Federal investigators say Washington's Metro transit authority did a poor job using ventilation fans to push smoke out of a subway tunnel during a fatal accident last month.

The National Transportation Safety Board issued recommendations on Wednesday urging Metro and other transit networks nationwide to improve their ventilation procedures during smoke or fire events.

The NTSB says Metro's ventilation procedures are inadequate and that the agency can't even pinpoint the exact location of smoke in a tunnel. The ventilation fans are supposed to be able to push smoke out of tunnels and pump in fresh air.

One woman died and more than 80 others were sent to hospitals for smoke inhalation after an electrical malfunction caused smoke to fill a subway train in downtown Washington last month.