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Develop rugged, cost-effective fire protection for hydraulic shovels and backhoes. Approach Automatic fire sensing and suppression systems were designed and built for use on hydraulic shovels and backhoes. How It Works A line-type temperature sensor is mounted in the machine's engine and hydraulic pump areas to detect the heat from a fire while it is still small and easy to control. Two systems were tested. In one, the inside of the sensor consists of two conductors separated by a ceramic material whose electrical resistance decreases with increases in temperature. When heated to a predetermined temperature) the control circuit responds to the resistance drop. In the second system, the detection element of the sensor is comprised of a thin metal tube containing a hydrogen charged metal hydride wire. The tube is sealed at one end and is connected to a sensitive pressure switch at the other end. When exposed to the heat from a fire, hydrogen gas released from the metal hydride wire actuates the pressure switch.

Jan 1, 1980

Reduce dust at the auger mine face by modifying airflow patterns, around the minim machine. Approach Limited clearance between an auger miner and the mine root restricts airflow across the face and causes dust rollback. Directional sprays arc used to direct air across the face, thereby reducing dust rollback and increasing dust dilution (fig. 1). Laboratory and underground studies were used to test and optimize effectiveness of the directional sprays. Results of Laboratory Study Laboratory experiments were conducted in a simulated auger gallery equipped with a full-scale mock auger miner and bridge conveyor. A dual curtain configuration was used to direct the, ventilation, which averaged 2,700 cfm throughout the experiment. Testing variables included spray location, pressure, spacing, orientation, and number. Figure 2 shows the optimized directional spray system, also called the auger clearer spray system. The system consists of three sprays mounted alone the intake side of the miner. Sprays arc spaced 16 to 24 inches apart, and angled 30° toward the return side of the miner. The 24-inch spacing moved about 7% more air across the face than the 16-inch spacing; however, it resulted in some additional misting on the return side of the miner. A 30° orientation was more effective than a 60° orientation for moving air across the face and minimizing misting on the return side of the miner. Flat fan sprays arc used because their spray paths arc not obstructed by the top of the miner and mine roof, A 50° fan angle is used to minimize misting on the intake side of the miner.

Jan 1, 1989

Reduce methane levels around the shearer machine during longwall mining by directing more of the available airflow along the face and over the shearer body. Approach To address the entire mining cycle, two techniques were combined to dilute and clear the methane liberated from the face by the shearer during cutting. The first is the modified shearer clearer system, which is used during the entire face pass. This is combined with the walkway curtain which is used only during the headgate cutout. How It Works Methane ignitions are one of the most potentially serious hazards facing longwall mine operators. The high rate of coal extraction on longwall sections can liberate a significant quantity of methane during a pass. The modified shearer clearer is used to dilute methane concentrations along the entire face for both cut directions. The shearer clearer system, originally designed as a dust control technique, uses a series of water sprays located on the shearer body to direct more airflow along the face and over the shearer. (See Technology News issues, #112, #118, and #221). The only change from the original shearer clearer design is the addition of three sprays to the return-side splitter-arm/ shearer interface. The additional sprays help to ventilate the area behind the shearer body.

Jan 1, 1985

Impermeable geologic faults in the coal seam can cause intermittent production problems or can cause unexpected amounts of water or gas to issue from degasification boreholes. These faults also can impact methane emissions into the mine workings, especially if they hinder proper and effective degasification of the coal bed. They may also act as barriers for methane flow in the coal seam. Although this might seem beneficial for advancing mine workings, faulting may also cause gas pressure buildups and result in compartmentalization of the gassy regions from which large quantities of water and methane may rush into mine workings. This study uses reservoir simulations to illustrate the effects of impermeable faults, with and without throws, on the production performance of vertical and horizontal degasification boreholes. These boreholes were drilled from the surface to intercept the coal layer and fault and were assumed to produce methane two years prior to mining of the coal seam. Longwall advances and face position related emissions and reservoir properties were characterized using sector definitions along the path of the panel grids. This work numerically evaluates water and gas productions of each borehole and presents the effects and the impacts of impermeable faults on methane emissions due to an advancing coal face. The results can be used to understand the effects of impermeable faults on borehole productions and face emissions due to these coal seam anomalies.

