Reducing Materials Handling Injuries In Underground Mines · REDUCING MATERIALS HANDLING INJURIES IN UNDERGROUND MINES Phil W. Patton Montana Tech of the University of Montana, Butte,

REDUCING MATERIALS HANDLING INJURIES IN UNDERGROUND MINES

Phil W. PattonMontana Tech of the University of Montana, Butte, MT

Bill M. Stewart, Mining Engineer Curtis C. Clark, Mechanical Engineer

Spokane Research Laboratory, National Institute for Occupational Safety and Health, Spokane, WA.

ABSTRACT

Back injuries from handling materials inunderground mines continue to be a majorsafety problem. In spite of the ingenuity ofmany people and the development of numerousmechanized aids, the number of materials-handling injuries remains second only to thenumber of roof fall injuries in underground coalmines. Relocation and repositioning of electricalcable, conveyor belt parts, and roof bolt sup-plies in particular are the sources of significantnumbers of back injuries.

To help reduce such injuries, researchers atthe Spokane Research Laboratory of theNational Institute for Occupational Safety andHealth are examining Mine Safety and HealthAdministration accident data to determinecorrelations between materials-handling tasksand the number of back injuries. Also beinginvestigated are new technologies used inunderground mines in the United States. Equip-ment is being developed or modified that wouldreplace the necessity of doing lifting tasksmanually. A Coleman manipulator was tested,and modifications were made to make it moresuitable for underground mine use. To reduce oreliminate the need to manually clean offmaterials that commonly plug grizzly openings,a track-guided pincher arm device was develop-ed. Oversized rock can be broken with thepincher arms in the up position, and the armscan be lowered to grab and remove debris. Thearm can also be used in a sweeping action toremove cohesive fines that may bridge grizzlyopenings.

INTRODUCTION

Materials-handling problems in under-ground mines and injuries associated withunderground materials handling have been welldocumented (Peay 1983; Gallagher et al. 1990).Although lost-workday injury rates related tomaterials handling in mines decreased between1988 and 1997 (Mine Safety and Health Admin-istration [MSHA] 1999; National Institute forOccupational Safety and Health [NIOSH]2000), the number of lost workdays was stillsignificant, and the cost to the mining industryeach year was tremendous. During that time,there were 58,661 lost-workday cases resultingin an average of 34 days lost (including restrict-ed days) per case. Over 21,000 of the lost-workday cases were in underground mines.

A review of 1999 data from undergroundmines in the United States indicated thatmaterials handling is still one of the leadingcauses of reportable injuries. Accident reportnarratives show numerous and varied materials-handling activities that result in injuries. Thisfinding is not much different from what wasreported in 1989 in an extensive investigation ofback injuries in underground coal mines (Stobleet al. 1989). Stoble et al. found “considerablediversity in the situations which produce backinjuries. Of the 156 scenarios which producedback injuries, 130 occurred only once, 17occurred twice, 4 occurred three times, 1occurred six times, 2 occurred eight times, and 2occurred 10 or more times.”

The number of such injuries is directly

related to the number of manual tasks. Hundredsof these tasks are performed in undergroundmines each day. They involve pulling, hanging,pushing, and lifting objects of different weights,shapes, and sizes. Many times, handling tasksare done in confined areas, on uneven ground,in slippery conditions, and without assistance. Thus, given the nature of the undergroundenvironment (poor lighting, poor footing,confined spaces, etc.), the amount of suppliesand equipment needed daily, and the diversityof tasks, injuries resulting from materialshandling will probably never be eliminated.

Large underground mines have fewermaterials-handling accidents than smallermines, because in large mines, there is room formechanized equipment. However, most under-ground mines have limited space. Numerousmaterials-handling tasks can only be donemanually, and lifting and re-lifting suppliesseveral times before they are used is notuncommon.

