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By Albert L. Toenges

This paper is the fourth of a series5/ that describes some methods and practices of mining coal mechanically where operations are conducted on more than one shift. Many inquiries have been received regarding methods of extracting pillars with mechanized equipment, and this paper deals primarily with this phase of mechanical mining. Some of the questions that have been asked are:

Jan 1, 1942

By R. V. Ramani

"In Part 1 of this two-part paper the characteristics of mine disasters and their effects are presented with case studies from coal, metal and non-metal mines leading to an amplification of their causes and opportunities for control. The disasters discussed encompass those which threaten the health and the safety of miners and those which affect the general population. In Part 2 of the paper, which will be published in the November 1995 issue of Natural Resources Forum, the approaches to hazard and disaster control are reviewed with particular attention to laws and regulations to promote health and safety at the workplace, and general welfare in mining communities. Further, a systems approach to disaster control is outlined.The mining industry is one of the three basic industries the other two being agriculture, and wildlife and fisheries. It is the process of mining which makes available the riches of the earth - the energy and mineral resources - to benefit humanity. In fact the progress of the human race through the ages is indelibly attached to prowess in exploiting these riches. The stone, iron and bronze ages are markers not just of a time in history but achievements of monumental proportions in the mining and beneficiation of natural resources. Even in agriculture, the remarkable success stories are associated with the prudent use of mined products to enhance production and productivity. The significance of a thriving mining industry to the wealth and security of a nation is therefore unquestioned.Unfortunately, the public's image of the mining industry is often associated with the mining disasters which receive wide coverage in the local and national media. Mine disasters command tremendous attention because of their infrequent occurrence and the extent of human suffering involved. Whether it is an explosion or a fire, or the opening or closing of a mine, the lives of people are touched by the personal and societal impacts of these events.Courts of inquiry of mining disasters have often concluded that the disaster situation was ever present and could have been detected with diligent search. In addition human error has been identified as one of the most frequent immediate causes for the precipitation of the disaster. For the most part, then, mining disasters are caused by man."

Dec 1, 1996

By Dale W. Richardson

Ductile hafnium was not obtained consistently by the conventional Kroll process. The bimetal reduction modification produced a more ductile hafnium by lowering the impurities, especially oxygen, in the sponge metal. Hafnium oxide was chlorinated in the presence of carbon to form anhydrous hafnium tetrachloride, which was reduced by sodium and magnesium in an inert atmosphere to produce sponge hafnium metal. After vacuum distillation to remove the byproducts, the sponge was arc-melted into ingot and rolled into strip. Metallic impurities were decreased by evaporating the hafnium tetrachloride from a fused salt. An excessive amount (over 1,200 parts per million (p.p.m.)) of aluminum was contained in some of the hafnium oxide, much of which remained as aluminum chloride in the hafnium tetrachloride during chlorination. Evaporation of the hafnium tetrachloride from a fused NaCI-KCI mixture during the Mg-Na reduction greatly lowered its aluminum content, as most of the aluminum and some of the other metallic impurities were retained by the fused salt.

Jan 1, 1961

By P. M. Ambrose, C. Travis Anderson, Cresap Moss, R. S. Dean

"MANGANESE METALMethods of PreparationMethods of preparing the manganese metal that has been used in chemical and metallurgical investigations have passed through a cycle. Most of the investigations made before the turn of the century used Moissan's pyrophoric manganese. 5/ This material was made by electrolysis into a mercury cathode and distillation in vacuo. It was essentially a pure material, and investigations in which it was employed (with proper precautions against oxida¬tion) led to accurate results concerning the intrinsic behavior of metallic manganese.An early investigation of the properties of ""Manganese-by-Mercury"" was made by M. Guntz. 6/ He prepared manganese by electrolysis of a concentrated MnCl2 solution with a mercury cathode. The manganese amalgam was pressed through chamois and distilled in vacuo (2 to 3 cm. of mercury) at 200°0., slowly rising to 250°0. Guntz recognized especially the decreased reactivity of manganese with increased temperature of mercury distillation. The most careful and com¬prehensive study of manganese made by this method is that of Kuh 7/ whose work unfortunately was never published in an accessible journal.Royce and Kahlenberg 8/ studied the electrode potential of manganese made by this method."

