Pennsylvania leaders want answers as to what caused Monday's deadly explosion at U.S. Steel's Clairton plant. 

The tragedy has rocked the Mon Valley, and its congresswoman wants answers. Democratic Congresswoman Summer Lee is appreciative of U.S. Steel's efforts to get to the bottom of this, but she said this can never happen again. 

Lee said leaders need to make sure the people who work in these facilities, whether here in Clairton or other parts of the Mon Valley, are in a safe environment.

"So that we can get the full truth on not just what happened, how it happened, and what do we do now, what needs to be done to make sure that something like this never happens again," Rep. Lee said.

According to Lee, the Occupational Safety and Health Administration and the Environmental Protection Agency will be involved in this process. They each have federal regulation and investigative power. 

Lee didn't have a timeline for when more details could come out. She said some of the investigation will need to be talking with the people who were there, some of whom are still recovering.

"Those are some of the folks who will be able to talk more in detail about what happened in real time," Lee said.

KDKA has been contacted by multiple steelworkers claiming U.S. Steel maintenance work is reactive and not preventative, and may have played a role in this explosion. CEO David Burritt had this response.

"I'm shocked and outraged at that statement. I find it unbelievable because of safety being in our DNA," Burritt said. "We take this extraordinarily seriously."

Congresswoman Lee said that, whether it be U.S. Steel or Nippon Steel, there must be a commitment and investments to fix whatever issues happened and make all mills safer.

"If there is no accountability, then we can't say for sure that safety is in the DNA," Rep. Lee said.

Her office is working on getting in contact with Nippon, which has put out a statement saying it's committed to giving all the resources needed to heal from this tragedy.

 U.S. Chemical Safety Board investigation   

The U.S. Chemical Safety Board has a team at the plant investigating. It is an independent agency that doesn't issue citations or fines but gives recommendations to companies and groups like OSHA

"Today, we were just able to see the initial debris field as the site is still being made safe to allow further entry," U.S. Chemical Safety Board chemical incident investigator William Steiner said.

Steiner said the agency will perform a thorough investigation, one that in Clairton's case is just getting started.  

"The work we do is important because if we do it correctly, we can issue recommendations that will improve the safety of all the workers at these sites," Steiner said.

Interviews with steelworkers also began on Wednesday, getting their perspective on what went wrong.

"We've already made document requests to U.S. Steel, and they're cooperating with the CSV," Steiner said. 

Burritt said it is important to avoid speculation.   

"We need to get the facts. Facts are friendly, and we're going to support the local investigators, the state investigators, the federal investigators," he said. "We're going to make sure that we get to the root cause, and when we get to that root cause, we can be assured that this doesn't happen again."

In past investigations at other companies, Steiner said the U.S. Chemical Safety Board has recommended more federal oversight. 

"We also have asked for federal oversight on reactive chemicals which have caused explosions and fatalities," Steiner said. 

He's unsure if Clairton would fall into that category.

A U.S. Steel spokesperson said OSHA visits their facilities as the federal safety regulator of the Mon Valley Works. Steiner says additional oversight can be important.

"As Governor [Josh] Shapiro said, it prevents us from forgetting these people that have lost their lives," Steiner said. 

KDKA is waiting to hear back from OSHA on how often crews inspect the plant in Clairton. 

It could take 18 months or more until the U.S. Chemical Safety Board finishes its report, but it does expect to release some updates in a few months.