An recent incident in which Washington D.C. subway cars filled with smoke, killing one woman and hospitalizing 80 others, happened because the train actually drew smoke inside the cars, according to members of Congress.

An electrical malfunction last week inside a tunnel caused a train to come to a halt near a downtown station bustling with passengers, causing the mass hospitalization as cars filled with smoke, according to an Associated Press report. Metro officials and the National Transportation Safety Board briefed 13 members of Congress from the D.C. area, who voiced concerns with both ventilation problems and poor communication between the fire department and the Metro transit agency due to encryption on their radios.

Rep. Don Beyer (D-Va.), who represents the district that was home to the one woman who died in the incident, said that the ventilation on the trains “sucked smoke into the trains.” Christopher Hart, chairman of the NTSB, said the agency was investigating the ventilation issues, but declined to address them now, and investigators had been unable to reproduce what had happened with the ventilation fans, so further work will need to be done to find out what happened.

It was the first fatal accident for the second-largest rail network in the country since 2009, when a train smashed into the back of another train, killing eight passengers and the operator of the train.

Passengers were stuck on the train for a half hour before firefighters arrived, and had to inhale smoke for much of that time. The train was delayed in evacuating because of problems communicating with Metro. The train’s operator told passengers to stay put, but some ignored this advice and evacuated anyway.

The Metro network serves Washington D.C. and the surrounding suburbs of Virginia and Maryland, carrying more than 700,000 passengers every day, surpassed in the United States only by New York’s subway system.

Although the investigation is supposed to take months, members of Congress are demanding that adjustments be made now, with Sen. Mark Warner (D-Va.) arguing that fire departments should be required to tell other agencies about its radio encryption.