LOUISVILLE, Ky. -- Two workers have been killed after an explosion at a Louisville chemical plant and firefighters are going to let the fire burn itself out.

Doug Hamilton, the city's emergency management director, says the initial explosion occurred Monday night at the Carbide Industries plant and was followed by another blast a few hours later. The second victim died at a hospital Tuesday from severe burns.

Officials say hazardous air quality is not a threat.

The plant makes calcium carbide products, which are used in metal fabrication and construction.

Two other plant employees were injured and have been released from the hospital.