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By Stanley W. Ivosevic

The South-Central area of the Osa Peninsula, Puntarenas Province, on the Pacific coast of southern Costa Rica, may have produced on the order of 30,000 kg (100,000 troy oz) of gold since prehistoric times. The Peninsula lies along an 800- to 900-km-long belt of late Mesozoic eugeosynclinal rock deposition, hydrothermal activity, and deformation (Campanian). The oldest rocks exposed in the area are basalt and tuffaceous mudstone of the Late Jurassic or Cretaceous Nicoya ophiolite complex. The Nicoya Complex is overlain by weakly lithified Pleistocene Older Sediments, predominantly conglomeratic sandstone and derived from erosion of the Nicoya Complex. Erosion reduced the Complex to a surface of high relief, so that the detrital source was in the area originally; the source retreated with subsidence. Stratigraphically, the Older Sediments are followed by surficial deposits of intermediate age, consolidated Younger Sediments reworked from Older Sediments, and unconsolidated Holocene surficial deposits reworked from Younger Sediments. The most prominent structures are a northeast-trending anticline and northeast and northwest fault sets. Some deformation was Cretaceous, but folding and much faulting occurred after deposition of the Older Sediments. Remnants of plainlike features and destructional terraces on the Older Sediments attest to stepwise downcutting of the terrain during successive stages of uplift. Near the end of this process, the present valley floors and coastal headlands developed. During a probable epeirogenic rise in sea level, Younger Sediments filled the valley bottoms and an aggradational coastal plain developed. Sea level dropped by stages and with some reversals to its present position; this caused stepwise incision of the valley fill, stepwise beveling of the coastal plain, and development of the present wave-cut platform. Spilitization around the time of the Campanian orogeny caused some parts of the Nicoya complex to be calcitized and others to be silicified. Gold, pyrite, and probably additional silica were introduced during subsequent hydrothermal activity. Native gold was eroded from Nicoya Complex lodes and reconcentrated through three generations of placer gold deposits. First, the gold was deposited as a detrital.

Jan 1, 1977

By Edward A. Vitunac

The emerging importance of pneumatic conveying systems for bulk materials is becoming recognized by more persons responsible for materials management as consultants, at the corporate level and at the plant level. They have learned that the economic advantages of a pneumatic system are frequently decisive when compared to alternate methods. Included in these advantages are relative simplicity, ease of installation, flexibility, ease of maintenance, cleanliness, safety and ease of automation to the degree desired. In general, installed costs favor a pneumatic system when compared to competing mechanical systems if the transporting distances are long or to and from many points. In addition, supplemental use such as cooling, heating, or drying may supply the incremental value required to justify its selection. (1). The main disadvantages of a pneumatic system is the greater horsepower required per unit weight of material conveyed and material limits in abrasiveness and density. In addition, there is a tendency to increase material breakage at changes of direction and at any obstruction such as the imperfect butting of one, piece of pipe to another in the conveying line. Classification of the material at the discharge may also cause problems in dusting and segregation. Materials weighing less than 4 pounds per cubic foot tend to cause feeding and collecting problems although they can be conveyed easily. Material between 4 and 20 pounds per cubic foot can be handled with less problems but flow rate is hard to predict. The 20 to 60 pounds per cubic foot range offers best results; whereas, over 60 pounds per cubic foot, materials tend to drop out of the air stream and settle in the pipe line unless careful provisions are made to prevent it. (2).

Jan 1, 1967

By W. A. Haley

As far back as 1939 state laws have required reclamation of mined lands. Reclamation has been the topic of many discussions and presentations, especially since the late 1960's. In the past ten years many states have added legislation concerning the reclamation of coal-mined lands. In the near future, it seems certain that some federal regulations will be passed that will set minimum guidelines for the states to regulate. Besides the requirement of returning the land to the approximate original contour, future regulations will more than likely demand replacing topsoil from one to five feet thick. As regulations become more stringent, costs will rise accordingly. Since no one has developed a machine that can do all reclamation work by itself, it is necessary to review in detail the tools available and to select the most economical means.

