The fire that Armand built was intended to burn Desiree's belongings and her child's. Fire, as s symbol of rebirth and destruction is also the element that disconects Armand from his present situation. However, we know that Armand also burned a letter which stated that he, himself, was part black. In this burning, he is also disconecting himself from his past, his present, and his future. He was basically doing everything in his power to burn the truth, and pretend that nothing ever was.