PETROLIA — The cause of the Sonneborn plant explosion that happened around 1:30 p.m. at the hydro plant was a result of malfunctioning exterior equipment.

“All we’re sure of at this point is it involved a heat exchanger,” said Sonneborn director of human resources Anita Oroczo.

Orozco said the device, which looks like a huge window air conditioner, transfers heat from one medium to another. There are other such devices in other areas of the site.

She said the company is investigating what caused the heat exchanger to go bad.

“They’ll be digging into that,” Orozco said.

The explosion caused large flames and= took two hours to extinguish by several emergency responders. Two employees suffered minor injuries.

Sonneborn makes products such as petroleum jelly, baby oils, and waxes. Orozco said the accident didn’t impact Sonneborn’s service. “We continued to ship,” Orozco said. “We’ve got inventory on stock.”