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By W. Z. Choi

In our previous work, a population balance model describing the simultaneous processes of size reduction and mineral liberation has been developed. The experimental verification of this model, however, has been limited to a binary mineral system containing only one composite particle class. When considering multiple classes of composite particles, the estimation of model parameters becomes much more difficult. In the present work, a procedure for estimating model parameters for a multiple composite class model has been developed. Emphasis is placed on the direct experimental determination of these parameters. The physical significance of the breakage rate function and the liberation function in characterizing the liberation process is also discussed.

Jan 1, 1987

By B. DANIEL MARJAVAARA, I. A. SOFIA LARSSON, ANNA-LENA LJUNG

The flow field and coal combustion process in a pilot-scale iron ore pelletizing kiln is simulated using a computational fluid dynamics (CFD) model. The objective of the work is to investigate how the thermal effects from the flame affect the flow field. As expected, the combustion process with the resulting temperature rise and volume expansion leads to an increase of the velocity in the kiln. Apart from that, the overall flow field looks similar regardless of whether combustion is present or not. The flow field though affects the combustion process by controlling the mixing rates of fuel and air, governing the flame propagation. This shows the importance of correctly predicting the flow field in this type of kiln, with a large amount of process gas circulating, in order to optimize the combustion process. The results also justify the use of down-scaled, geometrically similar, water models to investigate kiln aerodynamics in general and mixing properties in particular. Even if the heat release from the flame is neglected, valuable conclusions regarding the flow field can still be drawn.

Apr 20, 2021

By Rafael C. Castro, Paul V. Savard, Kathleen M. Murtagh

Preliminary design is underway for the Massachusetts Water Resources Authority’s (MWRA) next major tunnel program, the Metropolitan Water Tunnel Program (MWTP). The MWTP is the latest part of MWRA’s ongoing efforts to achieve redundancy for its metropolitan water transmission system including its historic deep rock City Tunnel, City Tunnel Extension and Dorchester Tunnels. The MWTP comprises several deep rock tunnels that will be approximately 10-foot to 12-foot finished diameter totaling just over fourteen miles long and ten connections to existing large diameter surface piping and pumping stations. This paper will present an update on current engineering and permitting efforts, packaging schemes, and the schedule to complete the MWTP.

Jun 13, 2023

By Denis Tepavac, Mark Trim

Structural performance of fiber reinforced concrete (FRC) depends on its ability to carry tensile forces after cracking. Australian Standards AS5100-2017 and AS3600-2018 are the only available design standards that establish a test procedure to determine strength and toughness of an FRC in direct tension. Direct tensile testing of fiber reinforced shotcrete samples was performed to determine if the model and guidelines in AS5100/3600 were applicable to shotcrete; all previous testing was from cast samples. In addition to direct testing, micro CT-scanning was also performed. The paper presents tests performed, results, and how the tests could be used on future projects. In addition, a brief summary is provided of the guiding structural mechanics used for estimating residual tensile strength and test methods utilized to verify those estimates.

Jun 13, 2023

By Justin Brown, Michael Kobler, Dave Ragland, Bob Shufflebotham

PROJECT OVERVIEW As the sun-bronzed San Diego students strolled casually to class, mining crews from Atkinson Construction were working only 9 meters below the surface. The330 meter long, 11.3 meter diameter squat ellipse NATM tunnel is part of the9.3 kilometer Mission Valley East Extension Light Rail Transit (MVE-LRT) being constructed for the San Diego Metropolitan Transit Development Board (MTDB). The SDSU segment of the MVE-LRT was awarded to the Clark Construction Group, the parent company of Atkinson Construction for $82.7 million. URS CORP was the prime designer and Hatch Mott MacDonald performed the NATM tunnel design. The construction managers were Washington Infrastructure Services with Underground Construction Managers, EPC Consultants, and ILF Consultants. A NATM tunnel design was chosen as the most cost-effective way to minimize disruption of the university activities. The tunnel passes close to several buildings and directly below access roads, tennis courts and a baseball field. The NATM method of conventional mining uses shotcrete for ground support often reinforced with steel orplastic fibers, welded wire mesh and lattice girders. The tunnel runs from a cut and cover box up a 4.2% grade in a 217 meter radius left-hand curve with several spirals and ends at the underground station 330 meters away. The depth of cover varies from 16 meters near the west portal to nine meters at the station. The design called for a two-pass system with a primary lining of 300 mm shotcrete with lattice girders at 1 m centers and two layers of welded wire mesh. The lattice girders are used primarily for profile control and are not considered a structural element. The top heading was designed to be excavated in one of three excavation sequences depending on ground conditions and depth of cover. In sequence one excavation, the top heading is excavated in two halves with a one-meter separation. In sequence two excavation, a side gallery is advanced 8 or more meters ahead of the

