If you read the Flash Point rules, it says to place a fire marker on each adjacent spot after an explosion. Does that mean place a fire on the other side of a wall? For instance, if the fire is in a corner of a room, would you put fire in another room after an explosion? The instructions don't say the wall becomes damaged, except from a shock wave. But it seems confusing because if you read that, it seems like fire is placed on the other side of wall or door, without causing any damage.
Squares are not adjacent if there is a wall or closed door between them. From Page 2 of the rules
An open door or a destroyed wall (one with two damage counters) does not prevent adjacency. So in each direction you will either find an adjacent space without fire (which you will add fire to) or run into a wall/door (doors are destroyed, walls are damaged) or reach outside (add fire but remove it at the end of the turn).