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Objective To identify techniques to reduce the probability of gob gas explosions. Background In the last 6 years, seven explosions of methane and/or coal dust occurred within worked-out, sealed areas (gobs) of underground U.S. coal mines. These explosions, believed to have been started by lightning, destroyed many mine seals and caused much damage external to the sealed area. Three of these gob gas explosions occurred in one mine in Alabama over a 3-year period. Fortunately, the explosion forces and the toxic gases that vented from the sealed gob area did not cause fatalities or injuries, but they destroyed several large seals. If miners had been inspecting or working near these areas, the potential for serious injury and/or death would have been high. The United Mine Workers of America and the Mine Safety and Health Administration (MSHA) requested that the National Institute for Occupational Safety and Health (NIOSH) help identify the mechanisms for lightning penetration into the gob and recommend ways to reduce the probability of occurrence of future explosions from such lightning penetrations into sealed areas of underground coal mines. Because three of the explosions occurred in a single mine, special attention was focused on these particular explosions. The first occurred in April 1994 in a sealed area, which enclosed about 1.35square miles of abandoned workings (gob). This explosion destroyed 3 of the 38 seals that surrounded the gob. These seals were less than 2,000 ft away from three 4.5-in-diam steel-cased test wells that extended from the surface into the mine entry. At the time of the explosion, the National Lightning Detection Network (NLDN)verified 12 lightning strikes within 10 miles of the mine, including several above the gob. After the 1994 explosion, the damaged seals were rebuilt using an acceptable seal design capable of with standing a 20-psi explosion, as required by 30 CFR 75.335. On January 26,1996, a second gob explosion destroyed five more cementitious pumpable seals less than 2,000 ft away from those destroyed in 1994and even closer to the steel-cased wells. The NLDN verified72 lightning strikes in the area of this second gob explosion. Compressive strength analyses of fragments from the destroyed seals showed that strengths ranged from 11 to 138 psi, with an average of83 psi. This is over 100 psi below the minimum 200-psi compressive strength requirement for cementitious pumpable seals. These seals were again replaced. On July 9, 1997, the third and most violent explosion occurred in the same vicinity of the last two explosions. Three more cementitious pumpable seals were destroyed, including one newer seal that exceeded the minimum 200-psi compressive strength requirement. The NLDN verified 695 lightning strikes above the mine during the time in which the explosion occurred. MSHA's

May 1, 2001

By Richard L. Rains

During this study in 1983, the U.S. Bureau of Mines examined one mine and five prospects in the Greenwater Valley Wilderness Study Area (WSA). No mineral resources were identified within the WSA. Principal mineral commodities in the WSA are gold and silver with minor lead, and zinc. Two properties have significance; sample analyses indicate the Salsberry Prospect may have gold-silver-lead-zinc resources, and the Graham Jem Mine may have gold resources. The likelihood for development is greatest at the Salsberry Prospect, although the only recorded production from the study area was from the Graham Jem Mine; in 1908 less than 1 ton of gold-bearing ore valued at $25,000 per ton was produced. Gold, silver, lead, zinc, and copper minerals in the WSA are associated with rhyolite dikes and quartz veins in Precambrian gneissic rocks, commonly concentrated in sheared zones along the dikes and veins. Although known to contain silver-lead deposits elsewhere, Precambrian Noonday Dolomite sampled inside the WSA contained no significant mineral values. Much of the WSA is covered by relatively unmineralized Tertiary and Quaternary volcanic rocks. The Bureau collected 140 rock samples at four adits, nine shafts, four trenches, and 33 prospect pits in the WSA. In 1983, 14 lone claims and one millsite within the study area were current. No patented claims, placer claims, or coal, mineral, oil and gas, or geothermal leases were in the WSA.