In the 1980's, several inexpensive, easy-to-construct materials-handling devices weredeveloped and tested for underground mines(Conway and Unger 1989). These devicesincluded a scoop-mounted lift boom for trans-porting and maneuvering heavy machinecomponents, a swing arm boom to lift compo-nents on and off transport vehicles, a floor-typemaintenance jack for lifting heavy machineparts, a mine mud car to aid in moving suppliesfrom storage areas to the point of use, a con-tainer workstation vehicle to transport tools andsupplies on a daily basis, and a timber car forinstalling crossbeams for roof support. All ofthese devices were designed to reducematerials-handling injuries. Research to reduceinjuries from specific materials-handling tasks,such as hanging cables, building stoppings, andhandling bags of rock dust, was also conducted(Unger and Bobick 1986).

The goal of the current research project is to

reduce materials-handling injuries by reducingmanual materials-handling tasks and to proposedesign considerations for underground materialshandling safety training and technological inno-vations. This paper describes the developmentand testing of specialized equipment to helpachieve this goal.

DESCRIPTION OF PROJECT

The research approach is to investigatecommon underground materials-handling tasksor activities that frequently result in injuries.Only underground mines are included in thisresearch, and the emphasis is on manual tasks.Specific targets were determined by reviewingMSHA accident report narratives, personaldiscussions with mine safety officers, and minetours to witness materials-handling activities.

Back injuries are a significant percentage ofthe materials-handling injuries in undergroundmine accidents. Some types of accidents areunique to metal mines, some to coal mines, andsome are common in both types of mines.Underground coal mines have a much higherpercentage of materials-handling back injuriesthan do underground metal/nonmetal mines. Abreakdown by activity is shown in the MSHAUnderground Accident Data Summary (table 1),and incident rates are shown in table 2. Todetermine changes in materials-handling acci-dents, accidents in 1989 were compared to thosein 1999.

With the extensive reduc-tion in workforceover the past 10 years, incident rate is a betterindicator of safety performance than totalnumber of workers. Incident rates are calculatedon the total number of hours worked associatedwith mine type (underground, surface) and notto the number of hours worked while actuallyhandling materials.

Table 1.—MSHA Underground Accident Data Summary

Category 1989 1999

No. of injuriesCauses of back injuries,

percentNo. of injuries

Causes of back injuries,

percent

METAL/NONMETAL:

Handling material, total . . . . 401 194

Back injuries while handling

materials: . . . . . . . . . . . . . .1 131 33 47 241 1

Handling supplies . . . . . . . 65 50 20 43

Move power cable . . . . . . 11 8 2 4

Handle timber . . . . . . . . . . 9 7 3 6

Move equipment . . . . . . . 9 7 6 13

Machine maintenance . . . 8 6 10 21

COAL:

Handling material, total . . . . 3,661 1,390

Back injuries while handling

materialsl: . . . . . . . . . . . . .1 1,737 47 548 391 1

Handling supplies . . . . . . . 808 47 257 47

Move power cable . . . . . . 265 15 105 19

Machine maintenance . . . 90 5 44 8

Hand load hand shoveling 126 7 33 6

Move equipment . . . . . . . 98 6 29 5

Handling coal, rock, waste 80 5 25 5

Handling timber . . . . . . . . 148 9 21 4

The category of “injuries while handling materials” is divided into subsets by body part, of which back injuries is1

one. Handling supplies, etc., are subsets of “back injuries while handling materials.” Percentages are calculated

accordingly.

Because of budget and time constraints, itwas not possible to develop and/or test solutionsto all common materials-handling problems.The detailed investigations described in thispaper include methods to reduce injuries frommanually moving objects (single lifting event)and from cleaning debris from grizzlies. Investi-gations included the use of existing equipment,modifications of existing equipment, anddevelopment of new equipment.

SINGLE LIFTING EVENT

A significant percentage of back injuries isthe result of lifting and pulling activities associ-ated with materials handling. Most of these backinjuries are thought to have occurred in asituation where, for reasons of expediency and

in the absence of help, the worker tried to liftmaterials or handle equipment that were tooheavy.

