If a machine-specific evaluation or other inspection
reveals areas of the machine whose moving parts pose a potential hazard
to operators or others nearby, guarding can be accomplished by one or
a combination of the methods below.
Whichever safeguard or comibation of safeguards is chosen, it must:
1. Prevent the worker’s body or clothing from contacting hazardous
moving parts
2. Be firmly secured to machine and not easily removed
3. Not allow falling objects to enter moving parts
4. Create no new hazards (must not have shear points, jagged edges or
unfinished surfaces)
5. Create no interference (must not prevent worker from performing the
job quickly and comfortably)
6. Allow safe lubrication (the person should be able to lubricate the
machine without removing the safeguard)
Guards
Fixed
A fixed guard provides a barrier, a permanent part of the machine, preferable
to all other types of guards.
Interlocked
When an interlocked guard is opened or removed, the tripping mechanism
or power automatically shuts off or disengages, and the machine cannot
cycle or be started until the guard is back in place.
An adjustable guard provides a barrier that may be adjusted to facilitate
a variety of production operations. Adjustable guards are useful because
they allow flexibility in accommodating various sizes of stock, but,
because they require adjusting, they are subject to human error.
Self-adjusting
A self-adjusting guard provides a barrier that moves according to the
size of the stock entering the danger area. Self-adjusting guards avoid
the potential for human error associated with adjustable guards.
Safety Devices
A safety device may perform one of several functions:
• It may stop the machine if a hand or any part of the body is
inadvertently placed in the danger area.
• It may restrain or withdraw the operator's hands from the danger
area during operation.
• It may require the operator to use both hands on machine controls,
thus keeping both hands and body out of danger.
• It may provide a barrier that is synchronized with the operating
cycle of the machine in order to prevent entry to the danger area during
the hazardous part of the cycle.
Presence Sensing
A presence-sensing device uses a system of light or radio beam (capacitance)
sources and controls that can interrupt the machine's operating cycle.
If the sensing field is broken, the machine stops and will not cycle.
This device must be used only on machines that can be stopped before
the worker can reach the danger area. The design and placement of the
guard depends upon the time it takes to stop the mechanism and the speed
at which the person’s hand can reach across the distance from
the guard to the danger zone.
Electromechanical Sensing Device
An electromechanical presence-sensing device has a probe or contact
bar that descends to a predetermined distance when the operator initiates
the machine cycle. If there is an obstruction preventing it from descending
its full pre-determined distance, the control unit does not actuate
the machine cycle.
Pullback
A pullback utilizes a series of cables attached to the operator’s
hands, wrists, or armswhich withdraws hands when the slide/ram begins
to descend. It is primarily used on machines with full-revolution stroking
action and allows access to the point of operation when the slide/ram
is up.
Restraint
A restraint uses cables or straps attached to the operator’s hands
and a fixed point. It must be adjusted to let the operator’s hands
travel within a predetermined safe area.
Safety Controls
Pressure-sensitive Body Bar
When depressed, a pressure-sensitive body bar will deactivate the machine.
If the operator or anyone trips, loses balance, or is drawn into the
machine, applying pressure to the bar will stop the operation.
Safety Triprod
When pressed by the operator's hand, a safety tripod deactivates the
machine. Because it has to be actuated by the operator during emergency
situations, proper position is critical.
Safety Tripwire Cable
A safety tripwire cable is a device located around the perimeter of
or near the danger area. Operator must be able to reach the cable to
stop the machine. Tripwire cables must be manually reset to restart
the machine.
Two-hand Control
A two-hand control requires constant, concurrent pressure to activate
the machine. This kind of control requires a part-revolution clutch,
brake, and a brake monitor if used on a power press. The operator’s
hands are required to be at a safe location (on control buttons) and
at a safe distance from the danger area while the machine completes
its closing cycle.
