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By Douglas D. Reynolds

Intense vibration can be transmitted to the hands and arms of workers who use hand-held percussive or vibrating devices, tools, and work pieces. Continued habitual exposure to vibration directed to the hands can cause patterns of various symptoms associated with hand-arm vibration syndrome (HVAS). The International Organization for Standardization (ISO) first published ISO 5349 in 1986.3 This standard specified methods for measuring and evaluating vibration directed into the hands from hand-held vibrating devices, tools, and work pieces. The American National Standards Institute (ANSI) published ANSI S3.34 the same year.1 This standard was modeled after ISO 5349-1986 and specified methods for assessing exposure to hand-arm vibration. The Parliament of the European Union has issued the European Union Human Vibration Directive-2002/44/EC, which specifies vibration daily exposure action values (DEAV) of 2.5 m/s2 and daily exposure limit values (DELV) of 5.0 m/s2. These values have generally been accepted by medical experts, scientists, and engineers in governmental agencies, research institutions, and industry in the USA and other countries.2 When they are achieved, they will reduce the potential for the development of symptoms related to HAVS among workers exposed to hand-arm vibration. Significant improvements in measurement and analysis instrumentation, miniature and subminiature accelerometers, and medical diagnostic and assessment protocols have being introduced since 1986 when ANSI S3.34 was first published. In response to these improvements and the introduction of the EU Human Vibration Directive, ANSI Working Group S2.39 developed the revision to ANSI S3.34, which has now been published as ANSI S2.70-2006.2 Method ANSI S2.70 specifies the use of the hand-arm vibration measurement procedures outlined in ISO 5349, Parts 1 and 2.2,4,5 It requires the measurement of ISO frequency-weighted acceleration values in three mutually orthogonal axes of vibration. These values are then vectorially added to obtain the vibration total value, ahv: [ ] where ahwx, ahwy, and ahwz are the measured r.m.s. ISO frequency-weighted acceleration values in the x, y, and z directions, respectively. If multiple vibration exposure events are experienced during a work day, the overall vibration total value is obtained from: [ ] where ahvi is the vibration total value of the ith operation, Ti is time duration in hours of the ith operation, n is the total number of operations, and T is total time in hours associated with the n

Jan 6, 2006

By Launa G. Mallett, Jr. Brnich

Overview: The first step to emergency preparedness and maintaining a safe workplace is defining and analyzing hazards. Although all hazards should be addressed, resource limitations usually do not allow this to happen at one time. Risk assessment can be used to establish priorities so that the most dangerous situations are addressed first and those least likely to occur and least likely to cause major problems can be considered later. Purpose: This training package was developed to assist instructors as they (1) determine how to use risk assessment to improve safety preparedness and (2) present risk assessment concepts and tools to trainees. The concepts and tools presented here can be applied to any mine hazard.

Jul 1, 2003

By David B. Doan

This regional report covers 1993 mining and related activity in approximately 40 countries and territories of Canada, Latin America, and the Caribbean Basin. These countries of the Western Hemisphere, as with the United States, are endowed with a great variety of minerals, including metals, industrial minerals, and energy minerals. For most of these countries, such mineral production helps form foundations for their economies and earns export credits including hard currencies. Table 1 depicts an overall view of Latin America and Canada's production of its major mineral commodities in 1993; subsequent tables show the role of Latin America and Canada in world mineral production, trade, and import dependency on minerals from Latin America and Canada by the United States. Overall, the picture emerges of a rich mineral diversity throughout the hemisphere, attracting increasing interest and investment, and complementing the mineral resources of the United States.

