Solutions to prevent materials-handling
 

injuries in underground coal mines
 

B.M. STEWART, J.R. WARNEKE, 

C.C. CLARK, B.P. STAPLETON 

B.M. Stewart, J.R. Warneke, C.C. Clark and B.R Stapleton 

are mining engineer (retired), associate research fellow, mechanical engineer and engineering technician, respectively, with the 

Spokane Research Laboratory, National Institute for Occupational 

Safety and Health (NIOSH), Spokane, Washington. 

Abstract 

Of the 28 accident/injury classifications listed by the 

Mine Safety and Health Administration, handling ma- terials is second only to roof falls in terms of generat- ing the highest number of reportable accidents in ac- tive underground coal mines. Two materials-handling 

activities that cause numerous injuries each year are 

the categories of "handling supplies or material, load 

and unload" and "moving power cables." Mechaniza- tion and mineworker activity training are two meth- ods that can aid in preventing these injuries. This paper describes three mechanical methods — the mobile 

manipulator, the in-mine hoist and a cable-handling 

system — that are being developed and tested at the 

Spokane Research Laboratory of the National Institute 

for Occupational Safety and Health. Two of the devices 

are specifically designed for loading, unloading and 

moving supplies and materials, and the third device is 

designed for handling trailing cables in the confined 

spaces of coal mines. Also described are safety solu- tions developed for underground coal mines geared 

towards showing miners safe and unsafe ways of per- forming various materials-handling tasks.1

1

The findings and conclusions in this report are those of the authors 

and do not necessarily represent the views of the National Institute 

for Occupational Safety and Health. 

Introduction 

Between June 1998 and the end 

of December 2002, 32,433 reportable accidents occurred in active underground coal mines in the United 

States (Fig. 1) (MSHA, 2002). The 

category "handling materials" accounted for 7,388 (22.8 percent) of 

these accidents and 244,365 days 

lost from work. Materials-handling 

tasks involve pulling, hanging,

pushing and lifting objects of different weights, shapes and sizes. Hundreds of these tasks 

are performed in underground coal mines each day. 

Supplies are often handled two or three times before 

end use. Often, these tasks require supplies to be lifted 

above the shoulders and/or the body to be twisted during a lift, resulting in overexertion of back and other 

muscles. In addition, these tasks are often performed 

without assistance and by a person who may be fatigued. The materials-handling tasks that cause the most 

injuries involve loading and unloading supplies and materials, machine 

maintenance and repair and moving 

power cables (Fig. 2). For example, 

roof bolt operators may handle over 

500 roof support items (bolts, resin, 

plates, mesh, etc.) in a single shift. 

Cable handling is another high-injury task; between 1997 and 2002, 

1,138 reportable injuries and more 

than 43,000 lost work days involved 

the task "moving power cables."

Since December 1988, 23 fatalities were associated 

with remote-control continuous miners; at least nine of 

these fatalities were related to moving the trailing cable. 

Two fatalities (one in 2003 and one in 2004) occurred 

when the victim was manually moving power cable and 

a roof fall occurred. 

Given the nature of underground coal mining environment (poor lighting, poor footing, confined spaces, 

etc.), the amount of supplies and equipment needed

daily, the use of electrically powered equipment and the 

wide range of tasks, it is to be expected that materials handling will continue to be a major cause of injury. The purpose of this paper is to make underground 

miners aware of the risk of injury when handling materials and to offer solutions to avoid injury through innovative training and mechanical aids. Behavior modifications include the development of a series of articles 

on safety solutions and training materials that address 

common lifting tasks. Mechanical solutions include the 

mobile manipulator system and the in-mine hoist system, both of which can aid in lifting and moving heavy 

objects. A proposal for future research addressing the 

prevention of injuries associated with lifting and moving heavy power cables is presented. 

Preventing materials-handling injuries

Behavior modification. Some miners do not think 

of handling materials as being a risky job, especially 

if the material is light and he or she has done the same 

task thousands of times without injury. However, while 

each person is equipped with excellent lifting parts 

(fingers, hands and arms) that are available on demand, 

the human body has limits, and over time injuries or fatal 

situations may occur. As Dr. John Snow once noted: "An 

occasional risk never stands in the way of ready availability." It is not until after an injury that a miner asks 
 

"Why did this happen? Why didn't I get help? Why didn't I 

think of a safer way?"

To prevent materials-handling accidents and reduce injuries, behavior and attitude must be changed. First, a miner 

must be aware that lifting, pulling, pushing or shoveling — 

even the lightest load — can result in unnecessary injury. 

