Heat is being blamed for causing 11 students and a teacher to fall ill and forcing the subsequent evacuation of their school.

The day was supposed to be one of celebration at St. Michael the Archangel School in Upper Saucon Twp., Lehigh Co. The school invited grandparents for the annual May crowning ceremony, but nothing went as planned.

Five students passed out during morning mass, prompting officials first to think high levels of carbon monoxide or gas were the culprit.

"Their eyes got wide. It was scary," said student Jack Ebert.

"It was really scary, just fell and the teachers were rushing around trying to help them," said 7th grader Drew Glemser.

"It freaked me out, honestly," 8th grader Caitlen Clemser said.

It also frightened school officials, who called emergency crews just after 9:30 a.m.

"The unusual thing about this is having all five at the same time. You think toxic exposure," said Dr. William Zajdel.

In total, 11 students and an adult were taken to a hospital.

Carbon monoxide and gas levels were checked by UGI and hazmat and fire crews, but all readings were normal, officials said.

"Hard to say what the cause was. At this point, it's a heat related issue," said Chief Chuck Castetter, Upper Saucon Twp. Fire Co.

Morning temperatures were only in the low 60s, and according to a school employee, the air conditioner was on inside the church.

The school also said most of the sick kids came from the same homeroom, leaving a lot of unanswered questions.

Blood work was taken from those admitted, and nothing toxic was found, according to officials at Lehigh Valley Hospital.

The hospital said all 12 people transported there were treated and released.