Abstract: Employees #1and #2 were pouring 60 yards of concrete with a Schwing, 28/24-186, 16-1166 concrete boom pumper. Employees #1 and #2 were on the top edge of an unguarded concrete form approximately 50 ft by 30 ft. Unintentional boom movement caused the hose to swing approximately 4 ft and strike Employee #2, the hose operator. Employee #2 fell into Employee #1, a concrete finisher who was walking on the unguarded form edge. Both employees fell approximately 6 ft 1 in. to a lower level. Employee #1 struck a 12 ft I- beam and fractured three ribs in his lower back. Employee #2, who fell on Employee #1, did not sustain any apparent injuries. The cause of the boom movement is unknown. The pump boom operator had been distracted and returned to on-going operations without observing the discharge boom. The pump boom operator stated that the boom kill switch had been activated. No work rules concerning concrete pumping have been established. The pump boom operator had held Concrete Assoc. of America certification until March 1992, but had not renewed. He had more than 20 years experience. The pumper had undergone a full overhaul approximately one month before the accident. No equipment defects were noted. Inadequate safety and health program, hazard recognition training, job site inspection, exposed rebar, inadequate access, and unguarded open sided platform (fall protection) were noted.