Officials Hunt for Clues in Deadly Bay Area Blast : San Francisco: Explosion killed three people and demolished a three-story building. ‘The force was . . . 100 times worse than an earthquake,’ one of the injured says.

Federal agents on Friday sifted through smoking rubble in a search for clues to a massive explosion that killed three people, demolished an unoccupied three-story building and sparked a fire in a neighborhood near Union Square.

The blast, which occurred shortly before 10 p.m. Thursday, shattered windows for several blocks and hurled boulder-sized debris hundreds of yards. One brick shot through the window of a passing car, leaving the driver with severe facial injuries. Four other people were injured, none critically.

Witnesses said the mysterious explosion packed the force of a bomb and gave the intersection of Post and Hyde streets below Nob Hill the look and feel of a war zone.

“The force was incredible--100 times worse than an earthquake,” said Elisa Magidoff, who was standing outside a grocery store and was badly cut by flying glass. “It came up from the ground, lifted my body and knocked me right over. Then there was screaming, smoke and chaos.”

Lisa Demitro, a palm reader, was closing her shop when the explosion blew out her front windows, shattered her crystal ball and knocked her sideways.

“I got jolted, and suddenly the street was filled with a big orange ball of fire,” Demitro said. “Then that building just disintegrated. Big pieces of it came flying down the street.”

Ten structures were damaged by the explosion, and 11 cars were battered by falling rubble. Fractured window frames, glass and mattress stuffing littered the pavement, and bedsheets hung from lampposts and overhead wires.

About 50 people were evacuated from nearby apartments; 34 spent Thursday night on cots in the ballroom of the St. Francis Hotel.

The explosion obliterated the 1907 apartment building, leaving only a blackened hole. The structure was owned by Margarita Delpeck, who was its sole occupant and lived there part time. She was elsewhere at the time of the blast.

By late Friday, investigators with the San Francisco Fire Department and the federal Bureau of Alcohol, Tobacco and Firearms had not pinpointed the source of the blast. Their hunt for clues in the rubble was slowed when the one wall left standing had to be demolished for safety reasons.

Several neighbors reported smelling gas in recent weeks, and noted that utility crews had done some work on their street last month.

But Pacific Gas & Electric officials said a survey turned up no leaks or other evidence suggesting that natural gas was to blame. The meter to the building was intact, as were pipes leading inside. And a check of the street work, concluded in early May, showed nothing was amiss, PG & E spokesman Paul Ward said.

Speculation also centered on the possibility that a methamphetamine lab had operated clandestinely in the basement of the building. Neighbors wondered whether there was a connection with the building owner’s long-running feud with drug dealers and prostitutes who work the neighborhood. Delpeck’s brother was assaulted after an argument with the loiterers more than a year ago, they said.

“Maybe it was a revenge thing,” said Kent Marone, who manages an apartment building across the street and has worked with Delpeck to fight crime in the neighborhood. “There are some tough crankster gangsters around here.”

Police said the three victims, all males, apparently were pedestrians crushed when the building collapsed. The coroner could not immediately identify the dead, but Marone said one victim was a transvestite prostitute well-known in the neighborhood.

Times researcher Norma Kaufman contributed to this story.