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By Yael Miron

Ammonium nitrate-fuel oil (AN-FO) mixtures are used as blasting agents in mining pyrite-bearing ores. The temperature of these ores can increase by the continuous, though at times slow, oxidation weathering of the pyrites. At elevated temperatures, AN-FO reacts exothermally with pyrite, and the reaction becomes self-sustained at 120° C ± 10° C. The Bureau of Mines has conducted an investigation to determine the reactivity of mixtures of AN-FO with pyrite containing ferrous sulfate. The results of tests in a heated vessel simulating a hot borehole demonstrate that small amounts of ferrous sulfate, a major product of pyrite weathering, initiate a self-sustained exothermic reaction with AN-FO at 80° C. Five pct by weight of urea was found sufficient to prevent a reaction among the three ingredients, at least within the limits of the test, which reached 180° C. Smaller amounts of urea and of potassium oxalate slowed down the reaction and delayed its onset to higher temperatures, but did not prevent it.

Jan 1, 1979

Objective A cable bolt can be a strain-measuring device as well as a supporting device in underground mines. Placing instruments on a cable bolt allows certain characteristics of a rock mass, such as high strain and load, to he evaluated during mining and provides a means for mining engineers and mine inspectors to forecast a potential roof fall. Background Thousands of cable bolts are installed in U.S. mines each year. Studies performed by NIOSH researchers show that support loads can exceed the yield point of the steel, which can result in unstable ground conditions that pose direct safety hazards for underground workers. Rock falls can also create secondary hazards, such as caved escape ways and blocked ventilation passages. Development of methods and tools to assist in the evaluation and selection of rock supports could reduce the number of unplanned rock falls significantly. Approach Instrumented cable bolts developed at NIOSH’s Spokane Research Laboratory were used along with existing ground control systems to monitor rock mass loads and movement Axial and shear loads on the cables are determined as these loads are transferred to strain gages embedded in the king wire. In longwall, room-and-pillar, or underhand cut-and-fill mines, rock mass loads and movements can be detected down to microstrains of stress or millimeters of movement. By detecting such small amounts of ground movement and support load, early intervention to prevent a roof fall is possible, and miner safety and health are increased. How it Works Up to 10 strain gages are embedded in the king wire at whatever locations a mine ground control engineer may specify. The gages m either be set in pairs in the same plane to detect shear or set at 90° angles to detect loading in three dimensions. The cables are up to 5 meters long if they arc to be grouted with resin or up to 15 meters: if they will be grouted with cement. They arc capable of holding m ultimate lend of 214 kN and produce reliable readings to 178 kN, as shown in the calibration curve. The cables are fitted with an instrument plug for monitoring the gages and a special head for insertion into the rock. A data acquisition system, such as a Vishay strain indicator box, Campbell Scientific, or Omnidata system, is required to obtain the data for load and displacement calculations.

Nov 1, 1998

By R. V. Ramani, R. Bhaskar

One of the primary means of .control of health hazards from respirable contaminants in mine atmospheres is through design and operation of mines to meet mine health and safety regulations and recommended practices. A U.S. National Academy of Sciences study concluded that for significant progress in coal mine dust control, research should be directed more toward obtaining fundamental understanding of the origin, transport and characteristics of respirable coal mine dust. Theoretical and experimental studies on transport of dust in mine airways, particularly coordinated efforts to validate theory with practice, are scarce. Some empirical models, developed on the basis of experimental data, are available but these models cannot be applied to new .conditions. The purpose of this paper· is to present the results of theoretical and experimental studies on the transport and deposition of dust in mine airways. This study is a part of an on-going research project in the Generic Mineral Technology Center on Respirable Dust. In the paper, the assumptions of the modeling phase of the project and the development of a convection-diffusion equation for dust transport in mine airways will be outlined. The important aspect of the modeling effort.is the capture of the deposition phenomenon. The experiments performed under controlled conditions in a typical mine airway as well as under normal mine operating conditions will be discussed. The comparison of the model predictions ·with experimental results will be made to identify critical areas of agreements and deviations. The implications of the findings and areas for further research and development will be identified.

