Investigation of Steel Plant Explosion Focuses on Gas Isolation Valve

A fatal explosion at a Pennsylvania steel plant in August occurred during maintenance on a gas isolation valve, according to an update issued by the Chemical Safety and Hazard Investigation Board (CSB). The explosion killed two employees and caused extensive damage at the U.S. Steel Clairton Coke Works facility, which processes raw coal into coke, a component in the making of steel and iron. Five other workers at the facility were seriously injured.

Workers performing a procedure to “exercise” the valve by closing and reopening it flushed the valve seat with water to remove accumulated residue from coke oven gas. The workers’ carbon monoxide monitors alarmed at this time, as did a four-gas monitor carried by one of the workers. According to CSB, workers reported hearing a popping sound and smelling gas. U.S. Steel ordered the workers to evacuate. Less than a minute later, the explosion occurred.

CSB found that the gas isolation valve had failed but has not yet determined whether the failure caused the explosion or resulted from it. The valve was manufactured in 1953 and refurbished in 2013. CSB’s investigation is ongoing. For more information, refer to the agency’s update (PDF) and related press release.