Jan 1, 1985

By O. P. Hood

The spontaneous combustion of coal lies at the bottom of the subject of storage. It is useless to store coal that is to be lost by fire from spontaneous combustion. Every engineer is familiar with the phenomena of the self-heating of coal, yet, for all that, spontaneous combustion is relatively rare. If we counted the times a portion of cod was stored where it would be undisturbed for a few weeks, the number of such storage operations in any one year would mount into the millions. Of these, a relatively small number show the phenomena of spontaneous combustion and time risk per ton is very small. It is extremely rare that in the smaller operations involving; only a few tons there is any heating. There is no spontaneous combustion of anthracite, and very rarely does the domestic consumer of bituminous coal find troublesome heating. The main interest in the subject lies in the large piles needed as reserves for public-service utilities, and the industries. Everyone desires to have directions for storage that are perfectly simple and yet will insure against loss. Unfortunately, the problem is too complicated for a simple solution. Many of the factors involved are difficult to determine, as we have no practical means of quantitative measurement. The factors involve chemistry, physics, and engineering, and the man who is

Jan 1, 1939

By E. R. Rodriguez

Improved practice resulting from recent changes in the method of supplying compressed air and in pneumatic drilling equipment used in secondary drilling and in development work at the Morenci mine of the Phelps Dodge Corp., has resulted in improved safety conditions, as well as in a reduced cost per foot of drilling. A large stationary compressor installed outside the mining area and the compressed-air pipelines in the mine were replaced by portable compressor units. A self-propelled, self-contained drilling unit was obtained for drilling large footages where short moves were involved. Large wagon-drill units were replaced by faster and lighter drill machines and conventional bits by carbide insert bits. The safe practices employed in air drilling and in the related blasting and scaling operations have contributed to an excellent safety record at this mine. The complete sets of instructions listed in the company codes of safe practice aid materially in training employees.

Jan 1, 1956

By R. T. Johansen

A gradual decrease in injection rates commonly occurs as a water-flooding project becomes older. This decrease can be attributed to changes in reservoir conditions, such as swelling of clay minerals, fillup, or gradual plugging of the sand face. However, a rapid decrease in the rate of injection indicates abnormal behavior and is cause for alarm. Extreme plugging conditions can completely stop injections into a formation. Such behavior in wells was the main concern of the tests described in this report. An accepted method of alleviating this condition is by backflowing input wells - closing the supply lines to the wells and allowing the reservoir pressure to force water back into the wellbore and to the surface. If backflowing is not successful, a string of smaller diameter pipe sometimes is run inside the casing, and the sand face is flushed with a waterspray. More drastic treatment is to inject acid into the wellbore to dissolve extraneous matter, or even part of the reservoir material, in an attempt to restore the permeability of the sand immediately around the wellbore. Any of these procedures can he coordinated with bailing and swabbing of the well for cleanout purposes.

Jan 1, 1957

By Ernest L. Corp

Seepage forces computed by a finite-element flow program are combined with gravity forces in an elastic-plastic stress-analysis program to determine the stability of mine-waste slopes. Computer output provides a cross-sectional plot of the dam or embankment showing the safety factors for each element. The combined finite-element program called SEEP-SLOPE was used to analyze several trial embankments and the 1972 Buffalo Creek Dam failure Safety factors computed by the finite-element method (FEM) were compared with those computed by Bishop limiting-equilibrium method. For individual slip circles, there was little correlation between the factors of safety computed by the two methods. Both predict failure, but FEM shows a different mode of failure plus development of potential failure zones not indicated by conventional methods. Besides having a better theoretical basis than the Bishop method, FEM requires no assumptions regarding the location or geometry of the failure surface. As a result, the program will show progressive development of a failure zone, and areas can be pinpointed where remedial measures should be taken. In addition, nonhomogeneous cross sections can be analyzed, and zones of potential piping can be defined.

