A chemical malfunction at a Wisconsin private school’s swimming pool sent 21 students to Children’s Wisconsin Hospital.

The incident occurred on Dec. 6 at the St. Augustine Preparatory Academy in Milwaukee, and injuries were isolated to a fourthgrade class.

According to Milwaukee Fire Battalion Chief Andrew Hargarten, the children were having respiratory problems when they were transported to the hospital.

Asked whether the children were conscious when taken to the hospital, Chief Hargarten said, “Generally, everyone did seem to be in pretty good condition when they were transported.”

Thirteen of the 21 children were treated at the hospital without being admitted. Six were admitted and released the following day, and the last two were released a day later in good condition, according to a hospital spokesperson.

Hargarten said the incident took place just after noon, while students were participating in a swim class. A buildup of chemicals compromised the air, and the pool was evacuated. A hazmat team responded to ventilate the pool and monitor the area.

There was no release of the pool chemicals to other parts of the school campus, Hargarten said, because the pool area has a separate ventilation system.

But older students, in a theater class on the floor above, said that a number of them began getting headaches around the same time as the pool incident.

A spokesperson for the school said staff are trying to understand what happened. As is done each day, the pool’s chemical levels were checked on the morning of the incident and appeared to be normal.

“We are working hard with our maintenance contractors to complete a thorough evaluation so we can understand better what happened and prevent a future occurrence,” the spokesperson wrote in an email.

The spokesperson for the school later said it appeared that a valve controlling the flow of chlorine malfunctioned, causing excessive chlorination and rapid deterioration of air quality.

School administrators sent a letter home to families, explaining that they were communicating with their vendor to better comprehend the cause of the chlorine buildup.

“We are working hard with our maintenance contractors to complete a thorough evaluation so we can understand better what happened and prevent a future occurrence,” the letter stated. “As we do, we can share that the pool in question passed its annual inspection at the beginning of the school year.”

Photo Credit: St. Augustine Prep Aquatic Center,