Civil Engineering Reference
In-Depth Information
The safety status of a system may be assessed by comparing the performance
requirements of the environment with the performance limitations of the operator (see
Figure 1.3). Let's take the example of driving a car. The driving task imposes a demand
for operator attention, but this demand varies over time. Sometimes a car driver must
look constantly at the traffic, and at other times the traffic situation is less demanding. At
the same time, operator attention varies over time. A sleepy driver has a low level of
attention, while an alert driver has a high level of attention. If the task demands are
greater than the available attention, there is an increased risk for accidents or errors.
Hence it is important to understand how the limitations imposed by operator perception,
decision making, and control action can be taken into consideration in design, so as to
create systems with low and stable performance requirements.
Injuries and accidents are relatively rare in the workplace. Rather than waiting for
accidents to happen it may be necessary to predict safety problems by analyzing other
indicators (or dependent variables) such as operator errors, subjective assessments, and
physiological response variables. These measures are indicated in Figure 1.3 under the
heading “Measures of Negative Outcome.”
If a system must be redesigned to make it safer, there are several things one can do:
1. Examine the allocation of tasks between workers and machines or computers. Workers
may be moved from a hazardous area and automation could take over their job.
2. Poor work posture leads to fatigue and poor work quality. Redesign work processes
and workstation to improve worker posture, comfort, and convenience.
3. The ambient environment—illumination, noise, vibration, and heat or cold—can be
stressful. For example, inadequate illumination makes it difficult to see safety hazards,
and therefore the low illumination imposes stress.
4. Organizational factors, such as allocation of responsibility and autonomy, as well as
policies for communication, can be changed. Sometimes operators are not in charge of
their own processes. Valuable time is lost if they must contact supervisors to get
permission to shut down a process.
5. Design features of a machine can be improved, including changes of controls and
displays.
1.7
THE GOAL OF PRODUCTIVITY
System design has three goals: safety, productivity, and operator satisfaction. Their
relative importance varies depending on the system. In a nuclear power plant, safety and
production of electricity are two self-evident goals, and together they determine the
design of the plant.
To enhance system performance, one can design a system which improves
performance affordances. This means that through efficient design of the system the
operator can excel in exercising his or her skills. Such system design makes it possible to
perceive quickly, make fast decisions, and exercise efficient control.
To improve systems performance an ergonomist could, for example, design systems
affordances so that they enhance important skill parameters: handling of machine
controls becomes intuitive (e.g., through control-response compatibility), and
