LOUISVILLE, Kentucky, January 16, 2007 (ENS) - In the second fiery train crash in Kentucky in two days, a number of train cars, at least three carrying liquid propane gas, derailed and exploded south of Louisville this morning.

The explosion closed Interstate 65 in both directions for 18 miles and forced evacuations of homes, businesses and a school, Kentucky officials said.

The Bullitt County Emergency Management Agency issued a Hazardous Materials Warning for the entire county.

The agency said dangerous chemicals released by the explosion could present a major inhalation hazard as the smoke plume moves off to the southeast.

"Close all windows and doors, block out all outside air, turn off furnaces and bring in your pets. Turn on your tv or radio for more information," the agency warned.

Five people were taken to hospital for treatment of chemical inhalation.

At the request of the Kentucky Department of Environmental Protection, the U.S. Environmental Protection Agency is responding to the tanker fire with air monitoring from a small plane fitted with an emergency response sensor package.

CSX spokesman Gary Sease reports the train consisted of four locomotives and 80 cars headed from Birmingham, Alabama to Louisville.

WAVE 3 television reports the railcars may contain the chemicals cyclohexane and aniline.

Cyclohexane is a colorless and volitile liquid with a slightly pungent odor resembling that of chloroform or benzene. Cyclohexane is used as a solvent for the chemical industry.

Aniline is an oily, poisonous benzene derivative used in the manufacture of dyes and pharmaceuticals.

The Kentucky National Guard has mobilized soldiers and airmen to check air quality.

On Monday, four runaway CSX rail cars struck two parked locomotives in central Kentucky's Estill County, catching fire and spilling a chemical that forced evacuation of area homes.

That crash released about 30,000 gallons of butyl acetate, a flammable liquid, from a burning tanker car, authorities said. Black smoke billowed high into the air and fuel or chemicals spilled into the Kentucky River caught fire.

The incident started when four CSX rail cars jumped their track just before noon and careened onto a main rail line, traveling several miles before hitting the parked CSX locomotives, Sease said. CSX had placed the locomotives in the path of the tankers to halt their run.

The tanker car fire was extinguished by mid-afternoon. No injuries were reported. The causes of both crashes are under investigation.