Orange Line train catches fire on bridge. Chaos ensues. It’s the latest T nightmare.

An Orange Line train ride approaching Somerville turned into a nightmare Thursday morning when the lead car caught fire on a bridge, sending terrified passengers scrambling to evacuate by pushing out windows, with one person even leaping into the Mystic River and swimming to safety.

Governor Charlie Baker called the train fire on the bridge a “colossal failure” — the latest in a year that has seen many. Since two Green Line trains crashed on July 30, 2021, sending 27 people to the hospital, T riders have had to endure a growing procession of malfunctions, derailments, delays, and deaths.

MBTA general manager Steve Poftak said Thursday that a metal side panel on the Orange Line train broke off and touched the high-voltage third rail, causing the flames. The T believes passengers removed four windows from the smoking car to escape, Poftak said, adding that no injuries were reported as a result of Thursday’s incident.

The MBTA is still waiting on the delivery of hundreds of new Orange and Red Line train cars from a Chinese company first contracted in 2014 that are supposed to replace the old cars like the one that caught fire Thursday.

“Obviously this is a frightening incident, and not the type of service that we want to provide to our customers,” Poftak said. “I want to offer my apology to the folks who were on that train, who had to experience that.”

At the time of the fire, there were around 200 passengers on board the train, Poftak said. The MBTA cut power to the third rail within two minutes, he said.

Jennifer Thomson-Sullivan, 42, said she was one of the passengers on the car that caught on fire and she saw flames leaping up on both sides of the train. “That’s when everyone started freaking out,” she said. “In my brain at that moment, I thought, ‘Oh my god.’ People rushed to the back of the car where I was sitting. There was a gentleman frantically trying to open the emergency exit. But the door would not open.”

When he couldn’t get the door open, the man got up on the seats and kicked out a window, she said.

“From that point on, people started throwing themselves out the window,” she said. “They didn’t stop to consider the third rail or what if another train was coming in the other direction. ... People just went for it.”

One passenger got out of the train and jumped into the water below.

“An unidentified female passenger jumped off the bridge into the river,” said Somerville Fire Chief Charles Breen in a phone interview. “Our marine boat happened to be in the river for training and was on scene immediately. The woman refused to get into the boat. She was provided a life jacket and proceeded to swim to shore ... then she walked away.”

Radio transmissions posted to Broadcastify.com indicated that T personnel who were working to remove passengers watched as the woman jumped into the water.

“201 to Control. I can see Medford Fire at the station. We’re almost done evacuating the train. We also have fire crews at Assembly,” the T supervisor reported.

She paused briefly.

“I have somebody jumping off the bridge into the water, actually, as we speak,’’ she said. “201 to Control. [They’re jumping] off the bridge into the water below.”

As with other T troubles over the last year, the past is prologue.

Thursday was not the first time an Orange Line train car panel, known as a “sill,” has come loose, causing smoke and a frantic evacuation. In 2016, a panel with “deteriorating fasteners” on an Orange Line car fell off the train and touched the third rail at State Street Station, spurring an evacuation, the Globe reported at the time. Riders on a second train that ran over the panel kicked out train car windows to escape the smoke. In response, the T began physically inspecting the panels, instead of doing simple visual checks, the Globe reported at the time.

Poftak said the train car involved in Thursday’s fire, car 1251, was put into service in January 1980 and was last inspected on June 23. During that inspection, the panel was checked, Poftak said. Cars are inspected every two to three months. Poftak said the T will be investigating whether the heat — it was around 75 degrees in Boston at 7 a.m. Thursday — or the speed of the train may have caused the panel to fall off. The panels are riveted to the body of the car, Poftak said.

William Tauro, a former candidate for Somerville mayor, who lives in Assembly Row near the bridge, said he looked out the window to see the train stopped with smoke billowing out and wondered: “What the hell is going on out there?”

Louis Bacon, 72, said he was working on his boat on the Mystic when he spotted a helicopter circling the area. Though he didn’t initially see flames, Bacon said, he wasn’t surprised to hear about the blaze.

“You don’t ever want to see it, but it’s on the news — there’s always something on the T going wrong,” Bacon said.

Broken windows on an Orange Line train at the Wellington Station in Medford on Thursday.David L. Ryan/Globe Staff

The damaged train, which officials said caught fire at around 6:45 a.m., was brought to the Wellington rail yard for an investigation. After the T inspected the track area, regular Orange Line service resumed Thursday at around 10:30 a.m.

Asked what grade he would give the T on Thursday, Baker said, “Today we all got an F.” Speaking at an unrelated event in Lawrence, he touted the MBTA’s on-time performance in recent months and investments the T has made to modernize the transit system. But, he said, more needs to be done.

“The T carries about 600,000 people every day here in the Commonwealth of Massachusetts from one place to another and the vast majority of the time does so without incident, but incidents like this are horrifying, unacceptable, and do tremendous damage to the work that the T does generally over time,” he said.

Since a Green Line collision in July 2021 — just under a year ago — the T has been beset by troubles: An escalator malfunctioned at Back Bay Station causing a bloody pileup and injuring nine people, a commuter rail train killed a woman in her car after a crossing signal in Wilmington malfunctioned, another two Green Line trains crashed and derailed injuring four people, and a man was dragged to his death by a Red Line train at Broadway Station after his arm got caught in a subway door.

The series of safety incidents drew the attention of the Federal Transit Administration, which began a nearly unprecedented safety inspection of the T’s subway system in mid-April.

The FTA’s final report is expected in August, but last month the agency issued four directives to the MBTA, ordering it to immediately address glaring safety errors around staffing, safety certifications, track maintenance, and runaway train incidents. The T slashed service last month on the Red, Orange, and Blue Lines to comply with the FTA’s finding that the T does not have enough dispatchers to safely operate the subway.

Local elected officials expressed concern about the neverending safety woes.

“I’m sick of it that the Commonwealth has allowed the T to reach a state of disrepair that these kinds of incidents are commonplace,” said Somerville Mayor Katjana Ballantyne, who also thanked Somerville fire officials for their response and voiced gratitude that the passengers and T employees were safe.

She said she wants to see more urgent investment in the public transit system.

“All of these accidents, issues with the T, it’s like what else needs to happen?” Ballantyne said. “We keep kicking the can down the road. It must stop.”

Boston Mayor Michelle Wu said the fire provided more evidence of an aging transit system in crisis.

“A broken MBTA threatens the safety of our community and the future of our city and region,” Wu said in a statement.

Tauro, the Assembly Row resident, also voiced exasperation with the state of the beleaguered transit agency.

“Whoever’s in charge of this MBTA, fix it,” Tauro said. “I wouldn’t want to be caught up there at 100 degrees on that bridge, jumping out a window on top of the Mystic River. Forget it.”

John R. Ellement of the Globe staff and Globe correspondents Anjali Huynh and Simon Levien contributed to this report.