EE ADN 2 COWORKERS WERE IN THE PROCESS OF HAND SCALING A DEVELOPMENT ROUND, PRIOR TO LOADING FOR BLASTING. EE AND 1 COWORKER WERE GETTING INTO THE BASKET OF THE POWDER TRACTOR, SO THE OTHER CO WORKER COULD RAISE THEM UP TO REACH THE HANGING. WHILE GETTING INTO THE BASKIET A CHUNK FELL FROM THE FACE OF THE ROUND, BOUNCED OFF THE FACE AT A LOWER LEVE AND STRUCK EE IN THE LOWER BACK.