Jan 1, 2003

By Mike Moody

"No matter what type of ore is being extracted from a mine, mucking with front loaders can be accompanied by wet fines that cling to every surface. Once loaded into a hopper or conveyer transfer chute, viscous material can quickly build up on the walls to create bottlenecks, clogging the chute and causing expensive downtime.Clearing material from hoppers, chutes, bins and vessels can be done using manpower and tools on hand, but safety experts recommend considering a solution that prevents exposing workers to potential hazards. Operators at modern mining sites, such as the Eagle Mine, located in Western Marquette County of Michigan’s Upper Peninsula, understand that using specialized equipment reduces worker exposure, offers the safest mode of production and provides the most cost-effective lasting results.“Safety is a top priority for us,” said Ted Lakomowski, lead reliability technician at the Eagle Mine. “When we experienced clogging and downtime at the processing mill, the crew naturally swung into action to resolve it, but we immediately sought a safer long-term solution.”Stope mining for nickel and copperOwned by Lundin Mining, a globally diversified base metals mining company headquartered in Toronto, ON, Canada, the Eagle Mine is the only primary nickel mine in the United States, producing 1.5 percent of the world’s total nickel production. The first operation permitted under Michigan’s Part 632 Non-Ferrous Mineral Mining Law, it opened in 2014 and is expected to produce 163 kt (360 million lbs) of nickel, 134 kt (295 million lbs) of copper and small amounts of other metals over its estimated nine-year lifespan.The company extracts approximately 2 kt/d (2,200 stpd) from the underground nickelcopper mine using a bench-and-fill stoping process. Accessed from the surface by specialized underground trucks, the vehicles carry about 45,400-kg (100,000-lb) loads through a 1.6-km (1- mile) long and 5.4-m (18-ft) diameter ramp shaft descending into the earth at a 13 percent grade. Stoping is a bottom-up method that involves systematically blasting columns of loosened ore that is then mucked by front loaders into trucks and backfilled using cemented and uncemented rockfill."

Aug 1, 2019

By Richard Campbell, MEHMET KIZIL, Ismet Canbulat, Serkan Saydam

The design and effectiveness of ground consolidation to regain stability of longwall faces vary widely and are often based predominantly on-site precedence or what were considered successful applications at other sites in similar situations. Little is known regarding product migration characteristics or change in rockmass conditions as a result of the application of consolidation chemicals. This paper presents the in-situ testing rationale designed and implemented recently across several longwall operations in the Bowen Basin, Queensland, Australia to provide quantitative measurement of the actual zone of influence of various resin injection products. Product migra- tion was physically measured by monitoring the change in rockmass temperature as a result of the exothermic chemical reaction of the various strata consolidation chemicals used. In conjunction with strata coring and Lugeon transmissivity testing pre- and post-injection to characterise the improvement in rockmass conditions due to consolidation product injection. The results of the testing programme, migration measurements, and rockmass assessment are presented, along with a discussion on how site- based Rock Mechanics Engineers can incorporate the data into the design of strata consolidation plans.

Jun 25, 2024

By Blair K. Salisbury

Dissolution within Permian evaporites of the Delaware basin has created extreme lateral geologic and physical property inhomogeneity within and above the evaporites. Discriminating a sulfur deposit's geophysical signature from other variances is difficult. This is particularly true of porosity-dependent gravity and electrical methods. However, other techniques that detect alteration of strata above sulfur deposits may be applicable individually or in combination with other types of data. Relationships between sulfur deposits and gravity, magnetic, gamma radiation, spontaneous potential, and soil geochemical measurements are illustrated by data from several Delaware basin geophysical and geochemical surveys.

