EMPLOYEE WAS LOADING HAUL TRUCKS WITH AN EXCAVATOR. A LOADED HAUL TRUCK WAS SIGNALED TO LEAVE THE LOADING SITE. AS IT PULLED AWAY, THE LEFT REAROUTSIDE TIRE FAILED VIOLENTLY. THE AIR BLAST FRO M THE TIRE FAILURE THREW A SMALL ROCK AT A HIGH VELOCITY INTO THE CAB OF THE EXCAVATOR STRIKING INJURED'S JAW ON LOWER LEFT SIDE. HIS MANDIBLE WAS FRACTURED & HE SUSTAINED A LACERATION.