June 1, 2008
Routine highwall safety instruction and best
practices protect workers from ground control concerns at the quarry
Highwalls jut across the landscape. The soaring
height of rock is breathtaking. The tall quarry walls are beautiful,
showing off faults and folds of shale and rock bands. The series of
layers, benches cut in the rock, resemble tiers on a cake, towering many
stories, sometimes more than 100 feet in height. They are especially
beautiful to those who make their living from mining operations, but
they are also potentially treacherous, particularly to those who work
close to them every day.
Very serious and sometimes fatal injuries occur
when heavy material — rock — falls, rolls, or slides from highwalls.
Workers at the crest — or the top — of a highwall may fall as the top of
the face drops, while workers down the wall and in the pit may be hit
and crushed. The rate of accidents and fatalities demonstrates the
necessity for ongoing safety training.
The Department of Labor and the Mine Safety and
Health Administration (MSHA) define a highwall “as the unexcavated face
of exposed overburden and material on an open face or bank” and are
conscientious about educating mining operators and workers about the
potential dangers of working close to it.
The term the government uses for managing the
physical aspects of surface mining is “ground control.” Ground control
encompasses the management of highwalls and other potential danger areas
that result from sand and gravel and crushed stone operations. The
government outlines basic job steps, describes potential hazards and
accidents, and recommends safe job procedures in Ground Control, module
11 of its Sand, Gravel, and Crushed Stone On-the-Job Training Modules.
MSHA also produced a short video called Highwall
Hazard Recognition, which is available on the Internet’s You Tube Web
site (www.youtube.com/watch?v=HFZZF7Khksc). A scene plays out between a
seasoned miner and a new miner traveling by haul truck to work in a
quarry after a heavy rain. When they encounter a boulder in the middle
of the road, they wonder where it came from. They call their boss who
comes to the spot and sees that the rock fell from the face of the highwall and the area will need to be scaled to make it safer. The rain
may have exacerbated a plane of weakness — a joint, fault, fracture,
bedding plate, mud sink, or blasting damage — loosening the large rock
and enabling it to fall. Other rocks may have been loosened, too. The
workers were praised for noticing the rock and making a call.
In an open pit with highwalls, the first step
toward achieving safety goals is to begin with a sound engineering
design that helps ensure the stability of the highwall. To maintain safe
control of the face as mining proceeds, the overall slope must be
established and followed by operators. The engineering design, whether
simply a gradual slope or a series of benches of particular widths and
angles, should consider carefully the nature of the ground and the type
of material mined. However, unknown structural weaknesses — the planes
of weakness mentioned above — are hidden in rock, and miners should use
continuous care when mining along the wall and scaling (cleaning the
face of loose rock).
Once a safe plan for mining and controlling the
wall has been developed and communicated, the supervisor should follow
basic safety guidelines for any mining site and specific guidelines
related to safe work on a highwall. For example, good housekeeping is
essential at all mine sites; clutter at a highwall site exacerbates
problems if rocks begin to slide.
Everyone at a site should participate in routine
highwall safety instruction, including sharing tips for working at the
top as well as on the bottom of a highwall. Safety belts and lines
should be worn by workers who are working within 6 feet of a crest or
unstable ground; hard hats should be worn by all workers.
A supervisor or other competent person must examine
the working area and the working faces for unsafe conditions at the
beginning of each shift and after blasting. Highwall banks, benches, and
terrain sloping into the work areas should be examined after each rain,
freeze, or thaw before work begins in the area. Overhanging highwalls
should be taken down and other unsafe ground conditions corrected or
warning signs posted.
Miners must inspect their working place before
starting work and be aware of any changes in conditions. Any unsafe
condition must be reported and corrected. Cracks, cavities, and other
unstable areas should be identified, marked, and avoided.
Heavy equipment can cause rock falls if driven on
unstable ground at the crest of a highwall or along a bench.
Miners should avoid working between mobile
equipment and the highwall, where escape routes may be blocked if a
To avoid accidents, MSHA recommends the following
Examine and monitor highwall often.
Follow ground control plan.
Train miners to recognize hazardous highwall conditions.
Scale down or support the hazardous highwall areas.
Keep drill and other mobile equipment
operators away from highwall face or highwall hazards by positioning
them in safe locations.
Employ mining methods that will maintain wall,
bank, and slope stability in places where persons work or travel.
Information contained in this
article was provided through the Safety & Health Committee of the
National Stone, Sand & Gravel Association.