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Hazardous Mechanical Motions
Safeguarding Against Machine Risks and Amputation Hazards
Amputations are among
the most
devastating workplace injuries. They are widespread and involve
various activities and equipment.
According to the Bureau of Labor Statistics,
one-half of all workplace amputations occur in the manufacturing
sector, and the rest occur across the construction, agriculture,
wholesale and retail trade, and service industries.
These injuries result from using stationary machines
such as saws, presses, conveyors, and bending, rolling, or shaping
machines, as well as powered and non-powered hand tools, forklifts,
doors, and trash compactors; and during materials handling
activities.
To prevent worker amputations, employees must be
able to recognize contributing factors, such as the mechanical
components of machinery, the mechanical motion that occurs at or
near these components, and the specific worker activities performed
with the mechanical operation.
OSHA says that machine safeguarding is the primary
way to control amputation hazards associated with stationary
machinery. Work practices, employee training, and administrative
controls also play an important role in preventing and controlling
hazards.
The Department of Labor has designated certain jobs
as particularly hazardous for employees younger than 18. Generally,
these workers are prohibited from operating: band saws, circular
saws, guillotine shears, punching and
shearing
machines, meatpacking or meat-processing machines, and certain
power-driven machines.
Recognizing Amputation Hazards
Anyone working around stationary
equipment should be able to identify amputation hazards. Three types
of mechanical components present amputation hazards:
Point of Operation is the area of
the machine where the machine performs work. Mechanical actions that
occur at the point of operation, including cutting, shaping, boring,
and forming.
Power-Transmission Apparatuses
are components of the mechanical system that transmit energy such as
flywheels, pulleys, belts, chains, couplings, connecting rods,
spindles, cams and gears.
Other Moving Parts are the parts
of the machine that move while the machine is operating, such as
reciprocating, rotating, and transverse moving parts as well as lead
mechanisms and auxiliary parts of the machine.
Hazardous Mechanical Motions
All mechanical motion is
potentially hazardous. Here are the basic types of hazardous
mechanical motions:
• Rotating Motion is circular
motion such as action generated by rotating collars, couplings,
cams, clutches, flywheels, shaft ends, and spindles that may grip
clothing or otherwise force a body part into a dangerous location.
Projections such as screws or
burrs on the rotating part increase the hazard potential.
• Reciprocating Motion is
back-and forth or up-and-down motion that may strike or entrap a
worker between a moving part and a fixed object.
• Transversing Motion is motion
in a straight, continuous line that may strike or catch a worker in
a pinch or shear point created by the moving part and a fixed
object.
• Cutting Action occurs by
sawing, boring and drilling, milling, and slicing or slitting
machinery.
• Punching Action begins when
power causes the machine to hit a slide (ram) to stamp or blank
metal or other material.
The hazard occurs at the point of
operation where the worker inserts, holds, or withdraws the stock by
hand.
• Shearing Action is when a
powered slide or knife movement used to trim or shear metal or other
materials generates the motion. The hazard occurs at the point of
operation where the worker inserts, holds or withdraws the stock by
hand.
• Bending Action is when power
applied to a slide to draw or stamp metal or other materials
generates the motion. The hazard occurs at the point of operation
where the worker inserts, holds, or withdraws the stock by hand.
• In-Running Nip Points, also
known as “pinch points,” develop when two parts move together and at
least one moves in rotary or circular motion. In-running nip points
occur whenever machine parts move toward each other or when one part
moves past a stationary object.
Typical nip points include gears,
rollers, belt drives and pulleys. When evaluating activities for
potential amputation hazards, you should consider the entire
operation, individual activities associated with the operation, and
the potential for injury to workers nearby.
Machine safeguarding is the
primary means of controlling amputation hazards associated with
stationary machinery during normal operations. In addition, work
practices, employee training, and administrative controls play an
important role in the prevention and control of workplace
amputations.
OSHA requires adequate safeguards
for all machines and equipment generating hazardous mechanical
movement. OSHA’s general industry and construction industry
requirements for machine guarding are listed at the end of this
chapter.
