Employees were using a forklift equipped with four wire slings to move a 20-foot by 6-foot roofing panel from the work area to the laydown yard. The slings were threaded through the forklift's forks (two slings per fork), and the other ends were secured to the panel with shackles. The forklift was reversing through a bay door opening and the injured employee was applying pressure to a corner of the panel so it would fit through the opening. The load shifted, causing a sling to slide off a fork. The roof panel then fell onto the injured employee's left foot, resulting in a fractured ankle.