Assisted lift devices (manipulators) arecurrently used in many manufacturing sectors toreduce injuries associated with manual equip-ment and materials handling. Manipulatorsallow workers to lift and maneuver heavyobjects throughout a work area, yet require thatthe operator exert only a few pounds of force.Underground shops where a variety of liftingactivities occur in the course of performingmaintenance activities are particularly goodcandidates for assisted lifting devices. In themining environment, attachments are beingincluded on many pieces of undergroundequipment to lift objects. Examples include

Table 2.—MSHA Underground Incident Rates Summary 1

Category1989 1999 Percentage of decrease in incident rate, 1989-

1999

METAL/NONMETAL:

Handling materials, total . . . . . . . . . 2.72 1.71 37

Back injuries while handling

materials: . . . . . . . . . . . . . . . . . . . .0.89 0.41 54

Handling supplies . . . . . . . . . . . 0.44 0.18 60

Move power cable . . . . . . . . . . 0.07 0.02 76

Handle timber . . . . . . . . . . . . . . 0.06 0.03 57

Move equipment . . . . . . . . . . . 0.06 0.05 14

Machine maintenance . . . . . . . 0.05 0.09 -62

COAL:

Handling materials, total . . . . . . . . . 5.60 3.61 36

Back injuries while handling

materials: . . . . . . . . . . . . . . . . . . . .2.66 1.42 47

Handling supplies . . . . . . . . . . . 1.24 0.67 46

Move power cable . . . . . . . . . . 0.41 0.27 33

Machine maintenance . . . . . . . 0.14 0.11 17

Hand load hand shoveling . . . . 0.19 0.09 56

Move equipment . . . . . . . . . . . 0.15 0.08 50

Handling coal, rock, waste . . . . 0.12 0.06 47

Handling timber . . . . . . . . . . . . 0.23 0.05 76

Incident rate = Injuries times 200,000 ÷ Total hours worked.1

grabbers on roof bolters for picking up flatsheets of wire mesh; attachments on longwallshearers for moving small parts, tools, etc.,down the longwall face; small revolving chainhoists fitted on stageloaders for moving partsover the stageloader; and grabbers for liftingand setting timbers and cribs.

Activities in which assisted lifting devicesmight reduce injuries include—

• Handling large pneumatic wheel-lugwrenches and changing out hydraulic motors,which are examples of maintenance-relatedlifting activities that involve lifting, positioning,and sometimes holding heavy objects.

• Getting needed materials from the surface tounderground laydown areas. Currently, such

work is done with forklifts or other mechanizeddevices. The materials are generally placed on apallet and tied together. Once in the laydownarea, however, materials are separated and mustbe handled manually by workers to get them tothe active work area.

• Maintenance of heavy equipment where nooverhead lifting system is in place, such asconveyor belt systems in underground mines,which are often manually disassembled, moved,and reassembled.

• Installing bulkheads, overcasts, andstoppings and hanging supply lines (waterlines,ventilation tubes, etc.) from the mine back.

Figure 1.–Can crib used to replace wood

crib in underground coal mines.

Figure 2.– Attachment used to pick up and

maneuver can cribs.

INNOVATIVE WAYS TO IMPROVEMATERIALS HANDLING

Several innovative designs, procedures, andequipment for reducing materials-handling in-juries were observed during mine visits. Manyof these involved the use of mechanized equip-ment to aid in lifting.

Can Cribs

General improvements in materialshandling in underground ore deposits in thewestern United States include replacing woodcribs with can cribs for roof control. Can cribsallow stress release, as do wood cribs. The canis a few inches shorter than seam height andconsists of a metal jacket approximately 76 cmin diameter with a wall thickness of 1 cm filledwith lightweight grout (figure 1). The can isfabricated off-site and shipped to the mine inpredetermined lengths so it can be transportedhorizontally. It is rotated to upright in place,

capped with wood, and wedged into place. Theuse of cans reduces lifting and pinch-pointexposures. An attachment adapted for existingequipment is used to grip and lift the can off thefloor or trailer and rotate it into position (figure2). Much less manual labor is required to set acan crib support than is required to set a woodcrib support because only the caps and wedgesare placed manually, resulting in fewermaterials-handling injuries.