Second, the "think-before-you-lift" mindset needs to be in 

place before every materials-handling activity. Third, the 

materials handler must always ask: "Is there a safer way to 

move this object?" What this means is that prior to every 

materials-handling task, no matter how small, a person must 

ask essential questions such as: "How heavy is this object? 

Where is the object moving to? How far? Is the path clear? 

What are the safe lifting methods? Is there help (mechanical or personnel) available?" There is always a safe way 

to move an object. Knowing and using the safest way will 

prevent injuries. 

FIGURE 1 

Reportable accidents in active underground coal mines: 1998-2002. 

FIGURE 2 

The five activities most responsible for materials-handling accidents in underground coal mines: 1998-2002. 

Safety solutions. The concept of safety solutions 

developed at the Spokane Research Laboratory (SRL) 

of the National Institute for Occupational Safety and 

Health (NIOSH) can aid miners in preventing materialshandling injuries. A safety solution is a two- or threepage article that describes an innovative method, procedure and/or equipment that was developed to reduce 

injuries and proven to be effective. The safety solution article includes a description of the problem, impact of the 

problem, solution to the problem and 

impact of the solution. Whenever 

possible, photographs and drawings 

are included. Once the safety solution is developed, it is placed on the 

NIOSH mining Website. In this case, 

the goal is to prevent injuries by sharing and making mine operators aware 

of innovative solutions to common 

materials-handling problems. 

Training. On-site training is an 

effective tool for the prevention of 

job-related injuries or deaths. SRL 

recently tested a concept to provide 

"expert knowledge" through the use 

of real miners working at an active 

mine to demonstrate right and wrong 

ways to perform a task or tasks. For 

the materials-handling task, two days 

were spent at an underground coal 

mine shooting video clips of miners 

performing various tasks that have 

had a high injury rate. These tasks 

included loading and unloading supply trailers and scoops (surface and 

underground), hanging power cables and ventilation tubing, cleaning 

around and shoveling materials onto 

moving conveyor belts, and moving 

conveyor belts. Figure 3 shows workers off-loading roof bolt supplies from 

a trailer to a scoop. 

Mechanical solutions. A host of 

mining activities are performed in 

which materials or equipment must 

be lifted, positioned, held and or moved. Often, supply 

movement and distribution is not well planned, resulting in 

handling the same supplies two or three times before end 

use. Off-loading barriers are also created when the supplies needed first are at the bottom of the load. These bar- riers increase material handling risk factors. Assisted-lift 

devices are currently used in many industrial sectors to 

reduce injuries associated with manual equipment and 

materials handling. In most underground coal mines, getting needed materials from the surface to underground 

drop-off areas is done with trailers or supply cars that 

are loaded on the surface with forklifts or other mechanized devices. The materials are generally palletized and 

banded for this process. Once in a drop-off area, however, the materials are separated and must be moved manually by workers. For example, roof bolt supplies are often 

manually loaded from the trailer into a scoop and then 

unloaded a second time from the scoop to the roof bolter.

Mobile manipulator system: Loading and unloading supplies and materials cause the most injuries in the 

“handling materials” category. An industrial manipulator was obtained, and a series of typical lifting tasks were 

performed to determine the baseline performance of the 

device. Although it operated as intended with regard to 

lifting, several shortcomings were found regarding inmine use. These included lack of mobility, instability, no 

self-leveling capability and excessive height and length. 
 

The manipulator was designed for use in medium to high

coal areas and in areas where clearance is not a problem 

(e.g., shops, lay-down areas and station landings), but not 

in low coal areas. 

Engineering solutions were pursued to address the functional limitations identified. An integrated design incorpo- rating a manipulator, a self-propelled platform, independently controlled leveling stabilizers and an integral power 

supply was conceived and named the mobile manipulator 

system. This device was designed to reduce manual lifting 

tasks such as moving supplies from lay down areas, lifting supplies off trailers, loading roof-bolt pods and lifting 

construction materials. The mobile manipulator system is a 

highly mobile, compact, self-propelled lifting arm mounted 

on a turret. It has real-time leveling and stabilizing outriggers and a self-contained power and control system (Fig. 

4). 

This device provides a load-handling solution for those 

situations where a single worker may need to do a job quickly and might attempt to handle materials or equipment that 

are too heavy. Development of the system required extensive redesign of the original manipulator, as well as initial 

design of a self-propelled mobile platform. A device 810 

mm (32 in.) wide, 1,620 mm (64 in.) long and 1,980 mm 

(78 in.) tall was determined to offer the widest range of applications. The specifications are provided in Fig. 5 and are 

discussed as follows: 

FIGURE 3 

Off-loading roof bolt supplies from a trailer to a scoop 

underground. 

