Design strategies for maximising human force capability (HFC) when using spanners

One of the principal ergonomic limitations experienced by those whose job it is to maintain equipment is the requirement for excessive levels of force in the use of spanners or “wrenches”. In studies conducted by the Institute of Occupational Medicine, designers of mining equipment reported that they would like to have guidelines on what force a man can be expected to exert. They also reported that they would like the information to show how the force capability is reduced as the designer moves away from the ergonomic optimum. However, information which could suit this purpose is almost non-existent. This paper describes a study of human force capability in which subjects adopting realistic working postures exerted maximal forces on a standard spanner. The extent to which maximal force is influenced by fastener height, direction of effort, and the use of rigid structures against which the man can brace himself is demonstrated. Guidelines for equipment designers were produced on the basis of the results of this study, and these also are described in this paper.