Jan 1, 1975

By William G. Pariseau

Elastic-plastic finite-element simulation of cut-and-fill stoping in deep, narrow veins shows substantial quantitative agreement with field measurements of stope closure and fill pressure made at two mines in the Coeur d'Alene mining district of northern Idaho. The simulation procedure, validated by field data, was used in an analytical study of vein-wall closure and sill-pillar stress as influenced by fill modulus, rock modulus, and premining stress. Ratios of closure and pillar stress in the filled stopes to closure and pillar stress in the unfilled stopes are used as prediction indices for fill performance. In general, the support capability of fill increases dramatically as the ratio of fill modulus to rock modulus approaches 1. A significant reduction in closure .from the open stope--up to 75 percent--occurs with a relatively low-quality 10-ksi-modulus fill (rock modulus of 1,000 ksi). However, a higher quality fill is needed to achieve a substantial reduction in pillar stress from that of the open stope. A 100-ksi-modulus fill reduces pillar stress in both the 36-foot and l6-foot pillars (vein width is 10 feet) by about 50 percent relative to the open stope.

Jan 1, 1976

By Constantine C. Popoff

"INTRODUCTION AND SUMMARYDuring 1946 several high-grade limestone deposits in western Washington were examined by the Bureau of Mines. This report presents the data obtained from investigation of the Sauk Mountain deposits in east-central Skagit County, Washington.The investigation consisted of transit and topcgraphic surveys and sampling. The areas selected for sampling were first cleaned by blasting; channel samples up to 40 pounds were cut where practical. Chip samples averaging 30 pounds were taken where channel samples could not be cut. A total of 21 samples in the Sauk Mountain area were taken and. analysed. The locations of the samples are shown in figures 2 and 4, and the analyses are listed in tables 1 and 2. This investigation is a part of a long-range program of general investigation of mineral resources for future industrial development of the Pacific Northwest. The Sauk Mountain deposits were investigated for the purpose of disclosing now sources of high-purity limestone, which could be mined and shipped at low cost to Seattle and other industrial cities in the Pacific Northwest."

Oct 1, 1948

By Raymond B. Ladoo

The uses of talc are many but are not, in general well known or fully developed within the last decade several companies have realized the possibilities of greatly increased use and have intelligently proceeded to develop some of the fields which seemed most promising. This has had a tendency to lift talc from the obscurity in which it had existed for years, but the work is only started and much remains to be done. Considerably more attention has been paid to the technology and utilization of talc in Germany and Austria than in this country, despite the fact that the United States produces 65 of the world's talc and Germany and Austria combined but 5.4%. In the "Bericht,uber die tatigkeit des verbends der talcum-interessenten in Oesterreich-Ungarn" (Proceedings of the Austro-Hungarian Talc Association), for the years 1912 and 1913, many notes upon new uses appeared, together with suggestions as to further development of old uses. Aside from a few notes on the use of tar in paper, little has been published in the English language upon this subject. By recent action of the Talc and Soapstone Producers Association (U.S.A.) funds for research into the properties and uses of talc have been made Available and it is hoped that markets will be materially broadened a a result of this work.

May 1, 1920

By M. C. McCall

When electric current of any appreciable magnitude flows from a power line into the earth, a change sometimes takes place in the conditions of resistivity immediately surrounding the electrode or medium of contact. If the conducting medium is composed of moist earth or clay the effect is to increase rapidly the resistance. If the conducting medium is coal or a coal bed, the effect is one of slowly decreasing resistance as the coal is carbonized, If, however, the flow of current is not enough to carbonize the coal, it will dry slowly, with a resultant increase in resistance. Measuring ground resistance, or impedance, with conventional commercial ground testers does not always indicate the current that will flow in the earth circuit from a direct-current or an alternating-current power circuit. The exact reason for this has not been determined however, it is thought to be due to the comparatively minute currents used for such testing. A typical ground, tester used by the authors for this work indicated a maximum current of 25 milli-amperes. The frequency of this testing current also has an effect on the readings in all probability. While the possibilities of the effects of varying frequencies has by no means been fully explored in this investigation, there are very definite indications that the impedance of a circuit through a section of earth will vary in some inverse relationship to the frequency of the applied voltages. This is evident at ordinary power-line frequencies ns well as at higher frequencies up to 200 kilocycles, which was the highest frequency available for tests in this investigation. This report is written in the hope that it will stimulate further investigation of the possibilities suggested for communication and the development of safety devices for increased electrical safety in coal mining.

