WITHIN 10 MINUTES OF STARTING THE VEHICLE ACTIVATING THE SEAT HEATER ASSOCIATED TO THE DRIVER SEAT A BURNING SMELL BEGAN TO BECOME APPARENT IN THE PASSENGER CABIN. EVENTUALLY THE SMELL DEVELOPED INTO PAIN IN THE LEGS AND THERE WAS A HOLE BURNED INTO THE DRIVER SEAT. THE SEAT HEATER WAS STILL OPERATING AT FULL CAPACITY AND SUPPLYING ENERGY TO THE SYSTEM AS IT WAS IGNITING THE DRIVER SEAT. THIS EVENT OCCURED ON 140TH IN RENTON, WASHINGTON. THE VEHICLE WAS ON THE ROADWAY TRAVELING WITH TRAFFIC WHEN IT OCCURED.