Nov 1, 1939

By Dennis S. Kostick

Salt is a universal mineral commodity used by virtually every person in the world. Although a very common mineral today, at one time, it was considered as precious as gold in certain cultures. This study traces the material flow of salt from its origin through the postconsumer phase of usage. The final disposition of salt in the estimated 14,000 different uses, grouped into several macrocategories, is traced from the dispersive loss of salt into the environment to the ultimate disposal of salt-base products into the waste stream after consumption. The base year for this study is 1990, in which an estimated 196 million short tons of municipal solid waste was discarded by the U.S. population. Approximately three-fourths of domestic salt consumed is released to the environment and unrecovered while about one-fourth is discharged to landfills and incinerators as products derived from salt. Cumulative historical domestic production, trade, and consumption data have been compiled to illustrate the long-term trends within the U.S. salt industry and the cumulative contribution that highway deicing salt has had on the environment.

Jan 1, 1993

By William H. Lyon

In 1950 the Program Staff of the Department of the Interior undertook an exploratory study in the projection of energy requirements of the nation. This work was reported in Bureau of Mines Information Circular 7582 by H. J. Barnett. In that preliminary study Mr. Barnett, after exploring the nature of the energy economy in some detail, evolved a method for estimating how much energy will be required in the future, based on estimates of trends in efficiency of energy utilization in specific applications, the physical output of specific energy-consuming industries, size of the population, productivity advances in the economy at large, consumer preferences, and other factors. Considerable new information was developed regarding the nature of energy demands and the possible levels of requirements for each fuel under various assumed business conditions. The study analyzed the interrelationships, including substitutions, among the fuels and emphasized the need for viewing the energy economy as an integrated albeit complex whole. This exploratory study showed a need for a single comprehensive statistical re-port that would assemble and show in a uniform manner the diverse published statistical data on energy commodities now scattered through many publications. A particularly important need was for a set of historical statistics showing the production and consumption of all energy on a B.t.u. basis. As the prospective size and nature of the future energy requirements of the nation are matters of continuing importance, this report was prepared to assist further investigations of the subject. In this report the authors undertake to assemble and present in tabular form, on a uniform basis, the production and use of each of the fuels and electric energy in the United states for three census years -1929, 1939, and 1947. The year 1947, rather than a later year, was selected because it is the most recent year for which census data are available showing the consumption of fuel by each of the manufacturing industries. It is hoped that making data for these 3 years available in one re-port will provide the needed statistical background for further studies of fuel requirements and supplies.

Jan 1, 1951

By D. J. Judy, D. J. Rabovsky, W. H. Pailes, V. Castranova, K. Van Dyke, J. Rabovsky, N. A. Sapola, M. McPeek

"Platelet activating factor (PAF) can be released from pneumocytes following exposure to occupational dust (Am. Rev. Respir. Dis. 135:83, 1987). In addition, PAF has been shown to induce pulmonary inflammation, edema, and bronchoconstriction (Hosp. Prac. 19, 67, 1983). This investigation reports the effects of PAF on the properties of three types of cells found in the lung. PAF (1-100, K1/2 = 2.5 pH) caused depolarization of neutrophils as well as generation of chemiluminescence and secretion of hydrogen peroxide. These responses were dependent on the presence of extracellular sodium. However, PAF did not alter oxygen consumption of neutrophils. Although PAF (10 uM) caused depolarization of alveolar macrophages, no stimulation of chemiluminestence, superoxide secretion, or oxygen consumption was observed. However, PAF (10 uM). did potentiate chemiluminescence and superoxide secretion in response to zymosan (2 mg/ml) by 55% and 36%, respectively. In addition, PAF (10-90 uM) caused aggregation of alveolar macrophages. PAF (2-10 uM) also caused depolarization of type II cells, but did not affect membrane integrity or oxygen consumption. However, PAF (10-18 PM) enhanced the activities of two distinct forms of cytochrome P-450 in type II cells and caused aggregation of type II cells at PAF doses above 18 uM. These data indicate that PAF can affect the secretory activity of pulmonary phagocytes and the ability• of type II cells to detoxify foreign compounds (Bureau of Mines Grant - G1175142).INTRODUCTIONPlatelet activating factor (PAF) is a glycerophospholipid (1-0-alkyl-2-acetylsn-glycerol-3-phosphoryl choline) which has been shown to Mediate a broad range of biological activities (1-3). Its pulmonary actions include contraction of pulmonary tissue (4), secretion of leukotrienes from leukocytes (5), airway constriction (6), pulmonary edema (7), and enhanced migration of neutrophils into the airspaces of the lungs (8,9).PAF can be released from several different cell types, such as, basophils, neutrophils and alveolar macrophages, in response to a variety of particulates or membrane stimulants which include zymosan, calcium ionophore, phorbol esters, chemotactic agents, and endotoxin (10-13). Therefore, PAP may play an important role in the development of pneumoconioses by mediating pulmonary responses of lung cells to a variety of occupational dusts. To investigate this possibility, we determined the effects of PAF on several physiological parameters of neutrophils, alveolar macrophages, and alveolar type II epithelial cells."

