Employees were moving a trailer frame. The frame's front and back had been raised with dollies. Four employees were in the back, pushing the trailer forward, when the back end of the trailer came in contact with a piece of angle iron steel in the floor and the dolly came to an abrupt stop. The weight of the trailer overcame the dolly and an employee was pinned between the dolly and the back (ramp) of the trailer. He suffered a collapsed left lung and was hospitalized.