EE WAS HELPING BUILD SCAFFOLDING INSIDE SOME LARGE DUCTING. PRIOR TO THAT HIS SUPERVISOR, HIMSELF AND OTHER WORKERS HAD CLEANED AND CHECKED THE DUCT FOR ANY LOOSE MATERIAL THEY COULD SEE. LAT ER A PIECE OF HARDENED FEED BUILD-UP FELL FROM ABOVE & HIT EE ON ARM CAUSING A CONTUSION & SORE ARM. X-RAY NEGATIVE & RETURNED TO WORK ON RESTRICTED DUTY. NO OTHER LOOSE MATERIAL FOUND AFTERWA