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By Lloyd A. Morley, Robert Stefanko

In addition to explosion-proof enclosures, the IEC has published recommendations: 1. 79-2 Pressurized Enclosures, 2. 79-3 Intrinsic Safety, 3. 79-5 Sand-Filled Apparatus, 4. 79-6 Oil-Immersed Apparatus, and 5. 79-7 Increased Safety. All these are valid methods of electrical hazard reduction and find wide use in industries other than mining. Magison (52) discusses in detail each technique and, therefore, such an examination will not be repeated. Two other systems, lamina and labyrinth, are but variations of common explosion-proof enclosures and, therefore, will not be cov¬ered. (34,35,46,53,54,61) By examining other national authorities' opinion, the following will investigate each system's applicability to coal mining. Intrinsic safety applies to any system which is incapable of re¬leasing sufficient energy to be an electrical hazard. (49) Not one foreign country contacted disagreed with the concept, and they find these systems totally acceptable. Only South Africa does not accept oil-immersed apparatus, but no reasons were given. (62) Healy (27) stated that Queenlands, Austrailia would accept all techniques, yet some were still to be employed. Japan specifications allow for all but sand filled. (42,43) Increased safety or Protection Type "e" is an approach in hazard reduction in which special design considerations are applied to ensure an extremely low probability of electrical or mechanical breakdown

Jan 1, 1974

By Sarkis G. Ampian

The Bureau of Mines has developed a method for identifying fine particles of beryl in mineral samples by preferentially staining the beryl grains. The sample is first subjected to a heated sodium hydroxide solution to etch the beryl particles, which are subsequently stained an intense blue color in a boiling alkaline solution of quinalizarin. Positive identification of beryl grains permits quantitative analyses by microscopic techniques. INTRODUCTION Beryl, a beryllium aluminum Silicate, is the principal ore mineral of beryllium. The only known commercial concentrations of this mineral are found in pegmatite dikes of granitic composition. Normally beryl is associated with muscovite mica, quartz, and the sodium-and potassium-bearing feldspars (orthoclase, microcline, and albite). Other beryllium-bearing minerals which are found occasionally in minor amounts with beryl are phenacite, a beryllium silicate, and chrysoberyl, a beryllium aluminate.

Jan 1, 1962

Prevent collisions between large mine-haulage trucks and smaller vehicles parked in areas not visible to the haulage-truck operator, Approach Two electronic systems were developed to detect the presence of vehicles in the blind areas of a parked haulage truck. The systems can warn haulage truck operators of presence of vehicles that are blocked from view. The systems do not apply for trucks in travel. How It Works The systems use electronic transmitting techniques-one system is based on low-frequency radio waves and the other on very-high-frequency radio waves. Each system requires that a signal transmitter be mounted on the smaller vehicle to be detected. Continuous signals from this transmitter are sensed by receiving antennas mounted on the right front and rear of the large haulage truck. Upon receiving a signal, the receiver energizes warning lights and a buzzer in the cab of the haulage truck, alerting the operator to a possible collision hazard. Detection distance is adjustable, depending upon the size of the haulage truck, but a minimum of 30 feet was the design goal.

Jan 1, 1990

By Charles P. Lazzara, Charles D. Litton, Frank J. Perzak

This U.S. Bureau of Mines report details the results of a series of large-scale experiments where small coal fires were used to ignite the conveyor belt at air velocities ranging from 0.76 to 6.1 m/s. In the tests, electrical strip heaters imbedded within a pile of coal were used to heat the coal to a point of flaming ignition. The flaming coal subsequently ignited the conveyor belt located approximately 5 to 10 cm above the coal pile. During the tests, temperature, CO, and smoke levels were continuously measured in order to determine both alarm time and level as the fire intensity progressed through the stages of smoldering coal, flaming coal, and flaming coal plus flaming belt. Analysis of the data leads to certain conditions of air velocity and sensor alarm levels that are required for early detection of conveyor belt entry fires. Two nomographs are presented, which define sensor alarm levels and sensor spacings as a function of belt entry cross-sectional area and belt entry air velocity.

