Rocky Hill High School is evacuated because of a small nitrate acid spill.
A science program was being held at the school and the custodial crew cleaning the science lab knocked over a beaker, according to the superintendent.
No one was injured and the students have been moved to the middle school.
"We didn't want to take any chances with anyone's safety. Anytime there's a chemical spill we're following the OSHA protocol," Superintendent Dr, Mark Zito said.
The school will not reopen until the cleanup is taken care of.