Two workers were killed and at least ten others injured when an explosion ripped through U.S. Steel’s Clairton Coke Works in southwestern Pennsylvania at 10:51 a.m. on Monday. Allegheny County officials said the blast, centred on coke-oven batteries 13 and 14, sent black smoke high above the Mon Valley and was followed by secondary explosions that shook nearby homes. Emergency crews from more than a dozen fire departments joined plant teams to battle flames and tunnel through debris. One employee was pulled alive from the wreckage hours after the initial blast. Five of the injured remain in critical but stable condition, while five have been treated and released. The county medical examiner identified 39-year-old father of three Timothy Quinn as one of the victims; the second fatality has not been named publicly. U.S. Steel said the rest of the sprawling plant is ‘stable and secure’. The two damaged batteries have been shut down, with two additional batteries taken offline for repairs, leaving only limited coke production. Air-quality monitors registered soot and sulfur-dioxide levels within federal standards, allowing authorities to lift a one-mile shelter-in-place advisory late Monday. The U.S. Chemical Safety Board, the Occupational Safety and Health Administration and local law-enforcement agencies have begun parallel investigations into the cause of the explosion. Governor Josh Shapiro, who visited the site on Tuesday, vowed that workers and families ‘will get answers,’ while Chief Executive David Burritt said the company is flying in outside experts and interviewing employees who were on shift at the time of the blast. Opened in 1901 and employing roughly 1,300 people, Clairton is North America’s largest coking facility. The plant, now owned by Japan’s Nippon Steel after its nearly US$15 billion acquisition of U.S. Steel in June, has faced previous safety and environmental violations, including a fatal 2009 accident and a 2010 explosion that injured 20. Investigators have not provided a timeframe for determining what triggered the latest disaster.