Jan 1, 2008

By Geo S. Rice

"Three men lost their lives in the Black Diamond Coal Mine near Seattle, Wash., recently while wearing oxygen breathing apparatus. The press dispatches stated that these men lost their lives while practicing with the apparatus. Later reports stated that the men died while attempting to make a trip 1200 feet down a 25 degree slope which was filled with black damp, in order to measure the amount of water that had accumulated at the bottom of the mine, and the trip was attempted with oxygen in the tanks of the apparatus with dials indicating only 45 minutes supply. The oxygen in the tank was used up and the men therefore lost their lives from a deficiency of air to breathe.In spite of all the education and training done by the Government to prevent accidents, men are prone occasionally to take unnecessary chances. Every piece of apparatus, no matter how perfect, has its limitations. The Government, through the agency of the Bureau of Mines, has trained many thousands of miners in the use of mine rescue apparatus. The training has been given to all miners who requested it, and the Bureau has gone to the extreme of urging miners to join the rescue and first-aid classes. In spite of all the efforts of the Government, men occasionally attempt the impossible."

Jul 1, 1920

By Christopher C. Jobes, N. Kumar Kittusamy, Alan G. Mayton, Dean H. Ambrose

Researchers with the National Institute for Occupational Safety and Health (NIOSH) conducted a systematic study to evaluate seat designs on low- and mid-coal-seam shuttle cars. The purpose was to gather additional data to support earlier findings that NIOSH seats, with unique viscoelastic foam padding, are indeed improved designs for coal mine shuttle cars. This study included a larger sample of shuttle car operators than a prior NIOSH investigation. Eight shuttle car operators participated in evaluating seat designs on the basis of perceived levels of vehicle jarring/jolting and discomfort. Researchers then compared the operators’ perceptions with field-measured levels of vehicle jarring/jolting. Seven seat designs were evaluated on low- and mid-coal-seam shuttle cars during production operations at two underground coal mines in southern West Virginia. These seat designs comprised the one already in use on each vehicle and five NIOSH designs. Experimental data were collected using accelerometers, signal conditioning amplifiers, and filters connected to a data recorder, whereas subjective data were gathered via a visual analog scale (VAS) and a questionnaire. Field trials included shuttle cars operating under full- and no-load conditions. VAS responses indicated that NIOSH-designed seats performed better relative to comfort and isolation from vehicle jarring/jolting than the existing seats used in the shuttle cars. Both mid- and low-coal-seam shuttle car operators, during no-load and full-load conditions, rated lower levels of jarring/jolting with the NIOSH seat design. Questionnaire responses indicated that shuttle car operators rated NIOSH seat designs as more comfortable. Vehicle operators most frequently suggested the addition of armrests as a way to improve the seats on the mid-seam shuttle car. The quantitative levels of vehicle jarring/jolting for the no-load condition (more severe condition for vehicle operation) showed that NIOSH seats for the mid-coal-seam shuttle car performed better than the existing seat in terms of peak acceleration and crest factor. Similarly, for the low-coal-seam shuttle car, NIOSH seats performed better than the existing seat in terms of peak acceleration, root-mean-square (RMS) acceleration, and crest factor.

Jan 11, 2006

Develop a curved ray geotomographic program with constraints to counteract non-uniqueness in order to improve the reliability of seismic tomographic imaging of geological structure in mining regions. Background Seismic tomography provides a two-dimensional image (tomographic reconstruction) of the distribution of the seismic velocity in geologic structures using measured travel times of seismic waves crossing the area. It can provide a more complete representation of features be¬tween boreholes than other crosshole processing methods that measure only average properties or borehole logging methods that measure properties only near each borehole. Seismic tomography has many mining applications. They include locating geologic structures of contrasting seismic velocity, detecting fractured regions where the seismic velocity is low, and monitoring solution injected above the water table where the increase in saturation increases the seismic velocity. Thus, tomographic imaging techniques show great promise for detecting and locating geologic hazards that affect the productivity, safety, and environment of mining operations.

