IOWA CITY, Iowa (AP) – Police say a University of Iowa residence hall was evacuated the night before classes began after an unknown chemical was reported and a student was found unresponsive.  The 500-person capacity Slater Hall was evacuated for about four hours Sunday night. Students were allowed to return around 11:30 p.m. after police said there were no toxic or explosive dangers. Police didn’t identify the chemical.

Police spokesman Chuck Green tells The Daily Iowan a male student was transported to an area hospital after he was found in a third-floor lounge. An update on his condition was not available Sunday night, but Green says no one was injured by the chemical. It’s unclear what was wrong with the student.

Green says the residence hall was evacuated as a “safety precaution.”