Abstract: At approximately 2:30 p.m. on June 23, 2000, a concrete batching machine had one of three hopper discharge ports become clogged. The port is at the bottom of a large material vat, with a compressed air operated gate mounted at the bottom to control flow. While a control room operator within view was manually holding the discharge gate open by depressing a button on a control panel, Employee #1 placed his right hand into the discharge port and attempted to free the stuck material. The control room operator's finger slipped off the gate control button and the gate slammed shut, amputating Employee #1's thumb. Employee #1 was hospitalized. The thumb was being supported by one tendon and a small flap of skin and was reattached by surgery.