Jan 1, 1992

A virtual reality approach is presented that can aid entities such as mining companies and land use planners in communicating a visual understanding of a mining operation to interested stakeholders, citizens? groups, and public committees. These visualizations are particularly useful in permitting, production planning and mining closures, contributing to accurate communication and evaluation of mine plans, ultimate land use and evaluation of potential design options A case study is presented, that was created using commercially available virtual reality tools, to emphasize the benefits of visualization technologies in the sustainable development of mineral resources.

Jan 1, 2003

By Dennis N. Poffenroth

One concern of the Mine Safety and Health Administration is the structural integrity of steel wire ropes used on mine personnel hoists and elevators. Failure of such ropes has resulted in loss of life and property. Although thorough and regular visual examinations are performed, hoist ropes may still fail from undetected internal wear, corrosion, and broken wires. To complement visual examinations, nondestructive rope inspection techniques have been developed to determine deterioration and removal criteria. The techniques use electromagnetic and permanent-magnet test instruments designed by a Canadian firm. This paper describes the operating principles, field and laboratory testing of these nondestructive testing instruments, and discusses the feasibility of using this type of testing as a supplement to visual examination and destructive tests.

Jan 1, 1983

By Stephen Njoloma, Ivan Hee, Ravi Jain, Mina Shinouda

"INTRODUCTION DC Water’s First Street Tunnel (FST) is comprised of a collaborative effort between DC Water, DC Water’s Project Consultants Organization (PCO) led by Greeley & Hansen and McMillen Jacobs Associates and the design-build team of Skanska, Jay Dee, and Parsons Brinckerhoff. The fast-track project includes elements that were designed by the PCO and released for construction by DC Water prior to Notice to Proceed (NTP) and elements designed by the Design-Builder from 30% to released for construction after NTP. This required effective communication and technical coordination for integrated engineering and efficient construction. The project, constructed in an urban residential neighborhood, included innovative construction methods such as multiple location ground freezing, utilizing a centralized freeze plant, to minimize community impact. The means and methods chosen for cast-in-place shaft linings, precast segmental tunnel lining, microtunneling, sequential excavation method (SEM) adits and near surface elements reflected the immediate and sensitive surroundings, which varied by construction staging area (CSA). Technical aspects of the project, relative to the evolution from pre-bid to construction documents, are discussed along with modified designs to suit means and methods. SCOPE OF WORK In 2012, four major storm events swept through the District of Columbia and hit the Northeast Boundary sewer shed particularly hard with the neighborhood experiencing severe flooding. The extreme nature of the flooding, the damage to private property, and the health risks associated with exposure to sewage led to a multi-agency response and community calls for answers and action. The Mayor assembled a Task Force to evaluate a range of potential actions to address combined sewer flooding including engineering, regulatory, code revision, and management improvements. The Northeast Boundary Neighborhood Protection Project was the outcome of the Mayor’s Task Force; it is a three-step infrastructure initiative designed to offload the undersized sections of the existing collection system that serves the Northeast Boundary drainage area by implementing the McMillan Stormwater Storage Project, First Street Tunnel Project and the future Northeast Boundary Tunnel Project. Until the Northeast Boundary Tunnel Project is completed, the First Street Tunnel Project will add 8 million gallons of combined temporary sewer storage in a new tunnel under First Street NW to relieve undersized sewers that traverse the Bloomingdale neighborhood."

Jan 1, 2016

By Antonio Tafra, Rene Dominguez, James Spenceley, Brady Hays

"Extracting one of the world’s most valuable natural resources — copper — hinges on the availability of the world’s most essential resource: fresh water. But try sourcing fresh water in one of the driest places on Earth, Chile’s Atacama Desert.BHP, majority owner of the Escondida copper mine in Chile’s Antofagasta region and Minera Escondida Limitada (MEL), operator of the mine, were looking for sustainable solutions to deliver desalinated water to the mine, while protecting the environment and complying with the local water authorityregulations.The mining giant chose Black & Veatch to solve this challenge.Solving a global miningchallengeMines use large quantities of water for mineral processing and metal recovery. Water supply, and not mineral ore, is often the major constraint to mining production and development of projects, especially in Chile. Mining operations must have a reliable water source that complies with local regulations, without adversely impacting the environment or affecting the water supply of nearby communities.Worldwide, mining companies and their owners, shareholders and regulators are placing new levels of focus on minimizing the impact of mines on the surrounding landscape and communities. Balancing the economic benefits and needs of mining operations with the potential freshwater impacts requires mines to pay serious heed to the environmental and social issues related to water. Today, mining companies are being proactive and are taking action to protect precious freshwater resources while seeking opportunities to reduce and mitigate their water impact.Delivering a desalination solutionBHP and MEL needed an efficient, technologically advanced seawater desalination plant, along with a conveyance system and infrastructure that would carry desalinated water more than 180 km (112 miles) from the ocean to the mine. Four pumping stations convey the water to a reservoir at the mine site, which is 3,200 m (10,500 ft) above sea level."

