No. 475 August 1998

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Roof Monitoring Safety System for Underground

Stone Mines

Objective

The Roof Monitoring Safety System (RMSS) provides a first

step in roof behavior awareness. By understanding and measuring

roof movement in an underground mine, the potential for injuries

or fatalities to mine workers from fall of ground can be lessened.

Also, officials at an underground mine with a history of data on

roof movement are better prepared to make a decision on remedial

actions if falls of ground become a problem. The RMSS provides

a safer, simple, and inexpensive means for measuring roof

movement.

Background

Statistics show that falls of ground (i.e., roof or rib rock) are

responsible for a high number of mining injuries and fatalities. In

all of mining, workers in the underground stone sector face the

most serious risk from fall of ground, according to Mine Safety

and Health Administration injury statistics from 1992 to 1996.

In addition to the present dangers associated with underground

stone mining, national trends indicate that this sector will expand

in future years. A proactive approach toward understanding roof

behavior allows for mine planning and development that affords

the safest conditions for the mine worker. In the United States,

there are currently approximately 95 underground stone mines

(predominantly limestone). The stone produced is used primarily

for construction and secondarily for lime in chemical applications.

Approach

During the past few years, the Pittsburgh Research Laboratory

of the National Institute for Occupational Safety and Health

(NIOSH) examined and characterized conditions at

43 underground stone mines. Observations during these visits

revealed a limited degree of roof monitoring beyond visual

inspection. Existin g

monitors typically require the miner to measure movement at the

roof. If conditions are unstable, the miner may be in harm's way

while recording data.

Based on these circumstances, researchers concluded that a

simple, inexpensive monitoring instrument with the capability for

remote readings could lead to a safer way of recording data, as

well as more widespread monitoring and understanding of roof

movements. A monitor to meet this need was subsequently

designed and tested. The key features of this monitor are

(1) remote capability, i.e., it allows a miner to determine if roof

movement occurred while at a location away from where

dangerous conditions may exist, and (2) inexpensive and simple

design, i.e., it allows for fabrication of the monitor at the mine

site, as most of the monitor parts are readily available at local

hardware or supply stores.

How It Works

An overview of the RMSS components is shown in figure 1.

Movement of rock layers within the mine roof is measured relative

to a fixed-point calibration at the monitor housing. The housing

contains a spring-loaded cable attached to a plastic rack and spur

gear. Movements are detected by the transfer of electromotive

forces through the rack to the spur gear, which is attached to a

500-ohm potentiometer. Movements are measured through the

tension spring that is attached to one end of the monitor. When

movement occurs, the cable is pulled and the resultant

electromotive force is recorded by the potentiometer. Movement

is precisely measured by comparing the output of the

potentiometer to a control-level calibration and can be read from

cable extended from the roof to a ground-level location. A reading

can be made with a voltmeter at appropriate time intervals or

hooked to a data acquisition system for more thorough data

collection. The monitor requires a 2-in-diam hole extending

approximately 12 to 20 ft into the roof.
Figure 1.COverview of RMSS components.

Accomplishments

The RMSS was introduced at a NIOSH "Safety Seminar for

Underground Stone Mines" in Evansville, IN, on December 10,

1997. During the first half of 1998, monitors were installed at

five mines—one in Illinois, three in Kentucky, and one in

Pennsylvania, with plans for installations in another mine in

Pennsylvania and two mines in Indiana. A summary report

detailing use of the monitors and evaluation by mine workers and

operators is planned for January 1999. 

Patent Status

An application for a patent on the RMSS has been filed.

For More Information

An instruction booklet is available giving complete details on

parts, assembly, and installation of the RMSS. To receive a free

copy, contact L. J. Prosser, Jr., or Anthony T. Iannacchione,

Ph.D., NIOSH Pittsburgh Research Laboratory, Cochrans Mill

Rd., P.O. Box 18070, Pittsburgh, PA 15236-0070, phone: (412)

892-4423 or (412) 892-6581, fax: (412) 892-6891, e-mail:

lfp2@cdc.gov or aai3@cdc.gov

To receive additional information about mining issues or

other occupational safety and health problems, call 1-800-

35-NIOSH (1-800-356-4674), or visit the NIOSH

Home Page on the World Wide Web at http://www.cdc.

gov/niosh 

Mention of any company name or product does not

constitute endorsement by the National Institute for

Occupational Safety and Health.