What happens if I burn my card accidentally while clearing it?

In that situation, you have damaged your piece of card stock. If it is only very slightly damaged, there's no reason why you couldn't continue to work with it. If the edges are damaged, however, you will always know where it is in the deck when shuffling and drawing, and that is counterproductive. It is not necessary to have a flame anywhere near your cards to 'clear' them. It is YOU who may need 'clearing' rather than your cards. YOU are the one who reads the Tarot. Anything that clears your mood or your mind clears your cards for Tarot work.