Engineered Timber

In the eastern United States, engineeredtimber is replacing conventional timber in somemines. Engineered timber offers the sameadvantage as can cribs. Engineered timbers arewood posts that have steel bands and wedgesadded to increase post strength. Mechanizedsetting attachments similar to those used withthe can crib can be used. Engineered timber hasless strength than a can crib, thus requiringmore trips, so it has fewer economicadvantages.

Figure 3.–Belt weight as a function of width.

Conveyor Belts

Labor-intensive handling of belt structureshas become commonplace. The phenomenalproduction gains experienced by mining com-panies in the past few years has resulted inwider and faster conveyor belts. The weight ofmaterials handled by workers has doubled as aresult of using the wider belts, and this hasincreased the potential for back injuries. Beltweight as a function of width is shown in figure3. Belt suppliers and mine personnel are copingwith the demands of increased weight in severalways, as discussed below.

Increasing Space

Mechanization of belt installation under-ground is an engineering challenge. Theworking space is narrow and uneven. A widerworking space beside the belt in the same entryas the belt would greatly enhance materialshandling for installation, removal, and main-tenance of the belt line. However, in most cases,belt entries cannot be widened without jeopar-dizing roof control.

There are two approaches to creating moreworking space without widening total entrywidth. One is better utilization of present

working space through the use of smallerequipment. Underground mines are using smallloaders to meet this demand. Manufacturershave an assortment of attachments that haveworked very satisfactorily with fewmodifications for underground settings.

However, new diesel particulate regulationsare challenging the gains made by smallerequipment by restricting the use of surfaceloaders underground. Another concernpresented by regulatory constraints is the typeof air in which the equipment is operating.Because of the dangers of explosive charges andMSHA regulations, small nonpermissableloaders cannot be used in return air or beyondthe last open crosscuts. Small, permissibleloaders can be purchased as an option to replacestandard-sized loaders, but none were observedon any of the mine trips.

A second approach is to eliminate space onthe nonworking side (off side) of the belt byinstalling the belt closer to the off-side rib(figure 4). Because the belt line must bestraight, the offside space is used to compensatefor developing an entry that is not straight.However, with the use of lasers and with bettertraining, miner operators can eliminate errors incutting the entry and thus reduce the offsidewidth, which can permit the use of smallerequipment designed for belt work. Moving thebelt closer to the off-side rib and using smallerequipment has resulted in keeping entry widthsunder 6 m, and, in some cases, under 5.5 m.

Having a roadway beside the belt in thesame entry has several materials-handlingaccessibility advantages. These include— • Increasing the likelihood of having a pieceof equipment available for lifting materialsduring installation.

Figure 4.–Layout for belt entry to accommodate materials-handling equipment.

• Eliminating the need to carry materialsbetween crosscuts during maintenance.

• Allowing better inspection of the belt formaintenance and during a belt shutdown.

• Allowing better access for cleaning under-neath the belt with mechanized equipment.

• Allowing more thorough rock dusting.

A disadvantage is that clearance is limitedwhen belt repairs are needed on the off side.

Placing and Removing Belt Rollers

The process of placing and removing rollersin belt extensions on continuous miner advance,during longwall retreat, and for maintenancechange-out involves bending and manuallylifting the heavy rollers. Innovative methodshave been developed to separate the belt forremoving rollers on the longwall. In one mine,the last top belt roller is mounted to one end oftwo H-beams, and two hydraulic jacks aremounted to the other end. The H-beams arepinned to the tailpiece near the middle of thebeam. Through a lever-type arrangement, whenthe two hydraulic jacks push one end of thebeam down, the top roller and belt are lifted.

