CHICAGO (CBS) — At least nine people, including six children, were taken to the hospital Friday morning, after a chlorine leak at a swim school in Naperville.

The Naperville Fire Department confirmed it responded to a chlorine leak at Goldfish Swim School, at 1688 Quincy Av., around 10:45 a.m.

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Several people were treated at the scene after the building was evacuated, and six adults and three children were taken to Edward Hospital for treatment. All nine were in good condition, and were taken to the hospital for further analysis.

“It was really quite strong, you could smell it,” said one witness.

When first responders arrived, the swim school and a nearby business were evacuated.

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Nine people were treated at the hospital.

“A couple of people were on respirators,” said Evan Jasek, who works nearby, told CBS 2’s Jeremy Ross. “They were out on the lawn with their towels.”

It took about 90 minutes for the chlorine to dissipate.

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Officials said this was the first incident of a leak at the facility.