MSHA STATE GRANT PROGRAM FOR MICHIGAN
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Improved Visibility for Operating By C.M.K. Boldt, Civil Engineer, Spokane Research Center, Spokane, WA The U.S. Bureau of Mines (USBM) has been solving problems in surface mine haulage safety for almost as long as it has been around (100 years). The old adage of "Been There, Done That" is very true. However, the more things change, the more they stay the same. We’re still digging ore out of the ground. But now it’s with million-pound (loaded weight) haulage trucks, satellite uplinks, and microchip maintenance. What was science fiction 10 years ago is commonplace today. So, when I say that 20 years ago, haulage truck visibility tools like mirrors and cameras were studied by the USBM, maybe it’s time to look again. Introduction Powered haulage has been, and continues to be, the major source of severe accidents and
fatalities in surface mining. From 1972 through 1974, truck haulage accidents were the
leading cause of fatalities at metal and nonmetal surface mines (Miller, 1976). Figure 1
illustrates that from 1989 through 1991, accidents involving surface mine haulage trucks
accounted for the greatest number of accidents with the most severe injuries and
fatalities (Aldinger, 1995). The latest preliminary accident statistics from MSHA indicate
that over 33% (again, the largest single category) of the 1995 fatalities were
attributable to powered haulage. This article summarizes past USBM research and currently available technologies pertaining to mirrors and video cameras for blind area viewing on large surface haulage trucks. After abolishment of the USBM in 1996, some of the health and safety research functions were continued—the project on surface mine hazard reduction is presented here. Although this article highlights safety tools for large haulage trucks, there is no substitute for a dynamic safety program which includes proper preventative maintenance and safe driving. Background In 1995, the USBM presented an overview of the research conducted in surface haulage safety (May, 1995). Excerpts from this Blacksburg, VA conference paper are presented here along with references for the reader’s convenience. Not all research topics are given in this article. For a complete summary, it is suggested that the reader obtain a copy of the May report. In 1977, the USBM published recommendations for haul road design and construction, taking into account haulage truck size, road alignment, construction materials, cross slope and drainage design, runaway vehicle safety provisions, etc. (Kaufman and Ault, 1977). Associated with this effort was the design and construction of berms and runaway vehicle protection measures. In the 1980s, several techniques to stop runaway trucks were evaluated. These included road berms, guardrails, boulders, concrete barriers, center safety berms, and escape lanes. Follow-up studies on escape lanes and center berms were then evaluated and construction techniques documented (Hays, 1983). In the late 1980s, active collision avoidance systems using radio transmitters and receivers were field tested (Griffin, 1988). In these systems, the transmitter was installed in the smaller vehicle, in this test case, a pickup-sized truck. The receiver was installed in 130- and 170-ton haulage trucks. The premise was that the transmitter would trigger an audible and/or visual signal in the haulage truck when it was within a 30-foot radius. There were problems with false alarms triggered by the mine communication system, the truck’s electrical system, and other outside bodies, such as berms and passing vehicles. Recommendations were made to improve the system. More recently, in 1995 the USBM concluded studies evaluating two technologies capable of monitoring the position of a vehicle in relation to a potential hazard such as a road edge, highwall, dump point, or other mining equipment. These technologies were (1) radar positioning with dead reckoning and (2) a differential global position system combined with dead reckoning. The radar system had an accuracy within 3.5-meters, which was not deemed sensitive enough for positioning the vehicle in relation to hazards. The global positioning system tested was accurate, but could not relay the information within a target time frame of 1 second. There are other systems now on the market that were not available at the time and that claim to have the accuracies needed to meet the objectives of the project. This technology may be pursued in the future with continuing health and safety research. Blind Area Viewing Aids For a while, bigger was better in surface haulage. The bigger the machine, the more it could haul. The more it could haul, the better the production numbers. The statement has now been made that bigger is better only if bigger is better. There comes a time when the sheer size of a piece of equipment exceeds the limits of the infrastructure (such as haulage road widths), loader configurations, and maintenance costs. One of the newest behemoths on the mine haul market today is a 300-short ton (st), two-axle, rear dump truck. At 24 feet high and a little over 50 feet long, it has a gross vehicle weight of 1.1 million lbs.—as compared to an empty DC-10 jetliner at 244,000 lbs. The payload is 300 st, but the truck dimensions are comparable to smaller capacity 240 st trucks. This engineering feat of increasing the payload by minimally increasing truck dimension is welcomed not only for its efficiency in using existing mine resources, but also because the truck operator is not blinded a quarter of a mile around. Although the 300-st truck is considered an "ultra class," all mine haulage trucks are large and heavy, and operate in less-than-ideal weather and geotechnical conditions. The extensive blind areas of such trucks have been documented years ago (MB Associates, 1978). These blind areas are dependent on the size of the truck, position of the operator, obstructions, and modifications obscuring the operator’s vision, etc. Figure 2A is a generalized look at the blind areas around a rear-dump haulage truck. A 6-foot tall person will not be seen by the driver of a 150-ton haulage truck within 70 feet from the right side of the truck and ground level is not visible for 105 feet.