When the belt roller is lifted, the distancebetween the belts is increased, and the belt iscompletely lifted up from the second roller fromthe tailpiece. Lifting the top belt makes the sec-ond roller accessible for removal and eliminatesthe need to lift the belt manually. The tailpieceuses hydraulics for normal operation. Thismethod could be used on any tailpiece andreduces the potential for accidents whenremoving the roller.

Another technique is to use an air bag toseparate the belt to facilitate adding rollers inthe belt advance process. Access to compressedair is necessary, but a mine may be able toutilize this in combination with other tech-niques.

A very successful approach for lifting thetop belt for adding the roller has been to usesmall loaders with an attachment bar (a standardhard-roll steel bar bolted horizontally to thebucket). The advantage of the loader is that itcan be employed to carry the roller and lift thebelt. The loader is faster and eliminates theprocess of a worker lifting and bending whileholding a come-along and chains or manuallyplacing an air bag prior to inflating it.

Conveyor Belt Cleaning

Underground coal mines in the UnitedStates utilize belt conveyors to transport coalfrom the working face to the portal. Fine coalparticles stick to the belt beyond the dischargepoint. Residual materials (carryback) stick tothe bottom belt. Belt cleaners are installed at thehead roller area to remove the sticky materials.If in good mechanical condition, the cleanersclean off approximately 95% of the carryback.The remainder is jarred and scraped off as thebelt returns to the tail roller. In a three-shift perday operation, it is not uncommon for 2 tonnesor more of carryback to be deposited on themine floor per week of belt operation. Thecarryback is usually wet when deposited, butdries over time. This becomes very dangerous.Coal dust particles are very small and, if ignited,burn very quickly, to the point of exploding.U.S. regulations require cleaning belt lines toremove the danger from the carrybackexploding.

The standard method of cleaning the carry-back is to use a long-handled, flat shovel to pickup coal dust and place it back on the belt. How-ever, the coal dust is sticky and clings to theshovel blade. Cleaning is time consuming, andworkers are prone to back injuries while twist-ing and dumping. To reduce costs and accidents,some mines have purchased specialty scoops toclean under the belts. The scoops must be smallto operate in narrow spaces and should have anextended flat bucket to reach under the belt line.A roadway along the belt lines must also bepresent to operate the scoops. Hanging the beltfrom the roof allows better access for cleaning.

Industrial vacuums can also be used to cleanthe area around conveyor belts. In most cases,the vacuums are used to clean high-spillageareas, such as dumping points and the bottom ofdeclines. Vacuum suppliers and undergroundmines are working to develop a lower-profile,mobile version for belt lines.

Washing material from under the belt with ahigh pressure hose, once an unacceptablepractice, is becoming accepted. In the past, thewashed material was picked up in solution withsludge pumps and placed back on the belt. Thewet material caused further cleanup problemsdown the belt line. Now the washed material isbeing channeled into a concrete sump largeenough to allow the coal to settle. The water isreused, and the material is allowed to dry andput back on the belt. Other operations usingcyclones to separate the water and material toeliminate putting high-moisture material on thebelt line . All these procedures eliminate the1

need to shovel material and lift materialmanually.

Reduction of Materials Rehandling

Innovative approaches to reducing materialsrehandling include loading skids and specialtytrailers on the surface and using face equipmentto take the loaded skids and trailers directly toan underground worksite. The trailer should bedesigned to haul different items efficiently.Skids and trailers are loaded with all thematerial needed to complete a specific job.Loading outside can be done in better light, withbetter footing, and with better use of equipment,all of which can reduce the potential foraccidents. Job-specific trailers or skids can havespecial racks for hauling large water jugs andhydraulic hoses or specially designed skids formoving conveyor belt parts or cable boltingcomponents.

The use of lightweight materials is anothermeans of reducing the exertion required inmanual materials-handling tasks. For example,aluminum can be used instead of steel bars formonorail systems on which high-voltage cableis transported in longwall mines, lightweightconcrete blocks can be used for ventilationstoppings, and lightweight rollers can be

MSHA’s home page contains useful tips on controlling1

spillage around conveyor belts.