Jan 1, 1988

By J. J. Taber

This is the final report on Grant No. G0144067. The report presents the results of a number of laboratory studies carried cut in several different ways to determine the effectiveness of foam for blocking the flow of gas in coal. The effectiveness; (of foam for retarding or blocking the flow gas in various porous media has been observed by many investigators1-4 but we are not aware of similar detailed studies in coal. Because of the diversity of our experiments, the key findings and general conclusions are presented very briefly in Section II. As a convenience to the reader a complete table of cements is included to enable the reader to find those experiments and studies of greatest interest.

Jan 1, 1976

By McHenry Mosier

Diamond -drilling blast holes at Eastern Magnetite Mine C is proving economical in boundary shrinks , in removing pillars not readily accessible for percussion drilling , and in driving scraper drifts . The cost per foot drilled is greater than for percussion drilling , but savings in associated factors outweigh this handicap . The rocks drilled include trap rock and magnetite ore . The mining method is the panel , block- caving system utilizing scraper sublevel drifts instead of branch raises to convey the ore to the haulage level . Diamond -drilling blast holes was begun early in 1945. Three rigs equipped with noncoring bits are now in active operation two shifts per day . They are owned by the company , and the drill operators are paid by the day . In shrinkage stopes the drill is mounted on a horizontal bar set against opposite walls of the stope . Stoping holes are horizontal , which gives better results in blasting and requires fewer set ups . In scraper drifts the drill is mounted on a horizontal bar clamped to two columns about feet apart . Trim holes around the periphery of the drift and reliever holes are drilled 50 to 80 feet in length . A 10 - foot wedge cut drilled with a stoper is blasted in conjunction with a corresponding length of the trim holes to effect a 10 -foot advance of the full- sized drift . Recent drilling averages 97 feet per machine shift , excluding time utilized in setting up and moving the machine , hand mucking , and barring down . The feet drilled per bit at present is 417. These data represent the average for drilling in both rock (waste) and ore . Percussion drilling utilizes three types of wet drills . Detachable bits are standard . Gage changes for new bits is 1/8 inch and for reconditioned bits 1/16 inch . The life of a bit is five uses . Resharpening is on contract . A drill carriage is used in haulage headings .

Feb 1, 1948

By William E. Eckard

Production of oil from a narrow shoestring sand presents problems unique in the oil industry. Especially important, from both an engineering end an economic standpoint, are the limitations imposed upon well patterns and spacings by the shape of the field. This report concerns a study of the Paola shoestring, Miami and Franklin Counties, Kane., where well density of 0.85 acre per well was not uncommon to insure profitable primary recovery in a reasonable time. However, such a great number of wells increased the operator's investment and reduced his profit considerably. It was the purpose of this study to investigate various well patterns and spacings applicable to water-flooding a shoestring reservoir and the effect of these factors upon recovery of oil and the most profitable operation of the pool. The designer of well patterns for a shoestring sand should evaluate carefully the edges of the shoestring, even though they may be considered too thin to drill. These comparatively thin edges contain large quantities of recoverable oil; moreover they are resaturated with oil as the pool is water-flooded.

Jan 1, 1951

By Synthia N. McIntosh

The U.S. Bureau of Mines investigated the feasibility of using ammonium carbamate (NH2CO2NH4) leaching to recover manganese from steel plant slag. This investigation showed that treatment of the slag in hydrogen prior to leaching enhanced manganese extraction. Up to 80 pct of the manganese and 50 pct of the iron could be extracted from a silicon steel slag that had been pretreated in hydrogen at 700° C. Two 4-h leaching stages conducted at ambient temperature with a solution containing ammonia and carbon dioxide dissolved manganese and iron as their carbamate complexes. Heating the pregnant solution to 65° to 85° C decomposed the complexes and precipitated the metals as insoluble carbonate salts. Ammonium carbamate leaching of other slags from several steelmaking plants produced lower manganese extractions, which suggests that the method cannot be applied satisfactorily to all steelmaking slags

Jan 1, 2010

By R. L. Solmer

During 1959-61, the Bureau of Mines investigated the strain and deformation induced in rock and concrete linings around mine openings by retreat panel caving at the Climax Molybdenum mine. Two concrete-lined slusher drifts on the Phillipson level of the mine were instrumented with both electrical strain gages and extensometers. Changes in strain and deformation were recorded over an 18-month period during the undercutting and caving of the mining panel. General agreement was found between the strain and deformation measurements and the hypothesis that the vertical component of the stress field on the openings is almost completely removed by undercutting. This phenomenon is a possible explanation for the structural failures that occur in the slusher drifts during the undercutting cycle.