Jan 1, 1991

Eliminate accidental tramming of a cleanup tractor. Approach A switch was installed in the operator's seat cushion to pre-vent the cleanup tractor from tramming without an operator in the driver's seat. How It Works The operator must be seated, and the Forward/Reverse Switch (that controls tramming direction) must pass through the NEUTRAL position before the vehicle will tram. See Figure 1. A pressure-sensitive seat cushion switch, a solid-state relay, and a double-contact relay were added to the control circuitry of an S & S BMUAT -88 cleanup tractor to create this tramming interlock. The weight of the operator on the cushion closes the seat cushion switch (Figure 2, A). This activates the solid-state relay (B), which completes the initial circuitry. Moving the For- ward/Reverse Switch (C) to NEUTRAL energizes the coil in the double-contact relay (D) and closes both contacts. One contact completes a sustaining circuit which keeps the double-contact relay energized. The second contact transfers power to the remaining contacts within the Forward/ Reverse Switch. These circuits are shown in greater de- tail in Figure 2.

Jan 1, 1978

Provide longwall operators with practical information and guidelines concerning mine design to reduce problems associated with the interaction of adjacent workings in multiple-scam longwall mines. Background The high productivity achieved by longwall mining demonstrates its potential to provide a substantial segment of underground coal production. Longwall mines produce more than 30 pct of underground coal, up from pct just 15 years ago. However, the continued growth of this mining method without appropriate multiple-seam planning may increase the cost and risk of mining. Research by the U.S. Bureau of Mines (USBM) indicates that 25 longwall mines (32 pct of the total number in the United States) have mining in adjacent coalbeds either above or below. About half of these longwall mines report some type of interaction problem with the adjacent workings, such as caving due to subsidence. Optimization of mine design factors is the best means for controlling interactions between operations in adjacent scams. To avoid higher mining costs, operators should focus on adopting practices and procedures that prevent and control interactions in multiple scams. The USBM, in an effort to improve longwall mine planning, has been investigating multiple-seam longwall design and development.

Jan 1, 1994

By X. Shi, V. Vallyathan, N. S. Dalai

"Electron spin resonance (ESR) measurements show that grinding of quartz particles in air produces silicon-based (Si- and SiO-) radicals which decay with aging in air. ESR spin trapping measurements provide evidence for the generation of hydroxyl and possibly superoxide radicals from a suspension of fresh quartz particles. The hydroxyl radical generation potential of the fresh quartz particles decreases on storing in ambient air and on the addition of catalase, superoxide dismutase, desferoxamine, or DMSO. Silica-induced lipid peroxidation also decreases on storing the fresh particles in ambient air. These findings suggest that oxygenated radicals play a role in the biochemical mechanism of pneumoconiosis in general and acute silicosis in particular.INTRODUCTIONThis communication summarizes our electron spin resonance (ESR) investigation of the formation of oxygenated radicals by freshly crushed quartz particles in a cell-free aqueous medium, and its potential role in the biochemical mechanism of acute silicosis. This study was undertaken because the mechanisms by which the quartz particles exert their toxic action on cells and the process(es) by which these actions progress to fibrogenesis are still not well understood. 1-3 It is generally believed, however, that the action of quartz particles on the cell membrane is the starting point of the silicotic process. 1,4 Since the first step must involve surface reactions, characterization of the chemical structure of the surface of quartz particles has been the subject of several recent studies!-' For example, we reported that mechanical crushing of quartz under normal atmosphere generates silicon-based (Si• and SiO•) radicals which decay with time, and that these radicals are associated with a higher cytotoxicity of fresh quartz dust as compared to that of an aged dust from the same stock. 6,8 Independently Fubini and coworkers' have also reported on the formation of Si• and SiO• -type of radicals from quartz particles crushed under atmospheric conditions. Gulumian and van Wyk9 have reported that quartz particles react with hydrogen peroxide (H202) to generate hydroxyl (•OH) radicals. These authors9 suggested that this process might contribute to quartz's pathogenicity but the mechanism of the -OH radical formation was not clarified. Earlier, Gabor and Anca10 had suggested that the cytotoxicity of quartz particles might be associated with the generation of some factor or factors possessing the properties of a free radical and hence capable of promoting the peroxidative chain cleavage of polyunsaturated fatty acid moieties of the phospholipids in the cell membrane. More recently, Weitzman and Graceffa 11 reported that asbestos is able to catalyze the generation of -OH radicals from H2O2. Their later work12 indicated that lipid peroxidation might be one of the mechanisms of tissue injury by asbestos."

