Employees and customers at Walmart Supercenter in Dayton, Tennessee were forced to evacuate the store early this morning after the store filled with high levels of carbon monoxide. One woman complained of dizziness but refused medical treatment. Officials say the incident started when crews were using propane-powered sanders to clean the floor. Investigators believe the machine malfunctioned, raising carbon monoxide levels to 250 parts per million. That level is not enough to be deadly, but it would be enough to cause headaches, dizziness and nausea. The building was ventilated and has since re-opened to customers.