• Manipulator: The manipulator configuration was 

extensively modified to fit the target dimensions of 810 by 

1,620 by 1,980 mm (32 by 65 by 78 in.). The final manipulator configuration has a horizontal reach of 1,270 mm (50 

in.) and a vertical reach of 1,040 mm (41 in.) and a lift capacity of 136 kg (300 lb). The device features a four-bar 

linkage system that allows mailbox-type insertion of materials and equipment not accessible from above.

• Self-propelled platform: The self-propelled platform is 1,610 mm (63.5 in.) long by 810 mm (32 in.) wide, 

with a wheelbase of 1,206 mm (47.5 in.) and a ground clearance of 76 mm (3 in.). Tram speed is either 0.8 or 3.2 km/h 

(0.5 or 2 mph). The unit consists of a 25-mm- (1-in.-) thick 

steel base plate to which four 406-mm- (16-in.-) diameter, 

foam-filled, hard-rubber-tired wheels are mounted. The 

front wheels are steered to the left or right via a hydraulic 

cylinder to a spindle tie rod-to-spindle arrangement. The 

left rear wheel is driven forward or reverse by a positivedisplacement hydraulic drive motor.

FIGURE 4 

Design drawing of the mobile manipulator system. 

FIGURE 5
 

Specifications of the mobile manipulator system. 

• Leveling stabilizers: The leveling stabilizers consist 

of four independently controlled legs mounted on the mobile platform. The legs extend hydraulically in a scissoring 

motion when actuated to form a 1,118-mm- (44-in.-) wide 

by 965-mm- (38-in.-) long base and provide leveling for up 

to ±76 mm (±3 in.) of floor inclination. When retracted, the 

legs can be stowed within the 810-mm (32-in.) tram width 

of the manipulator. Extension of the legs and leveling control takes 15 sec. 

• Hydraulic power: Hydraulic power is provided by 

a 24-V dc motor connected to a single, axially mounted, 

15-L/min (4-gpm) pump. The pump drives the slow and fast 

tram speeds, steering and leveling stabilizers.

• Pneumatic power: Pneumatic power is provided by either shop air or a 120-V ac, 12.5-amp compressor unit with twin 7.6-L (2-gal) tanks that provides air at 

0.136 m3

/min (4.8-cu ft per min) at 690 kPa (100 psi). 
 

The compressor system, in conjunction with the power supply, is capable of providing air for approximately 60 cycles 

(0.028 m3

/min [1 cu ft per min] per cycle) of the manipulator arm between charges. It is used for "tram-to-site" intermittent lifting. For fixed-location, high-repetition lifting, 

the manipulator is powered by shop air after it is put into 

position.

• Electric power: Electrical power is generated by 

two 12-V, deep-cycle, dc batteries connected in series. An 

interlock switch routes the 24-V dc power to the hydraulic 

system's 24-V dc motor and to a 24-V dc to 120-V ac inverter. Charging is via a 120-V ac charger integral to the 

inverter. 

• Controls: The current control system consists of 

a tethered box that uses rubber-booted toggle switches to 

control all machine movements. Fabrication of the mobile 

manipulator system was recently completed (Fig. 6). 

FIGURE 6 

Mobile manipulator system in final stages of fabrication. 

Project personnel will conduct tests at SRL by operating the system in a manner consistent with what would be expected 

during mine-specific materials-handling and maintenance 

tasks. Detailed data sheets will be prepared for each activity 

as the basis of a series of trials. This information will also 

indicate the mobile manipulator's suitability for a mine environment. 

In-mine hoist system. At defined material-handling 

locations or when the mechanized movement of supplies 

and materials down to a work area becomes impractical 

because of space limitations, power requirements or the 

unavailability of equipment, other means of moving materials is needed. A portable in-mine hoisting device was 

designed to be lightweight, easy to assemble, capable 

of carrying a payload up to 136 kg (300 lb) over a span 

of 12 m (40 ft) and not require any power source. The 

in-mine hoisting device can be readily set up to bridge 

the gap between the limits of where a mechanized lifting device can go and where the work needs to be done.

The design incorporated the use of 3-m (10-ft) sections of 100-mm (4-in.) aluminum I-beams that functioned as a track for a 454-kg- (1,000-lb-) capacity hoist 

attached to a small trolley (Fig. 7). 

