ERGONOMICS OF MANUAL MATERIALS HANDLING - Environmentally Conscious Materials Handling - page 51

conservative approach. Other manual handling activities — such as carrying, hold-
ing, pushing, pulling, one-handed exertions, and materials handling in unusual
postures or under harsh environmental conditions — have yet to be addressed
by NIOSH. However, researchers have investigated many of these non-NIOSH
lifting activities and have reported their results in the literature. Researchers at
Liberty Mutual have utilized the psychophysical approach to examine maximum
acceptable push, pull, and carry loads (Snook and Ciriello 1991). Tables of psy-
chophysically determined capabilities for materials handling in unusual postures
can be found in Smith et al. (1989 and 1992). The most comprehensive summary
of nonlifting task capabilities can be found in A Guide to Manual Materials Han-
dling , second edition (Mital et al. 1997). Although there are no NIOSH guides for
these “other” manual materials handling activities, the ergonomist is responsible
to use the available information to design or redesign workplaces to insure a safe
work environment for employees.

3 MECHANICAL MATERIALS HANDLING

Ergonomists have focused on reducing injuries to workers who perform man-
ual materials handling tasks. After utilizing the appropriate tools, such as the
NIOSH guidelines, the engineering and administrative control recommendations
may represent the best solution to protecting the worker. However, the human
impacts of mechanical materials handling devices should be examined before
such devices are recommended.

3.1 Device Types and Uses

When an ergonomic analysis of a manual materials handling job (such as the
NIOSH Work Practices Guide ) indicates that tasks components are too strenuous
to be safely performed, the use of an automated or semi-automated mechanical
material handling device is often prescribed. Automated devices require very
little human interaction and are not considered in this section. Semiautomated
devices or materials handling assist devices replace a component of the materials
handling task, while requiring the worker to manually perform other components
of the task. This section describes common material handling assist devices.

3.1.1 Hoists
Hoists are devices used to lift a load and transport it within a prescribed geometric
space. Hoist types include triaxial manipulators (Figure 2.5), balancing hoists, jib
cranes, and overhead trolley suspension hoists. These devices include a mechani-
cal linkage that supports the load within the prescribed space, some end-of-device
tooling that connects the load to the device, and some type of control system
for the operator. Although some devices provide assistance in moving the load,
most only lift the object and require the operator to push or pull it to the desired