Abstract: At approximately 8:25 p.m. on June 5, 1991, Employee #1 was replacing a connecting pin on a hydraulic cylinder used to raise and lower a Hyrail assembly mounted on a bucket truck. The Hyrail was in a raised position that was supported by a mechanical latch. Employee #1 was lying on his back under the Hyrail assembly, attempting to install the new pin in the hydraulic cylinder when the latch holding the Hyrail wheels and axles in the raised position slipped. The wheels and axles were not supported by stands and four wheels and two axles fell to the ground. With the wheels on the ground, there was only a 7 in. clearance between the axles and the ground. Employee #1 was struck by one of the falling axles, sustaining chest and abdominal injuries.