An ozone machine used to prevent mold and purify air is being blamed for creating fumes that overcame more than a dozen high school football players in a locker room Friday night.

First responders and hazmat crews were dispatched to Penncrest High School in Delaware County, Penn., after a fire alarm triggered an evacuation of the building, according to NBC Philadelphia.

13 players in all were impacted by the fumes and were treated at area hospitals for symptoms ranging from watery eyes to coughing, according to officials. They were later released.

“We’re very pleased that all of our students are doing fine and are grateful to the many emergency responders who were on the scene so swiftly,” superintendent Jim Wigo said.

District officials said that hazmat crews unplugged the ceiling ozone unit, and found within the hour that air quality was good. After an investigation, the district said the ozone purifier discharge timing was out of sync, which led to the incident.

The school was set to host an all-day basketball tournament on Saturday, which reportedly went on as scheduled after the locker room was cleaned and sanitized.

Jason Scott is Online Managing Editor of Athletic Business.