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Summary
Workers in underground stone mines have a high fatality rate caused by
falls of ground from the mine roof or rib. NIOSH recommendations to reduce
ground fall injuries and deaths address baskets, mechanical scalers, mechanical
bolters, drill steel changing, personal protective equipment, and training.
Description of Exposure
An informal National Institute for Occupational Safety and Health (NIOSH)
review in 1998 identified approximately 17 new underground limestone operations
in various stages of planning; as many as 35 new underground stone mines
are expected by 2005. Many of these new underground stone mines will employ
new or inexperienced workers with minimal knowledge of the hazardous conditions
that exist underground.
Workers in underground stone mines have a fatality rate nearly 20 times
that of workers in the manufacturing sector. Three quarters of the fatalities
in underground stone mines are caused by falls of ground from the mine
roof or rib (Figure 1) [Statistical Abstract of the United States 1985–1999;
MSHA 1983–1999]. During 1983–1999, nonfatal ground falls resulted
in 140 injuries, or 15% of all underground, lost-time stone mine injuries.
These nonfatal ground fall injuries resulted in more than 13,800 lost
workdays (one third of all lost workdays). Ground falls generate more
disabling injuries and time away from work than any other type of incident.
Because of the high ground fall fatality rate and high number of lost
workdays from injuries, NIOSH examined the Mine Safety and Health Administration
(MSHA) accident and employment databases for worker activity at the time
of injury for the period 1983–1999 (mine worker activity codes and
accident narratives) [MSHA 1983–1999]. During this period, 156 injuries
(both fatal and lost-time) related to ground falls were reported. These
incidents included all roof and rib falls listed in the database as well
as incidents classified as machinery, for which the source of injury was
caving rock. The frequency of ground fall injuries was associated with
worker activities as follows: scaling activities, 47%; handling explosives,
24%; other activities, 10%; roof bolting, 8%; drilling face, 6%; and handling
supplies, 5%.
Figure 1. Large roof fall at underground limestone
mine. |
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Injury and Fatality Review
To identify work practices for improving the safety of miners, the MSHA
injury narratives and fatal accident reports noted above were reviewed
for each lost-time and fatal ground fall injury (includes mines with bolted
and unbolted roofs). The results are summarized by the type of work activity
at the time of the ground fall.
- Scaling was the most common worker activity at the time of a ground
fall; almost one half of all ground falls were related to scaling. Nearly
a third of the scaling incidents were associated with roof or rib rock
falling onto the basket, scaling machine, or outrigger equipment used
to reach the remote areas of the mine. The jarring of the basket or
scaling machine caused by the falling rock often caused workers to fall
from the basket or against the basket rail.
- According to one incident narrative, two miners were hand scaling
the roof from a bucket when a large rock dislodged and struck the corner
of the bucket. The weight of the rock on the bucket caused the boom
of the scaling rig to bend toward the mine floor until the rock fell
to the floor. The boom then catapulted upward, throwing the two scalers
from the bucket. A second narrative described a worker who was hand
scaling while leaning out of a basket. When a massive slab of rock fell
and struck the outrigger of the scaling machine, it caused the machine
to fall on its side. The worker was thrown from the basket, but a harness
apparently prevented the worker from being thrown to the floor or crushed
by the machine. The worker suffered a fractured skull.
- Handling explosives accounted for a high number of lost-work-time
injuries from ground falls. Most of these incidents occurred while the
worker was loading explosives into the hole. These incidents resulted
in injury to the victim’s neck, back, or shoulder from small rock
pieces that fell from the mine face and roof. Two fatalities from ground
falls occurred while a miner was cleaning out bottom holes. According
to the MSHA [1983–1999] fatality report, the workers routinely
cleaned the bottom holes before entering the basket and going up to
check the roof. They relied entirely on visual inspection of roof conditions.
- Roof bolting activities involving ground fall injuries accounted
for more than twice the typical number of days lost per incident for
all underground stone mine incidents. Miners working from a basket to
install the bolts have more injuries than miners using an automated
bolter.