Jan 1, 1995

By Hisataka Sakakibara

Although the pathophysiology of vibration-induced white finger (VWF) is still under discussion, evidence has been accumulated to understand the underlying mechanism. VWF is pathophysiologically characterized by an enhanced vasospastic response to cold, which can result from an imbalance between vasoconstriction and vasodilation in the digital arteries in response to cold (i.e., vasoconstriction-dominant). The imbalance is supposed to be due to faults in vascular vessels and sympathetically mediated vascular tone. Enhanced vasospastic response to cold Narrowing of arterial lumen with medial smooth muscle hypertrophy. Possible functional factors for enhanced vasoconstriction • Increased sympathetic nervous activity to cold (e.g., norepinephrine) • Increased release of endothelin-1 (ET-1; an endothelial-dependent vasoconstrictor) from the endothelium • Increased reactivity of alpha2-adrenoreceptors to cold Possible functional factors for decreased vasodilation • Decreased release of nitric oxide (NO; an endothelial-dependent vasodilator) from the endothelium • Decreased release of calcitonin gene-related peptide (CGRP; a vasodilatory neuropeptide) from sensory afferents The question is how their interrelations or imbalances among them are Vibration and arterial damage The next question is, how does hand-arm vibration exposure induce such pathophysiological changes in VWF patients? Recent morphological evidence from animal experiments shows that vibration acceleration stress (including shear stress) and smooth muscle contraction contribute to arterial damage of smooth muscle and endothelial cells. The vibration-induced arterial damage is frequency-amplitude-dependent.

Jan 6, 2006

By J. B. Cheung

The results of a program to demonstrate the technical feasibility of hydraulic borehole coal mining are presented in this report. The hydraulic borehole method of coal mining involves inserting a hydraulic mining device into a borehole that has been drilled from the surface into the underground coal bed. The borehole mining device issues a jet of water under high pressure, which breaks the coal. These pieces of coal, along with the water, form a slurry, which flows to the base of the borehole where it is pumped to the -surface. Phase I of the program encompassed the design, fabrication and factory-testing of a hydraulic borehole mining device. The program was successfully completed with the field tests being conducted at the Wilkeson-Carbonado Coal Field near Wilkeson, Washington. The technical feasibility of hydraulic borehole coal mining was demonstrated by mining 32 tons of coal at a depth of about 75 ft over a period of 4 hours.

Jan 1, 1976

According to contemporary psychophysical theory, the relationship between the strength of a perceived sensation (S) and the intensity of a physical stimulus (1) is best expressed by a power relationship.(1) S=kln (1) This psychophysical principle has been applied to many practical problems, including the development of scales or guidelines for effective temperature, loudness, brightness, and ratings of perceived exertion. Based on the results of a number of experiments using a variety of scaling methods and a number of different muscle groups, the pooled estimate of the exponent for muscular effort and force is 1.7.(2) When applying this principle to work situations, it is assumed that individuals are capable and willing to consistently identify a specified level of perceived sensation (S). For manual materials handling tasks, this specified level is usually the maximum acceptable weight or maximum acceptable force. These phrases are defined by the instructions given to the test subject:(3) You are to work on an incentive basis, working as hard as you can without straining yourself or becoming unusually tired, weakened, overheated, or out of breath. If the task involves lifting, the experiment measures the maximum acceptable weight of lift. Similarly, there are maximum acceptable weights for lowering and carrying. Such tests are isoinertial in nature; however, in contrast to the tests described in Chapter 3, they are typically used to test submaximal, repetitive handling capabilities. Data are also available for pushing and pulling. These are reported as maximum acceptable forces and include data for initial as well as sustained pulling or pushing. Why Use Psychophysical Methods? Snook identified several advantages and disadvantages to using psychophysical methods for determining maximum acceptable weights.(4) The advantages include: • Realistic simulation of industrial work (face validity); • Ability to study intermittent tasks (physiological steady state not required); • Results are consistent with the industrial engineering concept of "a fair day's work for a fair day's pay"; • Results are reproducible; and • Results appear to be related to low-back pain (content validity).

Jan 1, 1998

By Eric R. Bauer

This U.S. Bureau of Mines study was conducted to gain a basis for recommending methods to predict and prevent the occurrence of cutter roof failure, a common ground control problem in mines of the Northern Appalachian Coal Basin. This was accomplished by determining the geologic and engineering factors responsible for cutter development at six mines affected by cutter roof failure. Three distinct factors were found to be initiators of cutter roof failure: (1) high horizontal roof stress, (2) surface topographic variations, and (3) geologic anomalies. Effective control of cutter roof was obtained through improved bolting techniques, entry and mine reorientation, and entry and pillar size modifications, but only when selected based on the actual cause of failure.

