How do i treat a really bad burn that has busted open?

Keep clean. See doc.: You don't give a time course for how long it's been since you were burned or the depth of the burn. 2nd-degree (i.e., partial-thickness) burns will heal in 1-3 weeks. 3rd-degree (i.e., full-thickness) burns will usually require skin grafting to fully heal. If your burn wound does not fully heal, a burn, plastic, or general surgeon should evaluate the wound.