Indiana Investigating Slag Pit Explosion

The state of Indiana is investigating a slag pit explosion at a northwestern Indiana steel mill, it said Tuesday.

The explosion Sunday in a raw materials section of the sprawling Cleveland-Cliffs Indiana Harbor West mill on the Lake Michigan shoreline “was caused by rainwater meeting the hot slag,” the Indiana Department of Environmental Management said.

“IDEM has not observed any materials or debris falling from the sky,” the department said. “The content of the plume would be predominately particulate matter associated with the slag.”

The explosion sent up a cloud of smoke visible from more than 20 miles (32 kilometers) away, The Times of Northwest Indiana reported.

“Cleveland-Cliffs’ contractor is responsible for taking precautions to prevent these types of explosions from occurring, and they are currently investigating the incident,” IDEM said.

No one was injured in the explosion at the facility that turns slag into cement and is operated by contractor Lafarge North America, Cleveland-Cliffs spokeswoman Patricia Persico said.

Several small fires at the mill were extinguished, she said.

Slag is a highly volatile byproduct of steelmaking prone to exploding when mixed with water.

“With slag, it looks and sounds worse than it is,” Persico said.

United Steelworkers Union District 7 Director Mike Millsap said the explosion was under investigation.