Jan 6, 2018

By C. Vasilescu

Phytotechnologies use plants to remediate various media impacted with different types of contaminants. These technologies can be implemented either in situ or ex situ. The affected media in which phytotechnologies can be applied include soil, sediments, groundwater and surface water. They are best applied at sites with shallow contamination of organic, nutrient, or metal pollutants that are amenable to one of five treatment options: phytoextraction, phytotrans-formation, rhizosphere, bioremediation, phyto-stabilization or rhizofiltration. Phytoremediation can be used along or, in some cases, in place of mechanical cleanup methods. Phytoremediation can be used to clean up metals, pesticides, solvents, explosives, crude oil, polycyclic aromatic hydrocarbons and landfill leachates.

Jan 1, 2006

By S. K. Kawatra, J. E. D. McDonald, S. C. Roache

"The formation of geopolymers from mine tailings using cold-bonding processes is known to be possible. Numerous cold-bonding methods exist, but the hydrothermal processes involving high temperatures and pressures in the presence of steam have been found to be the most ideal. This paper presents the results of successful preliminary studies to apply hydrothermal bonding processes to mine tailings agglomerates. Particle-size analysis revealed the particle size of the tailings waste to be 80 percent passing at 35 µm. The compressive strengths of the tailings pellets were shown to increase with time in the curing vessel, closely approaching the 400 lbf of standard iron ore concentrate pellets. These strengths are sufficient to allow use of the tailings pellets as aggregate materials for asphalt and cement. Additional applications may be possible, including reprocessing to extract more valuable materials and usage as agglomerated road-bed materials, backfills for building foundations, and replacements for sand and lime in cement.IntroductionMine tailings are a waste byproduct of ore concentration and are available in large quantities across the world. Despite their abundance, they have received little attention or consideration for beneficial use. One reason is that the chemical nature of the material is not well known. Another factor that has hindered direct usage is the fine particle size. This raises the questions: what is the composition of the tailings, and how can such fine solids be beneficially used? Because the mining industry produces concentrates, the tailings may be treated as concentrates and processed in the same fashion, but it would be inefficient to consider full sintering or induration conditions for materials that have little ore content. To achieve sustainable operation, the development of technologies to use these tailings is necessary. Mine tailings should not be considered waste, and an “out of sight, out of mind” mentality does not represent a sustainable solution for the future.One iron ore mine in Michigan is estimated to have accumulated more than 400 million metric tons of tailings during its last 30 years of operation, with an additional 180 million metric tons accumulated before the ore body is depleted. These mine tailings currently have no practical use, largely due to a scarcity of knowledge of their true physiochemical nature. It is thought that lack of quality control of the waste material prevents its use, but variability in the unprocessed ore prevents a consistent waste stream composition. The fact that the tailings are available in such great quantities makes them an extremely attractive resource. However, developing a sustainable, low-cost means of repurposing the mine tailings waste as a construction material may only be completed once the tailings are physically and chemically understood. Due to the high silica content of the material studied, cold bonding was determined to be the most viable method for processing the tailings into a usable product."

Jan 1, 2016

By W. M. Aubrey

The use of solid fuel in shaft furnaces to indurate iron ore pellets was originally considered a necessary evil, which the industry worked long and hard to eliminate. Since then changes have taken place in furnace design and operating practices that have led us to our suggestion that solid fuel additions could again be used. In essence, what has happened is that the developments which made it possible to operate without solid fuel have also created new operating conditions favorable to the effective use of solid fuel. Because these new conditions* were brought about in part by the desire to eliminate solid fuel and because the development was a gradual one, the industry failed to reassess its position and for years neglected the possibility of returning to solid fuel.