Jan 1, 1990

By Henry P. Chandler

TONNAGE of natural abrasives sold or used in the United States in 1959 increased 12 percent. Artificial abrasives produced in the United States and Canada jumped 24 percent. Imports, exports, and reexports of abrasive materials also showed gains. Sales of grinding wheels were up 33 percent and coated abrasives 17 percent. FOREIGN TRADE Imports of abrasive materials totaled $91 million, an increase of nearly 51 percent over 1958. Chief commodities contributing to [ ]

Jan 1, 1960

Tennessee is the largest federal program state in the nation, with 62 active surface and underground coal mines. Tennessee's coal resources lie in 22 coal seams in 22 counties. Twelve seams are being mined at this time. Mining in the northern counties is primarily in steep slope areas in the Cumberland Mountains. The relatively flat terrain associated with the Cumberland Plateau makes area-rnining the most common production method in Tennessee's southern counties. The State of Tennessee gained primacy August 10,1982, when its regulatory program was conditionally approved, subject to the correction of certain deficiencies. On May 16,1984, the Tennessee General Assembly repealed most of the Tennessee Coal Surface Mining Law of 1980, effective October 1, 1984. With this action, withdrawal of the state regulatory program was formalized, and on October 1,1984, the Office of Surface Mining's Knoxville Field Office became the regulatory authority. Tennessee is not eligible to receive funds for an abandoned mine reclamation program because it does not have an approved regulatory program. Accordingly, the Tennessee Abandoned Mine Lands Program does not receive federal AML grants. Since 1984, AML projects have been completed under cooperative agreements between OSM and the state; emergency projects are completed by the Office of Surface Mining.

Jan 1, 1992

By N. Grosland, G. Kopp, T. Hunstad, D. Wilder, M. Contratto, S. Rahmatalla, T. Xia

Chronic whole-body vibration exposure, as expected in large construction and mining vehicles, has been associated with neck and back pain and injury.1 While work has been done towards gaining a better understanding of the relationship between vibration and shock and muscle activity of the back musculature2, relatively little information regarding the activity of neck, shoulder and upper arm muscles is known. Today’s equipment designs must conform to domestic and international standards, however these standards do not specifically address the vibration exposure in the head and upper quarter. Further it is not well known how the control configuration within a vehicle (e.g. steering wheel versus arm controls) influences muscle voluntary and reflex activity levels. Greater muscle activity may lead to greater muscle fatigue – which in turn may be associated with greater risk of injury.2 Thus, muscle contractions needed to maintain static postures as well as those resulting reflexively should be considered during an analysis of seating position. Unfortunately, little is known regarding the influence of arm position on head and neck muscle function. The purpose of this study was to investigate the relative muscle activities of 5 neck, shoulder, and upper arm muscles during riding simulations of large construction equipment, using three different arm control options. Methods Five typical heavy equipment ride files were “played back” through a man-rated Servo Test 6-degree of freedom (dof) vibration system. Each ride was repeated using 3 seat and control configurations (steering wheel (SW), floor mounted arm-rest controls (FM), seat mounted arm-rest controls (SM)). Two trials were performed for each ride and seat control combination (each trial: 60 sec of 6-dof and 60 sec of vertical vibration). Five channels of surface electromyography (EMG) of the right-side cervical erector spinae muscles (neck extensors), sternocleidomastoid (neck flexor), upper trapezius (shoulder elevator), biceps brachii (elbow flexor) and triceps brachii (elbow extensor) muscles were collected throughout each ride (~ 2min) using pre-amplified (10x), 1 cm silver bar electrodes, with 1 cm fixed inter-electrode distances (Delsys, Inc). Further analog amplification was set at 10k (1k for one subject), and sampled at 1000Hz using a 12-bit DAQ card and Labview 7.1 software (National Instruments). A total of 7 right-handed male subjects were tested, but only 5 had complete EMG data sets to analyze for this sub-study. EMG was analyzed using root mean square (RMS, in mV) of 20 ms moving windows, and then averaged across the entire trial for a measure of mean total muscle activity (voluntary and reflexive). The muscle activity to maintain the static posture was estimated as the mean RMS EMG over a 1 sec interval just prior to and/or after completion of the ride. Repeated Measures ANOVAs were used to test for with-in subject differences using a = 0.05.

Jan 6, 2006

By N. Kumar Kittusamy

The purpose of this study was to assess the adequacy of the cab design and to determine the percentage of musculoskeletal symptoms among operators of mobile equipment used in mining and construction. A questionnaire was designed to assess demographics, work information, job history, and musculoskeletal symptoms in operators of heavy mobile equipment. Information concerning equipment included design of the seat/chair, levers, pedals, bothersome vibration, quality of ingress/egress from the equipment, proper preventative maintenance and repairs, and age of the equipment. The body regions that were evaluated included the neck, middle/upper back, low-back, shoulder/upper-arm, elbow/forearm, wrist/hand, hip, knee, and ankle/foot. Five hundred and eighty six operators completed the questionnaire. The results indicate that these workers are at risk for developing musculoskeletal disorders, and the need to quantify risk factors (i.e., whole-body vibration and static sitting postures).

