The explosion happened at the Mersen USA facility on Trout Run Road at just after 9 a.m.
St. Marys Mersen USA General Manager Noah Nichelson said in a news release that one employee was killed and two were injured following "an equipment related accident" at the plant. Nichelson said one of the employees was hospitalized with serious injuries and the other was expected to recover. The names of the employees have not been released yet.
The company "will continue to cooperate with the appropriate officials with our immediate focus on the three employees and their families who have been impacted by this accident as well as supporting the rest of our workforce," the new release said.