The incident began at 12:10 p.m. Wednesday at a building located at 2 Scott Way in the Scott Plaza.
Police say a faulty heater caused high levels of carbon monoxide in the building.
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Ten people were taken to Taylor Hospital and Chester Crozer Medical Center for treatment.
The building was evacuated as crews worked to ventilate the space.
The all-clear was given around 1:50 p.m. and people were allowed back inside.
The heater has been red-tagged for service.