Jan 6, 2006

By Welby G. Courtney

This publication reviews recent U.S. Bureau of Mines studies of frictional ignition of a methane-air environment by coal mining bits cutting into sandstone and the effectiveness of remedial techniques to reduce the likelihood of frictional ignition. Frictional ignition with a mining bit always involves a worn bit having a wear flat on the tip of the bit. The worn bit forms hot spots on the surface of the sandstone because of frictional abrasion. The hot spots then can ignite the methane-air environment. A small wear flat forms a small hot spot, which does not give ignition, while a large wear flat forms a large hot spot, which gives ignition. The likelihood of frictional ignition can be somewhat reduced by using a mushroom-shaped tungsten-carbide bit tip on the mining bit and by increasing the bit clearance angle; it can be significantly reduced by using a water spray nozzle in back of each bit, which is carefully oriented to direct the water spray onto the sandstone surface directly behind the bit and thereby cool the hot spots formed by the worn bit. A bit replacement schedule must be used to avoid the formation of a dangerously worn bit.

Jan 1, 1990

By R. M. Santmyers

Umber and sienna, like ocher, are naturally occurring mineral pig- ments composed largely of clay permeated with hydrated iron (ferric oxide), but they differ from ocher in that they also contain hydrated manganese oxide. The presence of manganese accounts for their browner color. In addition to silica and alumina (clay) and the coloring oxides of iron and manganese, these pigments often contain lime, barium, and other metallic salts as impurities. Sienna most nearly approaches ocher in chemical composition, and the chief distinction is its physical character. It grades into ocher with de- creasing iron content and into umber with increasing manganese content. Sienna is translucent rather than opaque and is more of a stain than a pigment; as the iron oxide content is rather high (often 60 to 80 per cent), the color is strong and rich and varies from pure brown to reddish brown. This pigment raw sienna, terra di Siena, and Italian earth. is known under several names: Burnt sienna is a pigment of an orange-brown tint made by cautionsly calcining raw sienna. It is divided into two grades; American, and Italian burnt sienna. American burnt sienna is a reddish-brown pigment containing from 25 to 60 per cent iron oxide (Fe2O3). One grade, found in Pennsylvania, analyses as high as 80 per cent and is mown as double strength sienna. Italian burnt sienna is a pigment generally containing more iron than the American product, averaging 60 to 75 per cent iron oxide.3 American pig- ments of the same iron content differ materially in shade, having a Havana- brown color, whereas the Italian is more of a maroon. Italian siennas when tinted with 20 per cent of white, show a bluish tint, whereas American siennas yield a brownish or yellowish hue. Raw umber, also known as Turkey umber, Levant umber, and terra ombra, is a greenish to yellowish brown siliceous and ferruginous earth, containing a considerable proportion of one or other of the higher oxides of manganese, Mng04 and MnO2." It is similar in many respects to raw sienna except that it is much coarser and contains more manganese oxide. All umbers contain over 5 per cent of manganese dioxide. Like sienna, umber is a permanent pigment, not being injured by light or by impure atmospheres. Burnt umber (velvet brown, chestnut brown, etc.), results from the calcination of raw umber. The color is much richer and warmer than that of the raw umber. The colors are equally permanent and can be used in conjunc- tion with all other durable pigments.

Sep 1, 1931

By E. W. Parsons

Permanent support of the back is an important economic factor in maintaining a tunnel or other underground opening in condition to render the service for which it was driven. Timber has been most commonly used for support in tunneling and drifting because of its strength and ease of installation. Even when treated for decay, however, timber is subject to deterioration and, over a long period of time, should not be considered a permanent support. Concrete support or lining is permanent and has been used in tunnels of every size for many years but has been almost exclusively cast in place, a difficult, costly process. This report deals with the design and installation of precast concrete supports to combine the best features of both methods.

