The force that an operator is able to apply to a valve wheel depends on the location of the wheel relative to the operator, the orientation of the valve stem, the diameter of the wheel, and the quality of the interface between the wheel and the hands. The objectives of this study were three-fold. The first objective was to provide information on human force capabilities to valve designers to assist them with the design of new valves. The second objective was to assist piping designers with the layout of valves in a new plant. The third objective was to help plant operations staff determine whether the turning force required to operate existing valves exceeds the capability of process operators. Participants were 66 volunteer process operators and managers from a refinery and a chemical plant located on the Gulf Coast of the United States. Turning strength was measured by recording the force applied to the rim of the valve wheel during an isometric contraction in which there was no movement of the body. The data collected in this study clearly demonstrate a relationship between the posture of the operator, as defined by the height and orientation of the valve wheel, and the maximum turning force that can be applied. For a horizontal stem, the most force could be applied when the valve was in the knee or waist area. For vertical stem valves, operators appear to be able to apply the maximum force when the valve is located between the waist and the shoulder. (C) 2002 Elsevier Science Ltd. All rights reserved.