The superintendent of Gaskill Prep School on Hyde Park Boulevard says a chlorine cloud near the pool area forced the evacuation.

Fire officials say a maintenance worker mixed muriatic acid with chlorine around 9:30 a.m. Monday, forming the cloud.

Two workers were taken to the hospital just as a precaution.

The students were taken to evacuation sites, and were bussed home or released once parents were contacted.

First responders say the students weren't really in danger.

"For the person in the room, it could be potentially very dangerous for their lungs, but where it was in the building, it was underneath the pool in the basement, so for it to get up to where the students were, it would have taken a long time," said Thomas Collangelo, Niagara Falls Fire Department.

Niagara Falls Police tell us surrounding neighborhoods were not evacuated and there were no road closures.