Jan 1, 1992

Permit visual inspection of underground cavities dam the surface. Approach A closed circuit TV camera and a 35mm still camera are lowered down a borehole, and remotely operated. How It Works A platform holding the cameras, and other equipment is lowered on a graduated cable until the depth of interest is reached. Then a quartz lamp and the TV camera are turned on. The television picture is monitored at the surface and recorded on video tape. Areas of special interest are photographed with a 35mm still camera. These photographs contain more detail than TV images because photographic film is capable of higher resolution than a TV transmission.

Jan 1, 1979

By M. E. Tyrrell

Work in this investigation was undertaken by the Bureau of Mines to demonstrate how waste glass might be utilized to lower the required firing temperature and firing time of structural clay products. Mixtures of waste glass and common clays were formed by stiff-mud extrusion and fired to the temperature required to produce a body having 6 to 7 percent absorption. Substitution of glass for one-half of the clay in a red body reduced the firing temperature 500° F, which made possible a 30-percent increase in production; in a tan body, the firing temperature was reduced 400° F, which made possible a 23-percent increase in production.

Jan 1, 1972

By T. O. Llewellyn

The Bureau of Mines conducted laboratory batch beneficiation tests on a waste granite sludge from New Hampshire to determine the feasibility of recovering a reusable silicon carbide product. The granite sludge responded to attrition scrubbing, desliming, and flotation in either alkaline or acid circuits using fatty acid as a collector. Recovery of over 80 percent of the contained silicon carbide at grades of up to 96 percent SiC was obtained.

Jan 1, 1975

Minimize failures or inefficiency in the operation of in situ mining wells. Approach The proper design, construction and development of wells are important to any in situ leaching operation. To permit cost-effective production from an underground ore body by leaching it in place, many wells are normally installed. Construction and maintenance costs increase with the number of wells, and poor construction and maintenance procedures result in production losses and negative environmental impacts, To minimize these losses and impacts, the Bureau of Mines conducted an investigation to determine the optimum in situ well construction and operating procedures for the minerals industry. Factors considered during the investigation included drilling equipment and procedures; types of well casing and grouting; completion methods, e.g, screening or perforation; and system maintenance. The data collected were used to prepare a manual that offers guidelines

Jan 1, 1984

By D. G. Kesterke

Research was conducted to determine the feasibility of extracting elemental oxygen from silicate-bearing melts by high-temperature electrolysis. The method was based on a modification of existing processes for electrowinning metals from their oxides dissolved in molten halide systems. Electrolyses were performed at temperatures ranging from 1,050° to 1,250° C in boron nitride cells that incorporated a silicon carbide cathode and an iridium anode. The electrolytes contained volcanic scoria as the oxygen source, plus mixtures of BaF2 and LiF as fluxing agents. Cell gases containing almost 14 volume-percent oxygen were obtained. The average anode current efficiency for several experiments of extended duration was calculated to be 55 percent. Cell design and operating conditions are described, and some of the problems associated with the process are discussed.

