Longwall Shield Recovery Using Mobile Roof Supports 

Frank Chase, Research Engineer 

NIOSH, Pittsburgh Research Laboratory, Pittsburgh, PA 

Phyllip Worley, Senior Manager of Engineering 

Peabody Energy, Wharton, WV
 

Allen McComas, President 

Mobile Mining Support, Inc., Peach Creek, WV
 

ABSTRACT 

Longwall mining has gained the reputation as being the safest 

extraction method in underground coal mines. However, one of the 

most difficult tasks associated with longwall mining is moving the 

face once a panel is completed. Based on Mine Safety and Health 

Administration (MSHA) fatality reports since 1996, longwall face 

recovery operations have claimed the lives of 5 U.S. miners and 

have resulted in numerous injuries. Recovery operations can be 

hazardous because they involve moving large pieces of equipment 

in very confined spaces. They are also conducted in highly stressed 

ground conditions due to front abutment loads generated by panel 

extraction. Shield removal is the most hazardous operation during 

face recovery because miners are constantly exposed to the 

unpredictable gob edge. To protect the miners, one or more 

walking shields, cribbing and/or other supplemental roof and 

standing supports are typically employed as breaker line supports 

as each shield is removed. 

At the Harris No. 1 Mine in southern WV, mobile roof supports 

(MRS’s) have been used in lieu of traditional walking shields on 17 

face moves since 1997. MRS’s are shield-like support units 

mounted on crawler tracks and are commonly used during roomand-pillar retreat mining operations. For longwall recovery, the 

two biggest advantages that MRS’s have over traditional walking 

shields are that they are remotely controlled and are highly 

maneuverable. MRS’s have contributed to safer shield recovery 

and shorter move times at the Harris No. 1 Mine. This paper will 

address both the safety and the operational issues associated with 

MRS usage during shield recovery. It will also discuss new 

developments, including the use of the inherently safer battery 

powered MRS’s, which have been recently certified by the Mine 

Safety and Health Administration. 

INTRODUCTION 

Longwall mining is considered to be the safest extraction 

method employed in underground coal mines. However, based on 

Mine Safety and Health Administration (MSHA) fatality reports 

since 1996, longwall face recovery operations have claimed the 

lives of 5 U.S. miners and have resulted in numerous injuries 

(MSHA, 1996-2006). Three fatalities were attributed to meshing 

installation during recovery room preparation. Another fatality 

occurred during recovery operations while loading a shield on a flat 

car. And, the last fatality happened while trying to free an ironbound shield in a recovery room. The mission of the National 

Institute for Occupational Safety and Health (NIOSH) is to help 

assure safe and healthful working conditions for men and women 

by providing research, information, education, and training in the 

field of occupational safety and health. In keeping with this goal, 

NIOSH Mining Program researchers, in conjunction with industry 

experts, examined a novel approach in removing shields during 

longwall face recovery operations. During this investigation, 

several State and Federal Roof Control Specialists were questioned 

about shield recovery operations and they all indicated that shield 

removal is the most hazardous operation conducted during longwall 

mining. In addition, every longwall operator and miner queried 

concurred. Miners in the teardown or recovery room area are 

exposed to highly stressed ground conditions due to front abutment 

loads generated by panel extraction. Additionally, the miners are in 

close proximity to the unpredictable gob edge, which can cave or 

flush into the working area, while trying to maneuver shields 

weighing over 20 tons in confined spaces. 

Over the past few decades, longwall mining technology has 

evolved significantly. Longwall shield recovery operations are no 

exception. Initially, conventional wood cribs or timber posts were 

set in place for every shield recovered to break off the roof cave 

and prevent gob material from flushing into the working area. 

Later, some operators began employing walking shields in 

conjunction with engineered standing supports. It seems like a 

natural progression that inherently safer MRS’s would replace 

walking shields. MRS’s are shield-like support units mounted on 

crawler tracks. The Harris No. 1 Mine pioneered the successful 

usage of MRS’s during shield recovery operations in the United 

States. MRS utilization at Harris has been responsible for injury 

reductions, both ground control and material handling related, and 

record move times. The purpose of this investigation is to expose 

other longwall mining operators to the advantages of MRS usage 

during shield recovery operations. 

