Photo by Rolenz.

The National Transportation Safety Board has released their preliminary report in the investigation of Monday’s fatal smoke incident at the L’Enfant Plaza station.

While the NTSB is still trying to figure out what exactly caused “severe electrical arcing damage” to the third rail, which caused the tunnel outside the L’Enfant Station to fill with smoke, their preliminary investigation has shed a little light on what went wrong. The biggest revelation? It took Metro 44 minutes to shut off power to the third rail damaged by electrical arcing. From the NTSB’s preliminary report:

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. The electrical breaker at the other end of the third rail section remained closed; supplying power until the WMATA OCC remotely sent a command to open the breaker at about 3:50 p.m.

According to the report, not one but two trains were affected by the arcing event. The first train, train 302, stopped after it encountered “an accumulation of heavy smoke while traveling southbound in a tunnel between the L’Enfant Plaza Station and the Potomac Rive Bridge.” The end of the train was about 386 feet from the south end of the L’Enfant platform.

Another train following 302 stopped about 100 feet short of the south end of the platform at about 3:25 p.m. There, smoke began to fill all six passenger cars of both trains, resulting in one fatality. In all, 86 people were transported to area hospitals.

The NTSB says they’re continuing their investigation, “reviewing maintenance records of track, signal and power inspections, and railcar vehicles; documentation on previous events with smoke generation; maintenance and repair records of the tunnel exhaust fan/ventilation operations; WMATA emergency response and evacuation plans; and employee training records.”