Jan 1, 1952

By N. H. Coates

A small, special-purpose centrifugal compressor was developed to circulate 60 pounds per hour of helium at 1,000° F and 250 psig because standard, commercial units were not available. Performance characteristics of this compressor were determined at helium flows of 2,000 to 18,000 std cu ft per hour, pressures of 100 to 250 psig, and temperatures of 100° to 1,000° F. This range is 2 to 90 actual cu ft per minute. Several graphs show the adiabatic head developed by the compressor over this wide flow range at various combinations of temperature and pressure. A compressor performance map relates pressure ratio to mass flow, temperature, pressure, and speed. This map can be used to accurately predict compressor performance factors within the range of operating conditions covered by the experiments.

Jan 1, 1963

By R. Blickensderfer

Several thin film absorber stacks with spectrally selective characteristics were developed by the Bureau of Mines. The stacks consisted of a silicon thick film or a zirconium compound thin film on a reflective thin film of silver. The zirconium absorber films, with the general formula ZrCxOyNz, were prepared by reactively sputtering zirconium or zirconium carbide in argon with small amounts of oxygen, nitrogen, or both, or by oxidizing zirconium films in air. A few similar types of films were prepared from titanium. The short-wave absorptance over the solar spectrum, a(s), and thermal emittance at 600 K, e(600 K), of the solar absorber stacks were calculated from room-temperature reflectance data. The values of a(s) ranged from 0.47 to 0.93, e(600 K) from 0.49 to 0.034, and the ratio a(s)/e(600 K) from 1.7 to 34. The specimen with the best combination of properties, a ZrNx-Ag stack, had a solar absorptance a(s) of 0.85 and a ratio, a(s)/e(600 K), of 24. The effect of film thickness and composition on spectral selectivity was determined. An emissometer for measuring normal total emittance up to 800 K and a method for determining a (s), e(T) (hemispherical), and a(s)/e(T) using simulated solar radiation are described. A calorimetric method for measuring a(s) and e(T) (hemispherical) at elevated temperature is also described. Measurements made on several specimens agreed favorably with calculated values.

Jan 1, 1976

By Robert C. Ellman

Stockpiles containing 2.3 million tons of lignite constructed in the period 1948-56 in conjunction with the construction of Garrison Dam on the Missouri River demonstrate successful stable long-term storage of lignite. Uniform and thorough compaction of each of the I-foot-thick layers by which the piles were constructed produced a bulk density of 70 Ib/cu ft. Air penetration into the stockpiles was restricted to a degree that prevents spontaneous heating or deterioration of the stored lignite, A continuing record of observations beginning with stockpiling operations in 1948 has been accumulated, This includes periodic fuel analysis, analysis of pile gases, and measurement of pile temperatures on the first large stock-pile, pile 5. This report describes the stockpiling method, the changes in heating value, pile gas composition, and pile temperature and summarizes observations from 1953 to 1964, Data accumulated attest to the stability of the stored lignite. The variation of the average heating value of periodic pile-depth samples is only 160 Btu/lb (11,990 to 11,830) on the moisture" and ash-free (maf) basis during almost 10 years of storage. Temperature levels of the pile interior are progressively decreasing. At pile surface, cyclic variations occur with the season. The only problem encountered with the large stockpiles is wind and water erosion of the pile surface. The partially successful control measures used are described.

