Investigators said Saturday that they have eliminated a drug lab or bomb as the cause of a building explosion that killed three men, and believe the blast was accidental.
Attention has shifted to a natural gas furnace or water heater within the three-story apartment building, said San Francisco Fire Chief Joe Medina. But he added that evidence is still sketchy.
"Any kind of a gas leak from the street has been ruled out, an illegal drug lab has been ruled out," he said. "Right now we're still looking . . . but we haven't come up with a cause yet."
The blast Thursday night leveled the building, raining debris over the Tenderloin district neighborhood and shattering windows within half a block. Three bystanders were found dead in the rubble.
Mark Logan, assistant chief of the U.S. Bureau of Alcohol, Tobacco and Firearms in San Francisco, said the explosion and fire were not set deliberately.
"We have found no evidence of an explosive device, no evidence of an incendiary device, or somebody pouring gasoline," he said.
While ruling out a natural gas leak from the street or in the pipes within the building, authorities believe that gas may still have been the cause, Medina said.
It is possible that gas leaked out of the furnace or water heater, and built up until it ignited, he said.
Logan said there was no evidence that the three victims had anything to do with the explosion.
The San Francisco coroner's office Saturday released the names of the men and said they were all city residents. They were identified as Armando Gonzalez, Adalberto Flores-Diaz and Adolpho Salinas.
They were apparently standing or walking along the sidewalk beside the building when it erupted into flames and collapsed about 9:45 p.m.