MINE SETTING, GEOLOGY AND HISTORY 

The Harris No. 1 Mine is operated by Eastern Associated Coal 

Corporation which is a subsidiary of Peabody Energy. Harris is 

located in Wharton, WV and began operations in 1966 (figure 1). 
 

 

 

 

 

 

 

No. 2 Gas

Lower No. 2 Gas

Powellton "A

Powellton

Matewan

Upper Eagle

Eagle

Vertical Scale: 1" 40'

Legend

Coal

Shale

Sandstone

No. 2 Gas 

Lower No. 2 Gas 

Powellton "A" 

Powellton 

Matewan 

Upper Eagle 

Eagle 

Vertical Scale: 1" = 40' 

Legend 

Coal 

Shale 

Sandstone 

Figure 1. Harris No. 1 Mine location map. 

The topography at this site is fairly rugged. The valleys are narrow 

and “V” shaped and ridges are steep and prominent. These 

physiographical features can cause rapid changes in cover over 

relatively short horizontal distances. The overburden ranges from 

100 ft at the drift to slightly over 1,400 ft under the highest ridges 

and the mining height ranges from approximately 6 to 7.5 ft. As is 

the case with most Central Appalachian coal mines, the overburden 

is relatively competent. 

Harris is mining in the Eagle Coalbed. Figure 2 is a generalized 

stratigraphic column of the mine roof above the Eagle Coalbed up 

to the No. 2 Gas Coalbed, which has been extensively mined. It 

should also be noted that the major sandstone and shale units 

shown in figure 2 vary in thickness. For example, in a few of the 

core holes the upper two sandstone units merge into a 100-ft-thick 

unit. The same can be said for the lower two sandstone units. 

These rock unit thickness variations indicate ancient stream 

Figure 2. Immediate and main roof stratigraphy at Harris 

No. 1 Mine. 

channel activity. Usually, the interburden contains 6 distinct rock 

units; however, the actual number varies from 4 to 7. In general, 

the interburden is rather competent, with the percentage of 

sandstone, sandy shale, and limestone ranging from 59 to 80 

percent. The shale unit, shown in figure 2, directly above the Eagle 

Coalbed varies in thickness from 0 to 10 ft. In areas of the Harris 

Mine, this shale unit can either be laminated, sandy, or nonexistent 

(replaced by a sandstone scour). These fluctuations explain the 

range in Coal Mine Roof Rating values from 44 to 71 (Molinda and 

Mark, 1994). These values indicate that the immediate roof rock is 

of moderate strength to strong. 

Harris has mined over 60 longwall panels in the Eagle Coalbed. 

Harris began longwall operations with a 300-ft-wide plow face and 

40-ton walking frames in 1966. Since then, numerous 

technological innovations have led to improvements in the longwall 

systems and gateroad supplemental supports employed. Currently, 

Harris is mining 3.2 million clean tons of coal per year. Gateroad 

pillar design and supplemental support selection have also gone 

through an evolutionary process at Harris based on the performance 

of past longwall faces and gateroads. In fact, twelve different 

gateroad designs, which incorporated various elements of a 3-entry, 

4-entry, and yield pillar system have been tried at Harris. The 

gateroad system design was progressively refined and calibrated 

through the back analyses of previous successful and difficult 

mining attempts. 

For the past 9 years, Harris has been using a 3-entry gateroad 

system with entries on 90-ft and crosscuts on 140-ft centers. This 

system has worked well and no gateroad blockages have occurred 

since its usage began. Harris uses 5-ft, full column resin bolts on 4-

ft centers in the headgate entry. In the remaining gates and 

bleeders, 4-ft, full column resin bolts on 4-ft centers are standard. 

The roof control plan also stipulates that a minimum of 2 cribs or 

equivalent supports be installed every 12 ft in the tailgate. Floor 

heave has always been a major concern at Harris. Because 

conventional cribs (both 4-and 9-point) are inclined to roll out 

when subjected to heave, Harris began using 30-in, engineered 

timber supports. These supports have performed well in that the 

floor tends to heave up around the supports without causing 

instability of the support. 

