permeability which in turn is a consequence of the fine grain size (ca. 15 ¦m). Dewatering is extremely slow, and incursion of oxygenated water is negligible. Calculations suggest that water movement over 30 m will take at least 100 years and possibly 1000 years. The contingency plan is to capitalise on the very low permeability and keep the tailings from drying with a semipermeable cap. A layer of limestone will be added to the top of the tailings, beneath the cap, to enhance alkalinity of any percolating water. If acidification does occur, contrary to expectations, any acid produced will be neutralised by underlying calcite-bearing schist, schist in the concentrate impoundment wall, and the flotation tailings immediately downstream. In addition, dilution by alkaline ground and surface waters would further ameliorate any acidic discharge.

Jan 1, 1998

By J. Tanner Blackburn, James R. Gingery, Lisheng Shao

Rigid inclusions consist of grout columns installed using displacement auger or vibrated tooling. The columns are typically installed in an array to provide support for footings, mats, or embankments. Due to the relative small column diameter and low replacement ratio, the surrounding soils typically have minimal densification or improvement. A gravel load transfer platform is commonly used above the rigid inclusion head to distribute stresses more broadly to the supported structure. The axial stiffness and geotechnical engineering mechanics of rigid inclusion design are similar to those of deep foundation systems, but they are typically only lightly- or un-reinforced and are not structurally connected to the above-grade structure. The popularity of rigid inclusions is increasing in the Western U.S., where many urban areas are subject to moderate to high seismic hazard levels. However, the performance of rigid inclusions under seismic loading is poorly understood, and seldom addressed in current designs. The elements are brittle, with limited or no ductility and relatively low moment capacity, and therefore may be prone to damage under seismic loading. Three modes of seismic loading should be considered: inertial loading from the structure, kinematic loading from vertically propagating shear waves, and kinematic loading from ground failure- related permanent ground deformation. This paper focuses on the first two modes. A simplified procedure for evaluating kinematic and inertial loading of rigid inclusions is described, and its use is illustrated through application to a site in Southern California. The results show that moderate to severe kinematic loading can generate plastic hinges in the rigid inclusions. Engineering consequences of this hinging could include settlement or bearing failure. INTRODUCTION In this paper the term ‘rigid inclusion’ (RI) refers to grout or grouted aggregate columns that are installed using either drilled or vibration displacement techniques. They are commonly installed in arrays to support vertical loads from footings, mats, or embankments. RIs are not structurally connected to footings they support. Rather, it is typical for a dense gravel load transfer platform (LTP) to be installed as a cushion between the RI head and supported footing or new fill. In cases of RI support of fill embankments, the LTP may be reinforced with horizontal layers of geogrid.

Jan 1, 2018

By Edward A. Barrett, Roberta A. Calhoun

Introduction This Instructor’s Copy contains most of the information needed to use the Wearing Hearing Protection Properly 3-D training reel. It offers practical suggestions on how to use the reel as a training aid, performance objectives for deciding if the training is appropriate for your needs, and discussion notes that provide additional information to the user. The 3-D reel was designed as a self-teaching aid that drillers and others who work at a drill site can use wherever the opportunity for such training presents itself. The latter could be a company preshift requirement or a tailgate session where workers would have an opportunity to view and discuss the reel. It could also be an individual looking at the reel in a pickup truck prior to beginning work at a drill site. The 3-D training reel is versatile in that it can be used for a small group of persons or for a single worker. For any of these situations, information is transferred to the individual by viewing each of the seven colorful, in-depth 3-D scenes and relating the words that appear in each scene to what is depicted in the visual. Acknowledgment The authors thank Linda J. McWilliams, Statistician, NIOSH Pittsburgh Research Laboratory, for her assistance in analyzing the experimental data in this document.

Jan 11, 2004