WHILE DRIVING ON A SMOOTH STRAIGHT SECTION OF INTERSTATE 75 AT 80 MPH I APPARENTLY RAN OVER A PIECE OF METAL WHICH FLIPPED UP AND HIT THE UNDER SIDE OF THE CAR UNDER THE DRIVERS SEAT TOWARD THE OUTSIDE. THEN THE SIDE AIR BAG DEPLOYED ON THE DRIVER'S SIDE STRIKING MY UPPER ARM,CAUSING A LARGE BRUISE. I WAS ABLE TO MAINTAIN CONTROL OF THE CAR. I CHECKED FOR DAMAGE AT THE NEXT LIGHTED EXIT. FINDING NONE I PROCEEDED ON MY TRIP HOME. THE NEXT MORNING I DROVE TO THE LINCOLN DEALER. THEY DISCOVERED A 2-3 INCH GASH UNDER THE DRIVERS SEAT AND SAID THAT CAUSED THE AIR BAG TO DEPLOY. THEY DENIED A WARRENTY CLAIM FOR THE REPAIR AND REFUSED TO STATE IN WRITING THAT THE IMPACT TO THE UNDER SIDE OF THE CAR CAUSED THE AIR BAG TO DEPLOY PROPERLY AND THEREFOR WAS NOT A COVERED DEFECT. AT THIS TIME I AM TRYING TO CONTACT THE LINCOLN 800 NUNBER TO GET THE REPAIR COVERED UNDER THE WARRENTY AND HAVE THE PROBLEM CHECKED INTO FOR OTHER DRIVER'S SAFETY.*AK