EMPLOYEE WAS DRIVING AN EIMCO M3 SHIELD HAULER UP THE FAULT WHEN THE RIGHT REAR TIRE BEHIND THE DRIVER'S COMPARTMENT BLEW, CAUSING THE MACHINE TO DROP TO THE GROUND AND JARRING THE EMPLOYEE'S LOWER BACK. OPERATOR'S SEAT WAS AN AIR RIDE SEAT, WHICH APPEARED TO BE WORKING. EMPLOYEE WAS WEARING HIS SEAT BELT. EMPLOYEE SUSTAINED INJURY TO LOWER BACK. HE HAS PRE-EXISTING BACK CONDITION.