PHILADELPHIA — An elementary school in Philadelphia had to be evacuated after carbon monoxide fumes from roofing work wafted into the building, sending 26 kids and four staffers to the hospital.

School district spokesman Lee Whack says the ordeal happened just before 12:30 p.m. Friday at William H. Loesche School. He says the children and adults were taken to the hospital for observation. Most of the children were from the same second-grade classroom.

After about 30 minutes, the school fire marshals and city fire department determined the building was safe and children could return to classes. He says the fumes came from a generator being used by a roofing contractor.

Whack says some of the children have been released from the hospital, but he didn’t have exact numbers yet.