Those of us wo have done accidents together know I love my NTSB!!
Well this is identical to what happened MOn - a year ago :
As a result of the smoke, 86 passengers were transported to local medical facilities for treatment. There was one passenger fatality.
A following train, stopped at the LEnfant Plaza Station at about 3:25 p.m., and was also affected by the heavy smoke.
Passengers of both trains, as well as passengers on the station platforms, were exposed to the heavy smoke.
NTSB investigators have inspected the area of the incident, where they observed severe electrical arcing damage to the third rail and electrical cables about 1,100 feet ahead of train 302.
Recorded data shows that at about 3:06 p.m., an electrical breaker at one end of a section of third rail tripped (opened). At about 3:16 p.m. the WMATA Operations Control Center (OCC) began activating ventilation fans in an effort to exhaust smoke from the area.
http://www.ntsb.gov/investigations/accidentreports/pages/DCA15FR004_preliminary.aspx