Sue -- As hot air leaves the attic through vents, it is replaced by air entering through those lower vents. During a wildfire there is a lot of hot air moving inside and outside. If the fire is close enough an ember can easily enter an attic. That's how some of the house fires in SOCAL got started. Nice house, tile roof, fire gets too close and a fire starts in the attic.

You need a very healthy set-back anywhere in the SW. Peeps that build their dream home "cabin-in-the-woods" will find themselves unable to get rid of that treeline fast enough.