Figure 1. Roof screen effectively controlling weak roof skin.

ROOF SCREENING: BEST PRACTICES AND ROOF BOLTING MACHINES

Susan B. Robertson, Mining Engineer

National Institute for Occupational Safety and Health

Pittsburgh Research Laboratory

Pittsburgh, Pennsylvania USA

Gregory E. Hinshaw, Vice President of Engineering

J.H. Fletcher and Company

Huntington, West Virginia USA

ABSTRACT

Many injuries are caused each year by rock falls in coal mines.

Most of these injuries are not caused by major roof collapses, but

from falls of smaller rocks from the immediate top or roof skin.

Various surface controls are used in mines to control this surface

rock. One that has been found to be very effective is roof screening.

Depending on the size of the screen, roof coverage approaching 100%

can be achieved. Many mines are reluctant to use screen for primary

skin control because of additional costs of time and materials, but

others are having great success at both controlling costs and surface

rock. Data is presented from two mines that show a dramatic

reduction in roof skin injuries when screening is used. Much of this

success is due to innovations in roof bolting machines. Four case

studies of roof screen experience are presented along with associated

costs of materials, impact on bolting advance rates, and potential

ergonomic risks. The effects of roof screening on skin control and

safety are also included. Finally, this paper will provide information

about features of different roof bolting machines that affect

production and safety.

INTRODUCTION

The chances are high that anyone who has worked at a coal mine

face area has been struck by or injured from falling rock. These

chances are even greater if the miner was a roof bolter operator. From

1995-1999, an average of 700 reported injuries per year, including 1

or 2 fatalities per year, resulted from rock falls of coal mine roof. All

of these injuries occurred under supported roof. The majority of these

injuries, about 99%, are not caused by a major roof collapse, but from

falls of smaller rocks from the immediate roof (1).

This type of roof failure has also been termed skin or surface fall.

These are falls that do not extend more than a few ft into the roof.

The supports used to prevent these falls are called surface controls.

Greater use of surface controls has been found to decrease roof skin

falls, decrease the likeliness of an injury, and possibly reduce clean up

time.

Coal mines make use of various surface controls such as large

roof bolt plates, steel straps, header boards, large bearing plates, and

steel screen or mesh. Each control has its own application and

effectiveness depending on the geology of the roof and the life of the

entry in which it was installed. Some roof is of such poor quality that

nothing short of full coverage will provide the best protection. In

such adverse conditions, roof screen can provide the necessary

protection for miners. Figure 1 shows roof screen effectively

controlling weak roof skin.

Unfortunately, many operators, especially in the eastern United

States, do not yet think of screening as an appropriate support,

especially in cycle. There are a number of barriers, which prevent its

full acceptance, including material costs, time for installation, and

possible ergonomic risks to the operators. Handling of screen can be

difficult, especially with an aging workforce. The concern is that the

use of roof screen may increase the likelihood of musculoskeletal

injuries such as strains and sprains. One factor affecting these injuries

is the design of the roof bolting machine utilized. 

The purpose of this investigation is to provide information about

roof screening and the current practices used today, and to address

barriers preventing acceptance of this support. Analyses of injury

data pertaining to roof screening, along with a review of four case

studies of roof screening are included in this report. In addition, a

state-of-the-art roof bolting machine with a new material handling

system (MHS) is discussed. This system focuses on eliminating

difficulties with loading and handling screen and as well as other roof

bolting supplies. 
Figure 2. Roof screen achieving up to 94% roof coverage.

8100

7400

5600

4200

3.1

2.9

2.1

1.6

3000

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3 4 5 6 7 8 9 10

Gauge of Steel 

Steel Screen Strength 

(pounds)

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Rock Load Height (feet)

Steel Screen Strength

Rock Load Height

Figure 3. Different strengths and rock load heights for

4 gauges of steel screen.

5

1

00000

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1991

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Number of Injuries

Began installing 

screen in 1994

Figure 5. Number of skin fall injuries per year at a central U.S.

coal mine before and after the implementation of screening.

4

3 3

1

14 14

0

2

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16

1995 1996 1997 1998 1999 2000

Number of Injuries

Began installing 

screen in Sept. 

