UPDATED with latest info from the T.
Around 8:50 a.m., an inbound Orange Line train pulled into State Street and there was a large "bang." Chuck Giroux photographed people rushing out of the station.
Although initial reports seemed to indicate the train had hit part of a fallen light fixture on the tracks, a T spokesman says the bang came from the subway equivalent of a shock absorber giving out:
An air bag blew. It was in the undercarriage of the train's 4th car. The air bags on subway cars are similar to shock absorbers on motor vehicles.
Kurt Salaman reports:
it was a very loud booming sound, but i think it was something with the train. We didn't stick around to find out though.
The T pulled the train out of service.