The bump-bump-bump sounded like someone falling down a flight of stairs, a brief, rhythmic clatter that turned into a catastrophic boom and suddenly halted Amtrak’s Northeast Regional Train 188.

In the next instant, everything and everyone aboard the train — a cut of humanity that included the grandmother in her seat, the couple from Singapore in theirs, a former congressman in the cafe car — began tipping over, then tumbling and crashing into a contorted mess of steel.

“Am I going to die?” Andrew Cheng, 64, asked himself, as he landed on his wife, seated next to him in the fifth of the train’s six cars.

Another passenger, maybe two or three of them, fell on top of Cheng, everyone shrieking in the darkness.

It was just before 9:30 p.m. on a Tuesday — a night that should have been another forgettable run for a train that turns the commute between Washington and New York into a routine ride.

Only here was Amtrak Train 188, derailed and unhinged in north Philadelphia, seven dead out of its 238 passengers and five crew members. More than 200 people were battered, bloodied and in need of medical care.

In one car, now tipped over on its side, Carol Cissel, 53, could hear a woman trapped beneath a seat and moaning. She and others reached to free her, but the woman screamed to be left alone, the pain so overwhelming that she preferred to remain where she was.

In the last car, Jeremy Wladis, 51, a restaurateur, was pushed up against the wall. Laptops, phones and purses were flying. Above his head, he could see two women who had been hurled up into the luggage rack, as if by magic, desperate to free themselves.

Patrick J. Murphy, a former congressman from Pennsylvania, felt himself thrown about the cafe car like a rag doll, first to the left, then to the right, a convulsion that ended with him landing on his head.

Murphy touched his arms and legs, making sure his limbs were still there. The man next to him was unconscious.

Murphy propped him up.

Investigators combed the Philadelphia site where a New York-bound Amtrak train derailed after leaving D.C.

“Wake up, buddy,” he told him, patting his face as the sounds of moaning, sobbing and screaming filled the car.

Another man groaned from a corner. The man couldn’t feel his arms or legs.

“Hear the sirens?” Murphy told him. “They’re coming.”

At that moment, Chris Culver, a Philadelphia police officer, and his partner, Joe Carter, sprinted toward the wreckage.

Hill staffers and tourists

Amtrak Train 188 regularly leaves Washington’s Union Station at 7:10 p.m., transporting a collection of commuters that often includes legislators, lawyers, business executives, lobbyists and consultants from whatever business they had in the nation’s capital.

Murphy, who served in Congress from 2007 to 2011, had spoken to a group assisting military veterans at the Rayburn House Office Building on Tuesday and was rushing home before his two small children fell asleep.

He sat in the cafe car, working on his iPad, near U.S. Sen. Thomas R. Carper (D), who was heading home to Delaware. Cheng, the tourist from Singapore, also boarded the train, along with more than a dozen relatives who had convened in Washington for a one-day family reunion. The group was too large to sit together, so it split up between several cars.

Wladis took a seat in the last car. He had been in Washington sampling the offerings at his four Fuel Pizza restaurants and checking on the construction of a Latin-themed eatery he’s opening in Silver Spring, Md. His assistant had booked him on the Acela express to New York, but he exchanged his ticket at the last moment for a less expensive seat on Train 188.

The doors closed, and the train pushed off, traveling for a dozen or so minutes before its first stop, New Carrollton, where Cissel was waiting. The 7:22 p.m. out of New Carrollton is her train every Tuesday, taking her back to New Jersey from a weekly visit with her baby grandson.

The train headed north toward Baltimore, the sun setting and the passing lights flickering. In Wilmington, Carper said goodbye to Murphy and got off.

Around that time, Wladis stood and walked the length of the train, a routine of his to break up his frequent commutes to and from Washington. As he strolled, he took note of the faces of the other passengers, including a couple in first class, looking comfortable stretched out together.

Returning to his seat, Wladis bit into a slice of cheese pizza that had turned cold.

The train made it to Philadelphia around 9:10 p.m., stopping to allow passengers on and off, before inching out of 30th Street Station. The train traveled several miles before reaching Port Richmond, a working-class neighborhood in the northeastern part of the city.

At 9:21 p.m., the train rounded a left hand curve, barreling at a speed of 106 mph. The engineer applied the brake, slowing to 102 mph on a portion of the track in which the maximum authorized speed is 50 mph.

On Arcadia Street, which is close enough to the tracks that the sound of a passing train whistle is a regular part of the daily soundtrack, a group of kids was playing basketball. Alisa Wells was hanging out with her family at her nephew’s house, grilling burgers and talking.

Then, a bright flash lit the sky, and there was a thundering blast that was the loudest sound Wells could remember ever hearing.

Was it lightning? Fireworks?

Somehow, Keyauna Riggins knew it had to be a train. She ran toward the corner and saw 100 yards in the distance the smoldering carcass of Amtrak Train 188.

Sudden screeching

In the train’s second-to-last car, Cheng felt a series of bumps and then what felt like the train slipping off the tracks. For an instant, he blacked out, awakening to someone shouting that the car was about to tip over.

In the last car, Wladis felt a bump, then another that happened so quickly he sensed something was wrong. By the third bump, the train was shaking enough that he grabbed his seat and lowered his head for protection.

Then the crunching and screeching of metal.

His neck twisted. A few inches away, a colleague suffered a deep gash to his head.

In the cafe car, Murphy got on his feet, acclimating himself to the helter-skelter of a space in which the train’s ceiling now seemed like the wall, and the window was where the ceiling should have been.

Murphy grabbed the red safety handle and pushed out the window, and passengers started climbing out. He felt the same rush of adrenaline that he could recall experiencing as a paratrooper in Iraq more than a decade ago, heading toward the wounded.

He saw a man who “was just bleeding from everywhere.” Another man, also bleeding, cried out, “We’re going to die.”

Murphy went toward the man, trying to calm him, before imagining his own wife, at home, hearing about the crash.

“Hey Jen,” the former congressman texted her, “I’m on that Amtrak train. I’m ok. I’ll call you when I can.”

Just then, Culver and Carter, the two Philadelphia police officers, were sprinting toward the train. Culver kicked through a cafe car window and dived inside. He found a cluster of trapped passengers. He kicked through a second window, and five passengers jumped down to the tracks below, including a woman who wrapped her arms around him, refusing to let go.

“I got to go back in,” he told her.

Riggins, who had run to the wreckage from Arcadia Street, felt herself choking in the noxious air. Margaret Crawford, who also lives nearby, ran toward the tracks, as passengers were climbing out, their faces caked in blood.

She helped guide some of them to a sidewalk, including one woman who was walking without shoes, shards of glass stuck in her feet. Crawford held the hand of another woman, crying with her as she writhed from the pain of a dislocated shoulder.

From the last car, dozens of people poured through a door that had been pried open. Wladis stepped through the dangling live wires and walked over a metal fence that he was afraid could electrocute him.

He felt fortunate and surprised that he was alive.

He thought about that couple he saw in first class, relaxing just before chaos and terror engulfed their night.

“Oh God,” he told himself, “I hope they’re still with us.”

Julie Zauzmer contributed to this story.