1996

Figure 4. Number of skin fall injuries per year at a northeastern

U.S. mine before and after the implementation of screening.

EFFECTS OF ROOF SCREENING ON SKIN CONTROL

The mines visited for this study had a variety of roof skin

conditions that were difficult to control. The roof skin commonly

consisted of clayshale, soapstone, or highly laminated shale. The

rock was of poor quality. Clay veins, slickensides, and/or potting

were problematic. Roof skin fell immediately during mining or soon

after between bolts because of three primary factors: weak rock,

horizontal stress, or weathering. 

An advantage of using roof screen is the large amount of coverage

achievable compared to other surface controls. Close to 100% roof

coverage can be achieved. Taken from a recent study conducted by

the National Institute for Occupational Safety and Health (NIOSH),

a mine with 18-ft entries using a 16 ft x 6 in steel strap every 4-ft of

advance achieves an 11% roof coverage. If the mine used 13 x 5 ft

sheets of screen (4-in grid), it can achieve 72% coverage (1). 

While some mines use plastic geogrid screen for surface control,

most that are currently roof screening make use of steel wire sheets

with a 4-in grid pattern. Screen can be ordered in many sizes

depending on the coverage desired or attainable. One problem is that

the reach of some bolting units limits how far screen can be bolted

toward the rib. A gap may exist between the end of the last bolt and

the rib, allowing guttering to occur. To combat this problem, brow

tenders (also known as short straps or extended straps) can be used to

extend the coverage of roof screen. Bolting machines capable of

installing angle bolts also make it possible for the roof screen to be

extended further to the rib. Figure 2 shows how roof screen can be

supported to within in from the rib. In this figure, 94% roof coverage

was achieved by roof screening.

Besides screen size, sheets can also be ordered in different steel

gauge strengths. These strengths (2) along with the rock load height

they support are shown in figure 3. The rock density used to calculate

rock load height was 162 psf. All the mines visited during this

investigation used 8-gauge steel wire sheets with a 4-in grid pattern

capable of supporting 2.1 ft of roof skin. This is quite sufficient to

contain most skin falls, especially after weathering effects.

THE EFFECTS OF ROOF SCREENING ON SAFETY AND

ERGONOMICS

The Mine Safety and Health Administration (MSHA) injury data

from two mines was analyzed to determine the effect of screening on

safety. One, located in the northeastern U.S., had roof conditions that

deteriorated to a point where roof screening was necessary

everywhere. After screening was implemented, injuries dropped from

an average of 14 to 3 per year (figure 4). At the other, in the central

U.S, similar circumstances were encountered that required roof

screening. Injuries there subsequently dropped from an average of 7.0

to 0.25 per year (figure 5). Clearly, screening can dramatically reduce

rock fall injuries.
This effectiveness of roof screening may be due to its being the

only type of skin control that protects roof bolter operators during the

drilling process. The screen is placed against the roof when the

ATRS is raised. According to a study conducted by the U.S. Bureau

of Mines in 1993, drilling is the most hazardous job task performed

by the bolter operator, producing 31.4% of all roof bolting injuries.

Out of these drilling injuries, almost half (45.9%) were due to falling

rocks or coal from the roof. (3). Therefore, this immediate protection

while drilling is quite significant. These percentages may be slightly

lower now because of the higher use of roof bolter canopies.

There is also a cost savings when injuries are prevented or

decreased. In 2000, NIOSH created a model to estimate “societal”

costs for MSHA lost-time injuries (4). The average cost for this

injury type (injuries from roof due to broken rock or coal) from 1997-

1999 was $9,937 per injury. This cost is specific for underground

coal mines at the face area and does not include outby injuries from

roof skin falls. The cost to the mine may be higher because this model

does not take into account the cost of damaged equipment/materials,

replacement, or retraining. For example, the cost savings from the

reduction of injuries for the mine in figure 4 would be over $100,000

per year. This is achieved by reducing lost-time injuries from an

average of 14 to 3 per year. 

