CHICAGO (CBS) – Classes at a Bourbonnais elementary school returned to normal on Friday, after dozens of student fell sick Thursday causing the school to be evacuated.

Forty-eight students and faculty from Noel LeVasseur Elementary School in Bourbonnais were taken to hospitals on Thursday, after complaining of headaches and nausea. WBBM’s Bernie Tafoya reports.

The Bourbonnais Township Fire Department responded Thursday afternoon to a call at Noel LeVasseur Elementary School for an unknown odor in the building. The fire department said many students and faculty had low levels of carbon monoxide in their systems, but no carbon monoxide leak had been found in the school.

As a precaution, the school was evacuated and those not taken to hospitals were bused to Liberty Intermediate School in Bourbonnais.

On the school’s website, District 53 School Superintendent said a ventilation issues has been fixed and that classes will be in session on Friday.

“LeVasseur School will be open Friday, March 17th. A ventilation issue was addressed and both the Bourbonnais Township Fire Department and our HVAC contractor have certified that the building is free from any dangerous levels of carbon monoxide or other gases. Although no harmful levels of Carbon Monoxide were present in the building today [Thursday], we took precaution by evacuating the building, and having any staff or student not feeling well evaluated at the local medical centers. We thank everyone for their help and support today [Thursday].” -Dr. Hollowell

In addition, some parents refused treatment of their children, but later transported them to hospitals for evaluation.