Police said nine people with breathing problems were sent to hospitals and 10 others with throat and eye irritation or nausea were treated at the scene.
Police were called Monday afternoon on a report of a chemical spill at the Tarrytown YMCA building. They say a 5-gallon container of hydrochloric acid for use in the pool water had been knocked over accidentally.
The acid is highly corrosive and can damage respiratory organs, eyes and skin. It can even remove rust from iron or steel.
The building was closed temporarily.