From what I've heard, the firefighters have been preparing for quite some time making fire breaks and other preparations. There are also a lot of firefighters there, as it is a top priority. The only way that I can see it going down is if the winds pick up. If they got going fast enough, the wind would blow super hot embers over the fire breaks and over run the firefighters. Strong winds have been known to throw embers well over a mile, so if they did pick up, it wouldn't be that hard for one to land on the observatory.