Crews search ash-covered homes after blast kills 4 [September 11 2010]

All that was left of some houses Friday were chimneys, rising from still smoldering ruins. Burned-out cars sat along ash-covered streets. And a rescue worker with a dog searched door to door for missing people.

The day after a gas line ruptured and a towering fireball roared through a suburban San Francisco neighborhood, killing four people, officials were trying to determine what led to a blast that raised questions about the safety of similar lines that crisscross towns across America. "It was pretty devastating," Fire Chief Dennis Haag said. "It looks like a moonscape in some areas."

At least 50 people were hurt, with seven suffering critical injuries in the explosion Thursday evening that left a giant crater and laid waste to dozens of 1960s-era homes in the hills overlooking San Francisco Bay. The utility that operates the 30-inch diameter line said it was trying to find out what caused the steel gas pipe to rupture and ignite. Federal pipeline safety inspectors were also on the scene Friday afternoon.