A series of powerful explosions rocked the Clairton Coke Works, a steel plant near Pittsburgh in Pennsylvania.

The blast claimed life of one worker and leaving another unaccounted for. 10 others were hurt as flames and thick smoke engulfed the site. The incident has sparked urgent search for the missing employee.

The blast at the Clairton Coke Works occurred just before 11am ET at the plant, which is also the part of large industrial complex along the Monongahela river. The plant was owned by US Steels, a subsidiary of Nippon Steel 5401.T.

Initially, only two workers were reported to be missing. According to Allegheny County Police Assistant Superintendent Victor Joseph in a afternoon briefing stated that One person was found and transported to a local hospital, the other individual remains missing.

Joseph further said “it is still a rescue mission” and also indicated that the investigation into explosion will be “a time consuming and technical investigation”. The cause of explosion remains unknown.

President and CEO of US Steel, David Burritt said in a statement that the company was working with local authorities to discover the cause.

Executive Vice President and Chief Manufacturing Officer for US Steel Scott Buckiso stated that authorities believe they know the general location of the missing employee but were not completely sure.

Pennsylvania Governor Josh Shapiro posted on X that there were multiple explosions at the plant and that his administration was in touch with local officials.

Although air quality monitors showed no dangerous rise in sulfur dioxide levels following the explosions, residents within a mile of the plant were advised to stay indoors, close windows and doors, and set HVAC systems to recirculate air.

Clairton Mayor Rich Lattanzi said it was a horrible day for the city, about 20 miles (32 km) south of Pittsburgh, long known as America’s Steel City.

US Steel has produced steel in the area since the late 19th century, but in recent decades, the industry has been in decline, leading to plant closures and restructurings.

In June, Nippon Steel, Japan’s biggest steelmaker, closed its $14.9 billion acquisition of US Steel after an 18-month struggle to obtain US government approval for the deal, which faced scrutiny due to national security concerns.

The Clairton Coke Works is the largest coke manufacturing facility in the United States, employing about 1,300 workers. It operates 10 coke oven batteries, which produce about 4.3 million tonnes of coke a year.

Coke is produced by heating coal at high temperatures. It is used in blast furnaces as part of the process of making steel.