Abstract: On January 21, 1988, Employee #1, an iron worker, was replacing 17 defective steel columns in a building in Frederick, MD. Employee #1 was on a platform at the 10 ft level of one of the shoring towers. The steel fabricator's guidelines for proper replacement of the columns had been followed and 16 columns had been replaced without incident. However, while the last column was being replaced, a knife clip weld pulled away completely from a column further down the horizontal beam line, causing a beam to pull away from the shoring towers and collapse. The collapsing beam pushed through the framework of the tower that Employee #1 was on. He suffered a fractured left leg, pelvis, and vertebrae in his lower back. Employee #1 did not routinely replace defective steel. He was hospitalized for his injuries.