(AP) — Workers were pushing coke out of huge ovens and preparing for maintenance when an explosion rocked a U.S. Steel plant outside Pittsburgh, a company executive said Tuesday, a day after the blast killed two workers.

The explosion, which was powerful enough to shake nearby homes, injured more than 10 other steelworkers, including one who spent hours trapped in rubble. It also knocked down a wall, scorched a pickup truck and sent a huge plume of black smoke into the air.

Initially, the plant’s own fire department and local responders rescued some of the workers. When it was determined that the area wasn’t stable enough for the rescue workers to continue their efforts, a specialized rescue team went in, said Matthew Brown, chief of Allegheny County Emergency Services.

The Pennsylvania Urban Search & Rescue Strike Team One, based in Pittsburgh, stabilized a wall and used a specialized camera to detect the trapped worker’s location and then carefully removed the debris to free him.

“That’s what gave us that success,” Brown said.

U.S. Steel’s chief manufacturing officer, Scott Buckiso, said workers were conducting routine operations at the time of the accident. Two loud booms that followed the initial blast were initially thought to be subsequent explosions, but he said they were from the activation of two relief pressure valves — a safety mechanism that operated as expected.

The cause of the explosion remained under investigation, and Democratic Gov. Josh Shapiro told reporters Tuesday that workers deserve an “answer for what happened.”

“We owe them the answers to their questions, and we owe them to never forget the sacrifices that occurred here yesterday,” Shapiro said. Before arriving at a news conference, he met with family members of a worker who died.

Allegheny County Executive Sara Innamorato told reporters she had assurances from U.S. Steel that the company would continue to cooperate fully with investigators.

“We all share a common goal. We want to get to the bottom of what happened, and we want to prevent it from happening ever again,” Innamorato said.

Remembering the dead
Shapiro also used the news conference to pay tribute to the workers who died. The county medical examiner’s office identified one of the dead as Timothy Quinn, 39. A second worker was not identified, with his family requesting privacy.

The Allegheny County Police Department said five people were hospitalized in critical but stable condition Monday night, and five others were treated and released.

Shapiro described Quinn as a devoted father of three known to his friends as “TQ.” He served as a mentor and leader to other workers and was known for cracking jokes. The second-generation steelworker followed in his father’s footsteps and was a “mama’s boy” who, after working long shifts, would take care of his mother and look after his children and his girlfriend’s two children.

“His life was cut too short because of what happened here at this plant,” Shapiro said. “We have a responsibly to remember his legacy, to make sure his memory lives on … We will make sure his children know his dad was a special man, a good man and a man who helped build this community with his hands the way his father did.”

U.S. Steel CEO David Burritt called it an “extraordinarily difficult day” for a U.S. Steel family that has “suffered heartbreaking losses.” According to the company, the plant has approximately 1,400 workers.

The company, he said, is working closely with local, state and federal authorities. He would not speculate about the cause of the explosion.

“We will share as much as we can, as soon as we can, and we will take every step necessary to keep our people safe,” Burritt said.

Deanna Forkey was working behind the counter at the Hometown Burgers & Deli, which her family owns, near the plant when she heard the explosion. She said the restaurant door popped open.

“When I looked out, all you could see was black smoke,” she said. “Explosions over there aren’t really uncommon. We hear them a lot. But that one obviously was much worse.”

She said many plant workers are regulars at the restaurant.

“You start to build a little bit of a relationship,” Forkey said. “So it kind of pulls a little harder at the heartstrings.”

Plant has seen explosions in the past
It’s not the first explosion at the plant. A maintenance worker was killed in a blast in September 2009. In July 2010, another explosion injured 14 employees and six contractors. According to online OSHA records of workplace fatalities, the last death at the plant was in 2014, when a worker was burned and died after falling into a trench.

After the 2010 explosion, the Occupational Safety and Health Administration fined U.S. Steel and a subcontractor $175,000 for safety violations. U.S. Steel appealed its citations and fines, which were later reduced under a settlement agreement.

In February, a problem with a battery at the plant led to a “buildup of combustible material” that ignited, causing an audible boom, officials said.

Two workers received first aid treatment but were not seriously injured.

Richard Lattanzi, who retired from another nearby U.S. Steel plant and is now the mayor in Clairton, where the coke plant is based, recalled that the company once sought to ensure that workers “go home the way they came in.”

“Apparently it’s not happening right now, so we’ve got to get better,” Lattanzi said. “We have to rally around this plant right now.”

Pittsburgh attorney John Gismondi represented the widow of the worker who was killed in the 2009 explosion at the plant and three men who were badly burned in the 2010 explosion. In a phone interview Tuesday, Gismondi said his immediate thought a day earlier was “Oh my God, not again at Clairton.”

Both lawsuits were settled out of court for “significant” amounts, he said.

“There was no question in both of those cases we established that appropriate safety protocols weren’t followed, and that’s what led to the explosions,” he said. “There’s a lot of gas on the premises. That’s fine, it’s part and parcel of what they do. But gas is a dangerous substance, and you need to make sure safety protocols are being followed.”

In the 2010 case, Gismondi’s clients claimed managers directed them to repair a live gas line even after an alarm went off warning of high levels of natural gas.

The plant, a massive industrial facility along the Monongahela River, converts coal to coke, a key component in the steelmaking process. It is considered the largest coking operation in North America and is one of four major U.S. Steel plants in Pennsylvania.

To make coke, coal is baked in special ovens for hours at high temperatures to remove impurities that could otherwise weaken steel. The process creates what’s known as coke gas — a lethal mix of methane, carbon dioxide and carbon monoxide.
___
Levy reported from Harrisburg, Pennsylvania. Casey reported from Boston. Associated Press reporters Holly Ramer in Concord, New Hampshire, Beatrice Dupuy in New York City and Audrey McAvoy in Honolulu contributed to this report.