Figure2A.- Front view of vision limitations from the cab of a 150-ton rear-dump truck (from Miller, 1975) Between 1976 and 1981, the USBM contracted studies to improve the visibility system for large (100+ ton) haulage trucks in surface mines (MB Associates, 1978; Tracor MBA, 1982). The components designed and tested were a flat-planed, left-hand driver’s mirror; a right-hand, rectangular, 30-in radius convex mirror; a right-front-mounted Fresnel lens blind-area viewer that allowed the driver to see the right front side of the truck; and a closed-circuit television for viewing the rear of the truck. Modifications were made to all the units after laboratory mock-ups and in-mine testing. The units were installed on 150- and 170-ton haulage trucks at three different mines for year-long durability testing. At the end of the test period, the contractor concluded that left-hand mirrors were already widely used in the industry, and, therefore not necessary to pursue the topic further. The blind-area viewer with a night light for night dumping was well liked by the drivers and was offered commercially. The right-hand, rectangular convex mirror seemed to work better than what was available in the mines at the time, namely, a round convex mirror. Mirrors could not give drivers a view directly to the rear of the truck. However, the components of the closed-circuit television camera (particularly the automatic iris) were not rugged enough to withstand the mining environment.
Figure2b.- Plan view of vision limitations from the cab of a 150-ton rear-dump truck (from Miller, 1975) Today, many large haulage trucks are equipped on the driver’s side with flat plane mirrors with a small convex mirror that enlarges the field of vision. As with all mirrors, though, their durability under loading and off road haulage is still a problem. Manually adjusting mirrors to suit the individual drivers’ field of view has also been known to cause breakage. An electronically adjustable left-hand mirror has been used at one mine to reduce the need for mirror replacement. The most common right-hand mirror configuration is the rectangular, convex mirror. Since it is usually used only to check the right side of the truck for obstructions before moving, the reduced size of the image on the convex mirror is not critical, but improvements can still be made. Currently, surveillance cameras are used to give back-up warnings on top-of-the-line recreational vehicles, utility trucks, and municipal refuse trucks. Some video cameras designed for surveillance claim to have shock and vibration ratings of 9 G’s. This specific camera has a minimum illumination requirement of 0.3 lux, the widest field of view (127_ horizontal by 100_ vertical), an automatic shutter that covers the lens when not in use, and black-and-white monitors rated to withstand 4.4 G’s. In 1995, the USBM had completed initial shock tests on various machines in a surface mine to study the effects of vibrations on driver fatigue and health. Self-contained field recorders were installed on the smaller sized equipment typical of quarries: a 35-ton haulage truck, a 7- to 8-cubic yard bucket capacity front-end loader, and a bulldozer. These field tests were conducted in a limestone quarry under actual working conditions. The haulage truck’s peak acceleration recorded 11 G’s on the cab floor during the first pass at loading. The bulldozer recorded over 23 G’s, and 8 G’s were recorded for the front-end loader. These peak shock loads indicate that video cameras may still have a problem withstanding the mining environment. However, further tests are warranted to field test the cameras and monitors on today’s larger equipment under shocks and vibrations found in mine conditions. Radar is being used to provide warnings to a driver about obstacles during backing operations. Currently, these systems are being used on some commercial vehicles, motor coaches, and is being used at one mine for proximity warning. They are also being tested on highways to promote collision avoidance, especially where one vehicle is closing on another. Improvements in radar sensing are leading to the point where the technology can be used in mud- and ice-caked conditions. These concepts are being pursued by industry, academia, and government research laboratories. Current status of surface mine hazards reduction efforts Although the USBM was abolished by Congress in 1996, the Health and Safety research program in Pittsburgh, Pa., and Spokane, Wa., were transferred to the Department of Energy, and according to administration plans, in 1997, will continue within the National Institute of Occupational Safety and Health, an agency within the Department of Health and Human Services. The project, "Hazard Reduction for Surface Mining," is continuing to build on past accomplishments while re-focusing future goals to meet the health and safety needs of the mining industry. The objective for the project is to reduce accidents and injuries associated with coal and metal/nonmetal surface mining. MSHA provides extensive training support and visual aids for safety training. Much of the development of training materials has been done by the USBM and continues through the mine health and safety research of the Pittsburgh and Spokane centers. Relevant topics pertaining to large surface haulage equipment can be requested from the National Mine Health and Safety Academy, P.O. Box 1166, Beckley, W.Va. 25802-1166, telephone (304) 256-3257. References Aldinger, Jeffrey A., and C.M. Keran, "A Review of Accidents During Surface Mine Mobile Equipment Operation," Proceedings of the Twenty-Fifth Annual Institute on Mining Health, Safety and Research, Blacksburg, VA, 1994, pp. 99-108. Griffin, R.E., "Anticollision Systems for large Mine Haulage Trucks," USBM RI 9212, NTIS PB 90-266602, 1988, 14 pp. Hays, R.M., "Applicability of Center Safety Berms in surface Mines," USBM Contract Report P3330440, Ronald M. Hays and Assoc., 1983, 31 pp. May, James P., and J.A. Aldinger, "Overview of Bureau Research Directed Toward Surface Powered Haulage Safety," Proceedings of the Twenty-Sixth Annual Institute on Mining Health, Safety and Research, Blacksburg, VA, August 28-30, 1995, Miller, Wayne K., "Analysis of Haulage Truck Visibility Hazards at Metal and Nonmetal Surface Mines-1975," MESA Information Report 1038, 19 pp. Hawley, Kent W., and S. F. Holbert, "Improved Visibility Systems for Large Haulage Vehicles, Vol. I," USBM Contract H0262022, MB Associates, San Ramon, CA, 1978, 121 pp. Kaufman, W. W., and J.C. Ault. "Design of Surface Mine Haulage Roads - A
Manual," USBM IC 8758, 1977, NTIS PB 277 251, 68 pp.
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For Mine Safety Training in Michigan - Contact Dave Carlson at dcarlson@mtu.edu
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