Jan 1, 1965

By William H. Lesser

A recent survey of pumping plants in the anthracite region of Pennsyl¬vania showed that more than 90 percent of the pumps in use are the horizontal centrifugal types (1).2/ This report on the design and operation of centrifugal pumps should be helpful to engineers of the region who must select pumps that are best suited to particular pumping conditions in anthracite mines. Before a centrifugal mine pumping plant is designed, the special features of the pumps that may be used should be considered, especially when low repair costs and continuous operation during flood periods are prerequisites, and when acid mine water is to be pumped. Two important advantages of a centrifugal pump are that the flow is continuous and that it can be throttled without developing excessive pressure or overloading its driving unit.

Jan 1, 1950

By Richard Havens

A flotation procedure was devised by the Federal Bureau of Mines for beneficiating Mount Wheeler, Nev., beryllium ores that contain the beryllium minerals bertrandite and phenacite in a complex association with calcite, fluorspar, mica, quartz, and other accessory minerals, The method also has proven to be effective in trials on ore from the Lake George, Colo., area. Samples used in most of the research ranged from 0.49 to 0.73 percent BeO. Beryllium mineralization varied from two-thirds bertrandite to all phenacite. An unusually high grade sample containing 5 percent BeO as phenacite was floated on a batch basis to prepare concentrate for utilization studies. The beryllium minerals were floated from undeslimed pulps at natural pH using sodium fluoride and sodium hexametaphosphate (HMP), as modifiers, and a fatty acid-fuel oil combination as the collector. Key factors were the use of a minimum of about 4 pounds of sodium fluoride and between 2 and 4 pounds of HMP per ton of ore. Efficacy of the HMP was related to the grind, mineralogical composition, corollary reagents, and type and time of conditioning. Addition of the fluoride, HMP, and collector in that order, followed by appropriate conditioning after each addition, was essential for satisfactory flotation.

Jan 1, 1961

By Wilson Blake

The Bureau of Mines used a mathematical model based on the finite element method of stress analysis to calculate stresses and displacements surrounding an open pit mine in a gravity-loaded rock mass. Comparison of the finite element solution for a semicircular notch in a gravity-loaded plate with the theoretical solution for a semicircular notch in a plate under uniform compression parallel to the free boundary demonstrates the inapplicability of the latter method to openings at the free surface of a gravity-loaded medium. High stress concentrations are formed at irregularities along the boundary of an open pit in a gravity-loaded continuous competent rock; however, for this type of rock the magnitudes of the stresses are too low to be considered a major factor in open pit slope stability. High stress magnitudes will occur if, in addition to the gravity stress field, a large horizontal stress field exists.

Jan 1, 1967

By E. B. Swanson

Atlantic seaboard refining and marketing companies , dependent largely upon other producing and refining areas for the crude and refined petroleum needed to meet the demand for petroleum products within the Atlantic Coast States , reported an increase in 1929 receipts of 2,542,000 barrels of crude petroleum and 13,479,000 barrels of gasoline over the quantities received during the preceding year . The relatively large expansion in gasoline receipts undoubtedly resulted from the unexpected increase in gasoline consumption which characterized the petroleum industry during 1929. Gasoline receipts from California increased 6,354,000 barrels and shipments from foreign countries were 5,381,000 barrels in excess of the 1928 figures , while receipts from Gulf Coast ports , the major source of outside supply, declined 811,000 barrels . Shipments of domestic crude oil by tanker from Gulf Coast ports during 1929 continued the average annual increase of approximately 7,000,000 barrels which has been recorded during the five years of this annual survey . These shipments have increased from 72,556,000 barrels during 1925 to 99,828,000 barrels during 1929. Shioments of Mid- Continent crude by pipe- line to Atlantic Coast refineries have , on the other hand , dropped from 11,903,000 barrels in 1925 to 1,409,000 barrels during 1929. Receipts of foreign crude oil declined 1,461,000 barrels from the preceding year . : Gasoline demand within the Atlantic Coast area reached a total of 123,345,000 barrels , an increase of 15.7 per cent over 1928. Gasoline production increased 4,157,000 barrels , while tanker receipts were nearly 11,000,000 barrels larger than in 1928. Indicated shioments from Appalachian refineries were somewhat larger than in the preceding year . Gasoline production showed an average of 33.5 per cent of the crude throughout , as compared with 31.5 per cent in 1928 and 32.7 per cent in 1927. Cracking operations accounted for 44.6 per cent of the gasoline produced , as compared with 40.6 per cent in 1928 and 35.3 per cent in 1927. Gas oil and fuel oil production averaged 52.8 per cent of the crude throughput , as compared with 55.1 per cent in 1928 and 49.5 per cent in 1927 , the decline reflecting the smaller quantities of foreign crude refined during the year .

