CLAIRTON, Pa. — The CEO of U.S. Steel pledged a transparent investigation into the Clairton Coke Works explosion that killed two and injured 10 Monday morning.

CEO David Burritt was joined at a press conference Tuesday afternoon by Pennsylvania Gov. Josh Shapiro and Allegheny County Executive Sara Innamorato where officials offered an update on the deadly incident.

“Today is a terribly sad day here in Allegheny County, as all of us mourn the loss of two steelworkers here from the explosion that occurred yesterday at batteries 13 and 14,” Innamorato said.

Late Monday the Allegheny County medical examiner identified one of the deceased as 39-year-old Timothy Quinn of Smithton.

Shapiro said he spent time with Quinn’s sister and girlfriend Tuesday morning. He said Quinn went by “TQ,” and described him as a second generation steelworker.

“TQ was a special person, a devoted father of three. Someone who I understand served as a mentor to the other steelworkers who were here. Someone that apparently you would go to on a rough day when you needed a joke, when you needed your stones busted. He was the guy who was there for others while being there as a leader in this plant,” Shapiro said.

Shapiro added that Quinn was a “momma’s boy” who took care of his mother after working long shifts at the plant, while also caring for his three kids and the two children of his girlfriend.

“He was devoted to them. He cared about them. And his life was cut too short because of what happened here at this plant,” Shapiro said.

The governor did not identify the other person who died in the explosion, saying the family had requested privacy.

According to a press release from Allegheny County, five of the 10 people who were injured are in critical but stable condition. The other five were treated and have been released from area hospitals.

Shapiro said that steelworkers at Clairton Coke Works are owed an explanation of what caused the explosion.

“I want to say just how thankful I am to each and every first responder. To each and every member of the United Steelworkers, who literally every day go forward in their jobs to help build this region, build this commonwealth and build this country. It is dangerous work that they do. It shouldn’t be as dangerous as it was yesterday,” Shapiro said.

Speaking after Shapiro, Burritt said it was “an extraordinarily difficult day” for U.S. Steel, now a subsidiary of Japan-based Nippon Steel Corp.

Burritt said the company is working with local, state and federal authorities “to understand exactly what happened.”

“We’re not going to speculate. We’re going to let the people do their work and support them in that important job. 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.

It was still not clear what exactly caused the explosion. Scott Buckiso, executive vice president and chief manufacturing officer of U.S. Steel’s North American Flat-Rolled Segment, did offer some insight into what was happening immediately prior.

According to Buckiso, workers were going through the “normal course of business.”

“We were charging ovens, and we were pushing coke out of ovens. We had individuals that were prepping for a maintenance job in the area, and that’s where we are in the investigation right now,” Buckiso said.

Buckiso clarified that the “maintenance job” was routine. He also said that initial reports that there may have been two smaller blasts following the explosion were not accurate.

“There was one explosion that involved coke oven gas. The other two, I think, two explosions that were called explosions were actually relief pressure valves,” Buckiso said.

According to Buckiso, these “rupture valves” operated as they were supposed to, and that batteries 19 and 20 were taken offline so those valves could be repaired.

“They will remain offline until they are safe, and 13 and 14 battery is shut down until we get to the bottom of the investigation,” Buckiso said.

The remainder of the plant is operating.

The Clairton plant converts coal to coke as part of the steel-making process. 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 – made up of a lethal mix of methane, carbon dioxide and carbon monoxide.

According to U.S. Steel, the plant produces 4.3 million tons (3.9 million metric tons) of coke annually and has approximately 1,400 workers.

Innamorato said the Allegheny County Health Department found the air quality in the area to be safe. Residents within one mile of the plant were advised to stay indoors in the immediate aftermath of the explosion, but that order was lifted Monday evening.

The Associated Press contributed to this story.