Two-hand Trip
A two-hand trip requires concurrent application of both of the operator’s
control buttons to activate the machine cycle, after which the hands
are free. This device is used with machines equipped with full-revolution
clutches. The trips must be placed far enough from the point of operation
to make it impossible for the operators to move their hands from the
trip buttons or handles into the point of operation before the first
half of the cycle is completed to prevent them from being accidentally
placed in the danger area prior to the slide/ram or blade reaching the
full “down” position.
Gate
Gates are movable barriers that protect the operator at the point of
operation before the machine cycle text can be started. Gates are, in
many instances, designed to be operated with each machine cycle. If
the gate does not fully close, machine will not function.
Guarding by Location/Distance
Locate the machine and its dangerous moving parts so that they are not
accessible or do not present a hazard to a worker during normal operation.
Maintain a safe distance fromthe danger area. To consider a part of
a machine to be safeguarded by location, the dangerous moving part of
a machine must be so positioned that those areas are not accessible
or do not present a hazard to a worker during the normal operation of
the machine. This may be accomplished by locating a machine so that
the hazardous parts of the machine are located away from operator work
stations or other areas where employees walk or work. Additionally,
enclosure walls or fences can restrict access to machines. Another possible
solution is to have dangerous parts located high enough to be out of
the normal reach of any worker.
Feeding and Ejection Methods
Many feeding and ejection methods do not require operators to place
their hands in the danger area. In some cases, no operator involvement
is necessary after the machine is set up. In other situations, operators
can manually feed the stock with the assistance of a feeding mechanism.
Properly designed ejection methods do not require operator involvement
after the machine starts to function. Using feeding and ejection methods
does not eliminate the need for safeguarding. Guards and other devices
must be used wherever they are necessary to provide protection from
hazards. Automatic feeds reduce the operator exposure during the work
process, and sometimes do not require any effort by the operator after
the machine is set up and running.
Miscellaneous Aids
Although these aids do not give complete protection from machine hazards,
they may provide the operator with an extra margin of safety. Sound
judgment is needed in their use.
Awareness Barriers
Awareness barriers do not provide physical protection but serve only
as reminders to a person that he or she is approaching the danger area.
Generally, awareness barriers are not considered adequate where continual
exposure to the hazard exists.
Protective Shields
Aids such as clear protective shields do not give complete protection
from machine hazards, but do provide some protection from flying particles,
splashing cutting oils, and coolants. They provide the operator with
an extra margin of safety.
Hand-feeding or retrieving Tools
Hand-feeding or retrieving tools can place or remove stock. Hand-feeding
tools are intended for placing and removing materials into the in the
danger area of a machine. Hand-feeding tools are not a point-of-operation
guard or protection device and shall not be used in lieu of appropriate
safeguards, but as a supplement. A typical use would be for reaching
in the danger area of a press or press brake. Another example would
be a push stick or block used when feeding stock into a saw blade. When
it becomes necessary for hands to be in close proximity to the blade,
the push stick or block may provide a fewinches of safety and prevent
a severe injury.
Guard Construction
Builders of many single-purpose machines provide point-of-operation
and power-transmission safeguards as standard equipment. Unfortunately,
not all machines in use have built-in safeguards provided by the manufacturer.
Guards designed and built by the manufacturer offer two main advantages:
1. They usually conform to the design and function of the machine.
2. They can be designed to strengthen the machine in some way or to
serve someadditional functional purposes.
Guards fabricated by the machine tool user are sometimes necessary for
a variety of reasons, and offer these advantages:
• Often, with older machinery, they are the only practical solution.
• In older plants, they may be the only choice for mechanical
power transmission apparatus, where machinery is not powered by individual
motor drives.
• They permit options for point-of-operation safeguards when skilled
personnel and machinery are available to make them.
• They can be designed and built to fit unique and even changing
situations.
• They can be installed on individual dies and feeding mechanisms.
User-fabricated guards also have disadvantages. They may
• Not conform well to the configuration and function of the machine
• Be poorly designed or built
• Not comply with regulatory requirements