Jan 1, 1971

By N. S. Dalal, V. Castranova, K. Van Dyke, V. Vallyathan

"IntroductionInhalation of crystalline silica is often associated with the development of pulmonary disease (Ziskind et al., 1976). Recently, it has been proposed that freshly sheared silica .may have surface properties that make it more reactive with lung tissue than aged silica, and that this unique reactivity ·of freshly crushed silica enhances its pathogenicity. A recent study in our laboratory strongly supports this theory (Vallyathan, et al., 1988a; 1988b). We found that grinding of silica cleaves bonds in a silica tetrahedral lattice generating reactive free radicals sites on the surface of the silica particles. The presence of surface radicals on freshly ground silica was monitored by electron spin resonance (ESR) spectroscopy. The ESR signal generated from fresh silica in air is characteristic of Si-0 and Si radicals. Evidence, i.e., the ESR signal after the addition of a spin trap (DMPO) and its sensitivity to ethanol, indicates that these silicon-based surface radicals can react with water to form hydroxyl radicals (OH). Results also indicate that these surface radicals make fresh silica more cytotoxic than aged silica; i.e., fresh silica causes more membrane damage as evidenced by hemolysis and lipid peroxidation. Therefore, the presence of reactive sites on the surface of freshly cleaved silica may play a significant role in its pathogenicity.If surface· free radicals are related to cytotoxicity, then screening dusts for the existence of such radicals may predict their relative pathogenicity. Since an ESR spectrometer is not available to many laboratories, the objective of this study was to develop a quick and simple technique to monitor the existence of reactive surface sites on dust. The technique chosen was the measurement of chemiluminescence using a liquid scintillation counter; i.e., an instrument which·would be accessible to most investigators."

Jan 1, 1989

Reduce the number of conveyor-related accidents in the mining industry by providing recommendations for effective operation of conveyor belt cleaning systems. The Problem Troughed belt conveyors provide effective, and efficient materials transport and their use has increased throughout the mining industry. Carryback, the spillage that accumulates under the belt, is a problem even with belt cleaning systems installed. Mining personnel are exposed to safety and health hazard; as they attempt to clean up this spillage. Approach To investigate the influence of metal-segmented-blade belt cleaners on the amount of carryback spillage, the. Bureau identified and tested the following parameters: (1) amount of pressure applied to the cleaner blades, (2) friction between the blades and conveyor belt, and (3) wear rates of different metal blades. The test parameters were quantified by recording the amount of carryback material passing the metal cleaner blade, and the weight loss of the blades. The data collected were used to identify the following critic d operational parameters of a segmented-blade conveyor cleaner system: (1) the existence of an optimal operating pressure for the conveyor and cleaning systems and (2) elimination of recessed patterns on the working side of the conveyor belt.

Jan 1, 1989

Provide respiratory protection for escape in a toxic or oxygen-deficient atmosphere with a device small and light enough to be belt-worn. Approach Combine a 10-minute, belt-worn respirator with a stored, larger, long-duration (60-minute) attachment that can be plugged into the 10-minute unit without removing the mouthpiece. How It Works The 10-minute device will be carried by the miner at all times, and the 60-minute canister or attachment will be stored near the miner. In the event of a disaster, the 10-minute device would be donned immediately. The miner would then proceed to the stored 60-minute unit and plug it into the 10-minute unit. For the 10-minute unit, a breathing circuit was developed in which air is passed through the KO2 bed twice per respiration. The 60-minute canister differs from the 10-minute unit in that air is drawn only once through the chemical bed per respira-

Jan 1, 1981

Determine the dust reduction capabilities of various bag valves available to the minerals processing industry. The Problem Many different types of ground mineral products are packaged into 50-and 100-lb paper bags. Although bag technology is continually improving, dust contamination from bags still remains a significant problem for workers. The greatest source of dust is the bag filling valve. Ideally, the bag filling valve should close after it fills the bag with the ground mineral product. However, the valve usually fails to close properly since some mineral product gets trapped inside the valve during filling and ejection. As a result, when the bag has been filled and falls from the fill station, a rooster-tail of product is discharged from the bag valve. As the bag hits the conveyor belt, additional product discharges from the bag valve. The dust from these sources contaminates the air inspired by the workers filling the bags as well as the work area. Dust also clings to the outside of the bag, contaminating the pallet loading station. Because the various commercial bag valves are composed of different materials, a dust analysis was performed on five of these valves to determine their dust reduction capabilities. The five valves analyzed were: standard paper, polyethylene, extended polyethylene, double trap, and foam.

