Police and firefighters respond Tuesday after a train fire was reported at the Silver Spring Metro station. (Sarah L. Voisin/THE WASHINGTON POST)

Metro said an initial investigation into Tuesday evening’s fire on the Red Line showed that a power cable under a train was struck by a loose part, touching off a fire that filled the Silver Spring station with smoke and delayed riders for hours.

Officials said Wednesday that the “root cause of the incident remains under investigation” and that there has been “no final determination.”

The Tri-State Oversight Committee, which monitors the safety of Metro operations, said it is tracking the investigation. “We are going to make sure they’ve done a thorough job looking into this so they can get to the bottom and stop these types of incidents from happening in the future,” said Jim Benton, the committee’s chairman.

Benton said initial reports appear to indicate damage to the equipment that carries power from the electrified third rail to the train. The damage to the train’s “collector shoe” may have allowed the power cable, carrying 750 volts, to come into contact with the metal-lined hose, sparking the fire, according to Benton.

“When power cables come into contact with hoses, that’s like putting a paper clip in an electrical outlet on a much smaller scale,” he said.

Investigators inspect cables beneath Car 1091 after a fire at the Silver Spring station on Tuesday. (Courtesy of Metro)

Metro said late Wednesday that the rail car was part of the aging 1000 series and that hoses and cables on all of the 1000 series cars would be inspected by the end of the week.

The location of the incident, on an elevated track over downtown Silver Spring, made it the object of considerable attention. It froze traffic at key junctions at the height of the evening rush hour and blocked Colesville Road, forcing drivers to seek alternative routes.

The incident began just after 6 p.m. when Metro’s control center received reports of smoke, fire and three small explosions coming from an empty train in the Silver Spring station, according to Metro officials. There were no passengers on the train because they had been told to get off at the previous station, Takoma.

Metro spokesman Dan Stessel declined to say what prompted the evacuation at Takoma.

Mark Berman and Robert Thomson contributed to this report.