- Drilling the face accounted for the highest number of days lost per
incident of all worker activities. MSHA face drilling operation narratives
indicated that in at least 75% of the drilling incidents, the victim
was outside the cab. In most instances, the victims were changing drill
steel or checking the drill alignment.
- Miscellaneous activities account for more than 40% of fatal ground
fall injuries. The MSHA fatality reports were reviewed to find other
causes [MSHA 1986–1996]. Four of the seven recorded fatalities
occurred while the victims were entering a recently blasted face area.
These fatalities resulted from the fall of roof or face loosened by
the recent blast. In two of the cases, MSHA was unable to determine
why the victims had entered the blast area.
Controls
The following measures are recommended to reduce ground fall injuries
in underground stone mines:
- Minimize scaling injuries that occur from the impact of rock
falling onto the basket or lift:
— Make sure that safety harnesses and hard hats with chin
straps are used correctly during scaling operations.
— Fasten harnesses to structurally secure locations on the
basket with proper rope length to minimize the momentum of the
fall.
— Provide proper training in putting on a harness and operating
the basket manually in case the hydraulic system is damaged because
of a ground fall or malfunction.
- Equip baskets that are used for scaling and roof bolting with
padded railings and a canopy or caging to absorb and deflect ground
falls. Ensure that canopies are convenient to workers and that
they allow easy access to the roof. If possible, use a retractable
canopy with a partially removable roof section.
- Use mechanical scalers with protective cabs instead of hand
scaling if possible.
- Use personal protective equipment such as a hard hat with a
back rim (similar to a fire fighters helmet) to help deflect small
rock pieces from hitting the neck and back while loading explosives.
In severe conditions, use flack jackets or padding devices worn
by athletes for additional protection for the back [Grau and Prosser
1997].
- When roof bolting, use mechanical bolters with a protective
cab if possible.
- Move the location for changing the drill steel away from the
drilled face to an area where the rib and roof are stable.
- Use hazard training to emphasize the severe ground fall risk
associated with a freshly blasted mine face and the proper procedures
for entering the area.
- Develop a complete checklist of all critical safety procedures
related to ground falls that can be used as a training tool.
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Acknowledgments
The principal contributors to this publication were Deno Pappas and
Leonard Prosser, Pittsburgh Research Laboratory, National Institute for
Occupational Safety and Health.
References
Grau III RH, Prosser LJ [1997]. Scaling accidents in underground stone mines.
Rock Products, January, pp. 39–41.
MSHA [1983–1999]. Quarterly employment and coal production: accidents/injuries/illnesses
reported to MSHA under 30 CFR Part 50. Denver, CO: U.S. Department of
Labor, Mine Safety and Health Administration, Office of Injury and Employment
Information.
MSHA [1986–1996]. Accident investigation reports: fatal fall of
face; fatal fall of roof. November 24, 1986; November 25, 1991; August
4, 1992; March 3, 1993; November 4, 1993; May 10, 1996. Washington, DC:
U.S. Department of Labor, Mine Safety and Health Administration.
Statistical Abstract of the United States [1985–1999]. Washington,
DC: U.S. Census Bureau.
For More Information
NIOSH research on ground fall injuries in underground stone mines has
been published in a journal:
Pappas DM, Prosser LJ [2001]. An overview of groundfall injuries and worker
activity in underground stone mines. Falls Church, VA: Joseph A. Holmes
Safety Association Bulletin, August, pp. 8–14.
To receive more information about occupational safety and health topics,
contact NIOSH at
NIOSH
Publications Dissemination4676 Columbia Parkway
Cincinnati, OH 45226–1998
Telephone: 1–800–35–NIOSH (1–800–356–4674
Fax: 513–533–8573
E-mail: pubstaft@cdc.gov
or visit the NIOSH Web site at www.cdc.gov/niosh
For a monthly update on news at NIOSH, subscribe to NIOSH eNews by visiting
www.cdc.gov/niosh/eNews
This document is in the public domain and may be freely copied or reprinted.
NIOSH encourages all readers of the Workplace Solutions to make them available
to all interested employers and workers.
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