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ORLANDO (CBSMiami) – More than a dozen Walmart employees were treated carbon monoxide poisoning over the weekend.

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Fire rescue crews were called to the store in Avalon Park, just west of Orlando, just after 3 a.m. Sunday when employees began complaining of headaches and dizziness. First responders noted construction crew using propane tools inside the store and then detected very high levels of carbon monoxide.

The store was immediately evacuated.

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Orange County Fire Rescue spokeswoman Kathleen Kennedy said the levels of carbon monoxide had reached 400 parts per million inside the store by 4 a.m. Sunday. Levels above 35 parts per million are considered excessive.

Seven people were taken to the hospital as a precaution. Six others were treated at the scene.

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The store was cleared to reopen around 7:30 a.m. Sunday.