Jan 1, 1967

By A. Wahab Khair, Richard D. Begley

"This paper presents results of destructive tests performed on rectangular coal specimen under the influence of two vertical and simultaneous wedge indentation forces. Several wedge designs and spacings were utilized in compression tests. The objective of these experiments was to qualitatively monitor the effect of different wedge designs and spacings on the stress distribution within the coal specimen.Coal samples from the Waynesburg coal seam were cut and trimmed to cubical dimensions of approximately 5 X 10 X 20 cm. These specimen were subjected to parallel compressive forces through two vertically applied wedge indentors. Loading was achieved with a hydraulic hand pump in order to facilitate interferogram construction. The load increments were limited due to the sensitivity of the holographic interferometric technique (holometry) in measuring small displacements; therefore, interferograms were taken only during similar increments in order to allow for a qualitative comparison between different wedge design and spacings. In some cases, interferograms were taken immediately before and after failure of the specimen.Introduction Failure Modes Three distinct modes of failure occur when geologic materials are subjected to wedge indentation forces. As shown in Figure 1, a crushed zone is located immediately adjacent to the indentor while chipping can occur if the fractures initiated in the crushed zone extend upwards to the free surface.. The third failure mode is a zone of intricate frac¬tures located between the crushed zone and the chipping zone. Several experiments have been conducted over the years to better understand crater formation and stress distribution within geologic materials under the influence of an indentor. Generally speaking, crack initiation and propogation observed in these experi¬ments correlate fairly well with wedge indentation theory; however, the nature of the .fractures is greatly influenced by different material properties such as grain size and cleavage planes. In other words, a wide range of behavior has been found in different rocks subjected to wedge penetration. For example, it has been observed that some rocks are merely crushed and indented while others are more prone to cracking and chip formation. Therefore, the development or nondevelopment of chips depends mostly on wedge geometry, rock type and depth of penetration. This work is part of the study associated with opti¬mization of cutting parameters, which is best modeled by using brittle materials and subjecting them to rigid wedge penetration tests."

Jun 1, 1988

By T. L. Marchewka

As part of its program to conserve the Nation's natural resources by developing improved performance materials, the Bureau of Mines, U.S. Department of the Interior, in cooperation with the U.S. Department of Energy, has conducted an investigation of materials of construction able to withstand the high temperature and hostile environments encountered in coal gasification units. Refractory pipe liners are required when extremely hot gases or abrasive solids are transported between processing units in the gasification plants. One promising technique for producing refractory pipe (or refractory pipe liners) is centrifugal casting. For this study, the effect of processing variables such as workability, additives, reinforcement and spinning time, and centrifugal force were evaluated using four commercial refractory concretes. In addition, data on characteristics such as strength, density, abrasion, and spalling resistance of 5-inch-diam refractory pipe were developed. Techniques for forming large-diameter (19-inch) refractory pipe also were evaluated. The test results indicated that all four refractory concretes could be made into strong, homogeneous pipe, but that optimum casting parameters had to be determined for each specific composition. The investigation revealed that the major controlling factor in the production of the centrifugally cast pipe was the workability of the refractory concrete.

Jan 1, 1979

By J. Douglas Causey

The Bureau of Mines conducted mineral investigations of the Peace Rock and Deadwood River roadless areas in Idaho, in 1992. Literature research was done by the Idaho Geological Survey. The study areas contain black sand placers (thorium, columbium, tantalum, titanium, uranium, and rare earth elements), gold, and molybdenum prospects. Except for unrecorded placer gold, there has been no mineral production from the areas. No mineral resources were delineated, but a multi-million tonne molybdenum resource is in the Big Pine Creek area and a 142 million m' black sand deposit is in the Stolle Meadows, Peace Valley, and Deadwood River areas. The Deadwood mine produced zinc, lead, and silver. There are six mining districts in and adjoining the areas; Warm Lake, Deadwood, Garden Valley/Lowman, Banner, Summit Flat, and Grimes Pass. Few claims, mostly placer, were active in the study area in 1992. The study areas are underlain by granitic rocks of the Idaho batholith. Most of the deposits are alluvial accumulations of heavy minerals weathered out of the Idaho batholith. Stockwork and narrow veins along shears account for the base and precious metal concentrations. Eleven prospects were examined. Workings consist of drill holes, pits and adits. Geothermal resources (hot springs) occur mainly along the Middle Fork Payette River; Vulcan Hot Springs is a designated Known Geothermal Resource Area. Sand and gravel resources are of local interest.

