ERGONOMICS OF MANUAL MATERIALS HANDLING - Environmentally Conscious Materials Handling - page 41

AL = 14 . 25 kg

MPL = 42 . 75 kg

If the object mass were 10 kg, then the load would be less than the AL and
consequently no further consideration is required — the task represents minimal
risk to the workers.
If the object mass were 20 kg, then the task would represent more than minimal
risk and require attention. In this case, administrative or engineering controls
would be suggested to increase the AL to a value greater than 20 kg. In modifying
the task, the factors in the AL calculation can provide valuable insights as to
which modifications will provide the greatest benefit. In this case, increasing the
height of the feed conveyor to 75 cm would yield only a 2 percent gain in AL,
which is insufficient. The strategy should be to examine the lowest factors to
see if they can be increased to yield the greatest increase in the AL. In this
case, the horizontal factor of 0.545 is the greatest limitation, followed by the
frequency factor at 0.667. Can the box size be reduced to get the load closer
to the body? If not, then the frequency factor must be examined. In this case,
limiting exposure of the employee to one hour will result in about a 10 percent
increase in the AL, which is still not satisfactory. Raising the feed conveyor
will result in about a 19 percent increase in AL (2 percent from vertical factor
and 17 percent from frequency factor). This will still leave the AL below 20.
Therefore, in this case the horizontal factor is the only factor that will allow
the AL to become greater than 20 (assuming that reducing the frequency to
1/minute would not be acceptable). Therefore, engineering controls would be
the appropriate answer to this problem. Obviously, if the load were greater than
42.75 kg, it would be above the MPL and engineering controls would also be
required. Potential engineering controls might include automation (automated
packing, robotic lifting, mechanical lift assists, etc.) or repackaging of the product
into small, lighter packages, or possibly repackaging into larger unit loads that
would be handled with automated equipment (sometimes referred to as the unit
load principle in materials handling).
The 1981 NIOSH lifting guide represented a widely used method for assess-
ment of manual materials handling. One of the primary concerns in using the
AL/MPL calculations involved the assumptions used for the equations develop-
ment. How many tasks in industry were smooth, two-handed sagittal plane lifting
of moderate width packages with handles under favorable ambient conditions?
Despite the limitations, the lifting guide gave ergonomists a starting point for
analysis of lifting tasks. Recognizing the widespread availability of the NIOSH
Work Practices Guide , OSHA began issuing citations (under the General Duty
Clause) for situations where workers were being exposed to high-risk manual
materials handling tasks, and companies were taking no action to reduce those
injuries.