Jan 1, 1990

By D. Harrington

"Since its establishment in 1910 the Bureau of Mines has consistently recommended the rock-dusting of bituminous and lignitic coal mines as a preventive of widespread explosions. As with many other proposed innovations, the response to the bureau's recommendation has been slow; but during the past 10 years many coal mines have done some rock-dusting, even though probably fewer than 50 of the country's approximately 6,000 coal mines are thoroughly rock-dusted. Notwithstanding the inadequacy of the rock-dusting which has been done in most of the mines which have adopted the new system, numerous cases are at hand. indicating the well-founded basis of the bureau's claims regarding the effectiveness of rock-dust in stopping explosions. Very brief descriptions will be given of several cases in which explosions in coal mines of the United States are fairly definitely known to have been stopped by rock-dust during the past 5 or 6 years; in addition, several cases are cited in which explosions were stopped through the agency of rock-dust and moisture.A rock-dusted mine is one in which the floor, roof, and sides of every accessible working place, including haulage ways, airways, manways, and rooms and connections have an application of rock-dust - for instance, limestone - such that the incombustible content of the aggregate dust on those surfaces is over 60 per cent. The dust in these workings should be sampled at regular intervals to determine whether the incombustible matter in the coal-dust is less than the necessary minimum of 60 per cent; another application of rock-dust should be given when the incombustible percentage is less than 60. (As an example of thorough rock-dusting, see Bureau of Mines Information Circular 6578, 1932, which describes how rock-dusting is done in Alabama at a cost of 1.8 cents per ton of coal for a thorough application; Report of Investigations 3060, February, 1931, Rock-Dusting In A Pennsylvania Coal Mine; or Information Circular 6244, 1930, giving data, including costs, on rock-dusting in coal mines in New Mexico.)An explosion may be started by the ignition of gas, even when rock-dust is present; hence it is not correct to say that rock-dust will prevent an explosion of gas; however, if rock-dust has been applied to a working place which has present an explosive mixture of me-thane and air, and if an open light is used or a blown-out shot or an electric arc occurs, although there will very likely be an ignition and possibly an explosion, the rock-dust will certainly prevent ignition of the coal-dust nearby, and unless the general atmosphere has an explosive gas mixture, the rock-dust will stop propagation of the flame throughout the mine. In other words, if an explosion is started by gas or by coal-dust and the mine has been rock-dusted as defined, the rock-dust will prevent widespread extension of the explosion, unless the general atmosphere contains methane and air in explosive proportions.With these definitions clearly in mind, instances are now given where rock-dust has played a prominent part in the stopping of several explosions. No cases have been included where there was any reasonable doubt that rock-dust had taken a definite part in the limiting of the explosions."

Apr 1, 1932

During the summer of 1973 we were asked to perform a theoretical investigation of the propagation of low frequency (LF) radio waves down deep (10,000 feet) hoistshafts* for the case where the hoist cable ("rope") is the only metal conductor present. Propagation is by means of the TEM coaxial mode of transmission in which the hoist cable serves as the inner conductor and the surrounding rock acts as the outer conductor. Since the rock is a relatively poor electrical conductor the current in the outer conductor of the coaxial line is not confined to a very thin surface layer as in a metal coaxial cable, but spreads radially to a distance that is generally many times the shaft diameter. This feature of the wave propagation requires a more sophisticated theoretical treatment than the approximate skin-depth theory that is adequate for metal coaxial lines. In this Part we treat the hoist shaft wave propagation loss, characteristic impedance, and the field current distributions in the surrounding rock medium. We also show that the large penetration of the wave into the rock outer conductor does not present a difficult problem with regard to coupling the transmitter or receiver to the transmission line with a minimum of insertion loss, but that the large impedance mismatch caused by the capacitance termination between the cage and shaft wall may well be the most significant contribution to overall system loss. Inductive coupling and impedance matching to the hoist rope/shaft transmission line are also treated briefly. Preliminary results indicate that a broad minimum in overall system loss should occur between 100 kHz and 1 MHz, possibly centered around 300 kHz. Further work is needed to better quantify this signal loss behavior, compare it with hoist shaft electromagnetic noise spectral data recently acquired by NBS, and identify the most favorable operating frequencies.