Jan 1, 1989

By C. A. Rhoades

A major contributor to the problem of short life expectancy for blade-type conveyor belt cleaners is uneven wear along the blade edge. Uneven wear results in the formation of channels in the blade edge, which allow material to be carried back between the blade and the belt. In an effort to reduce the uneven wear problem, the U.S. Bureau of Mines has studied the mechanisms responsible for effective belt cleaning. From this study emerged a design for a cleaner blade that would greatly reduce uneven edge wear. The design consists of a standard cleaner blade incorporating air passages that allow for the expulsion of air along that part of the blade edge in contact with the conveyor belt surface. The results of 18-h tests indicated that the expulsion of air on the blade edge prevents scratches from developing into deep grooves. These tests showed that effective blade cleaning life can be extended 25 times using the pneumatic cleaning blade, compared with solid metal cleaning blades.

Jan 1, 1989

By P. G. Clites

This study was conducted to determine the patterns of heat transfer to water-cooled copper crucibles during vacuum arc melting. Values of heat flux from the ingot to the crucible were determined during nonconsumable electrode vacuum arc melting of zirconium and during consumable electrode vacuum arc melting of titanium) zirconium) and steel. The results of these studies con-firm the existence of a high thermal resistance between the ingot and the crucible wall which results from the shrinkage of the ingot as the metal solidifies. Maximum heat flux occurs near the top of the ingot where maximum values of heat flux of 1.4 X 106 Btu/ft2 hr were observed during small-scale consumable electrode arc melting of zirconium and titanium. The maximum heat flux for consumable electrode arc melting of 8-inch-diameter ingots was 0.5 X 106 Btu/ft2 hr. The effects of electrode material) electrode diameter) arc current) and arc potential on heat flux from the ingot to the crucible were studied. Data were also obtained on crucible wall temperatures and on the effect of very narrow annular water jackets.

Jan 1, 1967

By Charles Vaught

This paper discusses the fact that US coal mining organisations are losing the knowledge they need in order to be able to respond to emergencies. The authors note that knowledge management provides a useful perspective from which to view the problem, but that the debate about what constitutes knowledge should be broadened to include a debate about what constitutes management. It is argued here that knowledge is actually shared knowing distributed across group members; that such knowledge can be managed by cultivating it; and that narrative is the medium through which this may be done. The paper then examines NIOSH research that has attempted to use such an alternative knowledge management approach to help potential mine emergency responders better deal with the predicaments they are likely to encounter on-site.

Jan 1, 2006

To inexpensively monitor the ventilating airflow anywhere in underground working places. The Approach: The Bureau has developed a small self-contained monitor which sounds an audible alarm and energizes a flashing lamp if air velocity decreases below normal. How It Works: The sensing element of this inexpensive monitor is a thermistor, which is self-heated by a constant-current electrical source. Airflow over the thermistor increases heat removal and lowers the thermistor temperature. Since the electrical resistance of a thermistor is a function of temperature change, the voltage across it varies with temperature, and, therefore, the air velocity. Changes in the voltage across the thermistor are amplified, and can be used to trigger the alarms.

Jan 1, 1975

Improve mine refrigeration system efficiency while providing free electrical energy to mines. Approach Convert the potential energy of incoming mine water falling down long vertical shafts into electrical energy by means of a turbine-generator system located at the bottom of the mine shaft. How it Works Converting the energy of falling water into useful work is a well-developed engineering concept. Water flowing down long vertical pipelines into deep mines develops high pressure that can be used to operate a turbine-generator system at the bottom of the pipeline. A thermal energy recovery system of this type offers three advantages: 1. In systems without turbines, the potential energy of the water is converted to heat. The water temper-ture will automatically

Jan 1, 1985

Improve the dust control effectiveness of dry collection systems on surface coal mine drills. Approach Use a dust pelletizer to convert the respirable dust particles discharged by the dry collector into dust pellets that present no health hazard. Background Blasthole drills are well-known sources of respirable dust that can contain significant amounts of quartz. The drills frequently use a dry cyclone-filter type collector that can obtain dust reductions theoretically greater than 95 pct. However, surface mine drills using dry collectors typically have three major dust sources that significantly reduce the overall effectiveness of the collection system: (1) the dust collector dump cycle, (2) drill shroud leakage, and (3) leakage around the drill stem seal in the drill table.

