Some people in Greenup County were told to shelter in their homes on Friday after someone smelled chlorine.
The odor came from an empty tanker car at the CSX rail yard in Raceland. Firefighters say the smell likely came from residue in that car.
The shelter in place order has since been lifted.
Haz-mat teams responded to the scene to monitor the air quality.
The same rail yard was the scene of two accidents that caused shelter in place orders last year.