An employee was working atop a horizontal whaler (steel I-beam) within a coffer cell approximately 12 feet from ground level. The employee was tied off to a cable lifeline above. When the crane hoisted the rigging out of the cell, one of the rigging hooks caught the whaler and broke the welds. This caused the whaler and the employee to fall. The employee struck the top of a concrete pile during the fall and sustained a fracture to his right acetabular bone (hip).