Jan 1, 1976

By C. D. Broadbent

Open pit blasting can be a low cost routine or a high cost bottleneck depending on geology, environment and the operator's ability to master site conditions. Because blasting is a repetitive operation, there should be ample opportunity to optimize the process; but ordinarily this optimization is rarely achieved and then only if conditions remain consistent and predictable. Often, however, and particularly with porphyry coppers, hidden differences in rock characteristics nullify the operator's best efforts. At a porphyry copper deposit being mined by Kennecott Copper Corporation, there are all of the following rock types: oxidized and fresh porphyry, altered and silicified limestone, explosion breccia, rhyolite, sandstone, shale and several others. The units can cover large areas or be limited to a few tens of feet in maximum dimension. They are rarely visible on the bench surface and often do not show up in the bench slope. Even though the blastability of these rocks varies substantially, a generally-uniform blasting pattern was formerly used with disappointing results. Secondary blasting was often required and high bottoms occurred frequently; overblasting wasted drilling time, and explosives caused excessive throw. Several possible methods for improving the blast design were considered and a geophysical method was chosen for testing. There had been reports in the journals that seismic methods were being used in Europe as aids for blasting design. A literature search turned up work by Haxby 1/ on use of a refraction seismograph for measuring pit bench rock strength. Using his work as a springboard, equipment was purchased and a program was planned and carried out for developing, evaluating and implementing the seismic method for routine mine use. Following are discussions of the development program and results.

Jan 1, 1974

By Byron R. Berger

Disseminated Au-As-Hg mineralization is localized along the Getchell Fault system at the Getchell Mine in north-central Nevada. Replacement ore bodies occur in Cambrian carbonaceous limestone and limy shale beds. Cretaceous granodiorite, dacite porphyry, and andesite porphyry dikes parallel the fault zone and are spatially associated with the mineralization. Hydrothermal alteration and mineralization occur continuously along 4-5 km of the fault system, and extend more than 1 km down-dip. Alteration consists primarily of removal of carbonate and deposition of quartz, pyrite, and carbonaceous material. Marcasite, sericite, kaolinite, calcite, barite, and fluorite are common. Gold content reaches more than 43 ppm in parts of the altered zones and averaged 9.3 ppm in the mined ore bodies. For the mineralized zones as a whole arsenic averages 0.28%, and occurs primarily as realgar, orpiment, and arsenopyrite. Mercury (22 ppm) is finely disseminated and mercury-bearing minerals are seldom recognizeable. Accessory mineralization includes antimony (100 ppm), copper (47 ppm) , lead (18 ppm) , molybdenum (10 ppm) , tungsten (16 ppm) , and zinc (50 ppm) . Geologic field studies and K-Ar dating suggest that the mineralization is related to a hydrothermal system produced by the granodiorite and related dikes.

Jan 1, 1975

By R. Ribeiro

The designers of the new Arafertil concentrator in Brazil provided for complete automatic control of the grinding circuit to meet the operating objective of maximum throughput at a specified grind. Analog control methods were selected because of proven reliability and simple maintenance, and in order to minimize commissioning time and effort. This paper summarizes the step-by-step effort required to progress from local loop control of certain individual parameters to an integrated system capable of achieving the design goal. Emphasis is placed on the practical aspects of commissioning a control system.

Jan 1, 1979

By J. Richard Lucas

Today, the future of the coal industry is extremely bright because coal can be produced at a cost which makes it competitive with other energy sources. However, the industry has been forewarned that further cost reductions must be made if it expects to remain a serious contender in the growing energy market. Surface as well as underground operations must be improved. The very same elements which affected production a. few years ago still exist today and will continue to be present in the future. Improvement's in production mining equipment, mining methods, and auxiliary equipment have resulted in reduced costs over the past few years. Efforts must be continued toward further reducing costs in areas which have been improved previously, and new areas should be investigated for possible improvements. Therefore, new techniques must be developed which will enable the industry to augment its current efforts in reducing the cost of mining. The logical place to begin evaluating the factors affecting production and cost is in the immediate face area where a substantial part of the total cost of mining is incurred. The coal industry stands to gain much through the development of new techniques for analyzing the numerous variables affecting production and by establishing methods for eliminating or minimizing the adverse effect of those variables which can be controlled. Intuition and trial-and-error methods have been the standard means used to resolve many of the factors which influence production. As a result, many elements are overlooked or ignored because their effect on production is not pronounced and cannot be readily resolved. The need for a method of analyzing such factors was recognized by the Office of Coal Research. Therefore, in April 1962, under OCR sponsorship, a. research project was initiated at Virginia Polytechnic Institute (VPI). The objective of the project was to identify the factors which influence mining costs in the immediate production area, and to develop methods and techniques which will enable the coal operator to minimize production costs. The objective of the research at VPI has been successful, and techniques have been developed for establishing quantitative facts concerning the interrelationships of production activities.

