Civil Engineering Reference
In-Depth Information
49.11.2 Probability of High-Risk Group Membership (LBD Risk)
The software will produce information that compares the job tasks of interest with a database of jobs
previously determined to have high or low injury rates to the low back associated with them. The
interpretation of data is best described through use of the food packager example.
In the food packaging job, two tasks were defined. The first task involved placing individual frozen
food packages into a box (12 in all), and the second task involved loading the filled box of packages
onto a pallet. Risk probability charts are shown for each task in Figure 49.9. In Figure 49.9(a), the
package loading task was found to have a risk probability of 42%. (Probability values are calculated
by averaging the
individual
logits
from each of
the five risk factors—in Figure 49.8(a),
(98%
42%). The risk charts for this first task that were produced
using the iLMM software are shown in the appendix. The probability value for the palletizing task
(Figure 49.9b) was calculated to be 62%, clearly the task more similar to those considered “high risk.”
These two probability values are to be used only for comparison purposes. It is the chart in
Figure 49.9(c) that reflects the true risk value for the entire job. This chart summarizes the largest
values for each risk factor across both tasks making up the job. The value shown on this chart, and
thus the risk for this material handling job, is 66%.
A closer examination of the top two charts in Figure 49.9 shows which factors most contributed to the
job summary values in Figure 49.9(c). Each of the five factors is discussed separately.
þ
31%
þ
1%
þ
29%
þ
49%)
5
/
¼
.
Lift rate. The lifting frequency for the entire job was 420 lifts
h. Because this variable is composed
of the total number of lifts from both tasks, this value is shown to be the same on all charts in
Figure 49.9. As indicated by the length of the lift rate bar on the charts, this rate is very rapid
and is comparable to some of the highest frequency material handling jobs found in industry.
.
Average twisting velocity. The amount of twisting velocity required for the package loading task was
fairly low, but it was moderately high for the palletizing task, as indicated by the length of the bars
on these charts in Figure 49.9. The greater value of the two is used in the job summary chart in
Figure 49.9(c), which was taken from the palletizing task.
.
Maximum moment. As shown on the charts in Figure 49.9, the external moment values were low
for both tasks comprising this job. The low weight of the individual packages (each at one pound)
and the fully packed box being palletized (12 lb) generated low maximum external moment values.
The greater moment value from the palletizing task was used in the job summary chart.
.
Maximum sagittal flexion. The package loading task was performed while employees were in rela-
tively upright postures. This is reflected in Figure 49.9(a) by a short sagittal flexion bar on the chart.
However, during box palletizing, those boxes placed on the lower layers of the stack required much
forward trunk flexion. Figure 49.9(b) depicts these higher angles by the long bar for this factor.
Subsequently, this higher value of the two tasks resulted in it being used in the job summary
chart in Figure 49.9(c).
.
Maximum lateral velocity. The iLMM determined that lateral velocities generated during the
package loading task were higher than those found during box palletizing. The values for the pre-
vious four factors all were larger during handing of the full box and, thus, were used in the job
summary chart. However, it is the lateral velocity value from the package loading task that must
be used in the job summary, since it is the greater of the two tasks analyzed.
/
It is the job summary value of 66% (taken from the chart in Figure 49.9c) that represents the prob-
ability of LBD risk for this example food processing job. The value indicates that, on the continuum
of low-risk jobs (0%) to high-risk jobs (100%), this particular job has a 66% likelihood of being con-
sidered “high risk.” As stated earlier in this chapter, a high-risk job was defined as one having 12 or
more (with an average of 26.4) low back strains per 200,000 h (or 100 workers
yr) of employee exposure.
Results here could be interpreted as indicating that this particular job has a relatively high chance of pro-
ducing a large number of low back strain injuries among individuals who do this job.
/
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