Ergonomics
follows a very simple basic model that derives from physics: When you impact
any body with a certain stress, the body will react with a corresponding strain.
For example, when you push a wooden stick that is fixed at one end from the
side (= stress), it will get bowed (= strain). When we release the stress, the
stick will become straight again. This means that the strain will release, too.
But if the
stress exceeds a certain threshold, the strain can overcome the resistance of
the stick, so that it will break. This limit to damage defines the maximum
stress that the wooden stick can bear.
When we
transfer this simple model to working conditions, it must be modified in a
couple of points.
On the
stress side, the working method is connected with typical stresses. For
example at motor-manual processing: The chainsaw produces noise and vibration, has
toxic emissions and is very dangerous. The natural working site can be heavy
and dangerous, and the social relations with colleagues and superiors may cause
stress, too. This stress seems very complex.
But social stress
from group dynamics normally has nothing to do with the standard work method
and pertains to social science, not ergonomics... And stress coming from the
natural environment causes a percentual scaling of the stress that is connected
with the working method as such. So, the composition of stress is very typical
for this specific working method. Thus: Without knowing how the stressing
factors are combined and how they work together, the complex stress is typical
for this standard method and can be assessed by expert opinion.
The simple
model that we had above feigns that the stress of a standard method will permanently
cause the same strain for the worker. But here the reality is much more
complex, too, because all workers are different concerning attributes, health, conditions
etc.