The No. 2 Gas Coalbed is situated approximately 200 ft above 

the Harris workings. Both longwall and room-and-pillar retreat 

mining have been conducted in the No. 2 Gas. In many cases, 

remnant structures such as barrier pillars, isolated gateroads 

(gateroads with gob on both sides), etc. that were left in the 2 Gas 

have caused difficult ground conditions in Harris due to downward 

load transfer (Chase et al., 2005). Difficult mining conditions 

associated with high horizontal stresses have also been a problem at 

Harris. The engineers also use the LaModel program (Heasley, 

1998) to identify high vertical stress areas which are caused by 

deep cover, abutment loads, and/or multiple seam stress transfer. 

In highly stressed areas, either two or four, 12-ft-long cable bolts 

are installed between each row of primary supports. Sometimes, 

additional engineered timber supports are warranted in tailgate 

locations. The spacing of these supports is dependent upon the 

expected level of stress. 

Prior to MRS implementation, it became apparent that the injury 

rates sustained during longwall move operations were higher at 

Harris than during panel extraction. In fact, a statistical study 

conducted by Harris Mine officials indicated that when compared 

to normal face operations, injury rates were 26% higher during 

recovery operations. In an attempt to reduce these injuries, 
 

 

 

 

management turned to the novel approach of using MRS’s during 

shield recovery. 

SHIELD RECOVERY USING WALKING SHIELDS 

After the shearer, pan line, and other longwall face equipment 

are removed from the recovery room area, shield recovery is 

commenced. At this point, most operators have already installed a 

spare set of new or rebuilt face equipment with the exception of 

shields in the setup room for the new panel. Only a few operations 

have an entire set of duplicate shields, so it is of paramount 

importance to safely recover, move, and transport the shields to the 

setup room so that the mining of the next panel can begin. 

For the most part, there are three general methods that operators 

employ in order to prevent gob flushing into the working area. The 

first method relies solely on primary and supplementary intrinsic 

and standing supports. Traditionally, the standing supports were 

two or three 4-point cribs installed for each face shield removed. 

One needs to keep in mind that a shield is being lowered and 

adequate support needs to be installed to maintain the immediate 

roof. Many operators have opted to use hydraulic or engineered 

timber props (figure 3) to reduce the amount of time required to 

install compared to a wood crib. This reduces miner exposure to 

the unpredictable gob edge and shortens the move time. 

Figure 3. Engineered yieldable timber props equipped with active 

presetressing mechanical devices used as breaker line supports. 

Another method which operators utilize to prevent gob flushing 

are walking or trailing shields. The majority of the mining 

community is accustomed to using the terms “walker” or “walking 

shields.” Therefore, this paper will comply and will use this 

terminology. If one shield is used, a chain or 1-in-diameter steel 

wire rope is hooked to the shield’s frame (legs or pontoons). The 

shield is moved out of the face area with a shield retriever. As 

shown in figure 4, some retrievers have a long boom with a hook 

on the end. The hook is manually placed in a large clevis that is 

attached to the chain or wire rope. The boom is raised and the 

shield is dragged out of the face so that the long axis of its canopy 

is situated parallel to the face (unmined block of coal) and 

perpendicular to the other face shields. This shield now functions 

as a walking shield, and is pressurized a few inches slightly in front 

of the shield tip and canopy corner to retrieve the next shield. After 

the next shield is removed, the walking shield is dragged forward 

Figure 4. Shield retriever advancing walking shield. 

and the process continues. Barring adverse ground conditions, less 

supplemental roof support (usually cable bolts and free standing 

support) is required when walking shields are used as compared to 

the first recovery method. Prior to MRS usage, a single walking 

shield was employed during shield recovery at Harris. 

Some operators use two walking shields during recovery 

operations. These shields may be operated independently or in 

tandem. If the shields are not connected to each other, they are 

advanced separately as previously explained. Most operators have 

the shields joined together via a “F” or other type of bar which is 

anchored to the base plates. The bar attachment enables the shields 

to advance on their own. With one canopy lowered, the adjacent 

pressurized shield extends its hydraulic ram which pushes the 

connected bar ahead. The lowered shield then retracts its ram, 

thereby pulling or “walking” the shield forward. Thus the name 

walker or walking shield. There is a considerable amount of 

variability with the bar design. Some are designed in-house while 

others are manufactured at fabrication shops. As was the previous 

case, in general, less standing support is used when two walkers are 

employed as breaker line supports. 

