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Prefabrication:
Assembly Tasks
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Prefabrication
assembly may improve efficiency and allow
companies to have greater control over the workplace.
However, it may also expose employees to a number of ergonomics-related
risk factors
including forceful exertion, highly
repetitive motions, awkward postures and contact stress.
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| Workstations |
Potential
Hazards:
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Figure
1
Work table with sharp, unpadded edges.
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Figure
2
Tool with padded, rounded handle.
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Figure
3
Sit-stand stool.
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Employees may work around a table or other
flat work surface, either in a sitting or
standing position. Improper placement of
materials can require repetitive reaching or torso twisting
and bending.
- Inappropriate height of the work surface may
force employees to bend forward at the waist
or the neck if it is too low, or continually
lift and support the weight of their arms if
it is too high.
- Sharp edges on work tables
(Figure 1) may create contact stress to soft tissues of the forearm, hand
and wrist.
Possible Solutions:
- Pad tools and work surfaces where they come
in contact with body parts.
- Use hand tools and work surfaces with
rounded edges (Figure 2).
- Provide adjustable workstations so that employees
may properly adjust the height and tilt of work surface.
- Provide lighted, adjustable magnifying glasses
to increase visibility while assembling smaller
parts such as screws and wire couplings.
- Provide sit/stand stools (Figure 3) so that employees
may rest while remaining in an upright position.
It provides
periods of change in posture, a chance to rest while working, and increases the
range of movement.
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| Hand Intensive Repetitive Tasks |
Potential
Hazards:
- Tools with short handles can
press into the palm of the hand (Figure 4).
- Tools that require highly repetitive exertion
such as crimpers or side cutters may stress
the muscles and tendons of the hands and forearms.
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Employees who use tools that require significant
repetitive force, such as using side cutters
to cut large-gauge wire, may stretch and fray tendons and fatigue
muscles.
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Figure
4
Handle rubbing the palm. |
- Improper size tools when in use require more force to complete
a task increasing the risk of overexertion injury.
- Tools that require repeated opening such as pliers or
cutters, create contact stress on the fingers increasing the risk of
soft tissue injury.
- The assembly line process forces users to perform the same
motion over and over. Twisting wire with regular
pliers or using a manual screwdriver may be
appropriate for on-site jobs with many differing
tasks. However, in prefabrication jobs this greatly increases the chance of
repetitive-motion injuries such as tendonitis
or epicondylitis.
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Possible Solutions:
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- Use mechanical assists (Figure 5) or self-opening tools (Figure 6) for tools such
as snips and crimpers that require repeated opening and closing.
- Ensure that tool handles extend across the
entire palm of the hand.
- Use pistol-grip and padded handles to protect
the entire palm of the hand.
- Use hand tools and work surfaces with
rounded edges.
- Provide tools that are appropriately sized
for the employee.
- Use a properly designed tool to promote neutral
posture of the wrist and hand (Figure
7).
Generally, an
inline tool is best
on horizontal surfaces at about waist
height, and a
pistol grip is
preferable for vertical surfaces
at about waist height.
Bent-handled tools
can be designed to accommodate differing
work positions and angles.
- Use powered tools for tasks that require exertion of significant force.
- Increase scope of tasks so that employees have
a greater variety of things to do and are not
doing the same thing for an extended period
(or length) of time.
This provides rest for affected muscles.
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Figure
5
Powered tool actuator.
Figure
6
Self-opening pliers.
Figure 7
Bent-handled tools help maintain straight
wrist postures (left panel) as opposed
to bending the wrist to use
straight handed tools (right panel). |
- Take regular breaks to stretch and move around.
- Use broad range of pneumatic tools when working in an assembly
setting for crimping,
stripping, and cutting wires. These
tools can help to reduce the risk of injury and increase productivity.
- Use a balancer for tools weighing 5 pounds or more or when
heavy tools are used for an extended period of
time.
- Sharpen cutting tools frequently.
- Keep tools lubricated and well maintained.
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| Static Postures |
Potential
Hazards:
- Working at an assembly process exposes employees
to static postures maintained for long periods of time. This
may involve prolonged standing to perform tasks which are
difficult to handle from a seated position.
- Standing on hard floor surfaces may cause discomfort, fatigue,
swelling in the lower extremities and increase the risk of low back
pain.
- Standing in one spot may reduce muscle activity,
which is needed to pump blood throughout the
lower extremities. Muscles may become deprived
of nutrients and fatigued leading to stiffness
as well as swelling and varicose veins.
- Employees may need to use one hand to hold
work pieces during assembly. This forces
employees to use their fingers to grasp for extended
periods.
Possible Solutions:
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Figure 8
Adjustable-height table.
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Figure 9
Anti-fatigue mat.
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Provide adjustable-height workstations (Figure
8) so that employees may change their work height
to maintain neutral body postures.
- Use adjustable clamps or fixtures to hold
parts during assembly.
- Provide sit/stand stools (Figure 3) that allow
employees to rest while remaining in an upright
position. It provides
periods of change in posture, increases the
range of movement, and provides a chance to
rest while working.
- Alternate posture between sitting and standing when
performing work tasks, if possible.
- Increase scope of tasks so that employees have a
greater variety of things to do and are not
doing the same thing for extended periods of time.
This provides rest for affected muscles.
- Provide anti-fatigue mats (Figure 9) and shoe inserts to reduce
stress on the lower extremities and lower back caused by prolonged
standing on hard floor surfaces.
- Take regular breaks to stretch and move around.
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