OCONOMOWOC, Wis. -- Authorities said a resort employee mixed chlorine with another chemical, sparking an explosion that left her with broken bones and a mild chemical burn in Oconomwoc.

Oconomowoc police said that the explosion was reported at about 8:45 a.m. on Tuesday at the Olympia Resort & Conference Center.

Police Chief Dave Beguhn said the employee was mixing the chemicals in the laundry room in the basement. He said employees are told which chemicals can be mixed, and in this case, the employee apparently made "an unfortunate error."

Thirty other resort employees and four emergency responders went to the hospital as a precaution. Beguhn said one emergency worker suffered a mild chemical burn to the foot.

Hazardous materials handlers from Waukesha were called to the scene.