Even though roof screening has been shown to reduce skin fall

injuries, a concern remains that material handling injuries may

increase due to increased materials and supplies. Additional materials

and bolts used in conjunction with roof screen offer a challenge for

the roof bolter operator. Roof bolting machines do not have space to

hold roof screen and associated supplies. In one instance, a mine

needs 4-ft bolts to install the first sheet of screen in a new cut where

the primary support is already in place. Also, 12 x12 in header

boards (figure 2) made of plywood are needed to place between the

screen and the bolt plate to avoid damaging the screen. 

Besides additional materials and not enough storage capacity on

roof bolting machines, screen handling is also a challenge for the

operators. The hand loading of roof screen onto the machine occurs

quite often during uneven and muddy floor conditions. Overhead

lifts and awkward positioning, along with lifting, pulling, and

twisting movements, may have negative ergonomic consequences on

operators. 

In addition, sheets of screen can be cumbersome to handle. A

16 x 5 ft sheet of 8-gauge steel weighs approximately 30 pounds.

Therefore, handling screen may increase the chance of

musculoskeletal injuries such as sprains/strains. This is a significant

issue. As much as 29.7% of all mining industry lost time days

(1997-1999, excluding fatalities) are from strain/sprain injuries of the

back, knee, or shoulder. Also, 27% of all lost time days were from

material handling injuries. Using the NIOSH cost model, the average

cost of material handling injuries from 1997-1999 was $22,284 per

injury (4). Therefore, an increase or difficulty in material handling

should be a major concern for mine operators. Any innovations in

bolting machines, supplies, or processes that could eliminate or

reduce material handling are worthy of consideration for the safety of

the workforce. 

THE EFFECTS OF ROOF SCREENING ON MATERIAL

COSTS AND BOLTING ADVANCE RATES

Two barriers to roof screening are material costs and slower

bolting advance rates due to screen handling. A comparison of

material costs was recently conducted by NIOSH between the use of

steel straps and roof screen. Costs for roof bolts and plates were not

included. The cost of a 16 ft x 6 in steel strap was $8.00. The cost of

a 13 x 5 ft sheet of 8-gauge steel screen was $10.32. Assuming a 4-ft

spacing between straps and a 12-in overlap between sheets of screen,

the material cost per foot of advance for steel straps is $2.00. The

cost per foot of advance for steel screen is $2.58. As previously

mentioned, the roof coverage in an 18-ft wide entry was 11% for steel

straps and 72% for roof screen. The use of roof screen provides a

significant increase in roof coverage (61%) with only a $0.58/ft

increase in costs over the use of steel straps (1).

The other barrier to the widespread use of screen for primary skin

control is the additional time and labor required to handle and install.

Four in-mine studies to document the impact of screening (in cycle)

on bolting advance rates are presented below. For these studies, only

activities that delayed the bolting advance rates were considered as

time to handle the screen. For example, a scoop operator delivering

screen to a cut does not slow down bolting. But, the time taken by the

roof bolt operators to load the screen onto the bolter and then handle

these sheets does slow down bolting. The following factors influence

the bolting advance rate and labor costs as well as safety when

handling and installing screen:

1. Design of the bolting machine – storage and maneuverability to

handle screen, and the positioning of the roof bolt operators.

2. Installation procedure for handling screen and loading it onto the

bolter.

3. Number of persons involved in handling screen.

CASE 1

A mine in central West Virginia recently began roof screening

because of difficulties with a weak claystone, weathering, clay veins,

and potting. In general, the newly exposed roof skin shows little

damage, but can be expected to deteriorate in 3 to 4 months after

mining. The coal mine roof rating (CMRR) is 22, which is in the

weak to very weak range. The CMRR, ranging from 0 to 100, is the

NIOSH system for classifying the integrity of a coal mine roof (5). 

Two roof bolter operators and one bolter helper install roof

screen. They operate a J. H. Fletcher DDR, twin boom bolter with

mast feed that enables angle bolting. The mining height is 65 to 75 in

and entries are 18 ft wide. They install 8-gauge steel screen that is

13 ft long and 5 ft wide. An overlap of 6 to12 in between sheets

makes for a 4- to 4.5-ft of advance per sheet of screen. Because the

sheets are only 13 ft long, the potential of guttering along the ribline

still remains. 

Activities included in installing mesh are the following:

• The scoop pulls up behind the bolting machine loaded with

screen. 