Nov 1, 1930

By R. V. Ramani, J. Qin

"During the mining process, the insitu material is broken into different size ranges, from very, large pieces to very fine particles. Some of the fine particles become airborne. In underground coal mining, airborne respirable. dust is associated with health and safety of the miners: The amount and size distributions of airborne dust are important parameters to effective dust control measures. The design of underground mine experiments, including sampling procedures and sample analyses methods to determine these parameters are presented in this paper.. A total of fifteen continuous miner cuts were sampled. The amount of dust generated during the cutting process and the relationship between total and respirable airborne dust concentrations and amounts are examined.The amount of respirable dust airborne is on the average only. 0.016% of the respirable dust generated. On the average, 61% of the total .airborne dust measured is in the respirable size range. The amount of respirable airborne' is on the average 36% of the respirable size fraction in the total airborne dust. For equal proportion of rock and coal material cut, rock contributes about twice as much fines (<0.22 mm) as coal. Additional fundamental research is necessary to further the understanding of 'the airborne propensity of respirable dusts in mine atmospheres.INTRODUCTIONMining is a sequential process of breaking, gathering, loading, and transporting the in-situ .materials.' In underground coal mines, duet in both the non-respirable and respirable size ranges is generated and entrained in every phase of the process. Even though large amounts of dust particles' adhere to run-of-mine coals, part of the dust generated becomes airborne (Cheng and Zukovich, 1973). Studies have shown that bit type affects the amount of dust generated'(Evans and Pomeroy, 1966; Kurth et al., 1975; Roepke et al., 1976; Stecklein et al., 1982; and Khair and 'Reddy, 1986). Deep cutting can reduce airborne dust generation (Black and Schmidt, 1977 arid, Black et 1978). Mechanical properties of. coal seams are also important factors in dust generation. Laboratory studies have shown that Hardgrove Grindability Index (HGI) of the coal has a relationship with the amount of respirable. dust generated (Beafi and Ramani, 1979; Moore and Bise, 1984; and Moore, 1986). However, these relationships have not yet been validated with' data from the mines. The amount of dust airborne depends on a number of factors. Suppression of the airborne propensity of dust by water sprays is'widely practiced and is very effective. Water flow rate; pressure and configuration of water sprays have been identified as major factors affecting dust capture by sprays (Courtney and Cheng, 1977; Courtney et al., 1978; and Kissell et al., 1979). Ventilation is a very important means of controlling the dust level at the coal face (Jayaraman, 1977). According to a National Academy of Sciences study (1980), the mechanism of dust generation and the process by which the generated dust becomes airborne are complex and not yet completely understood coal seams are also important factors in dust generation. Laboratory studies have shown that Hardgrove Grindability Index (HGI) of the coal has a relationship with the amount of respirable dust generated (Beafi and Ramani, 1979; Moore and Bise, 1984; and Moore, 1986). However, these relationships have not yet been validated with data from the mines. The amount of dust airborne depends on a number of factors. Suppression of the airborne propensity of dust by water sprays is widely practiced and is very effective. Water flow rate; pressure and configuration of water sprays have been identified as major factors affecting dust capture by sprays (Courtney and Cheng, 1977; Courtney et al., 1978; and Kissell et al., 1979). Ventilation is a very important means of controlling the dust level at the coal face (Jayaraman, 1977). According to a National Academy of Sciences study (1980), the mechanism"

