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DALLAS (CBSDFW.COM) – There were headaches and upset stomachs at one Dallas elementary school more than 24 hours ago, but this wasn’t about some virus or bug making its way across campus.

The problem was carbon monoxide — caused by an animal, of all things.

The carbon monoxide buildup meant children, faculty, and staff were rushed from the campus of Lakewood Elementary Tuesday morning. But there were indicators of a problem on Monday, that’s when some students complained of headaches and vomiting.

Officials with the Dallas Independent School District say a dead owl was caught in the ventilation system and clogged it.

The subsequent gas buildup was serious enough that in addition to the school evacuation, five staff members were sent to the hospital. A DISD spokesperson says three adults drove themselves to the hospital, while another two went by ambulance.

Principal Toni Goodman called 911 Tuesday morning, after a contractor picked up high levels of carbon monoxide in the school. At approximately 10 a.m., the entire campus, some 840 students, was evacuated to Lakehill Preparatory School. Parents wanting to pick up their children met them there.

A DISD spokesperson said the CO levels were checked Monday night and they were fine. A check again this morning led to the evacuation.

But there were some 50 complaints of headaches and nausea on Monday. Now, parents are asking if the hazardous situation could have been detected before it got to that point.

Parent Deborah Stewart said, “Some of the teachers even went home sick yesterday. So they were chiming in on the Facebook feed saying, ‘I have a really bad headache. I have a really bad headache.’ So some of them even stayed home today.”

The art room at Lakewood is right above the basement furnace system and that’s where many 5th grade children were when they got sick Monday.

CBS 11 News reported last week about the need for facility improvements and upgrades at the aging school building.

Jason Whiteside wonders how much the carbon monoxide affected his son, Jackson. The little boy complained of having a headache after school on Monday.

“My wife was at school yesterday and mentioned that there might have been some kids, in the art room I think, that had had headaches, but that was about all that I heard,” Whiteside said.

For Stephanie Kuhlman’s daughter, Mackenzie, it was much worse. The girl said, “My head was pounding like so bad.”

Kuhlman says Mackenzie’s symptoms were so severe that she kept her home from school today. And when the concerned mom jumped on social media, she learned other parents were equally worried.

“We all started talking about what was going on,” Kuhlman recalled. “They [children] all had splitting, migraine headaches. They were all vomiting and they were all sleeping as soon as they came home. And she [Mackenzie] was sleeping as soon as she came home.”

DISD officials say as long as carbon monoxide levels check out tonight and again early Wednesday morning, school will be held as usual.

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