Jan 1, 1958

By Forest J. Sur

"This report describes an exploratory project conducted by the Bureau of Mines on a fluorite deposit near Vado, N. Mex. Results of trenching are given. Together with analyses made upon samples of the ore. The Federal Geological Survey3/ completed a preliminary geologic study and mapped the deposit during the summer of 1944. A Bureau engineer examined the deposit in August 1944. As a result of these investigations, it was concluded that the deposit contained substantial inferred ore reserves. Exploratory work was recommended to obtain information that might possibly lead to production from the property. Assistance was given the Bureau by the Geological Survey.A gasoline-powered air compressor, other equipment, and supplies were delivered to the property from January 20 to 25, 1943. Trenching began under the direction of a Bureau of Mines engineer on January 25, 1947, and ended on March 15, 1945. The results of trenching and sampling form he basis of this report.In 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, R.G. Knickerbocker, chief, analyzes samples and performs beneficiation tests. Both these branches are under the supervisions of Dr. R. S. Dean, assistant director."

Sep 1, 1946

By S. G. McAnally

This is one of a series of papers describing mining and crushing methods and costs at cement plant quarries throughout the United States and deals directly with the methods employed and costs obtained at the Reliance quarry of the Giant Portland Cement Co. at Egypt, Pa., although it is more or less descriptive of the methods used throughout the Lehigh Valley cement district. Systems of transportation vary according to local conditions, such as proximity to the mill, depth of quarry floor with relation to the mill level, etc. Methods of prospecting differ mainly in the type f drills used. Systems of storage, crushing, and grinding vary chiefly in the types of units. ACKNOWLEDGMENTS Most of the information regarding the early history of the Lehigh cement district was obtained from the History f the Portland Cement Industry of the United States, by Robert W. Lesley, the first president of the Portland Cement Association. The writer is indebted also to Charles Clader, Giant Portland Cement Co. quarry superintendent, for valuable information regarding present and past methods and equipment.

Jan 1, 1931

By Michael L. Boninger, Erik J. Wolf, Rory A. Cooper

Although wheelchair users are regularly subjected to whole-body vibrations little research has been conducted to assess these vibrations or attempt to reduce them [2,3,5]. Most of the wheelchair and whole-body vibration research done to this point has been conducted on manual wheelchairs. Van Sickle et al showed that manual wheelchair propulsion over a simulated road course produces vibration loads that exceed the ISO 2631-1 standards for the fatigue-decreased proficiency boundary at the seat of the wheelchair as well as the head of the user [6]. In a study by Boninger et al [1], 66% of wheelchair users reported neck pain since acquiring their wheelchair. One of the key reasons believed to be the cause of pain, was the exposure to whole-body vibration. Kwarciak et al [4] and Wolf et al [7] performed similar studies using two methods of analysis to evaluate vibrations on suspension and non-suspension wheelchairs while descending curbs of varying heights. Both studies revealed no significant difference in the abilities of the wheelchairs to reduce the amounts of vibrations transferred to the wheelchair user. Although the efforts of wheelchair companies to reduce the amounts of whole-body vibration transmitted to wheelchair users through the addition of suspension systems is encouraging, the technology is not yet ideal. Additionally, the research to date has focused on manual wheelchairs exclusively, while little attention has been shown to powered wheelchairs. Methods This study includes the use of two suspension electric powered wheelchairs: The Quickie S-626 and the Invacare 3G Torque SP Storm Series. Each subject tested all of the configurations of the suspension wheelchairs. These included the Invacare with suspension, the Quickie with suspension set to three settings (most stiff, least stiff, and 50% stiffness), and both wheelchairs with solid inserts to act as non-suspension wheelchairs. Sixteen able bodied subjects have been recruited for this study so far. In each of the configurations of the wheelchairs, the subjects traversed an Activities of Daily Living (ADL) course. Vibrations were collected from a tri-axial accelerometer attached to a seat plate beneath the cushion during driving over the activities course. A mixed model ANOVA was used to determine if there were differences between suspensions based on Vibration Dose Value (VDV). Results Statistical analyses of the VDV data revealed significant differences between the six different suspensions over each of the obstacles in the activities of daily living course. Post-hoc analyses revealed that for each of the obstacles, significant differences existed between the Invacare suspension and the Invacare solid insert. For the Quickie power wheelchair the solid insert setting was not significantly different from the most-stiff setting for each of the obstacles

