Authorities said it hadn't been determined whether the explosion was related to terrorism or was simply the suicide of a troubled man.
The so-called Sand fire tripled in size to more than 33,000 acres by Sunday night, fueled by dry brush, soaring temperatures and winds.
The victims were in a van that collided with the bus on a northwestern Arizona highway.
A SEPTA bus collided with a Jeep as it pulled out of a driveway in Yeadon, Pa., and the Jeep then struck the tractor-trailer, authorities said.
A computerized brain training program cut the risk of dementia among healthy people by 48 percent.