Emergency crews from the state Department of Energy and Environmental Protection responded to Fulton Park in Waterbury after a container of pool chemicals inside the park began to leak Monday morning, officials said.
The 15-gallon container held hydrochloric acid, which is used for the pool at the park.
In the high heat and humidity, gas built up inside the container, which was emitting a cloud of vapor, DEEP officials said.
Two park employees noticed the container and called police.
Police and DEEP officials were worried about the high concentration of the chemical and taped off a section of the park as they deal with the situation. Half the park is currently blocked off, according to DEEP.
DEEP officials said an environmental contractor will dispose of the drum.
No evacuations, road closures or injuries have been reported.
A HazMat crew remains at the scene.
The park is located at 500 Cooke Street.