Jan 1, 1965

By Ronald W. Marrs

Kimberlite contains a unique assemblage of minerals and exhibits a characteristic pattern of spectral reflectance in the visible and near-infrared wavelength region. This spectral pattern is readily discerned in well-exposed kimberlite outcrops, but becomes increasingly difficult to identify when outcrops are partially covered by vegetation or soils derived from non-kiaberlitic materials. Detection of poorly exposed kimberlite diatremes is possible using multispectral imaging techniques in which spectral bands are chosen to optimize contrast between he kimberlitic soils, non-kimberlitic soils and vegetation. Careful processing of the multi-spectral data is also essential in order to separate the spectral signature of kimberlite from the signatures of other components of the scene.

Jan 1, 1984

By E. J. Wasp

An upsurge of interest in slurry pipelines to move coal from Wyoming, Montana, and Colorado to markets in the southwest, west, midwest and northwest has recently developed. Specific pipelines have been proposed to serve these markets; the routes of these lines are depicted in Exhibit I. It is, therefore, timely to discuss some technical aspects of the terminal facilities for these western coal pipelines. The discussion will be based on experience with the Ohio and Black Mesa pipelines as well as detailed planning and testing for a proposed 1,000-mile system from Wyoming to the middle south area. The economics of the pipeline terminal processes are heavily depend¬ent on site, type of process used, and other specifics of the situation. However, the following approximate breakdown of costs for a 1,000 mile, large capacity pipeline will be useful for orientation purposes. [Water supply 4 Coal cleaning 5 Feed preparation 10 Slurry transportation 72 Dewatering terminal 9 100%]

Jan 1, 1976

By J. R. Schafler, J. L. Brinkman

"Since the year 2000, 59 miners have lost their lives to explosions occurring in underground coal mines in the US. More accurately, those explosions were methane ignitions that propagated through the mines due to coal dust involvement; despite current explosion prevention standards. There are 4 basic strategies employed to manage the risk of coal dust explosions in many other coal mining countries around the world: removal of the coal dust, wetting of the coal dust to prevent it from becoming airborne, mixing of the coal dust with stone dust to increase the total incombustible content, and explosion activated barriers which make the entire roadway inert. However, American standards only mandate the first 3 of these 4 methods. It is possible that US coal mine safety measures could benefit from the implementation of the 4th method, the use of explosion barriers. This paper will discuss differences/similarities in barrier regulations used in other countries, as well as some potential difficulties with adapting a stone dust bag barrier system to US underground coal mines. Also, details and feedback gathered from two operating mine site trial barrier installations will be shared.INTRODUCTION Since the year 2000, 59 miners have lost their lives to explosions occurring in underground coal mines in the United States (US); 29 miners were killed at the Upper Big Branch mine in 2010, 5 at the Darby Mine No. 1 in 2006, 12 at the Sago Mine also in 2006, and 13 at the Jim Walter No. 5 Mine in 2001.[14] To be more accurate, the explosions that killed those miners were methane ignitions that propagated through the mines due to coal dust involvement.[18, 19, 20, 21] These deaths occurred despite current explosion prevention strategies, standards, and regulatory oversight. This poses the question, can more be done in the US to prevent coal dust explosions and their widespread damage. In review of current practices and regulations from several large coal mining countries, a disparity in prevention strategies arose. The main difference between the US and other countries was that the US does not encourage, mandate, or regulate the use of explosion barrier systems as an additional coal dust explosion mitigation measure. This raised many questions. First and foremost was whether or not the US coal mining industry and its miners could benefit, in terms of safety and fatality prevention, from the implementation of the explosion barrier systems that are used in other countries. Furthermore, are there significant differences between the coal mines in countries where explosion barriers are used and US coal mines, which would preclude the system from being adapted and implemented in the US? Also, what are the similarities and differences in explosion barrier systems, use, and regulations between other countries that use them?"

