Factory safety expert witness was engaged to determine the cause of a worker injury to an experienced operator/supervisor. The superviser was threading the machine with plastic sheet material when her hand was crushed. The accepted practice for threading was to feed the plastic sheet from the top and reach underneath to pull it through while another operator (i.e helper) pressed the “advance” (Arrow C) function on the control panel. In this instance the helper accidentally pushed the start button ( Arrow A). Both buttons are the same color and are very near each other. When the supervisor realized that her hand was being squeezed by the machines heated platens, she ordered the operator to “stop” the machine. The operator pressed the red stop button (Arrow B) instead of the E-stop. The stop button stops the machine after it has completed a full cycle. The “E-Stop” immediately stops all functions. Since the machine completed its cycle, the supervisor’s hand was severly injured. This is a case of poor machine design with respect to machine safety and operator safety. Because both the advance and start buttons are adjacent and the same color, it is forseable that one could push the wrong button. In addition to the “helper”the emergency stop and the “stop” buttons are the same color and perform the same apparent function (i.e. it is forseeable that an operator would assume that both perform the same function). Machine guards are not appropriate because the operator must reach in to the thread the machine; in addition, the machine must be on for the threading operation to be performed.
Solution: Provide an on/off foot switch to control the advance function. This assures operator safety by allowing the person threading the machine to have absolute control over starting and stopping the machine as it is being threaded.