Figure 5.– Laboratory tests on Coleman manipulator

as received from factory.

incorporated as conveyor components.

Application of Sport Conditioning Principles tothe Workplace

It is generally accepted that a period ofwarm-up exercises should take place before anexertion in a sports environment. That samephilosophy is being followed in the work place.At one mine visited, miners were trained oncorrect stretching techniques. Plastic-protectedcards showing the appropriate stretchingtechniques and that were easy to place in a shirtpocket or lunch box were given to the miners.To prepare workers for physical tasks, the minesare allowing time for stretching exercises beforework starts and after long breaks. The stretchingexercises are a good first step to reducing musculo-skeletal injuries. The other part of thewarm up, a moderate exercise to increase themechanical properties of muscles, was notobserved.

MECHANICAL LIFTING AIDINVESTIGATIONS

Manipulators

After purchasing a standard manipulator(figure 5), Spokane Research Laboratorypersonnel conducted a series of typical liftingactivities to determine the manipulator’s base-line performance. The device operated asintended with regard to lifting; however, severalfunctional limitations and operational capabili-ties were identified as needing improvementbefore the device would be practical. The mostsignificant limitation was its lack of mobility.With a weighted pallet jack base of 680 kg, themanipulator was too heavy for one person tomove and position. A second limitation was themanipulator’s lack of stability and levelingcapability; that is, the device would rock on twoof its four contact pads if the floor had anyuneven or low spots. The manipulator arm

would also list to the low side of a flat butinclined floor. A third limitation was the heightand length of the unit, which made it difficult tomove from one work area to another. Doorwayswere difficult to pass through because of theheight, and corners were hard to navigatearound because of the length.

Thus, researchers decided to modify themanipulator to improve its basic function. Forthe device to be practical, it would have to beself-propelled, compact enough to fit throughopenings and around corners, and stable andlevel once positioned. Also, the device shouldbe self-contained with regard to the air andelectrical supply for the lifting/driving/levelingsystem. An integrated design incorporating themanipulator was designed and named themobile manipulator system (MMS).

The MMS is currently in the engineeringdesign phase. Designs will involve modifica-tions to the manipulator arm and the develop-

Figure 6.– Artist’s concept of mobile manipulator after modifications.

ment of several subsystems that form the basisof the MMS. These subsystems will form thebasis of an integrated lifting system. Whencompleted, the MMS will be composed of amanipulator mounted on a mobile base. Thebase will be equipped with telescoping outriggerstabilizers and independently controlled levelinglegs. In addition, an air compressor, inverter,and battery system will also be mounted on themobile unit. The resulting MMS will tram to thelocation needed, deploy outriggers, level thebase unit, then operate via the self-containedair-hydraulic system, all in a timely manner andrequiring only a single user/operator. An artist’sconcept of the MMS is shown in figure 6. If thebaseline performance is satisfactory, then thedevice will undergo a series of tests designed toapproximate the manual materials handling andmaintenance activities in mining environments.

Track-Guided Pincher Arm

Grizzlies are used in underground mines toprevent large boulders from entering ore passesand obstructing them. Some grizzlies areinstalled at ground level and others are recessedbelow ground level to accommodate sidecar or

truck dumping. Typically, grizzly surfacesbecome clogged by the oversized boulders theyare designed to retain; by fine cohesivematerials that bridge openings; and by roofbolts, timbers, wire mesh, and other debris thathave broken away and mixed with the minedore. A recent search of an MSHA database toobtain information on accidents associated withore passes showed that 20% of these accidentswere caused by manually breaking and cleaningrock off of grizzlies.