Jan 1, 2017

By A. Cecala, J. Noll, J. Organiscak

Many underground metal/nonmetal mines are using enclosed cabs on mining equipment to reduce the exposure of miners to diesel particulate matter (DPM). However, some enclosed cab systems may not be meeting their expected efficiency in capturing DPM, which could be a result of inappropriate filter use, cab leaks or insufficient pressurization. NIOSH investigated several types of filters for reducing DPM to determine which type had the best capture efficiency. The laboratory results indicated that a MERV 8 (minimum efficiency reporting value, as defined by the American Society of Heating, Refrigerating and Air- Conditioning Engineers) filter captured about 50% of the DPM, a MERV 16 filter collected 96-98% of the DPM and two HEPA (high efficiency particulate air) grade filters captured over 99% of the DPM. NIOSH also performed a field study to measure the efficiency of two cabs at a limestone mine. The cab filtration systems of a loader and haul truck were found to be over 90% effective in removing DPM, except under certain operating conditions when the efficiency was as low as 41%. A possible reason for the low efficiencies is an open window in the cab, but more studies need performed to obtain a better understanding of the cause and solution of the problem.

Jan 1, 2011

By Patrick Browne

Drilling programs and the study of active geothermal systems have shown that the reservoir rocks in many fields contain minor quantities of base and precious metals. Commonly, base-metal sulfides occur in the subsurface but, where present, Au, Ag, Hg, As, T1 and Sb rich precipitates deposit near, or at, the surface. Although in some fields (Geysers, Larderello, Tongonan) some of the ore minerals (and others) are relict, there is evidence that they are now depositing in a few systems. Recent work on active hydrothermal systems in New Zealand shows that: (1) Sphalerite, galena, chalcopyrite (forming veins and disseminated discrete crystals) plus rare pentlandite, cobaltite and arsenopyrite, occur at Broadlands, NZ. Rare quantities of base-metal sulfides also occur in cores and cuttings from the geothermal fields of Waiotapu, Kawerau, Tauhara, and Ngawha. Further, Kakimoto (1983) has identified cassiterite, native silver, and trace gold in cores from Tauhara, in the south-eastern part of the Wairakei field. Bore temperatures at the depths from which these minerals were recovered are mostly between 220° and 300°C, but at Broadlands are locally as low as 120°C. The host rocks are Quaternary talc-alkali, silicic lavas and pyroclastic rocks, andesites, dacite and deep Mesozoic greywackes and argillites; however, there is no obvious relationship between mineralization and stratigraphy, permeability or well output. (2) The deposition of amorphous precious metal precipitates (Au, Ag, Hg, As, Sb, T1) from hot springs and well discharges has taken place at Broadlands, Waiotapu and Rotokawa; it also occurs at Kawerau. (3) Water discharging from Frying Pan Lake, Waimangu, is presently depositing siliceous sinter containing up to 4.1% tungsten. A characteristic of mineral-depositing fluids in the New Zealand geothermal fields is their very low salinity (total dissolved salts of 3000 ppm or less but with high CO2); they are of near- neutral alkali chloride composition, although water discharging from Frying Pan Lake has a pH of 4.5, and very low metal contents. Very effective concentration processes (10 times for gold at Broadlands) must occur: in the subsurface these include boiling and rapid cooling but near, and at, the surface, mixing of waters of different pH seems to dominate. In particular, descending acid condensate, derived from separated steam and oxidation of H2S mixes with its parent alkali chloride water, resulting in precipitation of amorphous ore metals. Base-metal sulfides also occur in veins and as disseminated grains in geothermal fields at Tongonan, Leyte and Southern Negros, Philippines. These fields have a porphyry-type setting with host rocks of Miocene andesitic lavas and pyroclastics intruded by diorites so that the fields have undergone complicated thermal histories before cooling to their present base temperatures of about 325°C. Precious metals have precipitated from waters from some wells (Leach, pers. comm.) but they do not, as yet, form ore-grade deposits.

