PETROLIA — A week after an explosion at the Sonneborn plant, the cause of that explosion is unclear.

“We’re continuing to employ some outside sources to do the investigation and that’s about it,” said Anita Orozco, Sonneborn director of human resources.

The explosion hit at 1:30 p.m. March 31 and caused a fire that took about two hours to extinguish.

Orozco previously told the Butler Eagle that heat exchangers were involved, but she said Thursday she wasn’t sure if that was the cause.

“I just think assuming anything at this point is not good,” she said. “We knew that the heat exchangers were involved, but we don’t know what the root cause is yet.”

Orozco said engineering firms will be doing tests to identify what happened.

“Hopefully we’ll have a good idea in the next couple of weeks as they do their analysis,” she said.

In the meantime, the hydro plant will be shut down, and Sonneborn will rely on a high stock of inventory.

“We had already planned to do a shutdown in May, so we just moved it up a month,” Orozco said. “We were in a good spot inventory wise.”

Sonneborn makes products such as petroleum jelly, baby oils and waxes.