Jan 1, 1974

By K. Rubow, Z. Zhlqun, V. Marple

A theoretical technique has been developed and verified experimentally for determining the aerodynamic diameter of irregular shaped particles. The aerodynamic diameter of a particle is a very important property in determining where that particle deposits in the respiratory tract. Many instruments, such as impactors and cyclones, will determine the aerodynamic size distributions of aerosol particles but few analyze the particles individually. The theoretical approach of our technique is to solve, by use of high speed computers, the three dimensional Navier-Stokes equations to obtain the flow field around an irregular shaped particle of any contour. The computer program will then determine the drag on the particle, and thus the aerodynamic diameter of the particle can be calculated. The experimental approach has been to pass the particles through a centrifuge and collect the particles upon a collection foil. The position of a particle on the foil is an indication of its aerodynamic diameter. These particles were then shadowed in two orthogonal directions and inspected under an SEM. The top view of the particle in the SEM plus the views of the two orthogonal shadows allows one to determine the three dimensional shape of the particle. Studies have been performed on silica, coal and talc particles with aerodynamic diameters in the 1 to 4 um size range. The three dimensional shape, as is determined from SEM analysis was used in the theoretical computer program and the results compared. It was found that in most 'cases the agreement between the experimentally and theoretically determined aerodynamic diameters was within 5%.

Jan 1, 1988

By E. V. Cilento, K. A. DiGregorio, R. C. Lantz

This laboratory has developed a sensitive electro-optical method to quantify the initial rate (R) and total amount.(MAX) of superoxide (SO) produced by single pulmonary alveolar macrophages (PAM). The method uses a microscope to visualize PAM in culture, and to video record the images during the time the cells produce SO. MAX and R are calculated from measurement of temporal changes in optical density in the images due to precipitated diformazan formed by the reaction of SO, produced by each PAM, with nitroblue tetrazolium present in the culture medium. To date, values of Rand MAX, measured due to adherence of PAM to the dish, have been compared to values obtained when quartz, coal mine dust (CMD), and kaolin were added to the medium (in vitro). R and MAX have also been calculated for PAM lavaged from animals exposed to quartz and CMD in the WVU Inhalation Facility. Presently, experiments are being done using serum which permits PAM to be restimulated by different dusts to help establish a dose response effect, and a means to study the effects of lung surfactant on modifying the toxicity of inhaled dusts. Long term, this methodology should provide useful insight· into establishing the role SO plays in the phagocytosis of inhaled dusts and bacteria, in PAM dysfunction, and in lung diseases such as pneumoconioses. Supported by the Department of the Interior's Mineral Institute Program administered by the Bureau of Mines through the Generic Mineral Technology Center for Respirable Dust (G1135142).

Jan 1, 1988

Objective Develop a method to warn of hazardous conditions and enhance safety during operation and inspection of vertical mine shafts and hoists. Background Mine hoisting is the most critical and potentially the most dan¬gerous operation in underground mining. Many hazards are related to falls of miners and materials, ground instability, and malfunction or lack of safety devices. All have the potential to cause a cata¬strophic accident. A condition known as "slack rope" is particularly dangerous, expecially if it occurs without the operator's awareness. The most common occurrence of slack rope is in metal or nonmetal mines that have a history of ground control problems near the "haft. Approach Studies of hoist safety features and Mine Safely a and Heath Administration (MSHA) accident statistics suggests a need to measure wire rope tension, conveyance speed and position, and shaft guide misalignment. The most accurate data are obtained directly from the conveyance. Such data could warn of potentially dangerous situations during hoisting operations, as well as during inspections, maintenance, and lowering of large equipment. Figure I shows the concept for monitoring wire rope tension, conveyance position, and guide displacement. Progress to Date A conveyance-mounted system has been developed that monitors rope tension: hoist conveyance position, speed, and load; and shaft guide misalignment. A "flex-beam" load sensor mounted just above the- conveyance protects against slack and tight rope. The measurements are transmitted 60 times a second via wireless equipment from the conveyance to the hoist room. An encoder mounted on the conveyance eliminates the need to correct the position because of rope stretch. Figure 2 shows the encoder wheel and guide displacement sensors being mounted on a cage in¬spection deck. A potentiometer monitors misalignment of the shaft guides during inspections. Information about the cage or skip can be acquired by the shaft inspector using a hand-held indicator. Inspection can also he conducted remotely from a station or hoist room using the wireless link to a laptop computer. Figure 3 shows test results from a simulated slack rope condition. Patent Status NIOSH has a patent pending on this device entitled "Cable-Load¬Sensing Device." For More Information NIOSH is seeking cooperators to assist in further tests of this technology to improve hoisting safety. Additional information can he obtained by contacting Michael J. Beus, Steven Iverson, or Elaine Cullen, Technology Transfer Officer, NIOSH, Spokane Research Laboratory, Spokane, WA 99207 at (509) 354-8000.