Jan 1, 1967

By A. Konya

"INTRODUCTION Underground Mining and Construction projects face several challenges unique to the underground environment compared to the surface environment. The goals of an effective blasting program are the development of a blast pattern that minimizes cost, maximizes face advance, and provides the desired fragmentation and face profile. In addition to these , mines must consider the very real operational problems that occur such as drill deviation, ground vibration, and deadpressing or sympathetic detonation of explosives. These operation problems lead to increased costs and decreased production in the mine, hurting the bottom line. Combined with these problems, underground blasts can be difficult to monitor and evaluate due to tight spaces, dust during the blast obscuring video, and the need to evacuate the immediate area with no clear line of sight to observe performance. This creates an environment which most mines know that blasting can be improved in their underground operations, yet most are hesitant to change due to fears of the shot freezing, misfires occurring, and questions about how to achieve a proper design. The explosive companies and shot service providers also offer limited assistance or knowledge in the underground blasting realm, unlike with surface blasting, leaving many underground operations in the dark. It is for these reasons that most underground operations are operating decades behind the current technologies and incurring significant costs, both real and hidden, from there blasting operations. This paper discusses philosophical changes to designs that need to be made for effective design and modifications of underground blast patterns to prevent deadpressing and precompression of modern explosive products (Konya, Konya, & Worsey, Modern Blasting Method Selection, 2017). While numerous different methods of underground heading development exist, there are two types that are used in a majority of mines around the world, these are the burn cut and the V-cut. The burn cut is a parallel cut that has holes that go straight into the face and are primarily used in smaller opening (due to ability to pull deep rounds with smaller room widths) and metal mines (helps in ore dilution and greater fragmentation). The V-Cut is a cut that uses angled drilling towards the center of the face (in the traditional method) and is primarily used in underground aggregate operations due to its cheap cost but larger fragmentation sizes and greater throw of the muckpile. This paper will discuss these two forms of cuts specifically with the understanding that modifications to these can be applied to other parallel and angled underground heading techniques. BURN CUT The burn cut is one of the older forms of underground blasting, where a part of the blast (burn) of a shot is heavily loaded with additional empty (relief) holes with the goal of smashing (aka burn) and pushing/blowing all the material in the burn out to provide relief for subsequent blastholes. The relief holes in the burn cut provide a parallel relief for the holes that are firing to break too creating a second plane of relief, however these are extremely small and can cause many problems if a design is improper."

Jan 1, 2018

By Sathit Tandanand

Geological differences among various coalfields restrain the applicability of subsidence prediction using existing European methods. To modify these methods for domestic conditions, the Bureau of Mines, U.S. Department of the Interior, developed a method of assessment to evaluate the lithological effects on subsidence in the Northern Appalachian basin by examining data collected from 16 longwall panels in the coalfield. The assessment is partially completed, and the results to date show that the ratio of maximum subsidence to the extraction thickness, known as the subsidence factor, can be expressed in terms of the width-to-depth ratio by a simple exponential equation which has a coefficient tentatively considered as the subsidence index. This index varies with the lithology of a particular site and can be expressed in terms of the percent distribution of weak and strong rocks in the overburden.

