WCVB reports the T is blaming "a blown motor" on a Red Line train for filling Andrew station with smoke.
At 2:43 p.m., Greg Simoneau reported it was more than just smoke suddenly appearing:
Two huge electrical arcs just shook Andrew station like explosions. The whole station just lit up like it was struck by lightning. We can now smell something burning and smoke everywhere.
Everyone at the station and on the opposite train was scared and started running. I could hear the blasts with my music all the way up in the other train.
The MBTA reported full resumption of service around 3:20 p.m.