Psychophysical Approach to Task Analysis - Fundamentals and Assessment Tools for Occupational Ergonomics - page 899

47.2 The Psychophysical Approach to Designing Manual
Materials Handling Tasks

One of the first approaches to the control of MMH injuries through specifying task limits was the
psychophysical approach. Applications in the military which relied on subjective estimates of load hand-
ling limits 15,16 were followed by the psychophysical approach being utilized to set industrial materials
handling limits. 17 The methodologies and database developed by Snook and his colleagues 1,17 - 20 at
the Liberty Mutual Research Center have been used by researchers and practitioners for the past
several decades. This has resulted in the availability of a wide range of data available for designing
MMH tasks. 6,20 - 23

47.2.1 Setting Weight and Force Limits
The application of the psychophysical approach to MMH task design is performed by using databases
in the literature which provide limits specific to task conditions such as frequency, pushing or pulling
distance, and load dimensions. Figure 47.1 presents a general model of the procedures associated with
applying psychophysical data.

Start

Record Relevant
Task/Workplace
Parameters

Using Data Collected
Determine % of
Population Accommodated

If Necessary,
Redesign Task or
Workplace to
Accommodate
90% of Population
if Possible

Is Task
Acceptable to
At Least 75% of
Population?

Stop

Yes

No

Can Workplace Be
Redesigned?
Can Weight, Force or
Frequency be Reduced?

Utilize
Preplacement
Testing

No

Yes

Redesign
Task or
Workplace

FIGURE 47.1 General model of the psychophysical approach to analyzing manual tasks.