First responders converged on Hightstown High School on Leshin Lane in Hightstown at 9:00 a.m.
Students told Action News they smelled an odor in the air near Room 602, a science lab, and that one of the school's science teachers had become ill.
"There must have been an experiment yesterday and it was being held in the frame hood," said School Superintendent Ed Forsthoffer. "And then this morning one of our teachers opened the frame hood, and I guess some fumes came out."
Science teacher Franco Paoletti was hospitalized after pulling open the window of that frame hood, where experiments involving hydrochloric acid and zinc sat overnight without the fan on.
"My teacher is the person that passed out," said Kiani Bonner. "Mr. Paoletti, he was in my first period class, and he came in and he wasn't feeling good."
Officials say the fume hood was closed overnight but the fan was not on, so when the teacher lifted up the glass Friday morning, he got a face full of noxious fumes.
"It's the fumes," explained Hightstown Fire Chief Scott Jenkins. "When they mix together the fumes go airborne, and it apparently made some of the people sick."
"They took him out on a stretcher after everything happened, and that's when the whole fire drill happened and everyone had to just evacuate the building," said student Tasia Teele.
"We evacuated the kids out of the facility, off the campus and put them on buses for temporary shelter," said Hightstown Police Director James LeTellier.
While hazmat teams, the New Jersey Department of Environmental Protection and the EPA vented the frame hood and monitored the situation, students were taken to the nearby Peddie School, then brought back and dismissed early. All activities at the school were cancelled for the rest of the day.
"Because it was cold out and many of them didn't have their jackets and materials, so we brought the buses over just to keep them warm. And then when we realized it was going to take a little longer than we were thinking it might initially, we decided to send them home early," said Ed Forsthoffer, School Superintendent.
"I got a text from my son and daughter who are students here and they told us there was a hazmat spill at school," said Catherine Smith.
No students were hurt. But along with Paoletti, three other teachers went to the hospital as well: two with headaches from the fumes, and another who suffered a head injury after falling during the evacuation.
There was no immediate word on any of the teachers' conditions.
Action News spoke with a local school board member, who praised officials' handling of the incident.
"It looks like they did handle it the way we practice for these things.... The fire companies rehearse, the police rehearse, so [it's] all in a day," said Suzanne Fallon.
Cleanup crews are sanitizing the fume hood and the school has been declared safe.
Many students had to leave behind coats and other possessions because they were evacuated so quickly.
Officials say their belongings will be secured until Tuesday when classes will reopen.
