Abstract: On December 5, 1994, Employee #1, a carpenter, was cutting wood panels at a construction site in Redondo Beach, CA. He was using a 7 1/4 in. portable power circular saw, model 77, serial #HD581479. He took a 2 ft by 6 in. panel and cut a notch in it about 1 in. by 6 in. His coworker working on the ceiling found that the cut panel did not fit and gave it back for a deeper cut of the same length as before. This time, Employee #1 was holding the saw with his right hand and the wood panel with his left hand, with his thumb placed on the panel surface. During the cut, the saw kicked back and cut off his left thumb. He was transported to South Bay Hospital where surgeons rejoined his thumb. Causal factors include: (1) Employee #1 held the saw with one hand rather than with both hands; and (2) presumably the lower guard of the saw was moved up and locked with a pin or wedge, because subsequent inspection revealed that the spring tension on the lower guard was all right, if not perfect.