WEST OCEAN CITY, Md. (AP) — A woman and 6-year-old girl were taken to a hospital after they were exposed to a toxic gas while swimming at an indoor pool in West Ocean City on Thursday, officials said.

The Worcester County Fire Marshal’s Office said firefighter paramedics responded to the Francis Scott Key Family Resort around 4:30 p.m. for a report of two people complaining of having difficulty breathing from a possible chemical leak, news outlets reported. They found the girl and a 41-year-old woman complaining of severe difficulty breathing and they were flown to Johns Hopkins Hospital in Baltimore.

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The investigation revealed that during routine maintenance, muriatic acid and chlorine were both accidentally released, forming a toxic gas that was discharged into the pool where the woman and child were swimming, the fire marshal’s office said.

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The pool was closed indefinitely.

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