SHIELD RECOVERY USING MRS’S 

The third method to prevent gob over-runs is to use MRS’s as 

breaker line supports. MRS’s were first utilized in the U.S. in 1988 

at the Donaldson Mine, which was a room-and-pillar operation 

(Chase et al., 1996). Since then, their use in room-and-pillar 

operations has become widespread throughout the Appalachian 

Coalfields. MRS’s are almost exclusively used during room-andpillar retreat mining operations. They have proven to be inherently 

safer and more cost efficient than conventional timbering plans. 

MRS’s technology was pioneered by the U.S. Bureau of Mines 

(Thompson and Frederick, 1986). Commercial units, which are 

currently being used underground, include those manufactured by 

J. H. Fletcher and Co. and Voest-Alpine. As the name implies, 

MRS’s are mobile and also highly maneuverable. Based on Harris 

No. 1 Mine’s experiences, MRS’s have proven to be safer, more 

efficient, and also faster than walking shields for longwall 

recovery. 
FACE LINE 40" 20" 40" 20" 40"

5' 4' 6' 7.5' 

14' 

4" X 8" X 12' Wooden Headers

GOB MRS UNIT 1 5' 

SHIELD SHIELD SHIELD SHIELD 

6" X 6" X 30"CRIBS A B C D 

4" X 8" X 12' WOODEN HEADER 

30" X 30" WOODEN CRIB 

ROOF BOLT WITH 8" X 8" PLATE 

HEINTZMANN JACK 

Figure 5. Harris No. 1 Mine shield recovery plan. 

FACE LINE 

TIP OF SHIELD CANOPY 

SHIELD SHIELD SHIELD SHIELD 

 D C B A 

FRONT OF CANOPY 

MRS UNIT 1 

FRONT OF PLOW 

FRONT OF CANOPY 

MRS UNIT 2 

FRONT OF PLOW 

GOB 

Figure 6. Shield recovery plan using two MRS’s. 

 Figure 5 depicts the current support plan and MRS positioning 

for shield recovery operations at Harris. If ground conditions 

permit, Harris pulls shields from mid-face to both the headgate and 

tailgate, or bidirectional. As figure 5 suggests, after shield “A” is 

retrieved and begins being dragged to the tail (or to the right in 

figure 5), a crib is built in its place, in line with the previous ones 

shown. Then the MRS is lowered, trammed forward and reset. As 

the operator trams the MRS forward to recover the next shield, they 

align the canopy edge of the MRS with the leg socket connection to 

the shield’s canopy as shown in figure 5. The process then repeats 

itself. As previously indicated, walkers are pressurized only a few 

inches in front of the shield canopy of the next shield to be 

recovered. Based on the manufacturer, the cable reel and/or plow 

necessitates the MRS’s canopy to be pressurized approximately 3-4 

ft away from the shield toward the gob side as illustrated in figure 

5. This has not constituted a problem at Harris; however, under 

weak immediate roof rock conditions it should be considered. 

MRS’s used on previous models at Harris had 4-ft extensions 

welded on the canopy’s duck bill enabling them be situated a few 

inches from the shield corner, similar to walkers. 

 Harris has determined that MRS’s usage has improved both the 

safety and efficiency of longwall shield recovery operations. Since 

MRS utilization began, only one non lost-time injury has occurred 

at Harris during shield recovery. A review of the accident 

indicated that the injury would have most probably occurred 

regardless of what breaker line support was being used. During the 

last longwall teardown operation in April 2007, a record 189 

shields were recovered in 6.5, 8-hour shifts (15 shields per crew in 

an 8-hour shift). 

 Figure 6 illustrates a MSHA-approved plan employing two 

MRS’s that was submitted by another mining company. As 

compared to figure 5, significantly less support is required when 

using two MRS’s. Harris has opted to use a single MRS due to the 

restricted width of the recovery room. The MRS canopy width for 

the model used at Harris is greater than that of a standard shield. 

This places the side of a second MRS in close proximity to the roof 

caving area, and gob flushing causes frequent machine fouling. 

 Only two mines in the U.S. have MSHA-approved Roof 

Control Plans to use MRS’s for shield recovery operations, and the 

following safety precautions are listed in the plans: 

1. A MRS may be used as roof support while roof bolting 

the longwall face line in lieu of timbers or safety jacks. 
 

 

 

 

 

2.	 The distance between the fronts of the plow of the MRS 

to the shield shall not exceed 7 feet. 