FIGURE 7
 

In-mine hoist system attached to wire mesh. 

The I-beams were 

connected with a locking system in which a steel pin on

one end of the beam fits into a groove connector on the adjacent beam. A heavy-duty latch was used to secure the bottom portion of the two beams together. An additional steel 

plate was bolted on the web of the I-beams to provide additional stability and support (Fig. 8). The entire system was 

hung from wire mesh by a chain-and-roller system. Four 

3-m (10-ft) sections of the in-mine hoisting device can be 

put together and hung from the ceiling of a mine by two 

workers in less than 20 min without any special tools.

After many trials and modifications, a 136-kg (300-lb) 

weight was lifted successfully and moved a distance of 12 

m (40 ft). However, there are some limits as to how the inmine hoisting device can be employed. These limits are as 

follows: 

• When the 136-kg (300-lb) weight is moved from 

one end of the I-beam to the other, a significant amount of 

axial force is generated at the joints between each beam. 

The wire mesh holding the system then flexes under the 

payload as I-beam sections act as levers, which creates an 

axial force in excess of 6,230 N (1,400 lb/f). To overcome 

this axial force requires the use of heavy-duty steel connectors and latches to secure the beams together.

• The system also generates tremendous strain on 

the joint connectors whenever the device moves through a 

curved section, so that straight line movement is the only 

option.

• The chains supporting the system to the mine roof 

should be secure enough to offer less than 13 mm (0.5 in.) 

of flex to the overall system to ensure that the axial force 

remains under a more manageable 2,250 N (500 lb/f) while 

hauling the 136-kg (300-lb) payload. 

Because of the limitations and flexing problems encountered when moving the load across I-beams hanging from wire mesh and because of safety concerns 

about placing additional loads on the primary roof support, tests are currently underway to test the feasibility 

of hanging the I-beams from roof bolts rather than wire 

mesh. Supplemental bolts outside the roof support plan 
 

would be used and the I-beams hung from scissor type

hangers connected to the bolt heads. Although this approach 

will result in longer set-up times (supplemental bolt installation), it will be more stable and safe.

Some specific applications of the in-mine hoist system 

include off-loading supplies into scoops in crosscuts where 

supply trailers/cars are dropped off; moving supplies from 

the front of the lay down to the back (for storage) and vice 

versa (for use); moving/lifting blocks and timbers in construction areas; lifting pumps for repair or removal; and lifting and moving parts in underground machine shops. 

FIGURE 8 

Locking system for aluminum joint sections on in-mine 

hoist. 

Directions for future materials-handling research 

On April 29, 2004, the Mine Safety and Health Administration (MSHA) held a workshop to address problems in 

handling the trailing cables on continuous miners. From 

that workshop, three ideas came to the forefront: wireless 

communication for workers at the face, remote-control shut 

down (multiple e-stops) for miners working around the machine and cable reels. 

The Materials Handling Group at SRL did additional 

research on cable handling injuries and generated the following statistics: 

• Currently, there are about 620 continuous-mining 

machines operated by remote control in underground coal 

mines in the United States (MSHA, 2004a).

• From December 1988 to December 2003,21 fatalities have been associated with the operation, assistance 

and maintenance of remote-controlled continuous miners 

(MSHA, 2003). Between March 1995 and March 2004, 

nine fatal accidents occurred among people either handling 

or watching the cable on a remote-controlled continuous 

miner (Gandy, 2004). Five fatalities occurred when the operator or assistant was crushed while manually moving or 

positioning the cable.

• During the five-year period between 1998 and 

2002, moving power cables in active underground coal 

mines was the cause of 921 injuries. The words “miner 

cable” (short for continuous miner cable) appeared in the 

descriptions of 497 (54 percent) of these injuries. In looking at the most recent statistics (for 2002), 149 entries 

were moving power cable injuries with 8,114 days lost from 

work. 

Based on 2004 MSHA data (MSHA, 2004b) and on the 

workshop, the Materials Handling Group decided to take an 

in-depth look at a concept of cable reels as an aid to automating the cable-handling task. This project will look at a 

total cable management system consisting of the following 

two parts: 

• Part 1: The problem of manually moving that portion of trailing cable lying on the ground between the continuous miner and the point where the cable is hung from 

the roof or rib will be addressed. The goal is to devise an 

automated handling system that will keep the operator (or 

operator assistant) and the cable clear of the continuous 

miner as it moves forward and backward. Figure 9 is an 

artist’s concept of a cable reel drawn in the 1970s for the 

U.S. Bureau of Mines on contract with FMC Corp. 

