Niagara County emergency crews were called to Lewiston-Porter High School Tuesday morning.
Niagara County Fire officials said eight to nine gallons of hydrochloric acid was mixed with a gallon of chlorine into the swimming pool.
Hydrochloric acid is a very strong acid produced in the human body. It also has with many industrial uses, among them, lowering the pH of water or cleaning an empty pool. Mixed with chlorine, it can produce a flammable, toxic gas.
In a notice posted on the school's website, officials described the incident as a "minor chemical emergency in our pool filter room." They said all students and staff were moved from the Physical Education wing to the main section of the school.
School officials said there were no safety concerns for students or staff.
"We are working with the Lewiston Police Department, Lewiston #1 Fire Company, Youngstown Fire Company and the U.S. Air Force Hazmat Team to rectify the situation," officials said.