Impact hammers are effective in breakingoversized rock, but they are very limited in theirability to clean off fines and are incapable ofremoving debris. In some hard-rock mines,especially those with recessed grizzlies,oversized rock is broken using permanentlymounted hydraulic impact hammers. Thehammer head is mounted on a backhoe-type armand is controlled remotely from a control panel.In mines with accessible ground-level grizzlies,oversized rock is scooped from the grizzly andbroken by secondary blasting and/or crushing.In some mines without impact hammers, therock is broken manually with a double-jacksledgehammer. Roof bolts, timbers, wire mesh,

Figure 7.– Track-guided pincher arm attached

to hydraulic impact hammer head.

and other debris are generally removed by aworker who climbs onto the grizzly and throwsthe debris off to the side, which is especiallydifficult in recessed grizz-lies. The materialsthen have to be picked up, placed in the trash,and hauled to the surface or other undergrounddisposal area.

In cooperation with Gonzaga University,Spokane, WA, a device was designed, con-structed, and tested to pick debris from grizzliesmechanically (figure 7). The device, called atrack-guided pincher arm (TGPA), can beattached to any existing impact hammer. Itemploys two arms that come together at the endof their travel to create a clamp. The TGPA isdesigned so that the arms can extend into theclamping position, pick up debris, and retractout of the way of the hammer pick, whichbreaks up oversized rock. The arms can openwide to accommodate large objects. The deviceis capable of withstanding the daily pounding ofthe impact hammer and is fully functional in amine environment.

The impact head for the TGPA was ahammer being used in an underground mine innorthern Idaho. Measurements were obtainedfrom both the mine and the manufacturer. Tobuild the TGPA, detailed AutoCAD drawings ofTGPA parts were prepared and sent to a ma-chine shop for cutting into the necessary shapes.After the steel was cut, holes for the attachmentbolts were bored through the steel, and thecomponents were welded and assembled. Afterattaching the hydraulic cylinders for extendingand retracting the pincher arms, the entireassembly was welded onto mounting plates. TheTGPA was taken to the mine, installed on theimpact hammer, and tested. The installation,including hydraulic hose hookup to the impacthammer control box, took about 1 hour.

During the initial test, the operator of thedevice ran the equipment in a slower, more-deliberate manner than usual. Under these

slower operating conditions, the test was verysuccessful. The pincher arms extended and retracted by moving the hydraulic lever at thecontrol panel as designed. Several pieces ofdebris, including wire mesh, pipe (figure 8),wood pieces, and roof bolting pressure plates,were picked up from the recessed grizzly by theTGPA and dropped onto the ground. The impacthammer appeared to operate normally, andseveral rocks were broken with the arms of theTGPA in the retracted position. A bonus was theincreased sweeping capability of the device. TheTGPA has 30 cm (15 cm on each side) of baseplate metal that can be used to sweep or pullback fines over the grizzly openings. Withoutthe TGPA attached, only the hammer pick canbe used for sweeping. Removing cohesive fineswas probably three times faster with the TGPA.

After the initial test, the TGPA was left atthe mine for long-term tests under typical

Figure 8.–Track-guided pincher arm picking up pipe debris

from recessed grizzly.

operating conditions. Problems during this 3-month test included breakage of hydraulic fittings, less control of boom swing because ofthe additional weight of the TGPA attachment,exceeding relief valve pressures during maxi-mum boom extension, and difficulty in reachingboulders in the corners of the recessed grizzlybecause of the added width of the TGPA.

Better protection of the hydraulic fittingsand making the attachment lighter so that it doesnot affect the action and movement of the ham-mer are problems currently being addressed.The impact hammer operators appeared to besatisfied with the picking and sweepingcapabilities of the TGPA.

CONCLUSIONS

The research described in this paper is notnew. For years, underground miners, mineforemen, safety engineers, researchers, andothers have been designing, developing, and

testing innovative equipment and tools thatcan be used to make jobs easier and reduceinjuries.

Yet, in spite of the ingenuity of manypeople and the development of manymechanized aids, materials handlingcontinues to be the MSHA category with thehighest percentage of accidents and injuriesin underground mines. Hundreds ofmaterials-handling tasks are performed inunderground mines each day. It would behard to find one of these tasks that has notresulted in an injury at least once.