FIGURE 9 

Artist’s concept of off-machine cable reel system. 

This reel 

system was never fabricated. The configuration of a continuous miner prevents a cable reel from being mounted on 

the miner itself, as is available on other mining machines. 

The system will have to be capable of advancing as the continuous miner advances. If successful, this system will remove miners from a dangerous location and the cable can 

be moved remotely. 

• Part 2: The second part of the project will addressmechanical methods to hang and remove cable from the 

roof. This is currently done manually. Figure 10 shows a 

miner in an underground coal mine hanging a cable from 

the roof (a cause of many of the reported injuries). 

Most of the technical aspects of the cable management 

problem have been solved, including heating of the cable, 

cable bending radius and cable hangers. The development 

of a system that will take miners out of harm’s way should 

become a critical goal. It is now time that stakeholders, who 

include organized labor, mining companies and government, make solving cable-handling problems a key concern. 

Once these problems of cable handling have been solved, a 

major safety issue will have been resolved in underground 

coal mining. 
 

FIGURE 10 

Miner manually hanging cable from mine roof. 

Conclusions 

Hundreds of materials-handling tasks are performed in 

underground mines each day. It would be hard to find one 

of these tasks that has not resulted in an injury at least once. 

Materials-handling innovations and research efforts have 

paid off, considering that the number of materials-handling 

injuries has been reduced by over 60 percent in the last 10 

years. However, materials handling continues to be one of 

the MSHA category with the highest percentages of accidents and injuries in underground mines. Additional research 

efforts are warranted and must continue. Some solutions are 

simple, such as reducing “package” weight. Other solutions 

are not so simple, such as hanging objects overhead and 

moving trailing cables. Whether simple or complex, the solutions must be practical to be accepted and used. Because 

of the diversity of materials-handling tasks, no single solution exists to eliminate materials-handling injuries.

Research and development of mechanized materialshandling tools and equipment need to continue with an 

emphasis on those tasks that result in numerous injuries, 

such as loading and unloading supplies, machine repair, 

moving power cables, moving roof bolt supplies, handling and shoveling coal and waste rock, and moving conveyor belt parts. One of the best sources for identifying 

materials-handling mechanization needs is the miners who 

daily handle the supplies and materials. Managers need 

to listen to their needs and then supply the resources to make 

their jobs safer.

It is neither technically or economically feasible to 

mechanize all underground materials-handling tasks. Some 

tasks need to be done manually. However, injuries can be 

minimized if mandatory site materials-handling safety criteria are established. The criteria would be designed by the 

safety manager as per injury records, task location, type 

of task and other factors. However, mandatory materialshandling criteria are useless unless the individual performing the task follows them. It is up to the individual to think 

about every lifting action prior to doing it. Unfortunately, 

many people have to experience the pain of a serious injury 

before they learn this. There is always a better, easier, less 

injurious way to handle materials. Even if the lifting job 

is delayed while waiting for proper help or equipment, it 

is better for the individual and the company than a longterm back injury. Management at all levels should mandate 

smart, risk-free materials handling with a “take time to do 

it right” attitude.

Materials handling should be an integral part of every 

safety and training meeting. Any materials-handling task 

that increases risk factors should be a warning sign for injury. Mine safety officers should identify those tasks that 

cause frequent injuries at their mine and conduct specialized 

materials handling safety training with individuals performing these tasks. Such training would be valuable for new 

miners because they frequently get jobs involving supplies 

and materials handling. Constant (daily) safe materialshandling reminders from safety managers and shift foremen 

will aid in getting miners into the habit of not only “thinking 

before they lift,” but also thinking before they carry, pull, 

hang, or push supplies and materials. 

References 

Gandy, B.. 2004, Engineer, MSHA, personal communication. 

Mine Safety and Health Administration (MSHA), 2002. “Accident, 

Illness, and Injury and Employment Self-Extracting Files,” available at 

www. MSHA.gov. 

Mine Safety and Health Administration (MSHA). 2003, “Remote 

Control Fatal Accident Analysis Report of Victim’s Physical Location 

with Respect to the Mining Machine,” prepared by J. Dransite and C. 

Huntley. 

Mine Safety and Health Administration (MSHA), 2004a, Author 

notes from Webcast on remote-controlled continuous miner fatalities, 

January 28. 

Mine Safety and Health Administration (MSHA), 2004b, “Summary 

Report of the Cable-Handling Workshop,” Staff, Applied Engineering 

Division, MSHA.