• The roof bolter helper and scoop operator then load

approximately 10 sheets (1 or 2 cuts) onto the rear of the machine

on top of bolting supplies. During this time, primary roof bolting

operations and screen installation are not interrupted.
• After each 4-ft of advance, the ATRS is lowered and an auger is

placed in the chuck to help control movement of the screen on the

ATRS

• Operators then lift and carry the sheets from the rear to the front

of the machine, then onto the lowered ATRS. 

• Operators center the screen across the ATRS, maneuver into

position for a 6-in overlap between sheets, and raise the ATRS.

At this point, the screen handling time is over unless the screen

needs to be adjusted. 

No time can be attributed to the loading of screen because the

roof bolter helper and scoop operator do it. It takes an average of

1.72 minutes to place each sheet of screen onto the ATRS and slide

it into position, per 4-ft of advance. For a bolting advance of 120 ft

per shift, screening time would add an additional 52 minutes per shift.

During this screening process, operators encountered ergonomic

problems and time delays due to material handling. The screen

sometimes snagged on bolting materials or on other pieces of

damaged screen. The damage occurred when the scoop moved the

screen from place to place before loading it onto the bolter. The

screen also got damaged when tramming around corners. Because of

this damage, the operators had to jerk the sheets apart from each

other, therefore subjecting themselves to injury. 

Also, the sheets were cumbersome to handle, and involved lifting,

pulling, reaching, and twisting motions. The bolters had difficulty

keeping the screen from sliding around on the ATRS. Twice during

the study, the screen slid inby the ATRS making the sheets difficult

to recover. This sliding made up a majority of the time spent on

handling screen. 

In summary, the screen effectively controlled the roof. The timely

use of screening minimized skin hazards in high travel entries and

reduced cleanup. However, even with three miners, the crew

struggled with the installation procedures. This may have been

partially owing to the recentness of screen implementation at this

mine. The miners had not yet adjusted to the installation procedures.

Lost time for installation and ergonomic risks were hurdles that this

mine must combat. 

CASE 2

A mine in the northeastern U.S. has been screening because of

difficulties with clay shale roof, which is highly slickensided and

brittle. It appears wet, but is actually glassy due to the extreme

number of slickensides. Loose rock falls immediately upon mining

and also spalls out because of mine humidity. Miner operators

normally must cut down 3 to 30 in of drawrock and try to hold the

rest with screen. The CMRR at this mine is 19-33 and is in the weak

to very weak range. They install screen mine-wide. The mine claims

that without the use of screening, mining would be very tough due to

an increased cleanup time, higher risk of injury, and slower bolting

advance rates.

Two roof bolter operators and one bolter helper, also serving as

a rib bolter, install roof screen. In the mine’s approved roof control

plan, roof screening and rib bolting must occur in cycle. The rib

bolter operator installs two rib bolts and still has time to help the

bolter operators handle roof screen. The bolting machine is a Fletcher

CHDDR walk-thru bolter. A rib bolting machine, retrofitted onto the

bolter, inhibits screen from being loaded onto the rear of the bolter.

Entries are an average of 16.5 ft wide. They install 8-gauge steel

sheets of screen that are 14 ft long and 5 ft wide. The sheets extend to

within 1.25 ft from the rib after screen installation. Screen installation

activities are the following:

• The scoop operator delivers screen for each cut along the rib.

• The rib bolter carries the screen along side of the bolter and then

lifts the screen up to the roof bolt operators.

• The roof bolters grab and pull the screen up and across the

ATRS..

• Operators center the screen across the ATRS, maneuver into

position for a 6-in overlap, and raise the ATRS. At this point, the

screen handling operations are complete unless screen

adjustments are required.

It takes an average of 0.42 minutes to handle each piece of screen

per 4-ft advance. This time includes operators waiting for and taking

the screen from the rib bolter operator, and then placing it across the

ATRS. Any adjustment of screen position was also included. The

total bolting time for a 4-ft advance, including drilling, installing,

maneuvering, setting the ATRS, and screening, was 8.36 minutes.

The screening time comprised only 5% of this total. For a bolting

advance of 120 ft, screening would add an additional 12.6 minutes.

Mine management feels that this is a small price to pay for superior

roof coverage and decreased risk of injury (figure 4).

