D.C. Metro incident: What went wrong?

WASHINGTON - Hundreds of rush-hour passengers were trapped inside a Metro train here Monday as it filled with thick smoke. Sounds of coughing mingled with instructions to "please stay calm."

Some were vomiting, others were choking and gasping for air.

"There was no oxygen," one woman told CBS News. "People started panicking and people started hitting the floor."

The passengers were eventually escorted by firefighters, hundreds of feet through the dark smoke-filled tunnel.

A 61-year-old Virginia woman died. More than 80 others were taken to hospitals, at least one in critical condition.

"I am particularly concerned about the time that it took to evacuated the passengers," said Mark Rosenker, the former chairman of the National Transportation Safety Board and a CBS News consultant.

Fire officials say they asked the passengers to stay in the cars until they were certain the high-voltage third rail had been turned off -- so that no one would be electrocuted. Some passengers ignored the request and exited the cars -- making it too dangerous for the train to return to the station.

Rosenker said "there is a plan" for a faster evacuation than what happened Monday. "The question is, was the plan followed? Were there mistakes made in the plan or was the plan itself flawed?"

The NTSB says the smoke appears to have been the result of an electrical malfunction on the tracks. But it could be months before they reach a firm conclusion about why the evacuation took so long.