The appearance of the San Francisco Police Department's bomb squad heightened concerns at the station. The explosion, at about 1:25 p.m., sparked fears that a bomb had gone off underground. Those fears then turned into reports of a possible train derailment.
In the end, an explosion and the resulting smoke turned out to be far more benign, "There was a system malfunction of some sort, either an overpowering," SFFD Chief Lorrie Kalos said. "The police did an investigation and there doesn't seem to be any criminal intent."
The Civic Center BART station was evacuated and closed while police investigated the incident. Police and fire units also closed off Market Street just in case there was something more sinister going on. After an initial investigation it seemed the third rail, which powers the trains, had arced, ""They don't know if something touched the third rail and then also touched the actual tracks," Kalos said.
Officials do, however, know that the arcing caused the explosion and resulting smoke. Fire officials say that paramedics treated one person for possible smoke inhalation. There were no other reported injuries.
Service resumed around 3 p.m. The offending BART train was taken to the East Bay to be inspected and maintained.