Jan 1, 1984

By K. L. Lamb

At the Sierrita mine, 40 km (25 miles) south of Tucson, Arizona, Duval Corporation is rapidly gaining operating experience with its new Portable Crushing and Conveying System, (PCCS). As of November 23, 1983, over 4.5 million tons (5.0 million st) of ore have passed through the system. Mining cost per ton for the months of July, August and September was 83% below the average for the first five months of 1983. Although all the cost reductions experienced cannot be attributed to the Portable Crusher, it was a major contributing factor. The Sierrita ore deposit has several natural topographic and geologic conditions which are not favorable to mining. It is not a sidehill deposit and therefore no low-level exit points exist to facilitate truck haulage. The ore is very hard. Quartz diorite, hardest of the three major rock types, averages 172-207 MPa (25-30 000 psi) unconfined compressive strength and may run as high as 345 MPa (50 000 psi). Blasting in this rock produces oversize material which runs approximately 20% 51 centimeters (20 inches). The ore is low grade, averaging slightly better than .30% contained copper and .035% contained molybdenum, with small amounts of silver. These conditions, plus high design production tonnages, make the Portable Crushing and Conveying System (PCCS) practical for Sierrita. Without crushing and conveying, truck haulage would be prohibitively expensive. A typical, October, 1983, ore haul from the bottom of the pit would involve a vertical lift of 260 meters (850 ft) and a horizontal distance of 3 860 meters (12 200 ft) were not in-pit crushing and conveying available. The corresponding cycle time would be nearly 32 minutes.

Jan 1, 1984

By Joe Hachey, Jerry Dorn, Jeff Schutt, Derek Penrice

"Sound Transit’s East Link Project, a $3.7 billion (2015 $), 14-mile light rail extension, will connect downtown Seattle with the rapidly developing east side cities of Bellevue and Redmond. Among the most technically challenging aspects of the Project is the 2,435 foot long Downtown Bellevue Tunnel (DBT), which will be constructed through the central core of Bellevue underneath 110th Avenue NE using a combination of Sequential Excavation Methods (SEM) and cut and cover tunneling. The 1,980 foot long central SEM component of the DBT will be mined at shallow depth through challenging and complex geology, comprised of glacially overconsolidated soils, containing both regional and perched groundwater conditions and in close proximity to existing high rise buildings. The paper shares lessons learned from the planning decisions and risk based approach to the investigation, design and procurement processes which shaped the DBT configuration and enabled a successful transition to the project’s construction stage. INTRODUCTION The East Link Project is a voter-approved $3.7 billion (2015 $), 14-mile extension of the existing Sound Transit (ST) light rail transit (LRT) system from downtown Seattle, across Lake Washington via I-90, to the cities of Bellevue and Redmond on the east side of Lake Washington. With targeted completion in 2023, East Link will provide riders with an efficient and reliable connection between the largest population and employment centers on the east side and downtown Seattle. The project alignment is indicated in Figure 1 below.ST completed the Preliminary Engineering (PE) phase of the East Link project in late 2011. Subsequently the final design contract for the easternmost seven miles of the project was awarded to the H-J-H Team, a joint venture comprised of HNTB, Jacobs Engineering and Hatch Mott MacDonald in February 2012. H-J-H’s final design scope includes approximately 7 miles of double-track LRT between the east end of the I-90 East Channel Bridge and the Overlake Transit Center Station. While the project scope is extensive and diverse, the focus of this paper is the DBT. The DBT is located immediately north of the East Main Station, and travels approximately one half mile through downtown Bellevue under 110th Avenue NE between Main Street and NE 6th Street; terminating at the Downtown Bellevue Transit Center (BTC) Station. The location and extent of the DBT is indicated in Figure 2."

Jan 1, 2016

By R. H. King

This paper describes the results of an underground coal mine trial installation of a shielded trailing cable. The cable was a three conductor, round, type SHC-GC, and was installed on a shuttle car in a conventional room and pillar mining section. The purpose of presenting the information is to prepare mine operators for proposed legislation that will require shielding on low-voltage trailing cables. Specifically, machine modifications are required to cable reels, packing glands, and couplers. Cable splicing is not as complex as expected but additional materials are needed in the kit and splice training is necessary. Even though shielding will cause some problems for the mine operator, it can reduce the hazard of electrical shock to mine workers. This paper will present information that mine operators can use to solve most of the problems that will be encountered if they are required to install shielded cables. The in-mine evaluation was funded by the U.S. Bureau of Mines.

