EMPLOYEE WAS CLEANING THE BASEMENT, APPROX. 8-10' FROM CO-WORKER WHO HEARD EE CALLING HIS NAME. WHEN THE CO-WORKER TURNED AROUND THE INJURED EE WAS SITTING ON THE GROUND. CO-WORKER ASKED WHAT HAPPENED AND THE EE SAID HE FELL DOWN & HIT HIS BACK ON THE STEPS. CO-WORKER DID NOT HEAR OR SEE EE FALL.