My dad was a fireman, and as kids we got to go to a few of these planned demo structure fires and hang out in his pickup. Good times. Eople would "donate" their buildings to the department, and they would do a couple if small isolated burns,, do a few practice exercises, and then light the whole thing up and let it burn. Though, before doing it, they required that all shingles and tar paper be removed, and some people weren't willing to do it, so then they would just have to bulldoze it and/or take it apart.