CHICAGO (CBS) — A candy factory in suburban Itasca was evacuated overnight and more than a dozen workers became ill after a chemical spill.

Shift workers at the Willy Wonka Candy Factory were returning to work early this morning, but overnight about 18 workers had to be treated after lithium chloride–a product used for humidity control–was spilled.

When firefighters arrived around 1:30 a.m., workers were already outside, CBS 2’s Susanna Song reports.

About 18 workers complained of respiratory issues and around a dozen of them were taken to the hospital for treatment.

“Our companies got on the scene evaluated, found the building evacuated,” said Deputy Fire Chief John Radzinskil. “The product was not the main problem. It was a water soluble product that we didn’t have much to do with. They’re going to clean that up on their own.”

Wonka is a Nestle company.

The company says the spill happened at 9:30 p.m. when a pipe carrying the lithium chloride burst.

The company says it is a non-hazardous material and that the spill was contained.

However, hours later, some employees began complaining of nausea and difficulty breathing.

Spokeswoman Roz O’Hearn says that, at first, two or three employees complained of nausea 2.5 hours after the spill had been contained. Later, more employees began complaining of sickness.