PLEASANT GROVE, Utah (AP) — Chlorine gas has sickened dozens of swimmers at a Utah public pool in what police called a freak accident.

A pump malfunctioned Tuesday and forced too much chlorine out of a jet at Pleasant Grove Veterans Memorial Pool about 36 miles (58 kilometers) south of Salt Lake City, Pleasant Grove Police Capt. Britt Smith said.

About 50 people, mostly children, were sickened and ambulances took more than 20 people to hospitals, Smith said. The chlorine caused people to cough, vomit and bleed from their noses, he said.

Martha Vickers said she grabbed her children and ran when the gas enveloped them.

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“I just turned around and saw some bubbling from the pool — some yellow bubbling — and I knew it wasn’t good,” Vickers told KSL-TV .

Vickers saw people coughing and gagging as they left the pool. Her 2-year-old nephew was among those being treated, she said.

Patients who inhaled the gas could have chronic respiratory issues, said Nathan Miller, an emergency room doctor at the American Fork Hospital where some of the patients were taken.

“The more serious patients have some wheezing and then even more serious that their oxygen numbers drop and they require oxygen, then require breathing treatments,” Miller said. “Essentially, it would be like a severe asthma attack where they could potentially suffocate.”

Doctors at an Orem hospital treated 15 children and one adult, with three admitted to its pediatric intensive care unit, Timpanogos Regional Hospital officials said.