Some solutions are simple, such asreducing “package” weight. Other solutionsare not so simple, such as hanging objectsoverhead and moving trailing cables.Because of the diversity of materials-handling tasks, no single solution exists toeliminate materials-handling injuries. It is

neither technically or economically feasible tomechanize all underground materials-handlingtasks. Some tasks need to be done manually.The individual performing any materials-handling task, no matter how large or small,must take special precautions and get into thehabit of thinking about the lift prior to doing it.No one likes to get hurt, and there is always abetter, less strenuous way to lift a heavy object.

Research and development of materials-handling tools and equipment should continuewith an emphasis on those tasks that result innumerous materials-handling injuries, such asmoving roof bolt supplies, hanging waterlinesand ventilation tubes, and moving cables. Oneapproach is to have mine safety officers identifythose tasks that cause frequent injuries at agiven mine and conduct specialized materials-handling safety training to individuals perform-ing these tasks. This would be valuable for newminers because they frequently get jobsinvolving supplies and materials. Constant(daily) safe materials-handling reminders from

safety managers and shift foremen will aid ingetting miners into the habit of not only“thinking before they lift,” but also thinkingbefore they carry, pull, hang, or push suppliesand materials.

Improvements in production as well assafety have been accomplished over the past 10years. The makeup of the work force hasremained unchanged but is getting older. Themottos of the industry have been Think safety,Work smarter, Quality first, Production andsafety go hand in hand, Team building, Qualitycircles, Employee empowerment. Futureproductivity and safety gains will be driven bytechnological improvements as it has been inthe past 10 years. Those technologies will bedeveloped by better-trained and coordinatedorganizations. University and research groupssuch as NIOSH have industrial advisory boardsto help coordinate training and research efforts.The mining industry has been successful inreducing materials-handling injuries over thepast 10 years. Continuation of this trend will bethe challenge of the future.

ACKNOWLEDGMENTS

Our gratitude goes to Mr. Harvey Keim, Mr.Jim Taylor, and Mr. Clyde Peppin, HeclaMining Company-Lucky Friday Unit, Mullan,ID, for their cooperation during the tests of thetrack-guided pincher arm. Not only did theyallow us to use one of their active impacthammers for the tests, but they helped install thedevice, hooked up the hydraulic hoses, operatedthe hammer controls during the initial 60-min,short-term test, and gave us feedback on thelong-term tests.

The effort put in by the mining companiesand mine personnel to provide mine tours andthe time they spent discussing their materials-handling activities are greatly appreciated.

Finally, the authors would like to thank KenStrunk for his graphics expertise and PriscillaWopat for her editorial expertise in completingthis paper.

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National Institute for Occupational Safety andHealth. Ch. 6. Worker Health Chart Book, 2000.Publi. No. 2000-127, Sept. 2000, 29 pp.

Stobbe, T.J., Plummer, R.W., and Jaraiedi, M.Back Injuries in Underground Coal Mines: FinalReport. U.S. Bureau of Mines research contractJ0 348044-05. West Virginia University. 1989.

Conway, E.J., and Unger, R.L. MaterialsHandling Devices for Underground Mines. U.S.Bureau of Mines Information Circular 9212,1989, 48 pp.

Unger, R.L., and Bobick, T.G. Bureau of MinesResearch into Reducing Materials-HandlingInjuries. Bureau of Mines Information Circular9097, 1986, 22 pp.

List of Figures

Figure 1.–Can crib used to replace wood crib in underground coal mines.

Figure 2.–Attachment used to pick up and maneuver can cribs.

Figure 3.–Belt weight as a function of width.

Figure 4.–Layout for belt entry to accommodate materials-handling equipment.

Figure 5.–Laboratory tests on Coleman manipulator as received from factory.

Figure 6.–Artist’s concept of mobile manipulator after modifications.

Figure 7.–Track-guided pincher arm attached to hydraulic impact hammer head.

Figure 8.–Track-guided pincher arm picking up pipe debris from recessed grizzly.