Jan 1, 1986

By George S. Koch

The distribution of gold in part of the Getchell mine, Humboldt County, Nev., is presented through the statistical analysis of 956 assays of rock cuttings from wagon-drill holes. Two methods to predict grade in undeveloped parts of the ore body are evaluated, and the possibility of sampling bias is tested. The distribution of gold is compared with that in three other Nevada gold deposits of the same type characterized by gold particles mostly of submicron size associated with carbonaceous rocks, and also with that in deposits with coarse-grained gold. Usually, fewer samples of a given type are required to make a satisfactory grade estimate for submicron deposits than for coarse-grained deposits. The economic consequence is that submicron gold deposits are likely to be less expensive to sample and evaluate than coarse-grained deposits.

Jan 1, 1970

To concentrate coarse mica particles using a dry beneficiation technique. Approach Concentrate coarse, II berated mica particles using a Bureau-designed system of crushers, screens, and a two-stage zigzag air classifier. How It Works Because mica has a flat plate-like crystalline structure, mica particles are significantly lighter than blocky gangue particles of the same size fraction. Thus an air classification technique can separate the flat, light mica particles from the heavier gangue particles. The ore, which Is first run through a standard jaw crusher, a roll crusher, and a hammer mill to liberate the mica, enters the rougher Zig-zag section through a rotating air lock. See photograph and diagram of a 2-stage air classifier. Airflow through the classifier can be varied according to the size of the particles being separated. The gangue material falls through the airstream of the rougher zigzag section and is discarded as tailings. The mica flakes are carried by the air-stream to the cyclone shown on the right side of the diagram, where they are collected. This rougher mica concentrate is fed to the cleaner zigzag section through another rotating air lock. The mica particles are again carried by the airstream but they are now collected In the cyclone on the left side. The cleaner concentrate leaves the left-side cyclone through a third rotating air lock and is rescreened to remove under-size material missed by the first screening. The final product of this pneumatic process is generally a high-grade mica concentrate. A generalized flow diagram for the pneumatic concentration method Is shown In the second diagram.

Jan 1, 1981

By Carlton E. Brown

The purpose of this report is to present results of tests on the effectiveness of a spray of water mist, commonly called compressed-air water blast or water blast, in reducing the concentration of dust present in the air shortly after blasting and during mucking of the blasted material. Many observations have been male on the effectiveness of such ,sprays, but published quantitative information on comparative dust concentrations with and without their use, obtained by dust-sampling methods in use in this country, is rare if not absent. Tests conducted in South Africa about 19164/ and more recently in England5/, 6/ have shown that such sprays reduce the dust concentration to very low values within a fen minutes after blasting,

Jan 1, 1938

By Thomas E. Marshall, Timothy Batchler, Anthony T. Iannacchione

As the amount of new fractured surfaces or "damaged rock layers" within roof rock increases, the stability of the rock mass decreases. While direct measurements of this phenomenon are not easily made, there is good circumstantial evidence to support this hypothesis. For example, it is common to observe increased cracks or fractures in the immediate mine roof rock before a roof fall. Likewise, roof drill holes placed in areas that later fail often reveal increased numbers and/or separations of fractures within the rock column through time. And finally, the frequency of microseismic activity, representative of rock fracturing, increases before a roof fall. For this study, more than 700 microseismic emissions were collected from two underground limestone mine roof fall areas in southwestern Pennsylvania. Microseismic events were located and magnitudes determined using the moment magnitude technique. Moment magnitude is based on the event seismic moment, which is a measure of the seismic deformation. The amount of new fracture surface length was calculated based on the stored strain energy within the rock prior to fracture. In the two case studies presented, a significant amount of microseismic activity was observed as much as two days before the first signs of failure in the roof fall areas. Additionally, results from this analysis reveal much about the behavior of strata prone to failure and allows for the construction of hazard maps based on microseismic emissions. The potential use of this technique as a means of anticipating roof falls is analyzed and discussed.