'Crown fire' hurts control efforts

Firefighters have said heavy smoke has hurt their efforts to use water-dropping aircraft on the Tahoe fire. Flames leaping from treetop to treetop cause "crown fires," widely acknowledged as the most dangerous and destructive of wildland fires. Even aerial drops can be relatively ineffective because such fires burn so hot that water is vaporized before it can do any good, said Gary Zunino, director of the Fire Science Academy at the University of Nevada in Reno.

-- Steve Chawkins