An employee was rebuilding a diesel engine at a customer's power generation plant when he attempted to move a four-wheel trailer out of the building that was in his way. The trailer was on a slight incline and, due to the size and weight, got away from him and headed toward some valves and piping along the fence line. He attempted to get in front of it to redirect and steer it when he twisted his lower back and pelvis area, causing factures to the lower vertebra and pelvis. He was hospitalized.