ERGONOMICS OF MANUAL MATERIALS HANDLING - Environmentally Conscious Materials Handling - page 32

2.1.1 Epidemiological Approach
The epidemiological approach focused on the cause-effect relationships that
might exist between manual materials handling accidents and injuries and the
characteristics of the worker, job, and work environment. The epidemiological
approach had received less attention than the other approaches because of the dif-
ficulties in establishing the relationships between workers, the work environment,
and accidents and injuries. As stated in the 1981 NIOSH guide:
For injuries to the limbs and those which are superficial, the evidence is usually
well documented because the cause and effect are often simple to diagnose. Mus-
culoskeletal injuries (especially to the lower back) are less clear cut and the extent
of trauma is seldom defined. The interpretation of such injuries therefore depends
mainly on the mechanism of injury and this (due to inexperienced, incomplete or
subjective reporting) is difficult to analyze. (NIOSH, 1981)
Although traumatic injuries, such as breaking a leg from a fall while carrying
a load, might be relatively simple to analyze, cumulative injuries occurring after
repetitive exposure to a particular materials handling situation is much more
difficult to analyze. For example, why is it that one person could lift loads
repeatedly over days, months, or years and not be injured, while another person
performing the same job develops lower back pain after a much shorter exposure
time on the job?
The epidemiological approach identifies seven job risk factors that are haz-
ardous to a manual materials handler (NIOSH 1981):
1. Weight . What is the force required?
2. Location/site . What is the position of the load center of gravity with
respect to the worker?
3. Frequency/duration/pace . What are the temporal aspects of the task in
terms of repetitiveness of handling?
4. Stability . Where is the consistency in location of load center of gravity
in handling such things as bulky or liquid materials?
5. Coupling . What are the texture, handle size and location, shape, color,
and so on?
6. Workplace geometry . What are the spatial aspects of the task in terms of
movement distance, direction, obstacles, postural constraints, and so on?
7. Environment . What factors such as temperature, humidity, illumination,
noise, vibration, frictional stability of the foot, are involved?
In addition, the epidemiological approach briefly discussed seven personal risk
factors (NIOSH 1981):
1. Gender . There is no consistent effect, secondary to the strength factor.
2. Age . The greatest incidence of low back pain is in the 30- to 50-year-old
group.