Basic Safeguarding Methods
Two basic methods are used to
safe-guard machines: guards and devices. Guards provide physical
barriers that prevent access to danger areas. Devices function by
interrupting the machine’s operating cycle to prevent workers from
reaching or entering the danger area while the machine is cycling.
Both types of safeguards should be designed and installed to ensure
worker protection.
Criteria for Machine Safeguarding
• Prevents worker contact with
the hazard area during the operating cycle.
• Avoids creating additional
hazards.
• Is secure, tamper-resistant,
and durable.
• Avoids interfering with normal
operation of the machine.
• Allows for safe lubrication and
maintenance.
Guards are physical barriers that
enclose dangerous machine parts and prevent worker contact with
them. Guards must be secure and strong. Workers should not be able
to bypass, remove, or tamper with guards. To prevent tampering,
guards typically require a tool to unfasten and remove them.
Guards should not create
additional hazards such as pinch points or shear points between
guards and other machine parts. Guards should not obstruct the
operator’s view or prevent workers from doing a job. Metal bars,
Plexiglass™, or similar guards are suitable. Guard openings should
be small enough to prevent workers from accessing danger areas.
Safeguarding devices typically
help prevent operator contact with the point of operation. They may
be used in place of guards or as a supplemental control when
guarding alone does not adequately enclose the hazard. Safeguarding
devices either (1) interrupt the normal cycle of the machine if the
operator’s hands are at the point of operation, (2) prevent the
operator from reaching into the point of operation, or (3) withdraw
the operator’s hands if they are located in or near the point of
operation when the machine cycles.
Employers are responsible for
safeguarding machines and should consider this need when purchasing
machinery.
Most new machinery is available
with safeguards installed by the manufacturer, but used equipment
may not be.
In cases where machinery has no
safeguards, you can purchase safeguards from the original machine
manufacturer or an after-market manufacturer. You can also build and
install the safeguards in-house. Safeguarding equipment should be
designed and installed only by technically qualified professionals.
In addition, the original
equipment manufacturer should review the safeguard design to ensure
that it will protect employees without interfering with the
operation of the machine or creating additional hazards.
Regardless of the source of
safeguards, the guards and devices you use should be compatible with
a machine’s operation and designed to ensure safe operator use. The
type of operation, size, and shape of stock; method of feeding;
physical layout of the work area; and production requirements all
affect the selection of safeguards. Also, safeguards should be
designed with the machine operator in mind. To ensure effective and
safe operator use, guards and devices should suit the operation.
For example, if an operation is
prone to jamming, installing a fixed guard may not work. An
interlocked guard or presence-sensing device may be a more practical
solution.
As an employer, you need to
consider housekeeping practices, employee apparel, and employee
training. Implement good housekeeping practices to promote safe
working conditions around machinery by doing the following:
• Remove slip, trip, and fall
hazards from the areas surrounding machines;
• Use drip pans when oiling
equipment;
• Remove waste stock as it is
generated;
• Make the work area large enough
for machine operation and maintenance; and
• Place machines away from high
traffic areas to reduce worker distraction. Workers should not wear
loose-fitting clothing, jewelry or other items that could become
entangled in machinery, and long hair should be worn under a cap or
otherwise contained to prevent entanglement in moving machinery.
Adequate instruction in the safe
use of machines and supervised on-the-job training are essential in
preventing amputation injuries. Only trained employees should
operate machinery.
Train Employees in the Following:
• All hazards in the work area,
including machine-specific hazards;
• Safe work practices and machine
operating procedures;
• The purpose and proper use of
machine safeguards; and
• All procedures for responding
to safe-guarding problems such as immediately reporting unsafe
conditions such as missing or damaged guards and violations of safe
operating practices to supervisors.
In addition to employee
instruction and training, you should provide adequate supervision to
reinforce safe practices. Take disciplinary action to enforce safe
work practices and working conditions.
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