3.	 The MRS and adjacent shield shall be against the mine 

roof before a crib is installed. 

4.	 All personnel shall maintain adequate clearance under 

shields or stay a minimum of ten feet away from the unit 

when the MRS is being raised or lowered. 

5.	 The MRS cable hangers shall be light and disposable to 

eliminate the need of entering the unsupported area to 

retrieve hangers or unhook the cables. 

6.	 Should the MRS become disabled, cribs or timbers will 

be installed before work is attempted. 

7.	 Manual operation of the MRS unit(s) shall be for 

maintenance purposes only. If the unit is set against the 

mine roof, adequate temporary roof support shall be 

installed prior to lowering the unit manually. 

8.	 If the support relief pressure is being reached, the 

operator shall stop and notify the foreman. 

9.	 When using two MRS’s, both units will not be lowered at 

the same time and the units should not be offset more 

than one half unit length from its companion unit. 

MRS SAFETY AND COST SAVINGS ADVANTAGES 

When examining the safety and other advantages associated 

with the three recovery support methods previously discussed, it 

should be noted that all have proven to be safe. In this section, the 

advantages and disadvantages with each of the first two methods 

are compared with those for MRS usage. 

When evaluating supplemental roof and standing support usage 

as longwall recovery support against MRS’s, there are considerable 

differences. In addition to the supplemental roof support, which 

usually consists of some combination of regular bolts, cable bolts 

and/or other specialty bolts, meshing, 1-in-diameter steel or nylon 

rope, steel beams, etc, standing supports are also installed for each 

shield removed. Usually, these standing supports are engineered 

wood cribs or timber props, hydraulic jacks/props, or standard 

cribbing. Only the hydraulic jacks/props and engineered wooden 

props with prestressing bags or bladders have a limited active 

loading capability. Cribs are passive supports and require 2-4 

inches of convergence before they achieve significant (greater than 

40 tons) load bearing capacity. A least two and sometimes three 

cribs or equivalent supports must be installed for each shield 

removed. Therefore, miners are subjected to the face, roof, and gob 

edge for longer periods of time, and material handling issues also 

have to be considered. In contrast, MRS’s are active supports that 

can achieve several hundreds of tons of support immediately and 

provide much greater roof coverage. When using MRS’s, 

exposure to the gob edge and the highly stressed unmined coal face 

is reduced as compared to the other breaker line methods. 

A MRS system is also superior to a single walking shield 

approach based on safety and lost productivity issues. When 

miners hook up the retriever to the walking shield, they are highly 

exposed during the minute or so it takes to find and attach the 

clevis. Under adverse or highly stressed ground conditions, rib 

bolts have occasionally been known to shoot out of the unmined 

coal face. In 1994, a miner sustained a severe head injury by a 

shooting bolt when working under a walking shield near the face. 

Rib rolls and bounces are other possible hazards due to the close 

proximity of the miners to the face. Another problem which has 

occurred while trying to drag shields is that the chain or wire rope 

can break in a “whip-like” manner due to the large amount of strain 

energy stored in the rope. The latest fatality occurred in 2004 and 

involved a chain. Prior to that, a wire rope pulling a walking shield 

snapped and fatally injured a Pennsylvania coal miner. Obviously, 

the time spent hooking and dragging the walking shield is time lost 

recovering face shields. On a recent examination of a longwall 

move in the Pittsburgh Coalbed using a single walking shield, an 

average of 7 to 10 shields were recovered during a normal eighthour shift and ground and roadway conditions were excellent. The 

mine was pulling shields in only one direction and was using 

recovery chutes. 

A pair of connected walking shields has the advantage of being 

able to advance themselves, as compared to a single walking shield. 

There are benefits to using a single or two walking shields over 

MRS’s. For example, they are already owned by the mine, and 

they are at the face where they are readily available for recovery 

operations. Another potential advantage is that the shields have a 

higher support capacity than a standard MRS. However, a 600-ton 

MRS seems to do the job just fine at Harris, and 800-ton units are 

also available. Finally, as previously discussed, shields may be 

able to maneuver closer to the shield being recovered than MRS’s. 