Jan 1, 1980

By Y. C. Lo

This paper attempts to answer whether or not the mill performance at Bougainville could have, in fact, been predicted by the population balance approach, or whether other special considerations are required to explain their behavior. In recent studies, the plant tests were performed at Bougainville and batch tests were carried out at the Utah Comninution Center. In all tests power measurements were made and several levels of energy input to grinding were evaluated. Also, tracer tests were performed for mill residence time determination. The performance of Bougainville's 5.5 x 6.4 m mill has been very successfully predicted by population balance methods. The prediction errors are only about 1% on product size distribution and 4% on power with a mill volume scale-up of 3790 to 1. It is significant that this approach will reduce the risk of failure in large mill design that has been recognized in traditional methods.

Jan 1, 1987

By Jonathan G. Price

Silver-copper-lead deposlts in Precambrian, Permian, and Cretaceous red-bed sequences near Van Horn, Texas, have the following features In common: (1) mineralization controlled by steeply dipping fractures in sandstones, (2) lack of ore In overlying and interbedded limestones, (3) absence of igneous intrusions, (4) sulfide ores without typical hydrothermal gangue minerals, and (5) associated arsenic, molybdenum, zinc, and cadmium but not gold. Ore was probably deposited along fractures by reaction between low-temperature, oxidizing, metal-rich ground waters and sulfide-bearing waters or rocks. Detailed mapping and studies of fracture patterns indicate that mineralization occurred during Basin and Range extensional deformation, thereby postdating major Trans-Pecos igneous activity.

Jan 1, 1983

By Dan Nilsson

Rock from underground mining has a size-distribution, that varies from mine to mine, depends on rock conditions and mining method and on how much explosives etc, that is used. Because at the high costs, associated with full-scale studies of the size-distribution of blasted rock in a mine, detailed information is seldom published about such size-distributions. However, some facts can be noticed. Rock from tunnelling and other types of development work has a fine fragmentation. Cut-and- fill mining is a method that normally results in blasted rock with an advantageous size distribution. Block caving on the other hand often results in large amounts of boulders, since blasting of the rock is normally not used.

Jan 1, 1985

By M. D. Bishop

Early solvent extraction circuits in the uranium industry utilized bona fide kerosenes as diluents for extractant chemicals. These kerosenes were used successfully in the uranium industry; however, at least one plant was destroyed by fire resulting from the use of a low flash point kerosene. Although the term "kerosene" is used throughout the solvent extraction industry, the authors have been unable to find any use of kerosene in copper solvent extraction circuits. A term that is occasionally used with reference to diluents is "metallurgical kerosene." Such a term is unrecognizable in the petroleum industry. Kerosene [or kerosine] is a flammable hydrocarbon mixture that is less volatile than gasoline. It is produced for combustion purposes and may have variable compositions of organic compounds including alkanes, alkenes, alkines, and aromatics. Diluents are constant composition hydrocarbon mixtures developed specifically for use in solvent extraction processes. These products usually have much lower vapor pressures and higher flash points than kerosene. In solvent extraction systems, they typically comprise 70 to 95 v/o percent of the circuit organic. The primary purpose of the diluent is to adjust the extractant concentration to the working range of the operation. The diluent and extractant must be completely soluble or miscible with each other. Secondary diluent effects are to promote transfer kinetics, optimize phase disengagement, and minimize both organic in aqueous and aqueous in organic entrainment.

Jan 1, 1996

By R. W. Waytulonis

This paper is an update of the activities of the U.S. Bureau of Mines, other government agencies, and the automotive and truck industry concerning diesel emission control. Enacted and proposed regulations from the U.S. Mine Safety and Health Administration (MSHA) and developments in diesel emission control are presented in terms of their impact on underground coal, metal, and nonmetal mines. Mine air quality regulations proposed by MSHA may require the underground mining industry to comply with new standards. Some mines may be required to take additional actions to meet new diesel particulate and lower nitrogen dioxide exposure standards; however, the mining industry is in a position to benefit from emission controls developed for the on-highway diesel engine market. The U.S. Environmental Protection Agency (EPA) has enacted regulations to reduce emissions from on-highway diesel trucks and buses. Engine manufacturers have responded by developing cleaner burning engines. Fuel producers have responded by providing cleaner burning reformulated diesel fuel, and exhaust aftertreatment devices have been developed to provide additional emissions reductions. Bureau research and development projects seek to determine the advantages of using modern engines and fuels, and to evaluate the efficacy of new exhaust control devices on mining machines. It appears that the diesel engine will continue to be a practical power source for use in confined environments because no other available power source is as mobile and efficient.

Jan 1, 1993