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Information Circular (IC) 9453 Roof falls continue to be the greatest single safety hazard faced by underground coal miners. During1996-99, 44 coal miners lost their lives in rock falls and nearly 2,400 were injured. In addition, nearly 6,000 non injury roof collapses were reported. Roof supports are installed to protect the miners, but support system failures contributed to most of these incidents. Reducing the terrible toll taken by ground falls continues to be a major goal of research by the National Institute for Occupational Safety and Health (NIOSH).During 2000-01, NIOSH conducted a series of open industry briefings on New Technology for Coal Mine Roof Support in Norton, VA, Charleston, WV, Evansville, IN, Tuscaloosa, AL, Price, UT, Glenwood Springs, CO, and Washington, PA. Drawing on many years of research undertaken by the NIOSH Pittsburgh and Spokane Research Laboratories, the proceedings describe what types of coal mine roof support are available, how they work, and when they should be used. The major subjects covered include roof bolts, standing roof supports, cable supports, and longwall shields. Some special topics are also addressed, including an analysis of roof fall accident statistics, techniques for better skin control, and material handling considerations. The proceedings volume also contains information on several important new technologies, which are described for the first time, e.g., guidelines for selecting roof bolt

Aug 1, 2001

By Brian G. White, Theodore J. Williams, Jeffrey K. Whyatt

Detailed mapping and examination of the site of a large rock burst at the Lucky Friday Mine, Mullan, ID, demonstrated conclusively that damage was caused by a splitting and buckling failure mechanism initiated by separation of rock into layers along steeply dipping metamorphic shear foliation subparallel to the affected crosscut. The thin tablular layers then buckled into the crosscut from both sides. Rigorous control of the burst by these layers suggests practical measures for avoiding bursts in crosscuts in the future by repositioning and reorienting openings so that splitting and buckling are reduced or precluded.

By D. A. Hill

Introduction The fields of an infinite line source in the presence of a conducting half-space have been examined by Wait and Spies (1971). In any real communication link using a current-carrying cable for the transmitting antenna, the cable is of finite length. Here we examine the fields of a finite length cable carrying a constant current in the presence of a homogeneous conducting half-space. The constant current assumption is valid at sufficiently low frequencies when an insulated cable is grounded at the end points (Wait, 1952; Sunde, 1968). Here we examine both surface and buried cables since both downlink and uplink communication links are of interest. Also, we examine both frequency and time solutions since either CW or pulsed communications may be used. Finally, it is necessary to include both magnetic and electric field solutions since reception could be with either loops or dipoles. Since the finite cable solution is more complicated than both the infinite line source and the short dipole solutions, we explore under what conditions a cable appears to be either infinitely long or very short. Some special cases, such as- the low frequency limit, permit analytical solutions which exhibit the dependence on various parameters, such as cable length, quite clearly. Frequency Domain Subsurface Fields The geometry of a line source of length 2[l] located on a conducting half-space with the observer in the half-space is shown in Figure 1. The fields

Jan 1, 1973

By Thomas H. Dubaniewicz, Gerald R. Cucci, Gregory M. Green, Kenneth L. Cashdollar

New types of industrial instruments use fiber-coupled law energy to power remote serum. Fiber-optic based instruments are useful in classified (hazardous) locations found in many industrial plants because the fiber provides a natural barrier against accidental electrical discharge into potentially explosive atmospheres. However, current safety standards do not cover the use of laser-powered fiber-optic instruments in potentially explosive environments such as found in coal mines. The U. S. Bureau of Mines began an investigation of laser-powered fiber-optic instruments in explosive atmospheres in support of the standards-making process. A commercial fiber-optic interface system, modified to sin relate several worst-case operating conditions, ignited explosive hydrogen-air mixtures. Worst-am simulations consisted of disabling a safety shutoff feature, operating the laser at significantly higher powers than intended for normal operations, and cleaving fiber-optic connections to direct laser energy onto selected absorptive materials. At the highest power level available, the fiber-optic interface system did not ignite selected methane-air mixtures. The obtained data should prove useful in establishing appropriate safety standards.

By Christopher Mark

Since it was first introduced, the Coal Mine Roof Rating (CMRR) has been widely accepted as a tool for geologic characterization and mine planning. This paper discusses the application of the CMRR to another practical ground control problem. Extended cuts (cuts greater than 6 m (20 ft) in length) are commonly used with remote control continuous miners. Extended cuts can greatly increase productivity, but they have been associated with a number of fatal roof fall accidents. When extended cuts are attempted in weak roof, the roof may collapse before it can be bolted, causing hazardous conditions. Until now, it has not been possible to predict where conditions may not be suitable for extended cuts. In this study, data on the CMRR and extended cut experience were collected at 36 mines in 7 states. It was found that when the CMRR was greater than 55, deep cuts were routine in nearly every case. When the CMRR was less than 37, extended cuts were almost never taken. Between 38 and 55, extended cuts were feasible sometimes but not others. The data also shows that extended cuts are less likely to be stable if either the entry span or the depth of cover increases.