Feb 1, 1998

By L. C. Ilaley

The Buresa. ot Mines at its Pittsburgh Station conducted tests aa earl7 a.a 1911 looking into the satety of miniature electric bulba. The first teata were maie with bulbs euch as were being sold with the partly developed lamps then on the market. 'l'he.sa aarly teats demonstrated the da.nger of using minia.tu:re bulbs in explosive mine atmospheres unless the current that enet gized the glow!ng filament was in aome minner inter.N.ptecl if the glass surrounding the filanant should be broken.

Jun 1, 1922

By S. H. Katz

Tar and suspended matters are removed from manufactured gas used for domestic and industrial purpose.

Jul 1, 1922

By David W. Houseknecht

Probabilities of encountering coalbed discontinuities during vertical or horizontal drilling in a specific coalbed can be estimated based on analysis of mined-out areas of the coalbed where the size, shape, orientation, and distribution of discontinuities are known. The result-ant probability estimates can be applied to cost-risk evaluations of drilling programs proposed for exploratory, developmental, or methane drainage purposes in undeveloped areas of that coalbed. Data compiled from mine maps of the Beckley Coalbed in southern West Virginia were used to estimate the probabilities that discontinuities would be encountered in two illustrative hypothetical drilling programs--one for drilling vertical boreholes and the other for drilling horizontal boreholes. Analysis based on a mined-out area of the Beckley Coal bed indicated that vertical methane drainage boreholes spaced 1,000 feet apart in a square grid pattern would each have a 29 percent probability of encountering a discontinuity in a geologically unexplored area of the coalbed. It was also determined that exploratory vertical drilling could locate most of the discontinuities if a borehole spacing of 2,500 feet were used. For horizontal drainage boreholes in the Beckley Coalbed, the analysis indicated a linear relationship between hole length and the probability of encountering a discontinuity.

Jan 1, 1982

By Todd M. Ruff

The lack of visibility near earthmoving equipment resulted in six fatalities in U.S. surface mining operations during 2003. These accidents were the result of either a piece of equipment striking another vehicle or worker, or the equipment traveling over the edge of an embankment. Figure 1 is an example of a recent accident that resulted in serious injuries to one worker and fatal injuries to two others when a van parked in front of a haul truck. Two fatalities occurred in separate incidents when front-end loaders struck workers. Another two workers were killed when their equipment backed over the edge of a highwall or dump point [1]. There is clearly a need to provide better information to equipment operators regarding their surroundings. [ ] Researchers at the National Institute for Occupational Safety and Health (NIOSH), Spokane Research Laboratory, are working to reduce these accidents by developing systems that sense obstacles and changes in terrain near the equipment and provide this information to the operator. Many off-the-shelf proximity warning systems that were developed for automobiles, light trucks, and recreational vehicles were evaluated on off-highway dump trucks [2]. Many limitations were found with existing systems, including frequent false alarms, limited detection range, a lack of specific information on an obstacle (e.g., location, identity), difficulties in finding suitable mounting locations, and an inability to withstand the environment. These limitations have necessitated the development of new systems designed specifically for large, off-highway, earthmoving equipment. New off-the-shelf systems available for mining equipment include radar and tag-based detection systems. Prototype systems now being developed include a proximity warning system based on the Global Positioning System (GPS) and a computer-assisted stereovision system. Development of these new systems was accomplished by working with manufacturers to modify existing systems to meet the needs of surface mining and through cooperative research with organizations to develop completely new solutions. A typical proximity warning system consists of a sensor or antenna mounted on the equipment that detects the presence of obstacles and an alarm interface in the cab of the equipment. Some systems, as described in more detail below, also require that other vehicles and personnel on the ground be outfitted with electronic tags that transmit an “I’m here” signal back to the system (e.g., radio signal detection systems or GPS). Many types of proximity warning systems are on the market, but they are not all discussed in this paper. APPROACH In past work, engineers at NIOSH evaluated several off-the-shelf proximity warning technologies in order to verify their effectiveness on off-highway dump trucks [2]. Dump trucks were chosen because of the number and severity of accidents involving this type of equipment and because extensive blind areas around these trucks are typical. This experience allowed engineers to limit the number of systems chosen for long-term tests at mine sites to those systems showing