Jan 6, 2006

By Michael D. Balen

The U.S. Bureau of Mines (Bureau) is currently conducting a four-year study to assess the mineral resources and the mineral development potential of the 5.7 million acre Valdez Creek Mining District (VCMD) located in southcentral Alaska. The VCMD study is part of the Bureau's ongoing statewide mining district evaluation program. This report is a summary of the 1988 field work. The field work involved collection of reconnaissance placer and rock samples, and also involved sampling and examination of the mines, prospects, and mineral occurrences which were identified by literature research of the geology, exploration history, and mining history of the district. During the 1988 field season, Bureau personnel spent a total of 11 weeks in the field, collected 1,006 rock and placer samples, and located, mapped, and sampled 106 of the known mineral occurrences. The Bureau has visited 243 of the 250 known mineral occurrences during the course of the VCMD project. Reconnaissance sampling for placer occurrences resulted in the identification of 4 previously unreported gold placer occurrences, and identification of 5 occurrences that contain detectable levels of platinum or palladium. Reconnaissance sampling for lode sources of base and precious metals resulted in the identification of 5 new Lode gold-silver occurrences, identification of 2 occurrences that contain elevated quantities of chromium, cobalt, nickel, palladium, and platinum, and identification of one occurrence that contains elevated quantities of copper, molybdenum, anti zinc.

Jan 1, 2011

By Robert G. Gibson, Joel D. Gibbons

Measurements and analyses were conducted of whole-body vibration aboard seven commercially available passenger and/or recreational vehicles: sedan; sport-utility vehicle (SUV); pickup truck; moving truck; motorcycle; all-terrain vehicle (ATV); and boat. The purpose of the testing was to measure and assess whole-body vibration exposure in a range of typical vehicle environments in order to gain understanding of typical exposure levels characteristic of activities of daily living. Vehicle models tested (and model year) were: Ford Taurus (1995); Jeep Cherokee Sport (2000); Toyota Tundra SR5 (2002); Ford F-350 (1997); Harley-Davidson Electra Glide Classic (2004); Yamaha Kodiak 400 4x4; and Steiger Craft Model 21 Montauk. All vehicles were tested with their standard factory-installed seats and were operated under a range of normal operating conditions and speeds typical of intended vehicle use. Methods The measurement, processing, analysis, and exposure assessment methods follow the guidance of generally accepted, national and international consensus standards relevant to the evaluation of whole-body vibration, including ISO 2631-1 [1] and ANSI S3.18 [2]. Seats were instrumented with low-mass triaxial accelerometers mounted in seat pads. Accelerometers used in the test are specified to have flat frequency response over the frequency range of 0.5 to 80 Hz, and all accelerometers were recently calibrated traceable to the National Institute of Standards and Technology (NIST). Seat pads were installed following guidance in the relevant standards [1, 2], with sensitive axes of the accelerometers following the standard coordinate system with respect to the seated occupant. (The x-axis represents fore-aft motion; the y-axis represents side-to-side motion; and the z-axis represents vertical motion with respect to the occupant.) Vibration data processing and analysis, including filtering, sampling, frequency-weighting, averaging, summation, and determination of basic and additional metrics followed procedures in the relevant standards [1, 2]. Digitized time series data were acquired and stored using a PC-based data acquisition system. Whole-body vibration exposure analyses were conducted via post-processing. During data processing, recorded periods of seat acceleration that were identified and verified as resulting from occupant-induced motion rather than vehicle motion were excluded prior to exposure analysis. The basic evaluation metric for whole-body vibration is the frequency-weighted root-mean-square (r.m.s.) acceleration, aw. The primary additional evaluation metric is the fourth-power

Jan 6, 2006

Background: Frictional ignitions continue to be a problem facing the U.S. underground coal mining industry. Many methane igni-tions are associated with the impact of mining machine cutter bits on quartzitic material (e.g., sandstone) during the coal-cutting process. Most ignitions result in small methane-air fireballs often only a few feet in size and limited to the cutter head location. However, under certain conditions, frictional ignitions can lead to larger methane explosions and/or fires with the potential for causing serious injury or death to the mining machine operator and other nearby miners. The requirements for a frictional ignition are a flammable volume of methane-air and an ignition source. This source is usually the hot streak caused by the frictional impact of the mining bit on hard rock, and the frequency of occurrence increases with increased bit wear. Another possible ignition source is the fric-tional impact of rock on rock during a roof fall.

Mar 1, 2008