Jan 1, 1989

By W. W. Adams

[The quantity of explosives sold in the United States in January, 1931, for domestic consumption, amounted to 368,100 kegs (9,202,510 pounds) of black blasting powder, 4,810;000 pounds of permissible explosives, and 16,533,000 pounds of high explosives other than permissible. These figures are based on reports received by the United States Bureau of Mines, Department of Commerce, from nearly all manufacturing companies, and include an estimate of sues by several companies that do not furnish monthly reports. Reports actually received from manufacturers shored sales of 365,977 kegs of black blasting powder (consisting of 220,892 kegs of granular powder and 145,085 kegs of pellet powder), 4,687,900 pounds of permissible explosives, and 15,498,152 pounds of high explosives other than permissible. Sales in January, 1931, were smaller than in January last year, the decreases being 14 per cent for black blasting powder, 19 per cent for permissible, and 17 per cent for high explosives other than permissible. Sales in January 1931 when compared with soles in December 1930, show increases for all three classes of explosives as follows: 2 per cent for block blasting powder, 16 per cent for permissible explosives, and 7 per cent for other high explosives. PERMISSIBLE EXPLOSIVES: Of the 4,687,900 hounds of permissible reported sold during January, 97 per cent was used for coal-mining operations, Including 32 per cent for anthracite mines and 65 per cent for bituminous mines. The following Staten were the largest users of permissible explosives daring January: Pennsylvania, West Virginia, Illinois, Alabama, Kentucky, Indiana, and Utah. Their combined sales represented 89 per cent of the entire sales reported for this class of explosives.]

Jan 1, 1931

By John M. Dower, Ralph W. Plummer, Terrence J. Stobbe, Hyunwook Kim

"The relationship between exposure to coal mine dust and the development of various respiratory diseases is well recognized. The cause of these diseases however. Is still uncertain. To study this cause-effect relationship, It Is necessary to characterize the coal mine dust In terms of the quantity of dust present and mineral content of the dust. Dust samples were collected using a Portable Continuous Aerosol Monitor (PCAM) and 4-stage cassette Impactors at various locations in an upper Freeport seam coal mine In West Virginia. The samples were analyzed using an X-ray microdiffraction film technique and energy dispersive scanning electron microscopy. This paper presents the results of the first phase of this characterization work which Includes determining the size distribution of the dust and the mineral content of the size intervals.IntroductionDiseases associated with dusts in coal mine environments continue to afflict miners in today's modem mines. These diseases still persist because, as Olishifski points out an employee rarely experiences exposures to a single environmental stress but rather to an Intricate Interplay of multiple stresses.(1) In the case of coal mining the multiple stresses are varying sizes of dust particles originating from coal imbedded minerals. Immediate roof strata bottom strata. Incombustible rock and the coal itself. The site of this Intricate Interplay Is the miner's lungs and the resulting diseases are a function of the composite dust exposures.The proper study of coal mine dust toxicity requires that the dusts used replicate existing coal and mineral dust compositions in their relevant size fractions. The purpose of this project is to develop the size and mineral content data necessary to support this ongoing toxicological effort.Existing coal mining standards and regulations also address total and respirable dust exposures. These dust terms refer to both the quality and quantity of the dust segment in the mine atmosphere. Dust quality addresses its coal and mineral content. whereas dust quantity Is described by mass per unit volume (mg/m3) The comprehensive characterization of coal mine dust exposures will enable revision of these standards and regulations to address the specific minerals and size fractions found to be toxic to human lung tissue."

Mar 1, 1989

This Technical Memorandum Report is a collection of three working memoranda, prepared during the course of our work for the bureau of Mines and hound together for convenient reference. These working memoranda present preliminary performance estimates, for baseband voice and narrowband through-the-earth electromagnetic communications systems of principal interest to the Bureau, for operational/emergency mine communications. The calculations were prepared to obtain early indications of the feasibility and governing parameters of such communications systems. They are based on limited, but pertinent, coal mine electromagnetic noise data acquired to-date by Bureau of Mines contractors; and of theoretical signal-attenuation characteristics for two transmitter antenna types of present interest to the Bureau. The memoranda examine the cases of baseband voice and narrowband communications for uplink and downlink transmissions, for frequencies up to 3kHz. Downlink transmissions are via a horizontal wire antenna, up-link transmissions via a vertical-axis loop antenna, for typical mine depths of 300, b00, and 1000 feet. Representative coal-mine overburden conductivities of 10-2 mhos/meter (moderate and common) and 10-1 mhos/meter (high) were used; 10-2 for voice and narrowband, 10-1 for narrowband only. Examples of high, moderate, and low; surface and subsurface; harmonic and broadband-impulsive noise conditions were taken from NBS and Westinghouse (WGL) mine noise data, together with examples of high- and low-levels of ELF atmospheric noise taken from M.I.T. Lincoln Laboratory data.

Jan 1, 1972