A sudden blast totaled a car in the middle of a packed parking lot, moments before the driver was about to get in it. "I unlocked my car. I popped my trunk then my car exploded all over the parking lot," said Jackie Sugrue. The explosion sent shrapnel flying Sunday afternoon through the lot at a Stoneham store where shoppers at first weren’t sure what was going on. "I’ve seen car fires, but never an explosion like that," said a witness.