WHILE DRIVING VEHICLE NOTICED VERY STRONG BURNING SMELL. FELT BURNING SENSATION THROUGH SLACK LEG WHILE STILL DRIVING. NOTICED A HOLE HAD BURNED THROUGH LEATHER ON REAR LEFT SIDE OF DRIVERS SEAT. SMOKE WAS PUMPING OUT OF HOLE IN LEATHER (APPX 1/2-INCH ROUND) FROM SEAT PADDING. I IMMEDIATELY TURNED SEAT WARMER OFF AND THE BURNING STOPPED. AN HOUR LATER, I TURNED SEAT WARMER ON WHILE AUTO WAS RUNNING. SMOKE BEGAN COMING OUT OF SEAT HOLE WITHIN ABOUT 30-45 SECONDS. TURNED OFF SEAT WARMER IMMEDIATELY. BURNING STOPPED. VERY DANGEROUS SITUATION. INSIDE OF AUTO NOW STINKS OF BURNED PLASTIC/FOAM. *TR