Jan 1, 1989

Provide an inexpensive, simple means of supporting highly yielding ground In underground mines. Approach The Bureau of Mines developed a high capacity support post made from standard steel pipe which, when using a 60-inch post configuration, has a 45-ton capacity and a yield length of 24 inches. How It Works The post mechanism is a three-piece unit consisting of a top and bottom leg (made from standard steel pipe) and a separate foot bracket. During installation in the mine, the bottom leg is placed on a relatively flat surface on the mine floor and the top leg is placed over it until its flared end contacts an expansion ring attached to the bottom leg. As the roof and floor converge, the flared end of the top leg is forced into the expansion ring, causing the walls of the top leg to be deformed radially and along the axis. The mechanism will yield until the unit bottoms out after about 24 inches of yield.

Jan 1, 1987

By G. E. McElroy

[During the period July, 1923, to April, 1924, we made a large number of careful determinations of the resistance to the passage of air in selected sections of airways in the metal mines of Butte, Mont. The experiments were conducted with the cooperation of the Anaconda Copper Mining Co., Frank D. Cannon, mining engineer of that company, and Fred P. Gaethke, mining engineer of the bureau, assisted in carrying out this work. This paper summarizes the, main group of data obtained in the form of a table, of friction factors, or coefficients of friction that is, values of K in the generally accented formula or air flow of [P = KSV or H = KSV2 ] where, in units customary to mining practice;]

Jan 1, 1925

Enhance hydraulic fragmentation technology by developing alternative grout sealing methods. Traditional grout scaling methods rely on chemical adhesion and require large contact areas to restrict high-pressure fluids. Fluid injection into rock requires economical and effective seals. With economical and effective seals, rock is easily fractured in tension by high-pressure fluid injection (fig. 1). Approach An innovative grouting technique was developed and tested by the Bureau. Slowly hydrating expanding chemicals are placed within a borehole and around a section of high-pressure tubing. Testing was conducted using 9/16-inch-OD smooth-walled injection tubes in 1.5-inch-ID holes. Seal lengths weir less than 10 inches and curing times were less than 24 hours.

Jan 1, 1989

Reduce shaft sinking costs and workers exposure to mechanical hazards, drill dust, blast dangers, and fumes. Approach Replace drilling and blasting by using a large, cab-mounted impact breaker suspended from the bottom work deck of the galloway. How It Works The pneumatically actuated impact breaker is positioned by an articulated boom con-trolled from an operators cab. The breaker delivers 2,000 ft-lb blows that fragment the rock at the shaft bottom. Mucking is accomplished by a backhoe bucket on an articulated boom mounted on the cab. See photograph. The mucked material can be removed either by dumping into a previously drilled borehole or by being lifted out in a muck bucket as shown in the drawing. Positioning of the breaker, rotating the cab around its vertical axis, and moving the cab support frame around the perimeter of the shaft are all controlled by one joystick. Separate controls position the mucker boom, which can be swung horizontally through a 180° degree arc towards either side of the cab. Because the cab can be rotated to any position around its vertical axis, and can also be moved in a horizontal circle around the shaft, virtually any position on the bottom of the shaft can be reached by the breaker and mucker.

