An electrical surge near the Civic Center BART station caused a large, bright flash of light on the tracks during a Sept. 16 incident that shut down the station for nearly an hour, according to an agency investigation that differs from previous police reports on the matter.

Startled passengers witnessed a 1,000-watt arc of electricity flash before their eyes, caused when the BART train struck debris capable of carrying a current, the investigation found. Along with the bright light, the accident also caused loud booming noises and plumes of smoke from the point of impact.

The investigation from BART belies an earlier report from its Police Department, which made no mention of the bright flashes but did indicate that large quantities of smoke were present at the scene. While some passengers reported seeing flames pouring from beneath the train, BART engineers said that was not the case.

“This was not a fire in the sense of flames burning any solid material or causing any structural damage, but the bright flash of the arc has a fiery appearance,” said BART chief engineer Don Allen. “There was a cloud of heavy smoke, so it is understandable that to some passengers it seemed like fire.”

wreisman@sfexaminer.com