By S. B. Robertson, D. R. Dolinar, G. E. Hinshaw, G. M. Molinda, D. M. Pappas

Rock falls in coal mines cause many injuries each year. Most of these injuries are not caused by major roof collapses, but from falls of smaller rocks from the immediate top or roof skin. Even though safety professionals and mine operators strive to reduce these types of injuries, there has not been a substantial decrease in the rock fall injury rate over the past decade. Various surface controls are used in mines to control the roof skin. One control that has proven to be very effective is roof screening. Roof screen effectively controls roof skin and provides a high roof surface coverage. Although many mines are reluctant to use screen for primary skin control because of the additional costs of time and materials, others are having great success at controlling both the costs and surface rock. In this study, injury data are presented that show a dramatic reduction in roof skin injuries when screening is used. Much of this success is due to the protection from falling rock that the operators receive from roof screen. Five case studies in which roof screen was used are presented along with the associated costs of materials, impact on bolting advance rates, and potential ergonomic risks. The effects of roof screening on skin control and safety are also included. Finally, this paper provides information about best practices and features of roof bolting machines that affect production and safety.

By M. Beus, R. Iverson, A. Dreschler, V. Scott

This paper describes research to improve safety during transport of ore and waste in underground mines. Field tests are underway in mines in Idaho and Montana. Strains measured on structural support members in an ore pass provided information about total forces acting on the structure as material was dumped into it. Results show that measured static loads were considerably less than actual total weight of the material dumped and that dynamic loads were subject to many factors, such as effects of blasting to remove hang-ups. Comparisons of measurements and computer results using a particle flow code indicated that several difficulties remain before achieving realistic determinations and models of the dynamic effects of particle flow in ort: passes and impact loads on the gates. Impact loads were overestimated in computer analyses as compared to loads measured in field tests. An alternative design approach based on softening the chute and control gate assembly is being proposed.

By Michael A. Trevits

The National Institute for Occupational Safety and Health (NIOSH) in partnership with Strata Products tested the sealing capability of Ventstop®? as part of an ongoing mine fire control and suppression research program. Ventstop®? is a multi-purpose, inflatable device that is produced by Minvent Solutions and is available world wide for use in the metal and nonmetal mining industry. Ventstop®? is also used in the Australian coal industry as a temporary ventilation control device. The device can be quickly deployed, is reusable and can be placed in horizontal and vertical mine voids to control dust, fumes and smoke. Deployment, multi-day inflation and air leakage tests were conducted at the NIOSH Lake Lynn Laboratory to determine the capability and limitations of Ventstop®? in a simulated coal mine setting. During the tests, Ventstop®? was also subjected to low level forces of a nearby methane gas ignition. It is thought that Ventstop®? could be used by the US coal mining industry to temporarily close an underground mine area in response to a fire or spontaneous combustion heating event, to temporarily redirect mine ventilation during longwall equipment moves or during stopping construction. This paper describes this inflatable temporary mine sealing technology and presents the results of the NIOSH tests. Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of NIOSH.

Jan 1, 2009

By Isaac A. Zlochower, Michael J. Sapko, Eric S. Weiss, Kenneth L. Cashdollar

This paper describes dust explosion research conducted in an experimental mine and in a 20-L laboratory chamber at the Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH). The primary purpose of this research is to improve safety in mining, but the data are also useful to other industries that manufacture, process, or use combustible dusts. Explosion characteristics such as the minimum explosible concentration and the rock dust inerting requirements were measured for various combustible dusts from the mining industries. These dusts included bituminous coats, gilsonite, oil shales, and sulfide ores. The full-scale tests were conducted in the Lake Lynn experimental mine of NIOSH. The mine tests were initiated by a methane-air explosion at the face (closed end) that both entrained and ignited the dust. The laboratory-scale tests were conducted in the 20-L chamber using ignitors of various energies. One purpose of the laboratory and mine comparison is to determine the conditions under which the laboratory tests best simulate the full-scale tests. The results of this research showed relatively good agreement between the laboratory and the large-scale tests in determining explosion limits. Full-scale experiments in the experimental mine were also conducted to evaluate the explosion resistance characteristics of seals that are used to separate non-ventilated, inactive workings from active workings of a mine. Results of these explosion tests show significant increases in explosion overpressure due to added coal dust and indications of pressure piling.