Some difficulties or concerns are that the screen can get damaged

when moved around by the scoop. The rib bolter must carry the

screen along the side of the bolter, making it difficult to see his/her

footing. The screen must be lifted from the ground to an overhead

position, putting the person at risk of musculoskeletal injury. Adding

to these problems, the walk-thru bolters is about 1.5 ft higher because

of the elevated walkway. 

The bolter operator can load the screen from either the back or

side of the machine. But because it is easier, the bolters choose to

load screen from the side. This positioning between the rib and the

machine can subject operators to potential injury from rib falls and

machinery accidents. This mine did not have difficulty in keeping the

screen from sliding on the ATRS because of operator positioning.

While under support, one operator was able hold the screen in place

from the center while the other raised the ATRS. This in an advantage

of using a walk-thru bolter.

In summary, roof screen effectively controls the roof surface and

has been proven to dramatically decrease roof skin injuries. The mine

has been roof screening for over 5 years and operators have adjusted

quite well to the installation procedures. The mine can install screen

with only a 5% increase in the bolting advance rate utilizing the labor

of 3 miners. The positioning of the operators using the walk-thru

bolter enables them to control movement of the roof screen. However,

an ergonomic risk may be present due to the installation procedure.

CASE 3

This mine, located in Illinois, has a weak, laminated shale top

with a CMRR of 22. The unconfined compressive strength is

2,500 psi. Poor conditions were due to three primary factors: weak

roof, horizontal stress, and weathering. After moving from much

better roof conditions to the weaker roof, the mine’s strategy to

control this top was to begin installing roof screen. It has been found

that not only does the steel screen support the roof, but also injuries
LEFT MATERIAL POD

RIGHT MATERIAL POD SCREEN TRAY

Figure 6. The J.H. Fletcher material handling system: left and right

material pods and roof screen tray.

due to rock falls dramatically decreased at this mine from an average

of 7 to 0.25 per year (figure5).

Two roof bolters load and handle roof screen, and operate a

Fletcher CHDDR walk-thru bolter. There is a storage area at the rear

of this bolter for bolting supplies, with roof screen loaded on top of

these supplies. Mining height ranges from 7.5–9 ft. Entries are 16 ft

wide and dimensions of the screen are 15 x 5 ft. The screen extends

to within 6 in from the rib for an effective roof coverage of 94%. 

Activities included in installing and handling screen during this

study are the following:

• The scoop operator spots screen at an outby entry.

• Bolter operators back up the machine to where the screen is

spotted, then load enough sheets (5-7) to bolt the next cut.

• After each 4-ft advance, the ATRS is lowered and one bolter

operator walks back to where the screen is stored.

• Next, the operator lifts and pulls the screen towards the front of

the bolter, swings the screen towards the other operator, and they

then place it across the ATRS. 

• One operator holds the screen in place from the middle of the

machine, while the other raises the ATRS. At this point, the

handling time is over unless the screen needs adjustment.

It takes an average of 0.73 minutes to load each sheet onto the

rear of the bolter. It then takes 0.72 minutes to place the screen onto

the ATRS, including an adjustment for sliding. The total time

handling screen is 1.45 minutes per 4-ft advance. For a bolting

advance of 120 ft per shift, screening time would add an additional

39 minutes. With the walk-thru bolter, sliding of the screen is

minimal because an operator is able to hold the screen in place.

Because the sheets are quite long, sheets of screen can get

damaged while making a turn. Damaged wires on sheets snag on

other sheets. Sometimes the screen gets caught on the bolting

materials stored underneath. This makes it difficult for operators to

remove the sheets from each other or from the supplies. In addition,

it is strenuous to lift and pull the screen to the front of the bolter. The

operator must lift the screen overhead and then twists before the other

bolter handles the sheet. The screen must be placed over the bolter

canopies and on top of the ATRS. 

Like Case 2, roof screening at this mine effectively controls the

roof surface and has been proven to dramatically decrease roof skin

injuries. The walk-thru bolter allows the operators to better handle

the roof screen. This mine has been screening for over 7 years and

installation procedures have become routine. Installation time was not

as low as Case 2, but only two roof bolter operators installed the

screen instead of three. An ergonomic risk may be present due to the

awkward positioning, pulling, and overhead lifting during screen

installation. 

