As investigators look into the cause of the explosion at a steel plant near Pittsburgh that killed two and injured several others, officials are clarifying the number of blasts and offering reassurances the air around the facility is safe.

A social media post from Pennsylvania Gov. Josh Shapiro said there were "multiple explosions'' at the U.S. Steel Clairton Coke Works plant in Clairton, Pennsylvania, on Aug. 11, causing the two fatalities and sending 10 people to a hospital. In addition, numerous workers were treated onsite for minor injuries.

At a news conference Aug. 12 attended by Shapiro, U.S. Steel Vice President Scott Buckiso set the record straight on the blow-up.

“There was one explosion that involved coke oven gas,'' Buckiso said. "The other two that were called explosions were actually relief pressure valves. When we had the issue on 13, 14 battery, we had some back pressure into 19, 20 battery. Those ruptured − gates is what they’re called − they did their job, they released. That’s why we saw a bit of a plume when those two occurred.’’

Allegheny County Executive Sara Innamorato also told reporters air quality monitors showed levels of contaminants, including sulfur dioxide, hydrogen sulfide and tiny particulate matter, were below prescribed limits Monday and Tuesday.

All those present at the plant, about 15 miles outside Pittsburgh, had been accounted for by the evening of Aug. 11, officials said. One of the victims was identified by Allegheny County as Timothy Quinn, 39. The identity of the other person who was killed has not been released at the family's request, Shapiro said.

Five of the 10 sent to a hospital were in "critical but stable" condition, Allegheny County Emergency Services Chief Matt Brown told reporters.

Authorities have not yet indicated what could have caused the explosion, but U.S. Steel CEO David Burritt pledged full cooperation with the investigation, saying: "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.''

Blast victim was a second-generation steelworker

Shapiro said he spoke Tuesday morning with the sister and girlfriend of Quinn, one of the steelworkers killed in the blast.

“It is dangerous work that they do. It shouldn’t be as dangerous as it was yesterday,'' Shapiro said, lauding steelworkers for helping build communities.

The governor described Quinn, known as TQ, as a father of three, a mentor to many at the plant, where he had worked for nearly two decades, and a devoted son who regularly checked in on his mother after his shifts.

Quinn had followed in the footsteps of his father, also a steelworker before him.

“I want to make sure that, as was the case with TQ where he was a second-generation steelworker, the children of those who are working in this plant feel like they have a future in steelmaking right here,’’ Shapiro said.

What happened in the U.S. Steel plant explosion?

Emergency crews responded to a 911 call at 10:51 a.m. on Aug. 11 that there was an explosion at U.S. Steel Clairton Coke Works, the Allegheny County Emergency Services and Allegheny County Police Department said.

An initial fiery explosion was followed by secondary blasts. Photos and videos of the scene showed a large plume of dark smoke rising from the plant and firefighters battling flames.

The explosion "sounded like thunder," Zachary Buday, a construction worker who was nearby, told WTAE-TV.

"It shook my chest. It shook the building, then we saw the dark smoke rising from the steel mill," he said.

One person was initially confirmed dead, and two others were missing after the initial explosion. After an exhaustive search, another person was found deceased and the third was found and taken to a hospital with injuries.

Officials asked residents within a 1-mile radius of the plant to remain indoors.

What caused the explosion?

The probe into the cause of the explosion is underway. The initial calls to 911 indicated it happened inside a battery operating area of the plant, officials said.

The extent of the damage is not yet known, U.S. Steel spokesperson Kurt Barshick said. Barshick said part of the plant is still operable and would continue producing coke, which is used in the steel-producing process.

Who was killed? What is the condition of the injured?

Quinn was pronounced dead on the scene of the explosion at 11:24 a.m. on Aug. 11, officials said.

Five of the 10 people who were treated at hospitals are in stable but critical condition, and the other five were treated and released, Brown said.

There were dozens of "walking wounded" initially treated at the scene and sent home, Kasey Reigner, spokesperson for the Allegheny County Emergency Services, previously said.

What is a coking plant?

A coking plant produces coke, a porous, carbon-rich material that is used to make steel in a blast furnace, according to the Kentucky Geological Survey. Coal is heated without oxygen to extreme temperatures, as high as over 1,000 degrees Fahrenheit, to produce coke.

The plant in Clairton is the largest coke-manufacturing facility in the United States. It operates 10 coke oven batteries.

Contributing: Melina Khan, Phaedra Trethan, Matthew Rink and Marc Ramirez, USA TODAY; Reuters

This article originally appeared on USA TODAY: Air around US Steel plant is safe after explosion that killed 2, authorities say

Reporting by Jeanine Santucci and Jorge L. Ortiz, USA TODAY / USA TODAY

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