By Rudolf E. Greuer, Linneas W. Laage, Xinton Chang

MFIRE is a computer simulation program that performs normal ventilation network planning calculations and dynamic transient-state simulation of ventilation networks under a variety of conditions The program is useful for the analysis of ventilation networks under the influence of natural ventilation, fans, fires, or any combination of these MFIRE simulates a mine's ventilation system and its response to altered ventilation parameters such as the development of new mine workings or changes in ventilation control structures, external influences (varying outside temperatures), and internal influences (fires) Extensive output enables detailed, quantitative analysis of the effects that the alteration will cause to the ventilation system The program was developed at Michigan Technological University (MTU), Houghton, MI, with support from the Bureau of Mines A personal computer (PC) version of the program was completed under contract for the Bureau by MTU The purpose of this report is to document the installation and use of the PC version of the program MFIRE

Jan 1, 1990

By H. Foster Bain

Ten years ago there was no general , country-wide service for the systematic training of miners in matters relating to safety . A beginning only had been made at a few scattered points . Under the old conditions each man was left largely to look out for himself in meeting the hazards of his day's work, and the foreman , shift bosses , and superintendents chiefly relied upon improvision when major accidents occurred . So long as the mines were small and the workers highly intelligent and well trained in routine mining methods , and when too , the pressure for output had not yet speeded up industry to the extent it has since those days , there was something to be said for this lais- sez faire attitude . When , however , the rapid expansion of industry lead to the introduction of new and little trained labor and to units of production of greatly increased size , the natural dangers of mining were greatly intensified . An accident in a small mine affects only a few; the same accident in a large mine , unless proper precautions have been taken , may cost the lives of many . The public does not generally recognize that the greatly increased outputs of the mines , of coal mines in particular , have been in recent years , obtained from substantially the same number of miners as ten years ago but with a personnel not nearly so well trained in mining . It is inevitable under : such conditions that more care must be devoted to avoiding accidents and much more elaborate preparations made for meeting them . In the years immediately preceding the establishment of the Bureau of Mines this speeding up of industry , change in the character of mine labor , and increasing hazard had all begun to be felt . Immediately prior to the organization of the Bureau of Mines , public attention had been drawn to a series of disastrous coal-mine explosions , to the increasing frequency of these disasters , and to the terrible loss of human life . resulting therefrom. One of the first problems , therefore ; confronting the Bureau was clearly that of finding methods of reducing the number of such disasters and lessening the severity of those that continued to occur . Toward this object were immediately directed the energies not only of the Bureau of Mines but also those of State mine inspectors , mine operators and various other agencies , all of whom were urged to cooperate in this great humanitarian work. The results of this work naturally cannot be measured by figures only . Work for increasing the health , safety , comfort , and happiness of human beings may not be gaged with mathematical precision . But certain features of this work as revealed by the record from year to year are of much interest . ”

Apr 1, 1921

By T. Brady, R. Langston, J. C. Johnson, H. Kirsten

An experiment is described in which instrumented rock bolts were used to measure strain in the rock mass during drift development at the Stillwater Mine, Nye, Montana, USA. Two strain-gauged rock bolts were grouted into the middle of the rib next to the face. The drift was excavated in three advances, each one-half drift wide. Strains were recorded hourly by a data logger. Results show that the average change in axial bolt strain for the first and second advance was about the same and that there was almost no change in strain after the third advance. Bending strain was observed 19 cm from the head of the bolt.

By 1980, the U.S. mining community had reached a broad consensus regarding coal pillar design. The pillar load could be estimated from tributary area theory, and the pillar strength from empirical formulas and laboratory coal strength testing. Then the growth of longwall mining required new thinking. Recently, powerful design methods have emerged from analysis of large data bases of real-world pillar successes and failures. These include the Analysis of Retreat Mining Pillar Stability (ARMPS), the Analysis of Longwall Pillar Stability (ALPS), the Mark- Bieniawski rectangular pillar strength formula, and guidelines for preventing massive pillar collapses. Sophisticated numerical models have also helped transform the pillar design landscape. In the process, our understanding of pillar mechanics has been greatly enriched. A new paradigm divides pillar failure into three categories:

By Christopher Mark

Australia and the United States both have large, modern underground coal mining industries. Many companies have invested in both countries, and there is growing awareness that technological developments in one country can rapidly affect the other. Yet the ability of technology to pass between the countries depends on comparability of ground conditions. Many Australian observers believe that their ground conditions are significantly poorer than typical U.S. conditions, but some U.S. professionals are not convinced. The author recently visited 10 Australian longwall mines and two room-and-pillar mines. Each mine visit included determination of the Coal Mine Roof Rating, roof support installed, pillar design, and an in-depth discussion of ground control experience. The Australian conditions observed are compared with an extensive data base from U.S. mines. The paper also offers observations on geotechnical data collection, monitoring, and the roles of the mine inspectorate and research community.