By Robert J. Willard

This chapter includes tables for 1982 that were not available in time for publication of the 1982 Minerals Yearbook, but does not include corresponding tables for 1983. The value of raw nonfuel minerals produced in the United States during 1988 was estimated at $21.1 billion, an increase of $1.5 billion over the value for 1982. This is a reversal of last year's downturn in value from that of 1981, which was the only decrease noted since 1971; hence, an overall trend of increasing values has been maintained for 12 years, except for 1982. Although the reversal is a basis for cautious economic optimism, it is tempered by continued problems in the domestic mining industry: inadequate funds for capital investment and competition with other countries that have lower production costs. Output of metal commodities in 1983 increased for 8 out of 21 metals, and metal values, in general, increased for 9 of the metals. Output of nonmetal commodities was mixed, with 24 nonmetals showing increases, 20 showing decreases, and 2 unchanged. Nonmetal values were also mixed in 1982: 25 showed increases, 20 declined, and 1 was unchanged. Improvements in the international metals market have not been forthcoming because of the continued depressed prices for major metals. Governments in foreign producing countries have been concerned with maintaining employment and continuing foreign exchange flows through mineral exports. Consequently, the excess of supply in the face of shrinking demand brought downward pressure on metal prices in general, except for the precious metals. On the domestic front, this situation means U.S. mining companies must become even more cost efficient. The major trend in the mining industry in 1983 was to cut costs further, reduce or stabilize total production, reduce outlays for major capital equipment, modify existing systems and equipment, and streamline operations. Most of the accomplishments reported herein reflect this trend.

Jan 1, 1984

By L. C. IlsLey

A n'Ulllber or operators have installed f'lBJ!le-proot or so-called exploaion­ proot electrical outfits, under the impression that such equipments met· all of the reqiirements of the Bureau of Mines as regards safety, There a.re todq in gaseous mines a large nwnber of euipments that have not been approved by the Bureau ot Mines, and unless mod1f'iecl could not receive sucl1 approval.. These e qu.ipments represent in pa.rt the product of manufacturers whil ha.ve never submitted. equipments for insri?ction or tests. and iri pat types developed. previous to the safety work or the bureau. Sometiu.es saleimen advocate the use of unapproved. types in gaseous mines in place of Bureau of Mines approved outfits, the purchase price beini slightly less than approved types,

Sep 1, 1922

Objective To accurately measure very low air velocities (0-100 ft/min) in U.S. large-opening underground metal/nonmetal mines. Background Hundreds of metal/nonmetal underground mines operate throughout the United States. They extract commercial products from deposits such as limestone, salt, and gypsum. Mining generates a wide variety of gases and dusts, such as silica, diesel exhaust, radon, blasting byproducts, and perhaps even methane. If these substances become airborne, they can adversely affect the health and safety of underground workers. Many metal/nonmetal mines have large cross-sectional airways that could be 60 times larger than an average underground coal mine entry. These large airways require adequate volumes of fresh air to dilute, make harmless, and exhaust the toxic and, at times, explosive byproducts. However, in some underground mine sections, air movement is barely perceptible. The technology of measuring very low air velocities will become increasingly more important for operators of large-opening stone mines in order to monitor miner exposure to diesel particulate matter. Conventional anemometers (e.g., vane) are capable of accurately measuring air velocities only above 100 ft/min. Thus, it was necessary to investigate other anemometry technology to detect low air velocities in the range of 0-100 ft/min. Two different portable ultrasonic anemometers were tested. Actual testing was done in an underground limestone mine with openings about 51 ft wide by 29 ft high. Ultrasonic Anemometers Vane-type anemometers are commonly used by engineering personnel throughout the underground coal mine industry. They work well in measuring air velocities >100 ft/min. However, a separate technology, e.g., portable ultrasonics, is needed to measure air velocities much below 100 ft/min at various places within the large mine opening. Laser-doppler technology was also considered for this application, but was ruled out because of its high cost and other technical limitations. With no moving parts, the portable ultrasonic anemometers are claimed to be accurate down to about 1or 2 ft/min. The first type of ultrasonic anemometer that was examined underground is manufactured by Gill Instruments Ltd., Hampshire, U.K. The U.S. distributor is IN USA, Needham, MA. The Gill Instruments Solent Volometer (figure 1) is a battery-powered, single-axis anemometer meant for measuring low to medium air flows up to1,999 ft/min. It uses the ultrasonic "time of flight" principle where pulses of high-frequency sound are transmitted along the air flow path and the time taken to reach the receiver is measured. The faster the air speed, the quicker the pulses reach the receiver. The second ultrasonic anemometer that was examined under-ground is manufactured by Airflow Developments Ltd., Buckinghamshire, U.K. The U.S. distributor is Airflow Technical Products, Inc., Andover, NJ. The Anemosonic UA-6 (figure 2) is a battery-powered, handheld instrument with digital display. It measures air velocity (0 to 9,999 ft/min) or volume flow, flow turbulence intensity, and air temperature. Neither device is considered to be intrinsically safe for use in underground gassy coal mines. A comparison of salient specifications of both instruments is shown in table 1. The total suspended weight includes the instrument (Gill) or instrument probe (Airflow) plus about 35 ft of connecting cable attached to the pole. This combination of instrument plus cable length allows two operators to measure air velocities up to about 30 ft above the mine floor. Figures 1 and 2 show how each unit would be attached to an extensible, graduated fiberglass rod in order to position the sensor probe at a certain spatial point (centroid of the quadrate) within the underground large opening.

