Workers at the Walmart Supercenter on Rhea County Highway in Dayton were forced to evacuate the store early Wednesday morning after the store filled with dangerously high levels of carbon monoxide (CO).

One woman on the scene complained of dizziness to firefighters, but refused medical treatment. The building is being ventilated now.

Dayton Fire Chief Charles Suttles said the incident happened at about 4 a.m.

Chief Suttles says crews were using propane-powered sanders to clean the floor. He says investigators believe the machine malfunctioned, raising CO levels to 250 parts per million. Chief Suttles says that’s not enough to be deadly, but it would be enough to cause headaches, dizziness and nausea.

As of 7 a.m., Chief Suttles says CO levels are now down to 6 parts per million, and employees and customers will not be allowed to 5 parts per million, which should take a little longer.