CASE 4 

Case 4 is from a different section at the same Illinois mine in

Case 3. The section uses a Fletcher CHDDR walk-thru bolter

equipped with a material handling system (MHS) shown in figure 6.

This state-of-the-art system has many features that reduce material

handling and address ergonomic principles. There is a separate

screen tray that minimizes the potential for screen damage and

snagging on other supplies. Bolting supplies are not hand-loaded

onto the bolter while underground, but are loaded outside by vendors

into material pods (figure 6) and then brought into the mine on supply

cars. A larger left pod and smaller right pod contains supplies such

as bolts, plates, headers, and resin boxes. These pods are also pulled

onto the bolting machine by a winch. 

Bolter tram and the movement of the screen tray, material pods,

and winch are all controlled remotely. For roof bolt operators, the

only hands-on activity is to hook up the winch rope to the screen and

pods. Then the machine does the rest of the work with operations

being remotely controlled. 

In this case study, activities for operators installing screen are the

following:

• The scoop operator drops off a bundle of mesh containing

25 sheets behind the bolter.

• Utilizing remote control, the operator extends the screen tray

toward the rear of the machine. The front and rear lift cylinders

decline the tray towards the mine floor. The tray is placed at a

ramped angle making it easier to pull screen onto the tray.

• The winch rope is hooked to the bundle, and then the screen is

pulled onto the tray. The tray can move in 8 directions enabling

it to be positioned so that the screen is pulled on straight.

• The tray is then secured in place with a pin and sleeve assembly

and the winch attachment is then disconnected.

• The tray is then lowered and moved toward the center of the

machine protecting the screen from damage when tramming

around corners.

• At the next cut, the screen tray is raised to an ergonomically

friendly elevation so that each sheet is pulled straight off without

lifting the sheets.

• The screen is then handled and installed the same as in Case

No. 3.

It takes a total of 3.9 minutes to load a bundle of screen onto the

tray, which is an average of 0.16 minutes per sheet. It then takes 0.68

minutes to handle each sheet of screen. The total time for handling

and installing is 0.84 minutes per sheet or 4-foot advance. For a

bolting advance of 120 ft per shift, roof screening adds 25.2 minutes.

Compared to Case 3, the time for placing screen onto the ATRS is

very similar. But because of the MHS, load times were lower by as

much as 0.6 minutes per screen. In addition to the timesaving, the

operators’ exposure to ergonomic injury is decreased significantly.
 e strain/stress is reduced in handling screen because the operator

can pull off the screen at a more comfortable level. The screen has

less chance of becoming damaged because the bundles are handled

less and do not get damaged when turning corners. Roof bolters do

not have to struggle to retrieve bolting materials because the screen

is on a separate tray. Fatigue is reduced because operators do not

hand-load screen and supplies. The large sheets of screen would

obviously cover the walkway when loaded onto the machine. This

would not allow a clear exit from the machine boom in case of

emergency. But by design, the tray has eight directions of movement

and can be moved out of the way. 

In summary, roof screening effectively controls the roof surface

and has been proven to dramatically decrease roof skin injuries. The

screen handling time was lower than Case 3. This is due to the

loading procedure of the screen. Compared to case 2, the handling

time was slightly higher, but only two roof bolter operators are

needed instead of three. The material handling system practically

eliminates the hand loading of screen and provides an easier method

for handling the screen reducing ergonomic risks to the operators. 

ADDITIONAL FEATURES OF THE MATERIAL

HANDLING SYSTEM

Timesavings can be achieved when loading bolting supplies with

the MHS. A comparison was made of operators loading supplies in

Case 3 and Case 4. In Case 3, it takes 3 men approximately

13 minutes to hand-load a shift’s worth of supplies onto the bolter.

In Case 4, it takes 2 men about 6.0 minutes to load the left and right

material pods onto the bolter, including the removal of the empty

pods, based on accounts of bolter operators and mine personnel.

Each pod contains a shift’s worth of materials. Any supplies left on

the empty pods are taken outside, removed by vendors, and credited

to the mine’s account. 

