The Ergonomics Society The Society's Lecture 1978. THE DESIGN OF MANUAL HANDLING TASKS

Abstract

Manual materials handling is the principal source of compensatable work injuries in the United States, and 79% of the manual handling injuries affect the lower back. The prevention of low back injuries in industry has traditionally been attemped by (1) careful selection of workers, (2) good training procedures in safe lifting, and (3) designing the job to fit the worker. This paper discusses the latter approach by describing seven studies of lifting, lowering, pushing, pulling, carrying and walking. Among the variables investigated were the height, distance and frequency of the task; the size and weight of the object; the differences in worker sex. age, and physical physique; and the effects of heat stress. The psychophysical methodology used in six of the studies is discussed, and the results are used to develop a series of tables for evaluating the design ofmanual handling tasks. The tables present the maximum weights that are acceptable to 10, 25, 50, 75 and 90% of the working population. The effectiveness of this approach in reducing low back injuries was investigated by analyzing 191 randomly selected back injuries. The results indicate that designing the job to fit the worker can reduce up to one-third of industrial back injuries. Job design is obviously not a total solution to low back injuries, but it was found to be significantly more effective than selecting the worker for the job, or training the worker to lift properly.