Jan 1, 1982

By L. C. Lang

INTRODUCTION The introduction of 165-mm (61/z-in.) holes to underground mining operations has made possible the application of Canadian Industries Ltd's (CIL) vertical crater retreat (VCR) mining method, illustrated in the accompanying sketches. This unique and revolutionary new application of spherical charge technology (see the Appendix), when applied to primary stopes and pillar recovery, eliminates raise boring, slot cutting, and dilu¬tion of ore by backfill; greatly improves fragmentation; reduces labor and time requirements; eliminates uphole drilling and blasting; and minimizes or completely elimi¬nates damages by blasts to the walls and retreating backs of the stope or pillar. If vertical large diameter holes are drilled on a designed pattern from a cut over a stope or pillar to bottom in the back of the undercut, and spherical charges of explosives are placed within these holes at the calculated optimum distance from the back of the undercut and detonated, a vertical thickness of ore will be blasted downwards into the previously mined area. Repeating this loading and blasting procedure, min¬ing of the stope or pillar retreats in the form of horizontal slices in a vertical upwards direction until the top sill is blasted and the mining of a stope or pillar is completed. The VCR method is also applicable to drop raises and has the potential to replace all other raising methods under most circumstances. PILLAR RECOVERY Levack Mine Inco Metals Co., Ontario Div., provided the first opportunity for the method in pillar recovery. The Levack mine's high grade ore pillar No. 4800 on the 975-m (3200-ft) level was used for the production¬scale experiment (Figs. 1 to 3). The pillar was about 49 m (160 ft) long, 6 m (20 ft) wide, and 20 to 26 m (65 to 85 ft) high. The mined area on both sides of the pillar was backfilled with a 1:30 cement:sand mixture. The pillar was removed in two phases. In phase 1, the standard uphole method was used to blast down the 18-m (60-ft) long section of waste from the bottom of the ore into the undercut. From the pillar's top sill, 165-mm (61/a-in.) holes were drilled downward into the pillar, and by measuring the depth of the holes, the results of the uphole blast were determined and roof line 1 was established. The bottom of each hole was plugged, then filled with sand to place the center of gravity of each spherical charge (loaded from the top sill) at a predetermined optimum distance from the horizontal free surface. The charges were then detonated. After detonation, both draw drifts were full of extremely well-broken material. The depth of each hole was measured again, and the plot of these depths re¬sulted in roof line 2. The same blasting procedure was repeated and the resultant new back elevation was marked by roof line 3. The poor results of the initial uphole blast at one location (notice the peak in area 1) appeared to influ¬ence the subsequent new backs. A third blast success¬fully evened the back, and resulted in roof line 4. An unblasted slab averaging 6.3 m (20.9 ft) thick remained below the pillar's top elevation as the final sill. In all three spherical charge blasts fragmentation of the blasted material was extremely fine. The backfill was fully exposed on both sides of the now-blasted pillar. The backfill remained undamaged and the ore was not diluted by sand. The remnants of all the 165-mm (61/2 -in.) holes remained clean and undamaged, and the holes had well-defined bottoms that could be easily measured and plugged. Each blast took down a 3.9 to 4.2-m (13 to 14-ft) thick horizontal slab of ore. Productivity was three times greater than that of the previously practiced cut-and-fill method. Since this was the first such experiment, blasting the remaining 6-m (20-ft) thick final slab was the sub¬ject of some deliberation. If the described method was repeated, we could have ended up with a 1.8-m (6-ft) thick sill unsafe to work on. It was therefore decided to blast the whole sill using two spherical charges prop¬erly placed in each hole, but with the application of

Jan 1, 1982

By G. Kritikakis

Rehabilitation of sites contaminated by oil products and chlorinated organic compounds is a costly task which affects the planning of urban and infrastructure development. An integrated approach based on the non-invasive geophysical technology is utilized for subsurface characterization of contaminated land. In this approach the localized information, provided by chemical analysis of soil samples collected from bore-holes, is used for the calibration of the geophysical data. This information is subsequently extrapolated to the area under investigation by combining it with the geophysical results, providing thus information about pollution accumulation, contaminants? flow and pollution sources. Two case studies are presented from sites contaminated by heavy metals (Venice, Italy) and oil products (Athens, Greece). Resistivity, electromagnetic and seismic methods were used in this approach. Namely, electrical tomography, electromagnetic mapping, ground penetrating radar (GPR), multichannel analysis of surface waves (MASW) and seismic refraction experiments were conducted. In Italy, the sections from the multichannel analysis of surface waves imaged successfully a buried channel where the pollution is concentrated. Preliminary results are also discussed from the geophysical survey in Greece where the thickness of the oil phase located on top of the water layer is 60 cm.

Jan 1, 2006

By Joseph O. Cook

I know this is, at best, a frustrating period for the coal mining industry. About 20,000 miners have been laid off, mostly in the Appalachian and mid-western areas, and several mines are working less than 5 days a week; however, the industry is experiencing modern growth and, at least, there is the potential for future growth. The coal industry is probably only operating at about 80 percent of its present capacity, and it is certainly capable of helping this country solve its energy problems. Growth, as a rule, does not come easy, and growth in the coal industry is no exception to this rule. Many formidable challenges have to be overcome. As we all know, mining relies very heavily on the earth sciences, which have advanced significantly in the past few years, but we are always working in a changing environment which in most cases is a hostile environment. Large quantities of material are quickly extracted and rapidly moved in, generally speaking, a very confined area. The very nature of the mining business directly and constantly impacts our environment during this period in which the Nation and the world has become increasingly smaller and more concerned about protecting our environment. In addition, growth brings about an expanding work force which is increasingly younger and less experienced.

Jan 1, 1980