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MEMPHIS, Tenn. — Kate Bond Middle School will be closed Friday after a reported carbon monoxide leak.

The Memphis Fire Department says more than 1,000 students were evacuated from the school Thursday afternoon.

Officials on the scene told WREG that four students were treated for “suspected” carbon monoxide poisoning. Those students were taken to the hospital in non-critical condition.

Another 18 students were checked out by paramedics, who were able to take care of the kids on site.

The problem was discovered around 1 p.m. Thursday afternoon, when students in a second floor classroom started getting sick. Students were showing symptoms like dizziness and shortness of breath.

Investigators traced the issue to the classroom’s heating unit, where they detected levels of carbon monoxide. Carbon monoxide is an odorless, dangerous gas that can be deadly if you breathe it too long.

Shelby County Schools says that while initial reports indicated a carbon monoxide leak, carbon monoxide readings from the fire department and SCS Risk Management came back as negative.

SCS says that Kate Bond Middle will be closed on Friday so that an external agency can conduct more air quality tests.

A lot of parents say they didn’t know about the issue until their children called them. Some found out when they showed up around normal dismissal time.

SCS says parents were told, but claims some calls and texts may have been delayed.

“They don’t go out all at the same time if there is a mass number of those,” said Jerica Phillips with SCS. “A lot of the families who were arriving early found out through the media.”

Investigators are still trying to figure out why that heating unit malfunctioned. WREG asked school officials how old the unit is and when it was last inspected, but they haven’t answered those questions.

WREG also asked about how those students who were taken to the hospital are doing, but fire officials haven’t given an update on their condition.

We will continue to update this story as more information becomes available.