A forklift was left running inside Burnham Composites Inc last week, resulting in 10 people visiting the Wesley Medical Centre for carbon monoxide poisoning.
The Wichita Eagle reported seven others, who complained of nausea and headaches, were treated at the scene.
Two of the hospitalised employees were in serious condition while the other eight were sent to hospital as a precaution. Firefighters said some had been vomiting at the parking lot.
Fire Marshal Ed Bricknell said the forklift was left running, but no doors were open and the rubber flaps in front of a garage door did not let enough gas out.
The forklift was taken to a mechanic to be checked, Burnham company president Todd Dugan said.