Employee was reporting to work at 5:50pm 9/11/08. His scheduled shift was to begin at 6:00pm. Entering the main office building, he started ascending the stairs. The tip of one of his sandal type shoes caught the top of a stair riser causing the sole to fold under. This caused the foot/toes to directly contact the stair tread. The foot slipped off the stair & abraided toe.