One disadvantage of the walkers, as compared to MRS’s, is that 

they are advanced via a thin electrical umbilical cord that is 

connected to a control box or “packman.” With this packman, the 

walking shield’s electro-hydraulic control system can be activated 

causing the shields to rise, lower, or advance remotely with the 

operator safely under a face shield. Unfortunately, this cord is not 

durable and, depending on conditions, it can be severed by falling 

rock which necessitates repairs. Sometimes miners will enter into 

the area housing the shield’s hydraulic controls to advance the 

walkers manually. In contrast, MRS’s are remotely operated by 

radio control. 

The advantages of MRS’s are most evident in adverse 

conditions. Figure 7 exemplifies some less than desirable 

conditions in which MRS’s have performed well at Harris. This 

recovery room’s roof was highly fractured due to multiple seam 

stress load transfer and horizontal stress damage. The shield 

behind the MRS was abandoned because the conditions were 

extremely difficult at this location and because the shield was 

nearing the end of its useful life. The decision was made not to 

Figure 7. Shield recovery under adverse conditions. 
 

take the risk or spend the time recovering the shield under such 

adverse conditions. MRS’s also have the ability to bulldoze their 

way through excessive floor debris (figure 8). With walking 

shields, it is more likely that some of the debris may have to be 

removed to facilitate their advance. 

Figure 8. MRS’s plowing floor debris. 

Another positive feature of MRS’s is that they have two 

pressure gauges mounted on the front of each support (figure 8). 

These gauges can be visually monitored by operating personnel to 

determine loads and rates of loading on the units. In addition, 

MRS’s are equipped with a lighting array which can also be used to 

examine loading conditions. This array can be seen from farther 

distances compared to the pressure gages. Green, yellow, and red 

pulsating lights indicate different total load levels or incremental 

changes in loading. If a fall seems imminent based on either or 

both of these systems, the mobile can be quickly trammed out of 

harm’s way. Walkers on the other hand have been trapped, gone 

iron-bound, and lost because they leapfrog much more slowly. In 

the event of a high roof cavity or fall, walkers cannot advance if the 

canopy doesn’t pressurize against the roof. If this occurs, the 

walkers must be dragged with the retriever. Sometimes, the miners 

will place cribbing on top of the shield so that when the canopy is 

raised the cribbing will contact the roof allowing the walkers to 

advance. Obviously, this significantly increases miner exposure to 

hazardous conditions. MRS’s are also better designed for use in 

mines with floor abnormalities or excessively muddy roadway 

conditions. 

Gob flushing and face spalling pose another problem for 

walkers. If a sufficient amount of debris enters into the shield’s 

cavity where the hydraulic controls and hoses are located, miners 

must leave their safe location under the face shields and using a 

sledge hammer and slate bar, break and pry out the material. 

MRS’s have a steel chain curtain draped from the canopy and down 

the sides of the units to protect the interior compartment from gob 

flushing (figures 8 and 9). 

Shields are designed to be loaded vertically and also laterally 

along the long axis of the shield from the tip to the back. When 

shields are used as walkers, they are subjected to side loading, a 

type of loading which they were not designed for. Side loading 

occurs because the roof tends to deflect or rotate downwards as it 

cantilevers back towards the gob. The canopy on MRS’s is 

designed to tilt side-to-side in relation to the base structure. This 

better accommodates side loading conditions and allows the canopy 

to conform to most types of roof and floor orientations (Barczak 

and Gearhart, 1997). These concepts are exemplified in figure 9, 

which shows the canopy canted to the right or gob side of the 

photograph. The right side of the MRS is riding up on floor debris 

and the frame is articulated in relation to the canopy. 

Figure 9. Articulated MRS frame and canopy. 

BATTERY POWERED MRS’S 

As previously mentioned, cable handling has been a major 

concern of MSHA and various State Regulatory Agencies since the 

inception of MRS technology into the coalfields. In fact, cable 

handling was cited as a contributing factor is a recent double 

fatality on a pillar line in southern WV by the State of West 

Virginia Office of Miners’ Health, Safety & Training (2007). In 

order to prevent the MRS power cables from being cut by 

equipment, they are hung close to the roof on bolt plates. Initially, 

insulated “J” hooks were used. However, these hooks were so 

strong that the only way to release the cable was to manually 

remove it from the hook. Since the adjacent coal has just been 

pillared or mined out in the lift, this activity places miners in a 

compromising area. Cable removal is even more risky in high coal 

where the miner must climb a step ladder to remove the cable. In 

order to alleviate this situation, MSHA has begun requiring breakaway disposable cable hangers. With these hangers, a miner can 