By Lloyd A. Morley, Robert Stefanko

This report has presented a literature review of explosion proof¬ing of coal mine electrical equipment. The international "state-of¬the-art" is an extremely difficult definition to quantify but, from the preceding paragraphs, it is evident the international community be¬lieves that it is represented by the International Electrotechnical Commission's Publications. Five questions were set forth during the beginning of this report. Each will be evaluated in light of the preceding discussion. 1. Can Schedule 2G specifications on explosion-proof containers be substantiated? Literature was found in the three main problem areas, surface temperature, mechanical strength, and explosion transmission, to determine this. Surface temperature requirements are adequate except for equipment that can normally overload, and the required intern¬al pressure does afford some margin of safety. However, in terms of safety, gap dimensions are about ten times smaller than that needed. 2. Is it possible to replace the Schedule's design requirements with performance specifications? Two primary areas were determined as mechanical strength and explosion transmission. As was mentioned, for present flange and gap standards, the 150 psig requirement is adequate. Furthermore, it is the authors' opinion that the level cannot be re¬duced if the present gap requirements are retained. The Schedule now requires that 16 tests be run, but the literature suggests that only from three to six examinations are necessary. Then by using the abso¬lute maximum pressure from these measurements or 150 psig, whichever is

Jan 1, 1974

By G. R. Peterson, K. E. Porter

The U.S. Bureau of Mines has estimated the potential availability of copper from 204 mines and deposits in market economy countries (MEC's). The evaluated properties have demonstrated resources totaling 436.4 million metric tons of contained copper and account for 90% of the Bureau of Mimes reserve base for copper in market economy countries. Total recoverable MEC copper resources are 340.8 million metric tons, 69% of which is from producing mines and 31% from nonproducing mines and deposits. Chile had the lowest estimated average total cost from producing mines of W.48 per pound of recoverable copper at a 0% discounted cash-flow rate of return (DCFROR), with estimated average total costs ranging from $0.40 to $0.81 per pound. The estimated average total cost of production, per pound of copper, for producing mines in the United States amounts to $0.57 in January 1988 dollars at a Wo DCFROR, with estimated total costs ranging from $0.36 to $0.85 per pound. In both real and nominal terms, the United States has, on average, significantly lowered its copper production costs since 1981. Rationalization of the industry and significant increases in productivity have made a strong improvement in the competitiveness of the U.S. copper industry to the extent that the United States should no longer be considered as a marginal producer of copper.

Jan 1, 1992

By Dorsey A. Lyon

At the main experiment station of the U. S. Bureau of Mines , situated in Pittsburgh, Pa . , three phases of its work in behalf of the safety of the coal miner are the establishment of permissible explosives for use in gaseous and dusty mines , the development of electrical equipment that can be used with safety in mines of this character , and improvement in the safety of mechanical devices used in and about the mines . Also That these efforts are beginning to have a cumulative effect in lives. saved is evident from the fatality statistics of the industry . Although nearly 80,000 more men are employed in coal mining than ten years ago and much more coal is mined , the fatalities each year are considerably less than ten years ago . the amount of coal mined in a year for each life lost has risen between 60,000 and 70,000 tons . In 1909 , the year before the Bureau was created , the production of coal for each life lost was 174,416 tons . In 1920 , the production for each life lost was 285,000 tons .

Mar 1, 1921

The Mine Safety and Health Administration (MSHA) defines an independent contractor as "any person, partnership, corporation, subsidiary of a corporation, firm, association or other organization that contracts to perform services or construction at a mine." Contractors that perform specific types of work are required to report the number of employees who perform work at coal mines and at noncoal mines.

Feb 1, 2005

In 2004, a total of 4,401 stone mining operations reported employment to the Mine Safety and Health Administration (MSHA). Stone mines comprised 30.4% of all mining operations.

Sep 1, 2007

1. In 2003, a total of 7,070 sand and gravel mining operations reported employment to the Mine Safety and Health Administration (MSHA). The largest percentage of all mining sectors was sand and gravel mines (49.1%). • Sand and gravel mines are found throughout all 50 states.

Feb 1, 2005