National Institute for
INI Occupational Safety and Health

Technolo
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Milestones in Mining Safety and Health

chnology June 2000

UPDATE: Roof Monitoring Safety System
for Underground Stone Mines

Objective

The Roof Monitoring Safety System (RMSS) introduced in late
1997 has been modified to improve durability and simplify the
measurement of roof or rib movement. Greater knowledge about
the stability of roof and rib rock is expected to result in safer
conditions for the mine worker. Developing safety tools and
methods is part of NIOSH's mission to prevent work-related
injuries and deaths. A mining operation with a proactive approach
to control ground conditions is in a better position to make
essential decisions related to mine development and take remedial
actions in the event of roof or rib falls.

Background

Falls of roof and rib rock are responsible for a high number of
mining injuries and fatalities. Visual inspections and the sound of
breaking or cracking rock are often relied upon to indicate unstable
roof conditions. In some mines, roof bolt holes are checked for
separations or gaps with a scratch tool; this provides further
information about the stability of the roof. Monitors such as the
RMSS can confirm roof movement that was surmised only by eye
or-ear, or potentially detect movement that was missed by these
means. An added safety feature of the RMSS is the capability of
locating the measurement station at a distance from where the
monitor is placed in the roof.

Stone and other industrial minerals are the basic raw materials
used in construction. Continuing economic growth and highway
building in particular have resulted in record demand for stone.
This high demand, coupled with increasing constraints on surface
mining, have caused many new stone mines to be developed
underground. These new mines in many cases will be employing
new and inexperienced miners who may not have the ability to
recognize unstable ground conditions using just sight and sound.

From the initial introduction of the RMSS, it was anticipated
that improvements and modifications would-occur. We correctly
assumed that, once miners and operators were exposed to the
monitor, suggestions would evolve. In one case, the RMSS was
used to determine ifan impact hammer used on a mechanical scaler
was causing or increasing instability of roof rock. The test showed
little or no movement resulted from this method of scaling under
the particular conditions at this mine. In another instance, an
operator needed to monitor the stability of a haulageway in a
benched area that had very high ceilings. The RMSS requires a
2-in-diam hole for installation; however, only roof bolt holes of a
smaller diameter were available, and it was impossible to drill new
holes at that height. The operator attached a 2-in collar at the roof
line and was able to install the RMSS.

These examples illustrate the potential for further enhancements
of this tool. NIOSH continues to seek additional candidate sites
for use of the RMSS. As usage increases, we anticipate further
refinements and additional applications.

How It Works

The new RMSS, cable, and read-out box are shown in figure 1.
The read-out box has a green light that stays lit until battery
replacement is needed. The red light is set to come on to indicate
movement. The red light can be adjusted for increments of
movement as low as .010 inches. The RMSS red light should not
be considered as a primary or only means of determining the
stability of roof or rib. It is intended to serve as a supplement to
existing methods or procedures for determining stability.

An overview of the RMSS components is shown in figure 2.
Movement of rock layers within the mine roof is measured relative
to a fixed-point calibration at the monitor housing. The housing
contains a potentiometer, roller switch, plastic rack, and spur gear.
Movements are detected by the transfer of electromotive forces

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through the rack of the spur gear, which is attached to a 5,000-ohm
potentiometer. Movement is precisely measured by comparing the
output of the potentiometer to an initial reading. The indicator
light is controlled by an adjustable set screw. Cable is attached to
stereo plugs and extended from the roof to ground level. If the
RMSS is located at an active face, the cable can be unplugged

Figure 1.—RMSS cable and read-out box.

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B Steel nut, 0.25-in by 20

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Stee! nut, 0.25-in by 20,

during blasting and reconnected afterward to take readings with an
ohmmeter. The monitor requires a 2-in-diam hole extending 12 to
18 ft into the roof.

For More Information

For more information on the RMSS, contact Thomas E.
Marshall, phone: (412) 386-5077; Lou Prosser, phone: (412) 386-
4423; or Anthony T. Iannacchione, phone: (412) 386-6851. They
can also be contacted at the following address: NIOSH, Pittsburgh
Research Laboratory, Cochrans Mill Road, P.O. Box 18070,
Pittsburgh, PA 15236-0070. Inquiries may be sent by fax to (412)
386-6891.

To receive additional information about occupational safety
and health problems, call 1-800-35-NIOSH (1-800-356-
4674), or visit the NIOSH Web site at www.cdc.gov/niosh

Mention of any company name or product does not constitute
endorsement by the National Institute for Occupational Safety
and Health.

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Foller switch, SPST

Brass wosher, 2-56

Brass screw, 2-56 by 0.75-in

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Figure 2.—Overview of RMSS components.