Jan 1, 1981

By Maria I. De Rosa

Table 1 and figure 1 show the number of fires and fire in¬juries that occurred in underground coal mines by state during 1990-1999. Table 1 also shows by state the risk rates, employ¬ees' working hours, lost workdays, and coal production. Over¬all, 87 fires occurred in 12 states. Twenty-seven of those fires caused 34 injuries (the yearly average was 8.7 fires and 3.4 injuries). One fire and one injury involved a contractor. The underground mine fires required 25 mine rescue team interventions and 30 mine/section evacuations followed by 13 mine/section sealing/flooding/CO2/N2, gas injections. The Ewhr value was 1,003 x 106 hr (In = 0.007), the CP value was 4,008 x 106 st (Frr = 0.022), and the LWD value was 208. Virginia had the most fires (15 fires and 7 injuries). Pennsyl¬vania had the most fire injuries (12 fires and 9 injuries), fol¬lowed by Kentucky (12 fires and 6 injuries), and Alabama (12 fires and 4 injuries). Among these states, Alabama had the highest fire risk rate value (Frr = 0.073), whereas Pennsylvania had the highest injury risk rate value (In = 0.016). Table 2, partly illustrated in figure 2, shows by time period the number of fires, fire injuries, risk rates, employees' working hours, lost workdays, and coal production. The number of fires and fire injuries show a decrease followed by an increase during the five time periods (see table 2 and figure 2). This was ac¬companied by a decline in employees' working hours throughout the periods and an overall small decrease in coal production. The In and Frr values follow patterns similar to those shown by the fire and injury values. By comparison, data from Pomroy and Carigiet [1995] show that during 1978-1992 a total of 11 states were involved in 164 underground coal mine fires (yearly average, 10.8) with 43 injuries (yearly average, 2.9) and 27 fatalities (yearly average, 2; however, the 27 deaths occurred during a single fire caused by an overheated air compressor [MSHA 1984]). The CP value was 5,340 x 106 st (yearly average, 356 x 106 st) (Fn = 0.031). Data on employees' working hours and injury risk rates were not available. Tables 3-8 show the number of fires by ignition source, method of detection and suppression, equipment involved, location, and burning material by time period. Figure 3 shows the major variables during 1990-1999. Table 9 shows the number of fire injuries per number of fires causing injuries and total fires by year, ignition source, equipment involved, and location.

Jan 1, 2004

By Wing G. Agnew, Albert E. Long

"SUMMARY AND CONCLUSIONSTests conducted at Mount Weather indicate that clear water is the best bit coolant and cuttings-removal medium for diamond drilling. All of the mediums tested did show that drilling speed increased when drilling with the faster feed ratios (greatest pressure on the bits). In no case, how¬ever, did the increased drilling speed amount to over 16 percent, and even in a long hole the slight increase in drilling speed would be more than offset by the extra time consumed in setting up.Bit wear was excessive when lubricating agents were used, the most footage per bit was obtained when drilling with clear water in the normal manner, and the next best footage was obtained when drilling with circulated water containing no lubricating agent. The diamonds showed little or no wear in any of the bits, and all bits cut well throughout the tests. They were only taken out of service when erosion of the cast metal had progressed to the point where the diamonds were about to roll out. The lubricating agents evidently hold some of the cuttings in suspension, which in turn help to cut the rock but also wear the metal of the bit.No hard-matrix bits were tested, and it is possible that one or more of the lubricating agents might increase the efficiency of such a bit by keeping it sharp and doing away with the necessity of sharpening by sand blasting. Some tests are planned with hard-matrix-type bits and the same lubricating agents used in the tests under discussion, but it is realized that any drilling advantage gained by the bits sharpening themselves may but at least partly offset by excessive wear of the Pump parts."

Jan 1, 1945

By Joseph S. Coffman

The Bureau of Mines investigated the availability of barite (BaSO4) from 35 U.S. and 41 non-U.S. mines and deposits in 17 market economy countries (MEC's). This evaluation assesses the availability of mud-grade barite, and concentrates consumed by the chemicals and fillers industries. The demonstrated resources defined in this analysis totaled 130 million metric tons (Mmt) of barite (contained BaSO4), yielding a potential 115 Mmt of recoverable barite concentrates. At the 1984 MEC production rate, the evaluated resources would last about 30 yr; however, this would include production costs of up to $100/mt concentrate. An average price needed to cover all costs of production over the life of each operation was determined for both mud-grade and chemical- and filler-grade barite products. Including a 0-pct discounted-cash-flow rate of return (DCFROR), regional weighted- average total production cost ranged from $38/mt for barite concentrates in Asia to $71/mt for U.S. operations. Transportation costs have the greatest impact, contributing up to 60 pct of the total cost of production. Rail transportation costs from the mines to U.S. markets are generally significantly higher than ocean shipping rates on imports.

Jan 1, 1986