PARSIPPANY, N.J. (CBSNewYork) – Nearly two dozen people were exposed to toxic chemicals at a New Jersey pool.

Some of the children had to be rushed to the hospital.

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The Glacier Hills pool club in Parsippany is empty now, but early Friday morning it was packed with young children taking swimming lessons. Two of Katy Ferrante’s kids were among them.

“All of a sudden we heard the two coaches yelling for everyone to get out of the pool. We automatically thought it was a thunder call,” Ferrante said.

She quickly realized something was wrong.

“You kind of hear the difference between the thunder and a mom call. And it turned into a mom call. And we started ushering all the kids out of the pool,” she said.

Kids and swim coaches realized they were swimming in a cloud of toxic chemicals. It turns out a pool pump malfunctioned and pumped several gallons of muriatic acid into the water.

“Reacted with the chlorine in the pool and created a vapor cloud. The children who were swimming in the pool were exposed to the vapor cloud and experienced respiratory distress,” said Capt. John Wienners of the Parsippany-Troy Hills Police Department.

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Twenty three people were exposed to that vapor cloud. Five children had to be taken to the hospital with inhalation injuries. At least one was admitted to the hospital. Police say the injuries are not life-threatening.

For regulars at the private swim club, the incident was frightening.

“It scares me. Because my littlest guy, who is seven, he could’ve been in there,” said Danielle Roman.

Roman’s kids all swim daily at the pool. Her oldest was walking to the pool when the toxic spill happened.

“We were just really lucky. Our practice was, like, the next one,” said Joseph Roman.

Parents who were there say the pool staff and swim coaches did a great job getting kids out of the water to safety. Katy Ferrante said the event was terrifying, but that accidents happen.

“Our pool has always been super safe, even during COVID. It’s been very safe. We mask up, we socially distance. Our pool is great. So whatever happened, it was definitely an accident,” Ferrante said.

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Staff at the swim club said the pool will be closed for at least 24 hours, and that they won’t reopen until it is safe to do so, CBS2’s Nick Caloway reported.