Spokesman Paul Corah says two men were doing maintenance Thursday night near the chemical reactor at Wacker Siltronics. The reactor combines chemicals for manufacturing.
Corah says reports indicate the explosion occurred when oxygen interacted with a substance called trichlorosilane. He says that's a chemical compound of silicon, hydrogen and chlorine.
A 56-year-old man and a 58-year-old man reported respiratory problems after the explosion and were taken to a hospital.
Two plant technicians and two Portland Fire hazmat technicians assessed the chemical reactor's condition.
The explosion drew more than 40 Portland Fire personnel.
Corah says the explosion was confined to one part of the plant, which makes semiconductor wafers.