Civil Engineering Reference
In-Depth Information
49.8.2 Maximum Moment
Maximummoment is defined as the external horizontal moment generated about the spine. A moment is
composed of two factors, the weight of the object being lifted and the horizontal distance from the spine
at which it is handled.
49.8.2.1 Weight
Each object that is handled on a job must be weighed and recorded in the software or noted manually and
input during data analysis. If objects of varying weights are handled, then each must be weighed individu-
ally and recorded. This often occurs, for example, in mail and freight delivery operations. In the aforemen-
tioned food processing example, the weights are constant for each task. The combined weight of the two
food packages lifted together needs to be recorded, as does the weight of a fully packed box that is palletized.
49.8.2.2 Horizontal Distance
A tape measure is needed to determine how far from the spine objects are being handled for each task.
With the tape measure held horizontally, one must measure the distance from the spine at the lumbosa-
cral joint (near the top of the hips) to the center of the hands when the task is being performed.
Obviously, as an individual handles objects, this distance changes as the object is moved. It is important
to determine at what point during the task the distance is the greatest (i.e., generating the greatest exter-
nal moment about the spine) and to record this length. An ergonomist correctly measuring the horizon-
tal distance is shown in Figure 49.6(a). Here, the tape measure is kept level to determine the length from
the individual's lumbosacral joint to the center of the hands. The incorrect approach is being used in
Figure 49.6(b), since the distance being measured is not horizontal.
For some MMH jobs, such as those on an assembly line, jobs can be very repetitive and the employees'
actions and movements rather consistent. In these cases, the horizontal distances at which items are held
may not vary much as identical objects are handled during each work cycle. For other jobs, such as when
pallets are loaded or unloaded, each cycle can produce very different trunk motions, since objects are
being handled to
from different areas. This will likely change the horizontal distance at which an
employee handles the load. Because the maximum moment value is directly input into the LBD risk
model, it is important that these distances be accurately measured and that changes in the distances
for each task cycle being monitored by the iLMM are recorded.
/
(a)
(b)
Incorrect
Measurement
Correct
Measurement
FIGURE 49.6 Correct (a) and incorrect (b) methods of measuring the distance a load is held from the lumbosacral
joint.
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