Jan 1, 2003

Provide room-and-pillar operators with practical in- formation and guidelines concerning multiple-seam mine design to reduce ground problems associated with the interaction of adjacent working.

Jan 1, 1994

Provide ear protection which allows normal, unaltered hearing at low noise levels, yet protects the wearer from excessive noise. The Approach: A commercial earmuff with integral speakers has been adapted with a special amplifier so that low sound levels are not affected, but higher noise levels automatically reduced. How It Works: The discriminating earmuff developed by the Bureau of Mines has two modes of operation. In the first mode, where input sound levels are less than or equal to 83 decibels, the wearer will perceive noise at its actual level. For inputs in excess of 83 decibels, the second mode of operation begins and the sound perceived by the wearer is progressively attenuated, or reduced, as the input level is increased. A recognizable difference still exists between two adjacent sound levels enabling the wearer to differentiate between them.

Jan 1, 1975

By R. N. Roby

"INTRODUCTION A preliminary examination of the Green Monster and Benich copper prospects was made by engineers E. W. Newnan and George N. Bennett, of the Bureau of Mines, on December 13, 1943. In an unpublished report, it was stated that certain geologic features appeared to be similar to those associated with the copper deposits of the nearby Butte district. On these premises, a preliminary diamond-drilling program was recommended to explore 300 to 400 feet below the mineralized outcrops for the possible presence of a sulfide enrichment zone. In accordance with that recommendation, three holes were drilled. This report presents the data provided by that preliminary drilling exploration.ACKNOWLEDGMENTSIn its program of exploration of mineral deposits, the Bureau of Mines has as its primary objective the more effective utilization of our mineral resources to the end that they make the greatest possible contribution to national security and economy. It is the policy of the Bureau to publish the facts developed by each exploratory project as soon as practicable after its conclusion. The Mining Branch, Lowell D. Moon, chief, conducts preliminary exminations, perform the actual exploratory work, and prepares the final report. The Metallurgical Branch, R. G. Knickerbocker, chief, analyses samples and performs beneficiation tests.The field work on the Bull Run exploration project was supervised byE. W. Newman engineer in charge of the Helena field office. The chemical analyses and assays included in this report were performed under the direction of A. C. Rice, acting engineer in charge, Bureau of Minos Rare and Precious Metals Experiment Station at Reno, Nev. The diamond-drill cores were logged by geologists of the Federal Geological Survey."

Mar 1, 1947

By W. W. Weller

Low-temperature heat capacity measurements were conducted, and entropies at 298.15° K were evaluated for sodium monomolybdate (Na2Mo04), magnesium monomolybdate (MgMo04), and calcium monomolybdate (CaMo04). The 298.15° K entropy values were sodium monomolybdate, 38.1±0.3 cal/deg mole, magnesium monomolybdate, 28.4±0.2 cal/deg mole, and calcium monomolybdate, 29.3±0.2 cal/deg mole.

Jan 1, 1963

By A. B. Hooker, L. C. IlsLey

Several ignitions or mine pa, which might have led to explosions, and at least ona mine fire attributed to heated leg wires of electric detonators, have occm.rred. at rn1::.es in which outside shot firing is practiced. Photographs taken at one mine ind.la.ted. that the wires became red hot during firing. These results having been --i·-led. to the .Lttention of the electrical section of the Bureau of the Mines, ignitions the tests and to reportd aid in herein preventing were made future to trouble determine of if this possible kind, the cause of The investigation, which 1• considered preliminary, included tests to determine the conditions tha.t cause gas ignitions from heated. leg wires of electric and. of detonators, copper leg possible wires, remedies The tor samples such of heating, wire used. and in the the relative test were behavior the of reg\llar ironDa. Pont iron and copper leg wires (No, 22 A,W,G.) C\1t from Du. Pont electric detonators.

Aug 1, 1922