It may be days or weeks before we get anything more definitive about the cause of yesterday's massive home explosion on 22nd Avenue, but with speculation running rampant in the last 24 hours, we at least now have a clue.

Some mysterious, industrial sounding containers were removed from the home's debris on Friday morning, and the Chronicle is referring to them as "barrels, cylinders and 50-gallon drums."

Agents from the federal bureau of Alcohol Tobacco Firearms and Explosives (ATF) are now part of the investigation, given the suspiciously large nature of the blast that killed one person, damaged at least six homes, and completely destroyed two homes.

The San Francisco Fire Department hasn't officially commented on the ongoing investigation, but Public Information Officer Captain Jonathan Baxter tells the Chronicle, regarding the barrels, "They’re things that are unusual to find in a home," adding, "but that doesn’t mean they’re necessarily related to the cause of the fire."

Baxter said the containers contained some liquids, but he did not say what they were.

Supervisor Joel Engardio, in whose district the explosion and fire took place, made early, speculative comments that it could have been gas-line explosion of some kind. Now, though, he tells the Chronicle, it was likely something else. "The blast itself, the magnitude of it, makes you wonder about the cause. Houses usually don’t just explode like that," Engardio said.

The explosion happened on Thursday around 9:30 a.m., and at least one neighbor's account suggested that flames were visible at the home before the explosion occurred.

The home, one of a number of similar row-style homes on 22nd Avenue built in 1931, had five bedrooms and a garage on the lower level.

Earlier we learned that the person seriously injured in the blast was was a home health aide or nurse, and that she emerged from the burning building visibly charred and yelling about someone else inside.

A neighbor said that a husband and disabled wife lived in the building.

The remains pulled from the rubble on Thursday night have not yet been identified.

Previously: Body Recovered at Site of House Explosion and Fire In the Sunset; Six Homes and Five Cars Damaged In Blast

Photo via SFFD