Abstract: At approximately 7:40 p.m. on December 15, 1993, Employee #1, of Hohmann & Barnard, Inc.. was adjusting the drive chain tension on the welding head stroke arm of a Conventional truss machine. The permissive run switch, which was in the OFF position, allows the machine to run continually. Another switch, which is used to jog the machine and is wired independently from the permissive run switch, was pendant-mounted on a long cord. This switch fell off the machine bulkhead, fell to the floor with the button down, and energized the machine while Employee #1 was holding the chain and sprocket. Employee #1's right thumb was caught between the chain and sprocket and was amputated. Although the employee had been told to lock out the machine when performing "important" adjustments, he did not lock out the machine for this adjustment.