WASHINGTON — The Federal Transit Administration has launched an investigation into Saturday’s smoke and fire incident on Metro, a Metro spokesman has confirmed.

On Saturday, an outbound Red Line train nearing the Friendship Heights station was forced to reverse direction toward Tenleytown when smoke entered the tunnel.  No one was hurt. The rail system has since resumed normal operation.

Metro has not yet determined the exact cause of Saturday’s incident, but Metro spokesman Richard Jordan said an electrical arcing insulator likely was the cause.

Jordan said after repairs were made Saturday inspectors worked through the night checking inbound and outbound tracks in the area of the incident

“We’re very confident with the safety of the system right now,” Jordan said.

Jordan said the arcing is not uncommon in that section of track.

The portion of Metro’s Red Line route from Friendship Heights to Shady Grove has been plagued by water intrusions. When water gets into the third rail insulators it can cause sparking and smoking.

There had been another incident near the Bethesda station.