Update: MBTA says metal strip came loose from train and then into contact with the third rail.
The first car of an older inbound Orange Line train suffered an explosion, then burst into flames on the bridge over the Mystic River just before Assembly this morning, sending panicked riders onto the bridge while the third rail was still live. One rider jumped into the river; came out OK.
Jennifer Thomson-Sullivan, who was in the first car and who took video of the escape around 6:45 a.m., reports:
Explosions on first car followed by flames surrounding the car. People freaked, flames started engulfing and moving toward us. Emergency exit wouldn’t open so guy next to me kicked out window. People started jumping out, not even considering active third rail.