Milwaukee, WI – High levels of carbon monoxide forced the evacuation of a day care Friday, and 11 people, including some firefighters, were taken to a hospital for treatment, authorities said.

Milwaukee Fire Department spokesman Lt. Larry Jenkins said six firefighters and two adult workers at the structure, which includes a church and the Heavenly Day Care, were taken to St. Luke’s Medical Center in Milwaukee for treatment of exposure to the fumes. Three other people, all adults, sought medical help on their own, he said.

None of the injuries was life-threatening, he said.

No children were at the day care center at the time, Jenkins said.

Someone from the day care called 911 around 7:30 a.m. to report a person in and out of consciousness in the kitchen, according to fire department spokeswoman Amanda Lanaghan.

“When we came in the carbon monoxide readings were pretty high,” Jenkins said.

Jenkins said deadly gases came from swimming pool heater that had been turned on but its ventilation system was blocked, sending the fumes into the building.