WASHINGTON, (Xinhua) -- Initial findings show that an electrical problem caused the deadly Washington subway smoke, authorities said Tuesday.
Peter Knudson, spokesman for the National Transportation Safety Board, said, the smoke that filled six subway cars in a tunnel on Monday was electrical arcing involving the charged third rail about 1,100 feet (334 meters) ahead of the train. There was no fire on the train or derailment.
"What caused the electrical arcing is what we want to understand," Knudson said, the investigation into the accident could take 6 to 12 months.
Arcing happens when electricity from the power rail comes into contact with something that conducts electricity, like water, he said.
The smoke occurred in a tunnel leading to the Pentagon station which is about 800 feet (243 meters) south of the Washington Metro 's L'Enfant Plaza station. It caused the death of a woman, and sent over 80 people to hospital, 2 in critical conditions.
A spokeswoman for MedStar Washington Hospital Center said one of the critical patients was upgraded to serious.
Investigation will be conducted not only into the cause of the accident, but also emergency response, Knudson said. Some passengers told media that firefighters had taken an hour to reach the train in accident.
Tom Downs, chairman of the Washington Metropolitan Area Transit Authority, apologized in a statement, pledging to prevent it from happening again when the cause of the incident was determined.
The Monday smoke also caused disruption in some subway lines, as the L'Enfant Plaza is a transfer station for five lines. Delays of subway trains were reported on some lines Tuesday.