INJURED EE AND EQUIPMENT OPERATOR WERE IN THE PROCESS OF HANGING FIBER OPTIC CABLE, WITH INJUREDEE IN MANBASKET ABOUT 8' OFF THE GROUND. OPERATOR REACHED TO CLEAR CABLE FROM MAN CARRIER AND INADVERTANTLY BUMPED THE DUMP CONTROL LEVER. THE SAFETY CHAIN CAME LOOSE, ALLOWING THE BASKET TO DROP TO THE GROUND WHICH INJURED EMPLOYEE IN IT.