Jan 1, 1993

By Doris M. Hyde

Limited geographically by size and geo-logically by origin, smaller countries and territories of the Caribbean are nonetheless engaging in efforts to encourage the initiation of mineral and mineral-related industries. Petroleum dominates the minerals sector, which otherwise consists principally of minor quantities of construction-oriented materials, usually for local consumption. The increased cost of petroleum has adversely affected most of the world, but these islands with their economies precariously balanced on the uncertainties of agriculture and tourism are especially vulnerable to petroleum's direct and indirect costs. In 1975, the Government of Antigua acquired the financially troubled West Indies Oil Company refinery at St. Johns. The refinery ceased operations in 1976. In 1979, negotiations were underway to sell Ashland Oil Co. an interest in the small, 20,000-barrel-per-day refinery for $6.6 million. In 1977, Antigua granted petroleum exploration rights to the Antigua Mineral Exploration Company, which planned to drill in an undefined offshore area, possibly between Antigua and Barbuda. The company expected to spend about $200,000 per year through 1982. There have been no reports on its activity.

Jan 1, 1981

By Doris M. Hyde

The economy of Belize continued to be relatively unaffected by activity in the minerals sector. Mining production consisted of limestone, marl, and sand and gravel. All production was used for domestic construction projects. By the end of 1979 the major oil companies had, temporarily at least, ceased active exploration efforts. Esso Ventures, Inc., after drilling three dry holes in southern Belize, planned to reappraise its activities. The Reef Exploration, Ltd., concession was acquired by Anschutz Oil Co. (81.25%). with minority interests held by Anglo Oil Co. and Carolina Oil Co. The Anschutz group drilled offshore in the Gulf of Honduras and in Belize Harbor. Echo Exploration has a con-cession along the Mexican border and Spar-tan Petroleum Corp. obtained seven exploration licenses covering 768,000 acres in northern Belize. Spartan's concessions included about 130,000 acres offshore, with the remainder along the southeastern rim of the Yucatan Peninsula. Placid Oil Co. took an interest in the Spartan acreage and became operator. Seismic exploration was underway in 1979. A Mexican company, Pan American Oil and Gas, S.A., was awarded two exploration concessions, one in southern Belize and one near the Mexican border.

Jan 1, 1981

By Robert L. Mentch

CADMIUM is one of the metals apparently destined to remain relatively scarce. The en tire supply of primary cadmium is recovered as a byproduct, concurrently with the treatment of ores of other metals. Development of the cadmium industry is attributed to metallurgical improvements in the zinc industry; output depends almost wholly upon zinc production. Cadmium is a metal of specialized uses where its superior performance has developed a strong, expanding demand. The supply, however, has been relatively unresponsive to price because of its byproduct nature. Cadmium's outstanding properties would assure it a manyfold greater market if more were available at lower prices.

Jan 1, 1958

By Francis X. Cannaday

The Bureau of Mines developed equipment to measure the sonic velocity of pulses transmitted through rock samples varying in size from laboratory specimens to mine pillars in place. Pulses are produced by electronically excited piezoelectric ceramic transducers. Special equipment components were developed by Bureau facilities; other components are commercially available. The technique permits a nondestructive, repetitive, stable, shaped pulse to be used in place of explosive caps or hammer blows. Longitudinal wave travel time measurements were taken on an oscilloscope screen; transverse wave measurements were taken under special field conditions. Results were consistently repeatable within the accuracy of the oscilloscopes utilized.

Jan 1, 1966