WHILE WORKING ON MILL EMPLOYEE GRABBED RETAINING RING TO ENTER MILL WHEN RING GAVE WAY CAUSING HIM TO FALL BACKWARDS. HE REACHED BACK TO GRAB THE SAFETY HANDRAIL BUT MISSED AND FELL APPROXIMAT ELY 15 FEET TO GROUND LANDING ON HIS TAILBONE. 911 WAS CALLED AND HE WAS TAKEN TO HOSPITAL. ON RESTRICTED DUTY.