stand outby and pull down the cable. However, when the cable is 

retracted by the MRS to minimize slack before mining, the first 

hanger will often release and the weight of the cable causes the 

others to do the same. Then, all the cables have to be re-hung, 

which results in downtime. A MRS operator indicated that no 

matter how careful or good you are at “goosing” the cable intake 

control, the hangers often “pop off.” Time studies conducted by 

the third author of this paper at two WV mining operations 

indicated that cable handling required an average of 10 minutes per 

lift, which equates to 25 pct downtime. Cables also cause clearance 

problems and are aggravating during shield recovery operations. In 

general, you want to avoid any cables in the recovery area. 

However, Harris has determined that the advantages of using 

MRS’s far outweigh their disadvantages. 

In light of the above, a West Virginia-based, MRS leasing 

concern designed and fabricated the first battery powered MRS’s 

(figure 10). These units are powered by a single 1,000-amp-hour 

battery housed in a one-inch-thick steel compartment. The total 

weight of the battery and compartment is six tons for a total 

machine weight of 31 tons. The battery compartment is located at 

the front of the unit (figure 10) and is mounted onto the frame with 

a large hinge pin. The compartment can be moved up or down for 
 

 

 

 

clearance or to plow floor debris. A specially-designed, double 

bank charger is normally located at the charging station. A fully 

charged battery will power the unit for 5 to 6, 8-hour shifts. 

Twelve hours prior to being discharged, a battery indicator light 

will come on. This allows the battery to be switched-out at the 

most convenient time, for example, during a shift change. Usually, 

a scoop will bring a fresh battery to the MRS and battery switchout time is approximately 5 minutes. The spent battery is then 

recharged for 8 hours, allowed to cool for 8 hours, and then is ready 

for reuse. 

Figure 10. Battery powered MRS. 

Battery powered MRS’s have been certified by MSHA and 

successfully field tested at two room-and-pillar retreat mining 

operations. By eliminating the problems associated with cable 

handling, the battery powered MRS’s increase safety and minimize 

downtime. In fact, the increased mining time was determined to be 

as much as two additional hours per 8-hour mining shift. Although 

battery powered MRS’s have proven to be field worthy in roomand-pillar mines, they have not been tested in recovery room 

operations. It should be noted that the battery housing extends out 

six more inches than a standard MRS. Therefore, if they are to be 

used for shield recovery, a 4.5-ft extension might be warranted in 

weak roof. To date, Harris has not indicated an interest in trying 

battery units. 

SUMMARY 

The keys to a successful longwall move are to avoid injuries at 

all cost and move the equipment to the next face as quickly as 

possible. The personnel from management on down at Harris No. 1 

are convinced the MRS utilization is safer and faster than other 

recovery methods. After 17 successful moves, including a 

complete move in less than four days, Harris is committed to MRS 

usage. As was previously mentioned, all the methods described in 

the paper are safe. However, MRS’s have demonstrated that they 

are superior in all conditions, with the biggest advantage being 

realized under difficult to adverse conditions. 

Using face shields as walking shields has logistical and financial 

advantages. However, if a company has another longwall or roomand-pillar retreat mining operation in the area, it may make 

economic sense to consider the capital expenditure to purchase 

MRS’s. MRS’s can also be leased from companies that have the 

personnel to train miners on how to use them. As previously 

stated, the purpose of this paper is to make other longwall operators 

aware of the technology and success that Harris has had using 

MRS’s during shield recovery operations. It introduces a new 

approach of recovering longwall face equipment in a safe and more 

efficient way. Due to the importance and risk involved in moving a 

face, mine managers and longwall coordinators rely heavily on 

their past experiences and are reluctant to change. Mining history 

indicates that people become comfortable doing things the same 

way and resist change. This paper was written for their 

consideration, and attempts to provide them with successful 

examples of this emerging technology for longwall recovery. 

ACKNOWLEDGMENTS 

The authors would like to express their gratitude to Dr. Thomas 

Barczak for his technical advice on MRS, shield, and roof behavior 

characteristics. Special thanks go to Eastern Associated Coal Corp. 

and Peabody Energy for providing the information contained in this 

report and also for allowing their valuable experiences to be 

published. 

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