PORTLAND, Ore. (KOIN) — An unknown chemical forced students out of a modular classroom at Willamina High School on Tuesday, according to the school district.

Willamina School District said that students experienced nausea, rapid breathing, dizziness and burning in the chest. Students were evacuated from the classroom and those affected were treated by paramedics.

The origin of the chemical is still under investigation by local police, the district says.

According to the district, fire crews and custodians are working together to make sure the classroom will be safe. Since other buildings on campus weren’t affected, students will be back in class on Wednesday.