Material pods are easily pulled onto the scoop bucket because the

pod height is low enough to be pulled under the scoop ram. Both the

left and right pods can fit into the scoop bucket. The pods are pulled

onto the bolting machine directly off of the scoop. The machine has

a rear lift system that places the rear bumper on the mine floor. This

creates a ramp that allows the material pod to be pulled onto the

machine. The pod is manufactured with guides on each side that run

its full length and mate with the runners on the machine frame. These

guides also secure one pod atop another for transportation into and

out of the mine. The bottom of the pod is exposed to rollers on the

frame that reduce the force required to pull the pod onto the machine.

Once loaded, pins are placed through the pods and machine frame to

keep the pod in place. 

These pods are loaded by remote control without the necessity of

an operator near the machine. The operator has better visibility from

remote controls because he has freedom to move around the machine.

Comparing Case 3 and 4, there is a significant decrease in exposure

to injury due to the MHS. All trips made to the roof-bolting machine

while hand loading supplies are eliminated. The risk of sprain/strain,

slip/trip, crush, or cut type injury is reduced.

Designed in the MHS are flattop canopies and rounded ATRS edge

pads. These features reduce the physical effort required to move the

screen into place. They reduce the likelihood of material snagging.

There is another safety feature for controlling the movement of

screen. Clamps are built onto the ATRS that hold the screen in place

while being raised. Once the ATRS is against the roof, these clamps

retract. The operators in Case 4 do not have many problems keeping

the screen in place because of the walk-thru bolter unless they are in

bad top. In that case, they find the clamps to be very helpful. The

operators in Case 1 may have benefited from these clamps because

positioning with the bolter makes it difficult movement of the screen.

SUMMARY AND CONCLUSIONS

The use of screen has been found to be very effective in controlling

roof skin. Compared to other skin controls installed in cycle, roof

screening provides the most coverage for the mine roof. Analyses

thus far from mines using roof screen have shown that injuries from

rock falls have been reduced dramatically. This may be due in part to

the protection roof bolter operators receive during the hazardous

drilling process. Increased acceptance of regular, in cycle roof

screening in adverse conditions should help reduce the number of skin

fall injuries annually.

Time studies documenting the handling and installation of screen

have been presented. Results show significant variation in the

additional time necessary for screening. This reflects the experience

and resources of the individual mine. A lower bolting advance rate

is a barrier that can be reduced with time and practice. 

There is a concern, though, that injuries from handling screen may

be increased. The additional materials and awkward positioning can

increase fatigue for roof bolt operators. The design of the roof bolting

machine affects the costs of loading and handling screen times,

manpower requirements, and ergonomic exposure to risks. The new

J.H. Fletcher materials handling system is a state-of-the-art system

that decreases material handling of roof screen and supplies. It

reduces the risk of injury, screening time, and damaged materials.

Examples like the J.H. Fletcher MHS show how equipment

manufacturers are willing to listen to the needs and suggestions of a

safety conscious mine operator to create a safer workplace for miners.

REFERENCES

1. Molinda, G.M., Dolinar, D.R. and Robertson, S.B. Reducing

Injuries from the Fall of Roof in U.S. Coal Mines. In

publication for 2002 SME Annual Meeting, Phoenix, AZ, 2002.

2. Pakalnis, V. and Ames, D. Load Tests on Mine Screening.

Canadian Institute of Mining and Metallurgy’s Symposium on

Underground Support System, Sept. 19-21, 1983, Sudbury,

Ontario.

3. Klishis, M.J. and Althouse, R.C. Coal Mine Analysis: A Model

for Reduction Through Training. Volume VIII – Accident Risks

During the Roof Bolting Cycle: Analysis of Problems and

Potential Solutions. Contract Report with Cooperative

Agreements C0167023 and C0178052, West Virginia University

and USBM, August 1993.

4. Sacks, H.K. and Pana-Cryan, R. A Cost Model for Traumatic

Injuries in Mining. In publication for the NOIRS 2000 Poster

Session, 2000.

5. Molinda, G.M. and Mark, C.M. Coal Mine Roof Rating

(CMRR): A Practical Rock Mass Classification for Coal Mines.

USBM IC 9387, 1994, 83 pp.