A "friction ring," a part of the braking system on the 5000 series rail car. This item fell off a rail car Tuesday morning and struck the electrified third rail, causing a shutdown of a portion of the Blue and Orange lines. (Courtesy of WMATA)

Metro will inspect the brakes on all of its 5000 series rail cars — about 18 percent of its fleet — after a part fell off a moving train outside L’Enfant Plaza on Tuesday, damaged two more trains, and shut down service along the heart of the Orange and Blue lines for hours.

Adjacent stations filled with smoke and hundreds of passengers had to be evacuated after the incident, which occurred about 9:45 a.m. Metro officials said no major injuries were reported. By 1 p.m. service was running on a single track through the affected area and on both tracks an hour later.

During a news conference Tuesday afternoon, Metro General Manager Richard Sarles said it would be premature to guess why the “friction ring,” similar to a brake disc on a vehicle, became disconnected.

Sarles said it is “rare” for one of the parts to fall off. “An investigation will come to the root cause,” he said.

When the friction ring fell off a Blue Line train, there was a spark and smoke. The friction ring landed between the electrified third rail and the running rails of the track, Metro officials said. Two Orange Line trains that were behind the Blue Line train heading in the direction of Vienna were also damaged, Sarles said.

The Blue Line train kept going and passengers disembarked at the Smithsonian station. That train was taken out of service.

Roughly 300 passengers on the Orange Line train behind it were stranded when that train suffered damage to its “collector plates,” which pull power from the third rail, said Dan Stessel, Metro’s chief spokesman.

Passengers were evacuated as emergency personnel made a human chain to help guide them to the Smithsonian platform, D.C. Emergency Response officials said. Streets around the L’Enfant Plaza and Smithsonian stops were shut down as crews responded, and shuttle buses were used to move stranded passengers.

One female passenger experienced anxiety and received medical attention on the scene, D.C. Deputy Fire Chief Kevin Byrne said. Some reports of riders “self-evacuating” from trains streamed onto Twitter, but Stessel said he had no confirmed reports of that.

When smoke was reported on the track, the third rail power was shut off, which caused another Orange Line train to lose power; it had to glide to L’Enfant Plaza where passengers were offloaded, Stessel said. Part of the train was still in the tunnel so some passengers had to move to the front of the train to leave. That train suffered cable damage, Stessel said.

Metro said it has 190 of the 5000 series rail cars in service in its fleet of 1,100. The transit authority spent $383 million buying the rail cars, which have had a history of electrical, software and wheel problems, from CAF Inc. of Spain. Stessel said the trains were delivered to Metro between 1998 and 2003. The Blue Line train that lost the friction ring was last inspected on Dec. 8, he said.

Sarles said the investigation, which will start immediately, will involve examining “materials, running metallurgy tests, examining maintenance records, design of the brake assembly and wayside conditions.” He said no track damage occurred after the incident.

Matt Bassett, chairman of the Tri-State Oversight Committee, which monitors safety at Metro, said the watchdog group was “actively participating in the investigation.” Stessel said the National Transportation Safety Board, which is conducting three open investigations at Metro, had been notified about the incident.

Sarles said he would also review Metro’s response to the incident, including the performance of Metro Transit Police and the departments of rail, safety, customer service, communications and emergency management.

In October, Metro received criticism for its handling of delays after a 39-year-old McLean man was struck by a train at Clarendon station. Passengers were stuck on that train for more than an hour, and other Orange Line commuters faced major delays, crowded stations and escalators that stopped moving because they were packed with riders.

That incident led to a review of whether the transit authority’s response to emergencies is adequate. Metro promised to improve its communications with other emergency response teams in the region.

On Tuesday, dozens of Metro riders on Twitter and in online comments about the incident complained that the transit authority did a poor job communicating the problem and providing estimates of how long delays would last. Metro used e-mail and text alerts, Twitter and its own Web site to provide information.

Around lunchtime, riders at the Smithsonian stop expressed confusion as to where shuttle buses were going and whether the station was open.

Brad Fordham was trying to board a train at the Smithsonian station at around noon but found the entrance blocked with a yellow gate. Even with many riders concerned about the safety of trains, he said, he would continue to ride because “there is no alternative.”

Mark Dalessandro, who was late for a meeting at the Metro Center, took the incident in stride. It’s “just the reality of being in the big city,” he said.

Sarles expressed surprise to hear that stranded passengers had to pay exit fares at stations.

“That shouldn’t have happened,” he said. He promised to check into the matter.

It’s unclear if Metro will give passengers refunds.

“Customers should not have been charged,” Stessel said, “and if they were on one of these affected trains, we would very much like to hear from them.”

Staff writers Ashley Halsey III, Maggie Fazeli Fard , Robert Thomson and Timothy R. Smith contributed to this report.

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