Civil Engineering Reference
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which employees are rotated must also be considered, however. It should be cautioned that this
and the previous approach are most beneficial if the jobs that are rearranged or included in the
rotation allow employees to use different muscle groups to perform the job. Rotating individuals
into jobs that require the same muscles be used likely will have either no benefit or could produce
greater musculoskeletal stress.
3. Add employees. Dividing the job so that added personnel are available to perform the job will dis-
tribute the work across more people and lower the job's required lift rate. Of course, the cost of the
additional employees must be compared with the benefits of reduced low back strains and their
related costs.
4. Automate. It may be possible that some job tasks can be automated through new equipment or the
use of robotics. This method of assisting the material handler will undoubtedly reduce the lifting
frequency of the job and the overall job requirements.
49.11.2.2 Average Twisting Velocity
Rapid twisting of the trunk can result from a number of situations. If a work area is designed such that
material transfer from one location to another is difficult or if these two locations are not convenient to
one another, a high twisting velocity may result. High velocities often result because work areas do not
allow employees to move their feet to handle goods. In such a situation, a turning action normally done
that included movement of the trunk, hips, legs, and ankles would be more concentrated in the trunk,
and higher twisting velocities may occur. It would be difficult to reduce the speed at which individuals
twist simply by instructing them to “slow down.” However, engineering controls that can reduce twisting
velocity include:
1. Place work in front of material handler. Move the locations of the lifting origin and destination, so
that they are more convenient to one another. In other words, create a workplace in which the
material transfer requires moving in as few planes of motion as possible, thus allowing the
employee to remain is a more neutral posture.
2. Spread out congested work areas. Work areas that allow employees to walk or take at least one step
during handling often reduces the twisting velocity of the job. This occurs because the added
movement allows one to get into a position in which the entire body can assist in the transfer,
rather than just the trunk.
3. Raise working heights. Depending on the location of goods to be handled, lower levels of work that
require a great deal of sagittal flexion also may require additional trunk twisting. This is often the
case when the work requires asymmetric lifting. By raising the work heights, not only will forward
flexion be reduced, but twisting velocity can decrease because the handling distances are more
appropriately located.
49.11.2.3 Maximum Moment
Because an external moment is the product of an object's weight and the distance from the body at which
it is handled, reducing either of these two factors will reduce external moment. Various examples are
described next:
1. Reduce weight requirements. Some work situations allow employees to handle as many units or as
much weight as they feel is acceptable. However, to work faster, some employees may handle more
goods at one time than is physically safe. A limit on the numbers
weights of objects that can be
handled at any given time can reduce moment values. In some environments, raw materials
handled are received from a supplier in bulk quantities. The weights of these materials may
produce excessive moment values. By working with these suppliers, an arrangement may be poss-
ible to package materials in smaller, lower-weight containers. The weight changes just described
likely will increase the lifting frequency of the job, however, so this trade-off in the risk model
should be examined.
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